Engine/Transmission (1994 - 1998) Boost Question

[JGheen]

Ok,



I got this boost thing down pretty good but I am confused about something. Obviously, the wastegate prevents the turbo from over boosting and spooling too fast that it destroys itself. So, why does one get more boost when you throw more fuel into it?? My understanding is becasue it is a denser exhaust gas that makes the turbo spin faster. But even if it is a denser gas, the wastegate should still open at the same time and give you the same peak boost, right?? Or is it because when one goes to a bigger turbine housing, the larger housing makes the wheel spin faster, hence more boost?? I think I am on the right train of thought, can someone confirm?



Also, if I am correct, how much boost would one get with a non-wastegated 16cm housing?? I would think it would spin into oblivion without the wastegate and destroy itself, but it doesn't and I am confused as to why.



I am asking because when I went to my #10 plate I got about 2-4 more # of peak boost(38-40 psi total), not complaining just don't completely understand why. I am running the 14cm wastegated housing and am thinking of going to the 16cm housing to move more air for bigger injectors, 370s to be exact. Just need some info and advice.



Thanks, Joe

 

[mikel]

As I understand it, the bigger housing causes the turbo to spin slower, not faster. This is why if all else is equal, you will see lower boost going from a given size housing to a larger housing.



I went from a 12cm housing that I had disabled the wastegate on to a non wastegated 16cm housing and lost 4-6 psi.



You get more boost when you throw more fuel into it because ultimately fuel is what drives the turbo. If you burn more fuel you are making more energy, some of that energy gets turned into exhaust and the turbo captures some of the exhaust energy so if you are making more exhaust by burning more fuel then you'll make more boost.



The wastegate will still open whenever it is set to, but you can only bypass so much exhaust, so even if the wastegate is open if you are burning enough fuel you'll still see slightly higher boost.

Also, if I am correct, how much boost would one get with a non-wastegated 16cm housing?? I would think it would spin into oblivion without the wastegate and destroy itself, but it doesn't and I am confused as to why.

It will. If you put enough fuel into the engine the turbo can and will grenade. Several members have posted pictures of holes in their fenders and hoods from the debris associated with a disintegrating turbo.

I am running the 14cm wastegated housing and am thinking of going to the 16cm housing to move more air for bigger injectors, 370s to be exact. Just need some info and advice.

I doubt that a 16cm housing is going to help much. You don't say if you're still running a hx-35, but if you are then I'd think you need to step up to something bigger.

 

[JGheen]

Thanks!



I am thinking correctly about things. I definatley understand about the more boost from more fuel, and the wastegate is probably opening but I am moving so much exhaust through the turbine that it is causing the turbo to build that massive amount of boost.



I am still running the HX-35 and soon to have a buddy of mine that owns a turbo rebuilding shop make it a hybrid HX-35/40, so we'll see what that does.



If I go to a bigger turbo, such as an HX-40, what is an ideal turbine size to run with that??



Thanks again for the clarifcation. Oo.

 

[Rams-n-Hogs]

You'll like what that hybrid hx-35/40 and 370's can do. I'm running a 16 cm non-wastegated on mine. It will still hit 1500* if I'm hammering on it, which is why I don't. But it's there if I need it. It cruises real nice at 70, though. 2-4lbs of boost, 5-600*, and about 20 mpg.



Jim