Carb velocity stacks pro#
Carb velocity stacks trial#

They are out on the end of a long tube and can really buzz at certain rpm. With the long inlet tracts you will probably find the carbs vibrate badly. Secondly possibly the most important thing of all. For example - tune the exhaust for a 6800 rpm and the inlet for 6300. For road racing I think you should tune the inlet to fill in the low points on the hp curve from the exhaust lenght. There are two things I would add from my experience.įirstly as several others have said the inlet tuning needs to match the exhaust. It compares the calculated lenght for Blair and Vizard. Http:/ / forums/ ubbthreads.php?ubb=showflat&Number=268898&page=1 Sometimes on some applications of theory you need a different theory :o)

Carb velocity stacks trial#

However Trial and error will be the key as with any theory. The only real factor of carb positioning is that close to the head you don't get the same fuel 'dropout' at low revs that you would if the carb was mounted a long way out and needing high gas speed to keep the fuel particles suspended. These are just starting points for the dyno work.Ībsolutely right David, I agree with Stuart, To hit the middle of your range using 6500 RPM the second pulse would indicate a 20.3' tract, third pulse 14.9' and the fifth pulse is 11.4'. Unfortunately the second pulse needs the longest intake tract. The pulse weakens each time it reverses, so the second pulse is the strongest. The intake tract length needs to be tuned so the positive pulse hits the intake valve just before it closes.

The negative pulse in the intake reverses as it moves the end of the bell and turns positive and heads back down the intake tract. The intake is tuned just like the exhaust. He told me it ends at the bell mouth and it does not matter where the carb is. I also thought the intake tract length began at the valve and ended at the carb intake, but Stuart Hooper disabused me of that idea. No tape measure is needed to see the difference.! Tuning can be frustrating or it can be fun, but it does take a lot of time. If you see an up pipe that ends near the seat, that is darn short.! So a good example is look at a BSA Gold Star with a Clubman's pipe, then look at a Gold Star with a Scrambles pipe. I should make a separate WEB site with all the pictures I have of a bunch of race bikes, no two are the same on either intake or exhaust. That length also accounts for cam specs, and exhaust lenght, and of course desired result. Added the 2' and voile, it went back to where it was.Īnd you are correct, tuning the intake tunes more than one thing. A quick tape measurement showed it to be almost 2' short. The dyno instantly found it and told us all our settings (carb) were now off and the power was down, even after changing the jetting. When my guy made the new exhaust header pipe (to take a bunch of bends out of it). We found that even 1/4' on intake length made a noticable difference. Good job H.B.!! You did some homework and found out all those books and computer programs only get you so close.! To fine tune, you have to do the work yourself.

There is no absolutes here, you run what works best for your rider and machine.Īnd the new exhaust will need tuning along with carb and intake.Ī lot of trial and error.My recent ignition fiasco really sucks because it's still winter here and dyno operators are begging for business. This is the reason for the vast differences in intakes and exhaust on very similar engines on LSR bikes. Longer length appears to move peak HP to a higher rpm and moves the torque lower and flatter at the same time.įor my racing I need both torque and HP at higher rpm. There appears to be two things happening at once from intake and or velocity stack length. Obviously a formula is only a quess and time spent on a dyno and at the track is the only way to know for sure. Simplified Formula 3 - Intake Length is 12.83 inches Simplified Formula 2 - Intake Length is 13.60 inches Simplified Formula - Intake Length is 11.00 inches Simplified Chrysler Formula (with bigger cam) - Intake Length is 11.15 inches Simplified Chrysler Formula - Intake Length is 11.67 inches Gordon Blair Formula - Intake Length is 10.69 inches

Carb velocity stacks pro#

Using available formulas and plugging in my engine specification comes up with different results.Įngine Pro - Intake Port Length is 14.02 inches