Which of these perform better, i know there is a difference, but i have never really heard of any significant performance differences. is there any?

883 heads are smaller ports yet on a 1200 conversion it will outrun a "stock" 1200 smaller ports make faster velocities and better throttle response

As per NRHS, the 883 heads (in stock form) are the worst of the lot. This posting is a little old, but the data's still current.

http://xlforum.net/vbportal/forums/showthread.php?t=14000

That is the stupidest thing i have ever read.

883 heads are smaller ports yet on a 1200 conversion it will outrun a "stock" 1200 smaller ports make faster velocities and better throttle response

There is some truth to it.

You know about that late 70's technology Suzuki utilized called TSCC? They toyed around with higher velocities with their 4 valve GS engines by making the intake tracks narrower. 20 years later, enter the GSX-R line.

however a 1200 with 883 heads will not "outrun" a 1200 with 1200 heads, that is ridiculous.

There is some truth to it.

You know about that late 70's technology Suzuki utilized called TSCC? They toyed around with higher velocities with their 4 valve GS engines by making the intake tracks narrower. 20 years later, enter the GSX-R line.

Well, lets clear something up here...

The 883 had different gearing, this puts the stock 883 at an advantage from an acceleration standpoint over the 1200. If we are talking about a converted 883 where everything else is the same, then I'd put my money on the 883 converted to a 1200 with everything else being 883 parts, including the heads, just based on the different torque curve the rear tire will be getting.

If you have 2 sets of heads, 883 and 1200, tested on THE SAME 1200cc bike, then yes the 1200 heads will perform better.

and all this information is only relevant to the rigid mount sportys. I have no idea how the rubbermount bikes perform after conversions.

I think one thing needs to be adressed here. The smaller valves will result in more torque at lower RPM, but it won't breathe as well at higher RPM, resulting in lower peak power. With the 883's lower gearing the bike will likely feel livelier than a stock 1200, especially at the lower engine speeds most of us use: particularly in a rigid-mount pre-04 model.

I'd be curious as to the vibration levels of a conversion using NRHS parts. I've heard the smoothest (in terms of vibration level) running 1200 conversion is one using Wiseco pistons, as they weigh the same as the stock 883 pistons.

Any opinions? Right now my particualr Sporty runs real well and vibration is never a problem the way I normally ride: as long as I stay under about 70 or so. Even at that, I have to go a long time before the hand numbness sets in. I'd hate to trade more power for a bike that's less pleasant to ride when I'm just burbling along at 55-60 on some two lane back road.

Of coursse you could chance over to 1200 gearing and raise that vibration point up a few MPH.

I believe the 883 heads are better only when it comes to custom porting.More meat around the valves to shape.

The 883 heads aren't better for any real thing.

You can port them and get reasonable results out of them, but they still are a smaller head. You can enlarge the valves and add 1200 valves, but then you have to do a lot more machine work to unshroud them, then you have to mill them because you take up too much volume in the head, and still you're no better then doing the same work on a 1200 head and getting more performance out of it.

The only benefit that you can get from the 883 head is when you do a 1200 conversion and the larger piston with the smaller head creates a flat squish area, giving a little more power.

The 883 with a conversion will out perform a stock 1200 up to about 5000-5500 rpm, then the larger valves take over. The gearing of the 883 will create a quicker motorcycle Off the line. but in the long haul the 1200 will pull away from the 883 conversion. stop light to stop light, the true 1200 can't touch an 883 conversion (stock to stock)

Any good harley modification book will tell you what was just stated above check out motorbooks Harley davidson sportster pg49 "a modified 883 head can easily be made superior to a stock 1200 head. with careful mods the 883 converted to 1200cc outruns a stocker in Every way"
Do your reasearch

But,,, what if you modify the 1200??? If were talking stock 1200 vs. 883/1200mod, i'd bet the 883/1200 mod would be faster too.

Dave, the problem with the 1200 is that the chamber is already pretty much defined. Because of the extra material on the 883 heads, they can be dug out much more, and to the specific designs of the company doing the job without sacrificing wall integrity.

apples, oranges, bananas...

Stock to stock 1200 heads outflow 883 heads
stock to stock 883 heads have a better squish zone than 1200 heads, allowing a higher compression ratio without the risk of pinging...
stock to stock 1200 heads have larger valves, and higher better flow above 4500 rpms....
stage 2 to stage 2 1200 heads require less machining to achieve the same flow numbers as a 883 head
stage 3 to stage 3 (welding up the ports and re-machining, oversized valves, recontoured combustion chamber) The award goes slightly to the 883 head...
Stage 1 XB (or 2004 and up 1200 head) versus stage 3 883 heads... The XB style head performs better... stage 2 and up XB heads are dramatically better than anything that can be achieved through machining or voodoo with an 883 head.

Now real world... You are a smart guy with a dremel tool.... You can get more performance HOME porting a pre-2004 1200 head than you can with a 883 head. Read my signature before you ask how I would know.

If I had it to do again... I would use an XB (post 2004 1200) head to do my performance build.

If I want to get into the 70 HP club, and I want to do it cheap... 883 heads... 3.500 forged lightweight pistons... Cams.... Jets for carb....Gaskets.... Less than a thousand spent, and you will gain about 35 horse assuming you have a good exhaust and breather already.
With your Low 883 gearing you will be beating the factory stock 1200s on a stoplight to stoplight drag race.
You will have to figure out what kind of rider you are... will you want a few more HP, and be satisfied, or will this HP pursuit be a never ending quest. Most people fall into the latter catagory. If you are the latter type.. start purchasing parts so that you won't have to remove them at a later point.

Addertooth