I read somewhere that the lt4 head head came with 54cc chambers thus netting 10.8-1 compression. I was under the impression that the lt1 head was 54 cc. Which one is correct? Was there a change in size after '95? My '94 was rated at 10.5-1 compression as was the '95. I seem to remember the rating for the '96 and '97 models dropping to 10.4-1

 

Stock LT1s have 58cc combustion chambers.

 

By the way, what are your "few mods", if you don't mind?

 

They are 54's, not 58's.

 

I had a stock set CCed and they were 58.

 

Like he said....I did it myself and it was 58cc as well on my '95.

Rich Krause

 

Quote I stand corrected my old GTP's were 54cc after they were milled. 58cc is stock.

 

Thanks for the replies. What are the advantages of bumping compression and realisticly, how much power can be gained by doing this? I understand that compression is critical in blown applications but what is 1 compression point worth N/A?

 

I read a page comparing the two and it said that the increase in compression was from the swallower valve reliefs in the LT4 pistons. Both the head chambers where the same. Said 54.4cc
Is it standard to cc a head with a sparkplug in it or using a stop?
Maybe that's why the 4cc difference

Jeff D.

 

You can increase your compression by using a thinner head gasket, but it probably won't give you too much horsepower. If the heads are out of the car already, you might want to go ahead and get thinner gaskets (I believe Impala SS gaskets is one choice), but otherwise I wouldn't bother. Plus higher compression usually means Premium Gas.

 

The engineering/blueprint specs are 54.0 for LT1, and 54.4 for the LT4. Although some heads (and blocks) are machined on the plus side of the tolerances set, I'll MAYBE give ya 57, but to agree with 58, I'd have to measure/see it myself, to believe it. That being stated, if those here, state it is true, based on their own checks, so be it. The LT1s I've checked were earlier heads, so may or may not be an issue, but anyway, were 54 cc. The chambers varied +- 3 or 4 tenths.

Is it standard to cc a head with a sparkplug in it or using a stop? Maybe that's why the 4cc difference

Spark plug in place, in my book. I see it as pointless to check chamber volume with a stop in place, in lieu of a plug. Not too many engines will function/run with a stop inserted in head, so why check volume that way. That figure would be meaningless, for compression calcs as well.

 

anyone have a response the with plug with out plug size?

 

I cc'd my stock heads with no mill work and polished chambers. I took no material out of the chambers other than the rough as-cast finish. I got 55 cc. I said before in another post that it could be .5 cc on either side, but it's pretty close. I checked with the spark plug in place. There seems to be an ongoing discrepancy in what people say is stock, as well as what they measure. Given that, the only way to know is to measure your own set. I also measured the stock valve reliefs in a new LT1 piston. I got between 4 and 5 cc there.

 

My stock LT1 heads were 54.5 cc's with the spark plug in.