blower set back and plenum volume

what is the reason of using a small, front discharge pie opening 14-71 blower that dumps into a large long plenum? Has anyone done any research into using a centrally located plenum with spider like runners? ala AJPE's top fuel manifold. It would seem that dumping the pressurized charge out of the blower into a large amount of area and then eight runners, would not be the most efficient way to deal with pressure drop, fuel suspension, distribution, etc. It appears that all the commercially available BBC blower intakes are basically designed for a std opening 8-71. I am thinking about having a sheetmetal intake fabbed and the guys I talked to say no one has any real idea why the manifold design hasn't kept up with the blower outlet design over the last fifteen years? Am I wasting my time??? Looking for input to continue this idea.

 

I think a 4 barrel intake manifold concept is a good idea and Mike Sage (SCS) did this a long time ago (longer than 15 yrs ago). Unfortunately not every good idea catches on.

Our Indy manifolds rear 4 runners look similiar to the rear of a 4 barrel intake. Likewise the setback TF manifolds front 4 runners look similiar to the front of a 4 barrel intake. To me this makes more sense since the blower outlet air is coming out at an angle to the front.

Indy and Meirsch have better than the norm BBC intakes on the shelf.

 

Ditto

Good question. I have wondered the same thing. We took a single 4 barrel sbc intake, opened it up slightly to fit the pie shape of the Littlefield 14-71 HH. Welded / supported a flat plate for the blower to sit on with a 8" setback. Seems to be working good, good balance, with very little different between the intake nozzles. But old timers say we don't have a big enough plenum but we don't see a drop off in boost pressure at higher rpms so I don't know how we would be losing anything due to a small plenum. So back to your question, does size matter??

 

Please explain why a big plenum should show a drop off in boost at high RPM's.

One down side I see to a large plenum is throttle response.

 

Small

I said the opposite, small may run out of air. If the plenum is small, at the hit of the throttle there may not be enough air reserve to get the pressure up and again at higher rpms there would not be as much reserve air to keep the pressure up. I really don't know, just guessing. Just know with our small cu in. motor, big blower, thats not the case. Then again, we are only making 1700 hp so we may not be consuming enough air to make a difference.

 

I can't quite wrap my head around the smaller plenum, running out of air. I mean once the pressure (boost) leaves the blower opening, you should see a pressure drop, with the "hat" fuel falling out of suspension as the velocity drops off tremendously. That doesn't even take into account the forward rushing air/fuel from hitting the front of the intake and the fuel "wetting" the manifold as the air tries to turn around in the plenum. I could be over thinking this but I can't see how better mixture control and equalizing boost among cylinders could NOT make more power and/or less breakage???

 

Centrally Located Pie

Not sure on the plenum question. However, I had a BBC sheet metal intake fabbed up from Self Racing in Oklahoma and had the pie centrally located. I do not have to stagger my port jets and I do not "front load" my bottom end. I am very happy with it. However, If I had to do it over again I would buy a HEMI!!!!

 

Please send pics of your intake

 

runner lengths

How important do you think runner length is for a roots blown setup?

 

http://selfracing.com/wp-content/uploads/2009/06/100_5603.jpg

not the centered pie but looks real good.