13qtr

We start with my motor.. remaned lt1 with 14k on the motor. I've only had the car a year,had 10k on it when I bought it. It has the zz409 cam,1.6rr,58mm tb and 1 3/4 long tubes. I'm looking at a set of heads that's been ported, 2.0/1.55 valves and 62cc chambers. A mechanic said that I'd lose power by dropping compression ratio. I got to wondering what my current compression ratio is...and put on a pressure tester. Only did 1 cylinder....it showed 195psi...everytime. So...is that normal pressure on stock motor or has mine been shaved some? I can see they say below 100psi...you got problems. And if so...would the 62cc chambers drop it enough to hurt power. I can get the new heads shaved if needed.

RamAir95TA

Your compression psi does not exactly convert over to your compression ratio without knowing several variables (deck height, HG thickness, bore diameter, piston dish volume, current CC size, etc.). Without taking the engine apart and doing some measuring unfortunately it's just impossible to tell exactly what your current comp. ratio is.

Lower compression means lower power. But if the heads are ported then what you'd lose in compression you'd likely gain in port velocity and subsequent horsepower.

Injuneer

You can't accurately predict compression ratio based on a compression test. Too many variables, including the cam specs, temperature of the engine, condition of the rings, how much oil is on the cylinder walls, carbon buildup, etc.

Orr89rocz

Going from unported stock heads at 58cc to 62cc ported heads will not lose power. (ofcourse assuming heads were properly ported, not some hack job). More compression is more power but the gains in airflow are gonna make the big difference on your setup. You are only losing half point compression. Thats not a significant amount of power.

If they are used heads, they may need a good resurfacing before putting them on anyway to make sure you have good seal.

96capricemgr

What heads are they that they have a 62cc chamber? Might gain peak power but the engine could get a little lazy down low where you drive.

I would be more concerned with getting rid of that cam than buying heads that drop compression. Stay very far away from TPIS, their throttle body might be OK but not much else.

13qtr

I was aware of that....was thinking 195 was a little high. I can promise you there is NO carbon in there....every drive is a 'blow the soot out' drive. Pretty sure there is no oil leak by..plugs always looks good and no oil loss.

13qtr

It's stock heads that have been worked. The cam was in it when I bought it. I didn't think it was that bad of a cam. It made 330whp/348wtq and was running real rich....the peak power was at 6k and the peak tq was at 3k. It pulls hard..of course I got 3.90's.

RamAir95TA

Stock heads that have been worked?

Stock heads have 58cc chambers, so someone removed a ****-ton of material inside the chamber to get them to 62cc which might suggest an amateurish port job.

My AI 200cc ported stock castings ended up with 52.6cc chambers, for comparison.

Injuneer

I thought the last time we went through "how many cc's are the stock heads", the consensus, including a couple engine builders with measurements to back it up, was that they are 54cc.

RamAir95TA

I remember hearing both, but no one could ever come to some concrete evidence either way. I think I remember being part of those conversations too! Either way I think we can all agree, 54cc or 58cc, that that is still a lot of material to remove to achieve 62cc heads.

13qtr

My bad....I just looked at the numbers on the heads I'm looking at. There the 643's...it's 68cc ports,not 62cc chambers. They just listed the stock specs.

I'll post the link..ya'll can look at it..to see if there worth getting...
Ported LT1 aluminum cylinder heads ready to install | eBay

RamAir95TA

Before you make that purchase, demand DETAILED close-up images of the runners and chambers. The more the better.

96capricemgr

195 is maybe slightly LOWER than stock but it could be the cam doing it. Built NA LT1s will usually crank much higher than that 225+psi on stock shortblocks with ported/milled heads and thin head gasket custom cam.

The iron head b-body motor with 10:1 static compression cranks 195 and is tuned for 87 octane.

Far as the cam there is very little reason to use a single pattern cam in an NA LT1, look around and about the only other single pattern LT1 cam you will find is the Lingenfelter 219/219 BUT that was designed to compliment the VERY different superram intake. Basically everything else be it shelf or custom has more exhaust duration because gen 1 and gen 2 23 degree smallblock chevy heads are weaker on the exhaust side than intake, that is the way it has pretty much always been.

"pulling hard" is too subjective, particularly if you don't have experience with powerful cars. Early on in my modding I was happy with some mods that today I consider some of my biggest mistakes.

Far as the stock chamber size, seeing as we can get chambers in the 52-54cc range AFTER full CNC porting of the chamber and some milling I think it logical to guess they start out about 54cc. If they started out at 58cc then got opened up more by chamber shaping then it would be really hard to get them down into the low 50s again.

I would say based on that if the heads you are looking at are 62cc and aluminum(the iron heads were near that) then they are almost surely butchered, otherwise the seller doesn't know what he actually has which is another scary possibility that would send me running.

96capricemgr

You posted the link while I was typing(slowly) I would pass.

13qtr

Thanks for the responses....I retracted my bid.

As for having fast cars....I've had a few. I had a (don't laugh) srt-4 with a built motor/big turbo...that ran 11.8 in the qtr. I also had a G8 that I dropped a fully built Ls3 in..with a big cam and stall....it ran 11.9's.

I'm still gonna look for some heads...