Gt3540 .82

[R34NRG]

got a 44mm atm but for some reason (most likely manifold design or something else) is spiking up to 20psi with no gate.

a 44MM SHOULD be big enough rite?

spoke to kyle he thinks i should upgrade to a 60mm and redesign the manifold.

if a 40mm is big enough ill just modify the manifold rather then spending another 800bux on a new gate.

HELP PLZZZZZZ

[unique1]

my mate has the same exhuast manifold as you and gt3540 .82 and with no boost controller (just gate pressure) he can only get as low as 23-24psi, not ideal in anyones language if u ask me, also heard a few others who have same issues and cant get boost down below that. One of the tuners told me they weld a wastegate pipe straight off the exhauast housing to solve it and it works fine.

Edited April 22, 2008 by unique1

[RB120WHY]

I had a RB20 With 38mm gate with GT35r 0.63 rear and had no dramas from 10psi to 22psi.

[dano4127]

I had a RB20 With 38mm gate with GT35r 0.63 rear and had no dramas from 10psi to 22psi.

Would the small housing have much to do with that?

[RB120WHY]

Would the small housing have much to do with that?

I don't know. I was just posting my experience with slightly smaller turbo and gate on smaller engine. I had a nasty home grown manifold slapped together. So i guess my info is not relevant.

[R34NRG]

the amount of air the rb30 can flow over the rb20 is so much its pointless to even compare.

theres a r33 2.5L running the exactly same manifold, exact turbo and exhaust housing. almost identical. and it runs fine with a 44mm. but mine wont.

just dont understand how it could be to small when Xr6Ts are 4L and run internal gates and have no issue.

[R34GTFOUR]

just dont understand how it could be to small when Xr6Ts are 4L and run internal gates and have no issue.

and thats were the answers are...

whats different between the your turbo and the xr6 gt35r?

First the exhaust housing is larger, but thats mainly becuase its a 4L motor and its obviously going to pump more air and the last thing they want is the turbo to "choke" which would cause boost to DROP off. So if you housing was too small, you wouldnt have boost creep, but it would drop off in boost at the higher rpm mark so that cant be marked off as a problem

Secondly is obviously the fords run a internal wastegate version. At a stock level they dont seem to have much of a problem holding boost, but if you talk to some of the boys playing with these cars its quite common for them to port the wastegate out abit and stick a bigger wastegate "flapper" on and they hold boost fine after that. So with the internal wastegate setup they dont run into a problem of having the wastegate pipe in the wrong part of the manifold, or not in the best location on the collector since the whole thing is done in the actual exhaust housing itself, which leads to the only logical answer to your problem, it has to be the wastegate pipe location on the manifold.

Even without a wastegate wat so ever, i would still expect to see the turbo spool and make a psi or 2 boost, but no where near what your making. I dont see how a bigger wastegate will fix anything because your making 13psi (according to the dyno graph) with out any wastegate at all, the system is having trouble releasing the exhaust gases on the manifold side of things.

I hope you get this sorted cause im going to run the exact same manifold/turbo/wastegate setup as you, and i dont want these problems

Edited April 22, 2008 by R34GTFOUR

[Roy]

Do you have a picture of the manifold and how the wastegate is connected to the collector. Have seen a few manifolds that have poor boost modulation because of the way the wastegate pipe is connected to the manifold.

[paulr33]

Do you have a picture of the manifold and how the wastegate is connected to the collector. Have seen a few manifolds that have poor boost modulation because of the way the wastegate pipe is connected to the manifold.

http://www.skylinesaustralia.com/forums/in...t&id=155165

[Sydneykid]

There is a long thread on how to size wastegate correctly, here is the abreviated version.....

I have pretty good success using this formula to determine external wastegate sizes;

Airflow in lbs per minute = diameter of wastegate in mm X boost correction factor

So let's apply it to your car;

300 rwkw = 480 bhp

480 bhp = 44 lbs of airflow = 44 mm wastegate

Now if you want to run 19 psi, then that's the right size wastegate.

But we need to apply the boost correction....

My experience indicates that to get 300 rwkw out of a GT3040 you would need to run around 1.5 bar (22psi). So using the formula...

44 / 22 X 19 = 38 mm.

For those who haven't read the thread..............

http://www.skylinesaustralia.com/forums/sh...ead.php?t=43638

To apply the formula to this example I need some more information, what power it is at right now and the final power target?

Quite often I get guys who want to use a lower boost limit for running in than their final power target. This dual requirement can cause issues with the wastegate sizing, they need a larger than desirable one to bleed off enough exhaust for the running in boost level.

Cheers

Gary

[VB-]

car is looking to make a bit over 350 at ~20psi, maybe a lil bit more. i think this thread sorta came about because kyle (6boost guy) said he needs a bigger gate, even though the car was making ~13psi @ ~5krpm with no gate on it what so ever....

but for the purpose of this thread, do you think the 44mm will be big enough? i told him it would be lol, so dont make me look like a c*nt

[Sydneykid]

Airflow in lbs per minute = diameter of wastegate in mm X boost correction factor

350 rwkw = 550 bhp

550 bhp = 55 lbs of airflow = 55 mm wastegate

If you want to run 19 psi, then that's the right size wastegate.

But my experience has been that to get 350 rwkw out of a GT3540 you would need to run around 1.5 bar (22psi).

So we need to apply the boost correction, using the formula.

55 / 22 X 19 = 48 mm

So the 44 mm wastegate will be a bit too small even at 22 psi, let alone your optimistic 20 psi target. I think 48 mm is more like it.

Cheers

Gary

[Roy]

The fact that the car has no wastegate on it...you would think that the thing would struggle to make boost. Air is bloody lazy and will take the path of least resistance. So the fact that it makes 13psi with an open pipe...well i think that hints that the way the wastegate is tied into the collector is the issue.

Cant really see enough from the pic that Paul has taken. Surely putting a bigger wastegate on it is a band aid to the bigger progblem?

[DCIEVE]

this is the manifold in question

the turbo/manifold/gate is sold as a package. you would expect after so many people having the exact same problem they would change the design, or stop selling the package untill the problems are sorted out

my advice has been to modify the wastegate pipe off the manifold, fairly expensive exercise when everything has been fabricated to suit already

Edited April 26, 2008 by DCIEVE

[juggernaut1]

If its the manifold I'm thinking of there is a central spire inside - the bottom of the wastegate port needs to be at least level to the top of that spire and preferably higher but obviously the flange dicatates how high you can move the outlet port.

Which is why people are welding the wastegate port off the turbine housing.

[VB-]

well manifold has been modified now, no word on results yet

[msnismo]

:dave here..

yes the manifold is the issue.

6boost manifolds while almost as perfect as you can get for flow into the turbo, they are the worst for wastegate integration, as in all the gasses are aimed straight at the turbine with no turbulance. therefor its very hard for the air to make a 90 degree turn to a wastegate. and hence boost creep issues..

put the same wastegate on a generic one and its gonna hold boost rock steady because of the turbulance in the collector allows an easy path to the gate..

the only way you could fix the issue is to install an extra wastegate pipe into the collector and join them into the single wastegate. not hard to do with it on the bench.

perhaps putting a bigger gate on could fix it but its not the wastegates fault, rather the manifold.

oh, ps. the more boost you want the smaller the wastegate!!! (more air is going thru the turbo to create boost. and the more pressure in the manifold/turbine to make it easier to regulate... instead of relying on aerodynamics in the manifold for the wastegate, it is more of a pop off valve. if you get my point..

cheers

[VB-]

nothing to see here

Edited April 26, 2008 by VB-

[Sydneykid]

The fact that the car has no wastegate on it...you would think that the thing would struggle to make boost. Air is bloody lazy and will take the path of least resistance. So the fact that it makes 13psi with an open pipe...well i think that hints that the way the wastegate is tied into the collector is the issue.

Cant really see enough from the pic that Paul has taken. Surely putting a bigger wastegate on it is a band aid to the bigger progblem?

On a comparison basis, 13 psi with an open pipe and 20 psi with the wastegate fitted would seem to me to indicate that the wastegate isn't flowing enough. If the wastegate was of sufficient size then there should only be 1 or 2 psi difference.

As an asside, I have yet to find an externally gated exhaust manifold that faciliates zero boost. Anything decent accentuates the flow to the turbine, so some boost is always produced.

Cheers

Gary

[Roy]

On a comparison basis, 13 psi with an open pipe and 20 psi with the wastegate fitted would seem to me to indicate that the wastegate isn't flowing enough. If the wastegate was of sufficient size then there should only be 1 or 2 psi difference.

As an asside, I have yet to find an externally gated exhaust manifold that faciliates zero boost. Anything decent accentuates the flow to the turbine, so some boost is always produced.

Cheers

Gary

Or it simply has the wrong spring installed