Another garrett question

[32vspecII]

actually this is a gt3040 right ? would this be suitable for a rb25 or to big ?

[discopotato03]

Fellas I've not tried these on RB's or anything for that matter .

From a technical viewpoint the combination of a 60.1mm turbine and an 82mm compressor is not ideal . Thats not to say it wont work at all but , Garretts production engineers believe that the turbine cannot develop adequate shaft power to efficiently drive a compressor of that size and capacity . Even if it could the sort of airflow that a GT40 compressor can develop would be let down by the shortage of exhaust flow capacity of the GT30 turbine/housing .

American Honda tuning firms spend their lives doing back to back tests with GT30R's , GT3040R's and GT3540R's and the results are always the same . The 3040R can develop higher power levels than the GT30R but high turbine inlet pressure (back pressure) becomes the limitation . The GT3540R has the same compressor/cover as the GT3040R but its turbine in 8mm larger in diameter or a smidge over 1.25 times its cross sectional area . So in effect the levers driving the shaft and compressor are longer (more mechanical advantage to develop shaft torque) and the path for exhaust gasses is less restrictive .

The GT3540R will nearly always be capable of higher power outputs than the GT3040R because it can get lots of air in and lets lots of exhaust out - in balenced proportions . They can be hamstrung with too small an exhaust housing in an effort to spool it on an engine really too small for them , but the result is nearly always compressor surge .

You won't be the first or last to try bridging the gap between the GT30R and GT3540R . To a degree it can be done , this is why different sized (ARR) turbine and compressor housings are made . If response is important then larger housings on the GT30R can extend it beyond the norm . Alternatively the mid size turbine housing and one of the mid or smaller T04E comp covers could wake up the larger GT3540R . Its always going to be a compromise .

[HypeR33]

Hey Disco,

So you are saying the GT3540R is a better way to go?

[OFENSV]

which would be more suited to a 3ltr RB30det. the gt3040 or gt3540?

wats the difference in lag, much more from the gt3540?

Fellas I've not tried these on RB's or anything for that matter .

From a technical viewpoint the combination of a 60.1mm turbine and an 82mm compressor is not ideal . Thats not to say it wont work at all but , Garretts production engineers believe that the turbine cannot develop adequate shaft power to efficiently drive a compressor of that size and capacity . Even if it could the sort of airflow that a GT40 compressor can develop would be let down by the shortage of exhaust flow capacity of the GT30 turbine/housing .  

American Honda tuning firms spend their lives doing back to back tests with GT30R's , GT3040R's and GT3540R's and the results are always the same . The 3040R can develop higher power levels than the GT30R but high turbine inlet pressure (back pressure) becomes the limitation . The GT3540R has the same compressor/cover as the GT3040R but its turbine in 8mm larger in diameter or a smidge over 1.25 times its cross sectional area . So in effect the levers driving the shaft and compressor are longer (more mechanical advantage to develop shaft torque) and the path for exhaust gasses is less restrictive .  

The GT3540R will nearly always be capable of higher power outputs than the GT3040R because it can get lots of air in and lets lots of exhaust out - in balenced proportions . They can be hamstrung with too small an exhaust housing in an effort to spool it on an engine really too small for them , but the result is nearly always compressor surge .  

You won't be the first or last to try bridging the gap between the GT30R and GT3540R . To a degree it can be done , this is why different sized (ARR) turbine and compressor housings are made . If response is important then larger housings on the GT30R can extend it beyond the norm . Alternatively the mid size turbine housing and one of the mid or smaller T04E comp covers could wake up the larger GT3540R . Its always going to be a compromise .

[discopotato03]

which would be more suited to a 3ltr RB30det. the gt3040 or gt3540?

wats the difference in lag, much more from the gt3540?

I can only repeat what I was told by someone who's been there .

SK said that the RB25 or 26/31's make that much exhaust flow that they'll spool nearly anything . He said that ideally you want the turbo to spool up at approx 32-3300 revs otherwise it tries to spool up at the gearchange point and drinks copious amounts of fuel .

I imagine that twin cam RB30's are not lacking torque off boost as long as the compression ratio is adequate . This is where you need to understand the static and dynamic compression ratio part .

Static comp is worked out assuming no inlet restriction . Dynamic comp ratio takes into account the partly or nearly closed throttle plate/s . Obviously you can't have nearly as good cylinder filling with a closed throttle as an open one . The more air you can get into the cylinder the more there is to compress for high cylinder pressures post combustion . Higher static CR means all else being equal higher dynamic compression ie same volume of gas squeesed into smaller space = higher compression pressure .

Where this takes us to in the real world is more part throttle low rev torque to drive us down the road . This extra torque is not gained from boost so we get to start the onset of positive pressure higher up the rev range . We have the opportunity here to use larger turbines / housings to offset the restriction at the other end of the rev range and retain a little more volumetric efficiency . Part throttle driving off boost give us the ability to get good fuel mileage at 110 on the expressways .

I don't like the GT3040R personally (based on theory not practise) , and in the RB25 - 26/31 case we are not short of exhaust flow or part throttle torque so the bigger turbined GT3540R should pay off handsomely . My vote goes to the GT3540R .

Cheers Adrian .

[R31Nismoid]

RB25 speaking, actually using it.

I have a GT30, GT series wheel thats rated @ 600hp.

i wouldnt want it spooling any later than what it does now.

makes 16psi above 4000rpm and then power climbs nicely and fast, but limited to 7800rpm.

for the RB30DET/RB25DETT, the bigger GT35 is the go as the exhaust flow is a lot more.

a lot of the calaisturbo.com boys use the bigger GT35 on thier 30's and it gives them brilliant results as they can get away with running the slightly bigger version

[discopotato03]

Nismoid , is your "GT30" using the GT37 or GT40 compressor . Both are six bladed , the 37 is a 76mm wheel in a T04E cover while the 40 is 82mm usually in a T04S cover . The GT30R (76mm compressor) is normally rated at 500 hp .

[R31Nismoid]

i cant remember.

Roto-master built it and on the spec sheet it said 600hp. :|

[Cubes]

Apparently the GT35R .82 exh. a/r makes ~1bar by 3500rpm on the RB30DET.

It makes serious boost by 4000rpm.

Its only what I've been told by another GT35R user on his RB30DET.

He also had the GT30R, which was to put it bluntly, crap.

It just didn't have the airflow to keep up with the 3ltr over 5500rpm causing power to flatten out and torque drop off.

The RB30DET. I wouldn't select any turbo other than the GT35R.

Play with exhaust a/r's to get the response and top end you are after.

According to turbine maps the GT30R .82 a/r flows the same airflow at the same pressure as the GT35R .63 a/r does.

[discopotato03]

Cubes I will probably go with the 1.06 ARR GT3540R just not sure about which comp cover . My engine will have 9 to 1 CR via the JE VG30 Piston solution , expensive but worth it . Wont be built in the near future , so far have 33 26 top end and pistons so still gathering bits as funds allow .

Chow Adrian .

[Cubes]

Nice..

My build took me around 2 years from the purchase of the first bits.

The VLT boys say the 1.06 a/r isn't laggy. I'm going to play with exhaust a/rs depending on how the .82 is. If its sweet then I won't bother. If its slightly laggier than I want I will drop down to the .63.

According to the 3ltrs airflow and where I would expect the gt35R to spool with a .63, it shouldn't surge.

2.5ltr.. it will surge.

[discopotato03]

G'day Cubes , some Garrett contacts in Torrance Calif are trying to push the GT40R turbo for the 26/31 hybrid . They reckon full boost from 4000 but its getting seriously big . I'm getting them to chase up details of available turbine housings but LOL probably a bigger mouthful than I can chew on !

I do know of someone over here with a custom "GT3542R" hybrid that reckons it spools fine . Its using the 102mm GT42 compressor , big enough to hide under .

I've gotta get back to SK to see if more than 9:1 CR is of any benefit ie 9.2 ?

Cheers Adrian .

[R31Nismoid]

Yeah, thanks joel.

Thats exactly what i've seen here in Vic. GT30 - no go... GT35, the perfect mix. With it coming on good @4k i reckon thats sweet as

[Cubes]

If the GT35R is making 1bar by 3500rpm thats ~23.3lb/s which is some where around 250hp.

Torque = power / rpm * 5252

so to make around 250hp at 3500rpm it must be making around 375lb-ft or 500Nm of torque.

Some nice torque.

Obviously the calc is rough but gives us a rough idea.

Please tell me if I'm working it out wrong.. I think I have. I.e I have not taken in to account the compressors efficiency at that rpm & pr.