GT3071R opinions needed

[MSP2003.5_Nick]

Ok so at the end of last year I switched from a no-name t3/t4 to a garrett GT3076R .63 A/R. Obviously with the GT series and more tailored frame I noticed a huge difference in power all through the RPM range and the dyno sheet when we retuned it made my jaw drop. (close to 100 more HP at same boost level lol) But I dont know if I jumped the gun with it. I want over 400 this year so I can jam this protege in the 11s, but before I retune again I wanna make double sure I got the right turbo.

I've been doing a bunch of research and it seems a GT3071R with the larger .82 A/R would have been a much better match for our engine with drag race application (and street driving) According to the compressor maps with that A/R I'd make more power longer and more efficiently.

I'm more used to hondas where you have Vtec and rev to 9 grand so you can have that bigger turbo with small A/R to have good spool but still make crazy top end power.

Staring at compressor maps and calculating air flow and pressure ratios makes my head hurt, I'm sure someone has some good knowledge to share with me!!

 

[yudkib]

http://www.lovehorsepower.com/CFM1.htm
its what i use. a good adage to keep in mind is you need 1lb/m per 10chp (i think it was crank and not wheel). so you would be looking roughly at 45-50lbm.

if youre serious about 400whp, you might be best off with the 3076R. running 30lb (3 atm absolute) requires ~45lbm to maintain boost, so youd probably be right at 400 to the wheels with that.

 

[MSP2003.5_Nick]

I've got a decent understanding about the compressor side, but whats confusing me is choosing an A/R for the turbine. Theres so many options in size but no explaination to what exactly it does. Say right now I have the 3076 with .63 a/r what would be the difference with that same turbo had an .82 a/r or even 1.03 a/r. It is just a matter of shifting your powerband or does the bigger size yield more capacity for power adding.

 

[mazdaspeedp]

i thought that a .63 would have allot better low end response quicker spool but then when kinda even out at the top end. And a 1.03 would be really bad lowend but once you got the rpms up high it would pull like a mofo. Im planning on getting a adapter for my gt2871r with a .63ar

 

[MSP2003.5_Nick]

yeah I think thats about the jist of it. Our motors dont have a whole lot of usable rpm to play with so I'm thinking anything above .82 a/r would give you power too high in the revs. Even with my turbo cams the Power drops off after 6500 or so. I want to have high rpm power for drag racing, lag doesnt bother me as I have launch control and anti-lag shifting in my standalone to take car of that.

The question is should I get a 3071 or 3076 with the .82 a/r.

 

[NocturnalSpeed]

Sub

 

[2.0t03speed]

yeah I think thats about the jist of it. Our motors dont have a whole lot of usable rpm to play with so I'm thinking anything above .82 a/r would give you power too high in the revs. Even with my turbo cams the Power drops off after 6500 or so. I want to have high rpm power for drag racing, lag doesnt bother me as I have launch control and anti-lag shifting in my standalone to take car of that.

The question is should I get a 3071 or 3076 with the .82 a/r.

just some food for thought. im running the 505 manifold,MAM Exhaust manifold, and a 28rs w/ a .86ar backhalf and i dont ever feel like my car stops making power. it still feels like im making more power well after 6k

 

[MSP2003.5_Nick]

thats how I figured it would be. I havent run anything but a .63 a/r turbo on my car and although the car still goes after 6k it definetly doesnt keep up the same pull as say around 5k.

They say the 3071 is similar to the disco potato but just with T3 hot side so it flows a slight bit better. The biggest advantage of the 3071 over the 3076 is that they brag it spools 1k sooner which is hard to believe. I'm really torn between these two turbos!

 

[Spiced MSP]

definitely interested in the outcome of this!!

 

[yudkib]

there's no "empirical" way to gauge A/R, as there's SO many variables that come into play when you get to that point. how much resistance gets applied to the turbine vs. compressor side (aka, how well does your head flow compared to your exhaust manifold)? whats your actual VE? etc, etc, etc. its a very indirect science, and at that point all you do is look at what everyone else has done. heres how i try to figure it out...
-how much WHP do you want? multiply that by 1.15 to get crank hp, then divide by 10 to get lbm (prentend its 45)
-figure out how much boost you would need to run. use that calculator to figure it out. itll give you a few charts, then you can figure out the number in psi (pretend its 30psi)
-convert to atm, in absolute pressure, plot on turbo map (30 psi is roughly 3atm)
-be sure your compressor can keep up. you want your point closest to the outside of the furthestmost, uh, isobaric island (i think its called) without going much past.
-determine where you build full boost by drawing a horizontal line to where it intersects with the surge limit. find the lbm required, go back to your spreadsheet from the calculator and see at what RPM the engine requires that many lbm to operate at 100% efficiency.
.....(so if you get 25lbm from the intersection of the surge line and 3atm, go look under the 30psi row to see where at what RPM its close to 25lbm). this is not exactly how it works in practice, but its close enough to say where your spool is.

AR impacts the map in general -- kind of. loosely speaking, it shifts the entire group of islands and the surge limit to the left or right. smaller A/R shifts left, larger shifts right. shifting left means that youll spool earlier since the surge line is now at lower lbm, but it also means the turbo will run out of gas up top (since peak is now at a lower lbm). shifting right means the surge line -- again, loosely, moves to a higher lbm and later spool, but so does the peak output which can deliver more lbm at the top end.

so for a disco potato (and almost all the gt turbos), which have wide islands, it has a good powerband. older t3's, t4's, et al, are all much narrower, meaning theres more of a trade between spool and top end. so when you go to pick A/R, you want to keep these things in mind: if you want to autox, you probably want the smallest A/R for the fastest spool unless you plan to max out the turbo. if you want to drag, you want the smallest A/R without plotting outside the last island. thats where things get kind of weird, and you have to trust your reading and gut instinct since theres no empirical way to do it.

piece of cake, right?

 

[MSP2003.5_Nick]

Very nice explaination, I'm starting to grasp it a little better now. I know a lot of people usually dont go that deep into it to choose a turbo because most the time theres been a thousand people who have trialed and errored for you to say what works good. But with the ole mazda protege theres not that many people that go for that much power.

I put all this into practice and what I gathered was the gt3071r with the .82 a/r is going to be my best option. If I was going for maybe 450 than the 3076 would be a better choice but I just want 400.

The 3071 has just a smidgeon below peak efficiency at 30psi peak power rpm and the slightly larger a/r should shift it right to the butter zone. It's a lot of boost but with that combo I will have a lot more range of rpm with power. I could do the same hp with a gt35 but I would only have the very peak of my rpm range where I have the power.

May as well give it a shot, garrett is bragging this turbo right up, I wanna see what they're on about.

Basically the way it works out with the one I have now 3076 with .63 a/r it has the same compressor map as the 3071 .82 a/r but makes peak power too soon. Of course all this info is only relevant to the fact 400hp is my number of choice.

An just in cast anyone is interested a straight gt28rs is peak efficient at a little under 300hp. Basically you can go to 350 with it but its a gonna take a LOT of boost.

All this info really makes me wonder why these honda guys put gt35 turbos on their d16 vtec motors! It doesnt even make sense, sure you have 400hp at 16psi but your turbo isnt anywhere near its efficiency.

 

[2.0t03speed]

if your going to get a 3071 why not go for the new gtx3071r lets you run more boost had better flow with the same response as the normal 3071. http://www.atpturbo.com/mm5/merchan...tp&Product_Code=GRT-TBO-100&Category_Code=GTX

 

[MSP2003.5_Nick]

I was actually looking at the gtx compressor maps earlier and they give me half a chub, but they are also 300 bucks more expensive. It all depends on how much my tax return yields (and how much money I can hide from my wife to buy another turbo lol)

 

[blaineog]

if your going to get a 3071 why not go for the new gtx3071r lets you run more boost had better flow with the same response as the normal 3071. http://www.atpturbo.com/mm5/merchan...tp&Product_Code=GRT-TBO-100&Category_Code=GTX

If your gonna take off a good 3076, and change to a 3071, why not spend more and go for the best.. The GTX series, is the best of both worlds.. Take it from me, i am running a gt 3071 64 AR. It spools at 2200 rpm in 4th. I get to max boost by 3500 rpm in 2nd and 3rd gears, that is 15 psi for me. It made 280ft lbs at 4000rpm last time it was dynoed, 1 year ago at 14psi, and made 270 whp, it pulls hard all the way to the redline 7000rpm (that is with boost falling to 14 psi due to an ineffiecient internal wastegate). My experiences with the 3076 even on evo's is that the spool a lot later and power figure is always less than expected.
thats just my 2 cents.

 

[MSP2003.5_Nick]

true enough, I'm definetly gonna try and swing it, gtx3071r would make me cream my pants just to look at haha . I'll be able to sell the 3076 for close to what I paid, but for all of you guys that are married you know how it is. We have an expensive hobby and its hard enough for me to figure out why I want to tune cars let alone explain it to someone else. Shes already almost too scared to get in the car, she'll poop her pants with another 50-100 wheel lol

 

[yudkib]

are you running 9.5:1 or 8.5?
and personally, id damn near bet money that theres a better way to spend $1400 than a 3071. yeah youll get better spool, but really, how much is 400RPM worth to you? because thats the only gain youll get by downsizing your turbo...
at those numbers, you should think about having a spare trans on hand. how does the rest of your drivetrain look? do you have every other power adder? mfactory or quaife diff? and if you decide to go bigger, are you going to keep the 3076 on hand? throwing around the best turbo is great in theory, but in practice, id keep the difference. i ran a t3/t04e on a stock block because its what i had, and the 2554 blows. i would WAY sooner spend the money on EMS, gauges, and the bajillion other things i needed for my car over a smaller turbo.

 

[Carlinator]

Related question: I'm gonna be switching to a disco potato at some point. If I'm reading things right here, I'd want the .64 a/r for street/track use, and the .86 would be more for drag racing, correct?

 

[yudkib]

probably, but again, that assumes you dont plan to max out the turbo. what are your whp goals?

 

[MSP2003.5_Nick]

I have every other thing under the sun already, turbo is pretty much all I'm still working on perfecting. lets see.....

Haltech platinum sport 1000 ecu
Arias pistons with crower H beams (9:1)
5 angle valve job with port and polish
626 mani (not completely satisfied with)
CP Boost turbo manifold (the one of a kind demo one used on their 323)
3" custom straight pipe exhaust with straight thru Borla muffler
Tial Wastegate and BOV
Greddy 11x24x3 intercooler
Twiggy turbo cams
Adjustable cam gears (forget brand)
AWR 95 motor mounts all round
Quaff LSD
and so many more parts that I cant even remember.

I'm all set just need the right turbo to unlock the potential. I want that crazy 505 intake mani but the price is a little excessive for 10 bucks worth of aluminium.

Yudkib, 4000rpm is not important at all to me, as I said I want power up high for drag racing. Do you think the 3071 is a bad option for that even with the .86 a/r.

Either way I gotta change something, either get a completely different turbo with the 3071 or maybe just get the .86 a/r turbine for my 3076 which would save a bunch of money. Or should I look strickly into the gtx series because they are so mad tyte jdm?

Good job now you got me second guessing my decision lol, I just want someone to tell me what to get its so much easier!!!!!

 

[Carlinator]

probably, but again, that assumes you dont plan to max out the turbo. what are your whp goals?

Probably around 225-230 once I get my intake and FMIC, probably around 300 after I get the cash to go forged. I probably won't be dragging it as much as I will street driving, with the occasional autox/track day thrown in.