pickle311

iTrader: (31)

http://www.neobuggy.net/modules/news...?storyid=10043

I don't see the benefit, less air and less fuel = less power. If you want less power, use less throttle.

Am I wrong in how I'm reading this?

lazyboy12300

iTrader: (2)

It looks like it is just the same as changing the expo on the radio. Might be wrong

Scott

NitroVein

I know I should have taken a patent for it... Damn!
Been using that shape for a year now...

Lille-bror

A small venturi will generate a higher speed on the air that goes through the carb. Higher air speed will give a quicker fill of gas in the engine at low RPM.

The downside is, that air is sluggish (is that the right word?! ). That means that there is a limit in the amount of air comming through the the small venturi. Because of that, your engine has less top RPM.

If you use a big venturi, the big hole will not be able to accelerate the air. That means less bottom. On the other hand more air can get through the venturi and give you more topspeed.

Due to the increased air comming through the carb, you will need to set the HSN richer, to maintain the correct mixture.

I actually made some tests the other day. I wanted to learn more about the subject:

http://www.rctech.net/forum/8888392-post37.html

Cheers

sly6t

+100

its all about air speed .. smaller- speeds it up larged does not ..

we did the same thing when racing go-karts .. small tight tracks we ran a smaller CARB with a smaller dia inlet for more bottom punch,
larger flowing tracks a larger carb for top end ..

pickle311

iTrader: (31)

So explain this to me. By being smaller, it's flowing less air at a faster rate. The internal restrictions of the motor has to slow down the air at some point thus making it more dense. Well, to an extent. It's not like a forced induction. So more dense air will create a leaner condition, unless the density isn't enough to compensate for the amount of air volume lost by the size difference of the venturis and in turn creating a fuel rich condition. Which would explain why you are gaining bottom end with a smaller venturi. Is that correct?

sly6t

its also alot to do with throttle respons more than tune .. with a smaller inlet /faster air speed , when you hit the throttle the air is faster to respond to the larger area it has to fill , and does not STALL , so you get better punch out of a corner .

if you run a over size race carb on a engine from a moto or go-kart or any thing and from idle u go WOT , the engine will stall .. because the air speed is slow then u go WOT and it has to fill the new larger area in the carb and the air just stops then inturn stops drawing fuel and dies .

i put a massive over size race carb on my crf50 mini moto race bike . i found u have to ease the throttle on abit at a time to keep the air speed up in the carb untill u get to WOT then its all good and go's HARD

dburt86

iTrader: (3)

but what i think there "claim to fame" is that it flows the same amount of air at WOT than the standard venturi of the same size.

So from what im seeing, its better partial throttle mileage with the same WOT power.

NitroVein

It will be similar to using expo. If itīs oval or round with the same overall area they will flow the same (if only the area is taken in concern).
But the needle/throttle moves sideways so you get "more control" over the applied throttle, more like a long LSN.
But the airflow is also concentrated in the center, more in-line with the nozzle/needle so the flow is cleaner.
I know from experience from full-scale cars that changing the design slightly can improve both response, drive-ability and hp through the entire rpm-band. Not bigger or smaller, just better flow characteristic.

sly6t

back in in karting again , in "one engine make" class's that had to run all the same mill , exhaust, carb and header . every gain is faster over the next guy . so we even had a whole set of diffrent carb inlets (what the filter or air box go's onto ) that were all differant size's and shapes .. sum had abig taper's, large to small for the air to flow nicely into the carb , and sum had just a square shoulder that the air hits then go's into the carb .. they all do diffrent things at diffrent points in the rpm range .. its all just "r &d" and doing back to backs ..

the hard part about RC over most other forms of motorsport is its about fuel milleage not horse power. when i say that because most mills make to much hp to use .

sly6t

a lil off topic but has any one try'd modding a HEADER with a built in Venturi ? a few guys a few years ago got done "cheating " in KARTING by having a lil Venturi dangle down in side the header of the exhaust where air got sped up going around it and inturn sucking the exhaust gas out faster .. yes i now thats what a tuned pipe does but this was a lil bit extra . it would have to be way way way small tho in a RC header ..

NitroVein

I agree, they make more power than needed many times.
But itīs also how they make the power that will make a difference in fuel economy, as long as the car needs to accelerate it will need more fuel. So if it can get up to speed quick there will be a gain right there, if the theres enough traction... But the more you can control that the more you could gain, so in that perspective these venturis could help.

Itīs funny, but theres been times when they have tried to restrict the power to make it safer for the riders. But instead they gained power because all engines where built with to large carbs... I believe that was the case with speedway many years ago.

micke_b

Anyone done more testing with these oval venturis? I have a set but never done proper testing with them and it would be interesting to hear if someone else has notice any improved fuel milage with these?

Can't test it myself at the moment, waiting for the snow to melt for another couple of month here in Sweden :-(

Chris Peralta

I ran them most of last year, and found the 7.5 oval was the best for me. I race at a very high elevation so small venturi's make tuning a nightmare. The biggest increase I saw was about 30 seconds more run time. One thing you need to REALLY watch for is that you do not twist that venturi at all when installing your airfilter assembly. I made that mistake and it twisted about 25-30 degrees and it really messed with the tune.

Ben Burtle

iTrader: (10)

The fuel savings could be due to it just being tall. I ran a tall venturi insert and gained 30 seconds of run time. It would be nice to get a thorough test done. I would have to adhere mine in place if I got one.