please post your turbo model, comp ratio, exhuast size, and how much boost at 4000rpm - Page 2 - Miata Turbo Forum - Boost cars, acquire cats.

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Old 07-13-2007, 12:02 PM   #21
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A faster spooling turbo will be more fun on the street. I say go with the smallest turbo that will support your ultimate power goal. The problem is that your ultimate power goal will likely change once you get used to the power ... if you aren't too much of a ***** to got WOT every now and then.
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Old 07-13-2007, 12:50 PM   #22
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Quote:
Originally Posted by jayc72 View Post
A faster spooling turbo will be more fun on the street. I say go with the smallest turbo that will support your ultimate power goal. The problem is that your ultimate power goal will likely change once you get used to the power ... if you aren't too much of a ***** to got WOT every now and then.
Hopefully staying at 250whp means I can keep the 1.8 brakes with hawk blues...rather than pay $1600 for a bbk, then $160 for a set of front rotors, and $100 for pads. I'd rather swap pads and spend half as much on brake maintenance. I also don't want to deal with breaking transmissions and rear ends constantly.

I litterally went to ******* hell and back with the vw, and even though its a toy...I don't want to constantly search for transmissions and rear ends. The whole idea is to build a car which is cheap to take to the track.
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Old 07-13-2007, 12:54 PM   #23
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Quote:
Originally Posted by y8s View Post
Incidentally, with regard to the track use of a turbo car.... you wont notice spool with any of these turbos.



Basically when you shift at 7500 and the RPMs drop back down to 5000 something.... you'll have boost. no problem.
I understand this...but at 8.6:1 will the car move at all when the turbo isn't making boost? I have too many variable, and too much time to think about it.

Gary at TDR thinks the lower compression is a bad move, and this scared me.
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Old 07-13-2007, 01:05 PM   #24
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Coincidentially my new GT2871R will be here Monday. I got a pretty good deal on it and could probably get more at the same price, PM me for more info.

ALSO, there are more than one GT2871R (three in my catalog):
Compressors:
Inducer dia/exducer dia/trim/AR:
49.2/71.0/48/0.60
51.2/71.0/52/0.60 (plotted above)
53.1/71.0/56/0.60 (mine)

That last choice has the same specs as the GT3071R except for a "larger" 0.60A/R compared to the GT30's 0.50A/R. The GT3071's compressors can be used too, to make things even more complicated.

For turbines, all GT2871's use the same two exhaust housing options (either .64 A/R or .86 A/R). Y8S went with the .64 A/R on his larger GT2876R and is getting pretty decent spool.
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Old 07-13-2007, 10:22 PM   #25
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I'm starting to think I seriously fucked up with the 8.6:1 pistons. $400 down the *******.
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Old 07-13-2007, 10:56 PM   #26
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Dude, 4/10s of a point in static compression is not the end of the world. You'd probably be hard-pressed to tell the difference between 8.6:1 and the usual 9:1.

You'll be able to run a little more timing advance to help out.
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Old 07-13-2007, 11:00 PM   #27
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Dude, 4/10s of a point in static compression is not the end of the world. You'd probably be hard-pressed to tell the difference between 8.6:1 and the usual 9:1.

You'll be able to run a little more timing advance to help out.
So do I run with the gt28r to spool the thing faster and deal with high egt's, or swap it out for the gt28rs (that I ordered) and deal with the sluggish spool and run happy egt's?

I'm leaning toward the gt28r.
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Old 07-13-2007, 11:22 PM   #28
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slugish spool.....you're talking like 300rpm difference at most.
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Old 07-14-2007, 12:43 AM   #29
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if you got the .64 A/R 28RS it'll spool pretty well. that's the same hotside I have but it uses the T3-60 compressor which is a little smaller than mine.

Ask Jason Cuadra what he found by going from a 9.4:1 motor to an 8.2:1 motor and headwork. more low end that's what.
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Old 07-14-2007, 02:07 AM   #30
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I was just going to reccommend searching Jason's name. I knew he went with some low compresion pistons for his rebuild. Hustler, you remind me of myself in that we both seem to over think things and second guess decisions. the 8.6 pistons were a good choice, period. the car will be making boost all the time. it will be so much better than what you're used to. I'm no expert on these turbos but I have had mine for 5 years and tracked it for the last 3 and I would reccomend going with the larger turbo. because it will make more power per lb. of boost. if you want 250 (which is a number I like) then you may be able to reach it at 10 or 11 psi instead of 12 or 13 psi. less heat and backpressure is a good thing. on the track with sustained boost.
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Old 07-14-2007, 02:21 AM   #31
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Quote:
Originally Posted by Ben View Post
28rs and 2560 are similar turbos.
http://www.flyinmiata.com/tech/dyno_...emy_potato.pdf
honestly I don't think that makes the 28rs look very good.

I think you'd be exstatic with a GT2871r, but I've said that already. It's going to spool a little slower than the 28rs, but the tradeoff is minimal considering it will make a lot more power per psi.

You've also got more RPM to work with with your fancy rods and solid lifters.

If it were my motor, and I were playing with your budget, I'd go 3071r. My motor (which will be similar to yours) is probably getting an ebay T3 or T3/T4.
+1 on everything... that dyno graph made me completely disinterested in the potato and I posted it before for hustler i think... go big (3071) or get a 2560, don't get something that does neither very well.
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Old 07-14-2007, 08:33 AM   #32
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Originally Posted by Mymiataflys View Post
Hustler, you remind me of myself in that we both seem to over think things and second guess decisions. .
I'm a government planning analyst...over thinking is what I do.
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Old 07-14-2007, 08:52 AM   #33
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Quote:
Originally Posted by y8s View Post
if you got the .64 A/R 28RS it'll spool pretty well. that's the same hotside I have but it uses the T3-60 compressor which is a little smaller than mine.

Ask Jason Cuadra what he found by going from a 9.4:1 motor to an 8.2:1 motor and headwork. more low end that's what.
he got more low end torque and/or power by lowering compression?
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Old 07-14-2007, 08:54 AM   #34
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Originally Posted by Al Hounos View Post
+1 on everything... that dyno graph made me completely disinterested in the potato and I posted it before for hustler i think... go big (3071) or get a 2560, don't get something that does neither very well.
I like the gt2560 better in that dyno, but what are egt's doing at that boost level? I don't need melt-down from running the car for roughly 30 minutes at its maximum levels. I don't want this motor or turbo to come apart because of some stupid decision which I could avoid with a little more research. Also, if I stick with the 8.6:1 pistons I'll have to run more boost to compensate for the lower static compression...and is that outside the flow parameters for the turbo on the compressor side...because that's borderline on the turbine. That's why I am leaning toward the gt28rs...it has the larger turbine.
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Old 07-14-2007, 09:02 AM   #35
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well we are turbo planning analysts overmaking hp and getting **** done is what we do try to fit in :gay: If my 16g spools on a 1.6 very nicely then the 3071, or 2860 will be a wonderfull turbo on a worked over 1.8. Trust me a little lag at less than 1800 rpm is good for wet weather driveability and general fuel economy that being said it isn't hard to stay above 3K rpm in my setup where i was initialy making more torque than you did at redline with your setup now. So imagine if your motor skipped from 2K-6.5K instantaniusly and that is how the turbo feels from there on you have the G's telling you damn this torque isn't half bad, and the speedo telling you if cops could see this they would call ahead to get you picked up trust me man. The driving experiance excentuates stock and adds to it 1 million fold.
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Old 07-14-2007, 10:47 AM   #36
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QUICK SPOOL IS OVERRATED. As long as you make full boost by 4000-4500RPM you'll be plenty happy. When's the last time you shifted at WOT and you were below that mark?
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Old 07-14-2007, 10:52 AM   #37
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Quote:
Originally Posted by hustler View Post
he got more low end torque and/or power by lowering compression?
OK I did leave out that he uses the GT2554.

He also was running about 240 rwhp at 10 psi. on that turbo.


I *think* the GTX motor died though (the 8.2 one) and I think now he's running an old 94 short block that I sold him. for cheap :(
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Old 07-14-2007, 11:00 AM   #38
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QUICK SPOOL IS OVERRATED. As long as you make full boost by 4000-4500RPM you'll be plenty happy. When's the last time you shifted at WOT and you were below that mark?
I still want to get the car to move in traffic. My 8.5:1 turbo vw was a ******* turd off boost. It was really bad.
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Old 07-14-2007, 11:29 AM   #39
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that car also wieghed about 1000Lbs more didn't it?
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Old 07-15-2007, 01:00 AM   #40
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I'm a big fan of driveability myself. My T25 never surprises me. I don't ever have to worry about stomping it in a corner and gaining 80whp in 100rpm like you get on a big laggy bitch when it comes on boost.

The .80/.64 pulls steady and smooth and makes great torque down low. I love having 12psi and 160ftlbs on tap @3500rpm... too bad I'm down to 7psi on my craptastic Spec clutch.
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