Anyone know of any DIY information on setting up carbs for roots type blowers?
I Know there are plenty of off the shelf carbs for this application from all the carb makers, but I happen have two new Speed Demon mechanical 650s I'd like to prep myself.

I'll post the link after I highly recommend that you send them to a professional place as I have a Holley 850DP sitting on my shelf that is pretty much a paper weight now. Fortunately for me, both the carb shop and CSU are near me.

Mike

http://www.hangar18fabrication.com/blowthru.html

Thanks, but that link was geared towards a blow through setup. I'm looking for info on preparing carbs for a roots system.....anyone?

on a roots type blower, you dont really need a lot of work, as their not under boost like a cent. blower-all i have ever done to them(holleys) was cut the choke horn, mess with the squirters, jets, and a larger n/s's
if they were vac sec carbs, i tied the rear vac's together-the 650's should be crisper than 750's, depending on engine size, but i always ran 750's
no matter what you do, keep them rich, keep an eye on the plugs

You can boost reference the powervalves, thats all you need to do is plug the pv check valve, and drill through the main block until you get into the powervalve well, insert, and drive a steel tube into the main body that you can slip a piece of hose over to run to your intake. Some people don’t know about this, and there powervalves never open, requiring them to fatten the jets and run pig rich.

Thanks, boost referencing the PVs is my main concern, I understand the problem of making boost and the PVs remaining closed because they are actually seeing vacuum. I'll have to open these Speed Demons and get that much done. I'm sure the rest is just a matter of playing with jets and squirters etc.

http://img.photobucket.com/albums/v216/mutfish/Dsc01017.jpg

It is very easy, i dont know what i payed $50 a carb for from holley for? The only other thing is maby a set of holes in the throtle plates to clean up the idle.

On our Blower Calibrated carburetors (for a Roots style supercharger) the Power Valves are Boost referenced. If you don't do this the Power Valve will generally be open (rich) until you get higher in the boost level closing the PV (lean). From there we use a different fuel curve between a naturally aspirated single 4bl carb, and a 2x4 Blower Carb, the floats are different, as well as the linkage on the carburetors to equalize the distrabution.

On our Blower Calibrated carburetors (for a Roots style supercharger) the Power Valves are Boost referenced. If you don't do this the Power Valve will generally be open (rich) until you get higher in the boost level closing the PV (lean). From there we use a different fuel curve between a naturally aspirated single 4bl carb, and a 2x4 Blower Carb, the floats are different, as well as the linkage on the carburetors to equalize the distrabution.


Doug is that you replying???

Rob

Doug is that you replying???

Rob


Not if you're asking.... So did you guys make it back from Orlando in one piece?

Not if you're asking.... So did you guys make it back from Orlando in one piece?


Yea .How about you??Did ya have a good show and stay out of trouble ? JC and Zul landed in the snow he said Sunday.

We went to Popie's [Performance Marine] in Daytona Sat night and had a blast over there . They had some nice $$$$$boats . There fixing to do Birdmans boat.That should be a fast one!!

Rob....

Yea .How about you??Did ya have a good show and stay out of trouble ? JC and Zul landed in the snow he said Sunday.

We went to Popie's [Performance Marine] in Daytona Sat night and had a blast over there . They had some nice $$$$$boats . There fixing to do Birdmans boat.That should be a fast one!!

Rob....


Not too bad. A few Bottles of Patron silver later, and I was all good. This week has been too crazy trying to catch up.

From there we use a different fuel curve between a naturally aspirated single 4bl carb, and a 2x4 Blower Carb, the floats are different,
Thanks, What is different about the floats in a blower carb?

Thanks, What is different about the floats in a blower carb?


They're angled for use in 2x4 applications.

Not too bad. A few Bottles of Patron silver later, and I was all good.

GOOD choice! :beers:

Digging up an old post, but I am considering dropping Holley 170ci mini-blower on my K5 Blazer.

What changes are needed (if any) for a Q-Jet in a single carb roots setup on a mild 350?

No power valves either....

Thanks, boost referencing the PVs is my main concern, I understand the problem of making boost and the PVs remaining closed because they are actually seeing vacuum. I'll have to open these Speed Demons and get that much done. I'm sure the rest is just a matter of playing with jets and squirters etc.

http://img.photobucket.com/albums/v216/mutfish/Dsc01017.jpg

I personally have my PVs blocked and I just run the secondaries "pig fat". If the secondaries are open,chances are that I'm taking care of buisness. I don't believe that (the way I drive) I would benifit from boost referencing. Blower motors are usually on or off so I didn't see any reason to drill/alter my carbs when I could simply run fatter on the circut that is only open typically when I am under boost anyway. Again this is just my $.02!
You may want to do a little research on the idle circut though. The draw of the blower can pull the idle circuts dry and (some may disagree) this will cause some serging. which is why you will probably read about people enlarging the idle bleeds. DON'T hogg them out...we are talking a very small amount.But try the carbs first and like everyone has probably told you already start rich. You can always change jets but changing pistons requires an extra beer run.:beers:

has anyone used the predator carb on a blower setup was kinda wondering how that set up would work . on a 671 bbc

I gave up on twin Speed Demons & Grants tech support. I bought two QFT's Q650s and had them set up for boost reference. They work great & have a very crip throttle response.:thumbsup: