When do you need compression releases
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Seasoned HDF Member
Joined: Mar 2021
Posts: 18,548
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From: backwoods
When do you need compression releases
When do you need manual or automatic compression releases? Did they put ACR in the 103s when they first same out? I believe 103HO is around 10:1. What I am getting at also, is do you need them based on displacement for a 103 or 107 even if under 10:1 compression? I always associated with compression, but as these engines get bigger, I wonder.
Cruiser
Joined: Apr 2008
Posts: 108
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Cubic inches is not the problem, but the compression is. I got manuals for a 9.5 compression, which is not really necessary, but if I go over 10, I'm covered. With the 110 tooth ring gear on TC's (don't know what M8's have), your asking allot of that starter over 9.5 - Learned that lesson the hard way with a high compression build (10.5). A SB Chevy starter is 40-70 bucks, but an HD starter is 200+ After you replace three of them ,you get CR's. Timing is a big factor also. If that thing is advanced to the moon, even moderate builds will eat a starter/ring gear. Your first start is the easy one... after it gets hot, it gets so much worse.
So to answer the freaking question.. My personal figure is anything over 9.5, regardless if CI. - But, I would put them in even for a stocker. Makes starting so much easier on everything. And manuals are just fine. Once you get the mussel memory, you don't even think about it.
So to answer the freaking question.. My personal figure is anything over 9.5, regardless if CI. - But, I would put them in even for a stocker. Makes starting so much easier on everything. And manuals are just fine. Once you get the mussel memory, you don't even think about it.
Last edited by hawkdsl; Jan 30, 2024 at 12:32 AM.
Grand HDF Member
Joined: Sep 2017
Posts: 4,359
Likes: 1,219
From: Dubuque, IA
It's not the static compression. It's the CCP. IMO, anything over 180psi. Anything under, needs more compression. So put them in. It's foolish not to...for like the 5th time you've asked.
Stellar HDF Member
Joined: Jan 2017
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From: Massachusetts
Why? Then he cant start a new thread about ring gears and starters!
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Seasoned HDF Member
Joined: Mar 2021
Posts: 18,548
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From: backwoods
I realize it varies by area. But what is a guess on cost for machining and releases? I see a lot at $50 when I google and then Jims at $150. Brand preference. Just have a shop drill the holes, and screw in ?
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Grand HDF Member
Joined: Sep 2022
Posts: 4,489
Likes: 3,879
From: Florida
I turn over my 93” 11.7:1 mechanical compression (225 cold) Shovel with a stock AMG battery and Stock prestolite starter… Zero problems ever. About 28 degrees advance too, with 590 lift 264 duration. Collectively over 150,000 miles (rebuilt 4 times) springs are about 205 also.
Everyone for 25+ years has told me I can’t do that… they are wrong.
I can’t turn over my 127 without the compression releases. 10.3:1 mechanical aint sharing cam specs.. it couldn’t turn it over at all with the stock starter and a 460 cca battery with 2 guage cables. I’m using a All Balz now.
So don’t know. I suspect friction with vastly larger pistons could slow things a bit. They are both 4.5 cranks so the swept volume is close.. but 93 to 127 is a big jump.
Everyone for 25+ years has told me I can’t do that… they are wrong.
I can’t turn over my 127 without the compression releases. 10.3:1 mechanical aint sharing cam specs.. it couldn’t turn it over at all with the stock starter and a 460 cca battery with 2 guage cables. I’m using a All Balz now.
So don’t know. I suspect friction with vastly larger pistons could slow things a bit. They are both 4.5 cranks so the swept volume is close.. but 93 to 127 is a big jump.
Last edited by Rains2much; Jan 30, 2024 at 07:16 AM.
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