Need DOHC turbo answer ASAP

[fiero_silva]

A buddy of mine is selling a pair of upgraded HKS turbos off of his TT 300ZX. After doing some research I believe they are HKS GT25 series turbos. His motor is a 3.0L quad cam 6 cyl. He was making aroun 400hp at 11lbs boost and says he was nowhere near the limits of the turbos (the stocks max out around 18lbs). The turbos have 50,000km on them.


HKS GT2530 - 320 PS Output

COMPRESSOR:
-Wheel- 63 Trim - 47.7 Inducer / 60.1 Major
-Housing- 60 Inlet / 50 Outlet - 0.60 A/R
TURBINE:
-Wheel- 76 Trim - 53.8 Major / 47.0 Exducer
-Housing- GT25/T3 inlets / Internal GT25/Skyline Type oulets - 0.64 A/R


I need an answer ASAP because I can get a KILLER DEAL on these...
Would they work with a 3.4DOHC?

[BrianC72bgt]

RE: Need DOHC turbo answer ASAP

I think this is your turbocharger: http://www.turbobygarrett.com/turbob...S_739548_1.htm

If you look on the turbo by Garrett site, you will find the compressor and turbine maps for this turbo. To use them you have to do a little math first. You will find all of the formulas you need on their site. Put it together in a spreadsheet (like I did last night) and you can get some ideas regarding the right turbo for your application.

You need to make a bunch of assumptions for things like the temperature of the air when it reaches the intake ( 130 degrees with a good intercooler setup) Volumetric efficiency of your engine (lets say 92% for laughs) Your maximum rpm..how's 7000? and your target horsepower...400?
Air Fuel ratio of... 12 to 1..sound good?

Assuming all of the above, you would need 44 to 48 lb of air flow per minute and your pressure ratio works out to 2.1. Those are the two numbers you need to evaluate the compressor graphs for a single turbo application. For twin turbos, I am GUESSING that you divide your target airflow by 2, so 22 lbs/minute. I am not sure if you alter the pressure ratio. I am assuming you don't. If this is all true, then these two turbos might be pretty damn good on the compressor side...somewhere in the 75 to 76% efficiency range. As for the suitability of the turbine side, I have no idea. Maybe a little too big. The compressor still looks highly efficient at the 500 HP twin turbo level though.

Anyone with more understanding, please feel free to chime in.

Regards,

Brian C.

I suppose you could always call Garrett and ask them.

[BrianC72bgt]

Upon further reflection

The compressor map for your turbos is attached. The more I read about it, the less I know. Looking at this map, the sweet spot seems to be at a pressure ratio of 2.0 and up to 32 or so lb/minute of air. And if you had say a 2.7 liter engine, it would need aboult 12.5 pounds of boost to get you to that target. Weird thing is that a 3.4 spinning 7000 rpm at redline only needs 7lbs of boost to get there. That tells me that something ain't right. No way are you only going to be making seven pounds at teh intake manifold at redline. This sucker will be spinning like a top. So what does that say about this map.....I have no idea.

Flip side is two of them targeting 420HP gives you a pressure ratio of 2.18 with each of them flowing 24.3 lbs/minute at 15lbs of boost. When you plot that, you don't end up far enough to the right side of the map which I fear would make things a bit laggy at lower rpm.

So, my conclusion is that one is too small and two is too big. But, admittedly, I am a newbie to this process and could be way off for reasons I don't understand.

Good luck,

Brian C.

[BrianC72bgt]

Map attached this time, I hope.

[SappySE107]

You can email me the maps and I will get them up. Sappyse107@60degreev6.com

[BrianC72bgt]

Now this one is a Garrett GT2554R and two of them look like they would give you 420hp at 15psi with 70% efficiency and a pressure ratio of 2.18. It would also come on alot sooner than the pair you are looking at...of course they max out sooner too.

http://www.turbobygarrett.com/turbobygarrett/catelog/Turbochargers/GT25/GT2554R_471171_3.htm

http://www.turbobygarrett.com/turbobygarrett/catelog/Turbochargers/GT25/GT2554R_471171_3.htm