Why .82 A/r On Gt35?

[T-Rex]

Why do most people running GT35/40's use the .82A/R and not the 1.06A/R? Reason im asking is i come from a WRX past and even on the 2.5L setups they almost always use the 1.06A/R because the .82 seems to suffer from choke. It surprised me even more that those who have done the RB30 upgrade even use the .82! Can someone enlighten me?

[-_-StRyDeR-_-]

i did it for the ability to keep it street driven, running the car in with no boost controller nor a proper tune and im on full boost before 3800 and it holds past 8000. ummm choke up??? dont know about that, 600hp is a bit of a stretch for them however 500rwhp on a street car is still pretty crazy....?

[hypergear]

Why do most people running GT35/40's use the .82A/R and not the 1.06A/R? Reason im asking is i come from a WRX past and even on the 2.5L setups they almost always use the 1.06A/R because the .82 seems to suffer from choke. It surprised me even more that those who have done the RB30 upgrade even use the .82! Can someone enlighten me?

First of all GT35 turbine has very opening ends with large fins. It has great flow capacity due large fin space, unlikely to chock. Also means has less materials for combusted air to turn the shaft down low. Its some thing that I would only use for high-mid / Top end power applications.

Larger A/R means bigger snail, it flows better, less heat, and back pressure. How ever pressure reduction means slower to come on boost. .82 rear with a GT35 turbine wheel and 82mm comp is big enough to support a RB25det with over 350rwkw. But very laggy, I wouldn’t want to drive it as daily.

We've done many tests with various sizes of housings the .82 and modified GT30 turbine (taller inducer, larger exducer, ATR43G3 turbine) have proven to deliver the best result with consistency. For a streetable GT35 based turbine I would run that in a .63 rear with a 76mm comp, which is also very drivable and consistent, or run a GT3582 core in a small .63 rear with 50mm external gate.

[KiwiRS4T]

I,ve got a GT3540 on a sinco customs (similar to 6boost) manifold and 50mm ext w/g with a .63 A/R going on my RB30. Hopefully it will get my heavy Stagea moving quickly and still have an adequate max power. Will report when its going!

[-_-StRyDeR-_-]

sorry forgot to mention im running a pretty decent 25-30 so no lag for me...

[T-Rex]

Good info there guys. I guess people with different cars are often after different setups. With WRX's its pretty common for people to want 18-20psi between 3500-4500rpm. And that isn't really considered laggy. The dyno graph below is of a Cosworth built 2.5l engine (as good as you will get) with a GT35r with .82. This is one of the best graph's i have seen in terms of spool versus power output.

[hypergear]

Is above on Race fuel? what sort of block?

the WRX or Cosworth might have slightly shorter gear ratio so 4500RPMs @ 20psi might not feel laggy.

This is a ATR45 (modified GT3582 sleeve setup turbo with different comp trim for better response on RB25det) on a Fully stock RB25det with factory head, cam and cam gears on 98 fuel. Which is also the most responsive result out of all RB25det GT3582 readings with stock head/cams/cam gears on 98 fuel.

For FULLY STOCK, Power and boost curve doesn't look bad, 321rwkws with 22psi by 4400RPMs and 180rwkws by 4000RPMs. 4th gear on highway is pretty good, in low gears you really feel the lag.

(click to enlarge)

[T-Rex]

The above graph is on 98 pump fuel. Using a factory STi semi-closed deck block. They have been proven to handle 350-400kw under race conditions with no failures at all. Comparing the 2 graphs i'd say up until 4500rpm or so the WRX would feel much faster, and given their shorter gears it would probably feel faster altogether (from my own experience of owning both WRX and now GTR). Cubic capacity is cubic capacity i guess, it doesn't matter so much that one has 2 more cylinders.

Ps. The Cosworth engine package ranges from $15,000-$26,000 depending on spec, so its not an apples to apples comparo

[jarrod83]

I had a pretty laggy setup at first with my gt35 0.82 on my stock rb25 with 6boost manifold, plazmaman plenum, 3.5 inch exhaust.. was making full boost to about 5000 rpm, eventually i found out that the wastegate was missing its valve stem seal from when the exhaust got done, omg at the difference... these are the results recorded from my blitz i-colour

2400 rpm 0.53 bar 7.685psi

3000rpm 0.57 bar 8.265psi

3500rpm 0.96 bar 13.92psi

4000rpm 1.59bar 23.055psi

4200rpm 1.82bar 26.39psi

i wouldnt call it responsive, but i would hardly call it laggy, i never got it dynod with the valve steam seal fixed but it made 408rwhp on 18psi with it broken, my forged rb30 hasnt come close to making more power yet as its only running 21psi but it manages to make the boost by 3500... quite alot of fun on the street =), i think its a good compromise between power and response when your looking at the 450-500rwhp range... havent had any problems with choke.. only an annoying afm surge issue when i get off the power... map ftw

Jarrod

[TiTAN]

I had a pretty laggy setup at first with my gt35 0.82 on my stock rb25 with 6boost manifold, plazmaman plenum, 3.5 inch exhaust.. was making full boost to about 5000 rpm, eventually i found out that the wastegate was missing its valve stem seal from when the exhaust got done, omg at the difference... these are the results recorded from my blitz i-colour

2400 rpm 0.53 bar 7.685psi

3000rpm 0.57 bar 8.265psi

3500rpm 0.96 bar 13.92psi

4000rpm 1.59bar 23.055psi

4200rpm 1.82bar 26.39psi

i wouldnt call it responsive, but i would hardly call it laggy, i never got it dynod with the valve steam seal fixed but it made 408rwhp on 18psi with it broken, my forged rb30 hasnt come close to making more power yet as its only running 21psi but it manages to make the boost by 3500... quite alot of fun on the street =), i think its a good compromise between power and response when your looking at the 450-500rwhp range... havent had any problems with choke.. only an annoying afm surge issue when i get off the power... map ftw

Jarrod

i have a similar setup i was getting full boost at 5500 (didnt have any preload on the wastegate, fixed that up and brought it back down to ~3500), i agree that it is acceptable response for the street but compared to a friends 3076 setup (again on a 3L) you notice the lag switching between the two cars.

[snozzle]

I dont mean to hijack thread but i figure i may aswell ask some questions of my own while on topic and comparing turbos.

Ive been comparing gt3076 and gtr3582 for my rb26 for a while now and still have a few things im not sure about as my power goals arent too high.. im just want full boost at around 4200-4500 at the latest. Will a standard non split pulse 0.82 rear housing gt35r be on full song at the rpms that i want it to?

will any trim and A/R combo in the garrett catalogue for the gt3076 get me a safe 350awkw without being too much of a restriction?

Does anyone run a gt3076 with a 1.06 rear housing? how does that compare to the gt35r with a 0.82 ?

[TiTAN]

if its in a GTR why not go a set of bolt in 2860-9 turbos? to get ~330ish kw or 2860-5 turbos for ~400kw? there is a lot of $$ in changing to a single setup.

[snozzle]

well im one of those dudes who think top mounts > twins even though they make the same power, they just have a different feeling of power delivery, ive been in a car with -5s running 330kw and wasnt really impressed, sure its fast.. but ive been in a car with less power but big single and it just feels like alot more fun to drive and smoother power delivery

ontop of that some more weak excuses are....

i wante gate (option of plumbing back and screamer) that beloved turbo whistle on full boost, flutter.. and i love the look of a big single in a 26 engine bay aswell

i have a dejetro lined up, just a matter of buying some injectors, getting rid of the afms, -7's my tomei dumps and other twin turbo related gear and buyin the gear to replace it and some custom piping

im aware of all the costs and the fact that its more expensive and still prefer a big single other the twins even if it gets me the same power, just a matter of choosing the right turbo and A/R to get me onto full boost as early as possible without sacrificing that top end pull on highway runs

edit: im a mechanic btw so labour is free too

Edited October 9, 2010 by snozzle

[JonnoHR31]

whilst its possible on some cars and dynos theres no garuntee you'll make 350rwkw with a gt3076, even with a 1.06 housing. if your happy to lower your goal a touch in exchange for response a T4 twin scroll 1.06 gt3086 on a good manifold would be a nice setup.

only downside is ATP are the only ones who make a such a turbine housing and whilst it does the job its far from perfect

i have the same combo on a 30det in perth if you wanna see how it drives

[T-Rex]

No issues with hijacking here, any information is good information. I thought i would put my 2cents towards the twin versus single. The twins are so cramped, even with standard turbo's its a PITA to work on the car is you have any issues on that side. With a single you have pretty good access. Also with a single you have more room to design a high flowing dump pipe, possibly allowing for bigger power with minimal loss to response. I have 2860-7 on my GTR and im hoping there is something wrong like an exhaust leak because it is not very responsive at all. I would guess im getting 14.5psi after 4000rpm and 22psi after 5000rpm.. I like to work on my car myself but i feel its not possible with the twin setup, you need a hoist to do it safely.

[R31Nismoid]

What .82 vs 1.06?

Simple really, for a 2.5l its the best combo.

370rwkw or so can be done by a GT35 with a .82, if you are running a 3ltr then get the 1.06

Just about exhaust flow really and hence for the 2.5l you simply don't need the bigger housing as the .82 brings on nice and linear power without choking the top end at all.

For a 3ltr, you would get the 1.06 IMO.

well im one of those dudes who think top mounts > twins even though they make the same power, they just have a different feeling of power delivery, ive been in a car with -5s running 330kw and wasnt really impressed, sure its fast.. but ive been in a car with less power but big single and it just feels like alot more fun to drive and smoother power delivery

Of course you wouldnt be impressed. 330rwkw from -5's is nothing. They are a 380-400rwkw combination mate.

330rwkw they are asleep, and the wrong turbo choice.

[GTScotT]

I and a friend are seeing a similar issue with a pair of 2510s on a 32R. Half a bar before 3000 is a piece of piss but it wont start building serious boost till close to 5000.

T-Rex do you have cam gears in yours or no gears? What cams too etc? I find it very strange the two cars suffer from the same problem.

I am also (semi) encouraging my mate to swap to a single, while I dont want him to fork the cash I also think the twin setup is easily flawed by the smallest of issues. In this case its only going 302rwkw where as he could attain the same figure from a 3076 and possibly have a lot of action a lot sooner.

Personally I am also tossing up now between a 35R and a 3076, I have previously run a 3076 for a brief period of time on my RB25 which was not laggy at all. Best description for delivery was like a big T28 on an SR20. Now I am contemplating how to get above 350rwkw without the sacrifice of too much response. The 35R IS the go but just how much response will be sacrificed I dont know.. As mentioned above a thought would be a 3040 with TS 1.06 rear housing. I have considered this setup put together with a high rev limit and a goal of 350rwkw MAX. Yet as stated.. the ATP housings leave some to be desired, a cast that could use some work and the fact its only really a T3 flange despite being TS.

All in all it seems difficult to track down the right info on these housings, I would want to see if the 35R is available in a good T4 TS housing as that may be the key to getting the power AND the delivery out of a sub 3L motor.

[DR 32R]

All in all it seems difficult to track down the right info on these housings, I would want to see if the 35R is available in a good T4 TS housing as that may be the key to getting the power AND the delivery out of a sub 3L motor.

The answer may be in tracking down a twin scroll set up in the 35 housing side. I'm seeing if this can happen.

[JonnoHR31]

the ATP housings leave some to be desired, a cast that could use some work and the fact its only really a T3 flange despite being TS.

All in all it seems difficult to track down the right info on these housings, I would want to see if the 35R is available in a good T4 TS housing as that may be the key to getting the power AND the delivery out of a sub 3L motor.

they're available in T4 aswell

http://www.atpturbo.com/mm5/merchant.mvc?S...tegory_Code=GTH

They are a little shitty quality wise but its nothing you couldnt fix up before fitting if you were keen. it'd be nice if garrett offered such a housing but for whatever reason ATP is the only one i've found who does.

Before fitting one tho as a minimum you need to grind the housing where the nuts sit, otherwise they dont fit, make sure the housing bolts dont potrude into the scrolls and cut them if they do and idealy fix up the exit path and make it like the garrett housings. also make sure you have the housings rotated and all the lines properly fitted before fitting it to a low mount manifold as it borders on impossible once its on there.

[T-Rex]

Stock cams and has cam gears making 330rwkw on 21psi according to dyno graph i got when i bought the car. I really do believe there is a exhaust leak as i do often get fumes in the cabin! I love my car but at its age (94 GTR) i think almost every wearing part needs replacing lol. I have replaced 21 coolant lines so far, i didn't know they had 21 coolant lines..