Thread: Piston question?

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Hello.
I've got my hands on this 1968 390 engine.
And I'm currently trying to find out whats inside this machine.

I've tracked down almost every part, without the pistons. They are in aluminum and have valve reliefs. I can get a photo if that would make it easier.
The casting is this, C8AE - 6110A and maybe 4 or H after the A. Not sure, it could just be some dirt or casting faults.
There is also some castings on the side, it says 390 and 2V.

Does that mean that they where used in low comp 2V applications?
But i can not understant that either, why use alu pistons in low comp app?
Or maybe they are from the high comp 2V engine?

This is kinda confusing, because I've been searching around and haven't found out anything interesting about them on the web. Also been looking around in several different forums, but nothing.

So i was hoping someone in here could help out.


Nilsen

Yeah i know, it sounded kinda silly.
But didn't they use cast iron piston as standard on low comp?
Correct me if I'm wrong, since I'm not an expert on these engines.

Nilsen

most all the pistons I've ever seen are aluminum.....

Are they flat tops with eyebrows or just dished? Depending on which they are either 9.5:1 or 10.5:1 cast 390 slugs. Std issue for the most part.

pretty much all pistons are some form of aluminum. cast iron just weighs too much to be jerked around even at lower revs...

Ah, then i now..

I'm not sure if it is flat top pistons or dished.
Because they have those eyebrows on the sides, but it also has a little dish in the middel of the eyebrows.

So I'll post a picture of it, so you could se.


Nilsen

I'm interested to see what the FE guys say. I've worked on those things
since the sixties, never seen one like that
Ron

Those are the 9.5:1 2v 390 slugs. Forgot to mention they can de dished with eyebrows. There were quite a few variations thru the years.

Thanks for that.
Do you know how large the dish is in cc?

Nilsen.

Sure wait till i put the book away!!! LOL I beleive the dish is 10cc's. I'll double check and post if I'm wrong.

Hehe. Thanks again.

And for the final, when i got this engine, it had a 4V Edelbrock performer intake,
and the carb is a 600cfm, edelbrock too.
Cylinder bore honed, new piston rings, main bearings and rod bearings. The ring gap was in within the limits after the repair manual.
Stock heads with some porting job done. Stock valve size,not sure if there is a new valve seat, but the valves looks incredibly fresh and fine to be old ones.
I my self are going to get them milled a bit, so we get a little higher comp.

The cam i don't know, the guy i bought the engine from sayd that it was changed, but to what he didn't know.
I tryed to measure the cam lobe, but are not sure if I did it right, but it landed on 0.310". I didn't finde my degree wheel so no duration measuring.
So if my measurements where right, I would have a gross valve lift around 0.527".?
Stock rocker arms, dual valve springs.

So to the question, how much hp will this engine produce with these mods?
I was hoping i would be around 300hp
What do you think?

Nilsen.

You can also use a .015 steel shim head gasket to help a little with compression. Watch the rocker oil feed slot on the heads when milling. When they get milled to far the slot goes away and it needs to be slotted again. You won't get oil to the rockers. You can look at the thumbprints in the heads and see how deep they are.....and tell if they were already cut. Intake fit and rocker geometry can also change. Just something to be aware of.

Stock with 9.5:1 comp your 270 hp @ 4400 rpm and 390 tq at 2600 rpms.

I'm aware of that, the local machine shop said almost the same as you about the oiling, and fittings to the intake.
But I'll think I'm gonna try the engine first, and see how it runs.

So, thanks for all help.

Nilsen