Hammer Performance - for All Your Harley Davidson XL Sportster and Big Twin Performance Needs
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CONVERTING YOUR 883


Quick Links:


Background Information


Converting your 883 to a 1250 or 1275 is absolutely the most cost-effective way to add power to your bike. Nothing else even comes close on a dollar per horsepower basis. Converting your 883 is also a pretty simple operation, you can perform a conversion in a few hours without even removing the engine from the frame. Conversions can be done with no lower end work and they can be done using your stock heads and cams as well. For these reasons, conversions are very popular, and we get asked about them practically every day. So we put together this guide to help you understand the requirements and myriad of options associated with this very popular topic.

883 to 1250 Conversion Kit in Silver
883 to 1250 Conversion Kit with Silver 04+ Big Fin Cylinders
Note the Reverse Dome Conversion Pistons
These Are For Use With Stock 883 Heads




Before we get into the nuts and bolts, though, there are some background things you need to know:
  • One of the first decisions you'll want to make is whether to convert to a 1250 or 1275. HAMMER Performance provides a kit to do either. Here are some things to consider:
    • The 1250 kit runs $550 (small fin) or $650 (big fin) and comes with new, premium quality cylinders with extra thick iron liners to support the larger bore size. The 1250 kit is available with the basic conversion pistons only, for use with stock 883 heads. The higher power packages described below use the 1275 kit.
    • The 1275 kit runs $650 (small fin) or $750 (big fin) and comes with new, premium quality cylinders with extra thick high strength steel liners to support the even larger bore size.
    • Stock cylinders cannot be bored to the 1250 bore size (or the 1275 for that matter) as the liners are just too thin.
    • Factory cylinders through mid-year 2008 can be bored to 1212cc maximum - this is the largest bore size the factory cylinder can safely support. Factory cylinders after mid-year 2008 cannot be bored to a 1200 or 1212. Although we offer a 1212 kit, it runs $500 and it requires that you send us a serviceable set of 1986 through mid 2008 cylinders for boring. Considering that 1250 kits start at only $550 and include new, superior construction cylinders, we've all but stopped doing 1212 kits, it just doesn't make any sense. But if you'd like a 1212 kit, contact us for assistance.
  • In addition to the engine kit itself, other parts are needed for a successful conversion. Which specific pieces are needed is a function of the year of your bike. See our Complete and Matched Conversion Packages below to make sure you get everything you need.
  • XL cylinders from 1986 through 2003 use a small fin pattern, as opposed to the larger fin pattern found on 2004 and newer XL models:

    Big fin and small fin 1250 cylinders


    Notice what a large difference this is. It adds considerable cooling capacity.
  • Small fin cylinders (86-03) can be fitted to 2004 and newer models, however, be aware that they compromise the bike's intended cooling capacity, and also this swap has implications on the motor's appearance as the cylinder fins won't properly match the fins on the heads. Also, the lower fin on the pushrod side will need some grinding to clear the pushrod tube bases.
  • Big fin cylinders (04-up) will fit fine on 1986 to present bikes, and will add some cooling capacity to 86-03 models. However, consider the appearance issues if being used under 1986-2003 small fin cylinder heads.
  • The bottom line on cylinders is that if you have a 2004-up bike, we highly recommend staying with the large fin cylinders. If you have a 1986-2003 bike, we recommend getting cylinders to match your heads, which in stock form means small fin style, however, many people upgrade their 91-03 heads with 04-up heads (see below), and in that case, we recommend getting the large fin style. Both styles are readily available in HAMMER PERFORMANCE 1250 and 1275 kits.
  • In 2004, HD introduced oil squirters under the pistons to cool the underside of the piston domes. If pistons designed for 1986-2003 models are used in a 2004 or newer, you run the risk of the piston skirts hitting the oil squirters, breaking them off and requiring a full tear-down to fix. All Sledge Hammer Pistons from HAMMER PERFORMANCE will clear the factory oil squirters just fine.
  • With respect to interchangeability between cylinder heads, there are basically 4 generations to be aware of, with some interchangeability possible between them:
    • 1986-1990 (4-speed heads): These heads have different valvetrain geometry than 1991 and newer heads, and therefore it is not recommended that you interchange 4 speed heads and 5 speed heads.
    • 1991-2003: These are small fin heads with 5/16 stem valves and straight wound springs. The maximum valve lift they can safely support with stock hardware is .500". They can be interchanged with 2004-2006 heads except that a new front head mount bracket is required. A bracket designed to put a 2004 or newer head onto a 1991-2003 bike is readily available from HAMMER PERFORMANCE for $14. No bracket is currently available to fit this generation of head to a 2004 or newer bike, it would have to be fabricated.
    • 2004-2006: These are large fin heads with 7mm stem valves and beehive springs. The maximum valve lift they can safely support with stock hardware is .560". These can be put on 1991-2003 models with the use of a new front mount bracket. They cannot be used on 2007 or newer bikes without major modifications.
    • 2007-present: These are large fin heads with 7mm stem valves and beehive springs and a .560" maximum valve lift as with the 2004-2006 heads. However, these heads are made for fuel injection. The manifold surfaces are milled down .062" and the manifold flange bolt holes are also spread apart. These can be used on carb bikes with the addition of a special wider intake manifold offered by HAMMER PERFORMANCE.
    In summary, it's generally best to stay with the same generation of heads that your bike is made for. However, 2004-2006 heads can be fitted to 1991-2003 bikes without much trouble. You can read more about the various details of XL cylinder heads in this tech article.
  • 883 heads have shallower chambers than their 1200 counterparts, and longer valves to match. This makes the valves start out closer to each other and closer to the pistons. As a result, in stock form 883 heads cannot accommodate as much overlap in the cams as 1200 heads. The critical dimension is the "TDC lift" spec of the cam grind. If we prepare the heads, this changes of course, and we can put you into much more camshaft. Just keep in mind that you need to be very careful about cam selection when using 883 heads and understand what will fit and what will have clearance issues. If in doubt, ask us.
  • Since 1995, 883's and 1200's have shared the same crankshaft at any given model year. The crankshafts are balanced for a piston weight that's in between a stock 883 piston and a stock 1200 piston. The Sledge Hammer pistons from HAMMER PERFORMANCE that come in the 1250 and 1275 engine kits are in between the stock 883 and stock 1200 piston weights, so the balance actually comes out better than either a stock 883 or stock 1200. So there is no need to be concerned with hurting the balance of the motor when doing a conversion with either of these kits, you'll actually make it better.
  • When converting an 883 to 1250 or 1275, it's always required to adjust both the spark advance and the fuel delivery. See our engine kit installation instructions for details on how to do this. Also read FAQ #5 and FAQ #6 below
  • When considering what level of conversion to do from the descriptions below, keep in mind that stock heads require standard reverse dome conversion pistons, but a prepared head works best with our trick 30 degree reverse dome pistons:

    Sledge Hammer Pistons used in 883 to 1200 or 1212 or 1250 or 1275 conversions


    It's not that we can't prepare heads and continue to use the standard reverse dome conversion piston as shown on the left; we certainly can. However, it forces compromises and ultimately ends up with a sub-optimal result. The higher up the food chain you go with the heads, the larger the compromise. This is because head work, particularly large valve head work and/or head work done to complement high lift, high overlap cams, necessarily makes the chambers bigger. That puts downward pressure on the compression ratio, while at the same time, larger cams generally require a higher compression ratio, not lower. So the bottom line is that you need more piston dome as you move up the head prep and/or cam size scale. We can only deck the heads to recover compression so far before we start causing a host of other problems, the right place to address it is in the piston dome. The moral of the story is that pistons, cams and head work are a carefully matched set, and if you try to move up the power scale incrementally over time, you're likely to either need to buy pistons twice (and they're expensive) or end up with a compromised result. See FAQ #2 below for more information.
  • Through the 2003 model year, 883's and 1200's came with the exact same clutch setup. However, starting in 2004, the 883's got a lighter clutch spring. As a result, when you do a conversion on a 2004+ 883, it's necessary to upgrade this spring, either that or you can expect your clutch to slip. Many people take the opportunity to change the entire clutch pack at this time, swapping it for an aftermarket "Extra Plate" clutch pack to remove the failure prone factory compensator plate. HAMMER PERFORMANCE offers upgraded springs, extra plate clutch packs, the compressor tool needed to change the clutch spring, and the primary gasket you'll need. See FAQ #3 below for more information.
  • Can you do the work yourself? The answer is an emphatic yes if you have the tools and a place to do it. Read our detailed and illustrated installation instructions here. And never forget, we're only a phone call or email away if you have questions, that's what we're here for. We even answer emails evenings and weekends in most cases.
  • Achieving optimum results requires proper assembly, heat cycles, break-in, and tuning. Don't cut corners on any of these things! Also read our tech article on How to Optimize Squish Clearance. This little step will yield positive results in both power and fuel mileage.


Complete Conversion Packages


So how do you go about converting your bike, making sure you get all the right parts and services? Below, we've laid it out for you with a series of carefully matched, time-tested, proven packages, each of which is designed to deliver a specific target power level in the most cost-effective way possible. Packages range from a low-cost 70+hp configuration up through a 120+hp screamer. You'll find a description of each package, dyno sheets, pictures, and even sample quotes you can download showing each item included and what it costs. Here are some other things to keep in mind:

  • All of these packages are bolt-ons, and can be installed on a Saturday afternoon without even pulling the engine out of the frame.
  • Although they're complete with everything you need and nothing you don't, the sample quotes below are just samples. We're more than happy to add or remove things at your request to meet your needs, just contact us.
  • For the Basic Conversion Package, you don't need to send us anything (except money!). It works fine with your stock heads, cams, etc. So for this package, all you need to send is payment, and you can find payment instructions here. We generally turn this package around in 2-3 days, and you'll get a ship notification email from the carrier when it goes out.
  • All of the higher power packages require that you send us at least your cylinder heads, and in some cases your manifold and/or throttle body as well (although we may have cores available, contact us for details). Please DO NOT send us parts until we have paperwork in place and we're expecting the parts! That just causes mass confusion. So please, contact us first and we'll get a final estimate hammered out specific to your plans. Once the plan is in place, follow our shipping instructions. Your project will be kicked off when your parts hit our door. Turnaround varies with the season. It may be as short as two weeks in the slower months (August through October) or as long as 4-5 weeks in our busier months (February through May). There's no need to worry about payment until your order is ready to ship, and we'll contact you at that time.
  • All of the sample estimates below leave off both the exhaust and air cleaner. We do this because 99% of the guys who contact us already have aftermarket pieces for both, and in many cases, the parts you already have will be suitable for meeting your goals. However, keep in mind that both your exhaust and air cleaner are critical performance components with the potential to make or break your project. There are massive, massive performance differences from one aftermarket exhaust and/or air cleaner to another. The power of the motor tends to get defined by what holds it back, not by how great the motor package is, and it only takes one part to hold it back. If your exhaust and/or air cleaner are not capable of supporting the target power level, you'll come up short! We have enough experience that in most cases, we can advise you. One great resource is our XL exhaust system dyno test library. We can also provide air cleaners and exhausts that support your target power level.
  • The dyno sheets below were, for the most part, generated with 1250 kits. Over time, we will be replacing these 1250 dyno sheets with 1275 versions, but for now, just assume 2-3% more power over the entire rpm range for a 1275 as compared to a 1250.


The Basic Conversion


The basic 883 to 1250 or 1275 conversion is a simple affair that makes a massive difference in the torque and power of the bike at a very modest price. Many, many people do a basic conversion only for this very reason, in fact this is our number one selling package by a large margin. Here's what goes into a basic conversion:

  • The stock 883 heads are reused as-is. If they have a lot of miles on them, you may consider a valve job and new valve guide seals.
  • Either a 1250 kit ($550-$650) or 1275 kit ($650-$750) is used, and is configured with reverse dome conversion pistons to give 10:1 compression with the stock 883 heads. You should stay at 10:1 or less when using stock cams and pump gas.
  • Stock cams and valvetrain pieces are left in place.
  • Upgrades to the air cleaner and exhaust are completely optional.
  • If your bike is carbureted, a new ignition module is a standard part of this package. 86-03 owners may opt out of the module and readjust their ignition timing to suit the conversion kit instead, but the motor will run sub-optimally
  • Likewise, appropriate carb jets are a standard part of this package for 86-06 models.
  • If your bike is injected, a proper flash tuner is a standard part of this package.
That's it! With an afternoon of work, you've made a huge increase in the torque and power of your Sportster, and made it tremendously more fun to ride. How much more? Well, here is an actual result we got:


Dyno Sheet for Basic 883 to 1250 Conversion


Stock 2007 883 shown in red. In blue is the same bike after performing the basic 1250 conversion and adding a Patriot Defender exhaust and Air Hammer air cleaner. This package will absolutely transform your bike!



Sample Quotes and Pictures of the Basic Conversion Package

2007+ Basic Conversion Package (pdf): 1275 1250
04-06 Basic Conversion Package (pdf): 1275 1250
98-03 Basic Conversion Package (pdf): 1275 1250
91-97 Basic Conversion Package (pdf): 1275 1250
88-90 Basic Conversion Package (pdf): 1275 1250
86-87 Basic Conversion Package (pdf): 1275 1250
HAMMER PERFORMANCE 883 to 1250 & 1275 Basic Conversion Package
Click the Image Above for a
Slide Show of Packages for Different Model Years



NOTICE: We are currently out of stock on black and black highlighted 1250 cylinders, both big and small fin. This is a temporary condition, check back for availablity. Or better yet, upgrade to one of our 1275 kits!

Basic Conversion Package - 883 to 1275
Year of Bike
Cylinder color
Basic Conversion Package - 883 to 1250
Year of Bike
Cylinder color


Taking it to 80+ Horsepower


So let's say you want a little more than the 70ish horsepower available from a basic conversion. What's the next step?

Well, the key to making more power is always to identify and address the thing holding the motor back. In the case of a conversion done with 883 heads, that's mostly the air flow capability of the heads themselves. This airflow capability can be improved by working on the heads as well as holding the valves open longer with longer duration cams. To get to 80+ horsepower using an 883, we'll want to do both.

Competition Valve Job Being Performed on a Harley Davidson Sportster Head Here's what we'll do:

  • The stock 883 heads will be treated to a Competition Valve Job ($260 with new guides and seals). This work goes right to the heart of the biggest problem with 883 heads, which is how the full size ports and bowls neck down to the itty-bitty valves sitting on poorly blended seats. In stock form, it's a recipe for flow-killing turbulence. But the Competition Valve Job cleans this area up nicely. The seat i.d.'s are opened up substantially, and the seats are blended into both the bowls and chambers. It makes a massive improvement to the flow of the heads.
  • A 1275 kit ($600-$700) equipped with our trick 30 degree reverse dome pistons is part of the plan at this level.We'll set this package up at 10.5:1 compression.
  • A set of bolt-in style cams is used. For 86-03 models, the perfect match is the Andrews N4/V4 grind. For 2004 or newer models, the IMPACT 560's are the best choice. Cams are required if you want to run 10.5:1 compression on US pump gas. If you try to run 10.5:1 on your stock cams, detonation will be a problem and you may well damage your pistons. Note however that we do have a 10:1 version of the reverse dome conversion piston if you plan to run stock cams or a high torque cam grind like our JACKHAMMER 570's (the 570 cams are not compatible with 86-03 heads until you reach the 100+hp package head prep level, below).
  • Upgrades to the air cleaner and exhaust are required to hit 80 horsepower. The best air cleaners on the market are the Air Hammer units from HAMMER PERFORMANCE - the IMPACT model will do nicely for this package. See our XL Exhaust System Dyno Test Library for more information on exhausts. We can provide most any exhaust that's on the market.
  • At this level, a proper ignition module is required on all 86-06 models, as the increased compression and improved breathing demand a proper ignition curve. It's included as a standard part of the package, along with appropriate carb jets.
  • Likewise, a proper flash tuner is included as a standard part of this package for all 2007+ (EFI) models
With this basic package, we've had many customers make mid to even upper 80's torque and horsepower. It's a huge bang for the buck! Here's an actual dyno result using this package on a 2004 XL883, EFI bikes with their stock "W" cams make even more:


Dyno Sheet for 80+hp 883 to 1250 Conversion


You can see how well the motor responded to the head work and cams, as compared to the basic conversion, and there was no loss in bottom end power either. It's a great package for a very reasonable price.


Sample Quotes and Pictures of the 80+ Horsepower Conversion Package

2007+ 80+hp Package (pdf)
2004-2006 80+hp Package (pdf)
1998-2003 80+hp Package (pdf)
1991-1997 80+hp Package (pdf)
1988-1990 80+hp Package (pdf)
1986-1987 80+hp Package (pdf)
HAMMER PERFORMANCE 80+ Horsepower 883 to 1275 Conversion Package
Click the Image Above for a
Slide Show of Packages for Different Model Years



Taking it to 90+ Horsepower


Okay, enough messing around, let's get serious about making some power!


Dyno Sheet for 90+ Horsepower 883 to 1250 Conversion Package
The 90+hp Package Delivers a Huge Bang for the Buck!



CNC Porting a Harley Davidson Sportster Head Here's what we'll do:

  • The stock 883 heads will be treated to an IMPACT porting job ($550). This service includes the Competition Valve Job described in the 80+hp package above, but also includes CNC reshaping of the ports themselves, which results in a substantial increase in flow.
  • As with the 80+hp package, to get to this level you'll use a 1275 kit ($650-$750) equipped with our trick 30 degree reverse dome pistons. Again, we'll set this package up at 10.5:1 compression, but we do have a 10:1 piston available if you'd like to use milder cams and sacrifice some top end power for some additional bottom end power.
  • As above, a set of bolt-in style cams is used: Andrews N4's if you've got an 86-03 model, and IMPACT 560's if your bike is a 2004 or newer.
  • As above, upgrades to the air cleaner and exhaust are required.
  • As above, ignition timing and fueling are adjusted with either an aftermarket ignition and some carb jets, or with an EFI tuner, depending on the year of your bike.
With this basic package, 90+ horsepower is well within reach and costs are still reasonable.



Sample Quotes and Pictures of the 90+ Horsepower Conversion Package

2007+ 90+hp Package (pdf)
2004-2006 90+hp Package (pdf)
1998-2003 90+hp Package (pdf)
1991-1997 90+hp Package (pdf)
1988-1990 90+hp Package (pdf)
1986-1987 90+hp Package (pdf)
HAMMER PERFORMANCE 90+ Horsepower 883 to 1275 Conversion Package
Click the Image Above for a
Slide Show of Packages for Different Model Years



Taking it to 100+ Horsepower


Believe it or not, 100+ horsepower is available using your 883 heads, and at a very reasonable cost. HAMMER PERFORMANCE has a combination that can do it!


Dyno Sheet for 100+ horsepower 883 to 1250 Conversion
Yes, 100+hp is Possible Without Buying New Heads
Follow Our Formula to Get a Result Like This One


Here's how to get to the century mark and beyond at a very reasonable price:

  • The stock 883 heads will be treated to a SMASH porting job ($850). This service includes everything in the IMPACT porting service described above for the 90+hp package, but also adds our oversized conversion valves and conical springs. We take your valve sizes up to the largest sizes that will fit in the stock seats: 1.770" intake and 1.530" exhaust valves, in our stainless swirl polished high flow 7mm stem versions. We pair these terrific valves with state-of-the-art conical springs and titanium retainers, a combination we've tested and proven stable to 8000rpm. Despite the tremendous rpm capability, spring pressures remain mild to minimize wear and tear.
  • A 1275 kit ($650-$750) with 30 degree reverse dome pistons is again part of the plan, mirroring the 80+ and 90+ hp packages above. Again, we'll set this package up at 10.5:1 compression
  • To break 100hp, you're going to need a great set of cams, and the IMPACT 560's are exactly that. No worries if you have 86-03 heads as the SMASH service includes an upgrade to the hardware and your heads will now support these high lift cams. IMPACT 560's are easy on the valvetrain and quiet in operation, too. You can expect a long, trouble free life from this setup.
  • Don't even think about doing this with a substandard air cleaner. Use a genuine Air Hammer air cleaner. The IMPACT model will support this level nicely.
  • If you've got a carbureted bike, it's time to ditch the CV40 in favor of a Mikuni. The preferred setup is an HSR45 and one of our HAMMER PERFORMANCE Billet Manifolds. These are included as a standard part of the package. By going big like this, it allows us to do a better job on the ports, as we can maintain the proper taper from the carb to the choke point in the port. An HSR42 forces us to make a compromise here.
  • The exhaust selection becomes critical at this level. The above chart was done with a Patriot Defender pipe, which is a superb performer at a bargain price. See our library of XL Exhaust System Dyno Test Results for other candidate pipes.
  • An appropriate ignition module and is included as a standard part of the package for 86-06 (carbureted) bikes.
  • The best EFI tuner on the market is included as a standard part of the package for 2007+ (EFI) bikes.


Sample Quotes and Pictures of the 100+ Horsepower Conversion Package

2007+ 100+hp Package (pdf)
2004-2006 100+hp Package (pdf)
1998-2003 100+hp Package (pdf)
1991-1997 100+hp Package (pdf)
1988-1990 100+hp Package (pdf)
1986-1987 100+hp Package (pdf)
HAMMER PERFORMANCE 100+ Horsepower 883 to 1275 Conversion Package
Click the Image Above for a
Slide Show of Packages for Different Model Years



Taking it to 110+ Horsepower


Dyno Sheet for 121 horsepower Sportster
Actual Result From our 2007 XL883 Sportster With the 110+ Horsepower Package


Who says you need 1200 heads to make big power? Not at HAMMER PERFORMANCE! We've made over 120 horsepower on 883 heads with this package. You should have no problem breaking 110hp; truth be told even 115 is an easy mark for this combination.

Here's how to get past the 110hp  mark with your 883:

  • Hit it as hard as you can, use a SLEDGE HAMMER! Once you get to the SLEDGE level, 883 heads no longer give up anything to equivalently prepared XB or late model XL1200 heads. Four new seats and the largest valves we can make fit are just the beginning. We complement these valves with extensive chamber work and our exclusive SLEDGE custom tailored porting process. A set of state-of-the-art conical springs with Ti retainers gives you a valvetrain safe to 8000rpm, but because of the lightweight components and the advanced lobe design of the cams below, it's done without the high spring pressures that increase wear and tear. When it's all said and done, your 883 heads will perform every bit as good as the best prepared XB heads, but without the big expense!
  • It not only takes big valves to flow enough air to make 110hp, it also takes bigger cams. Our CRUSH 600 cams are proven power producers. But the lobe design is both quiet and easy on the valvetrain, and the gentle ramp rates don't need the brutal spring pressures required with other cams in this size range. Truly a real-world set of cams with longevity and reliability, and perfectly matched to our head work and engine kits, these are the ideal choice.
  • Your 1275 kit ($650-$750) will get a special set of 30 degree pistons, designed to push the compression a bit. Don't worry though, the later intake close timing of the CRUSH 600 cams bleeds much of this off. Expect 200-210psi of cranking compression when it's all said and done, which is fine with proper tuning.
  • To deliver all the air this monster needs, you'll need the best air cleaner made, and that means the CRUSH model Air Hammer.
  • If you've got a carbureted bike, the package includes an HSR45 Mikuni and a HAMMER PERFORMANCE Billet Manifold. If your bike is injected, you have a 45mm throttle body already, but the throttle body and manifold both benefit greatly from a little work. Send it to us along with your heads for porting ($100).
  • You're going to need the best exhaust on the market, and the best we've ever tested is the Patriot Defender. Set the baffle butterfly wide open and leave it there. See our exhaust system dyno test library for lots of information on XL exhaust system performance.
  • As with the other packages described above, this package includes an appropriate ignition module (carbureted bikes) or EFI tuner (injected bikes).
Assemble it correctly, optimizing your squish clearance along the way. Heat cycle and break it in correctly and then get it on the dyno for a thorough tune-up. 110 is an easy mark, and over 115 is well within range.

And just in case you're still worried you're somewhow giving up some power by sticking with your 883 heads, check out this sheet:


Dyno Sheet for 121-124 horsepower Sportster
In blue is a set of SLEDGE PLUS ported EFI 1200 heads with an HPI 55mm throttle body
In red is a set of SLEDGE ported EFI 1200 heads with a ported factory throttle body
In green is a set of SLEDGE ported EFI 883 heads with that same ported factory throttle body
SLEDGE PLUS service adds welding up of the port so that we can make an optimum shape
Collectively, the PLUS service ($+100) and the HPI throttle body ($790) added only 3hp



Sample Quotes and Pictures of the 110+ Horsepower Conversion Package

2007+ 110+hp Package (pdf)
2004-2006 110+hp Package (pdf)
1998-2003 110+hp Package (pdf)
1991-1997 110+hp Package (pdf)
1988-1990 110+hp Package (pdf)
1986-1987 110+hp Package (pdf)
HAMMER PERFORMANCE 110+ Horsepower 883 to 1275 Conversion Package
Click the Image Above for a
Slide Show of Packages for Different Model Years


Taking it to 120+ Horsepower


Dyno Sheet for 132 horsepower 1275cc Sportster
Actual Result From our 2007 XL883/1275 Sportster With the 120+ Horsepower Package


HAMMER PERFORMANCE raises the bar again! This package achieves levels of bolt-on performance never before seen in the industry! And we've done it in a reliable, pump gas friendly combination. The above motor has only 200psi of cranking compression and only moderate valve spring pressures. These results are achieved with modern technology and innovation, not excessively high compression and brutal cams!

Here's what goes into the 120+ package:

  • To get to this level, we had to invent a whole new head prep service. The BFH Head Porting Service has some major improvements over the SLEDGE service:
    1. We do a limited amount of welding on the floor of the ports, to add some material where they desperately need it. This allows us to make an even better port than is possible with our SLEDGE porting service. The floors are really the only place in the port that welding can be done without creating risk of other problems.
    2. We alter the valve angles, spreading the valves farther apart.


      3D Model of Harley Sportster Valve Angles
      The valve placement and angles were 3D modeled to determine the ideal angles for the valve sizes and cam overlap. Once the final design was determined, toolpaths were derived for the CNC machining operations.

      High tech valve spring in XL Sportster cylinder head prepared by HAMMER PERFORMANCE
      The larger valves and higher rpm potential called for the latest in valve spring technology. Beyond a beehive, these recently introduced high tech springs provide natural damping of oscillations via a different resonant frequency for each coil. Spring pressure is increased only slightly, to maintain a durable, long life valvetrain. The valvetrain is rock solid stable to at least 8000rpm with this combination.


      The valve tip remains in the same location so that no changes to the rocker arms are needed. This allows us to use larger diameter valves. 7mm stems are retained, to provide a lightweight valvetrain that does not require brutal spring pressures to maintain high rpm valve control. Special cone shaped single wound springs that provide natural damping of harmonic resonances are used to provide superb control of the larger valves with only a nominal increase in pressure. These springs are state of the art and only recently developed.


  • We invented the world's first bolt-on 1275 kit! The 1275 kit was invented specifically for this package, and then later filtered down to the other packages described above.

    HAMMER PERFORMANCE bolt-on 1275 kit for Harley Davidson XL Sportster
    The HAMMER PERFORMANCE Bolt-On 1275 Kit
    No Case boring Required!


    To accommodate the larger, more spread apart valves as described above, we increased the bore size on our world famous 1250 kits. This is made possible by a special 120,000psi tensile strength steel liner, which allows the cylinder spigots to be made thinner. NO CASE BORING IS REQUIRED, this continues to be a bolt-on kit just like the 1250. This new steel liner also does not compromise liner thickness in the working area of the cylinder. The extra strong material makes it even more structurally stable than our legendary 1250 cylinder!


    HAMMER PERFORMANCE bolt-on 1275 cylinder spigot Harley Davidson XL Sportster
    The 120,000psi Tensile Strength Steel Liner Enables a Thin Spigot for a Bigger Bore

    HAMMER PERFORMANCE bolt-on 1275 cylinder liner Harley Davidson XL Sportster
    The Working Area of the Liner Remains Thick to Promote a Straight, Round Bore that Doesn't Distort Under the Heat and Pressure of a Running Engine. This Results in Superb Ring Seal.


  • This power level starts to outrun the factory 45mm EFI throttle plate, as well as the HSR45 Mikuni on carb'ed bikes. So the EFI version of this package includes an HPI 51mm throttle body, and we port it's manifold as well. The carbureted version uses an HSR48 Mikuni mounted on one of our billet intake manifolds.
  • To complement the extra large valves, 1.725 ratio rocker arms are a standard part of this kit. Large valves bring in most of their flow gains at higher lifts, and the high ratio rockers allow us to achieve this higher lift without creating cam box clearance issues or problems with the factory lifter anti-rotation device.
  • As with the 110+ package, you're going to need the best exhaust on the market, and the best we've ever tested is the Patriot Defender. Set the baffle butterfly wide open and leave it there. See our exhaust system dyno test library for lots of information on XL exhaust system performance.


Sample Quotes and Pictures of the 120+ Horsepower Conversion Package

2007+ 120+hp Package (pdf)
2004-2006 120+hp Package (pdf)
1998-2003 120+hp Package (pdf)
1991-1997 120+hp Package (pdf)
1988-1990 120+hp Package (pdf)
1986-1987 120+hp Package (pdf)
HAMMER PERFORMANCE 120+ Horsepower 883 to 1275 Conversion Package


Frequently Asked Questions


  1. Can't I do a conversion with a set of cams but no head work?
    • Well, yes, you can, but there's very little benefit. The bottom line is that stock 883 heads kind of put you in a box with respect to cam selection. On the flow bench, they nose-over before they get to even .400" of valve lift, in other words, lifting the valves beyond .400" doesn't cause the flow to increase any more. So even the stock cams are lifting the valves more than does any good. Furthermore, 883 heads have shallow chambers and long valves to reach them. This puts the valves much closer to the pistons to begin with, and really compromises piston to valve clearance. Cams with more overlap, as reflected in higher TDC lift figures, can get you into trouble with 883 heads in a hurry. So there's limited opportunity for cams with more overlap. Bottom line, if you want to cam a bike with stock 883 heads, the factory "W" cams (stock in 2007-up 883's) are about as good as it gets. If your 883 has "D" cams (91-06), try to score a set of "W" cams for it, just make sure you get a set that's machined for the timing cup if your bike is a 91-03. Nearly as we can tell, they stopped machining the cams for a timing cup sometime during the 2006 model year, although you should always check.
  2. I'd like to do a basic conversion now, but work toward a higher power conversion over time, to spread out the cost. How can I do that?
    • Unfortunately, there's no good way to do this. The bottom line is that these power packages are very carefully matched with respect to the heads, cams, and pistons. They work together, not only for power production but also just to have enough physical clearance for everything to fit and work, as well as deliver an appropriate compression ratio. Just as an example, the IMPACT 560 cams will only work with 883 heads if the valves have been recessed in the seats significantly, both to correct the valvetrain geometry for the high lift and to gain the valve to valve and valve to piston clearance needed. This, and the unshrouding work that goes with it, makes the chambers bigger, requiring more piston dome to compensate. But that's just one example, there are several more. The bottom line is that if you try to do the project incrementally over time, either you'll need to buy some parts (like pistons) twice, or you'll severely compromise the end result. Not the answer we want to give, but we can't change the laws of physics.
  3. What are my options on the clutch?
    • 883 Models since 2004 have been coming from HD with a weak clutch spring. When you do a conversion on a 2004 or newer model, at a minimum you need to change the spring. A spring is only $27.50, however, to change it requires a $70 spring compressor tool and you'll also probably want a new primary gasket, we offer a high quality rubber coated steel gasket for $12.
    • Embedded into the middle of the factory clutch pack is a compensator plate that's held together by brass rivets. Failures of these assemblies aren't nearly as rare as they should be, in fact the compensator plate has been nicknamed the "grenade plate" in some circles. For this reason, many people will go ahead and change it out for an aftermarket "extra plate" clutch pack, especially if they're in there anyway to upgrade the spring as a part of a conversion. The extra friction disc and steel plate included in the extra plate kit together eliminates the factory grenade plate. It's a simple piece of preventive maintenance you can perform. We like and offer the Energy One extra plate clutch pack, which comes with the spring you need and runs $146. So the whole kit-and-kaboodle, the spring, extra plate clutch pack, and tool, runs $216, plus $12 for the gasket.
  4. What other things should I do to hold the extra power without compromising reliability?
    • Sportster models (except the XR1200) have an oil pump that's driven of the pinion shaft by a pair of gears. At higher power levels, the cranks tend to develop slightly more runout due to flywheel spread, and it causes the oil pump drive gear on the pinion shaft to wear badly on one side. You'll see the teeth getting sharp in one area, and 180 degrees from that spot they'll look like new. Eventually the teeth fail and it's ugly. This was an especially bad problem on stock Buells due to their higher power level, and in 2006 HD finally came out with a solution, a bronze drive gear. But they never put this gear onto Sportsters, it just wasn't a bad enough problem at 65hp. When you're hopping up an XL, it's a good idea to swap out your stock gear in favor of this bronze unit. HAMMER PERFORMANCE offers the gear as well as the special pinion locking tool you need to change it properly. It's cheap insurance against a catastrophic failure, especially if you're in the cam box anyway as a part of a hop-up project.
    • The stock primary chain tensioners on 1991-2000 models are failure prone at higher power levels. In 2001, HD introduced a new tensioner with a much thicker steel plate backing up the tensioner shoe. This piece can be had at your local HD dealer as part number 39975-90A, or we can get it for you if you'd like.
    • Similar to the primary chain tensioner issue, on 1991-2001 models the alternator hat was held to the front primary sprocket with 4 bolts, and at higher power levels, these like to shear off. In 2002, HD introduced a new rotor/sprocket assembly, part number 32413-92A, available from your dealer or we can get it for you. Additionally, the aftermarket has addressed this problem with an even nicer one, an 8-bolt sealed magnet unit that protects the very fragile rotor hat magnets from damage. We offer these for $179.95.
  5. Is a new ignition module really necessary?
    • When you convert an 883 to a 1250 or 1275, the speed of the burn goes up dramatically for a couple of reasons. For one, the engine kit almost always brings with it an increase in compression from the 883's stock 9:1. But in addition to that, a conversion generally adds a squish band to the chamber, which increases chamber turbulence, also increasing the speed of the burn.
    • This faster burn requires you to reduce the ignition advance. If you don't pull the timing back (see our installation instructions for specifics), you'll lose power, the engine will run hot, and it's highly likely you'll damage the pistons via detonation or scuffing.
    • If your bike is a 2007 or newer, the ignition is controlled by the ECM and the timing tables in the ECM need to be modified accordingly, using a good flash tuner like the Powervision. We can help with this task, be sure to contact us.
    • If your bike is a 2004-2006 model, you have no mechanical timing adjustments. The only way to adjust your ignition timing for the conversion is to replace the module itself with a unit that provides adjustability. We carry the Dyna 2000TC-3 (for 04-05 models only) as well as the Daytona Twin Tec TC88A (04-06 models). The Dyna is lower cost and works well on curve 28C. The DTT unit is more powerful due to it's programmability with the optional programming kit, and a bit more expensive.
    • If your bike is an 86-03 model, a new ignition module is highly suggested but not strictly necessary. These years have a mechanical adjustment that allows you to reduce overall timing advance which will keep the pistons from being damaged. However, this is less than ideal for a couple of reasons:
      • The faster burn of the engine kit really wants a much softer curve, i.e. the timing should be brought in more slowly. So in the ideal world, your idle timing should be close to stock, but the advance slope should be softer, reaching it's maximum advance of about 28-30 degrees at 4500-5000 rpm. The curve that's programmed into a stock 883 ignition module is much more aggressive than this. Retarding the timing via the mechanical adjustment moves the entire timing curve down but does nothing to change the shape of the timing curve. Bottom line, adjusting the timing instead of replacing the module will leave significant power on the table, because when you take out enough timing to make the engine kit safe, much of the curve will softer than optimum. In particular, you may have trouble with low speed operation, i.e. idling and pulling away from a dead stop under heavy load.
      • Adjusting the module does nothing to raise your rpm limit, which becomes especially important in a performance type build
    • Bottom line, if you have an 86-03, and you're just doing a basic conversion, and you're real tight on funds, you can get away with just retarding your timing per the instructions, although it's certainly not optimal. If you're converting an 04-06, or if you're doing any kind of a performance build on any 86-03, you need the ignition module. If you've got an 07 or newer, let us help you with a new ignition map for your ECM than you can install using a flash tuner.
  6. What tuner devices will work with a 1250 or 1275 kit??
    • Get a flash tuner. Flash tuners work by actually reprogramming the various settings and tables within the factory ECM, to teach it about the new engine configuration. This is the right way to do it.
    • Among flash tuners, the Dynojet Powervision really stands out for it's ease of use and tremendous capabilities. For that reason, this is the device we've chosen to primarily support for use with our engine kits. If you use a Powervision, we will provide you with a starting point map, which in many cases will be very close to what you need, as we've developed maps for a large number of combinations. You can then dial it in from there to your specific bike using the Powervision's built-in autotune capabilities. We've had hundreds of customers successfully tune their bikes using this method.
    • Customers have also had success using flash tuner products from TTS, Screamin Eagle, DirectLink, ECM Spy, and the V&H FuelPak 3 device (NOT the FP1 or FP2). For any of these devices, we will give instructions and certain table values and settings for setting up the initial tune. You will most likely be typing the values in manually. You will then use the logging & tuning process associated with that tuner to dial in your VE tables (Vtune for the TTS, SmartTune for the SEPST, etc).
    • We do not support any piggy-back type tuner devices (Power Commanders, Cobra, FuelPak 1 or 2, Patriot Top Fueler, etc). Piggy back tuners work by hanging off the outside of the factory ECM, intercepting and modifying signals coming and going to "fool" the ECM. The ECM doesn't even know it's there, as far as it's concerned it's operating a stock motor. This approach is fine for pipes and air cleaners, but it starts to break down when you go making 40% changes in displacement, which is what the 1250 & 1275 kit does. Many of them are simply not capable of providing the additional fuel required of a 40% change in displacement, and also many of them will not alter the ignition timing appropriately to compensate for the faster burn of the 1250/1275 kit, which will damage the pistons quickly. But even the piggy-backs that provide adequate fueling and timing control typically don't work well with a conversion. The reason is that there are numerous fine trim adjustments made to the fueling by the ECM to deal with various special conditions, and these fueling adjustments should not be amplified by the displacement difference the way the mainstream fueling is. The result is generally unsatisfactory low speed manners, and general running problems. You're welcome to try a piggy back tuner on your engine kit, but we've had several  customers do so, fail to achieve a satisfactory result (or worse, damage their engine kit), and give up and go get a good flash tuner. We don't think it's worth your trouble to even mess with it.


Final Thoughts


Hopefully the above does a reasonable job of describing the paths to various horsepower levels you can achieve with your conversion. But we fully understand that you may still have questions, so please don't hesitate to contact us at any time, we'll do our best to answer whatever questions you might have, and we'll roll the information into the above to help others. We want to make this article as complete and accurate as possible.

Also, if you're interested in any of the above packages, we would be happy to put together a formal estimate for you and fire it off by email. It helps if you fill out the form on the Contact Us page as it asks for all of the information we need to create a quote with shipping included.

Thanks in advance for your business with HAMMER PERFORMANCE, we sincerely appreciate it, and we look forward to working with you on your project.

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