jet placement: why not cool combustion, not the manifold????

[howracer]

while searching thru the archives of this excellent forum i really haven't found solid information relating to jet placement.

i run a 13 brew rotary that utilizes the typical intake manifolding. that would be an approx 3 inch aluminum tube from a very efficient intercooler. the tube feeds into a heavy cast aluminum Greddy elbow that turns the air 90 degrees. the charge air feeds thru a 3 butterfly (one for primary and 2 for secondary) throttle body and then runs into 4 runners. the runners are parallel to the ground and then turn 90 degrees downward (at which point the secondaries add fuel) then turn another 90 degrees and feed into the ports where the primaries add fuel into the port.

most rotary AI (auxiliary injectors) locate a single jet in either the intercooler to elbow tube or the intercooler tube before the elbow.

it sure doesn't seem to be the optimal location...

if you locate the jet in the elbow, placement would be extremely critical so as to insure even distribution thru the 3 butterflies and eventually into the 2 primary and 2 secondary runners servicing the 2 rotors. if you locate it further upstream in the tube before the elbow better distribution would be attained but the mxture would have to negotiate yet another 90 degree turn at the elbow.

it is common knowledge that on methonal powered racecars the intake manifolding is literally cooled to the point that it shouldn't be touched after a quartermile run... of course that's straight meth.

my concern w upstream (as above) injection is that a great deal of the cooling is LOST on the heavy cast aluminum manifolding. we all know aluminum is one of the greatest conductors of heat/cold.

on my car my charge air temperatures are already nice. i am interested in effecting the combustion chamber not the manifolds.

i also don't want the wet mixture to have to make all those 90 degree turns.

i plan to locate my jets in the lower manifold approx 5 inches from the intake port and one 90 degree turn.

i would be delighted to discuss my thoughts with anyone that might have valuable ideas both pro and con.

howard coleman

[keithmac]

The closer you place the nozzles to the valves the better the knock limiting effects but it lessens the charge cooling effect. Since you don`t need to cool the charge you don`t need a long run for the water to mix/ evapourate and cool the air. If you`re using wi soley for knock limiting you need to get as close to the inlets as possible, near port injection may be the best way to go for your setup?, also make sure each cylinder is getting the same amount of spray (ideally 1 jet per cylinder).