I was recently reading an old feature on a turbo Corvette that GM engineers put together in the late 70s. The throttle body was mounted ahead of the turbo and the article mentioned this was done to reduce turbo lag as the turbo outlet would never have closed throttle blades choking off flow. I assume the convenience of leaving the throttle body in the stock location is one reason why just about everyone uses a turbo to blow through the throttle body but would there be much benefit to setting it up as GM did? Pic below.
That's not a draw-through setup. A draw-through literally passes the fuel through the turbo. I'm not sure what the term for that design would be, but it doesn't seem to out of the ordinary to me.
The below pics are for a draw-through setup
In reply to Mr_Asa :
Yeah, I know it's not the same as a draw through carb set up but didn't know how else to describe it. All the turbo conversions I've seen have the throttle body on the outlet side of the turbo not the inlet. Just wondering how well it would work.
So, reaching back to my FSAE days, and when we finally ran a turbo on our one-lunger because SAE changed the rules: throttle response can suffer a bit if the throttle is before the turbo, you don't necessarily need a blow off valve if the throttle plate is before the turbo, and if the throttle is before the turbo you can potentially get oil sucked from the bearings when the throttle plate closes.
Lastly I think, but am not sure, that going from full boost to no throttle at all will put a huge amount of strain on the turbine blade/shaft.
Also, Chrysler did this on the early turbo 2.2's (84-87) and they had to be careful of vacuum leaks from the throttle body back.
They also had to be scrap a more ideal intake design because of crash concerns where the intake could break and cause a runaway situation.
With modern ECUs, the run away issue is lessened considerably, but still not ideal.
There's also the challenge of adding an intercooler as that increases the amount of intake tubing that is now under vacuum and boost.
Also running gasoline through the turbo requires different design and can make starting /idle more difficult in the case of a TBI or similar setup.
I guess it's good because you don't have to have a boost proof throttle body.
Mr_Asa said:
That's not a draw-through setup. A draw-through literally passes the fuel through the turbo. I'm not sure what the term for that design would be, but it doesn't seem to out of the ordinary to me.
The below pics are for a draw-through setup
I had that exact same turbo setup on the 250ci I6 in my '70 Chevelle. Originally off an '81 Trans Am.
Thanks for the replies, definitely seems like more cons than pros.
Turbos were not designed to have vacuum applied to the compressor.
Some work needs to be done to a standard turbo in the compressor oil seal area to keep it from sucking oil and to keep gas out of the oil.
The only benefit I can see from a draw through is mixture homogenization improving fuel distribution.
The detractors are many and then there is the safety issues around increasing the "wetted" area, you're going to need a plumber if it backfires!
Turbo sizing and wheel design has more to do with "turbo lag" than which side of the air valve the compressor is on.
Lota of OEMs did draw through setups, both fuel injected and carbureted.
Heck, some racing vehicles too.
The more volume there is between the throttle plate and the intake valves, the soggier throttle response is, is the main downside. And you need turbo seals meant to handle a vacuum, turbo oil seals are normally a labyrinth style seal that can't handle pressure difference too well.
