Best Way to Make Power / Power Limits of 951 Engine.
08-30-2010, 12:14 PM
#16
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Power; you can get two ways: either increase the force on the crankshaft (torque) or increase the speed at which the torque is made (RPM), or obviously a combination of both.
Cams and generally increasing the flow through the head basically results in the higher RPM route. Limitations there are the valve lifters, springs, the oiling system, and would all have to be addressed. But cylinder pressures do not go up when increasing power this way.
Cams and generally increasing the flow through the head basically results in the higher RPM route. Limitations there are the valve lifters, springs, the oiling system, and would all have to be addressed. But cylinder pressures do not go up when increasing power this way.
Also to make power the via the RPM method requires a very oversquare engine. The 951 engine bore:stroke is 1.33:1. Kawasaki at one point believed that to make an RPM engine, the bore:stroke should be about 1.7:1. Currently the top power/displacement streetbike engine is the BMW S1000RR with a bore:stroke of 1.61:1.
The increase in torque is due to higher cylinder pressure in this case.
But even if your turbo compressor has some room to move the boost up efficiently, the hotside needs to be big enough (and this is often overlooked). It gets to a point that exhaust back pressure rises waay faster than the increasing boost. The exhaust gases don't get expelled properly and there are pumping loses that take power from the crankshaft. Both of these greatly lessen the effect of the higher boost you want to run. So, I'd say the limitations here (if detonation is not a factor because of your race gas), is the exhaust side which includes the header and everything back.
Experts should chime in on the strength of the case.
Also, increasing both RPM and/or torque requires the turbo size (both cold and hotside) to be addressed, since more flow is needed in either case.
Also, if mass air flow increases, intercooling and pressure drops through the intake need to be looked at.
Experts should chime in on the strength of the case.
Also, increasing both RPM and/or torque requires the turbo size (both cold and hotside) to be addressed, since more flow is needed in either case.
Also, if mass air flow increases, intercooling and pressure drops through the intake need to be looked at.
Then you could argue that your gearing should be changed to get the most of how you added your power. If you take the RPM route, your car won't feel faster if you don't shorten up the gearing, for example.
Alot more technical discussions could come from this, I'm sure, and could go on and on.
Alot more technical discussions could come from this, I'm sure, and could go on and on.
But also keep in mind that sometimes too short of gearing means too much shifting which slows things down.
-Dana
08-30-2010, 12:17 PM
#17
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-Dana
08-30-2010, 12:21 PM
#18
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It is hard to say which intercooler would be best.
-Dana
08-30-2010, 07:05 PM
#19
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Drag racing can be fun.....
You are assuming constant boost levels when saying cylinder pressures don't go up? Also, one thing to keep in mind with the higher RPM is in general, is that increasing speeds of engine components starts to create a lot of additional forces on them. Decelerating at piston moving at 7000rpm is a lot harder than decelerating one at 6000rpm.
Also to make power the via the RPM method requires a very oversquare engine. The 951 engine bore:stroke is 1.33:1. Kawasaki at one point believed that to make an RPM engine, the bore:stroke should be about 1.7:1. Currently the top power/displacement streetbike engine is the BMW S1000RR with a bore:stroke of 1.61:1.
-Dana
You are assuming constant boost levels when saying cylinder pressures don't go up? Also, one thing to keep in mind with the higher RPM is in general, is that increasing speeds of engine components starts to create a lot of additional forces on them. Decelerating at piston moving at 7000rpm is a lot harder than decelerating one at 6000rpm.
Also to make power the via the RPM method requires a very oversquare engine. The 951 engine bore:stroke is 1.33:1. Kawasaki at one point believed that to make an RPM engine, the bore:stroke should be about 1.7:1. Currently the top power/displacement streetbike engine is the BMW S1000RR with a bore:stroke of 1.61:1.
-Dana
Yep, that's right; assuming same boost.
And yeah, higher RPM, different stresses other than cylinder pressure. Now that you mention it, I understand that the stresses are actually higher on an engine trying to get the same power from RPM vs forced induction. Those in the know about tensile strengths could say more.
And like you said, shorter strokes lessen those loads. Actually, for a car engine we have pretty oversquare configurations.
08-30-2010, 07:13 PM
#20
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( You're thinking that the shorter gearing results in getting through the RPM band quicker. But remember, there's also more RPMs to get through, which evens it out.)
08-30-2010, 08:08 PM
#21
Burning Brakes
How about this. FREE. Better power/wt. ratio, decreased stopping distance, increased aceleration, better realiblity, superior connering ability. Just get the lead out!
08-31-2010, 09:29 AM
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True – and horses worked just fine for 2000 years before that….
The reason that you will sense a little anti-drag sentiment here is that the transaxles just aren’t up to it and there is no easy fix. The half shafts aren’t very fond of it either and changing the clutch is not a 45 minute project…!
You can do a search about head studs – lots of opinions on that!
The reason that you will sense a little anti-drag sentiment here is that the transaxles just aren’t up to it and there is no easy fix. The half shafts aren’t very fond of it either and changing the clutch is not a 45 minute project…!
You can do a search about head studs – lots of opinions on that!
08-31-2010, 11:29 AM
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At what boost level was the 370whp Chris?
08-31-2010, 12:24 PM
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08-31-2010, 01:32 PM
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I have a lot of thoughts on this. Less on the math side and more on the theory side (There is a few numbers though).
DanaT, I read your comment about power, in relation to RPM and rod ratio. Problem is, the RPM deal is less of a rod ratio thing, and more of a piston speed thing. The fact that our engines have a 1.33:1 rr speaks wonders when you consider that other car engines run way higher rod ratios.
Prime example? Honda B16. That's an all day 9k rpm motor if you want. The rod ratio is 1.745:1 and it makes nearly no torque because of that. But also consider the piston speeds, therefore related stress and heat on all effected internals.
I looked into rod ratio and piston speed back when I was working on another 4cyl car. I found that although my car was only .3 liters larger than the Honda B16, my piston speeds were more than 1.5 times that of the Honda's at a lower redline. The reason that other 4cyl. and our 944 2.5L motors aren't rev happy is because that piston moves like Kimbo's left hook on a knockout hit. Increasing our piston speeds with a higher RPM is going to increase the stress on the piston by a similar factor. Accel, Decel, suction, compression... It could be catastrophic on stock internals. If not by the heat on the side skirts and cylinder walls etc.
I see that it was touched on earlier (I think), but not divulged;
"In order to increase HP, without increasing torque, you must increase RPM."
A Ferrari 360 makes within 10hp of a C5 Corvette Z06 at 2.1 liters less of displacement. However, it's torque doesn't even cross the 300 mark (Something like 270 ft/lbs). So you have a 3.6 liter motor creating nearly 400bhp, next to a 5.7 liter motor making roughly 405bhp, but the real difference comes in, when you look at the RPM and torque difference. The Chevy motor spins to 6500rpm and the Ferrari motor, 8500 RPM. That's a difference of 2k RPM for similar power numbers. But the raw rotational force resulting from the longer stroke of the 5.7 liter is more than 100 pound feet of torque than the 3.6, and at a much lower RPM.
To find a good compromise between rod ratio, and displacement (with our motors), one could offset grind a 2.5L crank for less stroke, and compensate by widening the bore, to retain the 2.5 liter displacement. This would create a motor that could rev higher, and would suffer little in torque. Not sure how much the crank could be ground, and I'm not sure how much of a difference it would make. And at this point you'd be using aftermarket rods and possibly pistons, pretty much nullifying my point. But if you see it the way I do, then it could be interesting to test for results!
Taking that into account, the general rule stating that in order to increase power without torque, is to increase RPM, you could strap on a larger turbo, raise the redline, bump flow numbers on the head etc. and make an absolute beast. We all know that turbochargers breathe better with higher RPM, so increasing that one factor would increase output by a lot. With a turbocharger that could keep up with the motor, and an intake track that flows well enough, 400hp is easy, and not incredibly stressful on the motor.
The problem with shooting nitrous at low RPM, is that you're getting low VE and low air-speeds. This causes a problem with air stalling, and nitrous pooling in the intake, instead of getting in the cylinder like it should. General rule is that you don't want to shoot before 4k or you risk nitrous backfire. If you want something that's reliable, you can't shoot at 2k or you're almost guaranteed to grant your intake manifold permission for lift-off.
The best application for spooling a turbo with nitrous, is if you have a turbo on our small motors capable of creating 1000hp and need it to do so before 5k. Usually done best with a two-step launch control at the drag strip.
Here's a good example of that kind of setup spooling a large turbo:
http://www.youtube.com/watch?v=tohCBKmc2HM
DanaT, I read your comment about power, in relation to RPM and rod ratio. Problem is, the RPM deal is less of a rod ratio thing, and more of a piston speed thing. The fact that our engines have a 1.33:1 rr speaks wonders when you consider that other car engines run way higher rod ratios.
Prime example? Honda B16. That's an all day 9k rpm motor if you want. The rod ratio is 1.745:1 and it makes nearly no torque because of that. But also consider the piston speeds, therefore related stress and heat on all effected internals.
I looked into rod ratio and piston speed back when I was working on another 4cyl car. I found that although my car was only .3 liters larger than the Honda B16, my piston speeds were more than 1.5 times that of the Honda's at a lower redline. The reason that other 4cyl. and our 944 2.5L motors aren't rev happy is because that piston moves like Kimbo's left hook on a knockout hit. Increasing our piston speeds with a higher RPM is going to increase the stress on the piston by a similar factor. Accel, Decel, suction, compression... It could be catastrophic on stock internals. If not by the heat on the side skirts and cylinder walls etc.
I see that it was touched on earlier (I think), but not divulged;
"In order to increase HP, without increasing torque, you must increase RPM."
A Ferrari 360 makes within 10hp of a C5 Corvette Z06 at 2.1 liters less of displacement. However, it's torque doesn't even cross the 300 mark (Something like 270 ft/lbs). So you have a 3.6 liter motor creating nearly 400bhp, next to a 5.7 liter motor making roughly 405bhp, but the real difference comes in, when you look at the RPM and torque difference. The Chevy motor spins to 6500rpm and the Ferrari motor, 8500 RPM. That's a difference of 2k RPM for similar power numbers. But the raw rotational force resulting from the longer stroke of the 5.7 liter is more than 100 pound feet of torque than the 3.6, and at a much lower RPM.
To find a good compromise between rod ratio, and displacement (with our motors), one could offset grind a 2.5L crank for less stroke, and compensate by widening the bore, to retain the 2.5 liter displacement. This would create a motor that could rev higher, and would suffer little in torque. Not sure how much the crank could be ground, and I'm not sure how much of a difference it would make. And at this point you'd be using aftermarket rods and possibly pistons, pretty much nullifying my point. But if you see it the way I do, then it could be interesting to test for results!
Taking that into account, the general rule stating that in order to increase power without torque, is to increase RPM, you could strap on a larger turbo, raise the redline, bump flow numbers on the head etc. and make an absolute beast. We all know that turbochargers breathe better with higher RPM, so increasing that one factor would increase output by a lot. With a turbocharger that could keep up with the motor, and an intake track that flows well enough, 400hp is easy, and not incredibly stressful on the motor.
what about the new ones from Borg Warner that are on the 997TT ?
Also, once the pandora's box of nitrous is opened, it is a great idea for spool up use and that would allow the tank to run much longer than for a top end shot.
So slap on a big fat laggy turbo for the top end and a 100 shot that would come on down low, 2K-4K, for "off the line/spool up"; i.e. to fill in the area under the curve from the big laggy turbo that can run to 7K. So when the nox is done, the turbo would be at full boost or close.
So you would have an area under the curve from 2K-7K.
Or propane injection. Something I don't think has ever been discussed on these boards.
Also, once the pandora's box of nitrous is opened, it is a great idea for spool up use and that would allow the tank to run much longer than for a top end shot.
So slap on a big fat laggy turbo for the top end and a 100 shot that would come on down low, 2K-4K, for "off the line/spool up"; i.e. to fill in the area under the curve from the big laggy turbo that can run to 7K. So when the nox is done, the turbo would be at full boost or close.
So you would have an area under the curve from 2K-7K.
Or propane injection. Something I don't think has ever been discussed on these boards.
The best application for spooling a turbo with nitrous, is if you have a turbo on our small motors capable of creating 1000hp and need it to do so before 5k. Usually done best with a two-step launch control at the drag strip.
Here's a good example of that kind of setup spooling a large turbo:
http://www.youtube.com/watch?v=tohCBKmc2HM
08-31-2010, 01:53 PM
#26
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944obscene, you need to check your numbers...
We have a much better rod:stroke ratio than the B16. The B16 has a stroke of 77.4mm and rod length of 134mm, for a ratio of 1.745:1. The 2.5L has a stroke of 78.9mm and a rod length of 150mm, for a ratio of 1.9:1.
In fact when I do the numbers, piston acceleration for the two motors is almost identical. The major difference is the B16 is swinging around tiny 81mm bore pistons & pencil rods that weigh nothing compared to our 100mm pistons & rods built for turbo-duty...
We have a much better rod:stroke ratio than the B16. The B16 has a stroke of 77.4mm and rod length of 134mm, for a ratio of 1.745:1. The 2.5L has a stroke of 78.9mm and a rod length of 150mm, for a ratio of 1.9:1.
In fact when I do the numbers, piston acceleration for the two motors is almost identical. The major difference is the B16 is swinging around tiny 81mm bore pistons & pencil rods that weigh nothing compared to our 100mm pistons & rods built for turbo-duty...
08-31-2010, 05:58 PM
#27
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I think nitrous evaporates pretty much the instant it leaves the nozzle; there's no pooling.
08-31-2010, 06:09 PM
#28
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A Ferrari 360 makes within 10hp of a C5 Corvette Z06 at 2.1 liters less of displacement. However, it's torque doesn't even cross the 300 mark (Something like 270 ft/lbs). So you have a 3.6 liter motor creating nearly 400bhp, next to a 5.7 liter motor making roughly 405bhp, but the real difference comes in, when you look at the RPM and torque difference. The Chevy motor spins to 6500rpm and the Ferrari motor, 8500 RPM. That's a difference of 2k RPM for similar power numbers. But the raw rotational force resulting from the longer stroke of the 5.7 liter is more than 100 pound feet of torque than the 3.6, and at a much lower RPM.
Yeah, we know; it's called power equals torque times RPM.
Yes of course, chances are that 5.7 liters of displacement will have greater torque than 3.6 liters; and basically it will also have a longer stroke, then.
Nothing more to it than that.
09-01-2010, 12:06 AM
#29
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My mistake, I was going by some numbers I read on here. If thats the case though (and I haven't looked at our motor specs in a while) then I guess we're better off, but I was thinking that we had a long stroke. Eh.
As far as nitrous issues, I have read about and have seen evidence of different nitrous blowouts. Watched as a mustang was reduced from over 400whp on a dyno to roughly 0whp because the guy tuning wanted to shoot at about 3000 rpm. I was because of a pooling issue that exploded the top end of the motor. Cost the owner a whole new rebuild out of the shop's pocket.
And turbo tommy. There is a lot more to it than that. Not just the bottom end, but the overall breathability related to intake dynamics etc. I was just addressing what I've noticed as far as engine design and overall performance characteristics.
As far as nitrous issues, I have read about and have seen evidence of different nitrous blowouts. Watched as a mustang was reduced from over 400whp on a dyno to roughly 0whp because the guy tuning wanted to shoot at about 3000 rpm. I was because of a pooling issue that exploded the top end of the motor. Cost the owner a whole new rebuild out of the shop's pocket.
And turbo tommy. There is a lot more to it than that. Not just the bottom end, but the overall breathability related to intake dynamics etc. I was just addressing what I've noticed as far as engine design and overall performance characteristics.
09-01-2010, 10:07 AM
#30
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A. Nox for low rpm, how much does the shot affect that? I was thinking in the lines of a 50 shot, not a 200 shot.
B. How much difference would a wet vs dry system be for use as spool up?
In regards to the internals, I have always gone by the rule of short stroke, big bore = high tq/low rev. No?
The 951 has a fairly large bore for the size of the motor doesn't it?
B. How much difference would a wet vs dry system be for use as spool up?
In regards to the internals, I have always gone by the rule of short stroke, big bore = high tq/low rev. No?
The 951 has a fairly large bore for the size of the motor doesn't it?