sl2ner

hey guys im in the middle of a 2.5 turbo build and im stuck between 2 turbos. most of its time will be driven on the street but will also see a lot of the drag strip and possibly a few road courses. looking to make around 500 whp. some of the supporting mods are....

-2.5 block .40 over
-JE 8.5:1 .40 over pistons
-carillo H-beam rods
-ARP head studs and rod nuts
-large oil cooler
-lindsey racing intake manifold and big TB
-lindsey valve springs
-titanium retainers
-272 cam
-port and polished head
-lindsey solid lifter package
-speed force racing blow through MAF
-#72 injectors
-speed force racing fuel system(pump, rail, and reg.)
-speed force racing turbo and cross over manifold
-3 inch down pipe connected to straight 3 inch out the back

the two turbos in question are both turbonetics GT-K series turbos, the 550 and the 650. the 550 is a 61mm turbo and has a .82 a/r exhaust housing and the 650 is a 66mm turbo with a .63 a/r exhaust housing. problem is im thinking the .82 a/r on the 550 might lag too much and im thinking the 66mm compressor side on the 650 might be too big and come in contact with the bottom of the intake. if both of these are going to be too laggy im probably going to go with the precision 6262 but one of the gt-k turbos would be nice since i got a deal on them.

so can any of you big HP guys help me sort out my delima? any help or advice on the project is much appreciated!

Paulyy

I did look into those turbos a few years ago. Because not many people use them here, you should search what the WRX guys with the 2.5 are getting. you'll have some indication of boost curves and power outputs.

From what i've been told, they are quite laggy turbos to begin with. But if i had to choose. the 650 will be the one. Because i don't have compressor maps to read and not sure how much boost you're planning on, you'll get a better chance with a 650 and running higher boost.

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sl2ner

haha ya ive been looking at the subby guys and the others running similar displacement engines. thinking i might run a precision 5858. seems like the perfect match for these cars and can support a little over 500hp.

Paulyy

500 rwhp has been done on a gt3076R before
His head and cam where pretty wild. just a little milder than mine IICR (same builder)

https://rennlist.com/forums/944-turb...oppin-***.html

Penguinracer

A quick question.

Why did you decide to go with a re-bore/alusil etch rather steel/nikasil liners?

Tim

Thom

Looking at the spec sheet for both turbos I would suggest the 550.
The 650 uses a smaller A/R turbine housing, and even if we suppose it flows more than the 550's larger A/R turbine housing/smaller turbine wheel (which I doubt), the larger compressor wheel of the 650 suggests you may get a peakier but narrower powerband.

If Patrick in OZ makes 500 actual whp with a GTX3582R, a much-prepped head and 1.5 bar of boost, I do not see how it would be possible to get anywhere close with a GT3076R.

333pg333

Our numbers have been proven to be upside down in Australia...fact!

Paulyy

Well i don't know how much the us dynos lie, but if you look at the link from spooln51s car, he dynos just under 500rwhp with a gt3076r after he has increased the boost. mind you this was at 7000 rpm he was getting these numbers.

gruhsy

The air turns the other way which is aided by the curvature of the turbo

Thom

Well, I just do not trust US dynos.
With "high hp" engines the error factor increases with the output of the engine.

Paulyy

I get your point.

Well looking at the gt30R compressor map, he would have been pushing it at it's limit to get "actual" 500rwhp. 23-25 psi = 1.5 - 1.7 bar = 2.5-2.7 absolute. Which is right on the ballpark on the map at it's limits.

He shouldn't have a problem with the GTX3076R though. at 25 psi you'll get 60 lbs/min which would be on par with the goals.
Just hope the head will flow enough air.

George D Ran a GTK 650. Looking at videos and the dyno by SFR it looked very laggy indeed. IICR he mentioned it too and swapped it out for something with more midrange. that was on a 3.1

sl2ner

read there were problems with certain steel motors so i decided to just stay with alusil. didnt seem like there would be any problems other than actually finding someone to do the machine work with alusil.

ya these gt-ks seem like they might be too laggy for this project. thinking about running either a 5858 or s 6262 from precision. would like the 6262 but if im only revving the 6.5k it might not be the best choice.

ya i did a lot of research around george d's red car using the gt-k 650 but didnt come up with a whole lot of info, just some basic specs. but i did see as your stated that he changed the turbo out but i didnt know the reasoning. figured it might be the lag.

sl2ner

decided to go with some precision but still stuck between a couple turbos. the 5858 seems like probably the best choice but wouldnt mind the bigger 6262 if it would work with this application.

blown 944

Id go 62 62. I don't trust us dynos either. Only trap speeds.

500 hp is not going to be easy with a 2.5

What are the head flow numbers?

Your injectors are also going to be too small.