Discussion Forum - Northstar Chevelle Club

jim larson · 2K+ Club

?'s regarding head volume and general overall condition/

67ss · 1K+ Club

I typically use a syring like that to cc heads and it has always come out pretty accurate. But in looking at your picture I think someone cut the chambers to deshroud the valves. Have you measured the valves to see if they are bigger, I think they should be 2.08 intake and 1.72 exhaust.

jim larson · 2K+ Club

67ss wrote:

I typically use a syring like that to cc heads and it has always come out pretty accurate. But in looking at your picture I think someone cut the chambers to deshroud the valves. Have you measured the valves to see if they are bigger, I think they should be 2.08 intake and 1.72 exhaust.

Original size valve should be 2.06 and 1.72. Do I have to remove a valve to measure them? I guess that would add some volume. But not as much as I was getting. I'll will have to try another type syringe. Would like to get something as accurate as possible. thanks.

Dave Seitz · Mega Poster

If you do shave the heads a tick it will bump up compression run a thin head gasket as well.

67ss · 1K+ Club

One other thing is you need to put something flat over the chamber to make sure you are getting an accurate reading. I have a clear piece of plexiglass with a couple holes drilled in it. One for filling and the other to let air escape.

John D · 2K+ Club

Beat me to it Chris...

A thin smear of vaseline or wheel bearing grease around the chamber, and press down firmly to get a good seal.

(This might affect your "actual/perfect" readings somewhat, but the error will be consistant from hole to hole... so who cares.)

jim larson · 2K+ Club

Use the vaseline with the Plexiglas method; but just rubbing alcohol. Got approximately 101CC's using a 12 cc syringe. I am going to have to find a larger syringe to be more accurate. Can't believe those 100 cc's syringes from China sold at jegs and sumitt are to accurate.

Stan, Car did not run the best on pump gas, unless I added octane supreme 130 to boost the octanes to around 98, that kind of why I want to determine the static and dynamic compression ratio, to see if I can change things to make it run better.

Dave Seitz · Mega Poster

Change cams and that can solve the problem or reduce octane needed.
The engine I just pulled off the dyno was running 93 BP pump gas and did not have one bit of knock. That has a 10.5:1 compression ratio and the cam I found out after the session is used for the Edlebrock 410HP crate engine.

Chris R · 2K+ Club

Are you CC'ing these heads for plans to do some porting?

jim larson · 2K+ Club

Chris R wrote:

Are you CC'ing these heads for plans to do some porting?

Just want to determine the correct static and dynamic compression ratio, then can deceided if I want to change cam, gasket thickness or some porting?

Scott Parkhurst · Super Poster

It sure looks like the valves are pretty deep into the seats.

Brand new valves and new seats allow the valve heads to extend into the chamber more, which will take up a few cc. If yours are 'flush' to the chamber surface like they appear, you'll have gained a few cc of chamber volume as a result.

It's not a bad thing, except for the reduced compression. Less shrouding and less edges in the chamber area are both good things for flow and detonation avoidance.

But if you're wondering how you could have possibly gained a few cc, I'd bet on the valves sinking a bit...

jim larson · 2K+ Club

Thanks for the info Scott. I recheck the volume yesterday with a 60 cc syringe I got from my vet. All 4 cylinders were just about exactly 100 CC, if the syringe was accurate. Don't think the heads were shaved very much in the rebuild years ago. I Was told the engine was rebuilt in the early 80's and had less then 10,000 miles on the rebuild. The camshaft turned out to by an old cam dynamics and the pistons were seal power piston. Does that seem logical. I bought the car in 2004. Compression checked out at 175-180 lb last fall on a warm engine and no oil usage except for about 1/4qt per year that I attributed to leaks that I am trying to fix.