with some of the throttle bodys that you can buy some quote cfm figures,but not many.
for us it was trial and error.but in saying that there wasn't much error.no backward steps.overal power was down but the torque curves were always higher.
i will see if i can find some dyno runs to show comparisions.i can remember a few of the top of my head.
basically you are making an extractor in reverse,so that each port is helping the next to draw in it's charge.ie. 1 into 2 into 4.different lenghts of primarys and secondarys give different torque curves.
research wise we have had to do it all with dyno testing.as there is nowhere to find anything helpfull.
we started with a car that use to run quad 50 throttles,it had no torque or divability until 6000rpm.
we knew that the 50mm throttles would out flow the head because we had flow figures.cfm wise.
all tests were on the same engine
4 x 50mm throttle bodies.172kw
@8600 107 mph on a 12.7
we went 76mm throttle it made 157kw but injectors maxed out.@7800. 109.9 12.4
next one was a 83mm throttle same plenuim with new injectors 157kw
@7000 111mph 11.97
there are many different way's to aproach it.we just went back to basics.bigger is not always better.they were perfect (quad 50mm) for 8600.but your not driving at 8600.the engine didn't have the draw in standard form.without cams ,valves and compression.etc etc.
the car when driving before was horrible until around 6k then it came on slowly like a turbo car until the rite rpm had been reached.after the single was put on i can not describe the amount of torque it produced,but the car now fry's 5 out of 6 gears in the dry.he doesn't drive it over 2000 rpm in the wet.
the best way to have a go with a vw is to buy some pvc and plumbin two cadrons together.make them knife egde where they join like and extractor.
you can only learn so much with this ,but you can play with lenghts and pipe diameters.
with the honda's it was a new manifold each time.
we are about to start all over again now with a few more ideas in hand.
i hope this helps alittle.
and i hope it makes sence,i am pretty tired.
i will have a look see if i can find some pic's.
down sharon.
