Question for Duke or Joe Lucia or any of our Engine Guys

[Larry E.]

Have a friend that has a older 327(300 HP Originally) cruiser Corvette. Just putts around town and low speeds. He has a set of #3884520 (283 Power Pack) heads on it. What I know about these heads is that they have small valves and small chambers.(CC's) With flat top pistons wonder what the Compression Ratio would be? Would this be a good combination for a car that never approaches top speed or raced??? Would low end Torque be better?? Thanks in Advance>Larry

[Duke W.]

Re: Question for Duke or Joe Lucia or any of our Engine Guys

Search for the compression ratio article co-authored by me and John McRae. It's here on the TDB and also the Corvette Forum. You'll need some accurate data like net piston volume, head chamber volume, and deck clearance to use the CR calculator. I believe the OE piston volume is about -5cc, and the heads are about 58cc, but you should verify with other sources. Use a nominal deck clearance of .025", but when the heads are removed, measure deck clearance of all 8 cylinders and use that data. Once you have the above data, use an appropriate gasket thickness to achieve a CR of about 10:1.

The small port, small valve heads effectively make it a 250 HP 327, which has excellent low and mid range torque, but only modest power and a useable power bandwidth to 4500 or so, but for the type of driving you describe, it should be quite satisfactory.

You should also read my tuning seminar and set up the distributor properly. The '66-67 327/300HP setup is best other than bringing in the full 30 degrees of centrifugal in at 3000-3500 rather than the OE 5100. If the car has a manual trans use a 15" VAC and 12" if it's Powerglide.

Duke

[Larry E.]

Re: Question for Duke or Joe Lucia or any of our Engine Guys

Thanks Duke for input. Now a quick follow-up question. Alan Colvin's book indicates that the original head(3782461) on the 66 300Hp
had a chamber volume of 62.076 CC's and the 3884520 Power Pack head had a volume of 60.53 CC's. ALL THINGS BEING EQUAL
EXCEPT FOR THE CLY. HEAD CHANGE WHAT WOULD BE THE DIFFERENCE IN THE INCREASE OF COMPRESSION RATIO?? I DO NOT NEED AN
EXACT FIGURE>JUST AN ESTIMATE. eg. Increase of .2 or increase of .5??? Thanks in Advance. Larry

[Duke W.]

Re: Question for Duke or Joe Lucia or any of our Engine Guys

I don't remember the exact amount. Download the compression ratio article and use the CR calculator. It's easy to use and now is the time to start.

Duke

[Larry E.]

Re: Question for Duke or Joe Lucia or any of our Engine Guys

Anybody else that has an educated guess on the increase of the ratio?? Thanks-Larry