[george kujanski]

gang: where's the website with info on head cc's, compression ratio numbers, etc. John TA IIRC?

Thanx in advance, george

[gtokid1968]

Walace Racing has it, I believe

[steve25]

If your building something and want to achieve a certain compression ratio here’s an easy formula that can be hard to find .

Say you have a .030” over 400 and want to achieve a 9.5 compression.

First figure out how many CCs a cylinder is.

4.150 x 4.150=17.223.
Stroke is 3.750”

17.223x 3.750” =64.586”
Times that by .7854, that gives a cylinder of 50.724 cid.

We need CCs so times that by 16.387.
That comes out to 831.223 CCs

Now take your 9.5 compression and minus 1 from it for 8.5.

Now divide 831.223 by 8.5.
That gives 97.79.

97.79 is the total number of CCs you need to get your 9.5 compression.

So that 97.79 is made up of

Chamber CCs
Deck height CCs
Valve notch CCs
Head gasket CCs
And just for good measure throw in 1.5 CCs for ring land volume.

[george kujanski]

Thanks, I'll give it a shot. Now that you pointed it out to me I think that's what I was trying to remember.

George

[george kujanski]

Thanks Steve. I was checking what I have; never looked before and had the car since '85. It's a reman455 from Jasper, today I checked using a borescope, hoping it did not have the 8 eyebrow pistons, it's ok there. It has 6X-8 heads so I'm thinking maybe I can use regular gas. For the little driving I do with it I have been using 93 octane.

The car had the 455 in it when I bought it and runs ok, but i'm getting a bit deeper into it now. It's about time.

George

[67Lemons]

This is the page that I use to reference cylinder head cc’s

https://ronspontiacpage.com/referenc...kheadspecs.htm

[steve25]

This site is F ing horrible, I just lost 10 minutes of typing out a reply so this one will be short .

George luckily there are no 8 valve notch pistons for 455 motors.

I will assume also here that your pistons have no OD chamfer on them because you did not mention such.

If they do have a chamfer a guess on the compression would be 8.2 to 1.

I will also assume that since in my photo it list the stock deck height as .013” that the block was decked to .009”.

I will also assumed that since the valve job done in rebuilding the heads sunk the valves some that the decking then done on the heads took them back to 101 CCs.


So when I use a .030” over 455 spec of 4.180” the compression I come up with is 8.81 to 1.
Which is not too bad depending on what you run for a cam .

If the motor was rebuilt with a stock cam it would have been a 067 type.

[ponjohn]

http://www.wallaceracing.com/

[george kujanski]

Thanx all. Interesting that from what I see on the charts the 6X-8 heads were used on 400s and at 101 cc.

I don't know where these 6x-8s I have came from, but they were on the car when I bought it back in '85. The engine supposedly only had about 100 miles on it since the "kids" blew up the previous engine.

One thing about these heads, once I got the car, I noticed blue smoke on startup and checked the valves; the guides were sloppy, so I took it to a local machine shop and they knurled the guides, which was common practice back in the day, i guess. The heads were clean but i was surprised that the guides were sloppy, this on a "fresh" engine.

I shouldn't have been surprised, seeing I had to back out of the "high performance" mods that the kids did to the car: ladder bars, headers that had the engine jammed against the frame, tinted windows, bent right rear axle flange. I got the car after "dad" took the keys away after several engines and a late nite front end meetup with a traffic barricade.

I probably need to pull the heads and have the guides redone, in any case, near term I'm going to try some 89 unleaded.

George

[Skip Fix]

My 6x-8 78 original heads with a fresh clean up mill were 97.5. Junk yard 350 6x-4s 94 cc

[george kujanski]

Thanx Skip.

[Skip Fix]

The 6X-4s I cleaned up and smoothed the chamber ridge down some milled 0.050 and were still 94cc. I had gotten a set of ported 6X-8s that also had the ridge smoothed that were 101cc.
I think Jim Hand would smooth the ridge as well as other porters.