Hello all,
I have a 2.2. Liter SR20 block I am in the process of building for a goal of 330 - 340 whp. I will be using an HKS exhaust manifold and Greddy intake, and cams that I have not decided on yet. The hold-up is the turbo. As I figure it, the motor will be putting out around 45lbs of air at 7500 rpm with a PR of 2.2. When I look at the map for the Disco Potato, this is well outside it's capability, yet I have read on this forum of people boosting 17psi on this turbo with no problem and enjoying rapid spool. I figure with 2.2 liters, the turbo should be responsive as all hell, but it looks to me that it will putter out of breath well before 7500 rpm.
The map of the GT2871R, with 56 trim, .60 A/R compressor, driven by a 76 trim, .86 A/R turbine looks to be just big enough to handle that much air. However, I have read that this turbo is mismatched with regard to the two wheel sizes, and not very good? It has been recommended that I use the GT30R, but not which size. The catalogue I have has several different sizes of GT30 turbos, and most use the same T2 turbine housing and internal wastegate as the GT28 series, so what's the benefit? I have also read that the DP turbo is good for up to 350 hp, but have not seen anyone produce this number at the wheels. If this is true, then I would just as soon use this turbo as it will meet my goals, but the map doesn't seem to support this.
Am I off on my figures? This motor will be in a RWD car for track days, and I would prefer the smallest, and therefore most responsive, turbo possible to reach 330-340 rwhp. Any corrections or advice will be greatly appreciated, thank you,
Will

With a 2.2l I'd say the GT30R as well... it should spool up about like the GT2871R. I don't know of ANYONE on here with a 2.2l block that could confirm that, but with 10% more volume that is my guestimation.

Greg Vogel pulled 333whp with a potato, stock 2.0l block of course, but with cams, I believe that was at 14psi as well, so 17psi 350 should be possible.

Wheres bigtoe when you need him.

With a 2.2l I'd say the GT30R as well... it should spool up about like the GT2871R. I don't know of ANYONE on here with a 2.2l block that could confirm that, but with 10% more volume that is my guestimation.

Greg Vogel pulled 333whp with a potato, stock 2.0l block of course, but with cams, I believe that was at 14psi as well, so 17psi 350 should be possible.
Thank you for the feedback. 333whp is pretty impressive with that turbo. It seems to me though that at 17 psi, it is WAY outside it's efficiency range by 7500 rpm, maybe down to 55-60%. That's just not going to fly for me. I am hoping with the extra discplacement I could get by with a slightly larger turbo and still have good response, but efficiency numbers that bad are going to cause a lot of extra heat on the track, and this will see some extended sessions running from 5000-7500 rpm, if not possibly higher. I am almost decided on the GT2871, but for the large amount of people recommending the GT30R, and just not sure why. I figure the smallest turbo to meet my needs the better. Also, I understand HKS has some turbos utilizing the newer wheels from Garrett's GT line, but where can their maps be found? I think they have always made some great hybrids. Any more feedback, suggestions, explanations as to why I am wrong- please, please let me know.
Will

The GT30R is a more efficient snail, no borderline mis-matched wheels like the 2871. The 2871 is essentially like what I have.. I'm running a T25 with T28 compressor wheel.. It works great, nearly as quick spool as a T25, but pulls hard all the way to redline with no drop-off. It's the same general thing in the 2871, they took the GT28R and changed wheels to allow for a bit higher boost up top.

Anyone correct me on that if I'm off but that is the way I understand it.

It seems to me that there is some conflict between wanting the best turbo for your intended track usage and the smallest turbo that will support 340whp on a 2.2L motor. If efficiency between 5000-7500 along with responsiveness is ideal without excessive heat, then that may put you into a turbo capable of 400-450whp that is used in the fat part of it's efficiency island such as a GT30R or the like. I suspect you will reach your power goals at perhaps 10-12psi with low back pressure. With a larger turbo you will also enjoy the ability to modulate your boost easier with the gas pedal rather than boost acting like an on-off switch which I imagine would be the case with a small turbo running at it's choke line. You may also find that on some high-speed tracks that you want a little more power, and the bigger turbo will give you that option without exhaust temps and pressures getting extreme. Just my $.02.

Look at the GT30R compressor map on ATP TURBO's website. It seems it may be about right for your app. For comparison look at the GT3071R map as the GT2871R uses the same compressor side as that. Remember that your goal is to push about 35lbs of air (@350whp), but to do it efficiently.

Ad Fabrication on this site has had some great prices on turbos lately, so you might check with them when you decide what you want to do.

b13bliss,
thanks. I think you're right, I have driven a SR20 with the Disco Potato and loved the modulation on that thing, it was incredibly responsive, but at a high pressure ratio, I could easily see it being an on/off switch like you said. The GT2871R might be the same way running so close to it's choke point. I have also been in a DSM with a 16G and thought, "this is crap on a road course" I had to give it throttle way in advance to ensure power was there on corner exit, otherwise it would be flat comming out and leave me waiting for the power to come on after the turn. This has me hesitant to go with "too big" a turbo, but I didn't think about the fact that at the rpm range I'll be in, a slightly larger turbo will definately be more efficient and probably easier to modulate. I'll check on the GT3071R, maybe the 76 trim version. I'll also look at ATP's site. Thanks again. Any other suggestions, comments?
Will
EDIT: Looked at the map of the GT3071 with the 76trim turbine, and found several dyno charts on ATP's site, this turbo is making a healthy 350-370hp on EVO VIII's. With an extra .2 Liters blowing on it, I'm sure this thing will be pretty responsive, but more power than I care to make. I question the reliability of the SR20 at this level for hours on end.