How do you measure your VE? Does it require dyno time, or are there other ways?

 

Please either post it, or email me a copy

That was an excelent post, and even though I have been aware of VE for some time I have to admit to being guilty of not giving it enough thought etc while building this engine (maybe because I dont have any reasonable way of measuring etc).

To be honest I really sort of put VE in the same perspective as flow and velocity (I guess they do kind of work together as well) in that without some reasonable measuring equipment and time to work with everything etc it will be tough to master. Sure it would be great to have the ability to know and not guess at the amount of air entering and exiting, and the speed at which it does, and even more important would be how the relate together and effect the VE, but I am not sure its practical for the majority of us who work on their own engines.

Maybe its just another one of the handicaps most of us face due to not being a professional engine builder with the right tools etc and having to work with what is available to the typical rider/builder lol.

Still you bring up an excelent point, and dont hesitate to offer more info on the subject!!

 

The easiest way to work out VE is to dyno the bike, and then use the HP figures to work out VE.

There are other ways to work out VE, but to do that, you need air flow figures, and that is a hell of a thing to get, if you don't have access to a flow bench and some very advance measuring tools.

Please note that dyno runs can be misleading, so VE depends on how accurate the dyno is and how well it is set up. If you dyno tune with stock tyres, HP figures will be lower, showing you less VE. Other factors also mess with the HP output, so keep it in mind, and use the same setup next time you dyno the bike.

Don't break your back trying to get 100% or better and get very accurate VE values. Use VE to guide you to figure out where the bikes makes good power and the best VE, and where you need to improve. Applying the Ve across the RPM range, you can figure out at what RPM range the bike makes best power. For trail bikes, having a wide spread of good VE means the bike will perform very nicely over a wide range of applications. For racing, you don't want good VE towards the bottom end, and you need to move it towards mid and top end. Changing the cam, intake and exhaust can move the VE to where you need it most. All out top end power is great for the track, but might not be good for trail riding.

If you are really cleaver and know how to design intakes to move the VE around the RPM range, you can make yourself differant intakes. One for trail, and another for racing or drags.

For example, a bike with very bad VE at max power is the YFZ450. I had a modified 450, with the motor being stock, only change was the head was gasflowed. It had a pipe, jetting and aftermarket air cleaner and open airbox, and is used for flat track racing. Using the VE, I knew the bike had a breathing problem at high RPM. Most people that look at a dyno, would think this is a potent motor and when it makes over 50HP, they smile big time, but the VE showed it had major breathing problems. Changing the intake to match the breathing requirements, we gained about 5 to 7 HP at the top end.

Now it is pushing 60HP plus, but it comes online like a 2 stroke power band. It's great for the track, but it also causes traction problems now and the rider had to change his riding style. Not so sure it made him go faster, with the traction problems and all, but that is what they wanted.

 

When you refer to "intake" are you referring to the manifold or the actual intake ports?

 

Intake is the whole intake system, meaning, manifold, carb, boot between carb and air cleaner and the whole airbox. The whole thing is matched to a specific RPM.

Mostly the length and the diameter of the intake boot before the carb is where you need to make most of your changes. You can make changes to the rest, but it is more expensive to modify the other parts, but sometimes necessary.

Generally, the longer the intake boot the better low down power and the shorter the intake the better the power at the top end. Keep in mind that we work with harmonics here, so the total length and diameter needs to resonate, helping airflow. Any old length or diameter is not going to work.

 

Freez,
does Deon and ATV Powersports ring any bells...

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