Throttle body before the turbo?

[240hoke]

I was wondering what the advantages and disadvantages there are to mounting the throttle body to the turbo inlet. I saw some pics of a setup like this in corky's book and made me curious. It would make for a really clean looking engine bay and make custom manifold building alot easier. Anyway I thought it was neat but was wondering why is is not done more, or really at all?

 

-Austin

[Brad-ManQ45]

Biggest reason I can think of is that with it before the turbo, the turbo will slow down too much when you close the throttle.

 

With a CBPV (Compressor ByPass Valve) and the TB after the turbo, the air stacked up after a run and closiing the throttle gets re-routed to in front of the turbo, keeping it spinning.

 

You would lose that and the turbo would slow much more. Plus, I would suspect that throttle response would not be as crisp on initial tip-in.

[Tony D]

actually, the throttle plate in front of the compressor would lead to hellacious surge problems on lift-throttle if you throttle it shut while the thing was still under boost.

Thisis a phenomenon that occurs in centrufugal air compressors in industrial applications, and they use very sophisticated blowoff schemes to keep the throttled inlet of the turbo away from the surge line.

Butthen again, that is for fixed-speed turbines.

On an automotive application, the variable speed nature would probably negate the surge problem.

With the throttle shut, the compressor wheel would be playing in a vacuum (or near to it) and with no load across the compressor, should coast down slower that it would fighting boost before the blowoff occurs to the front of the turbine (the way most people set it up). With a properly adjusted compressor bypass valve, even a slight lifting of the throttle will lift the bypass---and no slowing occurs.

Basically, I think the only setup with a throttled turbocharger inlet would be on diesel engines, and that is for shutdown/emergency shutdown.

[Guest obso]

dodges turbo I engines that went into the shelbys, daytonas, and turbo omni's were set up this way with the TB connected to the turbo inlet and the outlet connected to the intake manifold. not shure of the advantages/disadvantages of it tho.

[280zedx]

not to change the topic but...what are the differences in throttle body location in a supercharger application? All stock roots supercharger setups have the TB in front due to the fact that the SC bolts directly to the intake.

What is the difference between this and a turbo setup?

And if there is none then can the throttle body be between the supercharger and intake (like a stock turbo TB setup)?

I'm sure it would have something to do with the bypass or blowoff location. Anybody know?

[Guest obso]

it doesnt matter as much in SC applications simply because a superchargers speed is solely determined by engine rpm vs. a turbo which is effected by several different factors. that being said im just going by the mechanical factors of it i dont have that much expierence with SC's so someone else may know different.

[Ben]

Draw-through turbocharging works just as well as blow-through.

 

Things to bear in mind:

Throttle response is VERY dull if you draw-through & intercool (been there in my old L24T), the inlet tract was too long.

You must use a carbon seal in the compressor to avoid oil being drawn into the engine under vacuum conditions.

Turbo spin-down is limited on shifts, as the engine consumes all the compressed charge.

By fitting all vacuum signal ports between the throttle plate & the compressor, you can remove the requirement for check-valves etc in various pneumatic lines (the lines wont see any boost).

An alternative to a BOV in a blow-through app, is to fit a second synchronised throttle plate pre-compressor - effectively this gives you the best of both worlds. The response of blow-through & the compressor speed retention of draw-through. without a BOV buggering up your MAS (if fitted)