<VV> Draw through Turbo's

[Hugo Miller]

Yes, superchargers always suck (as far as I know!). The Spyder was the 
first turbo I ever saw that sucked. In fact it's the only one I ever 
saw, though I understand there are others out there, but not in the UK 
I'm fairly certain.

On 2020-03-23 02:49, FrankDuVal via VirtualVairs wrote:
> 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 significan
> t
>>   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
>
> _______________________________________________
> This message was sent by the VirtualVairs mailing list, all
> copyrights are the property
> of the writer, please attribute properly. For help,
> mailto:vv-help at corvair.org
> This list sponsored by the Corvair Society of America,
> http://www.corvair.org/
> Post messages to: VirtualVairs at corvair.org
> Change your options: 
> http://www.vv.corvair.org/mailman/options/virtualvairs
> Archives: http://www.vv.corvair.org/archive.htm
> _______________________________________________