Currently in my racecar I am using a Turbonetics T76 with an 0.96 AR s-trim exhaust side. It's making 510rwhp with ~400tq from 4500rpm up @ 11psi. This is a 100% road race car, and with some new developments in classification I may need to aim for something like 440-450rwhp and add ballast to qualify.

The T76 is extremely hard to drive as there's really no throttle modulation possible; it's either freight train or nothing, which is not only hard to drive but not particularly fast in the twisty parts either. I'd like something that has (don't laugh) 'instant' spool characteristics and will make ~450-500rwhp @ 17-18psi.

Any idea what turbo I could use to fulfill the criteria?

 

I've heard a GT42R is the go.

I've got a TA45 72mm front wheel with a 1.32 T04 rear and it is very similar in regard to throttle response to your by the sounds, theres no way you can squeeze power on through the corners. Mine made 450 rwhp wheel spinning on the dyno on 9psi with the old engine.

 

Zero R might be a good person to contact. See if you can use any info in this link...

https://www.rx7club.com/spec-tuning-154/how-size-matters-478915/

 

Gt40r will do the job very very nicely. Check the link here for the dyno chart. Pay close attention to the rpm and how early he reaches his torque peak. This was an 11psi run.

https://www.rx7club.com/showpost.php...1&postcount=16


Also check the link from with-in to see the full set-up. If you ask me the Gt40r is the perfect turbo for fast spool and will still flow for 600rwhp. Just keep in mind he is running hi-compression rotors so this increases the spool even faster.

 

a 42r is too big for that.

I'd say a 35 or 37r would be the way to go. Even a 40r is capable of more than that hp level. another option might be a to4Z. If you want to get creative look at some borg warner ETT turbos. I dont think they have any ball bearing options, but the compressor wheels are very advanced.

Just remember that whatever size turbo you get will still have to have a big enough hot side for the 20b mass flowrate...

also i think you should run more like 15psi on whatever turbo you get, that should put you more in the efficiency range. Look for a turbo that will give you the HP at that pressure ratio, not at 11 psi, and you should have much mroe luck finding a reasonable size

 

Interesting idea...what size hot side would you suggest on a T04Z sized turbo? Or even a 35R? Erik's car in that link is using a 40R with only 0.95AR!

 

You can't judge the turbos efficiency range just on the psi level. Remember, that 20b is running higher compression rotors so it doesn't need as much boost to make the same power as a lower compression 20b engine with the exact same set-up. Boost isn't whats making the power, it's the air flow. With the higher compression advantage, this also doesn't mean the turbo isn't working any less harder to flow the same volume of air. The only true way way to tell the efficiency range is with a turbo rpm tachometer.

Perfect example of boost vs air flow. If you where to somehow install a set of 13b twin turbos on a 8.0L viper engine, you would hit 15psi pretty damn quick with so much exhaust energy and volume. However, by that engines low 6k red-line, the turbos would be so maxed out (spool wide) that you could be seeing vaccum. At best this engine could be comsidered a gaseline version of a Diesel (more torque than hp).

 

Seems like a GT4088 (non-bb) with a 1.06AR might be the ticket. It's smaller than the GT40R, should spool pretty well and ATP sells it with a T-series compatible exhaust housing which means it should fit my downpipe without modification.

http://www.atpturbo.com/Merchant2/me...ory_Code=GTNBB

What are your thoughts?

 

I think that or a T04R would work great...

 

Rx7store.net is selling the same turbo for a $100 less
http://www.rx7store.net/product_p/ga...%20bearing.htm

Im looking at getting the same turbo, need to replace the greddy T78 I just blew up

 

How was the T78 on the 20B?

 

what does that have to do with anything? Obviously a tiny turbo wont work on a huge engine, but it is more a matter of airflow than displacement, and i didnt suggest a tiny turbo, i suggested a reasonable sized one.

it is obvious from his hp goal that he needs a smaller turbo, and any turbo he uses will be more efficient at 15psi than 11psi, because 11 is just too low of a pressure ratio for efficient compression. Most turbos are efficeint at more like 18-25psi, and a smaller turbo will need to run a little more boost for the same mass flowrate (read hp level) so that will help to meet his goals a little better.

It seems like everyone thinks bigger is better when it comes to turbo sizing, and most people run a turbo that is at least a little too big for their setup. Why deal with the lag of a 1000hp turbo when you only ever want 500?.

 

I think 450-460rwhp is really what I'm after with the flattest torque curve of all time.

 

I know what your saying but the turbo set-up in the link is not laggy. People forget you can run the smaller exhaust A/R to make the larger turbo more responsive. All the torque and power he would ever need is in the mid-range. Ultimately what difference does it make what psi hes making the hp at? Look at that dyno chart I posted in the link. This guy is destroying his competition with that set-up. I think he could care less what psi he's doing it at.

 

Check out the link I posted. That power band is freeking awesome.

 

500r.

 

What are the specs on the 500r? Don't see them anywhere on the A-Spec site.

 

They won't release the specs to it, just like GR doesn't release the specs to their custom turbos. Lots of custom work goes into it, to just tell everyone what you did. They generally only sell them in kits, but considering this is going on a 3 rotor, I'm sure if you ASK NICE they can sell you just the turbo. But people have made 450rwhp on it on a 2rotor, so...

 

Thanks for the heads up...I'll drop them a line and see what happens!

 

good thread