power pulses and rpm

[Cheapstreetduster]

i had a discussion the other day with a friend...
the subject of running 9000 rpm in nascar engines came up...
i was using data from my memory of motorcycle road racing..and
power pulses...
in those days the theory was how it effected traction or "forward grip" on motor cycles...as they drove off or out of the exit of a turn..
since the rear tire cantact patch is so small leaned over on a motor cycle...the power pulse or spikes...related to tire traction.. any way i digress..
The current conversation i had was that the rpm's we see today in nascar was due to a multitude of issues...
but one being momentum and inertia. of recipt parts...
the other being velocities and compounding volumetric effieciencies...
but if you take note of the power pulses that take place over a specified or limited distance or time span...
and say those power pulses had a value...lets say its pressure...but it could in some way be broken down...from hp or trq...and devided by rpm and by 8 cyl 4 stroke per cycle engine...
you would come to a specific number
i just cant seem to come up with the formula...
but say we took a 4 stroke engine with 8 cyclinders that makes 360 hp @ 4500 rpm...
how could i find the hp represented @ each individual pulse?
the if we doulbled the rpm like in a nascar engine to 9000 with the same values per pulse would we theoretically get more or double the hp?
strickly speeking in terms of power pulse and the value attactched to it?

do you see where i am going here...?
or would pressure be a better trem for value?
cheapst..

[OldSStroker]

i had a discussion the other day with a friend...
the subject of running 9000 rpm in nascar engines came up...
i was using data from my memory of motorcycle road racing..and
power pulses...
in those days the theory was how it effected traction or "forward grip" on motor cycles...as they drove off or out of the exit of a turn..
since the rear tire cantact patch is so small leaned over on a motor cycle...the power pulse or spikes...related to tire traction.. any way i digress..
The current conversation i had was that the rpm's we see today in nascar was due to a multitude of issues...
but one being momentum and inertia. of recipt parts...
the other being velocities and compounding volumetric effieciencies...
but if you take note of the power pulses that take place over a specified or limited distance or time span...
and say those power pulses had a value...lets say its pressure...but it could in some way be broken down...from hp or trq...and devided by rpm and by 8 cyl 4 stroke per cycle engine...
you would come to a specific number
i just cant seem to come up with the formula...
but say we took a 4 stroke engine with 8 cyclinders that makes 360 hp @ 4500 rpm...
how could i find the hp represented @ each individual pulse?
the if we doulbled the rpm like in a nascar engine to 9000 with the same values per pulse would we theoretically get more or double the hp?
strickly speeking in terms of power pulse and the value attactched to it?

do you see where i am going here...?
or would pressure be a better trem for value?
cheapst..

There was an interesting article recently in RACE ENGINE TECHNOLOGY magazine about Moto GP engines comparing "Big Bang" engines (odd-firing or multiple cylinder simultaneous firing) and "screamers" or even-firing engines. The firing pulses did have some effect on the shape of the torque curve and the rider's ability to get power down off the corner. Very interesting stuff.

There is some activity now in measuring individual cylinder pressure in real time on an operating engine. This is generally done on a dyno, but it's feasible to do in in-car if the car is big enough to hold the electronics. F1 cars probably aren't. By measuring dynamic cylinder pressures, you can figure how much indicated torque each cylinder is providing at every rpm, and therefore individual cylinder indicated horsepower.

Brake Mean Effective Pressure (BMEP) can be related directly to brake torque per cubic inch (or cubic cm). Brake (torque, power, pressure, etc.) is what's left after friction and pumping losses are subtracted from indicated (torque, power, ...).

Highest BMEP (torque/cube) is generally around torque peak, and decreases with increasing rpm above that. Because power is a function of torque x rpm, power continues to increase above torque peak rpm even though BMEP is decreasing. An F1 engine makes about 215-220 psi BMEP @ 18,500 or so, while a Cup engine makes closer to 210 psi at half that rpm. It's tougher to get the BMEP @ higher rpm. Of course, a Pro Stock engine makes a BMEP of about 225-230 @ ~9500, but not for very long at one time! That's only about a 9% range in BMEP @ power peak rpm for very different types of engines. I find that very interesting.

If you think of torque/cube and multiply it by the number of "pulses" or how often it is occuring, isn't that power? Because power is related to cycling rate (rpm), I'm not sure the "hp/pulse" has meaning; torque per pulse might. So, yes, if you could maintain a given BMEP (brake torque per cube) and double the rpm you would double the brake power. That's the reason we continually try to raise rpm while maintaining as much torque per cube as we can.

My $.02

[Cheapstreetduster]

thanks oldstroker...
just to go back or expand on the motor cycle thing...
yrs back we where discussing Ducati's dominance..this was around early to mid 90s
the arguement was that the ducks where bigger CCs or cubic inches.
880 vrs 750 ccs at the time...
my arguement was they they where a twin cyl.. Vtwin...
vrs the 4 cyls of the restof the field...
we where on the beach at daytona...with Mike smith and Dave sedowski and Colin Edwards..and a kid from australia cant remember his name but he had green or red died hair....drove the ducati...at teh time..a few others..maybe..
any way...
there was tracks in the sand ...presumeably from a motor cycle...
and you/we could see cupping or chatter at even spacings or intervals...on the tire tracks.. like say every 3' intervals
(i assume it was a single cyl type vehicle/engine)
When/during the disussion...I concluded that the chatter or feathering was the point of the power pulse..
wich is what continued the debate..and became part of the topic..
as to traction and how the power pulse effected grip...
the Ducati riders Dave S and Mike smith and the other kid? mentioned all had raced on the ducati's and how they always made good forward grip exiting the apex and when getting back on the throttle..
we /I argued/deduced it was that the ducati's vtwin had less spikes per rotation..than a 4cyl....so if the spikes created or initiated the loss of traction....
then the ducati's advantage was that it had less spikes per givin rotation..
or distnance..
but it prolly had a greater spike or pulse peak(bigger bang)...due to its equal hp or top speed down the straightaways.(from less cylinders).it seem' equal to the 4 cyl...and at the time was very close on a dyno...atleast as far as what the consensus was in those days.
so the power pulses and or this bmep has always stewed in my brain...and it surfaces from time to time...
back to your explaination....if we could double the bmep we would see a direct corelation to gains in power...
sort of the circumstances found in a 2 stroke engine...they are notoriously powerful for there size.
also i wonder do/would the you mention the prostocks bmep is not sustained is this due to load...?
as the vehicles mass reaches a certain speed does/would the load on the cyl change the bmep? as the load/resistance lessens.
cheapst.

[Cheapstreetduster]

those #s i assume is the peak or maximum psi @ RPM bmep for the examples you gave....
the rpm for instance i wonder what the bmep psi is at half the peak rpm #s?
are they half of the max numbers?
for instance in F1 do they get a reading of 110 psi bmep at 9250 rpm?
also just to complete a thought...
i know a nascar motors make 800 hp and is 358"
a prostock is 1250 hp at 500"
but i have no idea what a forumla 1 motor is as far
as cubic " or hp output..
but they make very similar peak psi bmep's
so changing the bmep psi even as much as 1% represents a huge gain?
cheapst.

[OldSStroker]

those #s i assume is the peak or maximum psi @ RPM bmep for the examples you gave....
the rpm for instance i wonder what the bmep psi is at half the peak rpm #s?
are they half of the max numbers?
for instance in F1 do they get a reading of 110 psi bmep at 9250 rpm?
also just to complete a thought...
i know a nascar motors make 800 hp and is 358"
a prostock is 1250 hp at 500"
but i have no idea what a forumla 1 motor is as far
as cubic " or hp output..
but they make very similar peak psi bmep's
so changing the bmep psi even as much as 1% represents a huge gain?
cheapst.

BMEP is equivalent to torque/cubic inch, or the engine's ability to pump air in and out and burn it effectively. It generally follows the Volumetric Efficiency and torque curves. It is highest about torque peak where volumetric efficiency is about the highest. 2 stroke engines make considerably higher BMEP because they process air/fuel every revolution rather than every other rev. As far as I know the best 2-strokes make about 50% more BMEP than the best 4-strokes, not 100% more.

A good Cup engine is about 850 hp @ 9000 rpm (using my example). That's 496 lb-ft @ 9000 or 1.385 lb-ft/cubic inch (BMEP=209 psi). If max torque were 575 lb-ft @ a 6000 rpm torque peak (just guessing here), torque per cube would be 1.606 (BMEP=242 psi).

Similarly most engines have highest BMEP around torque peak rpm where they process air/fuel most effectively.

F1 is currently 2.4L (~146cubic inches) and makes ~750 hp around 18-18,500 rpm. ProStock engines make ~1400 hp in the 9000+ area. They only run in anger about 7 seconds at a time, so some of their parts are in jeopardy if they run in that 10,000 rpm area for very long! Cup and F1 engines are "endurance" engines with considerably more than a million revolutions between rebuilds so they can't achieve the very high power pear rpm BMEP of the PS.

A 1% BMEP change at power peak rpm would represent a 1% change in torque and power.

[Cheapstreetduster]

very cool...thanks...
so since volumetric effieciency is the key point..
"wich it has always been"
there would be no quantification of 1/2 the peak torque would equal half the pressure.
because the engine or intake tract may be very inefficient at 1/2 the reference rpm.. so that would be understandable..
for instance a stumble or dip in the torque curve ,,wich are anomally's that happen...
i see...
so really its relative to volumetric effieciency...directly..when the bang is the biggest....so to speek..
at higher rpm levels i imagine exhaust scavenging might play a role.
just stuff to chew on..
you have cleared some of the haze...although re-reading what you say i usually find something i missed.....
thanks again...
beast regards
cheapst.

[beth]

Two cylinder and "Big bang" multi cylinder motorcycles give more time between power pulses and this allows the tire to recover some of the "twist" caused by the previous pulse. Because of the very limited tire patch motorcycles are very limited in how much torque they can transfer to the tire before slippage occurs. Engine design and/or rider input limits the torque applied to the point just before loss of traction. Spaced firing allows the tire to recover from maximum deflection thus cusioning the following pulse and allowing more net torque to be applied to the tire.

The increased traction is minimal but there and useable. I doubt a cup car, with a narrower rpm range, 8 cylinders and the attending rotating mass would benefit as much from this approach.


beth

[F1Fever]

A while back I studying a similar situation and found an equation which i wrote into a calculator. I am not sure how accurate it is but the math is there with the calculator and we can discuss it if you wish. I'd love to hear some thoughts on it. The formula is the "plan" method.

http://www.hotroddersauctions.com/calcs ... power.html

[hsutton]

those #s i assume is the peak or maximum psi @ RPM bmep for the examples you gave....
the rpm for instance i wonder what the bmep psi is at half the peak rpm #s?
are they half of the max numbers?
for instance in F1 do they get a reading of 110 psi bmep at 9250 rpm?
also just to complete a thought...
i know a nascar motors make 800 hp and is 358"
a prostock is 1250 hp at 500"
but i have no idea what a forumla 1 motor is as far
as cubic " or hp output..
but they make very similar peak psi bmep's
so changing the bmep psi even as much as 1% represents a huge gain?
cheapst.

BMEP is equivalent to torque/cubic inch, or the engine's ability to pump air in and out and burn it effectively. It generally follows the Volumetric Efficiency and torque curves. It is highest about torque peak where volumetric efficiency is about the highest. 2 stroke engines make considerably higher BMEP because they process air/fuel every revolution rather than every other rev. As far as I know the best 2-strokes make about 50% more BMEP than the best 4-strokes, not 100% more.

A good Cup engine is about 850 hp @ 9000 rpm (using my example). That's 496 lb-ft @ 9000 or 1.385 lb-ft/cubic inch (BMEP=209 psi). If max torque were 575 lb-ft @ a 6000 rpm torque peak (just guessing here), torque per cube would be 1.606 (BMEP=242 psi).

Similarly most engines have highest BMEP around torque peak rpm where they process air/fuel most effectively.

F1 is currently 2.4L (~146cubic inches) and makes ~750 hp around 18-18,500 rpm. ProStock engines make ~1400 hp in the 9000+ area. They only run in anger about 7 seconds at a time, so some of their parts are in jeopardy if they run in that 10,000 rpm area for very long! Cup and F1 engines are "endurance" engines with considerably more than a million revolutions between rebuilds so they can't achieve the very high power pear rpm BMEP of the PS.

A 1% BMEP change at power peak rpm would represent a 1% change in torque and power.

OldSStroker, I think your information is a little dated. I've heard that those Pro Stock cars are now routinely turning about 10,000-10,200 RPM at the finish line which is right at valve float for those big intake valves. This started when Greg Anderson and Jason Line started to dominate the class with the Nascar technology that Line brought with him concerning more powerful engine technology and lighter internal engine parts which led to minimum weights for rods, pistons, pins, etc. If they had deliberately lost a few races, and made the class championship picture closer, it might have furthered engine development technology.

[OldSStroker]

OldSStroker, I think your information is a little dated. I've heard that those Pro Stock cars are now routinely turning about 10,000-10,200 RPM at the finish line which is right at valve float for those big intake valves. This started when Greg Anderson and Jason Line started to dominate the class with the Nascar technology that Line brought with him concerning more powerful engine technology and lighter internal engine parts which led to minimum weights for rods, pistons, pins, etc. If they had deliberately lost a few races, and made the class championship picture closer, it might have furthered engine development technology.

Yes, I believe PS is turning above 10,000, and perhaps higher than 10,200. However, I do not think they are peaking power at those rpms. I used 9200-9500 for my BMEP estimates. I wouldn't be surprised if they are down ~40 or more hp from peak at the highest rpm they spin. Darin would know a lot more about that than I do. I'm conjecturing.

This goes back to why you would want to turn rpm significantly down the back side of the hp curve at the finish line....but that's another story.

As to what's happening to the valves @ those r's, it may be a combination of loft (uncontrolled by then?), seat bouncing (2-3 or ? times) and perhaps other antics. Folks that know probably aren't confirming exactly what is happening, especially those who are able to turn the most revs.

A while ago, Jason Line said rod strength (inertia loading) limited rpm. That's probable fixable within the NHRA rules if more rpm is available from the valvetrain.

[F1Fever]

This goes back to why you would want to turn rpm significantly down the back side of the hp curve at the finish line....but that's another story.

That's an easy one.

[Cheapstreetduster]

my hypothosis wich came directly from the ever increasing rpm thresholds seen each yr or over the past yrs on nascar engines..
was part of the reason you see the higer rpm was directly due to
seeing more bmep over a given point..
than thay had done previously in the past with slower rpm cycles..
again going back to a 2 stroke vrs 4 stroke..
a 2 stroke will see more power pulses infact twice as many as a 4 stroke for a givin rpm..
the nascar phenomina..may be working off the same pricipal..
(and is i suppose the opposite of the motor cycle issue...i just used it
because it was part of my memory or foundation. from the past)

but if you couldnt see higher psi ...or bmep ...than maybe you could put 2 of them in the place where there previously was one.
for instance seeing 4500 rpms of the big block engines in the early days.
now they run the motor twice the rpm so you will see twice as many BMEP events...over the course of a lap..
does this make sense..?
cheaspt.

[beth]

but if you couldnt see higher psi ...or bmep ...than maybe you could put 2 of them in the place where there previously was one.
for instance seeing 4500 rpms of the big block engines in the early days.
now they run the motor twice the rpm so you will see twice as many BMEP events...over the course of a lap..
does this make sense..?

Yes, but it is the same basic principle that keeps us from using gearing to idle down the freeway at 600rpm and 65mph rather than a nascar breakthrough. Maintaining the same bmep at higher engine speeds increases power but this increase is limited by increases in friction.

[Cheapstreetduster]

actually i might think to some aspects ,,,
friction might be less...at higher rpms..
parastectic losses ? may be greater for sure....
"object in motion stays in motion" vrs "equal and apposing forces/reaction.."?
mean losses..
however i can see how part failures , as a greater limiting factor..
but again..this has steadily improved as the need increases.
but attaining good bmep at the higer rpms is probably the hard part..
and the gains are made small increments at a time..
along with the balance... "cause and effect"
i am only seeing this relative to my perspect..
wich is how most of us see/realise things...
I may well be totally wrong....but it is neat to exercise my
thoughts
and listen to what people who know better than me think...as well.
thanks
best regards..
cheaspt

[hsutton]

OldSStroker, I think your information is a little dated. I've heard that those Pro Stock cars are now routinely turning about 10,000-10,200 RPM at the finish line which is right at valve float for those big intake valves. This started when Greg Anderson and Jason Line started to dominate the class with the Nascar technology that Line brought with him concerning more powerful engine technology and lighter internal engine parts which led to minimum weights for rods, pistons, pins, etc. If they had deliberately lost a few races, and made the class championship picture closer, it might have furthered engine development technology.

Yes, I believe PS is turning above 10,000, and perhaps higher than 10,200. However, I do not think they are peaking power at those rpms. I used 9200-9500 for my BMEP estimates. I wouldn't be surprised if they are down ~40 or more hp from peak at the highest rpm they spin. Darin would know a lot more about that than I do. I'm conjecturing.

This goes back to why you would want to turn rpm significantly down the back side of the hp curve at the finish line....but that's another story.

As to what's happening to the valves @ those r's, it may be a combination of loft (uncontrolled by then?), seat bouncing (2-3 or ? times) and perhaps other antics. Folks that know probably aren't confirming exactly what is happening, especially those who are able to turn the most revs.

A while ago, Jason Line said rod strength (inertia loading) limited rpm. That's probable fixable within the NHRA rules if more rpm is available from the valvetrain.

Your probably right in assuming that the motors are 500-1000 RPM over their power peak at the finish line. I think that Darin or David Reher wrote a article over on the R-M site that addresses this very subject. It was said that more power pulses over the same distance allowed the Pro Stock crowd to gear the motors lower and put down more power once they figured out how to keep the valves seated over 10,000 RPM. Lighter valves are helping the valvetrain parts longevity too. Hollow valve stems are now commonplace although no exact weights have been publicized by any of the companies suppling them. Lots of propriety parts and deals out their now. I did hear that they are very strong as well as being super light. Technology marches on and sooner or later we little guys will hear some details.