rewilson64
Member
when 206 hits rev limiter, will it stay at 6100 rpm, if you keep on the pedal, or does it drop off. How long can you run at max rpm, and would it cause any damage if you stay on it for 2, 3, 4, or more seconds ?
rpm
- Thread starter rewilson64
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Gab507
Member
It will stay at 6100. Actually most will read between 6000 and 6100 on the tach. It does not hurt the engine to ride the limiter. Some of the restricted classes ride it a lot. There is no set guide but depending on oval or road course you could be on it a lot or barely at all. Let the watch be your guide.
rewilson64
Member
thanks, that;s helpful
When you hit the rev limiter at full throttle, it actually bounces between about 4500 and 6100. If you ease up on the throttle, the low RPM on the "bounce" will be at a higher RPM, 5100 for example. That said, I have not seen any difference in lap times between the two. Perhaps because when concentrating on managing the rev limiter, its harder to drive a perfect lap. However, Being easier on the rev-limiter should help keep the keyway on the crank from getting destroyed. This is a bigger issue with the W/F because it uses a heavier clutch in is spinning at higher RPM when it hits.
Jimbo
You can fool some of the people some of the time
Since the rev limiter cuts out ignition pulses it seems to me that a Mycron might not be the best way to accurately measure maximum rpms. It the tach should work fine up to the point that the coil starts to cut them out but once it starts cutting them out it will only see the ones that fire the spark plug. The actual crankshaft rpms will be something else.
alvin l nunley
Site Supporter
Perhaps this is a place where my sig would explain what is needed. I'm sure I've heard the RPM doesn't drop. I could be wrong.
Flash-o-matic
Member
If you keep an eye on the Mychron when the engine hits the rev limiter it is very obvious that the rpm reading is all over the place. The max rpm read by the Mychron on the limiter is not a very accurate number.
CarlsonMotorsports
Site Supporter
Does anyone know if there is a way to smooth the rpm curve/reading on the Mychrons? I've noticed that on our Mychron 4 gauge that the rpm doesn't fluctuate nearly as much as it does on our Mychron 5 gauge. I know most dyno software has this available. Some software update from Aim possibly?
This raises another question....which tach (and how accurate) should be used in tech.
Obviously not the racer's, but a hand held unit that is used for all engines in tech.
What Al, Jimbo, and others have suggested, is absolutely true with rpm not decreasing immediately -- it decreases slowly and is heavily dependent on the kinetic energy of the flywheel. Again, a heavier and larger diameter flywheel will decrease rpm much slower than a lightweight smaller one. Not a problem with the spec flywheel being used...BUT, does this then cause people to look for heavier clutches to gain rotating mass if they race on a track where they know they will need to be against the rev limiter?
This rev limiter racing is just about enough to make one's head spin.
-----
Thanks and God bless,
Brian Carlson
Carlson Racing Engines
Vector Cutz
www.CarlsonMotorsports.com
27 years of service to the karting industry
Linden, IN
765-339-4407
bcarlson@CarlsonMotorsports.com
This raises another question....which tach (and how accurate) should be used in tech.
Obviously not the racer's, but a hand held unit that is used for all engines in tech.
What Al, Jimbo, and others have suggested, is absolutely true with rpm not decreasing immediately -- it decreases slowly and is heavily dependent on the kinetic energy of the flywheel. Again, a heavier and larger diameter flywheel will decrease rpm much slower than a lightweight smaller one. Not a problem with the spec flywheel being used...BUT, does this then cause people to look for heavier clutches to gain rotating mass if they race on a track where they know they will need to be against the rev limiter?
This rev limiter racing is just about enough to make one's head spin.
-----
Thanks and God bless,
Brian Carlson
Carlson Racing Engines
Vector Cutz
www.CarlsonMotorsports.com
27 years of service to the karting industry
Linden, IN
765-339-4407
bcarlson@CarlsonMotorsports.com
Flash-o-matic
Member
Some tracks require the gearing to be on the rev limiter, some, like PKRA, the limiter is rarely touched ( with 206) because of the torque/power range of the engine. I feel the track layout dictates how you race your competitors. As far as heavy vs. light clutches, inconsequential. Just more minutia to keep you from getting a good night's sleep. Ha! Here we go again, I'm sure !!! ( you awake Al?)
alvin l nunley
Site Supporter
Pete Muller once had an article on his website proving, beyond a doubt, that you want to run the heaviest shoes you can. Of course you want to have a spring that is strong enough to slip the clutch at peak torque RPM on the low-end. It seems the centrifugal force applied by the clutch shoes is a square function of the rpm times the weight of the shoe. in other words, the force of the shoe against the drum is squared as the weight of the shoe increases. In the 70s, the Burko and Hartman clutchs started using springs for this very reason. With the appearance of the Horstman spring-loaded disc clutch, the writing was on the wall.
Flash-o-matic
Member
Heavy vs. light clutch shoes is different from heavy vs. light clutches.
The pulses measured by the Tach drop, that is the function of the electronics. If you were using an actual hall effect pickup on the flywheel you would see a major difference. If you are on a long straight, the clutch locked up and then engine starts fluttering between actual 4500 RPM and 6100 RPM you would experience some severe engine damage.
CarlsonMotorsports
Site Supporter
John,
The actual engine rpm does not drop as dramatically as the tach shows. I think that's what these guys are saying. The flywheel continues to turn at 6050-ish although the tach shows the rpm bouncing. The flywheel (and subsequently the rotating assembly) obviously cannot be changing that radically in rpm when it hits the rev limiter.
My point of a heavy flywheel (not allowed) is that it would dorp in rpm slower than a lighter flywheel. Same can be said for the clutch. Again, a difference is likely from oval racing to road course racing where the extra kinetic energy of a heavy flywheel can help "pull" the car through momentum (oval) corners and not lose as much rpm as a light flywheel.
Minutia, maybe.
The actual engine rpm does not drop as dramatically as the tach shows. I think that's what these guys are saying. The flywheel continues to turn at 6050-ish although the tach shows the rpm bouncing. The flywheel (and subsequently the rotating assembly) obviously cannot be changing that radically in rpm when it hits the rev limiter.
My point of a heavy flywheel (not allowed) is that it would dorp in rpm slower than a lighter flywheel. Same can be said for the clutch. Again, a difference is likely from oval racing to road course racing where the extra kinetic energy of a heavy flywheel can help "pull" the car through momentum (oval) corners and not lose as much rpm as a light flywheel.
Minutia, maybe.
Jimbo
You can fool some of the people some of the time
Brian
Thank you for your post. The flywheel weight theory has been around for a very long time and I have always had the following concern about it.
It seems to me that once the clutch is locked up the entire weight of the kart has an affect on how quickly the engine rpm and vehicle speed will drop or increase.
It seems to me that this would also apply when the ignition coil cuts out the spark plug.
The entire weight of the kart becomes the " flywheel"
I'd be interested in your or anyone else's opinion on this theory.
Thank you for your post. The flywheel weight theory has been around for a very long time and I have always had the following concern about it.
It seems to me that once the clutch is locked up the entire weight of the kart has an affect on how quickly the engine rpm and vehicle speed will drop or increase.
It seems to me that this would also apply when the ignition coil cuts out the spark plug.
The entire weight of the kart becomes the " flywheel"
I'd be interested in your or anyone else's opinion on this theory.
Flash-o-matic
Member
Jimbo, that is the reason for my "inconsequential" comment in regards to clutch weight. The difference between weights of different clutches is so small compared to total weight of the kart. To be clear I am not talking about different weight shoes or sprigs in the clutch. A 370 # kart is 168,720 grams. even a 228 gram ( 1/2 lb.) difference in clutch weight is invisible to the engine (.001%).
CarlsonMotorsports
Site Supporter
But we're not comparing clutch weight to total kart weight.
We're comparing clutch weight to rotating assembly weight (crank rod, piston, wrist pin, circlips, rings, flywheel, & flywheel retaining nut.) Just throwing numbers out there....if someone were to develop a large diameter 4 pound clutch, it would most certainly have more inertia effect than a much lighter and smaller clutch (no differently than we see with flywheels.)
The result is not a gain in power, but sustained rpm via kinetic energy during deceleration or when the engine is leaning on the rev limiter.
The opposite is true with acceleration. We've all see the difference in using a lighter flywheel and even 3HP diameter flywheel on an open.
There's a reason that lightweight rotating assembly parts are produced for big car applications (Nascar, Indy cars, F1, WoO, etc.) The last crank I bought for our sprint car was in the $4000 neighborhood...Rule of thumb on small block crankshafts is to add around $100 per pound lighter. Guess what...everyone is using the ultra-light cranks in sprint cars today.
Now, for truck and tractor pulling, it's just the opposite...They are looking for massive heavy flywheels and balancers to add kinetic energy to keep the tires turning even when the engine is under extreme loads. No lightweight cranks going on there...HUGE counterbalance weights and dampeners.
How many of you currently use an inertia dyno?
How did you determine the size (OD) and weight of the flywheel you are using on said dyno?
How long does it take to decelerate after a pull? I hope you see what I'm getting at.
Yea, it "might" be minutia, then again, it might not. We're talking underpowered karts with a rev limiter. Any advantage (minute or not) is still an advantage. If we're talking halves of tenths, I'll accumulate all of them that I can.
I think the less HP you are dealing with, the more important this becomes. Consider that remote control oval racing takes this to a whole new level.
To this day, I still build small plate flatheads with heavy flywheels.
We're comparing clutch weight to rotating assembly weight (crank rod, piston, wrist pin, circlips, rings, flywheel, & flywheel retaining nut.) Just throwing numbers out there....if someone were to develop a large diameter 4 pound clutch, it would most certainly have more inertia effect than a much lighter and smaller clutch (no differently than we see with flywheels.)
The result is not a gain in power, but sustained rpm via kinetic energy during deceleration or when the engine is leaning on the rev limiter.
The opposite is true with acceleration. We've all see the difference in using a lighter flywheel and even 3HP diameter flywheel on an open.
There's a reason that lightweight rotating assembly parts are produced for big car applications (Nascar, Indy cars, F1, WoO, etc.) The last crank I bought for our sprint car was in the $4000 neighborhood...Rule of thumb on small block crankshafts is to add around $100 per pound lighter. Guess what...everyone is using the ultra-light cranks in sprint cars today.
Now, for truck and tractor pulling, it's just the opposite...They are looking for massive heavy flywheels and balancers to add kinetic energy to keep the tires turning even when the engine is under extreme loads. No lightweight cranks going on there...HUGE counterbalance weights and dampeners.
How many of you currently use an inertia dyno?
How did you determine the size (OD) and weight of the flywheel you are using on said dyno?
How long does it take to decelerate after a pull? I hope you see what I'm getting at.
Yea, it "might" be minutia, then again, it might not. We're talking underpowered karts with a rev limiter. Any advantage (minute or not) is still an advantage. If we're talking halves of tenths, I'll accumulate all of them that I can.
I think the less HP you are dealing with, the more important this becomes. Consider that remote control oval racing takes this to a whole new level.
To this day, I still build small plate flatheads with heavy flywheels.
alvin l nunley
Site Supporter
Any calculation of power needed for acceleration has to include a time factor. How fast are you are accelerating the object from dead stop to maximum.
If you go from a heavy flywheel to a light flywheel, you might measure the time it takes for the engine to go from idle to clutch stall. Has anybody done that? Has anybody measured the time difference between the two flywheels? Has anybody documented the difference in stall RPM, if any? If you had that information, you might be able to extrapolate it to determine the power difference it takes to go from lockup to the end of the straightaway with a light or heavy flywheel. I'm just speculating of course, but I think the results of that calculation would be very very small.
I'm no mathematician, far from it, but the fact that they once said you could not accelerate past 150 miles per hour in the quarter-mile shows me it's a very complicated piece of mathematics. I'm still amazed that mathematicians once said that, mathematically, the bumblebee can't fly.
If you put a lighter flywheel on, or a lighter clutch, (or the opposite) and you go faster, that's great, congratulations, but I think the explanation is far beyond our ability to comprehend, or explain, the finer details of why.
If you go from a heavy flywheel to a light flywheel, you might measure the time it takes for the engine to go from idle to clutch stall. Has anybody done that? Has anybody measured the time difference between the two flywheels? Has anybody documented the difference in stall RPM, if any? If you had that information, you might be able to extrapolate it to determine the power difference it takes to go from lockup to the end of the straightaway with a light or heavy flywheel. I'm just speculating of course, but I think the results of that calculation would be very very small.
I'm no mathematician, far from it, but the fact that they once said you could not accelerate past 150 miles per hour in the quarter-mile shows me it's a very complicated piece of mathematics. I'm still amazed that mathematicians once said that, mathematically, the bumblebee can't fly.
If you put a lighter flywheel on, or a lighter clutch, (or the opposite) and you go faster, that's great, congratulations, but I think the explanation is far beyond our ability to comprehend, or explain, the finer details of why.