Why are some turbos wastegated, others not?

[AMink]

I have been looking aroung at different turbos and housings and have noticed that some have no wastegate. How do they keep from overboosting? What are the pluses and minuses of wastegates or no wastegates? Thank you!

 

[trqmnstr]

You have to purchase an external wastegate for the turbos that don't come with one. If you had no wastegate the turbo would `spool up till it blows up` I don't think it would last very long and you would definitely be overboosting if you layed into it. But then again, I'm no expert. I could be wrong.

 

[Bob Wagner]

I would say the number one reason is cost, just look at the cost of turbo's these days.



Wastegated version are available in most cases for added dollars .





Blow off valve arent much cheaper and are loud too.

 

[tgbol]

On engines with non waste gated turbos the turbo is sized so that within the design perameters it can not be oversped. This usually means a larger turbo than what can actually needed and slow wind up. The waste gate allows a smaller turbo to build boost sooner then the waste gate will open and limit the boost on the top end. It also allows closer control of boost

 

[AMink]

So on a non wastedgated housing, you must put an external wastegate? I was wondering because the non wastegated ones are $$$ less expensive.

 

[paccool]

No, you do not have to put an external wastegate on all turbo. Like TGBol said, the housing are sized to keep from over spooling the turbo. None of the first gen trucks came with a wastegate. Dodge/Cumminns, in an attempt to eliminate turbo lag, put smaller exhaust housings on the second gen trucks and these had waste gates to prevent overspooling.



I have a modified HX-35 on my 93 with a nonwastegated 16 housing. I'm running about 35 PSI boost. Boost is also controlled with fuel so that is a way to also control the turbos. If I were to install a 12 housing, it would probably have to be wastegated to control things. The smaller the exhaust housing, the faster the turbo will build boost. This is not even addressing the compressor housing guys so don't beat me up too bad!

 

[nickleinonen]

would say the number one reason is cost, just look at the cost of turbo's these days.



Wastegated version are available in most cases for added dollars .





Blow off valve arent much cheaper and are loud too.

and a blow off valve does nothing to control shaft speed. . if it were to pop prematurely, it would cause a near instant overspeed of the turbocharger [no load on compressor side, exhaust side will speed up very quickly

 

[KLockliear]

Tgbol got it right. If the turbo is sized properly for the application, a wastegate is not needed. Actually, a non-wastegated turbo is more efficient, as it's not bypassing the exhaust volume and heat around the turbine.



It's harder to build one like that though, especially with the adjustable boxes that can change the HP 100+.

 

[TWilkening]

Another point would be concerning off-road/ag equipment. Most of these engines are ran at rated speed all the time, and the turbo is matched to perform best at this speed.