Compression Ratio

Jason_Charowsky

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So, I just got done building my 95 302 and when I put the specifications into the summit racing calculator, it spit out that I had a ratio of 8.38:1. Now I could be wrong but I would have assumed that my CR would have increased instead of decreasing over stock. I have AFR 1351 heads with a 64cc combustion chamber, pistons that have a head volume of 11cc's, deck height was 0, and then my compressed gasket thickness is 0.042. Is there any issue with running N/A with a lower compression ratio? And lastly is the number that the calculator gave me correct?
 

lwarrior1016

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So, I just got done building my 95 302 and when I put the specifications into the summit racing calculator, it spit out that I had a ratio of 8.38:1. Now I could be wrong but I would have assumed that my CR would have increased instead of decreasing over stock. I have AFR 1351 heads with a 64cc combustion chamber, pistons that have a head volume of 11cc's, deck height was 0, and then my compressed gasket thickness is 0.042. Is there any issue with running N/A with a lower compression ratio? And lastly is the number that the calculator gave me correct?
Are your pistons 11cc dish or 11cc dome? That makes ALL the difference.
 

lwarrior1016

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They are 11cc dish.
Well, I’m coming up with the same thing you are for compression. 8.38:1 and that’s really low. Apparently the stock E7 heads had 60-64cc chambers so that’s about the same as what you have. If you ordered those pistons with a dish, that’s where you lost your compression. They need to be flat top or domed to get any of that compression back.

You’re going to be down on hp and torque. It’s probably going to feel sluggish and need a lot of timing to try to help it out.
 
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Jason_Charowsky

Jason_Charowsky

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Well, I’m coming up with the same thing you are for compression. 8.38:1 and that’s really low. Apparently the stock E7 heads had 60-64cc chambers so that’s about the same as what you have. If you ordered those pistons with a dish, that’s where you lost your compression. They need to be flat top or domed to get any of that compression back.

You’re going to be down on hp and torque. It’s probably going to feel sluggish and need a lot of timing to try to help it out.
Here is a link to my pistons just incase i’m wrong. But when i ordered them i thought they were flats with just reliefs.
 

Musturd

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I’d order something in the 10-1 area even if boosted 10-1 is good . Just my opinion
 
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Jason_Charowsky

Jason_Charowsky

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I’d order something in the 10-1 area even if boosted 10-1 is good . Just my opinion
my block is already together so i’m unable to replace the pistons without undoing almost all the work done to the engine.
 

Snorky

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Yeah.. that low compression will allow you to run a metric shit ton of boost on 93 pump without predet.
 
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Jason_Charowsky

Jason_Charowsky

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I would love to boost it, but it is my daily driver to get back and forth from college lol.
 

Musturd

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You’ll get there faster . My cars had a blower on it for 20 years
 
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Jason_Charowsky

Jason_Charowsky

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I think for the time being I'm keeping the car N/A with the CR I have until I have the money to throw some real boost at it.
 
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Jason_Charowsky

Jason_Charowsky

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Does the college ban boost? I would assume you are in california if that is the case?
No I am in NJ and as far as I know they don't. But id rather keep it N/A until I get more money as I have thrown it all into the rebuild.
 

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