Hi Derek - I ran the numbers on the heads and they are 1969 heads. The build date is before the vehicle's build so I'd be willing to bet they are the original heads (vehicle is December of 1969 and Heads are late Feb of 1969) The vehicle in general is pretty darn original - Numbers matching motor, trans,diff and carb. So chances are pretty darn good these are the real deal.

 

Your heads are too far apart from the build date on the ride, almost all date related components would be around 60 days or so before the actual build.

We get to restore so many real 100% original units we can almost tell way beforehand whether or not they really are original by the dated pieces supplied to us??

Thanks, Gary in N.Y.

P.S. One "caveat" to the above time frame, 1969 was a major strike year for G.M. We recently finished an all original '69 DZ with the correct "010" block, most OEM '69 DZ's had a "618" block. Due to the strike G.M. grabbed the 010's to complete many builds.

 

Hi Gary - I do recall reading that GM had a big strike in 1969. My understanding is that 1969 Vette production was slightly pushed into 1970. To your point about 60 days - I do recall that the Rochester Carb on my vehicle has an October 69 build date which would support that. The vehicle itself is one of the latest 69 vehicles built - I recall the date in the code was around Christmas of 69. However, because of the strike, you're saying there is a possibility they snagged these older heads just to complete my vehicles build?

 

So bizarre turn of events - Just spoke with the machinist who just CC'ed the heads. He says they are coming in at 108 CC. This sounds very bizarre because my understanding is that oval ported heads were 100 out of the box and these for sure had a valve job done in the past which means they would have to be lower that 100 cc. I'm positive they're oval ports...maybe someone messed with them to jack up the CC volume? I have no idea how you could accomplish this without "hogging out" the ovals into rectangles...

 

valve jobs grind seats so the valve sits lower adding CC's.

 

Couple pics. Rectangle port, oval port, peanut port. These are all about intake flow, not compression ratio. The last 2 are a 119cc combustion chamber and I THINK orig semi-closed chamber on a 215 head, which is essentially the twin to yours. See the extra meat by the spark plug? That makes the chamber volume smaller this raising compression ratio. BUT, it also restricts cyl filling by being in the way when the intake charge is trying to blow into the cylinder.

 

That 215 and your 3931063 are rated the same 109 cc's. Now that is RATED. they are as-cast. If they have been opened up for 2.19 valves, they will be bigger. If head shaved they will be smaller. Here is an oval port opened up to TRY to approximate a rectangle port.

 

All this has nothing to do with the compression ratio. A million years ago everybody wanted rectangle ports. I am a boat guy, so I have a couple sets I scared up cheap. But they are gen 5 and 6 and you can tell them from a MK 4 at a glance. And you can see where the potting person sorta ran out of gas on 1 head and didnt raise the port roof like on the other head. Just opened the opening to the intake larger. Measure your intake valves. 2.06 or 2.19?

 

This head has 97.5 cc chambers. This is the true closed chamber nicknamed bathtub chamber. Pic 10 thru 12. https://m.ebay.com/itm/1965-Big-Bloc...c923%7Ciid%3A1

 

Here is another big block 100cc chamber. The 96-00 L29 aka vortec 454 head. You see how much meat was added between the valves? These are examples of how small a 100 cc chamber is.

 

 

So, looks like you are at about 11.2 to 1 as-is if the heads have never been decked. Did head guy say how much needs to be cut from the heads to fix head gasket burn-through damage? Cuz if 2 or 3 ccs could be removed from those chambers, you would be about 10.9 to 1 with those pistons.

 

Pic number 3 is late 70's round port truck-boat heads. Yours are pic #2, but that gasket looks a little small.

 

 

 

You won't hear valves. The detonation could have been the knocking, but I don't see any detonation damage on top of those pistons. Here is some very light detonation pitting. Did the head guy tell you the valve sizes? If they are still stock 2.06, does he have the equipment to open them up to 2.19 valves, and the chamber, port work that goes with? Cuz that would also lower compression to where you wanna be.

 

He felt stock valves would be fine. The only thing I'm still a bit worried about is the quench. I've confirmed the deck clearance is .025 with a feeler gauge and given the confirmed CC size of my heads at 108 I'm going to need a .060 head gasket to get me down to 10.5:1. This puts me at .085 quench - from my limited knowledge that is high. However, I do know that the motor has a large cam it in. I was told it was in the realm of 240 at .050. I've read that a cam with large duration like the one that is suspected to be in my car will help bring the quench down. Do you think a cam with the above spec will be enough to help with quench? I know I really should measure overlap to be totally sure and may shell out money for one of those gauges. Machinist thinks it's got a Comp Cams Thumpr in it.

 

You're confusing a lot of terms. Quench is related to the clearance between the head and the piston. Notice I said related....quench can be non existent in some engines even if piston is real close to head because the head design doesn't address it. Many Mopar's are that way. The quench area for a BBC is the flat portion of the piston and the side of the chamber opposite the spark plug. Your heads are at 108 cc which is not uncommon at all. As mentioned...valve jobs sink the valves and add cc's. New valves will shrink that number somewhat and if they add 2.19's and are able to raise seat back where it should be..it will shrink a little more.

Nothing wrong with doing some chamber work to unshroud the valves (especially if you add 2.19's) which will add a few cc's.

A tight piston to head distance is desirable for sure....but not the end of the world. Mine typically ran at only .028" total..but the pistons also lightly rubbed the heads. No need to go that crazy. Turbo and nitrous big HP guys routinely add a lot of distance on their engines on purpose. For something like this...do what you need to do to make it all work.

The cam has nothing to do with quench.

JIM

 

 

It all depends on tuning. I ran 11.2 compression on 93 octane with iron heads. You'll want to keep it cool as possible and work out the timing curve. Did you figure out why it blew head gasket previously? Detonation?

Cometic will make gaskets in any thickness you want and have quite a few on the shelf. Go to their website.

Me? I'd do as suggested and find some open chamber heads with 2.19's...or just use what you have. I'd install 2.19 intakes...wouldn't worry about exhausts a lot unless you just wanted larger. I've run awful hard with similar heads on my 427 using a solid flat tappet cam. Actually mine were some weird truck heads from a 366". Large oval ports, semi closed chambers like you have...and had small valves. I installed 2.19's and left exhaust valves alone. Even weirder is they were marked "Hi-Per"...not to be confused with "Hi-Perf" that is cast into rectangular port heads. Ran deep 11's on motor and high 9's with some N20 in my old Camaro.

JIM