I am doing some background research for a motor that a buddy and I will be building in the near future. It should turn out to be a pretty cool project- LT1 and six speed install into his 89 240SX. The fabbing and cutting will be hashed out by his father who has done this sort of thing before. For the time being, I need some help with the motor- specifically using cast iron heads on the it.

First off, we'll be using a pretty aggressive cam and a set of completely ported heads. The bottom end will be fully forged and retain the stock stroke. We're looking for mid 400 rwhp on motor with nitrous on top of that later.

I have an idea to use cast iron heads off of an Impala SS because I think it will be more durable than using aluminum heads(this coming from a guy that has blown 2 headgaskets on his camaro). If I am correct, the main advantage to aluminum heads is heat dissipation. The main disadvantage I see is differing expansion rate compared to the block(cast iron) which can cause headgasket problems if the temp gets a little high.

I feel like the motor will be more durable with cast heads, but I need to know what impact it will have on performance. At this point I could go either way, so if anyone could enlighten me with some pros and cons of each that would be great!

 

There are some advantages to iron heads, but essentially no one is using them who doesn't have to due to $$$ considerations or rules in the class they race in. There are also people who simply want to use them for the sake of authenticity or simple personal preference. But they nearly ubiquitous use of aluminum heads, even on iron block motors, has got to tell you something.

Aluminum heads will weigh nearly 100lbs less per set for a small block Chevy. They will allow a higher CR because they run cooler. This more than compensates for the small power advantage of iron heads due to their holding more heat in the combustion space. Al heads are also easier to port. If you use the right gaskets and the deck and heads are properly prepared there will be no gasket retnetion problems assuming the motor does not overheat or detonate.

Rich Krause

 

Listen to Rich.

Early on in the LS1 design for the iron block truck engines, the "truck guys" wanted Powertrain to use cast iron heads for better durability vs. aluminum. I believe some of the early 6L might have been iron.

The Powertrain folks favored aluminum because their testing showed it was MORE durable than iron. The durability tests convnced the truck folks, and aluminum was and still is used.

As an aside, when the truck guys saw the LS6 heads, they got ideas about a high hp 6L (for Cadillac). Now we have the 345 hp 390 lb-ft 6L with ports very similar to LS6 but slightly larger combustion chambers.

As much as I like my Imp with it's iron heads, go with the aluminum. You'll also like the 240's handling better with the aluminum.

Good luck.

 

I forgot about the weight advantage, and really didn't know that iron is about 100 lbs heavier than aluminum.

I figured that in working the bugs out of the cooling system, the motor might end up getting kind of hot. This scares me with aluminum but I'm sure there are some precautions. The obvious one being take extra caution when testing the cooling system. Other than that, will head studs make the block-head seal more durable? What about diferent materials of headgaskets?

 

It's not. It's closer to 50# For a BBC 100# is pretty close.

 

Typical SBC aluminum head ~23lbs, typical SBC iron head ~55lbs. total weight savings is ~64lbs. Typical BBC Al head ~29lbs, Fe ~75lbs. Total weight savings ~90lbs. You were closer than me!

Rich

 

Actually I remember reading an article on the later model cast iron heads that came standard on the lt1 equipped buick road master and impalla.The iron heads in stock form flow better than the stock aluminum f-body heads, this being due to the fact that the iron heads were released later and were in development longer so they were able to squeeze a few more cfm out of them. As mentioned obove they will also retain more heat in the combustion chamber and will yeild a few more ponies there.On the down side as mentioned above they are heavier and because of the heat retaining characteristics of cast iron, wont allow the use as high compression ratios without the worry of detonation.

 

The weight savings with aluminum is "good" for an F-Body.... I would think it is pretty much "essential" when stuffing an LT1 in a 240SX.

There are an appreciable number of aluminum head LT1's running nitrous, blowers and turbos in the 800-1,000+HP range, and not experiencing head gasket failures. It should not be a problem in a well built engine.

 

it is very common for us impala folks to switch to aluminum heads and it all goes to mush when you do a mild port and polish on either set of heads. Aluminum is easier to port.

 

Okay okay okay, you guys have talked me out of cast iron heads Gasket recommendations with ALUMINUM heads? Compression will be around 11:1, maybe a little lower, will be using nitrous some, but not very often.

 

You should be fine with the Fel Pro #1074.

Rich