I Bought this car on ebay without knowing too much about it. When I got it home I found that it is a 425 High compression with "C" heads.

 

Good deal. I would almost kill for that engine.

 

I like surprises like that - congrats!

My surprises are usually the opposite...

 

67 deltas would come stock with a 2bl 425 at 9 to 1 compression with C heads.

What did you find to make you think its high compression? Did you remove the heads and look at the pistons?

Either way it gos. The 425s are great motors and 9 to 1 or 10.25 to 1, both would work great!

 

I have a '67 Delta with a 425 2-bbl, and it's the high-compression version so far as I know. One thing I base that on is that, on the gas tank cap, it says "premium fuel only," and I think premium was required only on the high compression engines.

 

You can't see the small writing on the air cleaner in this picture but it says "ultra high compression" and use premium fuel only. the gas cap also says use premium fuel only.

 

When I bought my '67, it had a non-Oldsmobile air cleaner on it (I have no idea why). I have since gotten a correct one along with the "Super Rocket" plate that says "ultra high compression" and all on it and put that on the car. But I can't use that as evidence that the engine actually is the high-compression version! However, I have no reason to assume that the gas tank cap is not original, so I take that as the evidence.

 

True. So how would I find out for sure whether its the high or low compression version?

 

That's a good question. I don't really know.

This site does have a "tech" section

http://tech.classicoldsmobile.com/

but I don't see anything in there about how to tell what version of an engine you have if both high and low compression versions were offered.

Perhaps Joe Padavano can help.

 

The prefix / suffix codes on the passenger side head (if original) should also provide an indication of the engine's performance, so in the case of a 425, they can tell you whether the motor is low vs high comp, valve size (I think) Starfire vs non-Starfire, Toro, etc. Same is true for other engine series. I don't know all the codes, though there are others like Joe or Kurt who I think may have the breakdowns. Some info has previously been posted in these forums, I think, and may be available through the Olds FAQ/WIKI. If someone posts their codes,. its likely they will get a quick answer.

 

This site:

http://www.tpocr.com/oldsec.html

Has some info on prefix codes for Olds motors, and for 66-67, SOME of the numbers seem right to me, yet others I'm not so sure of. I seem to recall a resource for these numbers, but cannot seem to find.

I DO recall that the prefix code for the U.S.S. Reliant is 16309.

 

with a good light you can look at the top of the piston at TDC.