Originally Posted by bbundy (Post 652374)

If you look closely at the maps for the GT3071R with the .64 AR turbine and the .50 AR compressor housing it sort of seems to me that it could both spool quicker and make more top end than the GT2871R with the .86 AR turbine and the .60 AR compressor. Its just a matter of which one maches flow charicteristics between the two sides of the turbo better I would think.

Originally Posted by Savington (Post 652524)

Having owned and tracked both setups extensively, I disagree. The 2554 is an easier car to drive because the power comes on far more quickly when you move your right foot. I could practice fairly standard throttle application with the 2554 (pick it up at apex and roll into it slowly) and the car was fast (for 200whp). With the 2871, I have to consciously pre-apply throttle ASAP - even if it's just 10 or 15% worth, I feel like I need to get the turbine spinning a little to improve the response once I do actually want to apply throttle at the apex. If I wait until the apex to pick up the throttle, I never feel like I've got the throttle response I want on exit - it's always that split second behind me, whereas picking up early just to get everything started allows me the control I want on exit.

It also makes sweepers and transitions much more difficult, since I can't make minute throttle adjustments and have them quickly correlate to attitude changes - it takes a split second for the 2871 to wind up, but because it takes those few hundred milliseconds, I can't roll in and out to adjust the car's attitude as finely as I was able to with the 2554.

Once boost actually comes on it's a very smooth application, but it is delayed ever so slightly with the 28 frame turbo. This is the primary reason why I've wanted to stay with a 28-frame - the delayed spool RPM doesn't bug me, but transitional response does. I don't think I would want to have anything worse than what I have now. That's also why the new GTX turbos are so interesting - a lighter billet compressor wheel means less inertia to overcome when I am trying to alter turbine RPM rapidly, and improved aero on the wheels may mean that the turbos flow better at lower RPMs, giving the tip-in response I want. I'd pay a lot of money for a 500whp-capable turbo with the same transitional response as my 400whp-capable 2871R.

Originally Posted by jacob300zx (Post 652551)

I disagree, it seems with the smaller turbo's a 10% push on the go pedal gives 70% power. I feel its just too touchy. Which is what your describing. I prefer the more linear response from the larger frame turbo.

Originally Posted by Savington (Post 652524)

That's also why the new GTX turbos are so interesting - a lighter billet compressor wheel means less inertia to overcome when I am trying to alter turbine RPM rapidly, and improved aero on the wheels may mean that the turbos flow better at lower RPMs, giving the tip-in response I want. I'd pay a lot of money for a 500whp-capable turbo with the same transitional response as my 400whp-capable 2871R.

Originally Posted by hustler (Post 652396)

BTW, its also funny to think back to all those people who told me 4-years ago that my GT2860RS was "too big" and I wouldn't like it. The times have changed around here.

Originally Posted by Savington (Post 652554)

That's a problem with your boost control, not with the turbo. Proper TPS-referenced EBC control will totally eliminate partial-throttle full boost conditions.

What I was specifically referring to was the TIME it takes for the change in throttle to result in a change in power - it takes longer with a larger turbo due to less restrictive hotside, larger/heavier wheels, etc.

Originally Posted by Braineack (Post 652685)

yay

http://www.boostedmiata.com/gallery2...argets_ms3.jpg

Originally Posted by faeflora (Post 652584)

Actual driving may prove you might be correct about transitional response and lower RPM but the GTX map I've seen does not support those suppositions.

Originally Posted by Savington (Post 652534)

The question is this: If the 2871 has the same compressor, and a less restrictive (slower spooling) turbine, will it ultimately make more power?

Originally Posted by hustler (Post 652776)

1) what kind of a huge ****** quotes himself?
2) why does the GT2860rs exist if the 2871 surpasses it in all considerations

Originally Posted by Savington (Post 652787)

2) Because it existed first? I don't know, it's pretty clear that the 2871 performs the same as the 2860 except for where it will flow 80whp more up top for basically no spool loss.

Originally Posted by Savington (Post 652534)

Here's the 2871R turbine map, pay attention to the red .86 line. Peaks at around 21lb/min. http://www.turbobygarrett.com/turbob...47-1turb_e.jpg

Here's the 3071R turbine map, pay attention to the red .64 line. peaks at around 19lb/min. http://www.turbobygarrett.com/turbob...3&20turb_e.jpg

So it would appear that the 2871R .86 will spool a little slower than the 3071R .64. The question is this: If the 2871 has the same compressor, and a less restrictive (slower spooling) turbine, will it ultimately make more power?

Originally Posted by hustler (Post 652776)

2) why does the GT2860rs exist if the 2871 surpasses it in all considerations

Originally Posted by Savington (Post 652787)

2) Because it existed first?

Originally Posted by jasonb (Post 652788)

you could spend a lifetime searching other forums without ever finding an analysis like your posts on this thread. mad props sir.

Originally Posted by jasonb (Post 652788)

i wonder if we have ourselves a little 2 horse race going on. BW has some new stuff with a similar sounding cold side to GTX and an interesting sounding turbine wheel too.

Originally Posted by sixshooter (Post 652829)

I've been hearing that the leader in technology is definitely not Garrett anymore. Others, including BW are really making a name for themselves on some of the other forums. It sucks that they are so secretive with their compressor maps. I'd love to be able to compare them overlaid.

Originally Posted by faeflora (Post 652861)

Yah what is up with turbo manufacturers not posting their compressor maps? I just called precision and the guy who answered was very knowledgeable and helpful but he said that they don't do compressor maps, they "test their products on real cars". :|

Originally Posted by Savington (Post 652763)

Also, since the 2871 has smaller wheels and uses the A/R to make up the flow, will the lower inertia of the wheel provide better transitional response than a 30R turbine wheel while still out-flowing it?