I am trying to find the compression ratio for the flat top pistons in HD's 103" kit (29904-07). Anyone know?

If it helps here is the blurb:

SCREAMIN EAGLEŽ BIG BORE STAGE I KIT FOR EFI MODELS - 1690CC
This Big Bore Kit lets you increase the displacement of our Twin Cam 96-equipped model from 96 cubic inches (1584cc) to 103 cubic inches (1690cc). Includes Big Bore cylinders, Big Bore flat top pistons, rings, clips and a Stage I Air Cleaner Kit with one-piece backplate, integral breathers, all mounting hardware and gaskets. A high performance clutch spring is included to provide the additional clutch capacity required by the extra power. Requires separae purchase of primary cover gasket. This kit is street legal when used with with stock mufflers. All EFI-equipped models require ECM calibration (priced separately). Regulatory approvals pending for 07 models. Fits 07 Twin Cam-equipped models. OBSOLETE, SUPERSEDES TO 29904-07A
Silver


Thanks! Steve

 

I calculate it at 9.9 to 1 with a .030" head gasket and a 87 cc chamber. Dome volume -2 cc's for valve pockets..

 

what heads are you running?opps randy beat me to it,
kirby
vee twin racing

 

There is just so much I don't understand...

I am trying to save some $$ by buying a 103" kit off of ebay. My builder tells me that with the cam he is recommending, I should have a minimum of 10.25:1 Compression. My heads will be done by Baisley in Portland and I don't know any specifics about them.

On Baisley's website he sells "SCREAMIN' EAGLE PISTONS 10.25 CR 22661-99A" So I assumed compression ratio was determined solely by the pistons.

Anyway the reason I'm asking is the ebay kit is a really good deal if I can use the pistons in the kit. Not so good if I can't.

Steve

 

You'd be better off buying pistons, and having your stock jugs bored to match. What cams did you builder recommend? I've been running Baisley heads for about a year, and love them.

 

Yeah that is my understanding too, I'm just trying to save money. $300 for the 103" kit on ebay. Hard not to think about. I probably will have baisley bore my existing jugs though.

He recommended the SE 259 cams. They are new. Note the year designator: #25482-10. I think he said they were very similar to the 251's but designed for the EFI bikes.

Steve

 

Talk to Biesley. Pretty likely they mill the heads some, 0.060 probably. This lowere the chamber voluum some to 83 cc's maybe. This gets the 10.25 or about.

Adjustable pushrods and a tuner.

 

You can use the pistons. Snag the kit while you can knowing you have still to work out the detals of the build. You are looking at 9.9-10.1 depending on deck height and chamber volume but static CR should not be the control point. The specs on that cam are:

10*/47* 58*/12* 246*/250* .579"/.579"

With a 47* intake close, you are looking at corrected compression of about 8.9 which is probably a little low to get the most out of the cam. There are not a lot of people with first hand experience with these new H-D cams. The specs inidicate mid to high range performance but not much happening below 3000rpms with stock heads. Headwork and decking to get static CR to about 10.3, with a good pipe and tune, should get some power down around 2500rpms. But, I have no hands on experience with the cam, so I am speculating.

If I were you, I would talk to Baisley or any head porter with first hand experience with these cams before I locked in on one. There are certainly better alternatives and Baisley will probably point that out when you talk to them. You shoud select the cam first based on where you want the power and let the headwork follow.