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

BigD · 03-17-2009, 12:21 PM

I'm trying to learn about turbo setups and pick components. My goal is 400-450 flywheel HP out of the S52. 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.

///tyron · 03-17-2009, 01:27 PM

Run an S52 with a Gt3582r. You're not going to make your goal at 10 psi as its not in that turbos efficiency range. You'll more so make it at 15-22 psi.

BigD · 03-17-2009, 01:56 PM

Can you explain how you figured that? In my calculations, to get 400-450hp, I'm looking at 45-48 lb/min air at 1.93 pressure ratio. This is right under 10PSI and in the GT35r's meat of efficiency. If I'm wrong then I guess I'll have to go GT28.

EDIT: just to reiterate, this is not wheel HP, but flywheel. Wheel-hp I'm hoping for 350-380.

Axxe · 03-17-2009, 02:03 PM

Oh shit, you gone and got yourself on a slippery slope.

BigD · 03-17-2009, 02:04 PM

Quote:

Originally Posted by Axxe

Oh shit, you gone and got yourself on a slippery slope.

How so?

e30_kid89 · 03-17-2009, 04:59 PM

Looking at the GT35's compressor map I think it'll flow at that rate while staying at 77 -75% efficiency. If Flow is what you're worried about at 400 crank HP the GT35r is just getting started.

I'd go with the GT35 over the 28. I read of some M20 guys making the switch and never looking back.

EDIT: and to add since your're gonna run a MLS and ARP studs you can push more than 9 - 10psi and still be very safe, that is if you have a very good tune and fuel/spark timing all nailed down.

BigD · 03-17-2009, 07:26 PM

Cool beans, GT35r it is. Yeah I'll find the best guy for the tune. At this power level I'm going to stick with the 413. I still give BMW the benefit of the doubt of knowing how to make their engines run best - provided nothing's being overwhelmed. I'm told by a source I believe that the 413 will handle anything under 600rwhp.

**SickFinga** · 03-17-2009, 08:01 PM

Quote:

Originally Posted by ///tyron

Run an S52 with a Gt3582r. You're not going to make your goal at 10 psi as its not in that turbos efficiency range. You'll more so make it at 15-22 psi.

15-22psi?? There are people out there with ~450rwhp on Vortech's with just about 11-12psi.

///tyron · 03-17-2009, 10:08 PM

Quote:

Originally Posted by SickFinga

15-22psi?? There are people out there with ~450rwhp on Vortech's with just about 11-12psi.

thats irrelevant to anything. Turbo chargers and super charges are completely different types of forced induction. You have to be in the turbos correct efficiency range so it can perform at its best and make the most power available.

You dont see Gt42r's running at 15psi and making 700rwhp+ They are built to perform at 25psi+

To the OP i'd run a Gt3076 with a 1.06 for your power levels.

BigD · 03-17-2009, 10:22 PM

Yeah the GT30 looks like it would work too. But I'd still be well in the GT35r's efficiency range, even at 10psi (once again, if you disagree pls provide the math, I'd appreciate it).

///tyron · 03-17-2009, 10:28 PM

Quote:

Originally Posted by BigD

Yeah the GT30 looks like it would work too. But I'd still be well in the GT35r's efficiency range, even at 10psi (once again, if you disagree pls provide the math, I'd appreciate it).

Whats this car going to be used for? Street? Track?

What a/r would you get if you got the gt35r?

BigD · 03-17-2009, 10:37 PM

Quote:

Originally Posted by ///tyron

Whats this car going to be used for? Street? Track?

What a/r would you get if you got the gt35r?

Like I said S52, track whore. (edit: sorry I guess I didn't mention it's for the track, was thinking of somewhere else I asked this)

0.82 looks to be right on the money (or... I guess ballpark since I'm estimating).

///tyron · 03-17-2009, 10:46 PM

to answer your original question TRM makes a stage 1 turbo kit that uses a T3/T4 0.63 exhaust and it put down around 300-350rwhp at 15-18psi. I just think you're going to big of a turbo for your power goals. I found a compressor map of the t3/t4 and it looks like the amount of airflow/min this turbo is comparable to a gt28r, so i think the 30r with a 1.06a/r would get you to your goals a whole lot easier.

BigD · 03-17-2009, 10:54 PM

It's generically rated at 300-350rwhp at 15-18psi? Regardless if I have an M50 or S52? To get 350-380rwhp out of the S52 requires a little under or around 10psi according to my calculations. Again if you think I'm wrong, please provide the math and explain where I made a mistake.

e30_kid89 · 03-17-2009, 11:45 PM

.82ar will be good. size for a s52.

///tyron, I'd bet they use that t3/t4 for the m50 and maybe m52...I dunno if its me but a .63 seems on the small side for an s52 (3.2L)

Too much backpressure from small sizing = EGT's go through the roof.