9.25/1 is my present comp ratio. In order to optimize engine performance for the street, I would like to get it as close as possible to 10.0/1. From here 2 possibilities:

Milling the deck 0.015 (piston will be exactly at deck level), comp will then be around 9.65/1. Can I go any further than that, ie: 0.030 (assuming that I keep the good valve-piston clearance of course) ? or should I mill the alum heads ?

Or moving to a .200 domed piston which will get comp ration around 10.7/1 (running on 95 octane). I would like to avoid this option as it is more costly.

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Originally posted by capri man:
have you considered thinner head gaskets? i went from regular fel-pros to a mccord ..018 thick gasket. about the same as cutting the heads .030 dont really know how dependable they are though, for long term street use. good luck

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That sounds like a great solution, I would like hear more feedback on the product quality though.

www.cometic.com

They manufacture custom gaskets for high performance applications, and have a great customer service/tech department. Pierre, those .018 shim gaskets would be great if you were running iron heads, but aluminum expands/contracts at a far quicker rate than iron (block material) requiring an MLS (multi-layer spring steel) gasket, and that's where Cometic comes in. I've got .030 MLS gaskets on my motor, and that's about as thin as they can make a three-layered gasket I believe. I needed a specific steam hole pattern for my (PITA but worth it ) Trick Flow heads. I sent them a sample pattern, and they made me a pair

The head gaskets you run now are probably in the .045 compressed thickness range, you may still be into milling your heads a little bit to reach your 10:1 goal. I had my block decked to .005 (in the hole), matched with a .030 gasket nets a .035 quench; which is tight, thus the forged h-beam rods I run . If your pistons are .015 in the hole now, you'd have a .045 quench height which is perfect for a stock rod motor to keep your pistons from getting to know your cylinder heads

Decking the block is an option too, just be mindful of that quench height. A zero deck would need at least .045 gasket.

They're not cheap gaskets, about $75/each US. I spin my motor 7000 rpm regularly without any problems whatsoever

Oh hey, Bonne Annee to you as well! (I'm assuming that's Happy New Year )

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1965 GT coupe, 333ci aluminum headed/solid cammed stroker, four speed, 3.70:1 9"

Thanks for your detailled answer: I figured when I posted this that things wouldn't be that simple

If I understood the problem, using stock C80E rods, limits my quench height to 0.045 but that doesn't mean that I can't reach my 10.0/1 objective. I just have to reach it by using an additional method.

The present Fel-Pro 1101-2 have a 0.039 compressed thickness. So I can only shave 0.09 from the block (giving 9.4/1) to respect the above limitation. The additional compression will have to come from a domed piston (or smaller dish, presently 4.25cc)or from milling the heads (bothers me to cut into a 1000$ item !!)

Did I get this right ?

Jerry,

What is angle milling ?

As it is now, you've got an assembled quench of .054 which is huge. Without any machine work and with those Cometic gaskets you could in fact reduce that quench height to .045 which is still plenty safe. I don't blame you for not wanting to cut a high dollar pair of heads, but you may not need to shave them by much. That won't affect your quench, but decking the block would. If that's something you'd be willing to concider, I'd recommend calling Edelbrock. Give them all the specs, and ask how much to cut to have a combustion chamber volume of (x) to achieve a 10:1 ratio with a 4.030" bore, 3.000" stroke, 4.100 gasket bore .030 compressed, with 4.25cc of valve relief. That's not much dish... flat tops with reliefs, correct? I cc'd my reliefs at 6.8cc, and I thought that was fairly small.

Angle milling is cutting the heads deeper on the exhaust side (closest to the chambers). The intake flanges then would need to be squared up to the new deck geometry

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1965 GT coupe, 333ci aluminum headed/solid cammed stroker, four speed, 3.70:1 9"

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1965 GT coupe, 333ci aluminum headed/solid cammed stroker, four speed, 3.70:1 9"

All Blue Oval, no blue bottle
http://mustangsandmore.50megs.com/V8Thumper.html

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Originally posted by soaring:
Pierre,
I noticed you stated that going to .200 domed pistons would increase your compression. I am not a mechanic, nor do I have a heated up motor, but don't flat top pistons work better for the compression you are trying to reach?

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Originally posted by Pierre:
Thanks Todd, that all makes sense now.
Is there any down side to increasing comp ratio like this aside from a hotter running engine and more stress on the components ?

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There's a big downside if you can't get fuel with high enough octave to prevent detonation. You can destroy a good engine real fast with detonation.

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'70 Mustang Mach 1 - '72 Mustang Sprint - '94 F-150

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Originally posted by SteveLaRiviere:
There's a big downside if you can't get fuel with high enough octave to prevent detonation. You can destroy a good engine real fast with detonation.

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That's what I run in my car, 91 octane, and that's with a mathematical compression ratio of 10.06:1. Aluminum chambers are forgiving, allowing up to a full point higher ratio than iron heads on a given octane rating Besides, SBF's dont want/need much overall timing (I quote Alex's dyno testing). I run 36* overall, all in by 3500 rpm.

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1965 GT coupe, 333ci aluminum headed/solid cammed stroker, four speed, 3.70:1 9"

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Originally posted by V8 Thumper:
Oh yea, 95 would be great. 91 is the 'high performance' pump gas around here

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1965 GT coupe, 333ci aluminum headed/solid cammed stroker, four speed, 3.70:1 9"