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Old 05-11-2010, 09:34 PM
art015 art015 is offline
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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.
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Old 05-12-2010, 01:39 PM
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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.

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Old 05-12-2010, 04:09 PM
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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.
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Old 05-12-2010, 04:55 PM
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Quote:
Originally Posted by mcdonaldm View Post
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 to 1 should never require premium fuel if it is in fact actually 9.1 to1 and the timing is done right. Premium fuel comes in at about 9.5 to 1.
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Old 05-12-2010, 06:22 PM
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Originally Posted by olfordsnstone View Post
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.
I'd love to find a pair of C9VE, D0VE, D1VE but they're getting scarce...And I already had these 86 heads worked with new valves and guides.

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.
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Old 05-12-2010, 06:22 PM
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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?
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Old 05-12-2010, 06:50 PM
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Quote:
Originally Posted by mcdonaldm View Post
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
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Originally Posted by Bear 45/70 View Post
9.1 to 1 should never require premium fuel if it is in fact actually 9.1 to1 and the timing is done right. Premium fuel comes in at about 9.5 to 1.
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, 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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Old 05-12-2010, 06:58 PM
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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?
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Old 05-20-2010, 02:38 PM
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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.
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Old 05-20-2010, 06:18 PM
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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.
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Old 05-20-2010, 10:19 PM
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I would have just left it alone at 9:1. Who wants to be locked into premium fuel at these prices ?
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Old 05-20-2010, 10:45 PM
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I would have just left it alone at 9:1. Who wants to be locked into premium fuel at these prices ?
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.
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Old 05-21-2010, 03:00 AM
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[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.
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Old 05-21-2010, 11:35 AM
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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.
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Old 05-21-2010, 12:07 PM
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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.
I agree with cadunkle's assessment. With today's junk pump fuel, a close to 10 to 1 compression will not work. A much more reasonable number is 9.5 to 1 and a smarter number is 9.0 to 1. Besides that big compression makes big horsepower whereas, for towing you want TORQUE and at a reasonable RPM too. A cam with low duration and lots of lift will help with the towing, however it will hurt the ability of the engine to run on pump gas with a 9.76 to 1 compression.
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