As I continue with my rebuild efforts, it is becoming painfully obivious that there are a lot of other "GM family" parts in my 69 Cutlass than what came off the Olds/GM assembly line.

I have confirmed that I have a 1965 Chevy M22 trans and a 1984 (Chevy) quadrajet that was rebuilt in 1998. I hope that the rest of the engine isn't from a chevy line (if that matters) as well. There was a half hearted attempt at some point in the past to go from an automatic bench seat 2 dr to a 442 clone and it has taken me about 6 months to fix most of the "you have got to be kidding me" issues I have discovered so far.

But I want to figure out what the engine comp ratio is. Is there any kind of a guide that references something like cylinder pressure to determine CR?

Any assistance appreciated.

Steve P
El Paso

 

Not that I know of. If you are rebuilding the engine the compression will be determined based on the parts you select.

 

I got the engine to run OK with no leaks. Just trying to figure out what is there easily. I suppose I could send my bore scope down the spark hole to look at the top of the pistons.

Don't want to rebuild the engine this year if I don't have to.

 

OK. if you list the ID #'s off the block & heads you can get an idea what you have.

 

Why don't you post a pic of what you have so we can check it out?

 

If the engine has ever been touched, then you really won't know for certain.

Get a piston near the top and look at the piston with a flashlight. Is there a big dish lip near the edge (like 1/4" deep) or a very shallow one, or none?
What's the number on the heads?
Does it look like it has thick Fel Pro head gaskets or original metal shim gaskets?

Hopefully the engine is still an olds. That's easy to verify.
The carb isn't all that surprising. Folks commonly got annoyed at QJets and just grabbed whatever was handy that bolted up.

 

Chevy Q-jets come in from the side, Olds from the front, requiring fuel line mods.
Hopefully, didn't use rubber, as I've seen a few burn that way!!

 

Fuel ine for this carb comes in from the side. Fuel pump is mechanical with a vapor return line (car is an AC version). Metal line was cut at both the carb inlet and the pump feed line and a rubber re-inforced fuel flex line with an inline filter was installed. I have not had a chance to make a new metal line yet.

Will check on the piston this weekend when I get a chance to get dirty again.

 

If its the original '69 block (would have VIN derivative on pad), it came in 2 flavors. high-comp for the 4 bbl & low for the 2 bbl. The only way I can think of to confirm would be to scope the pistons...assuming they're original. Heads should be #5's.

 

Well, the heads are 5s. Will stick the scope down a spark plug over the wekend. I had hoped that someone who had a high compression engine would know what I could expect to see on a compression gauge. Same from a low compression.

Steve

 

The cranking compression has way too many variables to be a true indicator.
On my 9.5ish:1 build, cold cranking was around 170 to 180. I think it was around 150 or 160 when it was 8.5ish:1 stock. But there are a ton of factors.

 

After it a borescope, the pistons are dished, so I guess I have the lo compression 350 w a quadrajet, and I'm looking at about 260-270 hp?

 

If it is a 69 350 it should have the 14cc dished pistons. You can gain some compression if you 0 deck the block and mill the heads to gain a true 64cc chamber and that will get you to 9 to 1 compression with a .040 gasket with a .027 you will be at 9.5 to 1 . That is if you rebuild it and keep the original pistons if its in good shape. dished replacemnts re like 23 cc's plus .

 

The stock pistons in that engine are all dished, unless it's a W31.
The difference is in how much of a dish they have.

This picture shows the difference - note the cutout notched in the front edge of each piston.



- Eric

 

I think up until 70 they had 7 cc 14cc or flat tops. 71-72 i believe only had 23 cc and they went back to 14 cc in 73 and made the chambers bigger to lower compression.

 

For reference, you won't be able to tell compression ratio by compression test. My 455 is 10.63:1 compression RATIO but on compression test it only pulls 180 or so...I suspect cam timing events have a lot to do with what you see on the compression gauge.

Steve

 

I will look to see if I can find the notch, but it looked like the low compression piston when I scoped it before. Thanks for all of the info everyone. Most helpfull!

 

You might want to check out a 1966 Olds Qjet...

 

Stamping on the carb showed a 1984 chevy application (rebuilt in 1998) and the fuel line does come in from the side. A proper correct year carb and a new muncie (vice the 65 chevy that is installed now) are the two big things for next year, along with all new brake lines.

Steve

 

Thanks Joe - learn something everyday!!
Next time I'll say "99% of the time".