Does this mod worth??? Or no???? Does the bike run better????
Using the PAIR valves as a crankcase evacuation system
Lots of questions came up after a post I made about plumbing the PAIR valves into the crankscase vent to evacuate and create a vacuum internal to the engine.
Why do some thing like this? Well, on a 90 degree V twin as the crank spins, the internal volume of the engine changes significantly. The engine is also pumping air under the pistons back and forth to each other, and in and out of the engine. There are also basic aerodynamic principal at work too. The crank and rods and tranny are all spinning around in the engine pushing air around with it. This is drag added to the engine which takes power.
Conventional crank I4s do not change crank case volume during an engine revolution, but they still pump the air from under the piston back and forth and cause internal losses. We used to actually make cut outs between cylinders when we using ZX11 engines long ago for the F1 sidecars. It made a difference. This is why also many manufactures are cutting out the cylinder sleeves between adjacent cylinder, they want to get rid of internal pumping losses. I included a picture of a set of OEM GENII Hayabusa cylinders to show what I am talking about.
Next thing to talk about is the PAIR valves. How do they work? Well simply put, Bernoulli's priciple of high velocity air creates a low pressure region. The PAIR valves do exactly this. As the high speed exhaust gas goes by the hole in the exhaust port it creates low pressure that gets channeled through the reed valves in the head and up to PAIR valve control solenoid. When the solenoid opens, it draws cool air form the air box and mixes it with the out going exhaust to burn unspent hydro carbons on the way out of the exhaust.
So why not use the vac created by the PAIR ports to pump out the crank cases to take advantage of the benefits described above. Here is how I have been doing it on the SV1000. Quick and easy. Pull the air box out and pull the PAIR control solenoid out, but leave the hoses that go to the front and rear cylinders. Bridge the electrical on the harness side of the bike that was plugged into the solenoid with a 1Kohm 1/2 watt resistor. I take the old plug, and use a couple of connector s and such and make a nice little plug unit to keep the FI light from coming on. Now scrounge up a T fitting such as the one shown in the image below. Now connect the upper part of the crank case vent hose you disconnected to remove the air box, to the T fitting. Now just plug in the front and rear PAIR hoses into the T. Remember to plug the port in the airbox when it goes back together. The bike will now pump on the crankcases as soon as the bike starts. As the exhaust gas speed goes up, the lower pressure seen in the crankcases.
I would pull out the reed valves under the plastic PAIR caps bolted to the valve covers, and clean them very well and make sure they are sealing well. A poorly sealing valve will not allow the bike to hold best possible vacuum.
I have set up many SV1000 and a whole bunch others. In my experience with the SV1000 oil consumption will not be an issue because the vents are well baffled, and if it were pumping oil through the vent, it would have originally been pushing it into the air box to get consumed anyway.
I do not have any direct dyno data for the SV1000, but I can assure you it will help. Lots of info out there on SV650s, Ducatis and tons of other race engines and vehicles. All of our race bikes I set up have been pumping on the crankcases for many years.
I did collect some data a couple of times to see what the pressure level was actually getting to in the crank cases, but I am not sure if I can find it any more.
You also have to remember to pull the oil fill cap before draining out our oil, or it just wont drain, because the cases are not vented due to the reeds being closed.
-MS
Why do some thing like this? Well, on a 90 degree V twin as the crank spins, the internal volume of the engine changes significantly. The engine is also pumping air under the pistons back and forth to each other, and in and out of the engine. There are also basic aerodynamic principal at work too. The crank and rods and tranny are all spinning around in the engine pushing air around with it. This is drag added to the engine which takes power.
Conventional crank I4s do not change crank case volume during an engine revolution, but they still pump the air from under the piston back and forth and cause internal losses. We used to actually make cut outs between cylinders when we using ZX11 engines long ago for the F1 sidecars. It made a difference. This is why also many manufactures are cutting out the cylinder sleeves between adjacent cylinder, they want to get rid of internal pumping losses. I included a picture of a set of OEM GENII Hayabusa cylinders to show what I am talking about.
Next thing to talk about is the PAIR valves. How do they work? Well simply put, Bernoulli's priciple of high velocity air creates a low pressure region. The PAIR valves do exactly this. As the high speed exhaust gas goes by the hole in the exhaust port it creates low pressure that gets channeled through the reed valves in the head and up to PAIR valve control solenoid. When the solenoid opens, it draws cool air form the air box and mixes it with the out going exhaust to burn unspent hydro carbons on the way out of the exhaust.
So why not use the vac created by the PAIR ports to pump out the crank cases to take advantage of the benefits described above. Here is how I have been doing it on the SV1000. Quick and easy. Pull the air box out and pull the PAIR control solenoid out, but leave the hoses that go to the front and rear cylinders. Bridge the electrical on the harness side of the bike that was plugged into the solenoid with a 1Kohm 1/2 watt resistor. I take the old plug, and use a couple of connector s and such and make a nice little plug unit to keep the FI light from coming on. Now scrounge up a T fitting such as the one shown in the image below. Now connect the upper part of the crank case vent hose you disconnected to remove the air box, to the T fitting. Now just plug in the front and rear PAIR hoses into the T. Remember to plug the port in the airbox when it goes back together. The bike will now pump on the crankcases as soon as the bike starts. As the exhaust gas speed goes up, the lower pressure seen in the crankcases.
I would pull out the reed valves under the plastic PAIR caps bolted to the valve covers, and clean them very well and make sure they are sealing well. A poorly sealing valve will not allow the bike to hold best possible vacuum.
I have set up many SV1000 and a whole bunch others. In my experience with the SV1000 oil consumption will not be an issue because the vents are well baffled, and if it were pumping oil through the vent, it would have originally been pushing it into the air box to get consumed anyway.
I do not have any direct dyno data for the SV1000, but I can assure you it will help. Lots of info out there on SV650s, Ducatis and tons of other race engines and vehicles. All of our race bikes I set up have been pumping on the crankcases for many years.
I did collect some data a couple of times to see what the pressure level was actually getting to in the crank cases, but I am not sure if I can find it any more.
You also have to remember to pull the oil fill cap before draining out our oil, or it just wont drain, because the cases are not vented due to the reeds being closed.
-MS
Attachments
41 - 60 of 83 Posts
Yes. Yes it will. The reasons are very simple: the crankshaft and rotating assembly are rapidly spinning in the crankcase which contains air. This air creates resistance to rotation which takes some amount of power to overcome. Reduce the amount of air in the case...and you reduce the parasitic loss needed to spin the crank.
Being that the volume of the crankcase changes radically every revolution as the pistons rise and fall only 90 degrees out of phase (something around 750cc air being pumped out then pulled back in every rev) trying to move this air rapidly in and out takes energy. If we reduce this airflow we free up the power that was needed to make it move.
Being that the engine creates a natural pumping action all we need to do is restrict the breathing and it'll reduce the crankcase pressure all on its' own with no external pump required. This is neat!
Many engines with multiple cylinders don't experience radical crankcase volume changes and so a simple check valve won't work...they need an external pump incorporated to pull down the crankcase pressure and this has shown to be very effective in reducing pumping losses. Some ProStock V8's can make 30+HP more with the external pump so it's well worth doing if max efficiency is your goal.I don't have a functioning PAIR system in the heads anymore (plugged) so I can't use that for crankcase evacuation, but instead run a simple one-way valve in the breather hose. The pistons fall and push out that volume of air which goes up into the airbox, then when they rise the valve shuts and won't let them replace what they just pumped out....so they pull a vacuum. This repeats as long as the engine is running and maintains a nice negative pressure on the crankcase which has several benefits.
First is it allows the crank to rotate with less resistance being there is less air for it to have to fight its' way through, and the pistons on the power stroke have less air beneath them to restrict the push downward so more power is delivered to the output shaft. A good functioning tuned exhaust will also make power not just from lowered restriction but can actually create a low pressure in the pipe behind the slug of hot exhaust that is shooting down the tube. This can actually help pull the piston UP on the exhaust stroke...which is also good and if you have the PAIR port connected to the crankcase this negative exhaust pressure will add even more than the natural piston displacement change created. The PAIR has one-way valves in each head which do the same thing as my breather valve...so it works from the piston displacement even when the exhaust conditions might not be contributing anything more.
Another benefit of lowered crankcase pressure that many don't think about is the reduction of potential oil leaks. If the crank is running negative pressure...oil tends to be sucked in rather than pushed out so seals aren't nearly under so much strain doing their job. And the piston rings tend to work better as they're sealed by the pressure delta above and below during operation so the lower we make the underside pressure they just work better. It's all good.
I've done back to back to back to back testing with my breather one-way valve and have repeatedly seen several mpg's better fuel economy with it working along with a noticeable improvement in power delivery at light throttle. It's easy to tell if the valve is working or not during cruise...it just goes better.
Using the PAIR for crankcase evacuation isn't going to make 20 HP and be a massive improvement...but it IS something that WILL help and big gains are made up of a bunch of little ones, so it's well worth doing if you seek better performance. All upside...no downside IMHO.
Curious as to why you'd think that? Once the crankcase is evacuated there's little of anything in there (which is the whole objective of the exercise) and what's there would be contaminated with blow-by if anything so once the engine starts and is running for a few seconds the pressures should be very low and not an issue.
On overlap there is always the chance, depending on the exhaust system, of pulling fresh air back up the pipe at low speed which does contaminate the intake charge on overlap. But this should only happen at pretty low rpm's with stock SV cams so the tune isn't that likely to be much affected.
Mine would do weird things on the A/F meter especially running down a steep hill giving it only enough throttle to maintain speed. It would go super rich...like into the 10's and I've finally got it to pretty much stop doing this by leaning the SD maps at high manifold vacuums. But this also has caused some idle leanness here and there so with this system I'm not sure if it can be perfectly dialed in or not. We're getting closer....and I need to take another stab at it next time the weather cooperates. Pretty neat to see 16-17:1 during cruise with the engine running cool and smooth...just how we like it.
On overlap there is always the chance, depending on the exhaust system, of pulling fresh air back up the pipe at low speed which does contaminate the intake charge on overlap. But this should only happen at pretty low rpm's with stock SV cams so the tune isn't that likely to be much affected.
Mine would do weird things on the A/F meter especially running down a steep hill giving it only enough throttle to maintain speed. It would go super rich...like into the 10's and I've finally got it to pretty much stop doing this by leaning the SD maps at high manifold vacuums. But this also has caused some idle leanness here and there so with this system I'm not sure if it can be perfectly dialed in or not. We're getting closer....and I need to take another stab at it next time the weather cooperates. Pretty neat to see 16-17:1 during cruise with the engine running cool and smooth...just how we like it.
41 - 60 of 83 Posts
