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Old 07-29-2011, 03:52 AM   #1
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Default Fastest spooling 6PSI ish turbo

So, lets say someone only wanted to make 6-8PSI and wanted it to spool as fast as humanly possible. What would be the best turbo and how fast could one expect it to spool on a built 1.6L with cams/ headwork etc.

I'm thinking GT2550 ish? Or go smaller?
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Old 07-29-2011, 04:08 AM   #2
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2554. They can be had for cheap and will spool like it is telepathic.

Super fun for low end torque, around town driving.
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Old 07-29-2011, 04:26 AM   #3
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Dibs on the Rotrex.
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Old 07-29-2011, 04:31 AM   #4
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Seriously though. Is the rotrex not doing it for ya? You have a built 1.6 with head work. Are you thinking of changing it up? Disappointed with the power? Don't like the torque curve, or the lack there of? Whats going on here?
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Old 07-29-2011, 05:24 AM   #5
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Who says I am getting rid of the rotrex?

It's all a game for me. I love working on my car and now that it's basically done I need to figure something else out to do.

The Rotrex pumps a 2.0PR at 8k RPM on my motor. 4PSI = 1.272PR. So that times that = 2.544 = 22PSI. I could also put my old pulley on which would equate to about 12PSI at redline with the rotrex or about 21PSI compounded with 4PSI on a turbo. I know my motor will take more than the 15PSI it's getting right now. I'm just just brainstorming on how to do it without stepping up to a C38. Power Enterprise has done a twincharged S15 240SX as well as the R35.
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Old 07-29-2011, 06:54 AM   #6
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I assume you'll have it like this?:

Supercharger -> Turbo -> Engine

How do you read a compressor map for a compound supercharging situation? Some maps are in units of volume and some are in units of mass and feeding compressed air into the compressor will alter the relationship between mass and volume.
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Old 07-29-2011, 08:34 AM   #7
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a turbo to spool a SCer....who would of thought.
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Old 07-29-2011, 10:23 AM   #8
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I bought a turbo one time that the guy told me was from an SR20. It wasn't. It actually was from a 80's Sunbird turbo coupe, I think. It was a garrett with a .48 turbine/ .49 compressor. It spooled stupid fast and made decent power and torque, but anything over 8 psi and it would fall on it's face after 6,000 RPM. Might be what you're looking for.
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Old 07-29-2011, 11:22 AM   #9
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Thinking out loud here. Wouldn't the small turbine choke off the flow of the supercharger?
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Old 07-29-2011, 11:24 AM   #10
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they are talking about a no-torque-rex.
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Old 07-29-2011, 11:27 AM   #11
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I am still confused. But even at high rpm when the Rotrex is on boil, the 2554 turbine is going to be maxed out and chocking off power. Unless of course there is a huge wastegate allowing a lot of air to bypass the turbine housing.
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Old 07-29-2011, 11:42 AM   #12
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yeah, you'd need some sort of complete turbo bypass.
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Old 07-29-2011, 11:48 AM   #13
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Ok, that makes more sence. I wast trying to figure out how to get 22 psi out of a 2554 turbine at high revs.
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Old 07-29-2011, 11:58 AM   #14
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Oh lawdy, compound boost sounds like a good idea. Judging by your build thread you'll do it right too, I'll be exited to see results
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Old 07-29-2011, 12:28 PM   #15
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Quote:
Originally Posted by vw_nut View Post
I am still confused. But even at high rpm when the Rotrex is on boil, the 2554 turbine is going to be maxed out and chocking off power. Unless of course there is a huge wastegate allowing a lot of air to bypass the turbine housing.
*and a bypass around the compressor, which will also be maxed out at 240 hp.

The turbine won't choke til past 260 hp, and even then the wastegate will flow some % more.
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Old 07-29-2011, 12:42 PM   #16
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does the compressor need to be bypassed? if it's only compressing 6psi until the wastegate/bypass opens and the rotrex takes over, the compressor wheel wouldn't be overloaded.


I'm imagining a Begi S6 style manifold with an IWG turbo. There's a HUGE EWG on the collector back to the DP. The turbo boosts into the Rotrex inlet.

turbo runs on IWG, when you want to turn it off, open the EWG dump straight to exhaust.

Last edited by Braineack; 07-29-2011 at 01:09 PM.
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Old 07-29-2011, 01:14 PM   #17
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More cubes helps all….
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Old 07-29-2011, 01:17 PM   #18
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These are the problems with compound supercharging. The logistics of getting everybody to work together is a huge pain in the ***.

To answer the original question, a Garret GT15V would likely be the smallest turbo that would make any sort of reasonable compression ratio at your peak flow rate, but you're going to over run any small compressor like that at high rpm. You can get them for stupid cheap on ebay pretty regularly, though, as Garret used to give one to every FSAE team who asked for one each year. The VNT will likely be problematic as you put miles on it, as they don't like gasoline EGTs very much.

Further, you're really going about this backward using a micro turbo to fill in the torque lacking with the stupid centrifugal supercharger. Traditionally 'twincharging' is used to add to the top end of a restrictive roots or twin screw blower that will be peachy at low rpm, but doesn't make a peak power target. You're going to have to figure out some sort of boost activated compressor bypass that won't make the turbo freewheel over it's rated speed.
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Old 07-29-2011, 01:38 PM   #19
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here:




now time for Chipotle.
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Old 07-29-2011, 02:16 PM   #20
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Quote:
Originally Posted by Braineack View Post
a turbo to spool a SCer....who would of thought.
Not to say I don't like the power the Rotrex is putting down, I do. The car is 4 seconds faster than last year at our track without the wilwoods I had last year. With some aero and brakes (and driving skill) the car is capible of 1:15's which if you knew our track that's very fast. I just want a new project and the whole reason I did a 1.6L Rotrex was to do something different. This would be an addition to that idea.

Quote:
Originally Posted by giblets View Post
I assume you'll have it like this?:

Supercharger -> Turbo -> Engine

How do you read a compressor map for a compound supercharging situation? Some maps are in units of volume and some are in units of mass and feeding compressed air into the compressor will alter the relationship between mass and volume.
No... Intake -> Turbo -> Super -> Engine

At this point I'm ball parking based on what kind of boost my motor makes. It makes 15PSI at redline which is just over a 2.0PR. 5PSI is 1.34. You take the 1.34 and multiply it by 2.0 which is 2.68. Then remove atmospheric pressure (14.7) and you get 24.6PSI of boost at redline. It would be less in the lower RPMS and work off the same idea that the rotrex already does. Since boost rises with RPM, you will only be hitting 14-15PSI at peak VE. I'm running 26* of timing on 91octane right now with zero hint of detonation... going with this theory since 6PSI is fairly low and won't be too hot... the rotrex dosen't heat air up as much as a turbo it should still run pretty cool.

Just need to think if I need v-bands even for 6PSI. I doubt it. Some inconel hardware should be enough I think...? I do track the car so...


Quote:
Originally Posted by Braineack View Post
yeah, you'd need some sort of complete turbo bypass.
Would I really though? I'm trying to understand the concept here, but I guess I have it a bit off. I figured that the turbo would be run on an electronic boost control system with it's feed taken from the compressor housing. That way when the Rotrex starts pulling enough air to bring what is essentially 6PSI down to 2-3PSI and eventually start choking, the boost control would adapt, and hold the boost steady at 5-6PSI in relation to whatever vacuum the Rotrex is pulling.



Quote:
Originally Posted by Braineack View Post
does the compressor need to be bypassed? if it's only compressing 6psi until the wastegate/bypass opens and the rotrex takes over, the compressor wheel wouldn't be overloaded.


I'm imagining a Begi S6 style manifold with an IWG turbo. There's a HUGE EWG on the collector back to the DP. The turbo boosts into the Rotrex inlet.

turbo runs on IWG, when you want to turn it off, open the EWG dump straight to exhaust.
That's another way to do it, however this way you are not getting any benefit from the turbo in the upper RPMS through the pressure ratio multiplication of the Rotrex.
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