Turbos

[Porsche 935]

Maybe Tippy or one of the guys can help me. I run two turbos that I custom made myself. They have billet compressor wheels and are 51.3 mm inducer and 68mm exducer. They spool well relative to throttle input. But I think there is more left on the top end. I do have a set of 54mm inducer and 71mm exducer wheels I have not tried yet. Maybe looking at changing out the turbos with something in a 57 - 60 mm inducer because there is not enough compressor housing to go any larger than the 54"s but do not want to loose the bottom end throttle response. Any suggestions?

[kenikh]

How big is the the hotside housing?
Single or Divided?
Exhaust system?
Who is the OEM of the cold side?
What kind of CHRA are you running?

Everything is a trade off, so knowing all of the variables is important.

What are you actually trying to achieve? A power number? Character of power delivery (e.g. Strong push to redline)?

Speedy Squirrel could add a lot of value here.

[Porsche 935]

This is a twin turbo system, 935 headers. Turbos are highly upgraded IHI's off F40 Ferrari.

[kenikh]

Originally Posted by Porsche 935

This is a twin turbo system, 935 headers. Turbos are highly upgraded IHI's off F40 Ferrari.

Wow - totally off the rez. I love it. You're not getting any lag from the 935 system - the only negative is you aren't getting pulse energy multipliers as the primaries are unequal length. Anyhoo...

IHI - lots of parts bin goodies from Subaru for those. I think your intuition is right: Bump the exducer and inducer by what you have and try them out. You'll definitely get more on top, as well as the trade off in lag. You'll know pretty quickly if you've achieved what you are looking for, as well as which direction to go, should you not.

[Tippy]

GJF is your man on twins.

[Porsche 935]

GJF, are you out there. Would appreciate your opinion.

[kenikh]

Originally Posted by Porsche 935

GJF, are you out there. Would appreciate your opinion.

Did you try a PM?

[Tippy]

What hp are you aiming for? Modern twin 60's will get you well over 1000hp.

What's the specs of the motor? What AR on the turbines? What are the brand of sourced components?

What's your max RPM? What's your max boost?

Eddie Bello made 1400hp+ with twin 61's (GT35R's)

[GJF]

Sorry I Didn't see this post... F40's have some really small turbos. they spool nicely but leave a lot off the table on the upper end. Are you wanting to keep the same spool with extending your upper end or can you sacrifice spool time slightly for more on top? Try looking at a pair of GT3076R's. With the right tuning they should light well and pull like a freight train.

[TurboKraft]

You haven't said what your displacement is, or compression ratio, or camshafts, or headwork, or what manifold... Or what your power target is.
I've used everything from twin K16/K24/K26s, to Garrett GT25/28/30/35R and T3 and T3/4 hybrids, plus IHI, Switzer, etc. As little as as 410hp, up to over 900hp.
Happy to help with a recommendation, but a little more data is needed.

[GJF]

If I'm not mistaken:
3.6 crank
98mm bore
Extreme heads
And I can't remember cams.

[Porsche 935]

No it's still a 3.3. I did the port work when I was a Porsche mechanic years ago. Cams are T3. I machined heads years ago, so compression is probably 7.5 . Built engine years ago when Ed Pink was helping Powerhaus with their engine. High butterfly manifolds. The current compressor wheels are similar to 18g's. Similar engine made 704 hp at flywheel at 1.35 bar in 1992. I run 24 lbs. boost. I know Eddie, just don't want that kind of spool, too violent when they come on. Turbos spool well to 6800 but start to fall off a little after that. I shift car at 7400.

[quattrorunner]

Holy!

[TurboKraft]

Originally Posted by Porsche 935

No it's still a 3.3. I did the port work when I was a Porsche mechanic years ago. Cams are T3. I machined heads years ago, so compression is probably 7.5 . Built engine years ago when Ed Pink was helping Powerhaus with their engine. High butterfly manifolds. The current compressor wheels are similar to 18g's. Similar engine made 704 hp at flywheel at 1.35 bar in 1992. I run 24 lbs. boost. I know Eddie, just don't want that kind of spool, too violent when they come on. Turbos spool well to 6800 but start to fall off a little after that. I shift car at 7400.

I remember the old T3 engines built by Ed Pink, one crazy large K36 turbocharger and realtively small cams on a 3.5L with ITBs.
We've been in contact with a few of the owners of these engines, helped them refresh and upgrade them.
Modern cams and modern single turbocharger, and that same engine gains over 100hp and over 150ft.lb. torque with a much more useful power band.

If you're after 700hp at 1.5bar or so, consider a pair of GTX2867R turbos. Very progressive, very linear.
A little more top end, less punchy in the midrange: GTX3071R turbos.

[Porsche 935]

Yes, they were doing a single turbo engine at the same time mine was already twins. I did use the itb's but I never saw another working pair. I had to send my cable specs to Powerhaus so they could make the one's they were building for a customer in Japan work. The only advantage I see to the gtx2867 turbo is ball bearing. Already flow more than that. And my other wheels will flow as much as the 3071's. Remember, my turbos are custom machined housings and I have 3 sets of exhaust housings ranging from .48, .60 and .78 A/R. I think GJF might be closer when he suggested something in the 57mm range. Enjoy the work you guys are doing!

[GJF]

The turbos Chris listed will do exactly what he said. I took it that you wanted more mid range and top end. Your car will Respond well with the 3076's. But...If only you could add another point of compression. That thing would be godly!!!

[Tippy]

With modern wheels and low boost you're running, I'd imagine those turbos wouldn't hit that hard (Garrett's mentioned) since they really perform at high boost pressures.

Borg-Warner make a line of 200 series turbos that make great power too. Kind of keep that KKK/BW relationship going....

[Porsche 935]

Thanks guys! I have owned this car for 31 years now. I try to make an improvement to it or lighten it each year. 2 years ago I ran out of injector when I did the latest turbo upgrade. Was running 72 lbs and running too high in the duty cycles. Now run 1,000's. According to duty cycle and seat of pants, I'm pretty sure it's putting out 700 flywheel now. Was looking to get 750- 800 with a turbo change. Wasn't sure if my 54mm billet wheels would get me there. Would love to put new P & C's in but maybe another year. Car has always been fun and I can see my improvements by my acceleration times on my V- box I bought last year. After tuning the new injectors, I saw big improvements. Goal is to accelerate as fast as a 918 (Shoot for the moon). But I do have a weight advantage. I'm only at 2310 with half tank of fuel.

[TurboKraft]

Agreed, I'd want more compression or displacement before going with twin GT3076Rs, otherwise she'll feel like a Supra -- late hit and then a near-vertical power curve. Don't get me wrong, they'll do 800+whp and barely be working, but probably not much fun to drive.

In general, run the smallest turbos possible that will meet your goals. You can't fight physics -- the less the rotating mass, the better.

I don't know the efficiency of the turbos you're running, but we've done 800whp with those little GT2871R turbos at the same boost you're running on an ITB engine. Wonderful midrange torque, very responsive.

[Tippy]

Chris, did the GT28's hit like a sledgehammer, or pull somewhat linear/broad on that particular build?