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Old 12-28-2009, 12:41 PM   #21
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Could that amount of power be safely obtained with a bit higher compression with the benefit of better spool?
no

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It certainly looks good on paper, and the benefits on the straight bits should be excellent. The ring is very technical but it has plenty of straights
Once you get more seat time you'll understand that if he's under 4000rpm anywhere on any track, he wasn't in contention of a trophy anyway. Are there corners on the ring slower than lets say 30mph? If not, then there's no excuse for dropping below 4krpm aside from the reality that he'd need a new driver if this was ever discussed.
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Old 12-28-2009, 03:03 PM   #22
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.86 A/R, that's a given though. Minimal response loss for a huge upgrade in top-end flow. If you are actually going to stay at 300whp, do the 2860RS. If you want to push past that at some point, do the 2871.
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Old 12-28-2009, 03:27 PM   #23
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Are there corners on the ring slower than lets say 30mph?
There is no slow corners, just less fast.

+1 on the spool before 4k doesn't matter a whole lot on the ring, but one thing that has been talked about in the rotrex thead is throttle related boost control. This really makes a difference. Mostly in making the car a bit less exhausting to drive. Depends on the driver, but I'd like that on the ring. One lap there = 10 laps on most other tracks...


...man I want to go back there this summer.
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Old 12-28-2009, 03:38 PM   #24
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There is no slow corners, just less fast.

+1 on the spool before 4k doesn't matter a whole lot on the ring, but one thing that has been talked about in the rotrex thead is throttle related boost control. This really makes a difference. Mostly in making the car a bit less exhausting to drive. Depends on the driver, but I'd like that on the ring. One lap there = 10 laps on most other tracks...


...man I want to go back there this summer.
Even if it mattered, we're talking about what, a 10% drop in power for 1000 RPM? Its not the end of the world.
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Old 12-29-2009, 11:24 AM   #25
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It will probably spin-up lower because the HKS manifold is a bottom mount (lol) and will flow less than the BEGi manifold. You should really get with the times and build a tubular manifold or buy one from Tim and be a man. I'm making more boost with MUCH LESS backpressure (3" dp all the way back) 1200rpm sooner.

I don't know of anyone running a gt2871 on a log manifold because of reasons above.
I'm running (or was last summer) a custom log manifold with a 2871 .64 hotside with a 3" bellmouth and 3" exhaust @21psi (going to a holset). I'd have a tubular mani if I had the choice right now as the timing I have to pull in the higher boost cells sucks.

The way this turbo spools theres no way I would go any smaller, if you stay above 3500rpm your at full boost no problem.

I doubt your going to make 300hp with a 2871 unless you want to run 20psi of boost (you mentioned lower boost levels but who knows what that means to you really)
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Old 12-29-2009, 02:50 PM   #26
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Quote:
Originally Posted by hustler View Post
Once you get more seat time you'll understand that if he's under 4000rpm anywhere on any track, he wasn't in contention of a trophy anyway. Are there corners on the ring slower than lets say 30mph? If not, then there's no excuse for dropping below 4krpm aside from the reality that he'd need a new driver if this was ever discussed.
I completely agree with that, I think you misunderstood me. What I meant to say was that the added power would outweigh the decreased resoponse.
But yah, Ive only road raced NA cars in the past, so Im probably a bit out of my element here.
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Old 12-29-2009, 04:52 PM   #27
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I have my spool numbers for my 2871 posted around here somewhere, I think at least in the huge spoolz thread. 0.64 AR, 550cc injectors, tubular manifold, 3" enthuza exhaust (free flowing) internal wastegate with separated gas DP. MBC/EBC hybrid. FWIW the spool is plenty fine for me on the street, and way OK on the track. All I have to do is keep it above 3.5-4K RPM and the power is right there. Not a problem with the 3.63 gears and the 6-speed. Plus it is not like it is gutless at 3K either. So you could probably get away with the larger A/R IMHO.

The 2860 has a smaller compressor wheel (right?) so the on-off-on throttle transient response should be better. I did notice this when switching from the 2560 (much smaller compressor diameter) to the 2871. Even if I am at a high enough RPM to get full spool for either turbo, the 2560 definitely responded faster to the throttle. Much less rotating inertia. That is about the only thing I miss from the 2560, though it is not that big a deal.

Solution #3 - Put a LS1 in it
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Old 12-29-2009, 05:15 PM   #28
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this is the difference between a 2860 compressor wheel and 2871 wheel:

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Old 12-29-2009, 07:47 PM   #29
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I looked it up on Garret's site, 71mm versus 60mm. It may not look like much but IIRC the rotating inertia goes up by roughly the 4th power of the radius all else being equal. So 71mm versus 60mm on the compressor means roughly doubling the rotating inertia. (71^4)/(60^4) = 1.96

The turbine dia is the same on both depending on which flavor of 2860 you get.

For grins you might give ATP Turbo a call and see what they think on turbo selection for your app. Who knows, they may know of another similar turbo car (maybe even a customer of theirs) running the same tracks as you and be willing to share their experience. A good test is worth 1000 expert opinions, and worth about 10,000 of ours .

Oh yeah and +1 on YOU SUCK for getting to race on the ring on a regular basis. I hate you.
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Old 01-03-2010, 02:27 AM   #30
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8.xx ... at the ring... in an mx-5... you lucky SOB... if i got to take just one lap around that place, got 3/4 the way through and end up sliding off the track, flipping end over end in a ball of flames they would find my extra crispy remains with the biggest grin still plastered on my face. i would die happy, and consider my life as a gear-head complete.
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Old 01-03-2010, 12:59 PM   #31
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If you want better throttle response and a big turbo, get a super light clutch. After driving johnfag's car with the light flywheel, aluminum plate, and the large butt plug yesterday, I may get the 949 twin disc if a g-bar falls out of the sky, but its doubtfull.
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Old 01-03-2010, 06:12 PM   #32
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We're running several projects in 2010 and are using Facebook to keep you all up to date:
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Old 01-26-2010, 05:32 AM   #33
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I did the Nurburgring in a 1400 N/A Golf rental haha
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Old 01-26-2010, 06:27 AM   #34
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I did the Nurburgring in a 1400 N/A Golf rental haha
That can be pretty cool still The key is to keep momentum on that track.
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