Xr6 Gt35r

[Bl4cK32]

I think from more of a performance to $$ point of view.

<{POST_SNAPBACK}>

Same here Its all about research for me as turbos (in my eyes) are harder to understand....

I understand about the turbine side gains theory...As a wise man once said :

"Exhaust is the propulsion side, smaller A/R will provide greater restriction to flow due to higher velocity to exhaust

charge which imparts drive to the turbine blades. Compressor side is more an indicator of the overall efficiency island of the compressor."

What id really like to know is what exactly would be the difference in using the different size compressor covers. Its always going to come down to trial and error i suppose....and cost

[Cubes]

Just to throw a spanner in the works.

I went for a little drive to quieten down the bubs tonight.

I saw an XR6 booting it along off sets of lights, surprisingly it looked a little laggy, sure it had plenty of boost transition torque/acceleration due to the 4ltr but lag is lag. :|

Has made me think about stepping back to the GT30 -12 VG30 Hybrid.

There's a couple ppls bolting this setup on to their rb25's soon, hopefully the results are all consistent, 270-280rwkw. If so, that will be fine for me.

Will have to get my self some decent tyres and suspension/diff setup to get the mid range stump pulling power to the ground.

Edited October 15, 2005 by Cubes

[BHDave]

Hey cubes,

what would you class as lag? the reason i ask is i think the gt30 with .63 rear will be absolutely tiny on your rb30.

I run an old HKS T300s kit with .63 rear and T04s/.7 front, plain bearing (the wheels look identical to the current crop of GT30 turbos) on my 25 and have full boost (atm 17psi) by 3100 rpm and this is without the benefit of ball bearing centres. I'd have thought the next size up on the exhaust would be beneficial on the 3lt as you would free up the exhaust and be able to make some pretty good power without the need for stupid amounts of boost.

Interesting reading about the different comp cover configuations, funnily enough there was little difference between the WOT performance of my old highflow vs the t300s at the same boost level, they even acheived full boost at the same time (which was 14psi until i had the car on the dyno with the new setup) the t300s was within 5rwkw of the highflow at that point. Transient response at light throttle was completely different, the highflow shat all over the HKS (probably to do with the ball bearing core)

[Bl4cK32]

I think he means the GT30 CHRA with the vg30 exhaust (which is about ~0.7 ar)

Anyways, i think the 0.6 front on the GT35r will still be the best setup for me. If it cracks just over 300rwkw, then im happy ....at the slight cost of getting the turbo setup the way i want

[Cubes]

BHDave, The GT30 vg30 hybrid kicks you in the arse at around 3800-4000rpm on an rb25, drop 500-600rpmf if its bolted on the side of a rb30.

By lag I mean it didn't start screaming to what sounded like 3500-4000rpm when idling off the line, it seemed ok once rolling, just off the line in the lower gears she sounds a little laggy.

Edited October 16, 2005 by Cubes

[discopotato03]

Cubes if your not sure wait for some results . Your own experience shows what happens when the restrictions were removed from the exhaust side . If it makes you feel any better I know of one RB30DET that uses a GT3540R that has the compressor side of a GT42R grafted into it (102mm comp wheel) and it spools at around 33-3400 rpm .

The F'n Orrible Rusty Device is a late emission engine with drive by wire throttle and all sorts of torque limiting devices . Your R32 (probably 400 Kg lighter) and tuned for performance should eat it .

By the way have you put taller rear gears in it yet , that should make it feel better .

Cheers A .

[R31Nismoid]

Just to throw a spanner in the works.

I went for a little drive to quieten down the bubs tonight.

I saw an XR6 booting it along off sets of lights, surprisingly it looked a little laggy, sure it had plenty of boost transition torque/acceleration due to the 4ltr but lag is lag. :|

The XR6t doesnt even feel like its making boost man. Its the design, torque and weight (among other things) of the car itself.

A mate of mine has one and you couldnt tell if it was on or off boost. Even thats its turbo to be honest. There is no kick at all, no rush onto boost

Remember they are only running 5psi or whatever, the turbo is basically hanging on for the ride. Its not doing anything remotely interesting.

The exhaust noise etc isnt much to go by.

You cant call it "lag" well... totally depends on your definition i guess

[Warpspeed]

The compressor cover a/r will have absolutely no influence on lag, how can it ? It is only the cover around the wheel, it cannot influence how fast the wheel accelerates. Lag is all due to the turbine end.

Second point, compressor a/r changes the shape of the flow map. Small a/r covers give a tall skinny compressor flow map that leans to the right. Ideal for very high boost small engines.

Large a/r covers give a fat round looking flow map, with big flow numbers at lower boost levels. Ideal for big cube engines running low boost.

Take two engines both producing 350Kw, one is a five litre V8 in a boat running low boost. The other is a two litre high Rpm high boost race engine. Both make 350Kw, both have identical airflow, one runs about five times the boost pressure of the other.

The two litre engine will have small a/r turbine cover, and small a/r compressor cover. The V8 will run large a/r covers at both ends.

Small a/r is for high pressures, skinny passages, high air velocities.

Big a/r is massive flow, low pressures, and low air velocities.

That is the general way it works at BOTH ends of the turbo.

In this example both engines are 350Kw, same airflow, same turbo, radically different turbo Rpm and pressure ratios.

Edited October 16, 2005 by Warpspeed

[Cubes]

R31 Nismoid,

The XR6 was definitely not stock.

It had a rather loud exhaust, twin tips out the rear, Orange colour with big white stripes painted down the middle of the car, very much lowered on 18" wheels. It went hard there's no doubt about that.

It easily cleaned up a VY II Exec V8 that was caming over with a nice lope.

When it launched it didn't get up on boost straight away, it took roughly half way across the lights for it to really kick hard, and begin struggling for traction.

It was definitely not a linear boost build on the xr6, it seemed as if it was going hard then all of a sudden it would kick hard and scream off.

With regards to warpspeeds comments, I guess some times I mistake lag for response.

As I understand it, you do nothing else but use a larger compressor a/r and you will reduce response.

I'm still getting my head around turbo comp and turbine matching etc..

The XR6 boys with the stock turbo are running up to around 385rwkw on the stock .5 comp cover. Thats pretty much where it ends for the stock xr6 turbo, thats when they look at upgrading.

Generally to a T66 wheel of some sort and push 400rwkw+.

Now knowing this I wouldn't even look at the larger comp cover.

Edited October 16, 2005 by Cubes

[discopotato03]

There is a section in Hugh M's book on turbocharging that describes the workings of the comp cover . My understanding is that it sort of the reverse of the turbine and exhaust housing . Its about converting high velocity to high pressure without turbulence in the diffuser . I think its safe to assume that the larger the AR the lower the gas speed will be for a given mass flow .

More tomorrow cheers A .

[Warpspeed]

There is a section in Hugh M's book on turbocharging that describes the workings of the comp cover . My understanding is that it sort of the reverse of the turbine and exhaust housing . Its about converting high velocity to high pressure without turbulence in the diffuser . I think its safe to assume that the larger the AR the lower the gas speed will be for a given mass flow .

More tomorrow cheers  A .

<{POST_SNAPBACK}>

Spot on discopotato.

The compressor cover should not really effect lag, but it possibly might if the compressor was forced to work in a really low efficiency part of the flow map during spoolup.

There may be less boost and less exhaust flow and much poorer spooling if the cover is totally wrong for the engine.

Think of the cover as a long gradually tapered pipe section that matches the wheel to the engine. For any given compressor tip speed and engine boost/airflow combination, there is an optimum taper angle or ratio of inlet size to outlet size.

As disco says, it is like the turbine cover, but in reverse.

[Cubes]

So how does a large comp cover affect the power delivery and overall feel?

Would it be correct to assume a larger comp cover will give the feel that you require more throttle to have the same acceleration? Given nothing but the comp cover has been changed.

Edited October 16, 2005 by Cubes

[discopotato03]

Quote :

Compressor Design .

The centrifugal compressor consists of three elements which must be matched to each other for optimum efficiency :

The impeller , the diffuser and the housing .

The compressor impeller rotates at very high speeds and accelerates the gas passing through it to a high velocity by centrifugal force .

The diffuser acts as a nozzle in reverse , slowing the gas down without turbulence . This causes it to increase in pressure and , unfortunately , in temperature .

The housing around the diffuser is used to collect this high pressure gas and direct it to wherever it is used .

He also goes on to mention static and total pressures , a static probe into a compressor cover is not affected by the velocity of the gas . A total pressure probe measures the static pressure plus the velocity pressure of the gas .

A static pressure tap could be a hole drilled at 90 deg to the direction of flow through the housing eg waste gate actuator pressure supply .

A total pressure tap could look like a small "L" shaped tube with its hole facing the direction of the moving gas . In this book its called a pitot tube . Aircraft use them in the wings leading edge I believe to measure air speed which differs to ground speed .

So my understanding of the real world comp cover ARR is that because of the larger passage size of the higher ratios all else being the same the gas speed will be lower out of the cover .

I reckon a set volume of gas moving at a higher velocity has to benefit our humble piston pump (engine) more than the same volume at slower speeds .

With the Foulcoon Ford were not looking for really high performance so for the lowish boost pressure (4-6) , the GT40 compressor is not working very hard and compressor efficiency does not need to be brilliant at the flow rate required . The GT40 82mm compressor is usually found in T04S covers and back plates but I think its the larger diffuser area from the "S" cover and back plate that becomes critical at higher boost pressures . It would be interesting to know if Garrett make smaller ie .60 , .50 ARR T04S comp covers for the 82mm 56T GT40 compressor . That way you could get the best of both worlds ie the larger diffuser area and some control of the cover velocity to get decent total pressure .

If you look at the specs of the GT40R it uses a fifty something ARR comp cover but I think its for an 88mm compressor - more searching needed .

In Corky Bells book Maximum Boost he quotes some figures for gas speeds that he feels should not be exceeded for exhaust and inlet air , I don't have time to find it now but maybe later .

Please do not take my ramblings as gospel as its only my current thoughts and not based on experience .

Cheers Adrian .

[Warpspeed]

Yup, Disco, that is a pretty good explanation.

A low boost setup only needs low compressor Rpm and tip speed, so velocities everywhere will be much lower, wheel, diffuser, and housing.

High boost requires the turbo to spin much faster, tip speeds will be up, and so will velocities.

Cubes, if the housing is all wrong, boost will be down, and turbo discharge temperatures will be higher. It is an efficiency thing.

Which would make more acceleration, 10 psi boost at 180C or 12psi boost at 150C coming out of the compressor at identical compressor Rpm ?

[Cubes]

How is it possible to gain airflow potential at higher pm's and not loose response/airflow velocity at lower rpms?

Similiar to using 3.5" IC piping or running an IC that is too large for the application.

General driving conditions it will tend to make all its boost a little later yet on the dyno it will make all its boost at basically the same rpm, as there is time to fill the void so to speak.

Obviously a .7 comp cover is still very small compared to the area of an ic/ic piping. Bad example but hope it makes sense.

Once again I worded my question badly.

Here it goes again.

I'm interested in the transition period from zero vacuum to the set boost level. How will the larger comp cover affect this? Will it feel more linear as a result less responsive?

I should bolt the smaller RB20DET comp cover on to my VG30DET turbo (exactly the same compressor wheel between the two) and see how it directly affects the power delivery.

If my middle name was moneybags and not unibum I would spend $70 and have a before/after boost trace on the local dyno.

argg..

Edited October 17, 2005 by Cubes

[discopotato03]

I'd say the largest ARR cover will offer the lowest gas speed for a given wheel speed . The lower ARR covers will pull the optimum gas speed down the compressors flow and speed range .

I was asking a fellow who used to do lots of custom turbo work years ago about this , he said the larger ARR covers make the turbo hit hard when the gas speed gets up where the lower ARR ones tend to be more progressive .

Note HKS's GT3037's , the 52 trim version uses a .50ARR cover , the 56 trim version uses a .60 . I'm guessing the gas speed is similar but the ARR goes up with the higher flowing 56T because of the greater mass flow .

In my perfect world I want the 50T GT40 82mm wheel with a T04S .50 ARR cover because I think it would put the ideal air speed where in the engines speed range I want it , not where a 6L GM/Detroit or whatever needed it to be . Sadly HKS (they optimize things for petrol engines) didn't option a GT3540R . I basically want the same sort of result that WilliamsF1 got but with 3.1L and one turbo .

[discopotato03]

I just had a quick look at the HKS GT3040 which uses the 50T 82mm GT40 compressor in a .60 ARR cover (quoted as 500 PS) unlike the Garrett GT3540R with its 56T comp and .70ARR cover . On ya HKS , free development work through online specs - I like it .

Cheers A .

[Cubes]

Its all beginning to make sense now.

[Nightcrawler]

I am not a real turbo whiz, so I need some advice from you gurus

I am thinking about strapping a turbo to my R34. For a relatively stock RB25DET with the following mods:

Apexi Power Intake in a partition

Manual boost/bleed valve

Apexi SAFCII

Apexi Exhaust Control Valve

Jasma Cat-back zorst

Split front/dump pipe (from Batmbl)

Catco high-flow cat

No intercooler

Standard fuel system

I am thinking about getting a Garrett T3 T04E internal wastegate turbo with T3 flange. Not sure of the a/rs yet, but will post tomorrow. The seller says I will get an easy 210rwkw at low boost with no aftermarket ecu, or 250rwkw with some tuning. Obviously without a/rs it is hard for you all to say, but am I on the right track with my enquiries so far? Obviously with standard fuel system I am not going to boost at over say 12psi, but may get a Sard rising rate fuel reg. if necessary.

Ideas/comments? I am not after crazy numbers, and want the car to be VERY streetable and lag-free. Is this the right sort of setup, or am I miles off track? Thanks for any advice!

[Bl4cK32]

id say wheel sizes are more important than ar's