Hks Twin Turbo kit Prototype.

Scribe

Yeah, don't know what I was thinking, 1.85. But I did say 3, not 4 cylinders.

I come from a DSM background, so I am not new to turbocharged engines at all. I can get as technical as you want if that will help this discussion.

That being said, a certain power level corresponds to a certain airflow rate. Thinking of the VQ37 with twin turbos as two 1.85L engines with their individual turbos is a great place to start. If your goal is say somewhere in the 500 whp range (550-600 crank), then you only need a turbo capable of flowing efficiently at the given boost level at half the CFM to support this goal. Considering the lower boost levels run on a high compression engine like the VQ, a big T28, or even a 16g (again, coming from a DSM background) could conceivably reach those goals and have drastically better manners on the street. People get too obsessed with big turbos that could flow enough air to make 500+ each and they don't really understand what they are giving up by selecting a good turbo.

Too large a turbo mean you will never really be operating within the ideal area of the compressor map just as much as turbo that is too small, leading to excessive lag on the low end where smaller turbos run out of steam up top. All you need is a turbo that produce maybe 7-9psi max efficiently to a 1.85L three cylinder to 7500K.

Let me know if there is real interest in this discussion and I'll start looking for compressor maps, but otherwise I'd just be screaming in the wind. Also, if you want, start a new thread and PM me so we can publicly discuss what would be the ideal street kit for our cars.

Don't get me wrong, if this kit were to come out, I'd be one of the first in line, although I may make a few calls to get a better turbo match if they go the 'bigger is better' route.

Scribe

Just checked and the GT-RS by HKS is actually bigger than the GT28RS by Garret that I thought this was. The Garret would be a better match. HKS doesn't use Garret turbos, the naming convention is similar, hence the confusion everyone has.

You want something that is in it's efficient range around about a 1.4-1.6 pressure ratio as it sweeps up to enough CFM to support about 300 horsepower (about 33 lb/min of airflow). That would get you to the mid 400s at the wheels with the best street manners on each bank of three cylinders. The GT-RS supports about 400hp (400ps actually). That's about a 33% increase in capability that isn't utilized and only serves to create lag where a smaller turbo may server better in its place.

I understand that there is more at play and that the theoretical is when these turbos are pumping as much air as possible, etc etc. All of these turbos are more efficient at higher boost levels anyhow, but some are a better match for a stock VQ37 than others.

Here's some statistics on these turbos:

HKS GT-RS
========
400 PS Output
COMPRESSOR:
-Wheel- 52 Trim - 51.2 Inducer / 71.1 Major
-Housing- 60 Inlet / 50 Outlet - 0.60 A/R
TURBINE:
-Wheel- 76 Trim - 53.8 Major / 47.0 Exducer
-Housing- GT25 inlet / Internal GT25 outlet; 0.64 A/R

A close Garrett would be the GT2871R.

I went to the Garrett site, since they have compressor maps and HKS doesn't Any way, they have tons of information on these turbos if you are really interested. I could go through these, but I'm really tired.

TurboByGarrett.com - Turbochargers

LateralG'z

Great post, and info +1

__________________
2010 Mag Black, 6MT,

Scribe

Just checked and the GReddy kit, which makes a claimed 450rwp at 5.8psi utilizing two TD06-20G turbos. I bet there is more power under the curve with those as well, as the boost comes almost surely comes on faster and lower in the rpm range. I just really hate GReddy's plumbing.

Scribe

If HKS were to come out with this and I were able to be a little picky with the turbos, I would jump on this and the CAMP2 interface, since it works with the F-CON tuning system.

JB-370z

What about the greddys bushings instead of ballbearing, that kinda sucks. Also 20Gs are super old in design.

__________________
ll Baker Tuning ll GTM ll Powerhouse Amuse ll HKS ll Up-Rev ll iForged ll AP Racing ll Pioneer ll SPL ll Bride ll Top Secret ll OS Giken ll
GTM Stage 2 Twin Turboed 370z (First in Texas, Thanks To Baker Tuning)

Scribe

This was more a discussion of size. The ball bearing design of newer turbos is marginally better, but the 20Gs are proven and potent. The difference in bearings isn't so great as to make up a significant difference in turbo size.