carb sizing question

[pegscraper]

Is there really any advantage to running a carburetor with a larger throttle bore area than the cross section area of the intake port? I hear of people using 39mm flat slides and such, or even larger. The stock intake port is a 30mm x 40mm oval, and at the intake surface it has a cross section of 1007 square mm. That area translates to a circle of 35.8mm dia. Stock 35mm VMX carbs have an area of 962 sq. mm. And a 36mm carb would have an area of 1018 sq. mm., which is already larger than the intake area. So assuming a stock intake port - no porting it out larger - is there really advantage to using a carb bigger than about 36mm? Get larger than that and the air velocity through the carb will be less than that in the intake port. Wouldn't bigger carbs just be underutilized and unable to be taken full advantage of?

 

[TURBOVMAX]

Is there really any advantage to running a carburetor with a larger throttle bore area than the cross section area of the intake port? I hear of people using 39mm flat slides and such, or even larger. The stock intake port is a 30mm x 40mm oval, and at the intake surface it has a cross section of 1007 square mm. That area translates to a circle of 35.8mm dia. Stock 35mm VMX carbs have an area of 962 sq. mm. And a 36mm carb would have an area of 1018 sq. mm., which is already larger than the intake area. So assuming a stock intake port - no porting it out larger - is there really advantage to using a carb bigger than about 36mm? Get larger than that and the air velocity through the carb will be less than that in the intake port. Wouldn't bigger carbs just be underutilized and unable to be taken full advantage of?

YES! Here's a good read on TB sizing. http://www.vmaxforum.net/attachment.php?attachmentid=6865&d=1235882944 The same rules apply more or less. If the engine hasn't had some serious mods done to it, as in displacement and head porting. The stock carbs are just fine. The cost of lets say buying a set of flatslides verses the HP gains is very expensive. Here's a link to purchasing a set of flatslides... just for information. http://www.pcwracing.net/carburetor.htm IMOP $2000.00+ for 10HP is very outrageous. Plus I hate the clackety clack noise that those flatslides make.

Most people who own a VMAX enjoy the VBOOST. Which Yamaha has engineered to occur at a reasonable RPM where people ride at on a daily basis. The HP gains advertised are on a dyno at about 9500 RPM. So it all comes down to throttle response and drivablity doesn't it? After 17 years of doing all sorts of mods, I really enjoy just getting on a properly tuned VMAX with a Kerker and heading out for a full day of riding.

$2000.00 is a nice set of wheels, tires,shocks and a few more bolt on goodies.

Again just my opinion.

Gary