Lexus IS Forum banner

1 - 20 of 24 Posts

·
Registered
Joined
·
1,696 Posts
Discussion Starter #1
How do i determine what size of wastegate to use? How would a 44mm wastegate perform differently vs 38mm wastegate with same 7psi springs?

Thanks~
 

·
Registered
Joined
·
5,384 Posts
assuming both work better boost control
 

·
Registered
Joined
·
1,696 Posts
Discussion Starter #3
Is there such thing as too big of a wastegate? If not then i guess i'll go for the bigger ones... ;)
 

·
Banned
Joined
·
1,901 Posts
wastegate size is going to depend more on the turbo, and the boost level you want than anything. if you have a wastegate that is too small, it will cause boost creep. Meaning it physically won't be big enough to bypass enough exhaust gas to keep the turbo at the boost level you want. The exhaust will always follow the path of least resistance, if that happens to be through the turbine wheel instead of the wastegate, you will run more boost than you want to. If you go too large there could potentially be problems there as well. if the wastegate is allowing more exhaust to bypass the turbo than needed it would be tough to hold steady boost pressure.

I'm not too sure about your set up, but if your building a mild street set up, 38mm would be good. If your going for more than 500hp range, then go for something larger.
 

·
Registered
Joined
·
1,696 Posts
Discussion Starter #6
My setup is going to be anything around 300whp-350whp using a GT35R turbo. I'm guessing 38mm is enough? BTW this is going to be all custom so the wastegate flange doesn't really matter.
 

·
Registered
Joined
·
1,696 Posts
Discussion Starter #9
So should i go with 38mm or 40mm Tial? My car is going to be tracked often in the summer time...
 

·
Registered
Joined
·
1,833 Posts
fstrnldr said:
wastegate size is going to depend more on the turbo, and the boost level you want than anything. if you have a wastegate that is too small, it will cause boost creep. Meaning it physically won't be big enough to bypass enough exhaust gas to keep the turbo at the boost level you want. The exhaust will always follow the path of least resistance, if that happens to be through the turbine wheel instead of the wastegate, you will run more boost than you want to. If you go too large there could potentially be problems there as well. if the wastegate is allowing more exhaust to bypass the turbo than needed it would be tough to hold steady boost pressure.

I'm not too sure about your set up, but if your building a mild street set up, 38mm would be good. If your going for more than 500hp range, then go for something larger.
Couldn't have said it better myself. + rep!
 

·
Registered
Joined
·
5,384 Posts
LexIS307 said:
witht your predicted output on 300-350rwhp you'll be fine with the 38, can always upgrade if need be
Id go bigger unless you have a really well designed mani you may creep with a 38. Id go the biggest you can fit, I dont know of an down side to a oversized WG mine is 60mm for reference. Maybe on a small engine but our engine turbo wise is pretty large. But really the spring in it controls your boost levels.
 

·
Registered
Joined
·
5,670 Posts
Sentinel said:
Id go bigger unless you have a really well designed mani you may creep with a 38. Id go the biggest you can fit, I dont know of an down side to a oversized WG mine is 60mm for reference. Maybe on a small engine but our engine turbo wise is pretty large. But really the spring in it controls your boost levels.
60mm wow kinda big for such low power...nadim's monster uses close to a 44+ mm for his 1k monster....unless im mistaken... anyways best of luck to 86b, and sentienl ur just too cool for school! I lov u!
 

·
Registered
Joined
·
5,384 Posts
LOL I didnt need a 60mm I had a 46 but I boost crept badly so I had part of the mani redisgned and figured I might as well up the size just in case.
 

·
Registered
Joined
·
1,833 Posts
38 or 40mm. No need to for too large of a wastegate on that low of a power app.
 

·
Registered
Joined
·
5,384 Posts
its all about the mani a 38 "should" be enough
 

·
Banned
Joined
·
1,901 Posts
djlutchi said:
Couldn't have said it better myself. + rep!

thanks! :)

Sentinel: what kind of set up are you running w/ the 60mm? what kind of boost control etc? If there is a huge thread or something i missed on your car point me in the right direction, i don't get to spend as much time as i would like on here.
 

·
Registered
Joined
·
287 Posts
The boost creep will also depend on the way you route the wastegate... As fstrnldr previously stated, the exhaust gases will follow the path of least resistance. I originally had a 38mm wastegate... Then upgraded to a racegate (42mm I think), when I upgraded my turbo to a GT35R. I originally had it setup to vent into the atmosphere. This setup worked great... Except it was loud as hell... I really enjoyed scaring the hell out of those annoying bicyclist riding in the middle of the road as I passed them... But, it proved to be too loud for daily driving on the street, as I am always getting on the throttle. I then took the car down and had the wastegate recirculated into the exhaust system. It made a huge difference in the noise output... Now, I get a slight boost creep. I went with 2" tubing from the wastegate to the exhaust (a 3" PFS catback, no cats), using mandrel bends, no kinks, etc etc. The whole setup was designed to prevent boost creep. Keep this in mind and if you do decide to recirculate the wastegate, I would go with a slightly larger wastegate.
 
1 - 20 of 24 Posts
Top