<VV> Draw through Turbo's

[FrankDuVal]

My 1938 Supercharged Graham Model 97 (stock) draws through the Marvel 
Schebler carburetor.

Frank DuVal

On 3/22/2020 2:31 PM, kevin nash via VirtualVairs wrote:
>
>   Hugo- no the Spyder is not unique to use a draw through carburetor set-up!! not even close! In the early days of turbocharging, it was way more common to use a draw through arrangement on carbureted turbo's... the Olds jetfire, the late 70's buick grand national(?)
> numerous japanese makes in the early 80's also did it this way. One of the quirks of this set-up is the compressor has to have a special seal on it that will prevent lubricating oil from getting sucked into the intake when the throttle is closed, and because this draw through configuration used to be so common, Garret turbo's in particular, can be had with this type of seal. The advantage of that seal is that it is tough, can be used on anything blow through or not, the disadvantage is that it has a bit more drag.
> Although draw throughs would "seem" to not be the best way to turbo an engine, they do have some neat advantages... harder (nearly impossible) to send one into a surge, at least for the same conditions this usually happens on a blow through. Draw throughs tend to run cooler at part throttle/light loads than blow throughs do. It is the easiest, simplest way to get a carb to work, as the carb is always sensing vacuum. Theres no weird airflow changes being caused by blade angle on draw throughs either... I've seen a couple of youtube video's that test airflow variations to individual cylinders at various blade angles, and it is pretty amazing as to how large these variations can be. One test shows some cylinders down 50% on airflow compared to another at part throttle, and basically no variation at wide open throttle!! With blow throughs, if the butterfly is big enough to never be a significant restriction at wide open throttle and full boost, it is also big enough to cause significant
>   drivability problems out of boost, but on a draw though, they can be sized large enough to never be a restriction (if using EFI) and not have any drivability issues at all.
> Carbed blow throughs tend to have massive flow losses even when the carb is sized for the
> engine... one account that I read about, a guy bothered to test the manifold pressure at full boost before and after the carb... he was getting 28 psi before the carb, and 20psi after!!
> Kevin Nash
> Draw through EFI daily driver, max boost tested=22psi