I have been reserching turbochargers recently and I have gained quite a bit of knowledge from places like this board, this article, this website, and innovative's website. These are all great places to learn a thing or two for someone like me, but they have brought me to a few questions...

1.) On a turbocharged application (SBC of course) which heads are more appropriate; aluminium or cast iron? I realize that there are distinct advatages to aluminium when running NA, but it would just seem to me like cast iron would be the way to go because of its tolerance to heat, which obviously a turbo engine will have to endure. Is there a right and wrong here, or just a matter of opinion?

2.) Most people around here choose between a 170 and a 195 cc intake runner volume for their heads when building a 6-or-so liter small block for a mid-ranged power band. Ideally, would an intake runner size change or be the same for a simlarly ranged and sized turbo engine??

3.) Other than a lower compression ratio, are there any other desireable differences between a turbo long block and a similar (again size and desired powerband range) NA long block???



Thoughts and opinions on these or any other related subjects are much appreciated!! Thanks:hail:

 

You will get better answers from others, but:

1. People claim aluminum heads to be less prone to detonation. I think cam specs have more to do with it that what material your cylinder heads are composed of, but whatever.

2. Depends what you want to do with it and where you want to make your power.

3. A lot of people O-ring their blocks and run a nitrous/boost specific piston. Also, proper ring gap is important on a boosted or nitrous motor.

 

A proper turbo cam is a really critical issue, overlap = bad.

Also forged interals are nice to have.

 

Thanks for all the replies...

I realize that this is the case. My question was with all else equal, ie what you want to do with it and where you want to make your power, between a turbo and a NA application would you want to change the intake cc or keep it the same. Obviously your going to make more power with a turbo than without, I am just wondering how to go about choosing the right size head for a turbo app. The only way I am familiar with doing this is on a NA engine, hence my reason for comparing the two.

Also, o-ring blocks...is that a type of head gasket??

 

i would also like to know what a recomended cc would be, i was thinking some 215 iron eagles or pro action... and im looking for 600 HP with a lot of mid to high rpm power

as for the o-ringing the block it means that they actually cut a groove in the block and the head that goes around each cylinder, and tap whats basically wire (i think they use copper... but i know the material is diff between iron and aluminum) into the groove, you can also use felpro lockwire head gaskests which have this metal ring in the gasket already, but you still have to cut the groove in the block and head

 

OK, lets see if I can make some sensible comments:

1. Aluminum/iron… can of worms. Aluminum is less detonation prone since it allows more of the energy released during combustion to leave throught the waterjacket. In theory, if built for the type of heads on the engine you should be able to make more power with iron heads. The question is do you want to run the lower compression, timing… that you would need, can you find iron heads that are as good as some of the aluminum castings out there for equal amounts of work and is the power difference going to exceed the weight penalty. Factor in that aluminum heads tend to be easier to fix when damaged and easier to work but iron heads will match the expansion rate of an iron block better promoting better engine seal… You could make a good argument for either. Which do you want to go with? I'll argue for those

Really, in most cases I would choose good iron heads for a street car where money is an issue, and for a serious race car (especially one expected to handle) and where money is no object I'd go with aluminum and a lot of tricks…

2. Intake port cc depends a lot on actual cross section and what the rest of the combination is like. If it was a race only setup then you would simply go with as much flow as you can get, present the least restriction to the flow as you can and let the turbo, transbrake… do the rest for you. Real world, that setup would suck to drive on the street. So you compromise. How much you compromise depends on what an acceptable response is from the engine and how big it is. If you want a specific answer you'll have to give a lot more details on what you want and what you expect the engine to do. OTOH, if you're looking for under 700hp at the wheels or so who cares… just about anything will work with a little massaging.

3. Skip the o-ringing, there are plenty of modern head gaskets that will play nice with under 20psi boost. If you need more then 20psi boost in a 383 you're either doing something wrong or you should not be asking these questions. Generally, parts wise you need to choose parts for the power that you're making for the power dependant parts, but in a lot of cases you can get away with much lesser parts and clearances on things that are RPM dependant since you will not nearly have to rev the engine as high to make the same power. Generally what would make a healthy street engine with reasonable, somewhat overbuilt parts will make a killer turbocharged engine.

As for the rest of this… if you want more details you'll have to give more details. In a way your question is too broad to give a real answer to.