GT2871r or GT3071r?

[spanishricer]

Well I'm going to be upgrading the factory turbo after summer and am currently going through the planning phase. My goal is to have 400whp and maintain daily drivability.

Now the original plan was going to be a GT2871r w/.86 a/r tuned along with a Greddy IM and HKS step1 cams. I thought that would get me very close to 400whp if tuned correctly. Then I noticed that there's a GT3071r w/.64 a/r that is capable of 425whp. It's a little bit more expensive than the GT2871r, but I would probably skip the cams if I went with this turbo.

So which would be the easiest route to reach 400whp? Would I be able to run lower boost with the GT3071r and still reach my goals, compared to running higher boost with the GT2871r? Any input you guys have would be great.

[Nismo_Freak]

GT3071R

400whp will be much better on this turbo.

[USsil80]

yea i am going with a gt3076 and hks 264 step 2 cams

[PhoenixTurboEric]

The GT3071R

[Tipripping240]

So is the 3071r gunna be a laggy turbo or will it have good power all the way through? Im looking for the same numbers (400whp) but i need to know if a 3071 or a 2871 is gunna give hard boost at top or bottom or all through out.

[Nismo_Freak]

So is the 3071r gunna be a laggy turbo or will it have good power all the way through? Im looking for the same numbers (400whp) but i need to know if a 3071 or a 2871 is gunna give hard boost at top or bottom or all through out.

There is about a 300 - 400 RPM difference between the .86 A/R GT2871R and .63 A/R GT3071R from what I've seen.

With either you'll be moving good around 4000 - 8000 RPM.

[sil80hks]

Just go big! GT35R

[nissanrcer240]

Does the gt3071r use stock lines and manifold also like the gt2871r?

[Nismo_Freak]

Does the gt3071r use stock lines and manifold also like the gt2871r?

No, but you should be upgrading the manifold at that time anyways.

[mynismo]

they do make t25 versions of 3071r. should bolt right up to stock location.

friend dynoed 400whp with .86 2871r, it was at 21psi, megan manifold. 3071r should be a lot easier to get there but will suffer from additional lag with .86 version. .64 should have same spool as 2871 .86, but have a better topend.

[Tipripping240]

No, but you should be upgrading the manifold at that time anyways.

So i have heard that tubular manifolds are bad cuz they crack. What is a good manifold for that turbo? (3071r)

[RichthePoser]

So i have heard that tubular manifolds are bad cuz they crack. What is a good manifold for that turbo? (3071r)

the crappy ones, yes. If you want reliablity, your going to be spending between $700-$1100 on a great manifold.

Rich

[PhoenixTurboEric]

Well I'm going to be upgrading the factory turbo after summer and am currently going through the planning phase. My goal is to have 400whp and maintain daily drivability.

Now the original plan was going to be a GT2871r w/.86 a/r tuned along with a Greddy IM and HKS step1 cams. I thought that would get me very close to 400whp if tuned correctly. Then I noticed that there's a GT3071r w/.64 a/r that is capable of 425whp. It's a little bit more expensive than the GT2871r, but I would probably skip the cams if I went with this turbo.

So which would be the easiest route to reach 400whp? Would I be able to run lower boost with the GT3071r and still reach my goals, compared to running higher boost with the GT2871r? Any input you guys have would be great.

Good news, in the very near future we will be offering the 2871R in a T3 Turbine housing with a 4BOLT

[ETTInnov04]

Not true on the manifolds, even the $700-$900 HKS manifold cracks, the design is to blame more than the quality. There is nothing there to help support the weight of the turbo thereby putting stress on the welds.

[s13sr20chris]

a gt30r with external wastegate and screamer pipe should get you over 400whp without extreme boost or cams(though the cams would be really nice). of course you have the manifold issue though. for a manifold i would find a top notch(racecar level) fabricator and have them make a manifold out of weld-el's.

[spanishricer]

Well I planned on upgrading the manifold at the same time, but also forgot to mention the main reason I'm looking at either the GT2871r or GT3071r is because both are available with the T25 housing and with internal wastegates. That way I can go with a tubular bottom mount and avoid having to fabricate custom piping both entering and exiting the turbo and cut costs.

[s13sr20chris]

well, if you want a t25 flange then you are stuck with tiny turbine wheels and you should keep a modest(sub 400) hp goal. big power on tiny turbines makes for freaky cars.

[spanishricer]

well, if you want a t25 flange then you are stuck with tiny turbine wheels and you should keep a modest(sub 400) hp goal. big power on tiny turbines makes for freaky cars.

Just wondering what your reasoning is for this?

[s13sr20chris]

ok, most people dont mind the feel of a big compressor and small turbine. thats why those turbos sell good. just look at all the t3/t4 hybrids out there.

problem, big compressors have a lot of inertia and are harder to spool up. big turbines take more exhaust flow to transmit energy to the compressor. the solution to that is a smaller turbine to keep the energy up for your big compressor. that gives you huge power potential with out too high of a spool point. the problem is now you have a car that goes from 0 boost to full boost really quickly. thats ok for the street and a good driver. its not so hot if you need good control over your power output(like road racing). better when road racing to have linear power delivery(like a quality na motor) to avoid tire roast at corner exit. thats why i reccomend this order...1)size compressor for power goal2)find ideal turbine for compressor size3)adjust turbine size minimally to get a reasonable spoolup.

the last step is only nescesary because a big t4 turbine would be hard to spool on a little 4 banger.

[s13sr20chris]

btw,thats a mega oversimplification. im sure a really technical guy like nismo freak or someone could clear that up.

[PhoenixTurboEric]

Well I planned on upgrading the manifold at the same time, but also forgot to mention the main reason I'm looking at either the GT2871r or GT3071r is because both are available with the T25 housing and with internal wastegates. That way I can go with a tubular bottom mount and avoid having to fabricate custom piping both entering and exiting the turbo and cut costs.

Our Topmount/downpipe combo retains a/c and powersteering!!! http://store.yahoo.com/cheapturbo/pesrexma.html

[spanishricer]

Our Topmount/downpipe combo retains a/c and powersteering!!! http://store.yahoo.com/cheapturbo/pesrexma.html

I see the manifold, but no downpipe?

Anyways, if I go that route, I have to purchase a new downpipe/O2 extension/external wastegate/dumptube/fabricated hotpipe/etc...

Much simpler and cost efficient to stick with a stock location bottom mount and T25 flanged turbo w/internal wastegate.

[Nismo_Freak]

the problem is now you have a car that goes from 0 boost to full boost really quickly. thats ok for the street and a good driver. its not so hot if you need good control over your power output(like road racing). better when road racing to have linear power delivery(like a quality na motor) to avoid tire roast at corner exit. thats why i reccomend this order...1)size compressor for power goal2)find ideal turbine for compressor size3)adjust turbine size minimally to get a reasonable spoolup.

Either way you look at it you will get a sharp rise in power with any small displacement engine pushing twice it's stock power.

The larger turbo you are talking about would actually be harder to drive for a few reasons:

1. The lag of the turbocharger displaces your powerband even higher, causing you to have to accelerate much sooner at full throttle to get the turbo to come online. Once it does you will be around the engines peak VE typically and this causes instantaneous crap-load-o-torque. If you can get the turbocharger to spool sooner before the engine itself begins to flow well you create a much more linear response. Even if the driver finds himself putting too much power down he can back off the throttle and you won't lose as much time when you then respool the turbocharger.

2. A driver that is nuking the tires out of the exit has accelerated too soon. It is not hard to feel out the cars torque even with a responsive turbo. Partial throttle on apex, build it up around 2 - 5 psi and as soon as you start to straigten out the car you can lay on the throttle and you might get a little momentary spin but nothing crazy.

[s13sr20chris]

hmmmm, thats interesting. i will have to keep that in mind and see if i cant go to the track with a tiny turbo car.

what i am trying to reccomend against are the "on/off switch" turbos. the ones that are kinda laggy but suddenly go nuts at the "critical mass"(great use for that otherwise boring term eh?) airflow. know what im refering to?

still, your point is correct. at a certain specifice output you are bound to get some delivery problems.

[Alfa Turbo]

...1)size compressor for power goal2)find ideal turbine for compressor size3)adjust turbine size minimally to get a reasonable spoolup.

the last step is only nescesary because a big t4 turbine would be hard to spool on a little 4 banger.

If I understand you... you can read a compressor map to determine the flow and compare that to your engines required flow (based on VE) for a given HP number.

But... how do you go about #2 and #3?

-Brian

BTW I am running a tangential divided T4 on a 2 liter now... Getting 290WHP out of a T4B S compressor @ 15psi but do not see that pressure until 4300-4500rpm.
Modified by Alfa Turbo at 6:38 PM 5/24/2005

[spider_slayer]

i was under the impression that our stock manifold was actually pretty efficent. i know that it is rather durable which is why i have been thinking about the gt2871r.....so i could retain the stock manifold and avoid the cracking problem. i know that tublar manifolds ARE in fact more efficent but i didn't think that it made that much difference.

[s13sr20chris]

If I understand you... you can read a compressor map to determine the flow and compare that to your engines required flow (based on VE) for a given HP number.

But... how do you go about #2 and #3?

-Brian

BTW I am running a tangential divided T4 on a 2 liter now... Getting 290WHP out of a T3 S compressor @ 15psi but do not see that pressure until 4300-4500rpm.

its less exact and im not really an expert on it. the point is you want to keep the sizes of the wheels fairly close. i am guessing thet a turbine wheel should be about 90% the diameter of the copmressor. thats about the ratio that the really well matched turbos have.

and number 3 is only if you end up with something too big for reasonable use.

[Alfa Turbo]

Thanks... that is pretty much what I hear. There is ALL sorts of info on reading compressor maps... The turbine map info must all be locked up somewhere...

[s13sr20chris]

thats because its secret ninja stuff

sns for short.