Surge tank design on a 1-cyl 450cc

[Greg5OH]

I'm designing an intake for a single cyl 450 cc kawasaki motor. Need some clarification of the placement of certain areas of the intake pipe. What I'm thinking is run a bellmouth intake ontop of throttle body, tapers down to class mandated restrictor, peice of straight pipe (1.5" diameter-same as intake port), surge tank (looks like a spun metallic cat almost), to a peice of pipe that connects to the intake port.

Do I include surge tank length in the calculated intake runner length (19.8 inches for 2nd pressure wave)?

 

[BrianPetersen]

"Surge tank" = "Airbox"? What's wrong with the stock intake configuration modified to include that restrictor (if that restrictor is smaller than the stock intake snorkel)?

Snorkel with a bellmouth going down to the diameter of the restrictor (configuration not unlike the stock air intake), stock airbox (or if you insist on making one, make it as large as possible), velocity stack with a bellmouth intake going into the stock throttle body and stock throttle body connector and stock intake ports.

Your "surge tank" will probably look to the intake system like a far-too-small "airbox".

 

[gruntguru]

Sounds like Formula SAE or Formula Student, in which case the throttle plate must be located upstream of the restrictor.

No the airbox/plenum/surge-tank is not included in the tuned length. Air velocity in a plenum is approximated as zero. Nor should you include the length of pipe from plenum to atmosphere since this is assumed to be steady flow.

Engineering is the art of creating things you need, from things you can get.

 

[BrianPetersen]

I've done some tinkering that involved optimizing intake of a single cylinder engine. You need engine simulation software to get this right. A single cylinder engine has such unsteady intake flow that even upstream of an airbox ("surge tank"), the flow tends to be uneven, and the Helmholtz effects can't be ignored. If your restrictor is required by the rules to be so small that there is substantial pressure drop through the intake pipe to the airbox due to Bernoulli, then my experience has been that the Helmholtz effects go out the window and the bigger the airbox, the better, so make it as big as you practically can. If the throttle has to be upstream of the restrictor (airbox intake snorkel) as suggested above (we have no idea - original poster hasn't mentioned the application) then there will have to be a trade-off between throttle response and airbox size (power output), and your fuel injection system had better account for the delay between throttle motion and actual engine air intake. If you are using a carb or injector upstream of this "surge tank", and it's of significant size ... you had better not ever have a backfire through the intake system, or else!