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compression 

 

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 Post subject: compression
Posted: Mon May 05, 2008 9:55 pm 
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I have just got my 302 cleveland block back, bored out 10 thou and crack tested. I want to make it driveable but not a pig. i have a gut feeling that i might run too much compression and blow head gaskets and or rear mains on a regular basis. I will have 2V closed chamber heads on it (ported and polished) and i would like to have flat top pistons in it too with a mild cam and with a bit more fruit aswell. consider that I will shave the heads and block a tiny bit just to make it square when i bolt it together. do you think that it will have too much compression? advice?
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Posted: Mon May 05, 2008 10:52 pm 
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What are the specs ?? Chamber volume ?? etc??
Just machining head and block faces hardly brings comp too high.. I'd say not too much over 10 to 1 on a street motor with iron heads..
Cam does / can bring dynamic compression down..

 

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Posted: Mon May 05, 2008 11:27 pm 
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Have you got the pistons already? If not, have you had a look at the ACL Race Series web page? Once you get over 9.5:1 compression, you have to start using Premium fuel. Some people go overboard with the compression and have to run their cars on Avgas. Not practical if it's a daily driver.

Planing the block and heads shouldn't be a problem if you're just removing a few thou.

Here's a link to modifying the 302 which might be helpful:

http://www.popularhotrodding.com/engine ... index.html

 

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Posted: Mon May 05, 2008 11:46 pm 
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chamber volume.... just a bit over 4.9ltr its only been bored out, its pretty much a stocky. this is my first V8 rebuild and Im just a bit cautious
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Posted: Mon May 05, 2008 11:49 pm 
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havent got pistons yet
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 Post subject: Re: compression
Posted: Tue May 06, 2008 2:39 pm 
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kurt 351 wrote:
I have just got my 302 cleveland block back, bored out 10 thou and crack tested. I want to make it driveable but not a pig. i have a gut feeling that i might run too much compression and blow head gaskets and or rear mains on a regular basis. I will have 2V closed chamber heads on it (ported and polished) and i would like to have flat top pistons in it too with a mild cam and with a bit more fruit aswell. consider that I will shave the heads and block a tiny bit just to make it square when i bolt it together. do you think that it will have too much compression? advice?


Standard Australian Cleveland pistons are flat top, dished or dome are the unusual.

Standard 302C heads are close chamber, they were only used on 302C, chambers are to small standard for 351 unless relieved or after market pistons are used.

Speak to your engine machinist about CCing the heads and calculating your static compression ratio, in most cases as others have said unless a s**t has been machined off the heads you should be right.

Don't worry about blowing head gaskets, they are pretty hardy compared to something with alloy heads etc.

You have gone this far why not go the full hog and purchase a 351 crank and pistons to suit 302C rods (better rod to stroke ratio and more torque, but then again 350 Chevs are worse), it won't cost that much more, and unless someone runs something down the sparkplug hole and measures it has 3.5in stroke not 3", nobody knows the wise. Just need to get some pocket work done to the heads to bring down the compression ratio.

You could just run stock 351 rods and pistons, but combustion chambers still need to be relieved if using 302C heads unless a suitable dished piston is available.

Don't buy elcheapo pistons.

http://www.acl.com.au/web/acl00056.nsf/ ... c0007bb33f

Just putting a few more ideas into your head :twisted:

 

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