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Old 11-04-2010, 02:10 AM   #21
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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.
Look closer at the map for the 2871 56trim and the 3071 56trim - it's the same. The maps look different, but when you start comparing RPM lines vs. flow rate and pressure ratio they are virtually identical.

2871 56trim: http://www.turbobygarrett.com/turbob...-1&2comp_e.jpg

3071 56trim: http://www.turbobygarrett.com/turbob...3&20comp_e.jpg

What is interesting is the turbine maps. From what little info I've been able to find, I know two things:

1) turbine maps can fairly accurately predict how much boost will be produced at a certain RPM
2) the maps that Garrett publishes aren't enough to actually do the calculations.

Hopefully they are good enough to compare in-kind, though, so let's do that (and if they aren't I'm sure jkav or JasonC will be along shortly to embarass me).

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?
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Old 11-04-2010, 03:38 AM   #22
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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.
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.
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Old 11-04-2010, 04:15 AM   #23
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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.
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.
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Old 11-04-2010, 09:47 AM   #24
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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.
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. See this one for reference:



And the GTX compressor map by itself.



And the GT compressor map:



This is may just one of the turbos though but it looks like the GTX flows more at the top end, not the bottom.
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Old 11-04-2010, 12:56 PM   #25
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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.
tell me about it. when my buddy first put this begi/fm prototype kit on my car (formerly his car) the consensus among all miatadom (circa 2000) was that you were "pushing it" if you made over 170whp on a stock block 1.8L! lol... as a matter of fact he built this motor in my car so he could make 200whp "safely". crazy huh.
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Old 11-04-2010, 01:24 PM   #26
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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.
+1. I've been preaching TPS-controlled boost targeting since like 2002.

An improvement for those with a standalone EBC is to place its sense point in the ic pipe before the TB and not on the intake mani. It will help some for those with wee turbos, because it doesn't try to make the mani hit full boost when the throttle is partially closed.
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Old 11-04-2010, 01:27 PM   #27
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yay

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Old 11-04-2010, 01:28 PM   #28
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yay

MS3 FTW again.
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Old 11-04-2010, 03:31 PM   #29
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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.
I was referring to turbine RPM, not motor RPM, and the charts you posted actually support my theory.
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Old 11-04-2010, 03:38 PM   #30
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The question is this: If the 2871 has the same compressor, and a less restrictive (slower spooling) turbine, will it ultimately make more power?
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?

Also, since I've hijacked the **** out of this thread to blab more about turbine flow and wheel inertia and transitional response, the answer to the original question (IMO) is that the 71mm compressor gives up nothing to the 60mm compressor, and therefore you should use the 2871R over the 2860RS. The 3071 and the 2871 have the same compressor. The new GTX wheels change the game a bit but as of today, IMO, the best compressor for a 275whp+ track miata is the 71mm.
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Old 11-04-2010, 03:53 PM   #31
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1) what kind of a huge ****** quotes himself?
2) why does the GT2860rs exist if the 2871 surpasses it in all considerations
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Old 11-04-2010, 04:10 PM   #32
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1) what kind of a huge ****** quotes himself?
2) why does the GT2860rs exist if the 2871 surpasses it in all considerations
1) oops I preemptively forgot to buy your flameguard.

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.
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Old 11-04-2010, 04:26 PM   #33
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sav, i dunno if i would call that a jack. you could spend a lifetime searching other forums without ever finding an analysis like your posts on this thread. mad props sir.

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.

http://www.full-race.com/articles/bo...fr-turbos.html
http://www.motoiq.com/magazine_artic...ature-set.aspx

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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.
everybody is telling me to ditch my 2860 for just this reason. compressor runs out of lb/hr just when things were getting interesting.
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Old 11-04-2010, 05:56 PM   #34
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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?
I'm still thinking about this and wouldn't a more interesting comparison be: can the 2871 0.86 beat the 3071R 0.63? (actually, tie goes to 2871 because angular momentum advantage).

http://www.atpturbo.com/root/maps/gt3071rturbine.htm

I'm surprised nobody has spoken up for the 2871R 0.64 housing. I've heard really good things about this combo if you can overcome the problems caused by the lousy internal wastegate (boost control).

EDIT: i'm stupid. 0.64 housing covered in the other thread.
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Old 11-04-2010, 05:56 PM   #35
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2) why does the GT2860rs exist if the 2871 surpasses it in all considerations
Somebody has to wash the dishes when the master has finished eating.
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2) Because it existed first?
I think this is the real reason. When they came out with the GT2860RS it was just an experimental hybrid that happened to perform better than initially expected. It led to more experimentation.

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you could spend a lifetime searching other forums without ever finding an analysis like your posts on this thread. mad props sir.
This.
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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.
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.
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Old 11-04-2010, 06:34 PM   #36
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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.
I really like where Borg Warner is going. It's nice to see some new (and some recycled) tech with turbos that basically haven't been updated since the 60's. I'm curious to see results once they start getting adopted.

I think they haven't released maps yet because they were just announced officially at SEMA two or three days ago. You sure are impatient.

Edit: Leave it up to the Evo guys to track down all the BW EFR maps...

http://www.turbodriven.com/en/perfor...Reference.aspx

Last edited by Trackwhore; 11-04-2010 at 07:05 PM.
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Old 11-04-2010, 06:42 PM   #37
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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". :|

I called up ATP to get more info on the GT-X series.

The new GT-X3071 flows 60lbs
The new GT-X35 flows 80lbs.

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!

Full Vband turbine inlet and outlet is scheduled to be available early next year as well. GT-X2 frame series is in the works. GT-X2 might be the real shiznit. Could run an efficient street friendly 250hp with lottttts of headroom.
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Old 11-04-2010, 06:59 PM   #38
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I am excited to see these GTX turbos come out and get more smaller sizes.

the billet wheels are amazing.

ps there are tons of companies out there doing them... garrett just has their rep.
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Old 11-04-2010, 07:04 PM   #39
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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". :|
lol, rather than test their products on real cars, they most likely wait for TiAL to post it on their behalf. That piece of **** company somehow manages to stay in business.
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Old 11-04-2010, 08:32 PM   #40
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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?
I’m not so sure about that. On the exhaust side the 3071 has a bigger paddle wheel in housing with more throttling of the exhaust flow impacting the paddle wheel blades. More dynamic pressure acting on a larger surface area at a larger radius. Seems like it would be more responsive to sudden changes in exhaust gas flow rates with higher velocity gas impacting blades with a larger surface amd a larger radius making more torque to the spinning objects as it accelerates from the mid range in rpm. Inertia effects may not be primary to the difference in response.

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