Turbine a/r

[Bee-RSkyline]

Still learning to understand a/r values.

From what I understand the bigger the number the bigger the housing.

I have 3 options for my new turbine housing.

1.06
0.82
0.63

Engine 2.4L RB20

I'm leaning toward 0.63 but don't want to choke off the top end.
Thoughts?

[hozer]

Still learning to understand a/r values.

From what I understand the bigger the number the bigger the housing.

I have 3 options for my new turbine housing.

1.06
0.82
0.63

Engine 2.4L RB20

I'm leaning toward 0.63 but don't want to choke off the top end.
Thoughts?

The inlet cross-sectional area divided by the radius from the turbo centerline to the centroid of that area. Now this means absolutely nothing but what it translates too is bigger number = more flow.

Most important thing is matching it up for your engine as is, or as you intend to build it.

[Bee-RSkyline]

That much I get, not really that complicated.

However more flow is not always better. From what I understand more flow equates to longer/later spool.
I don't think my 2.4L will spool a 1.02 a/r turbine at a usable portion of the RPM band.
Or even a .82 a/r for that matter
I just don't want to go too small and choke off the top end with too much backpressure.

[Dragon Humper]

Turbine inducer/exducer sizing tells more of a picture than just the A/R. I would lean more towards the .82 as long as the turbine wheel isnt too big. The smaller the turbine the more chance of overspinning the turbo and turning it into a big heat pump and costing you a ton of power and most importantly, reliability.

I know this is the same drum I have beaten forever but, more and more hardcore engine builders are going this direction..you end up having a package that will last 10 times longer thanks to much lower intake temps.

What else have you got going on with your package other than the stroker angle?



Jon.

[merkmerc]

what turbo are you looking at . Do you know the specs of the turbine wheel like said above that will dictated what ar housing you pick .What are you hp goals , what are you using it for and what rpm spool time do you think you can live with aka whats your max rpm and what kind of powerband will work with what your going to do with the car .Is it an auto or manual car

[Bee-RSkyline]

Thanks for the help guys.

Manual street car, low RPM spool is definitely a plus.

Looking at a GTX3071R

Turbine specs:
60.0mm wheel diameter
84 Trim

Compressor specs:
Ind wheel diameter: 54.1mm
Exd wheel diameter: 71.4mm
58 trim

Supporting mods on the stroker:
Haltech ECU
555cc injectors w/ high flow fuel pump @ aftermarket FPR
Front facing GTR plenum w/ ITB's
Front mount intercooler
LS2 truck coils for ignition

[Skym]

Stock cams or aftermarket cams and are you going to dial the cam timing (adjustable cam gears) in for early spool or more peak hp????

[merkmerc]

if i recall the .82 to 0.63 the spool difference is about 800 rpm . The .63 ar with stock cams will put you around the 3800-4200 rpm spool depending on elevation. Where as the .82 will put you around that 4500-5000 mark thats on a rb20 so i would imagine you could expect 300 rpm lower spool time. Depends how hard you plan on turning the wick up if the .63 will restrict you . Do you have a power level in mind ? .. To be honest unless your taking the car to track days all the time id stick with the .63 just for the low end spool becasue at the 400+ rwhp mark I dont think you would really be seeing much more than 20 rwhp gain at the high rpm end with the .82

[Bee-RSkyline]

Thanks merkmerc, extremely helpful. 0.63 it is

[Dragon Humper]

You would see a hell of alot more than 20hp more with the larger turbine. You really should be sizing your turbo based on all the RB25 builds going on because...thats what you have now. Look at how large my turbo is...I am only 200cc bigver than you and I am all in by 5000rpm. With the right tuning you could be all in by 3500-3800rpm with the .82.

Any tuner who isnt a panzy can knock 500rpm off any spool time with crisp tuning at the onset of the transition. Small cams and your intake setup helps out a bunch. Part of the reason I get up on it so quick is my tiny little HKS 260 cams, gives a harder smack to the turbine to spool it quicker over a large cam.

And most importantly making your HP goal with less boost AKA, less heat.



Jon.

[merkmerc]

20 RWHP is a round about there is a huge room for improvement about the 20 if everything else is optimized but with out knowing everything like exhaust and tune cams and cam timing all play a big part .. Another thing to realize is the rb25 head does flow better than the rb20 head as well . Boost is relative to volume it has to fill best example i have ever found of this is on the ford turbo 2.3 with the t3 turbos when people are pushing the turbo hard after they do exhaust and ported head and gutted and ported intake and they put it all back together and find out they lost about 3 psi boost moving the same amount of air (because the turbo was maxed) but into a larger area decreasing boost yet making way more power .

[ToroGTS]

Currently running 0.63 on a stock bottom end rb20 and I can tell you that the spool time (have adjustable cams as well fyi) is about 3500 rpm, which compared to stock turbos feels pretty delayed. Your exhaust/comp wheel is a bit bigger than mine, but with the extra stroke you could expect similar spool. Honestly I don't feel a bigger turbo is necessary really given that at the 21 psi (320 whp) region, I am doing a pretty prolonged rolling burn out after engaging 2nd on 245 wide brand new yokohama's... From an actual driving perspective more power just starts to roast tires and squirrel up the handling a bit. Depends on what you are trying to achieve at days end.

[Bee-RSkyline]

ToroGTS, which turbo are you running?

[merkmerc]

Also heads up closer you are to sea level the slower the spool will because of the air being heavier (more dense) so a turbo will spool faster in say calgary than vancouver , as long as each setup is tuned to each altitude

[Bee-RSkyline]

I'm definitely below sea level here. Looking to make 350-400whp @ 14psi-18psi