[Cammer-6]

67 4 bbl head,250 block and .030+ stock configuration pistons

Ive run this combo before but never run the numbers.


Any idea what this combo yields?

[johnta1]

Your putting a 67 head on a 68 250 short block mainly? (at .030 over)
I don't know the cc of that head off hand, but it would probably be around 10.25/10.5 CR?

[Cammer-6]

Originally Posted by johnta1

Your putting a 67 head on a 68 250 short block mainly? (at .030 over)
I don't know the cc of that head off hand, but it would probably be around 10.25/10.5 CR?

that would be about right if I was using a 68 4bbl head

Im away from all my books and notes,but somewhere I have
the CCs

[einstein]

Remember you loaning me a ported/polished 66 Sprint head that I ran for a while on the 69 OHC TH350 coupe? Those 66/67 Sprint head chambers were pretty shallow. 55, 56cc? Not sure which engine (std or .030) it was but all I had were 69 250 blocks.

My notes are currently inaccessible as well.

If my seriously compromised memory isn't too far off, I was thinking it was well over 11:1, maybe closer to 12:1. Hottest OHC combo I've ever driven. Damn, that was over 30 years ago...

[Cammer-6]

Found it in Petes book.I remember giving him all the info for OHC-6,thinking it was close to 50 yrs ago.

67 4 bbl head CC is 47.7
68 4 bbl head CC is 55

so its gonna bump compression by 7.3CC

[johnta1]

If 47 cc head would be around 12 to 1 cr.

[einstein]

That comports with my recollection.

[Cammer-6]

Originally Posted by johnta1

If 47 cc head would be around 12 to 1 cr.

IIRC you can bump about .4 due to overbore also

[Jeff Hamlin]

If interested Rob still offers Jerry Woodlands REBUILD GUIDE with updates.
It covers all this type info in one convenient package.

Cheers.

[Cammer-6]

Jeff are you keeping it a secret?

[Cammer-6]

I used an online calculator to try and get close.
The variable is what the piston head cc is.
Specs say 5cc but dont say if thats + or -

11.27 if the dome is negative
13.05 if its positive

I have popup pistons that I think are +12cc

that would be 14.73
now thats what makes an engine bark

[Cammer-6]

Pic of piston

[Cammer-6]

Originally Posted by einstein

Remember you loaning me a ported/polished 66 Sprint head that I ran for a while on the 69 OHC TH350 coupe? Those 66/67 Sprint head chambers were pretty shallow. 55, 56cc? Not sure which engine (std or .030) it was but all I had were 69 250 blocks.

My notes are currently inaccessible as well.

If my seriously compromised memory isn't too far off, I was thinking it was well over 11:1, maybe closer to 12:1. Hottest OHC combo I've ever driven. Damn, that was over 30 years ago...

IIRC or if CRS hasnt completely set in,I remember some 50 ft patches you left from your 1ST to 2ND gear in the 69 coupe

[einstein]

That combo was pretty impressive.

[TheSilverBuick]

Originally Posted by Cammer-6

I used an online calculator to try and get close.
The variable is what the piston head cc is.
Specs say 5cc but dont say if thats + or -

11.27 if the dome is negative
13.05 if its positive

I have popup pistons that I think are +12cc

that would be 14.73
now thats what makes an engine bark

My experience is the factory under states the head cc's. I'd have to check my notes but I believe those 55cc heads are closer to 60cc. I haven't measured a '66 4bbl head. In any case, I'd measure the head if you can, but odds are you'll end up with a bit less compression than expected, with the exception of the '69 1bbl head that is significantly off published at 80 cc's.

I measured two types of over-bore replacement pistons and both were -5 cc's.

I suspect the heads cc high with factoring in future rebuilds shaving the head a bit and min-spec hits the published number. Similarly with block deck, the pistons are not zero decked from the factory and likely in the hole a fair bit. Need to measure. I've never measured an untouched OHC block. Buick's are often ~0.050" in the hole on a giant bore so cc's add up, the smaller bore has less impact, but still an impact. Then there is head gasket selection, factor in if you are using the steel shim gasket or a ~0.040" composite gasket.

MY opinion is, with an iron head, I get nervous about 91 pump gas over 9.5:1 measured static compression. Especially without a good cam with lots of overlap to bleed dynamic compression at low rpm. There's no E-85 around where I live.

[Cammer-6]

E85 very plentiful here

I used all factory specs on the CR calc
.014 deck height
Felpro HG .058 but I do have a few that are. 021
I may need to contact Cometic
block is O ringed
.540 lift cam

[sprintbird]

A couple years ago or so a fellow Cammer reached out to Cometic to make a head gasket. They said they could do it, but wanted about $4K? to cover necessary tooling. That tells me that they don’t want to do it. Probably because there is no market.

[Cammer-6]

I have a CAD plotter I use to cut gaskets but cant do anything as thick as that with the knife.
In this day and age of scanners,3D printers,laser cutters etc this shouldnt be a challenge.
I would explore intake/exhaust gasket too.Ive always run the fiber Cliffords but am now out.

[sprintbird]

Best Gasket makes composite manifold gaskets as well as Flatout Gasket. So they are out there for purchase. I have the Best Gasket version in stock.

[Cammer-6]

If I can find proper sheets or rolls of composite,I may be able to cut,just need to do multiple cuts.
But I still like the idea of copper.