GT3071R - T3 vs T25 housing - Miata Turbo Forum - Boost cars, acquire cats.

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Old 11-20-2007, 01:19 AM   #1
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Default GT3071R - T3 vs T25 housing

So I test drove a couple turbo Miatas and I really liked the performance characteristics of the GT3071R. It was the T25 .63AR internally gated version that FM offers. I'd prefer to run an external gate, 1) to keep a lid on boost creep and 2) improve turbine efficiency.

I found this GT 4-bolt turbine housing at ATP turbo and was looking for feedback from the 'experts' around here. The housing offers the same AR (.63) but in a T3 flange. The turbine outlet is 3" straight through, vs 2.5" for the T25 version. Which also works out nice for a 3" down pipe.

My question is this... Would I regret using this housing on a 1.8 Miata? The T25 housing was nice at low boost (8psi), but that's not what this turbo is about. My only concern is the 1.8 won't have enough breath to spool the big ol' turbine in this wide open housing.

And if it makes a difference, I would most likely hang it off a tubular manifold like BEGi's S4. I was hoping some of the big turbo crew could share their thoughts.

Last edited by MazDilla; 11-20-2007 at 01:54 AM. Reason: edited for readability
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Old 11-20-2007, 01:24 AM   #2
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If you are gonna use the S4, then you want the T25 housing.

Mark
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Old 11-20-2007, 01:31 AM   #3
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Ah, Markp, you are one of the folks I hoped would take a bite at this thread.

I figured Corky could weld on a T3 flange without much difficulty. How about the turbine housing though?
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Old 11-20-2007, 08:44 AM   #4
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Quote:
Originally Posted by MazDilla View Post
Ah, Markp, you are one of the folks I hoped would take a bite at this thread.

I figured Corky could weld on a T3 flange without much difficulty. How about the turbine housing though?
The housing is less important than the actual A/R and size of the holes. If the wheel/trim/ar stay the same then the turbo should be the same regardless of the housing. I don't know enough about that turbo to be the expert on it though.

I would think that the 3" exhaust would make for a cleaner exit from the turbine and in an externally gated app make more power.

Mark
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Old 11-20-2007, 02:57 PM   #5
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Maz,

Could you describe in a little more detail what you liked about the GT3071R you test drove? Any info on the car, boost level...etc? I'm also interested in the T3 flange with the 3" v-band. I already have a JGS manifold with an external gate and 3" downpipe.

J
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Old 11-21-2007, 12:18 AM   #6
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Bochinam, I speak from very limited experience so take my observations with a grain of salt. I've never owned any turbocharged cars and I only have about two hours of seat time in various turbo Miatas. I've also went for a few ride alongs at various track events, but that is the extent of my turbo experience.

My observation is a result of several back to back drives of FM's kits at their open house this past August. I test drove their BRP derived MP62 kit, the standard FMII/2560 kits (both Link & Hydra), Keith even took me for a spin in his wife's 1.6 equipped with a 2554 Voodoo kit. This was all in the course of an afternoon.

At the end of the day I was chatting up some of their staff about how the 3071 performs on a 1.8. To which one of them replied "I think we have one on our development car. Go ask Bill if you can drive it."

The car was Pokee, FM's development platform for the 94-97 Miatas. Pokee had a pretty much stock 1.8, current FMII manifold/downpipe, 2.5" turbo exhaust, and the Hydra EMS. The car was running 8psi on a manual boost controller and Bill Cardell did some street tuning while I drove.

Here's what I liked about the GT3071R:
It felt like it carried peak torque past 7k rpms, contrasted with the 2560 which starts running out of breath at 5.5k and is down substantially by redline.

Even though it spooled late (4.5k RPM at high altitude) I never felt like I was waiting for boost. Above 4k RPM the turbo was plenty responsive. At a normal altitude with electronic boost control... gravy.

The GT3071R @ 8psi felt faster than the GT2560 @ 10psi
I am certain this turbo would be wicked fast on a roadcourse and would still be fun on the street in all but the slowest traffic. Who needs more than stock power tooling around in bumper-to-bumper/stop-and-go traffic anyway?

As you can see I am pretty much sold on this turbo and I am looking for a housing that compliments the GT3071R without spoiling the responsiveness since 1.8L is considered a borderline application.
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Old 11-21-2007, 12:37 AM   #7
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Sounds like an awesome turbo. I just wish they weren't so damn expensive.
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Old 11-21-2007, 08:50 PM   #8
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Thanks for posting your observations Maz! Good to that it performed well on Pokee which I assume has a 94~97 head.
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Old 11-22-2007, 04:22 PM   #9
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I can't say for sure which head was on it, but I presume it had a 94-97 head since they use it as their 94-97 development car.
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Old 11-22-2007, 04:49 PM   #10
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Another tidbit...

The T25 version of the GT3071R actually has a smaller turbine wheel.

GT3071R-WG (CHRA: 700177-4)
Turbine Specs:
Inducer: 56.5mm
Exducer: 51.8 mm
Trim: 84

GT3071R (CHRA: 700177-23)

Turbine Specs:
Inducer: 60mm
Exducer: 55mm
Trim: 84

FWIW, I've only seen the 3in GT 4-bolt housing offered with the 60mm wheel.

Here's a good shot of the housing on a GT3076R (same 60mm turbine).
http://www.slowboyracing.com/estore/...5&cat=0&page=1

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Old 11-23-2007, 08:34 PM   #11
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There are some pics of the GT3071R with VB option on ATP's site:





They seem to imply that the VBand option is the most efficient housing and that the GT3071R as a whole is a "well matched turbo" what ever that truly means? The don't mention the turbine AR they use in the kit. Most likely the .63 since it's a 2.0L engine?

Details here:

Have you plotted the 1.8 against the compressor map?
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Old 11-23-2007, 09:02 PM   #12
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im actually thinking of upgrading to the gt3071r on my FM2 kit, i just cant stand how the turbo i have now just feels like it has nothing left after 5K RPM.....
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Old 11-24-2007, 02:58 AM   #13
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Quote:
Originally Posted by Bochinam View Post
Have you plotted the 1.8 against the compressor map?
Awhile back I did some back of the envelope plotting using the info/formulas from Garrett's site. Definitely not what most would consider a good street turbo for our app. More recently I have been playing around with a tool on this site:
http://www.squirrelpf.com/turbocalc/index.php

When I SWAG the parameters on this calculator it appears the compressor would sit astride the center (78%) efficiency island from approximately 6000rpm to 8000rpm at 15psi.

Using my estimates, the usable range for the GT3071R on a 1.8 Miata would start at around 8psi (25lb/min @ 8krpm) with an upper limit of 30psi (45lb/min @ 8krpm). My pressure ratio calculations assume sea level.

These numbers are only a SWAG (sophisticated wild *** guess); I encourage anyone to run the calcs themselves and see if you can corroborate my numbers.
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Old 11-25-2007, 02:12 PM   #14
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Here's my sWAG with an emphasis on WAG.

300 hp
1.8 L
12 A/F
.55 BSFC
1.5 IC loss

Redline: 8K 90%
Peak Power: 7K 95%
Max Boost: 4.5K 98%
Min Boost: 3K 90%

I massaged the efficiency numbers (pulled them out my ***). I left the intake temp numbers alone:



Bumping the hp # to 350 for a 300whp goal:



Honestly, I have no idea if this is even in the ballpark.
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Old 11-25-2007, 02:29 PM   #15
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lol, i didnt even want to try and fiddle with that.
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Old 11-25-2007, 02:37 PM   #16
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25psi to make 300rwph. I dont think so.





try this, even this seems high as ****....2.5PR or 20psi.


here's one at 10psi:


Last edited by Braineack; 11-25-2007 at 02:53 PM.
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Old 11-25-2007, 02:51 PM   #17
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more like 14-17 given tune etc.
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Old 11-25-2007, 02:57 PM   #18
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nice.
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Old 11-25-2007, 04:22 PM   #19
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I'm thinking 15-17 PSI for 300 RWHP. Depends on the turbine more than the compressor.

Mark
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Old 11-25-2007, 08:33 PM   #20
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Hey Mark how have you been? It looks like Rick's X-Block is working out well for you. I just pulled mine out of storage now that I have more time to devote to crazy pointless projects.

So, for a ~16psi 300whp shot are you implying that you would select the turbine with the .82 a/r vs the .63?
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