Help me make heads and tails of turbo selection/compressor maps

[BigD]

I'm trying to learn about turbo setups and pick components. My goal is 400-450 flywheel HP out of the S52 (first I'll do Sunbelt cams and 3.5 maf this winter, but I'd like to start hounding ebay etc for the turbo components, I need to know what to look for though). I don't want to rebuild the whole engine, just MLS gasket and ARP studs, so I'm hoping to get into my ballpark at a reasonably safe 9-10psi.

I've been reading Garrett's site and most things make sense except for the part about picking turbos. I tried to estimate things using their equations but I could be totally out to lunch on the figures. It seems like the ideal turbos for what I want is either the GT2876R or even the GT3582R. My estimated ratio and flow seem to fall into the ideal range for those. But I don't get how the surge lines work. I mean I understand the max. But how do I know if at lower RPM my engine won't put it in the choke area...

If someone has experience doing exactly what I'm talking about, any constructive comments or suggestions welcome.

[e30s52]

I wouldnt get sunblets if you are building your car for turbo because they are so aggresive.

[BigD]

I wouldnt get sunblets if you are building your car for turbo because they are so aggresive.

How come? I'm not challenging you, I just don't know... I assumed that getting more duration would be a good thing. Is it the extra advance that would be a problem?

[rhett325i]

How come? I'm not challenging you, I just don't know... I assumed that getting more duration would be a good thing. Is it the extra advance that would be a problem?

generally, a cam that is meant for a NA car does not do well on a FI engine. For a turbo motor, more overlap = bad. You are better off to stick with your stock cams and spend your money elsewhere on the turbo system. This is not my opinion from personal experience, but just my understanding after reading the book "Maximum Boost."

[BigD]

Makes sense, thanks dude! I certainly don't mind - I'll have enough to spend money on...

[e30s52]

generally, a cam that is meant for a NA car does not do well on a FI engine. For a turbo motor, more overlap = bad. You are better off to stick with your stock cams and spend your money elsewhere on the turbo system. This is not my opinion from personal experience, but just my understanding after reading the book "Maximum Boost."

Nailed it dead on. I plan on going FI too. The sunbelts though are great cams though if your motor is set up for them and you plan on staying na.

[BigD]

Nailed it dead on. I plan on going FI too. The sunbelts though are great cams though if your motor is set up for them and you plan on staying na.

Thanks man. Can you share some of your plans? Do you plan to change the internals? If not, what kind of power are you aiming for, what's your turbo choice, what thickness gasket you plan to run etc?

[e30s52]

Around the same power as you. About 400-450 wheel. I am not going to change the internals at first but after I run the motor for awhile I will tear it apart again. I plan on using the gt35r turbo along with the .140 headgasket. Once I tear the motor apart I am going to get some eagle rods and wiseco pistons or maybe JE and some new arp headstuds.

Right now I am still thinking about what I am going to do and how I am going to put it down. So its all subject to change.

[BigD]

Cool. I'm not aiming quite that high. I really love this car, it's an amazing track whore but I also can't ignore how cheap C5 Z06s are becoming. If I can get this thing to around 400 ponies, I won't even look at a C5 again. So my target is around 350-400 wheel.

Looks like the GT35r is gonna be my snail.

[e30s52]

/\ Yeah the z06's are going way down in price but alittle to crampt for me. I have been thinking about an s62 swap though instead of going FI.

[BigD]

/\ Yeah the z06's are going way down in price but alittle to crampt for me. I have been thinking about an s62 swap though instead of going FI.

An S62 only has 400hp and an even lamer 365 ft lbs (or something like that). For a 5L solid lifter, ITB V8 that's downright weak. Plus if it blows up you're out another 5 grand or whatever they go for nowadays, if you can find one. If you blow an S52 you go on ebay for 2500.

I just took my car out for a spin to make sure it didn't magically die in the winter. Man I forgot all about how hard this car pulls. Having no cats is awesome too. I punched it in 2nd, it took off making it's usual fat woman startling roar (made 3 jump) then off throttle it burbles and pops like mad. Thinking about trying the same thing under boost gives me a chubby.

[e30s52]

/\ I havent driven my car in about 6 or 8 months :(. But for the s62 I would go with standalone along with some new cams and a light wieght flywheel. Still toying with the idea though. I can get them for cheapish so thats why I was thinking about it.

What manifold are you thinking about using?

[nando]

generally, a cam that is meant for a NA car does not do well on a FI engine. For a turbo motor, more overlap = bad. You are better off to stick with your stock cams and spend your money elsewhere on the turbo system. This is not my opinion from personal experience, but just my understanding after reading the book "Maximum Boost."

wrong, wrong, wrong and wrong. ;)

you'll have a much easier time reaching 400whp with a good set of cams than you will without them.

[BigD]

/\ I havent driven my car in about 6 or 8 months :(. But for the s62 I would go with standalone along with some new cams and a light wieght flywheel. Still toying with the idea though. I can get them for cheapish so thats why I was thinking about it.

What manifold are you thinking about using?

The flywheel will only make a difference in the short gears, where it'll all be tire smoke anyway. I never really understood the appeal of standalone - the idea that you can do better than BMW M, with their limitless tuning budgets, tools and expertise, with some home made computer, the internet and some weekends seems far fetched.

I want to do as little hacking as possible, so I'd like to stick with my M50 manifold. Should be ok right? I'm not looking to run any ball busting pressure.

[e30s52]

Exhaust manifold I meant. But yeah the m50 is good till around 15-20 I think. I remember matt saying somthing that they flex around 25psi I think.