GregW

1) If you place a plennum(read box) arround the velocity stacks would that be optimal design. Or would it be better to weld a plennum to the velocity stacks and attach the IC inlet so the air is slammed right down the throat of the carbs?

2)I have an extra s4 ecu and harness sitting in my garage. How hard would it be to wire in just the spark system into this car using that ecu and CAS? Right now it has a locked distributor and in my opinion that is only optimal at WOT....and max boost....

Any thoughts???

Thanks

GregW

GregW

oh yeah this is on a 12A first gen with aftermarket Mukunis and all the stuff to get the job done safely. Well somewhat.....Grin

pillage6

The plenum I have doesn't have room for the air horns, so it goes directly into the throats.

It is very hard to wire the timing and ECU up, can you do that without FI?

You lose a little on the bottom end locking the distributor, but saves your *** at the top end.

rotarygod

iTrader: (1)

It doesn't matter if you weld the plenum on top of the velocity stacks or if they protrude into it so long as they aren't getting too close to other other side internally. the effect is still the same. As long as you have the radius of the velocity stack entrance you are good to go. Leave them on though.

GregW

Thanks guys. Will post pics once I get it tigged. Its too darn hard to discribe what it looks like. Heck its kinda hard to draw.

Thanks

GregW

purple82

You want the stacks to protrude into the plenum. The air horns will pull air from behind if it's available. A rule of thumb for the space to allow above the horn is this, you want at least the amount of open area into the horn as the area of the horn opening itself. Use this formula:

pi*r*r=2*pi*r*h

where r is the radius of the horn opening, pi is 3.14159 and h is the distance from the horn to the top or your plenum.

Take the inlet area of the horn, say the radius is 1 inch, the area is 3.14 square inches, you want to allow at least that much flow area into the horn around the diameter. In other words, 2*pi*r*h=3.14, so the min distance you want above the horn is 1/2 inches.

680RWHP12A

obviously you people have had no experience with blowthrough systems!!!!except for Pillage66.. the carb has a float breather in it wich must be pressurized also, the plenum must sit flat on the carb body as this is where the float breather is located on Mikuni and Weber carbs..the plenum design should isnt too critical and the velocity stacks make little if any difference on blowthrough systems...for pics and plenum designs please see my home page, good luck!

purple82

"Or would it be better to weld a plennum to the velocity stacks and attach the IC inlet so the air is slammed right down the throat of the carbs?"

So are you saying this can't be done?

MikeLMR

not unless you find another way of pressurising the float chambers

purple82

I'd think you still want the air horns though. Without it, the sharp turn into the carb is restricting airflow.

GregW

"obviously you people have had no experience with blowthrough systems!!!!except for Pillage66.. the carb has a float breather in it wich must be pressurized also, the plenum must sit flat on the carb body as this is where the float breather is located on Mikuni and Weber carbs..the plenum design should isnt too critical and the velocity stacks make little if any difference on blowthrough systems...for pics and plenum designs please see my home page, good luck!"

Yep there is a tube for the float breather going from the plate that bolts to the carbs to the plennum. Its gonna be tigged at each end. Just like the stacks. That way you dont need to fiddle with bolts inside of a little box when you want to take it off.

I cant see how it would make no difference when the air is pulled from behind the stacks vs. going straight through. It would seem to me that there would be much less flow restriction the way I am making mine.

Will post pics when done. I will most likely make both styles and take the thing to a dyno and see once and for all. Thats the only way to turely know.



GregW

rotarygod

iTrader: (1)

Yep you got me. I don't have any experience with a blow through system. I do know that no ram stacks is a bad idea from a turbulence standpoint. If the inside of the plenum chamber itself has a nice radius on it then thats a different story but a sharp edge there is going to hurt performance. As long as the float breather works properly with the ram stacks leave them on. I'd only leave them off if there was no other alternative.