Is there a way to find out what my 390 came out of? The p.o. said he thinks it was out of a t-bird or mustang but he want sure, the truck was in his family for ove 20 years. I would like to figure this out mainly so i can find what compression ratio its got so i can choose a cam. Would a compression test tell me the c.r.?

 

Unless the original metal tag is still on the engine, (under the coil according to other posts), and unless that's the correct tag, there is no way to know for certain.

Plus, do you know if the engine was ever rebuilt?

And if it hasn't been rebuilt, are you really going to put a cam in it, with all that's involved there, and NOT go through the engine?

Tbird and Mustang 4v 390s were either 10.1 or 10.5, depending on year.

Compression test will tell you cylinder pressure and how the cylinders compare to each other, but can't tell you the CR.

 

Thats what I thought with the comp test thanks, im not sure if it was rebuilt or not. The po said the heads were rebuilt about a year ago because of a burnt valve or something. I doubt the factory tag is on the motor, plus it has a giant accel coil on the manifold but ill look for it tomarow. Maybe I can get close by getting the head casting numbers and the block date code? Im not going to rebuild the motor to put in a cam seeing as it runs great and makes solid power. I just want to squeeze what i can out of it untill it is time for a rebuild. I was planing on changing the springs ofcourse. I read somewhere that the lowest comp on a 4v 390 was 9.6 but can go up to 10.5. Thanks for your help, atleast tomarow ill know what heads are on it and can do some desktop dynoing lol.

 

If it's got the original carb on it, you MIGHT have some luck finding out what it was on originally. I went through this with a 390 I got from my nephew-in-law as a freebie. Turned out, it was a 2bbl Thunderbird motor, based on the exhaust manifolds, the carb number, and a few other things. And yes, it was a completely stock unmolested motor

If your motor was ever upgraded with a 4bbl, or otherwise torn into, it can be a crap-shoot.

 

It is a 4v with am edelbrock carb, cast manifold, block date code is feb 26 1969, heads are ca8e-h. If it is a factory 4v it could be out of a number of cars but atleast 4v 390's in 69 were 10.5:1 and differed by ten hp as far as I could research. The p.o. was sure it was out of a car and was a 4v, he said his dad used to race it in 4wd on the street and the axles are trussed so I can believe that happened. Now i just need to find out if these heads are decent and if they can be worked over a bit. I read somewhere that they flow best at .517 lift? I got alot of research to do. Lol thanks for your help. Oh I almoast forgot, the intake has a big "S" on it, I dont know what that means exactly but i read that it was used on 69 mustang gt's.

 

C8AE-H heads are the same as D2TE-AA's (except for the exhaust valve seats) and are pretty decent to work with. The "S" intake was a car intake I believe, and if it was a completely stock 4bbl car engine, it's probably a higher compression version. If it was all kept stock, anyway.

 

I think if they swapped the 352 for a 390 and raced the truck then they wouldnt de-tune it but who knows. Ill probly never really figure this out untill it needs a rebuild. Ill put my cam choices on a board and throw darts at it I guess lol. thanks for your help!