Venturi, what they do.

[MattDuffy88]

What is a Venturi?
A venturi is a tapered tube, designed to 'neck down' the inrushing air and then allow it to widen out to the throttle bore causing a pressure difference and hence drawing fuel through the carb.

How do they work?
To get through the venturi the air must speed up, which reduces the pressure inside the the venturi to below atmospheric pressure. The difference in pressure allows the fuel system (HSN/LSN) to discharge fuel.

A small venturi will create a higher pressure difference at any given RPM than a large venturi. This a a VERY important aspect of setting up your carb and selecting the right size venturi for the task in hand:

If the venturi is too large (not usually a problem with R.C's as the fixed carb venturi is matched to the engine) then this could lead to delays in fuel delivery causing a lack of performance and flat spots in the engine acceleration. Smaller venturi's do not suffer with this problem.

Their Uses:
- For longer straights a larger venturi would be reccomended as it allows the engine to rev higher but have a slower throttle response, this however increases the fuel consumption causing shorter run times.

- For a track with a mixture of long straights a mid size venturi would be reccomended, giving a balance of quick throttle response with higher revs.

- For a tight, twisty track a smaller venturi would be reccomended, this causes a snappier throttle response but limits the engines rev range, but as a result causes longer run times

[Acksaw]

This is great, was looking at the new Go range of engines and they come with 4, had no idea what they were!

Thanks!

[stot]

would you use different one depending if on truggy rather than buggy

[MattDuffy88]

Kind of, but you're really better picking which venturi is best suited to your driving style, setup and track.

[GRB]

Hi Guys

I have an RB S7 L2G 1006 with an RB 2045 pipe and I have fitted a 7mm venturi/restrictor as the track is very twisty with a short straight.

I am not the best at tuning engines , will I have to change the tune much and which way richer/weaker?


Also if I fit a shrouded waterproof cover over the airfilter I presume the engine will run richer so I will have to lean it up a bit but I guess not a lot?

Thanks

[stevee]

can anyone answer as to how much longer run times you would get by going to a smaller venturi .......is it seconds longer or minutes ???

[duopkik]

Hi Guys

I have an RB S7 L2G 1006 with an RB 2045 pipe and I have fitted a 7mm venturi/restrictor as the track is very twisty with a short straight.

I am not the best at tuning engines , will I have to change the tune much and which way richer/weaker?


Also if I fit a shrouded waterproof cover over the airfilter I presume the engine will run richer so I will have to lean it up a bit but I guess not a lot?

Thanks

Can anyone answer this. If you put a smaller venturi on, do you have to richen/lean out?