[taalltheway]

Hi guys,

i have a 69 Firebird with an engine that is supposed to be a 467 stroker with edelbrock heads. Upon Closer inspection i found that they are the 72 cc Version. Wouldn´t that put the comperession ratio into crazy territory? What now?

[Skip Fix]

All depends on the pistons, and the 72 and 87 both have the same casting #.

[Scott65]

Depends on the pistons. If they were dished, it could be fine. More info required.

[steve25]

A compression gauge will be your friend in a situation like this and nail down for you what you have or don't have.

If you show way more then 185 psi then you have the 72 CC heads and near flat top Pistons.

[mgarblik]

One of those little flexible camera's might be your friend also. If the engine hasn't been run too long and hasn't been super rich, you can look in the cylinder and get a good idea of the piston design on the top. 2-4 eyebrows, D shaped dish, full dish. If it is all carboned up it is very difficult to see in there with a camera. You might have to de-carbonize and then try again. The little cameras are very inexpensive, depending what brand you buy. As little as $25-50. Good luck.

[taalltheway]

OK, i will check with a compression gauge. What numbers-range would be OK?

[ta man]

Also depends on if the heads had any chamber work done to them. Check the front of the heads for any stamping.

[Skip Fix]

Originally Posted by mgarblik

One of those little flexible camera's might be your friend also. If the engine hasn't been run too long and hasn't been super rich, you can look in the cylinder and get a good idea of the piston design on the top. 2-4 eyebrows, D shaped dish, full dish. If it is all carboned up it is very difficult to see in there with a camera. You might have to de-carbonize and then try again. The little cameras are very inexpensive, depending what brand you buy. As little as $25-50. Good luck.

Good thinking! I've been getting Facebook ads for a cheap gun bore camera almost every day lately.

[Murf]

Not to derail the OP’s question, but a what displacement do the 72cc heads become impractical for a pump gas motor?
I guess I’m asking if at some point would the dish size become too big, causing problems.

Thanks
Murf


Sent from my iPhone using Tapatalk Pro

[Steve C.]

Butler built a 601 cubic inch engine with a 5.000-inch stroke and a 4.375-inch bore using a Indian Adventures "Tall Deck" block. He opted for their heavily modified "Wide Port" version of the Edelbrock heads and I doubt they started out as 87cc castings.

Mild compression ratio of 9.7:1

https://www.flickr.com/photos/119296...n/photostream/


More often than not most of these 'big inch' Pontiac's using Edelbrock heads start out with the #60509 head which is semi-machined and are 72 cc.

[Murf]

Thanks Steve, I just assumed you could get to a point where the size of the dish would be problematic. Just shows what happens when I assume.

Thanks
Murf


Sent from my iPhone using Tapatalk Pro

[Steve C.]

"... get to a point where the size of the dish would be problematic."

That is an area I know little about. But understand the design has a factor.
My 505 uses 72cc castings with a JE Custom piston that uses a 27cc inverted dome ( or 26.9?) / depth 0.210
I have 10:1 compression with 79cc chambers.


.

[NeighborsComplaint]

Originally Posted by Steve C.

"... get to a point where the size of the dish would be problematic."

That is an area I know little about. But understand the design has a factor.
My 505 uses 72cc castings with a JE Custom piston that uses a 27cc inverted dome ( or 26.9?) / depth 0.210
I have 10:1 compression with 79cc chambers.


.

But in reality your compressed volume is 106cc. with 79cc heads, flat top pistons and zero deck you be in Detonate Beach, or Pingsville as you prefer.

[ponjohn]

I'd put a borescope down in there.

[Navy Horn 16]

Run premium with a little AVGAS and send it.

[Steve C.]

"But in reality your compressed volume is 106cc. with 79cc heads, flat top pistons and zero deck you be in Detonate Beach, or Pingsville as you prefer."

Wait what...... plain English please !

My situation....

4.350 bore
4.250 stroke
79 cc chamber volume
.040 gasket thickness
Piston to deck .003" ( above deck)
26.9 cc dish

About 10:1 compression

.

[NeighborsComplaint]

79+27=106cc

[Cliff R]

My current 455 has 76cc KRE heads, flat tops, 11.3 to 1 compression. It's been on a steady diet of pump gas now over 11 years and is fine. It doesn't like 87 octane that much, on really hot days it has a tendency to "run-on" after shut-down and "bucks" the starter just a tad, so I keep 92-93 octane in it.......Cliff

[78w72]

72cc E-heads on a 467 with 14cc dish ross pistons. calculates to about 10:7 & runs great on straight 91 no ethanol. will run ok on 87-89 also but as cliff mentioned it can get run on on hot summer days so i just stick with 91 or sometimes 93 with 10% ethanol.

[SRR]

Aluminum heads are more forgiving of higher compression because they wick away heat faster. I've tested a few engines on my test stand and the only two that didn't go nuclear were aluminum headed engines, they never went over 180 degrees...I was amazed.