:D I'm giving serious thought to building an 883 based dirt track style track bike to do track days and maybe a little vintage roadracing. Most of the vintage roadrace organizations have a class for 883 based racers.

Here's my questions for the NHRS folks and others involved with Harley Sportster based race engines:

I'll have to keep an 883 displacement. Are there good high compression 883 pistons available?

Can 883 heads be reworked to flow well enough to use a 42 Mikuni?

Both the AMA 883 Dirt Track & Roadrace series used basically stock 883 motors. I would like a little more bang than that without spending mega bucks.

Any input would be appreciated!

I have spent some time researching 883 stuff :-(

Here are a few of my thoughts.

W grind cams will give a good road (wide power band) tune but don`t really improve on top end HP due to the small 883 valves. Looking at around 53-55rwhp using the W grind cams, good flowing exhaust and filter.

One of the LSR runs a N4 cam (SNAL?) but i don`t have any further information on engine mods. IIRC he was able to hit 135mph.
Just guessing but to reach that sort of speed he must have been putting out anywhere between 65-70rwhp?

Inlet valve needs to be larger as it limits top end flow.
An 883-1200 *conversion valve* can be fitted as it is available in a shorter than stock 1200 length. I`ve yet to try this so don`t know how much shrouding occurs?

The hardest part with skimming the head, to gain a compression increase, is the available TDC overlap lift. Most of the performance *1200* cams have too much lift at TDC.

Any head work should involve welding the 883 chamber to build a squish band, think *Bathtub shape* as this will limit valve shrouding in the small chamber. This would also allow a higher compression without dropping the chamber nearer to the piston. Expensive but will help mix all the fuel/air mixture together. Also if a narrow ( squish band is formed it helps with detonation

Searched and searched for a high compression 883 piston but no luck so far.

Thinner, base (883 and 1200 are the same) and head gaskets, are available.
I got hold of some 883 Cometic head gaskets, Part # H08130027S 0.027". Stock are 0.050".

To get every last bit of *hidden HP* out a fast 883 a programmable ignition system would be a good investment. Also a few reports of reduced vibration levels as the ignition can be *fine tuned*.

Reliability and HP. If the engine uses the Sportster/Twin Cam 2000 and up hydraulic lifters. These are known to bleed down/wear out/make a racket when the engine is used HARD. Better quality lifters are available.

Carb. The stock CV is good enough for nearly 100hp so don`t waste money searching for another :-)

Increasing rpms and therefore hp.
Need to lighten valve train for increased rpms and reliability. As you are building a track day bike you will see high rpms for a longer period than any road bike.

Radical thoughts :-)
How much *meat* is there in the top of a stock 883 piston?
Can a *hollow* be machined so that combined with the combustion chamber a sphere is formed?

A search on the XL-LIST for posts by Dale Amsden or Phillydude will turn up lots opf info on a fast 883.

Hope this helps.

Tony UK
883R
RE350
FZR600

Tony,

Thanks for the detailed info on building up an 883 engine. Sounds like it would be more cost effective to go with a 1200. Better heads, after market pistons, etc.

I just picked up a C&J single shock XR-750 dirt track frame, which will serve as the chassis. Once I get it to the rolling chassis point, I'll start looking for a donor motor. Collectors have driven the real XR-750 motor prices through the roof, so that's out for now. Always wanted an XR and this is as close as I'll get. Hmmm, an XR1200? Isn't the first time someone shoved a big sporty motor into an XR race chassis.

Later,

Here's a photo of the C&J XR-750 frame for my project. It's a single shock chrome moly C&J Racing frame used by National #23 Kevin Atherton during the 95/96 AMA dirt track seasons.

Ordered a new set of 2003 XL1200S adjustable sport fork legs today. If I can't find a real XR motor at a reasonable price,yeah like that's going to happen, I may go with XB9 998cc short stroke Buell.:D

It would take custom pistons to get your compression raised up in 883 configuration. We can get them but it will take time for them to be made. Feel free to call me and we can discuss all your options.

Thanks Dan,

If I go with an XB, I'll probably skip the 883cc displacement and keep the 998 for a start. Don't know how hard it would be to change it to carbureted. Do you guys use a self generating CDI on your racer, or a stock total loss battery powered ignition on your Buell racers?