Selecting the correct size wastegate

[Wez]

Hey All,

 

I am trying to decide which size wastegate to go for, the turbo is likely to be a BW unit which will be bolted onto an Arnout cast manifold. I have just measured the manifold wastegate port and its 50mm.

 

Looking at the Tial range of wastegates there are a number of options ranging from 38mm up to 60mm with vband fitment.

 

MVS - 38mm

MVR - 44mm (replacement for V44)

V60 - 60mm

 

With my modest power level I am thinking the 38mm MVS may be sufficient, what are peoples thoughts?

 

http://www.tialsport.com/prod_wg.htm

[David Reid]

My Borg warner flows so much air I can't get the boost below 1.6 bar through 38mm pipework ( I have an hks 60 mm gate but mounted via 38mm pipework.)

 

I wouldn't go smaller than 50mm unless you want to run over 1.5 bar all the time and suffer boost creep

[Wez]

Looking at the 44mm unit

[Rinus]

Hi,

got a 35mm wastegate and a turbonetics castmanifold with a gt4082jb,

manifod was 32mm but ported this to 35mm...

when controller is off I run 0,9bar...

straight to inlet manifold it made 0,4 bar!

[johnny g]

Wez, I had an F46 on the MR2 (3.4ltr) engine, with a GT4094R - and had no boost control issue even as low as 1bar

[heckler]

I have, well due to fit the Tial MVR 44 on to my cast manifold... Which is probably more than suitable for my 550 Bhp

[Chris Wilson]

The point of wastegates is to divert gas around the turbine,

thus reducing the power transferred to the compressor. The key to good

wastegate control is proper sizing and calibration. Just slapping on a

wastegate with the "X psi" spring is a recipe for failure. If you're

doing a proper match (granted that's hard without turbine maps that show

shaft RPM), then you can compute the percentage of the exhaust flow that

has to be diverted around the turbine. From there you have to estimate a

discharge coefficient of the wastegate (at various openings) to

determine how much opening is required. A correctly sized wastegate will

have sufficient high end flow as well as good movement resolution. If

you're seeing a lot of boost creep, you either need to go to a larger

A/R or a larger wastegate. The problem with an oversized wastegate is

that it can dump too aggressively at lower amounts of travel. The

turbine may then not be able to power the compressor at higher flows

and/or boost levels, and you'll see the torque drop off. Logged data of

wastegate travel is a huge help in determining proper wastegate sizing

and control. Proper wastegate control is key to making a good,

engineered powerband.

 

If you don't log something, you're just guessing! DATA is the key!

[Wez]

Interesting Chris, I wonder if the 60mm unit I am using at the moment is part of the reason for my torque dropping, the size of the turbo would also affect this I know, it's only small

[Rinus]

This is also an interesting link;

http://www.fftec.com/WastegateSizing.html