Author Topic: Flywheel weight  (Read 7046 times)

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Offline Don Martin

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Flywheel weight
« on: May 12, 2015, 10:11:21 AM »
I am running an SB2.2 358 cu.in it made 863 HP on dyno at 8400. We are using a center force clutch with a 31 lb flywheel. Car ran well in Ohio. Engine builder is use to dirt cars with a lite flywheel. I say we need the mass to keep it turned up he wants it to turn quicker. Any input or am I just starting a pissing contest?
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Offline Dynoroom

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Re: Flywheel weight
« Reply #1 on: May 12, 2015, 10:16:22 AM »
It won't matter at Bonneville one lick.
Michael LeFevers
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Offline kiwi belly tank

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Re: Flywheel weight
« Reply #2 on: May 12, 2015, 02:44:48 PM »
On the dirt a lite flywheel or no flywheel is desirable for fast engine response both on & off the throttle to help accelerate & decelerate to back it into a corner. I don't find any of those characteristics desirable on the salt. If you get spooked & snap the throttle closed it could be the difference between going straight or going around.
A heavy flywheel won't cost you HP, it'll just get there a little slower.
  Sid. 

Offline jimmy six

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Re: Flywheel weight
« Reply #3 on: May 12, 2015, 04:20:06 PM »
Some dirt Modifieds are putting in a heavier ring gear. Coming off the throttle into a turn with 14-1 engine causing tire slip and not in a pleasant way. Their trannys are getting so good othe problems are popping up.
First GMC 6 powered Fuel roadster over 200, with 2 red hats. Pit crew for Patrick Tone's Super Stock #49 Camaro

Offline Milwaukee Midget

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Re: Flywheel weight
« Reply #4 on: May 12, 2015, 04:49:13 PM »
I'm going to argue that it depends on the characteristics of the car and which track you're on.

To Sid's point, "it'll just get there a little slower", nominally so, but in my case, I really don't have a lot of time.

I'm running a HP and aero challenged combination with a peaky engine, and the strategy I need to observe is to get it wound out as tightly as possible as soon as possible.  I'm running on the short course.

I found myself pulling - albeit quite slowly -  between the two and the three.

If I can achieve close to terminal velocity sooner in the run, it's possible I can pull a higher speed before I run out of track, rather than a creeping acceleration between the two and the three.

Don, on your car, Dynoroom is likely right, if you're on the long course at Bonneville.

But it might be worth a digit at Wilmington, where the traction is good and the course is short.
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Offline tortoise

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Re: Flywheel weight
« Reply #5 on: May 12, 2015, 05:00:01 PM »
If the engine builder uses an inertial dyno a light flywheel will show higher power readings.  This might prejudice him.

Offline JimL

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Re: Flywheel weight
« Reply #6 on: May 12, 2015, 11:30:00 PM »
If iron, or steel, or aluminum were actually solid....heavy flywheels might not require more power to spin.

But they are not solid, and every bit of mass in them is trying to go in a straight line at whatever velocity it is at along its vector.  It is being pulled into an arc by the atoms ahead of it who were trying to go straight....and so on.   Even if it was an actual solid, it would still create additional bearing surface drag when operated in a gravitational field.

On top of that, the flywheel is not moving at a constant speed during rotation at steady RPM.  It accelerates and decelerates multiple times per revolution.  If you dont believe that....OBD II misfire detection wouldnt have been working on all our cars for the last 21 years.

I have seen people claim that the deceleration of the crankshaft (during compression) offsets the acceleration of the crankshaft during the power stroke.  BS.  If that was true, the engine would not run.  Heavy flywheels are a diminishing return formula where you trade some power for the smoothing effect in the driveline components.

I dont know of any professional level racing choosing big heavy flywheels, over light and small.  During dyno cell testing (water brake engine dyno), I watched one of my V6 engines pick up over 15 hp when we cut the flywheel from 26 lbs to 13 lbs.  These guys built and tuned Indy car engines, off road engines, drag engines, and NASCAR engines.  

I dont think they steered me wrong.  They also taught me to run the flywheel as small diameter as I possibly can, regardless of what weight I have to use.

Which is exactly the same thing manufacturers do for racing programs.  Our turbo roadster, 20 years ago, used the small diameter flywheel/clutch/pressure plate design from the championship winning WRC cars.

Either none of the top engineers, race teams, Formula 1 designers etc know what they are doing.....or,

what?? :?

Sorry...getting cranky in my old age, but there are too many good reasons to run LIGHT flywheels for any kind of racing that needs pure, continous, peak horsepower.

« Last Edit: May 13, 2015, 03:15:50 AM by JimL »

Offline kiwi belly tank

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Re: Flywheel weight
« Reply #7 on: May 13, 2015, 01:02:29 AM »
I am running an SB2.2 358 cu.in it made 863 HP on dyno at 8400. We are using a center force clutch with a 31 lb flywheel. Car ran well in Ohio. Engine builder is use to dirt cars with a lite flywheel. I say we need the mass to keep it turned up he wants it to turn quicker. Any input or am I just starting a pissing contest?

It seems the fact your question was about your car & your combo has already been lost after only six posts.
ps I bet that sucker is playing some good music at 8400! 8-)
  Sid.

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Re: Flywheel weight
« Reply #8 on: May 13, 2015, 10:12:42 AM »
F1 cars no longer use flywheels (which supports JimL's post) but do have very small multi plate clutch cans. Interestingly, entirely separate flywheels popped up on the Williams F1 car a few years back as part of a standalone energy recovery system to add power to that coming from the engine. Williams now sell quite a lot of that technology to industry although they themselves now use batteries as part of the Mercedes ICE/ERS power plant. But standalone flywheels are used by Audi in their LMP1 cars - see note below from another website.

Up to now, Audi had been allowed to use four-wheel drive only above 120 km/h. But four driven wheels promise to deliver traction advantages particularly at low speed, for instance when the driver accelerates on exiting a tight corner. This year, this speed-related rule no longer applies.
A fundamentally new Motor Generator Unit (MGU), together with a differential, sits in the monocoque at the level of the front axle. Two drive shafts connect the system with the front wheels. Under braking, the kinetic energy of the race car is converted into electric current which flows into an optimized flywheel energy storage device located in the cockpit next to the driver. During acceleration, the recovered energy is converted again by the MGU and powers the front wheels.


Of course it would cost big bucks but no reason at all (unless the rules say no) why an Audi style MGU shouldn't be spun up by the engine while waiting at the start line and then used to drive the front wheels while the engine does the business at the back.  Bingo - four wheel drive and improved traction for acceleration. Anybody speak German............ Dear Audi, please can I have one of your MGUs so that .............. :-D

Robin

Offline Dynoroom

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Re: Flywheel weight
« Reply #9 on: May 13, 2015, 10:18:53 AM »
Jim, I will ask just a couple simple questions.

1) Did your V-6 engine make 15 more hp at a steady state or during an acceleration test?

2) Why do you suppose your V-6 picked up that hp?

This is just something I've noticed over the last 30 years of building and testing turbocharged engines. If the boost should climb or drop by even 1/4 of a pound you will see torque changes. Multiple dyno pulls can (do) saturate the exhaust system and cause power increases. Look at the data. I was involved in the Buick Indy V-6 program back in the 80's. We instrumented the engines and the cars for many things. We even changed the engine balance from 90 to 36.6 to move the harmonics from vertical to horizontal. We used light flywheels on the car but not on the dyno testing. Data showed no difference in power at the car.

Your examples of light clutch/flywheels in racing is great for acceleration/deceleration applications, it does "move" the engine into a higher power zone sooner. But it in no way compares to Bonneville where acceleration rates can be less the 10-50 rpm a second in high gear in the last mile, another words virtually steady state.  

Lastly, I have run both heavy and light flywheels at Bonneville, currently I run Quarter Master light weight 3 disk clutch because it is better hardware NOT because it is lighter. So in it's application, a light flywheel will show benefits in lower laps times, just not enough to make it worthwhile at Bonneville.

Again I will say to the OP, Don't worry about it.
Michael LeFevers
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Offline JimL

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Re: Flywheel weight
« Reply #10 on: May 13, 2015, 01:23:49 PM »
I am certainly not a great tuner, but I had the chance to work with some great ones and they tried to teach me a few things. :|

Neither V6 was a turbo.  Both tuned better at constant high power with less flywheel, but that may be a situation where the guys were able to obtain the results easier due to a better response rate.  Those load and rpm settings were often several minutes at a time, just adjusting fuel and spark.

There are a few engines that break off the back off their crankshaft, at Bonneville or El Mirage, if they dont run aluminum flywheels.  I have worked on some of those.  Precession at work can be your enemy and it has to get its energy from your power source, out there on the track.  Its just physics.

That is also why flywheel powered car experiments have been so deadly.....and rule 3.3.o is in the rule book we follow.

Besides, all my stuff has gone faster out there with less flywheel.  I have tried it both ways.  I saw the same  results with the bike I ran in '69, and the roadster in '98, or the various bikes in recent years.  I am certainly not the only guy doing it this way. 

I guess thats why I feel pretty strongly about this.  It has been faster and safer for many of us.



Offline Rex Schimmer

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Re: Flywheel weight
« Reply #11 on: May 13, 2015, 02:11:22 PM »

JimL said:

"On top of that, the flywheel is not moving at a constant speed during rotation at steady RPM.  It accelerates and decelerates multiple times per revolution.  If you dont believe that....OBD II misfire detection wouldnt have been working on all our cars for the last 21 years."

Jim is correct that the rotation of the crank,rod/piston/flywheel/clutch assemble is not steady. Each power stroke accelerates the rotating mass and each exhaust stroke decelerates the rotating mass. If you add additional rotationg weight at a distance from the center of rotation you are increasing the assembly polar moment of inertia which will require additional torque to accelerate it. The added mass can provide a "capacitance" affect that can smooth out the acceleration/deceleration forces that are applied by the piston/rod assembly during running. There can be some benefit to this additional smoothing which reminds me of the noted Harley race engine builder that found increased horsepower as he added flywheel to his engines and he found out the the rotational smoothness provided by the larger inertia flywheel provided additional stability to the engines valve train which in turn made the engine make more HPs!

Rex





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Not much matters and the rest doesn't matter at all.

Offline Milwaukee Midget

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Re: Flywheel weight
« Reply #12 on: May 13, 2015, 03:14:57 PM »
The added mass can provide a "capacitance" affect that can smooth out the acceleration/deceleration forces that are applied by the piston/rod assembly during running.
Rex

I had not thought of it in those terms - much like an electrical power supply.

Rex, thanks for that analogy.
"Problems are almost always a sign of progress."  Harold Bettes
Well, I guess we're making a LOT of progress . . .  :roll:

Offline Dynoroom

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Re: Flywheel weight
« Reply #13 on: May 13, 2015, 07:06:03 PM »
Jim is correct that the flywheel does oscillate during running, one of the reasons we use vibration dampers on engines. We also know from ECA (Engine Cycle Analyses) the fore runner to OBDII that every engine has misfires on a regular basis that we never know about or feel. The point being it doesn’t change the end game.
I think we are splitting hairs here. On a normally aspirated V-8 engine you will not likely “see” a steady state hp increase between a 35lb. vs 15lb. flywheel. It will not make the car any faster at Bonneville. If the OP has an engine that makes 850 hp, 17 hp is 2% of that and without doing A-B-A testing with an average of 3 test per change you are well within the rage of error of the dyno equipment.
Every application is different but I think we will need to agree to disagree on this subject.

By the way Jim I do enjoy your input on this and other topics, keeps things from getting boring around here.
« Last Edit: May 13, 2015, 07:09:18 PM by Dynoroom »
Michael LeFevers
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Offline tauruck

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Re: Flywheel weight
« Reply #14 on: May 13, 2015, 10:52:46 PM »
Well put Joe.

Thanks for your thoughts. :cheers: