Faeflora

iTrader: (2)

Above boost threshold in my 3071- about 4000rpm, throttle response is near instantaneous.

JasonC SBB

Do you know for a fact that the 2871 has the same or better transitional response than the 2860RS?

Savington

iTrader: (31)

Having driven both, I can pretty much say that, yeah. If you drove both turbos back to back at 12psi I honestly doubt you would be able to tell a difference.

Check out the compressor maps for both of those turbos - the 2871 outflows the 2860 by a solid 5lb/hr even at 50,000-80,000rpm. It's a larger wheel but it still feels good because it flows so well at low shaft speeds.

This thread makes me want a turbo speed sensor really badly.

jasonb

ahmen brotha

i was looking at repurposing this and putting a splotch of ink with a silver sharpie on the compressor wheel.



then i was looking at the LM2907 and wondering if the curcuit could be simplified. i dunno the switching speed of a LM2907. seems like it should work, we're only talking 2khz. otoh, you maybe could use an I/O channel on MS3 and just use a frequency divider down to some reasonable interrupt rate and leave off the voltage conversion piece entirely.

http://www.national.com/mpf/LM/LM2907.html

I'd be interested in making one of these, but i'm not sure how hard it would be to drive a laser diode/photodiode. they are a bit finicky...

Savington

iTrader: (31)

You may have a point. Everything I've read has said that once you are above boost threshold, shaft inertia is king, but there's not a lot out there on that topic. It will DEFINITELY spin down faster. The 30R turbine wheel has about 10% more rotational inertial than the 28R wheel.

jasonb

a datalog of shaft speed vs throttle position vs rpm vs intake pressure would be interesting. if you only look at the 71mm stuff you would only need to instrument one compressor housing and then pass it around to folks with t2/t3/tial <dot product> t28/t30

pm me if you would be willing help me with the photo side of the circuit above. i'll try to build something (should be < $20).

JKav

iTrader: (1)

Track-only 275 rwhp Miata = GT2871R. A 2860RS will work well too, though it'll make a bit more heat and backpressure. In the T25 housing, I like the 28 turbine better than the cutdown 30.

2871R and 2860RS coexist peacefully. 60 has better transient response and lower boost threshold and while it doesn't support as much power as 71, it won't surge in the apps that a 71 will.

Billet comp wheels offer no inherent performance advantage over cast for aftermarket use. They're simply a way to make wheels in low volume without needing to create a casting tool. They're blingy, but that's about it.

GTX has higher flow and PR potential but they shift the map to the right so there's the potential for surge operation.

B-W EFR looking promising. Feature rich. Very well thought out approach. Curious about turb aero performance on them.

Savington

iTrader: (31)

Jay, can you comment on whether turbine A/R, wheel size, or mass moment of inertia has the greatest effect on transitional response? (Transitional response defined as the time it takes for a change in throttle application to correlate to a similar change in boost pressure.)

Braineack

iTrader: (62)

I noticed something similar to this comparing my T3 Super 60 (pretty much same wheel as the 2860) with a 2871 at a dyno.

I would spool much faster than him, however, at lower boost levels he was actually making the same torque as me during spool up.

Savington

iTrader: (31)

Real Americans™ use 2871Rs.

JKav

iTrader: (1)

In the case of 2860 and 2871, the larger comp wheel has a touch more inertia but, overall, inertia is dominated by the turbine side.

The factor at play here is the turb/comp wheel speed match. The 2871's larger comp whl is forcing the turb whl to rotate slower than it really "wants" to, which adversely affects its efficiency (it wants its blade tip speed to be closer to the exhaust gas velocity that is impinging on the turb inducer).

Efficiency -- whether you get it on the turb or comp side -- is one of the most key ingredients to transient response, boost threshold and backpressure.

bbundy

Same here. I’ve had co drivers autocrossing my car this year and the comments are that throttle response is a non issue, what lag? If it is not an issue for autocross then it is definatly not an issue on the track. The car makes somewhat silly power around 300hp with 17 lbs of boost. Peak torque around 4500 rpm which dosn’t seem much different than the 2871 plots. I’m guessing some because I haven’t dyno tuned it since going from a built 2.0L to a stock internal 9.0:1 1.8l protégé bottom end with a stock 99 head. The 2.0L was closer to 370hp and made 320 ft lbs by 4500 rpm. At ~ $9,000 less for the stock motor it sure doesn’t feel like it gives up that much performance with the same turbo setup.

I also have a long runner equal length manifold which everyone says is not suppose to spool as well as a short manifold with a good collector.

Bob

bbundy

So a 3071 with a larger turbine wheel might be better matched to the 71 compressor?

What about the housing size AR effects? it looks like you can get the Turbine map to look the same or similar for different size wheels by changing the AR of the housing. I assume there is a matching effect going on there as well where some combos work better than others at optomizing some charicteristic of the behavior.

Bob

JKav

iTrader: (1)

The 30 turbine is 56.5mm (if I recall) and the 28 is 54.9mm. Pretty small potatoes, esp compared to going from 60mm to 71mm in the 2860/2871 situation.

A/R does soften transient response, if you're well above boost threshold you can feel it a bit during a gearchange but that's about it. The bigger effect of a/r is what it does to threshold and backpressure.

It is really hard to look at any one of these factors in isolation. There are many interactions. Even a detailed spreadsheet match involves a lot of assumptions and hand waving esp when it comes to transient effects. You really have to model the system to analyze those effects, and who has the money/resources to do that aside from OEMs.

aznDragonX

iTrader: (5)

The new GTX3071R turbo looks great from SEMA show!

aznDragonX

iTrader: (5)

I wonder the same thing..which turbo is best fit for 1.9L built motor for over 300HP.

jacob300zx

I once read this article 10 years ago about a guy building a turbo fox body to run some flying mile competition in Nevada? Anyways he was pushing say 600whp on say 8psi. He explained that he prefered to build the motor as efficient as possible to be able to run the lowest boost to achieve his power goal. He made an example of a stock motor would gain 20whp per psi and he had a delta of 400whp to gain so boost would be 20psi. He then compared that to the built motor making 400whp and boost gain per psi was say 25whp. The delta was now 200whp or 8psi. He spoke about the cost to build the motor was more than just running 20psi on a stock motor but that his low psi combo created less heat and had far superior reliablility. Does anyone have any graphs with built vs stock motors running the same psi? It would probably need higher comp, cams, head work, and intake to be a good comparision.

SKMetalworks

iTrader: (7)

I believe this needs some sticky hustler/jessica alba nutting action.

jacob300zx

lol, at the Xida thread. I also had a delicious sandwhich today made by a chick that looked just like Alba.

aznDragonX

iTrader: (5)

I'll scan GTX charts that I got from SEMA when I get home.