Compression ratio?

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Oct 26, 2009 | 12:04 PM

yso191

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Club Member

Joined: Aug 2008

Posts: 753

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From: Yakima, WA

Compression ratio?

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 EAGLE® 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

Oct 26, 2009 | 12:13 PM

Kingofcubes

Road Master

Joined: May 2007

Posts: 851

Likes: 5

From: Mitchellville, Ia.

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..

Oct 26, 2009 | 12:31 PM

prodrag1320

Banned

Joined: Sep 2009

Posts: 3,569

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From: deland,florida

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

Last edited by prodrag1320; Oct 26, 2009 at 12:39 PM.

Oct 26, 2009 | 03:49 PM

yso191

Thread Starter

Club Member

Joined: Aug 2008

Posts: 753

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From: Yakima, WA

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

Oct 26, 2009 | 08:13 PM

beaureed445

Outstanding HDF Member

Joined: Oct 2007

Posts: 2,018

Likes: 6

From: Edmond, Ok

Quote:

Originally Posted by yso191

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

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.

Oct 26, 2009 | 08:30 PM

yso191

Thread Starter

Club Member

Joined: Aug 2008

Posts: 753

Likes: 0

From: Yakima, WA

Quote:

Originally Posted by beaureed445

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

Oct 27, 2009 | 09:10 AM

Old Gunny

Road Warrior

Joined: Nov 2007

Posts: 1,984

Likes: 7

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.

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Oct 27, 2009 | 11:50 AM

djl

HDF Community Team

Joined: Jun 2006

Posts: 12,774

Likes: 2,606

From: san antonio

Quote:

Originally Posted by yso191

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

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 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.