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Discussion Starter #1
Is there any kind of formula to calculate what size wastegate you would need, as opposed to the "Oh, we're getting creep, we need a bigger WG" method?
And/Or is there any good way to calculate how much exhaust you would need to 'wastegate', depending on different things?

And, do you have better control of wastegating with a bigger WG vs a smaller WG (say a 44mm Tial vs 38mm Tial)?

Thanks.
 

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if your at a lower boost level a 44mm would control it better then a 38. since you will have more excess exhaust that needs flowed away from the turbo.
high boost i think 38mm is fine unless you want dual 44mm for twin scroll which will control the boost very well
 

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I guess this depends VERY much on exhaust manifold design, size of turbo
and size of the exhaust system, doesnt it?
 

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Discussion Starter #6 (Edited)
if your at a lower boost level a 44mm would control it better then a 38. since you will have more excess exhaust that needs flowed away from the turbo.
high boost i think 38mm is fine unless you want dual 44mm for twin scroll which will control the boost very well
What about in a set-up when your using a pretty small (relative to most common setups) turbine and a large compressor (where you NEED to vent a good portion of the exhaust and only a small amount keeps the turbine spinning)?
Like, we'll say maybe 45%+ needs to be gated, how do you calculate how big the WG needs to be?

I guess this depends VERY much on exhaust manifold design, size of turbo
and size of the exhaust system, doesnt it?
Manifold Design (not mine, but mine will be similar, I think):

 

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if the wastegate is connected to every runner like in the picture
this is a good thing. big turbo + small wg + bad manifold + open dp
is more suspect to boost creep than small turbo + big wg + nice manifold + small exhaust
 

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the LARGER your turbine, and the LOWER boost pressure you want to run, the LARGER your WG needs to be.


think about it.

the WG is a bypass valve. it allows exhaust gas to bypass the turbine so the turbine doesnt spin so fast.


so lets say your turbine is HUGE, and its easier for gasses to exit through the turbine than it is for the gas to exit via a waste gate... well its going to creep!

and of course, design plays a huge role.
 

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the LARGER your turbine, and the LOWER boost pressure you want to run, the LARGER your WG needs to be.


think about it.

the WG is a bypass valve. it allows exhaust gas to bypass the turbine so the turbine doesnt spin so fast.


so lets say your turbine is HUGE, and its easier for gasses to exit through the turbine than it is for the gas to exit via a waste gate... well its going to creep!

and of course, design plays a huge role.

Im not disagreeing with you, but I have always thought about it like this: Larger turbined you can get away with smaller wastegate because a lot more exhaust will flow through the turbine to get the wanted pressure. I've never tried back to back testing with the same setup and different housings, and I've never seen anyone other do it, so I dont know if I'm totally wrong, though... :p

But also... Smaller turbine means higher manifold pressure, so the wastegate would flow more cfm at maximum opening than with a larger turbine... meh... idk
 

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Discussion Starter #14
Steinar/danz both sound right from what I've right, but it doesn't make it any easier.

Especially with a F1/Hytech design type header, where people run a >small< turbine and <BIG> compressor (and run wastegate priority to have very fine control over boost pressure). I'm not John @ Hytech the exhaust wizard and I don't have a F1 engineering team to run the numbers, but Borg Warner's calculator somehow take into account engine effeciency/displacement/rpm, pressure ratio, and the Phi curve of a turbine housing, and calculates the percentage of exhaust gas that needs to pass through the wastegate for a certain cfm/power level. What I want to know is HOW to do that math.
 

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Classic Man
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Im not disagreeing with you, but I have always thought about it like this: Larger turbined you can get away with smaller wastegate because a lot more exhaust will flow through the turbine to get the wanted pressure. I've never tried back to back testing with the same setup and different housings, and I've never seen anyone other do it, so I dont know if I'm totally wrong, though... :p

But also... Smaller turbine means higher manifold pressure, so the wastegate would flow more cfm at maximum opening than with a larger turbine... meh... idk


my 38mm works for everything ive ever tried to throw at it. but thats because low boost is for bitches!! haha :bigok:
 
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