Carb wing modification

[Guaryzzzpode]

I just dropped by this thread at Holeshot, and thought I would put it here to get some Scientific bacground. The thread is :

http://www.holeshotforum.com/ubb/Forum1/HTML/002294.html

It states that by installing a flat wing inside the carb on the cylinder side, you reduce turbulence and gain several hp.

Any comments?

 

[spanky250]

Anyone that tells you that you can gain several horsepower just by installing a little piece of metal in the carb is full of BS. If anything, you will reduce the atomization of the fuel, as this needs turbulence to accomplish. If horsepower gains were so simple, we would be riding 50 hp 125s, and the factories wouldn't be spending millions just to gain 1 or 2 hp over their competition.

 

[fishhead]

Take a look at the canadian dave kdx forum under" Emergency Rbdesigns jetting info needed" you will find pics and info.

 

[spanky250]

Originally posted by fishhead
Take a look at the canadian dave kdx forum under" Emergency Rbdesigns jetting info needed" you will find pics and info.

The mod you are refering to is a divider plate. It's function is to fool the engine into thinking it has a smaller carb when the slide is below the divider, increasing intake velocity and throttle response. Once the slide is past the plate. the engine has access to the entire carb bore, for normal high rpm power. It will improve throttle response and low-end grunt, but it will not give you an increase of several horsepower. It has the same effect as an oval-bored carb.

 

[BRush]

Originally posted by spanky250
Anyone that tells you that you can gain several horsepower just by installing a little piece of metal in the carb is full of BS.

The claim that it's going to manufacture 4-5 hp is nonsense, however the divider plate is an effective way to clean up and improve low-end throttle response. It's one of the better woods-riding related mods I've done to my KDX

 

[Kramer]

Anyone have access to one of those nice flow visualization programs?

Sure would explain why you don't get horspower gain from that mod.

 

[spanky250]

Originally posted by Kramer
Anyone have access to one of those nice flow visualization programs?

Sure would explain why you don't get horspower gain from that mod.

Don't confuse response with power. You can have a very responsive engine with little power, or you can also have a very powerful engine with poor throttle response. Ideally, an engine will have the best of both, but in the real world, a large part of engine tuning is finding the best compromise between the two. As BRush stated, the divider plate will improve the low-end response, and allow the engine to pull into the meat of the power more cleanly, but there is only a modest increase in power. Increasing the horsepower output of an engine requires that you increase the amount of fuel-air mix that flows through the engine, and is burned, at a given rpm in a given amount of time. All the divider plate does is shorten the amount of time between opening the throttle and the fresh fuel being drawn through the jets and into the engine, because the smaller effective intake tract at below-the-plate throttle openings helps to increase the velocity of the intake charge beyond what it would be if it were flowing through the larger, unobstructed intake tract. In simple terms, the same amount of fuel-air mix flows through a smaller intake tract, so it flows faster. The end result is a slight improvement in response time and volumetric efficiency.

 

[Kramer]

Yup, your trying to make the most of your static pressure vs. dynamic pressure. I have a good grasp on the fluid dynamics, I just thought that a good flow vis. showing the difference between flow at different openings would, at a glance, enlighten all.

 

[socal scott]

hehehe! I'm the guilty party that started the Holeshot thread by posting my mod results on my 200 mxc. The hp jump was stated in a mag FMF product review. It stated there was an increase over stock at the same rpm's when the throttle went from half to full. No change in peak power was claimed. I first did this on my '92 KX250 and it was incredible. While in the mid-range it was like a supercross response otherwise it behaved as usual. My 200 stays close to my bros. '97 CR250 in top gear roll-on drags:p

 

[Layton]

My 200 stays close to my bros. '97 CR250 in top gear roll-on drags

Not saying that the divider does or doesn't work but the 200 would have stayed with the cr anyway especially if it was properly jetted.