Multiple carbs set up progressively on top of a Roots blower?

[fast Ed]

Just thinking out loud here, this is further to my questioning about the Carter YH sidedrafts as used on turbo Corvairs, early Corvettes, etc. ...

Could I run a pair of these large single barrel carbs in to a common plenum above the blower, with the linkage set up so that one of them comes in later, sort of like a factory progressive 2x4 or 3x2 setup? I'm thinking that one of these carbs would really be enough for the VW mill, even with a blower on top, but two would look more "balanced" ... and the 2nd carb could be jetted basically to be the enrichment when under boost. Unfortunately my very basic understanding of carburetors doesn't tell me if this could work, or if I'd be getting myself in to a huge quagmire.

Thanks for any advice or tips ...


cheers
Ed N.

[Loren]

Re: Multiple carbs set up progressively on top of a Roots blower?

Without actually knowing very much, I'd remark that one of the things a Roots blower does is mechanically "churn" the intake mixture, I'd bet that any distribution deficiencies caused by running oddball carb positions/combinations would be cured by the time it all exited the blower. A downside might be that if you are using a straight-vane pump (as opposed to the GMC twisted type) at a low speed because of the small displacement you're gonna get intake "pulsing" which might make tuning difficult. Just jet it rich, to start with? What's DG think?

[squirrel]

Re: Multiple carbs set up progressively on top of a Roots blower?

it would be like a progressive 2bbl?

I run progressive linkage on the two 4bbls on my 6-71. works fine

[dieselgeek]

Re: Multiple carbs set up progressively on top of a Roots blower?

Without actually knowing very much, I'd remark that one of the things a Roots blower does is mechanically "churn" the intake mixture, I'd bet that any distribution deficiencies caused by running oddball carb positions/combinations would be cured by the time it all exited the blower. A downside might be that if you are using a straight-vane pump (as opposed to the GMC twisted type) at a low speed because of the small displacement you're gonna get intake "pulsing" which might make tuning difficult. Just jet it rich, to start with? What's DG think?

I have a little experience with a 6-71 blower, and for the most part, they seem to do a good job of creating even distribution. We had one case where the owner put all the injectors at the back of the blower and had a little problem with distribution at low RPM/idle. WHen the same engine was single carb'd, they had the carb both forward AND on the back at different times with no noticeable difference in distribution, but then again this was sitting on top of a funky intake manifold for an inline-8 buick.

I think he would be perfectly fine in this case, but since I am no carb guy I cannot really comment on how well the progressive setup between the two carbs would work.

[fast Ed]

Re: Multiple carbs set up progressively on top of a Roots blower?

Thanks guys. I was thinking that once the mixture made its way through the blower, the distribution really wouldn't be an issue. On the ACVW engine, it would then have to travel from the outlet of the blower to the intakes on the top of each cyl. head, which would be about 10" on one side and maybe 16" on the other.

The carb adapter would be something like this idea, but for 2 singles instead:




thx,
Ed N.

[IRONHEAD]

Re: Multiple carbs set up progressively on top of a Roots blower?

with the 2 single bowls you want to run... is this engine overcarb'd??
if not. why make thinks hard on you and a pain to tune..
other than a single carb ,that you don't want for looks..
why not toss the progressive idea out the window..
and run the opening rate in tandim..
this will make it simply to tune and keep that way..
will still have the dual carb'd LOOK...
if over carb'n it down low is a concern. you can ad the efi throttle cable halfmoon to slow tip in. at low rpm..
so it has nice throttle response.. tho. with a blower that isn't gonna be that much of an issue

[fast Ed]

Re: Multiple carbs set up progressively on top of a Roots blower?

Good advice, I tend to overthink and overcomplicate things. A single Carter YF would be enough, but I'm sure that duals could be made to work OK with your suggestion on the throttle linkage.


thanks

Ed N.