I was dead set on a 4088 until I read this...

[TurboTiger]

Well, if you run 25psi or lower, the GT35 is more efficient.
But yah, if you run about 35psi or a 3.4 pressure ratio, the S258 is definitely more efficient.

I guess that's why I bought a S258 with the twin scroll housing and JMF Twin Scroll manifold. It took me forever to decide on that particular combination.

I overlayed the GT35 compressor map onto a S258 compressor map just to see where the efficiency islands are on the map.

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[dsm-onster]

25psi with a gt35r is a waste to me. I understand that some may do this because they want the the same turbo for the street, then turn up the boost for the track. . . So they look for the most efficient compressor for the boost they can get away with on the street. But why bother. I'm more concerned about the efficiency at the track. The s258 is still over 72% efficient at 25psi up to and a little past 55lb/min. There's really no way you can flow 55+ lb/min at 25 psi with either turbo.

Besides you have a faster spool with the s256. That to me is more important for the street. And when it comes to track time, it is more efficient, faster spool, AND can exhaust more gases for better VE. So I still think you made a great purchase for the strip turbo that is plenty suitable for good street/pumpgas power. It's also rebuildable. At the 25psi and the likely flow of 45lb/min it is still at 78% efficiency. . . Much better than a 20g and spools about as fast.

 

[We're on Boost]

I guess that's why I bought a S258 with the twin scroll housing and JMF Twin Scroll manifold. It took me forever to decide on that particular combination.

Hey way to go! That's the setup I've been thinking about getting lately. What a/r turbine housing did you get? And could you take a look at that housing and see if it actually says Borg Warner or has a BW logo on it somewhere - something to indicate it is actually made by BW.

Gary

 

[We're on Boost]

Look at the height of the graph ..... if you need to run more boost to flow that kind of mass, then the s258 can do it. No need to upgrade from one SMIM to another, and port the head, and run a stroker kit, or buy 288s and rev to kingdom come. So not only is the BW more affordable, but you don't need such an expensive supporting cast in your engine bay to get similar flow numbers. Just up the boost.

That's kinda like what I'm thinking.

35psi puts you at the highest rpm curve on the gt35r (56-trim) map at 55lb/min and off the map at 60 lb/min.

It's even worse than that if you get out your calculator and figure in typical losses.
Here we go with optimistic losses at sea level:

Given: GT3582 overspeed line goes through PR~3.25 at 55 lb/min

14.7 psi (atmospheric pressure, absolute, at sea level)
-0.5 psi (pressure losses in air filter & intake pipe, NO MAF)
=14.2 psi (pressure at compressor inlet, absolute)

x 3.25 (PR on the overspeed line at 55 lb/min)
=46.15 psi (pressure at compressor outlet, absolute)

-14.7 psi (subtracting atmospheric pressure to get gage pressure instead of absolute)
=31.5 psi (pressure at compressor outlet, gage)

-1.5 psi (pressure losses in IC, IC piping, throttle body, STILL NO MAF)
=30 psi (pressure in the intake manifold, gage, YOUR BOOST)

So really you'll be on the edge of the GT35 map at only 30 psi at 55 lb/min.
Just goes to show how far off the map people run these things.
If you want to stay on the map get a Borg!

Gary

 

[T9S1i]

<-------- Is glad he's running a s258!!! haha

I blew my t3 gasket, once it comes in i'll fix it and get some numbers for you guys shortly. (t3 .70 housing)
Looking to see what ~30psi will give me.

 

[twicks69]

Sorry to bring this thread back from the dead, but a member of the forum was wondering what relay I am using for the dual fuel pump setup.

It is a Signal Stat 192 relay - 12V, 5-prong, 40A relay. Here is a picture of it for reference at the bottom of the post. Any NAPA store can find it IF they know how to use a parts manual and look up a part number.

Just so you all know, I described my cylinder head in a previous post. I did not say anything about O-ringing the head or block -- I am not running an O-ringed head/or block setup -- Just good ole ARP L19 Head studs and a Mitsu MLS gasket (not copper-sprayed). Nothing special; seals 50psi just fine. Just perfectly flat surfaces on the head and block.

Stay away from MAFT -- you will be better off running AEM EMS with a 5-bar MAP sensor and an AIT sensor. This is a much better investment.

Axles -- contact Marty at Raxles ( Raxles - Raxles Home ) and tell him that you are looking at the same ones that Tim Zimmer has -- they are the Raxles RACE axles. You will be shocked how much less they are than the driveshaft shop, and they have a lifetime warranty against breaking -- they break or damage, replaced for free -- for life. Period.

Injectors -- You will need 1000cc injectors and dual fuel pumps (255HP in the tank, and a 255HP in-line) with -6AN feed line to the rail with an in-line filter, and a hardwire kit using a 5-prong relay with two signal prongs on it. Use 8-gauge power wire from the battery back to the relay, and a 8-gauge ground for the relay. Use 10-gauge from the relay to each fuel pump, with in-line 30-amp fuses on each pump power line. I also used a 60A in-line fuse at the 8-gauge wire by the battery. The stock fuel rail has no problems in this combination.

Intercooler -- Precision Turbo and Engine (PTE) large air-to-air intercooler core with 2.5" intercooler pipes will be plenty.

Intake -- Forced Performance Cast aluminum 4" intake pipe with large K&N filter.

Transmission -- you will want a good 4-spider center diff. Screw welding it if it is a street car, it will bind up alot and only make the car less enjoyable to drive. If possible, use a new viscous coupler, and a Quaife front differerntial. Also be sure to have a heavy duty 3/4 gearset (Early 1992 parts), and a late model input shaft and intermediate shaft (95-99-spec).

Clutch -- Quarter Master twin disk from Adam at DEVOTUNING, Home of the world's fastest EVO .

Start with these, and get some numbers on how much it is going to cost you.

 

[We're on Boost]

Twicks: never noticed this before from your profile - "1991 Unported Cylinder Head". Now that's pretty cool. Do you know if the 1990 and 1991 cyl heads are the same, ports and everything?
Nice to know there is a good shop in Green Bay. I lived there for a few years a long time ago, grew up in Milwaukee, Whitefish Bay actually.

Gary

 

[twicks69]

Twicks: never noticed this before from your profile - "1991 Unported Cylinder Head". Now that's pretty cool. Do you know if the 1990 and 1991 cyl heads are the same, ports and everything?
Nice to know there is a good shop in Green Bay. I lived there for a few years a long time ago, grew up in Milwaukee, Whitefish Bay actually.

Gary

Yes, all 1989-1992 6-bolt turbo cylinder heads are the same: MD147283
They have the same ports, and the same valvetrain.

Good luck!