460 Compression Ratio
Thread Starter
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Mountain Pass
Joined: Jan 2001
Posts: 108
Likes: 0
From: Cullman, Alabama
460 Compression Ratio
First off, not building a hot rod. Stock cam, stock heads.
Flat top (not dished) pistons.
1973 block
1986 heads
Got my short block together tonight, just for sh___ and giggles I thought I would check the compression ratio. Came up with 8.6/1
If I "zero" deck the block (.040") I would have 9.1/1
Is it worth the expense? I use this truck to pull my 8000# trailer up and down the road and want something that will PULL and not lose speed pulling hills.
My current motor has dished pistons and 1973 car heads so the compression would probably be a little less than 8.0/1. Weak motor.
Flat top (not dished) pistons.
1973 block
1986 heads
Got my short block together tonight, just for sh___ and giggles I thought I would check the compression ratio. Came up with 8.6/1
If I "zero" deck the block (.040") I would have 9.1/1
Is it worth the expense? I use this truck to pull my 8000# trailer up and down the road and want something that will PULL and not lose speed pulling hills.
My current motor has dished pistons and 1973 car heads so the compression would probably be a little less than 8.0/1. Weak motor.
Elder User
Joined: Jun 2004
Posts: 800
Likes: 6
From: Edmonton, Alberta Canada
yes it would be worth it. don't know how much it would cost to deck the block, but i can't see it being that expensive especially considering the gains by doing it.
9:1 is a good all around ratio to aim for. you will still need to run premium especially if pulling a load but shouldn't cause any detonation issues either.
rgds
Mike
9:1 is a good all around ratio to aim for. you will still need to run premium especially if pulling a load but shouldn't cause any detonation issues either.
rgds
Mike
Lead Driver
Joined: Sep 2003
Posts: 5,241
Likes: 3
From: Other side of the sunrise
Another option would be to replace the heads with some 1968 - 1970 heads. They were close chambered and higher compression. I just had my 68 460 rebuilt, had dished pistons installed and the compression ratio was calculated by the machine shop to be 9.3:1. Damn thing runs like a stripe-assed ape. Great torque. Good for pulling over tree stumps... Or houses or whatever.
Post Fiend
Joined: Mar 2004
Posts: 6,056
Likes: 8
From: Union, Washington
yes it would be worth it. don't know how much it would cost to deck the block, but i can't see it being that expensive especially considering the gains by doing it.
9:1 is a good all around ratio to aim for. you will still need to run premium especially if pulling a load but shouldn't cause any detonation issues either.
rgds
Mike
9:1 is a good all around ratio to aim for. you will still need to run premium especially if pulling a load but shouldn't cause any detonation issues either.
rgds
Mike
Thread Starter
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Mountain Pass
Joined: Jan 2001
Posts: 108
Likes: 0
From: Cullman, Alabama
Another option would be to replace the heads with some 1968 - 1970 heads. They were close chambered and higher compression. I just had my 68 460 rebuilt, had dished pistons installed and the compression ratio was calculated by the machine shop to be 9.3:1. Damn thing runs like a stripe-assed ape. Great torque. Good for pulling over tree stumps... Or houses or whatever.
Yeh, I remember how the 68, 69 and early 70's 429/460's ran. Night and day difference between them and the 73 up motors.
Cargo Master
Joined: Oct 2005
Posts: 2,298
Likes: 27
From: NJ
I find it hard to believe even at .040" in the hole with any flat top you are at only 8.6:1 with E6TE heads. Should be at least 9.5:1 likely a bit more. What model piston are you using and waht is the compression height?
Thread Starter
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Mountain Pass
Joined: Jan 2001
Posts: 108
Likes: 0
From: Cullman, Alabama
yes it would be worth it. don't know how much it would cost to deck the block, but i can't see it being that expensive especially considering the gains by doing it.
9:1 is a good all around ratio to aim for. you will still need to run premium especially if pulling a load but shouldn't cause any detonation issues either.
rgds
Mike
9:1 is a good all around ratio to aim for. you will still need to run premium especially if pulling a load but shouldn't cause any detonation issues either.
rgds
Mike
I was planning on mid-grade fuel, I'll play around with the advance/total timing until I get the thing humming.
Melling Cam specs;
............ @.050.............. SAE Specs (.060")
...........Opens Closes Dur. Opens closes Dur. ... Lift C/L ratio
INT. -14 BTC 27 ABC 193 18 BTC 75 ABC 273 .442 110 1.75
EXH. 39 BBC -13 ATC 206 72 BBC 35 ATC 287 .485 116
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Mountain Pass
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From: Cullman, Alabama
BDCV=1088 cc
TDCV=126 cc
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Senior User
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[quote=art015;8880966]Took the block back to the machine shop to have .040" slabbed off the deck. Pick it up Friday.
I was planning on mid-grade fuel,(/quote]
How much did it cost to get this done? I'm getting ready to rebuild my 460 & will end up zero decking the block on mine as well.
I was planning on mid-grade fuel,(/quote]
How much did it cost to get this done? I'm getting ready to rebuild my 460 & will end up zero decking the block on mine as well.
Cargo Master
Joined: Oct 2005
Posts: 2,298
Likes: 27
From: NJ
With those pistons .040" in the hole I come up with 9.03:1, at zero deck I figure 9.76:1. Either way you slice it you're talking premium. 91 is iffy, 93 is better. Depends on what cam you run and what your dynamic compression works out to. What cam were you thinking of running? Shoot for a dynamic compression ratio around 8:1, maybe a little higher. 8.5:1 is pretty much max with pump premium.
Definitely zero deck, because at .081" quench that thing will detonate like nobody's business on 93 with an 8000 lbs trailer. You'd have to retard your timing a lot and lose significant power and MPG.
Definitely zero deck, because at .081" quench that thing will detonate like nobody's business on 93 with an 8000 lbs trailer. You'd have to retard your timing a lot and lose significant power and MPG.
Cargo Master
Joined: Oct 2005
Posts: 2,298
Likes: 27
From: NJ
Higher compression will enable you to gewt better MPG and HP. Often times at cost per mile a higher compression build will be cheaper to drive. Everything I own burns 93 octane which is more cost effective for me than burning 87. The OP's engine was originally around 8.5:1, so not sure where you're getting that 9:1 from.
Post Fiend
Joined: Mar 2004
Posts: 6,056
Likes: 8
From: Union, Washington
[QUOTE=art015;8880966]..................I was planning on mid-grade fuel, I'll play around with the advance/total timing until I get the thing humming./QUOTE]
Do not exceed 38° max mechanical timing or you will end up with a holed piston. Initial will depend on the advance curve in your dist.
Do not exceed 38° max mechanical timing or you will end up with a holed piston. Initial will depend on the advance curve in your dist.
Cargo Master
Joined: Oct 2005
Posts: 2,298
Likes: 27
From: NJ
At 9.76:1 you will not be running 89 octane in a heavy truck with an 8000 lbs trailer. The thing would run so poorly if it didn't destroy itself. Plan on running the highest pump octane you can get in your area. Cam timing will have a lot to do with how the engine runs, octane requirements, and detonation resistance. What can are you thinking of running?
Also, I would recommend doing a mild exhaust port cleanup on the heads and polishing the chambers will increase detonation resistance.
Also, I would recommend doing a mild exhaust port cleanup on the heads and polishing the chambers will increase detonation resistance.
Post Fiend
Joined: Mar 2004
Posts: 6,056
Likes: 8
From: Union, Washington
At 9.76:1 you will not be running 89 octane in a heavy truck with an 8000 lbs trailer. The thing would run so poorly if it didn't destroy itself. Plan on running the highest pump octane you can get in your area. Cam timing will have a lot to do with how the engine runs, octane requirements, and detonation resistance. What can are you thinking of running?
Also, I would recommend doing a mild exhaust port cleanup on the heads and polishing the chambers will increase detonation resistance.
Also, I would recommend doing a mild exhaust port cleanup on the heads and polishing the chambers will increase detonation resistance.