intake manifold design help

[toon1]

what would be a better setup for a twin cyl. engine? single TB or Dual TB?

split plane or open plenum manifold?

I've been reading that a single TB is better for a low RPM engine. The engine I am converting will only see about 4,000 rpm max.

I want something that will give nice, controllable throttle between 1,500 and 3,000 rpm.

Thanks, Keith

[devastator]

A single TB should give you better control at lower RPM's as it lets you control the amount of air entering the engine during "tip in" much easier and at a slower rate.

[toon1]

Thanks for the reply.

What will create better low end torque, a split or open plenum? I am guessing that If I design a split plenum manifold, two TB's are in order.

Also, I have a 30mm bore TB that I would like to use. I have done calcs. in the MM and other web sites that suggest this will work just fine as a single TB for this engine but it seems really small.

The max. HP will be around 40HP. The Mega.Man. stated a 30mm bore TB will support up to 52hp.

The goal is a motor that will create good low end torque.

What's your thoughts?

[devastator]

I believe the plenum gives you better low end torque, but it's been years since I had the choice for my engines, so my memory might be a little fuzzy there.
30 mm should handle up to 52 horse power alright, but will certainly give you the low end control that you wanted.
Stock VW 40hp engines had a 26mm venturi and the "larger" 65 hp engines went as high as 34mm, although they were carbs. I'm confident that 30mm for 40 hp should work great.