Yes, no, maybe.
Does a top fuel dragster motor make more horsepower per cubic inch then a Ford V6? Yes. Would you be able to drive the top fuel dragster engine in traffic?
If you are only concerned with TOP speed, and a horsepower number on a dynometer, then a slide carb definitely offers some performance gains.
A clean, well tuned carburetor always works well. You replace dirty, old CV carbs with a new Slide valve carb, assuming proper jetting and tuning, you can honestly say the carburetor made a big improvement.
BUT, always a but, A clean, well tuned Keihin CV carb offers a different performance standard. If slide valves are so good, why don't all bikes have slide valve carbs? Why go through the complication of Constant velocity, 3 fuel circuit carburetors? The CV carb offers better part throttle driveability, a measure of altitude compensation, when working properly, a smoother transition from idle, part throttle to full throttle. They call this driveability. The CV carb is pretty complicated, and when clean and adjusted properly, works well. It also keeps the fuel mixture more even (and leaner) for better MPG. For "Street Performance", the CV carb is a better device.
Slide valve carbs are 2 fuel circuit devices. they allow the flow of more air, the the mixture is preset by throttle position. The presets are adjustable with jet sizing and needle tapers. they are a simpler carb, but still a lot of work to tune well across the range. When you go full throttle on one, the bore opens fully. At idle, the velocity across the bore is reduced, and the fuel doesn't atomize well. this creates a little bog, so if you have slide carbs, you can modulate this by not opening the throttle fully from idle or keep the mixture a little over rich with needles, slow jets and such . A CV carb will maintain a higher velocity (constant in fact) across the jets, give better atomization, and smoother transition from idle to full throttle. The slides on a CV take some time to rise, and racers do not want that, so straight slides work well for that application.
Also, racers run more often at wide throttle positions. The Slide carbs then are tuned for good flow and atomization at those higher throttle positions. A CV carb is designed for more part throttle, driving in traffic , idle well, low throttle well, and transition between fuel circuits smoothly. However, when you alter an engine from stock, re-tuning a CV carb with 3 overlapping circuits is difficult. A slide valve carb is easier to tune because it has less fuel circuits and is simpler in construction.
It's like Racing slicks versus car tire...which offer better performance? On a 1/4 mile track, I want race slicks...better traction. But on a rain slick highway? which is better?
So performance is in the eye of the beholder. If you are looking for normal riding comfort, reasonable performance levels, then CV carbs do a great job.
If you are racing, then Slide Carbs do a great job.
I don't race. If I want to be the fastest bike on the street, my CB360t isn't the wheels I would pick for that. My stock CV carbs work they way they are supposed to, and the bike runs nicely, thank you. The small performance gain I would get with a slide valve just doesn't have any value. Getting 36 HP instead of 34 HP doesn;t really mean much, the bike still isn't fast. I am not looking to look like I race the bike on weekends either.
Now, if you modify the heads, increase the displacement, more radical cam lift, duration and timing, the stock CV carb won't work, and will be hard to tune. A slide carb is appropriate for those type of engines. The amount of tuning needed for a CV carb is a skill most here do not have. Slide valves are easier.
So ask yourself..Am I building the ultimate racing Bike? If I have the fastest CBxxxx in the world, does it prove I am a real man (or woman?)? Or are you building a bike that looks nice, runs well, is reliable, and gets me places?
Because if you look close at a lot of the really radical bikes, you will not see worn tires. Pay attention to how many bikes on this site look really great, and have lots of hours of sweat and effort, and still the engine isn't running. the bike isn't being ridden. If your goal is to make a work of art, go for the little pods. If your goal tis to have a ridable bike that looks nice, get the engine running well first. then make it pretty. My humble opinion anyway. you will get different and opposite opiniions here, that's the wonderful thing about these forums.
