.64 to .86 AR
 

Curious if anyone has opinions on swapping turbine housings on a gt2871r. I've been running a .64ar and was curious how much top end gain and loss of spool I could expect from going with the larger housing. Anyone done this or have opinions on what the change would result in?

This is on a stock '99 head, with straight through 3" turboback exhaust, and ~20psi. My most recent dyno:

https://www.miataturbo.net/attachmen...ine=1346204609

It's hard to quantify the changes, but the hit will be later and much harder, according to what I've seen. Depending on what you're looking for in a powerband, it might not be any faster even if it makes more power.

I know my friend runs a pretty big precision turbo on his sr20 at about 15-17 psi and it got faster and a lot more responsive when he went down in exhaust housing size. The hit is more smooth and he makes less top end power tho.

Can't help much more...

I did exactly what you're talking about. But haven't bolted the setup on yet :(

Minimal spool loss and big mid-range gains. We've discussed it before, and more than a few folks here run 0.86a/r GT2860RS/GT2871R units.

unrelated, do you have the dynojet run file for that run? do you mind posting it?

Thanks Savington, sounds like it would make for a decent investment.

Soviet, I don't have anything electronic. The guy did print out several pages of data from the run though. If I can find them I'll scan and upload it.

I've not any solid figures yet, but my set up looks like this:

GT2871R .86
99 stock head, built bottom end
fm2 cast manifold, begi dp, 3" exhaust, no cat

What timing table are you running?

pd: Was that dyno run with pump gas only?

I'm curious about the timing map as well. I also have a GT2871R .64 with a stock '99 head, built bottom end (8.6:1), begi turbo parts, artech 3" exh.

PDEXTA, you are going to love your first track session at Sebring with that car. And you will learn things in a 25 minute session (probably 15 mins at full speed) you never knew about your car from a 15 second roll race. You will be hooked.

I went ahead and ordered the .86ar compressor housing, probably wait til after Sebring in October to swap it over though. I'll be sure to take several logs and post some before and after virtual dyno numbers.

Here's my current timing map:

https://www.miataturbo.net/attachmen...ine=1346462827

The dyno was on pump gas, 93 octane.

I dyno'd 319whp on a different dyno several months earlier with slightly less timing in a little warmer weather so I think the numbers are pretty reasonable. The same day my girlfriend's bolton RSX-S dyno'd 187whp which is right in line with what we were expecting as well (needs more Kpro and turbo).