Marcel Burkett

Man , this **** can be very confusing ! so many ideas and opinions ! Wish I had more examples of twin configurations to consider . I know the 3076's have been proven by HKS , but could they have done better ? would they do it differently today ? I could be wrong but , I don't think that there was another similarly sized (rated)turbo available at that time, so maybe they were some what limited in their choices ? am I wrong ?

Zero R

iTrader: (1)

No need to be pissy, when a lot of people refer to 35R's as 35-40's I just wanted it clear for people on here. I personally wouldn't mention the numbers 35 and 25psi on a rotary. I have seen them run that high and higher on piston motors and make good power. I agree with you about sizing in most apps. I also know there are good ways to make a large turbo act a lot more like a small one.

On running your setup I would look no larger then 3071's, I think you may find them a bit laggy but you can get around that some with good plumbing, properly done IC, and the wastegate setup. THey'll get you up to 40psi as well pretty comfortably and see 15lbs around 4500rpm+/-. The 2860 or 2871 would be better street choices. Though they will run about 5% less eff. They wouldn't give you much more than the 25psi you're after but would see boost much sooner. Roughly 4k or so. It's basically up to you where you want to size it. If it's a drag car then go with the larger setup and get bored quickly and turn the boost up. If it's a street car the 28's will look cool and may respond a touch better but I think a better setup single will out perform it in the end. ie Ernie or Ralph are both good examples of that. Practically the same spool as the twins and both in the upper 600whp range. You wont get that hp with two 28's.



-S-

GoRacer

iTrader: (2)

Well if you want crazy, here's my idea I thought of when I first saw the Border racing twins and the M2 twins...

Is there any reason why you can't run each turbo seperatley? Take the M2 twins, their weakness is using the OEM manifold. If you used those same small turbos but one for each rotor on seperate manifolds with seperate wastegates then wouldn't you get rid of the bottleneck? Yes, people have run dual singles before but allways Y'd to single exhaust. Aha, so you would run dual exhaust all the way (secret sauce). Wouldn't seperate 2" or more exhaust be similar to 4" on a 500R? I'm not shure what size turbos would be needed to acheive 800+hp but you get my point. Each rotor can be tuned seperately, correct? More efficient with less boost allowing for smaller turbos and the crazy dual manifolds. I should have built it last year.

Marcel Burkett

On the contrary , the 3071's were anything but laggy ! I already logged 20+ psi around 3500rpm's ! , I was never really able to go past 6500RPM on the street (for various other reasons) and my boost has hit 25 psi already !
the only reason I'm making a change is because I (and Howard) suspect that the a/r's on the turbines are a bit too small , its easier and cheaper to just change the whole turbo instead of buying the housings ! so while I'm at it I want to "upgrade" a bit .

Zero R

iTrader: (1)

I wasn't aware you were running 3071's already.... nice. You have to be running a pretty decent size port. Also my guess is if your running into that issue you're sized too small on the turbine housing itself. The turbo's should be good enough to get you about 40psi no need to upgrade. I think if you step up to the 76mm wheel you will be surprised at the difference in response for next to minimal gain if any. If you're get turbo's for less than housings let me in on your secret.

-S-

Marcel Burkett

They aren't less , but they cost $367 each ! if I buy two i'll have an extra two ($734) just sitting there , I am sure I wouldnt be able to sell them separately at anywhere near what they're worth, this is why I am looking at jsut selling everything (turbos) and taking the opportunity to make my setup better than it is .

fdracer

f' it and go with the 35's then. i think the only concern posters have here is that you would best be served having a purpose built car. if it sees significant street time and you need a measure of response and reliability then go smaller. if it's an all out strip car then go as big as you think you can spool. outside of that i think we all admire your willingness to experiment. as long as you're willing to put up with the steep learning curve of big twins, it should be great project.

mr2foryou

Steve definately has a GT47 on his maroon car now. Here is a pic.
http://www.rx7.com/04rotaryrevolution/22.html

Dee E.

Zero R

iTrader: (1)

I see your point to a degree, but I'm familiar with 3071's and 3076's both I've used quite a bit. You will see minimal gain if any with the 76's over 71's with a big difference in response, that's all I'm saying. If you step up to 35R's I think you'll have a much more purpose built car.

-S-

FCNAred

iTrader: (2)

it wasn't the lag, it was the surge. I have just one of his old turbos on my car now (similar to a 35R compressor, but with a big exhaust wheel) and i am confident that it makes every bit of 400hp on pump gas at 15psi.

Marcel Burkett

If one of his were similar to a 35 then its safe to say that I can experienxe some surging too ? or was this problem specific to that particular turbo ?

My car is daily driven , but I want it to be one of the BADDEST , MOST FEARED and admired street machines down here ! I also want to do some occasional drag racing with it , hence the idea to go twin .., same flow with less lag .

Could the differences in power gain and response be linked to the rest of the system and the characteristics of the motor ? . My FMIC is huge , I use a high flow Projay semi pp intake with their Holley style 1500+CFM TB , my porting is quite large too, the sides have been opened up to "Cosmo" size , and the internal ports are as big as they can be , the exhausts ports are also quite large , and I plan to have them opened up some more when I go in ........, I'm guessing that this will all count for something .
My buddy makes 305FWHP at 15psi on his B16 Civic , after blowing his turbo (with too much oil pressure) , he changed the CHRA , what he got wasn't exactly what he had , it was a bit smaller on the compressor side. He could not get past 280 with it ! he had to put on the larger wheel (previous one) to get the same power at the same boost , the extra 20-30 lbs/hr (in my case it would be 50 per turbo) makes a alot of difference. There was also no noticable difference in his turbos response.

Marcel Burkett

Think I've settled on a oair of these , GT3040's . I will let you know how it turns out , thanks for your thoughts and comments.

Dual Ball Bearing "GT30/GT40R" Turbo assembly. T3 style inlet flange with 4 bolt T31 style exit. This turbo incorporates the same exact GT40 compressor wheel found in the popular GT35/40R, but runs the smaller 60mm w/84 trim turbine wheel from the GT30R. Appropriate for smaller engine where the GT35/40R feels too big, but the high amount of compressor flow is needed for the desired HP and boost levels. Large T04S style compressor housing with 4.00 inlet and 2.50" outlet. This turbo has a flow capacity of about 600HP.

Turbine
-Wheel: 60mm w/ 84 trim
-Housing: .63 ar, .82 ar, 1.06 ar


Compressor
-Wheel: 82mm w/ 56 trim
-Housing: .70 ar