I just bought i totaled 84 trans am for the motor and trans to swap into my 85 sport coupe, there was evidence of a motor swap like loose bolts and all new hose clamps on old hoses, according to the vin it should be a lg4, but i started tearing down the motor and found it has a alumiunum intake which i thought was only on the l69, and it also has flat top pistons and i thought it should have dished pistons.

 

U.S.-delivered LG4's had aluminum intake manifolds, the same part used on L69's.

LG4's got flat top pistons in 1985 & 1986. The engine, or even just the shortblock, could be a replacement.

The only difference between an LG4 and L69 longblock is the cam (and pistons in '83 & '84).

 

Did the L69 require premium?

 

at lower elevation, yes.

 

My Lg4 seems to need at least mid grade. It looks like the timing cover has been removed at one time. I'd like to know if the stock cam has been replaced. It does perform nicely, but may be a bad knock sensor.

 

Stevolwevol re-read what Five7kid typed. You have the same compression as a L69, if it's the original LG4 in that 86.

Both the of 86's I've torn down had flat tops with valve reliefs.

I always run the crap fuel in mine and use 0 degrees timing and have no problems. But when you put hi grade fuel in you can tell by the way it's running, it's much more responsive to throttle.

 

Interesting.
Do you think I should be using premium in Louisiana?
I have a knocking or slapping noise from mine...but I think it's coming from just 1 place...#7 intake.
I'm about to post that up in tech. It's annoying because I can't find it.

 

I read it. I guess I would need to remove the cam shaft to tell if it is different. BTW, I believe the l69 came with a better intake, carb, cam, and exhaust ... 2 1/2".

 

Not exactly. Its the same exact carb with different secondary rods and hangers. Same intake manifold.

differences for 86' as I know it are; air cleaner, ECM, camshaft, exhaust.

 

I believe the carb can be modified to emulate the HO carb. I forgot how to replace a cam. It's been over 35 years. Would I need to replace the springs? I don't want to have the valves kiss the pistons either.

 

IIRC all you need to "emulate" the L69's carb is a G hanger and DR rods, or CK. You can get that from summit, jegs, ect. Or even a junk yard if you look hard enough.

You will need to replace the springs, lifters, and timing chain. (unless the chains new it's just a "since your in there" thing if its even remotely old.)

There is a really nice write up here on TGO for cam swaps, its a sticky I think. Don't have the link off hand.