external wastegate sizes....

[tridentt150v]

Your doing it right, they are wrong or mixing rw and crank hp. 300rwkw is 400rwhp.

For a 3076 and using SK's formula:

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 20 psi, then that's the right size wastegate.

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

To get 300 rwkw out of a GT3076 you would need to run around 18 psi. So using the formula...

44 /20 X 18 = 39.6 mm. So a 40mm watsegate is required.

I have to admit that I'm guessing a bit with the boost correction, but its not to far of [i'm running 16-17 psi and saw 292].

[vaccine]

bump fantastic thread!

What i dont have my head around is how a friend has an internally gated gt35R making 320awk+. The internally gate flapper is way way smaller yet can control enough gas for over 300kw at all 4 wheels. i am hopefully going to get close to 300kw @ all 4 with my gt3040, with 1.06 rear and .7 front. Boost wont be an issue once the motor is rebuilt. Just trying to work out what sized gate to get. another friend has a turbosmart 38mm gate i can get cheap second-hand, but was advised a Tial 44mm gate by Bill@ATS in adelaide.

[SirRacer]

SydneyKid isnt often wrong on things, however quite a few of us have has issues with various turbo manifolds and the way that the wastegates respond to that manifold.

My manifold is similar to a 6boost manifold and on a 3540 .82 running over 20psi on a 44mm tial gate i cant hold boost. Throw on a 50mm wastegate however (i havent done but others have) and the problem goes away.

This seems to be quite a common issue. I think the theor, the bigger is better on RB's with efficient manifolds is probably the way to go. If if could do it again, id perhaps think of going 2x 38's

[PSI Parts]

Great thread.

SK is using the factor of 1.2 to convert from hp to bhp (brake horsepower).

Thus 300rwkw = 402rwhp = 480 bhp

Just to rehash the formula in another way:

A = power figure in rwkw

B = A * 1.3 * 1.2 = power figure in bhp

Wastegate size in mm = B / 11

To confirm wastegate size we apply the boost correction by using the following:

C = wastegate size in mm

D = intended boost pressure in PSI

E = D / 14.5 = boost pressure in bar

Confirm = wastegate size / E * 1.4

The only problem I have is where the figure of 1.4 comes from, I assumed atmospheric pressure however thats only 1.01325. Also there has been various figures in PSI used (19,20) As 1.4bar = 20.31 I'm a little stumped.

Just on a side note, I'm keen to hear people's thoughts on mounting the wastegate directly to the exhaust housing as done by ETM, as they claim it improves wastegate efficiency and stabilises boost pressure much better.

[Zaver]

Well reading this thread i understood most of it, but just to confirm before i buy a wastegate for my application i wanted to be sure, im getting a GTX3076r 0.82 running on a unopened RB25 NEO will be running around 18-20psi to get 300KW, So would a 44-45mm Wastegate be good?? Im running stock manifold.. Later down the road i might want to push 340KW with race fuel, i dont know what psi ill need..

Thanks guyz!!

[R31Nismoid]

Did you read before posting?

Your doing it right, they are wrong or mixing rw and crank hp. 300rwkw is 400rwhp.

For a 3076 and using SK's formula:

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 20 psi, then that's the right size wastegate.

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

To get 300 rwkw out of a GT3076 you would need to run around 18 psi. So using the formula...

44 /20 X 18 = 39.6 mm. So a 40mm watsegate is required.

I have to admit that I'm guessing a bit with the boost correction, but its not to far of [i'm running 16-17 psi and saw 292].