I understand the differences between these two motors .... but what would 416 heads on a LG-4 do for compression, alot say the LG-4 had 416 heads but mine doesnt.

 

What heads were on yours 624s or 601s? The 601s are actually better heads than the 416s. The 624s are junk.

 

Shouldn't do a thing for compression, since LG4 heads are 58cc also. It's the pistons that are different - flat tops vs. dished...

 

my 86' LG4 has flat-tops, and 416 casting heads.

in either 85-86 gm switched the lg4 to flattop pistons and added a knock sensor.

what casting heads are on you're engine, jproz?

 

Forgot about that! -still won't do anything for compression though. I've always heard the 416 castings are the preferred ones, especially if you port them a bit.

Sitting Bull did it with great results....

 

sitting bull ported 601 heads. 601 and 416 have a different shaped combustion chamber, performance favoring the 601 chamber.

 

416s and 601s aren't all that bad if you hog them out. Nothing close to a performance head, but they'll do for a decent little street rod. match the rest of the combo and I'd figure ~300 hp wouldn't be incredibly difficult

 

well I tore into this 305 a little yes it is the matching nymbers block to this 82 trans am, However seems this motor has the 416 heads on it. I always thought the 416's came out in 83-84.

So to get this motor to 9.5 to 1 it would just need flatop and a better cam right. the block is drilled for a knock sensor so that won't be a issue. I am going to pull the heads soon and see if in fact it's pistons are dished.

Does anyone have a picture of the dished LG-4 pistons

 

These are the 3 piston designs used in the 305 over the years.

My factory 1983 LE9 305 had the middle piston combined with 53 cc chambers and a thin steel shim style head gasket!! The typical LG4 low compression piston is on the left and it is usually combined with 58 cc chambers. I used the same pistons (.040" oversize) and 081 TPI heads with 58 cc chambers when I rebuilt the engine.

The piston on the right was used in your typical L03 TBI engine and the later LG4 engines. It was used through 2002 in the Vortec 305s as well.



In order to get to 9.2:1 in trucks GM engineers used the 53 cc chambers of the 601 and the dished piston on the left. They then added a "929" 350 cam which was better than what came in the 305 cars. Why mine had the crossfire/L69 piston in it is a mystery to me. No wonder it ran best with the initial timing set at TDC. I calculated it out to be around 10.2-10.3:1.

 

your pistons should look like the one in the engine, that fast355 posted. Looks just like mine.

If you aren't planning on rebuilding the bottom end of the motor (ie swapping pistons), you can just mill the heads a bit to bump up cr. however the HP gain from a slightly higher CR isn't as much as if you port up the heads. Course why not do both?




DOOM! Your car running yet??? slacker

 

The 1982 LG4 that Car Craft turned into their 325 HP beast was the dished piston model. Most LG4/2bbl Truck engines came from GM with the dished pistons. The L69 and certain truck engines(esc equiped) came with the flattop ones.

I put my bets on the piston to the left.

 

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