883 to 1200

[chaos901]

All of my work/hobby has been on my own Twin-Cams and I really don't have much knowledge about Sportsters, so I need some education.  A friend at work has a 2007 883 Custom, and mentioned wanting to do convert it to 1200.  That is straight forward enough.

He believes he will have to do the lower end too, I have my doubts and believe that the stock lower end on the 883 and the 1200 are the same. 

My question, are they the same?

[rigidthumper]

Stroke & cases are the same. 3" bore for the 883 and 3.5" bore for the 1200. Factory 1200 heads flow better, and have bigger chambers & valves than the 883 heads, so a complete top end swap works well.

[aswracing]

All of my work/hobby has been on my own Twin-Cams and I really don't have much knowledge about Sportsters, so I need some education.  A friend at work has a 2007 883 Custom, and mentioned wanting to do convert it to 1200.  That is straight forward enough.

He believes he will have to do the lower end too, I have my doubts and believe that the stock lower end on the 883 and the 1200 are the same. 

My question, are they the same?

The primary gearing is different. 2004+ XL1200's have a 38/57 primary and 2004+ XL88'3 have a 34/57 primary. Changing this as part of a conversion is rare, the vast majority of conversions retain the stock 883 primary. If you do change it, and the bike has a gear indicator, and you want the gear indicator to keep working, you need to change it in the tune.

Likewise the clutch spring is different. Since 2004, they've been putting a weaker spring into 883 models, to reduce lever effort. When converting to a 1200/1250/1275, it's necessary to upgrade the spring, else the clutch will slip badly. It'll literally let go on you when you give it a handful of throttle in one of the higher gears, you'll think you kicked it into neutral.

And finally, the final drive front pulley is different. 2004-2010 XL883's came with a 28T front pulley, where 2007+ XL1200's came with a 29T front pulley. But again, there is no need to change this when doing a conversion, and few guys bother. Changing this won't affect the gear indicator, but you'll need to change the vss setting in the tune to correct the speedo & odo.

The rest of the lower end, including the cams, is the same on all 2007-2022 XL1200's and XL883's.

The vast majority of conversions are done with the stock 883 heads, over reverse dome conversion pistons. A set of new XL1200 heads is expensive.

This chart shows how an 883-1275 conversion with stock 883 heads and reverse dome conversion pistons, compares to an 883-1275 conversion with stock 1200 heads and flat top pistons:



Same bike, same exhaust and air cleaner and everything else, same dyno tuner (me). As you can see, the small valve 883 heads win up to about 4600rpm and the 1200 heads win above that. The 1200 heads add around a grand to the price of the conversion.

Many guys choose the 883 heads route specifically because they want more on the bottom to middle, as opposed to more on the middle to top.

[Garry Sr]

Correct me if I'm wrong but it seems like you'd really want to gear it if you didn't do the heads. 

[aswracing]

Correct me if I'm wrong but it seems like you'd really want to gear it if you didn't do the heads.

It's a personal preference thing, depending largely on whether you like quick acceleration or lower rpm at cruise speed. We don't make a recommendation one way or the other. We just provide the data and let the customer decide.

I can tell you that the vast majority of guys leave the 883 gearing in place, on both the primary and final.

[Garry Sr]

Correct me if I'm wrong but it seems like you'd really want to gear it if you didn't do the heads.

It's a personal preference thing, depending largely on whether you like quick acceleration or lower rpm at cruise speed. We don't make a recommendation one way or the other. We just provide the data and let the customer decide.

I can tell you that the vast majority of guys leave the 883 gearing in place, on both the primary and final.

I view it as a waste if you're not taking advantage of all that bottom end but I understand where you're coming from. 

[sfmichael]

A little off topic but hopefully you'll be willing to answer - the best donor bike to build a hot street Sporty would be a 1200 or 883 ? ... if one is going for maybe not maximum effort, but a seriously fast street bike with decent manners. I'm partial to the anniversary '03's but would love to build a torquey 80+ rwhp Sportster and want to start with an optimal foundation. Thanks:)

[Ohio HD]

I won't speak for Aaron, but a light weight bike, I'd want something like this. After all, they've worked out the best matching components to make an 883 a fire breather.

Hammer Performance 883-1275 Bolt-On Conversion Package

[aswracing]

A little off topic but hopefully you'll be willing to answer - the best donor bike to build a hot street Sporty would be a 1200 or 883 ? ... if one is going for maybe not maximum effort, but a seriously fast street bike with decent manners. I'm partial to the anniversary '03's but would love to build a torquey 80+ rwhp Sportster and want to start with an optimal foundation. Thanks:)

The 1988-2003 XL1200 heads have hemi chambers which results in really poor turbulence, which in turn makes them very detonation prone. This is why the bikes came from the factory with only a 9:1 compression ratio, and yet they're still known for detonation issues.

Here, let me show you a picture:



This is the 1988-2003 XL1200 chamber. Notice how it's just a big bowl, i.e. a hemispherical chamber. It's about 3-1/2 inches in diameter, which is the same as the piston. So as the piston passes through top dead center, there's no area where the piston comes in close proximity to the head, i.e. a "squish band". This means really poor chamber turbulence, which in turn means poor mixing, which in turn makes the heads very detonation prone. The whole world got away from hemi chambers decades ago, the 1988-2003 XL1200 was one of the last ones to use them. Even the Chrysler Hemi doesn't use hemi chambers, it's just a marketing term.

There's something else to know about the above picture, too. Look down inside the ports, into the area we call the "bowls", down near those stamped numbers. See that sharp transition there?

Now look at this head:



This is a 2003 XB chamber, but the same heads came on all XL1200's from 2004 through 2022. There were some slight changes in 2007 when EFI came out, but you can consider them the same heads through 2022.

First thing to notice is that it's a bathtub shape, with large squish bands on each side. As the piston passes through top dead center, fuel that's trapped between the piston and those squish bands gets squeezed out. Think of stepping on a tube of toothpaste. That creates chamber turbulence, which in turn promotes good mixing, which reduces detonation. Not only did these late model bikes come with compression ratios of 9.7:1 (XL) and 10:1 (XB), but the 2004+ XL1200's all got "W" cams with very early 25 degree intake close timing, resulting in a cold cranking compression of around 210psi right off the showroom floor. I've seen them pump 220psi. But these chambers, along with MAP based ignition and bigger fins for better cooling and oil jets under the pistons (all of which appeared t the same time), makes this high compression manageable.

Now look down into the bowls. See that same area by the stamped numbers? A much, much smoother transition there. They actually added material right there to smooth that transition, effectively shortening the roof of the port (the "long side" in head porter's lingo). Not shown is they also added material to the floor of the port, i.e. the "short side", lengthening it. This is important, because it's the difference between the short side and the long side that causes port turbulence which reduces flow (chamber turbulence = good, port turbulence = bad). So making the short side longer and the long side shorter makes for a more laminar air flow, increasing power despite the port being smaller.

All of this is a roundabout way of telling you that your preferred bike, the 2003 XL1200, has the worst heads HD ever made for a performance Sportster. Even 883 heads of that generation make a far, far better platform for a performance project than the 1200 hemi heads. Those hemi heads are the bottom rung on the ladder, in terms of a performance project.

So get the 2003 XL1200 if you want, but if you want to do a performance build, figure on replacing those heads. To make really good heads out of them, you basically have to weld them up and start over, which is not only expensive but it's opening a whole new pandora's box of issues.

Fortunately, there's a pretty good set of the late model heads, that'll fit the 2003 XL1200, and a pretty reasonable price. You'll have to contact me for that info, I'm not going to spam this board.

[Hossamania]

Great info, thanks for that, the visuals certainly help.

[sfmichael]

Thanks for the detailed explanation and I have no problem replacing the heads. I just really like the Siver/Black 100th model, especially since I have an 03 Deuce and an 03 F150 so I'll likely buy that particular donor bike and upgrade as needed. Any 883 or 1200 advantage in terms of bottom end or gearing differences that would make one modded bike faster than the other? I know you mentioned minor gearing differences and I prefer the chrome case 1200s over the cast appearance of the 883...but if the 883 would be noticeably quicker, I'd go that way.
Thanks for your time and sharing your experience 

[Breeze]

aswracing;  GREAT post above, thanks.