Vacuum Pumps (Or How A Part That Sucks Can Make More Horsepower)
The reason for the development of this technological advancement was due to rule changes in the Sportsman Class of NHRA Drag Racing. For years the NHRA rules allowed the Sportman Class to run open exhaust pipes on their Race Cars but recent rule change made the use of mufflers manditory.
Once the cars started running mufflers traditional pan evacuation systems no longer worked properly. Racers started using vacuum pumps because air pressure in the pan started blowing oil out the gaskets and oil was leaking all over the place.
The use of vacuum pumps also showed an additional benefit in Hi- performance automoble engines by making up to 30 HP more with the use of vacuum pumps that developed 15" inches of vacuum with a wet sump oiling system.
Too much vacuum, more than 15" inches, can reduce the oil mist to a point where you can lose lubrication to the wrist pins and cylinder walls. 15" inches of vacuum is fine for a drag race application because the engine is at HI- RPM for such a short period of time. Many Racers run between 10" to 12" inches of vacuum. There's no easy way to tell how much vacuum you're pulling at HI-RPM on your engine without a vacuum gauge.
Drag Racing Bikes using Alcohol for a fuel source seem to develop quite a bit more blowby than gasoline engines and thus the amount of vacuum you can get with a pump is reduced. In fact the richer you run your engine on alcohol the more blowby you'll get. If you run a lot of nitrous (N2O) you can create a lot of blowby, partially due to the wide end gaps many nitrous racers run.
Every Prostock Bike competitor racing on the NHRA circuit today uses a mechanical or electric vacuum pump.
Re: OSS "RACE" THREAD
Reply #117 - 24. Oct 2006 at 14:14
Hi Steve,
We've been using these vacuum pumps on our side of the pond for some years also and they work wonderfull.....in Drag-Race engines.
In a Street or Road-Race engine they seem to create problems with the lubrication of the cilinderwalls in particular , when downshifting and braking for corners. This is probably caused by the lean fuel/air mixture when closing the throttle i.e. when the weight of our machine and rider are trying to push the engine instead of the engine powering us forward.
So for Street and Road-Racing it is better to let the crankcase breathe itself. The system most manufacturers use is connecting the breather in the air box and let the engine be the vacuum pump.
But on our older air and oilcooled bikes we want free flowing pod filters or velocity stacks with additional jetting for more horsepower , so we need to take other measures to get the hot pressurized air out of the crankcase.
In our GS/GSX and GSX-R engines the no. 3 and 4 cylinders can breathe freely into the clutch department because of the room there is for our primary gears. For the no. 1 and 2 cylinders this is almost not possible. So that's the reason vacuum pumps work great, they help these cylinders to breathe, but there is still a pressure difference between the two pair of cylinders. To get the pressure as even as possible, we need to make modifications in this department.
I know there is much more to this subject, but I tried to keep it as simple as possible so the majority of readers can understand it.
I will get back to it as soon as possible with pictures.
Ron