When do you need compression releases?
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Road Captain
Joined: Jun 2008
Posts: 613
Likes: 2
From: Tallmadge, Ohio
When do you need compression releases?
I have been following most of the motor/cam hopup threads and I was wondering at what point Compression Releases (CR) are actually needed? I don't see the need for a stock cam setup and I don't see the need for a 96 to 103 build if your using flat top pistons or keep compression at the 10.1-1 compression or lower. I would assume that it's for builds that have a 10.5-1 compression ratio or higher. Does anybody really know the answer to this? I see so many "opinions" but was wondering if there is some real evidence for when they would come into play. Since I am going to do the 96-103 build in the near future and I will be using something similar to the woods 7H or Tman tr-590 cams, I figure this will help me and probably a lot of others wondering about the same thing. Thanks.
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Road Captain
Joined: Jun 2008
Posts: 613
Likes: 2
From: Tallmadge, Ohio
Bump
Wow, I thought somebody would have an answer for this. I guess I will bump it back to see if anybody looking tonight has an idea. This should prove to be very interesting.
Grand HDF Member
Joined: Jun 2008
Posts: 4,012
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From: Central Fl
I have the 103'' build and do not have compression releases. My feeling is if you leave the comp ratio alone you are ok. There are some that will argue the point but I have not had any problems. Just be sure to leave the compression ratio completely stock. Otherwise a 1.4 kw starter or comp releases will most likely be required.
Ultimate HDF Member
Joined: Feb 2006
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From: TX
Cam profile plays a huge part in the amount of cylinder pressue you make. Some cams bleed off enough that you can "get away" without CR's on an engine that with a differnet cam would require them.
I would NEVER build a motor w/10:1 + static CR without compression releases, but that's just me. Actually, 9.75:1 is the limit for me.
FWIW... when you drop those big bore jugs on a 96" motor, you're looking at 10:1 static CR.
Better SAFE than STUPID!
I would NEVER build a motor w/10:1 + static CR without compression releases, but that's just me. Actually, 9.75:1 is the limit for me.
FWIW... when you drop those big bore jugs on a 96" motor, you're looking at 10:1 static CR.
Better SAFE than STUPID!
Last edited by PhilM; Feb 2, 2010 at 10:58 PM.
Tourer
Joined: May 2007
Posts: 432
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From: Delray Beach, FL
I just had the 96 to 103 done with the screamin eagle big bore kit/255 cams and did not have the cr's installed on the advice of the dealer. Just had the dealer order a 1.4 KV high output starter under warrenty because hot starts are causing the starter to grind. The stock starter really strugles to get it started after the build.
Banned
Joined: Apr 2008
Posts: 2,492
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The new Ultra Limited comes with the automatic comp. releases.....I believe I would do it. They aren't that much, and if the heads come off to do it later, the base gaskets should be replaced,rings, break in again.
PIA factor too high.
Mark
PIA factor too high.
Mark
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Ultimate HDF Member
Joined: Nov 2007
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why do you think hd has em in the stock 103 factory motors? it isn't cause the greedy bastards just wanna be nice
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Club Member
Joined: Jun 2007
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From: Bedford UK
My S&S V107T came with automatic compression releases. I still use the stock 1990 starter which has no trouble turning it over.
I guess there are two reasons for fitting them, one being compression ratio, but also as cylinder size increases the pumping load of turning the bigger engine over also increases. Add cubic inches plus an increased compression and there is a starting problem!
That can either be overcome by using a larger starter or fitting comp releases. I guess they are mainly used so we don't have to fit a new starter. It seems to me they have not been around that long, but tuned Harleys have! The industry is making it easier for us to tune our bikes. Seems a good idea!
I guess there are two reasons for fitting them, one being compression ratio, but also as cylinder size increases the pumping load of turning the bigger engine over also increases. Add cubic inches plus an increased compression and there is a starting problem!
That can either be overcome by using a larger starter or fitting comp releases. I guess they are mainly used so we don't have to fit a new starter. It seems to me they have not been around that long, but tuned Harleys have! The industry is making it easier for us to tune our bikes. Seems a good idea!
