haha i have acquired 2871, just need to get a tial hotside. sounds like i should go with the 0.64 since i'm not going to be able to flow very well to use the 0.86 top end?

wish i could turbo tim! too little $ with too many projects

 

Right, but this is not a smaller turbo, it's just a smaller turbine A/R. Will it still make torque with the exhaust restriction? RHarris' did not. People typically suggest that a smaller AR turbine housing will shift the turbine map left (effectively shifting the compressor map RPM and pressure ratio up) and all else stays equal, I don't think that's the case. Again, I don't think anyone is running the .64 AR turbine housing and liking it.

 

Read this:
http://www.motoiq.com/magazine_artic...p-details.aspx

I believe one of the reasons I'm making so much torque at lower RPM is because I have so little pressure pre-turbo on the exhaust side.

 

Of course. A smaller A/R will shift the boost threshold down (RPM at which it makes full or parital boost) at the cost of max topend.
If the turbo with smaller A/R has a max topend below the OP's target, then the improved spoolup is worth it.

 

A turbine *requires* some pressure drop (i.e. there needs to be some TIP - turbine inlet pressure) to generate power to drive the compressor. The questions remaining are, what is the efficiency of said turbine, and where is its sweet spot of max efficiency? When efficiency is low the turbine will generate more TIP than otherwise, at the same RPM and boost... reducing engine volumetric efficiency.

A smaller turbine will have its max efficiency island at higher shaft RPMs and will be more efficient at lower flow rates, i.e. at spoolup. The "speed match" between a turbine and compressor tells you how well matched they are in that their sweet spots wrt shaft RPM. If for example, the compressor is oversized (or turbine undersized), spoolup will be affected because during spoolup the compressor is turning slower than the turbine's sweet spot, and the turbine can't deliver the shaft power the compressor needs.

A smaller a/r allows the turbine to operate more efficiently at low flow (spoolup), so spoolup is better. At higher flows (topend), however, it is less efficient and thus will generate more backpressure than a larger a/r.

 

Sorry for yet again bringing this thread back to life, but my question in very much related...

I have an old and broken Turbonetics T3/T4 E-50 that I am replacing, and I was initially thinking of a GT3071 since my tubular manifold has T3-flange, but I am wondering if anyone has experience with a T3 housing on the GT2871? I am aiming for a responsive 350rwhp setup for autoX and trackdays.

And if so what the larger flow/area of the T3 would do to the .63 VS .82 debate?

I can also get a GTX2867 bolted to the same T3-housing, which also is tempting to try... Too many choices as usual! The EFR6258 seems to be on a 4-8month backorder everywhere, so at least that takes one candidate out of the equation :-)

 

I've never even heard of a t3 hotside for a 2871, where did you find one? (or are you just making this up?)

 

ATP sells quite a few of them.

 

Ahh, totally forgot about them.
Also just realized my HKS(garrett) gt2535 had a t3 footprint.

Nevermind.

 

They actually sell a twin scroll housing for the 2871. That would be a wicked 350whp street setup.

 

I bet it would... My manifold is single port unfortunately.

 

ATP strongly urges me to go with the GTX2863R instead of the 2867, 2871 and 3071. The powerpotential, according to them, is equal to the 2871 with much better response and spoolup.

Almost sounds too good to be true, but I think I will give it a go and be the guinea pig for the 2863 in a miata.

 

I'd like to upgrade from my 2560 as I'm going built engine. Ive found a decent 2860 that needs a ex housing. Could you let
me know what that .86 housing might be worth in a pm?

 

Sorry, ARTech is getting it.

 

Now that 5-axis machining is cheaper, its true.

 

Well at least it's going to the best home....