math is bad...

 

Off TiaL's website: http://www.tialsport.com/questions_&_answers.htm

"Flow capacity. Contrary to popular belief, larger higher HP applications do not necessarily require the largest wastegate available. The lower the boost pressure you are gunning for the larger your wastegate needs to be. An engine/turbo combination that is set to 25+psi has a smaller wastegate flow requirement than the same application set to 7 psi. This is because the wastegate is used to lower the boost not raise it, the lower the boost pressure is set the more flow the wastegate must allow."

 

VaporTrail,
BIG thumbs-up for this thread!
This is the kind of question that seems so simple, yet very few actually know the answer(s). BTW, I'm not one of those few. Still listening and waiting for more responses.
Here's another turbo brain stumper that I can't find a good answer to:
https://honda-tech.com/zerothread?id=237369

 

You know now that I think of it that way, it makes total sense Figure since a high boost pressure engine is going to need more exhaust energy to spin the turbine and therefore won't need to bypass as much. So, that would also mean an engine set-up for dual purpose like a high pressure track/low pressure street would benefit from the larger wastegate. Specifically for it's street duty. Hmm, good thing I got that 40mm

 

Good point. Trying to hold lower boost will require a bigger waste gate opening. So, basically, bypassing large cfm's of exhaust requires a bigger wastegate either for larger engines or lower boost control.

What about the "sweep area" of the wastegate? I don't care too mucha bout the diameter, but how much it can open. i.e. if the 35mm can open a max of 2 mm and the 40mm can open a max of 1 mm, the 35mm has a more effective opening area. Do the wastegate manu's give the spec of the sweep area? On internals its easy to maesure, you just yank on the arm and pull out the caliper.

Anybody?

Randy

 

Gregg Jones at TiAL emailed me this when I asked him a question about wastegate sizing. Thought some of you guys might find it useful.

"There is a misunderstanding in the market place on how to size a wastegate.
You can not size a wastegate by HP rating. The information needed for this
is generally not available in the aftermarket. Primarily the wastegate size
is dependant on turbo build, engine size, and lowest boost level that will
be used. The application of the wastegate or fitment is often not optimized.
The 35 mm wastegate may be able to regulate your turbo at 10 psi and higher
if the flow path to and from the wastegate is not restricted. If you want to
go lower to say 5 psi it may not work. To get a know exact requirements
before starting would require turbo flow data for both compressor and
turbine in the specific A/R housings that are being used. All though some
compressor info is available the turbine is generally not. Other factors are
complete system flow capacity. Intake to turbo, intercooler and plumbing,
engine efficiency, exhaust manifold, exhaust flow after the turbo and
wastegate. If all of this info were available I can confidently select the
proper size gate. As you can see each turbo system is different and the same
turbo and wastegate may work in one installation but not on the next.
Experience or trial and error is used most time and so the wastegate is
often oversized to play it safe."