ok I think I'll have my LO3 running decent pretty soon, but it's obvious another engine should go in there in a couple of monts

I looked at different posts here regarding the Caprice LT1's vs Camaro LT1's ie iron heads vs aluminum heads, read it over and over again, still confused about a few things.

I understand the iron heads flow better stock than the early aluminum heads, and the later aluminum heads flow just as well stock.

One can put bigger valves in the iron ones by cutting the existing valve seats (a 45 degree cut I assume ?) while you need to change valve seat inserts on the aluminum ones.

Which ones flow better after full porting ? Can the iron heads be ported more than the aluminum ones ? Would the aluminum ones end up having too thin walls after being ported ?

Also very hard to find aluminum head LT1's here cheap, Caprice ones can be found now and then.

I'm not concerned about the stock LT1 camshaft, I got a spare one laying around, it may be a F-body one, may not.

I intend to later on supercharge the LT1 engine, would that make the iron heads a very bad choice ?

I know, tons and tons of questions.

 

The later aluminum heads do flow roughly the same as the iron heads - stock VS stock, but the port wall castings are thinner than the early aluminum heads. Thats why the early aluminum (#374) are preffered over the later aluminum heads for port work. I'm not sure what kind of numbers ported iron heads can give, but the flow numbers of ported 374 heads are pretty impressive - near 300cfm on the intake side, well over 200cfm on the exhaust with 2.00/1.55 valves. But thats a professional port job by someone who really knows what they are doing.

If you are going to use a supercharger, either head would work fine - iron or aluminum, use whichever head will flow more air. Get the appropriate camshaft for a blower motor though, and reducing the compression ratio is almost a necessity (stock LT1 aluminum head engine is 10.4:1) to be able to run any significant amount of boost. Drop it down to the 8.5 or 9.0 range, and use a cam designed for an EFI blower setup and you can build a monster.

 

so the iron heads would work too, ok kewl. cos it's so much easier finding iron head LT1's here.

what's the max size valves you can put in by cutting the seats ? cos I think I got a set of manley 1.625 severe duty exhaust valves laying around.

also how could I lower the compression ratio. I know by polishing the combustion chamber i'll lower it a tiny bit .. but not by much .... hmm ... thicker head gasket ?

 

Use head gasket thickness to establish proper quench height.

Use piston dish to control CR.

 

ah ... so in order to do it PROPERLY ie run enough boost I would have to get new pistons ? that's the only way to lower the compression enough ?

 

Define "enough". . .

Boost goes up, compression needs to come down. You can get away with stock compression for low boost levels, but you'll have to go forged anyway when you get beyond a certain level.

I would think the iron heads would be better for boost, but I'm no power adder 'spert.

 

ok thanks ... right now I'm all confused as what to look for. Car's in the auto hobby shop, I'm also looking for a newer rear end. Unfortunately the '99 V6 I looked at had dual exit muffler, however no the RPO codes were missing the G80 option. I suppose a 3.42 rear end out of an '85 Iroc wouldn't be the best deal either huh ?

How would this work anyway ? LT1 engine .. compared to the LO3 with 2.73 gears .. should one use higher or lower gears to get good acceleration on the highway ?