Originally Posted by Boosted Performance

Just to touch on that....


I will be doing a test on the next local dyno tune comming up in a couple of weeks here to figure this boost thing out.

I have done a lot of research, and it seems that the 1.32 a/r housing may just be optimal for these engines in the high RPM's. The dyno Gale posted is with the 1.15 a/r housing, and it still spools VERY fast. Because it does spool so fast, the turbine may still be a bit of a restriction in the upper RPM's. It makes perfect sense, but needs to be proven. To do this, I will log the EBP (exhaust back pressure) on the identical housing for a local tune with the 1.15 a/r housing. This is the exhaust pressure just before the turbine housing inlet (not after the turbo). This will give me (and I will share this as I do everything) a solid idea of what is going on, and if a larger turbine is indeed the way to go. This was my suspicion with with the 1.0 a/r housing, hence the upgrade in size. It did not work out as I had anticipated.


This engine is very efficient, and flows so well (and a lot) in the 6,000 to 8,000rpm that these (smaller) turbines may be a bit of a restriction. I have spend a lot of time trying to figure this out. I have also talked to a couple of shops that run these turbos on stroked 2JZ's, and they are making 700whp with these turbos and the 1.15 a/r housings. The guys are also saying that they would not even think about going to the 1.32 a/r housings as they are "for V8's". I am starting to think that the 370z engine at 7,500rpm flows a lot more than a V8 at 5,000rpm (for example). I also have a customer making 580whp with the identical twin scroll kit on a 350z, and the boost is solid from 3,500rpm to 7,000rpm on a 350z. But then again, on the VQ35, there is no point of going any higher with the RPM's, and there is a 200cc displacement difference.



It seems like the boost holds just fine up to about 6,500rpm, and then falls a bit after that. I am not sure why the EBC is unable to hold the boost steady/flat. I will get to the bottom of it, and as mentioned will report back.