If you take 4" diameter pipe that is 20' long and pressurize it to 15psi and the cap blows off, it will blow that cap 100' in the air. If you take a 1" diameter pipe of the same length and pressurize it to 15psi and the cap blows off it will be lucky to go 5' in the air. If psi remains constant, volume exponentially increases total pressure, right?

I have worked with superchargers on V8's running 9:1 compression, revving from 900 rpm to 5000 rpm at 6 - 7 psi of maximum boost at 5000 rpm. I was beginning to pre-ignite on 93 octane by about 4750 rpm and 6 lbs of boost. The power increase of 6 lbs of boost was 37%. To get the same 37% power increase on a little tiny motor like a DS650 with its itty bitty little intake manifold, porting and cylinder volume would take maybe 18 - 20 psi. (that is a guess).

Now the average hp increase of a forced induction system that is rpm driven that yields a maximum of 37% increase is going to be much greater on a 5000 rpm band than it will on a 9000 rpm band.........even with much higher boost levels for the lower volume motor setup. Since average hp is what really makes us quick, you will have to run much higher relative boost and have a much higher peak hp gain from your supercharger to equal average hp say between 2k and 3k rpm and then at 3k to 4k rpm on the DS motor. Since superchargers are typically not regulated by a wastegate, to make good power increases below 5000 rpm (comparable to Noss) you would be making huge, ginormous boost at 9000 rpm which would require very high octane leaded fuel.

To look at it another way, if you set your max boost so that you just start to pre-ignite at 9000 rpm on your DS650 motor on pump gas, you will not feel hardly any boost pressure until well beyond 5000 rpm because the revband is so broad. This is part of the reason Top Fuel uses superchargers with NM. A 7500 hp Top Fuel dragster requires over 900 hp just to turn the supercharger. At 98% NM, preignition is not a problem and those blowers are setup to make huge boost right now!

Does that make sense? I have no experience with superchargers on small engines, I am simply extrapelating what knowledge I do have from other areas to form a hypothesis.

 

 

No offense but you are talking peak numbers again. Turbo bikes are making huge peak numbers already and they getting it handed to them on the track and the shorter hills all the time by lower hp motors because they make too much of their power too late. That bike of AZsand's was getting killed out of the hole at 4sw's but when it made a clean pass it looked as though it was actually gaining on the fastest bikes there at the top of the hill......but there again, too little to late.

 

 

I don't look at superchargers as having good bottom end power right now. My experience with them is that they are still top end biased. They actually cost hp at low enough rpm before they become productive enough to overcome their own drag......which by the way should be more pronounced on a smaller, lower torque engine unless the unit is more efficient.

Btw, I am not trying to educate you or anyone else, I am simply thinking through this out loud. Let me try this way of looking at it. Lets say a DS650 motor has a supercharger on it. It started at 65 hp and at 20psi of boost is making 100 hp at 9000 rpm (these are all fake numbers for illustrative purposes). Lets also take a Noss motor that has equal variables with a base line of 65 hp and add a 35hp shot of Noss also making 100 peak hp. Physical forced induction vs Chemical forced induction.

At 3000 rpm the base motor was making 15 hp, the supercharged motor was making 14 hp because it was turning the blower and making no boost. The Noss motor will be making approx 23 hp because a 35 hp shot is a little over 50% increase on 65 hp so 15 hp would turn into 22 - 23 hp at 3k rpm. The stock bike is pulling ahead of the supercharged motor and the Noss motor has a two bike length lead.

Lets say by 4000 rpm the base motor is making 25 hp, the supercharged motor is now making 5 lbs of boost so it is making 26 hp. 5psi is roughly twice what the blower is costing in power. With me so far? The Noss motor is already making a whopping 39 hp. The Noss bike is way in front now and the supercharged bike is just pulling even with the base bike. We are second gear at 4000 rpm so right out of the hole.

To make a long story shorter, the supercharged bike will not make enough power at the top to make up for its slower start. It would probably have to make 150 hp to catch the Noss bike in 300' simply based on how a supercharger makes power. The supercharger setup might cost 3 to 4 times what a Noss kit does.

There are unlimited ways to poke holes in this story but I think it illustrates how a supercharger works on the bottom end and that is my only purpose.

 

 

Beech was right, (IMHO) when he pointed out the smaller turbo. A smaller turbo and smaller hoses that have less length will all contribute to less lag. I go back to the comparison of the two pipes. You will reach the boost threshold much quicker with a less volume to fill and an impellor that is quicker and lighter to turn.

I think the reason lag is associated with turbo's and not with superchargers is partly because the power curve stays flat longer before it starts up a sharper incline. A supercharger also starts at zero but builds much more evenly so there isn't much hit. If there isn't a noticable hit, lag is not acknowledged. A turbo is like going from poor to rich and skipping middle class. A super charger is like starting just as poor but hitting middle class then becomming rich from there.

Again, remember how the supercharger works. If you were able to "Tune" it for low rpms, lots of boost from the very bottom........unless you fit a wastegate to it, you will have such a huge amount of boost at high rpm that you would either blow your motor up or need 200 octane or the like. lol

I could be wrong about how a supercharger would effect a DS.

Btw, the stronger you can build the bottom end of the power curve, the more condusive the build will be to the addition of a blower. That Banshee had to already be turning 3.7's if a blower took it into the 3.6's I would bet. Not many bikes can claim 3.6's and a power adder is not going to make as high a percentage difference on a bike that fast as it will on a slower bike, at least in terms of ET's.

 

 

I am pretty comfortable with the path I am on. After thinking through this, a supercharger doesn't really appeal to me...............yet. But you can pursue it if you like. I tell you what, I will pass on everything I learn about my Noss system and tuning it in exchange for everything you learn about adapting and tuning a supercharger. Deal? [img]i/expressions/face-icon-small-smile.gif[/img]