NEWB Here.. NOT your typical 4.10 scenario question

[WNYGT5-0]

At the local .4 mile oval stock car track, the cars with the heavier flywheels all ran dead last.

Do you have any data to support this or actual experience to surmise this?

 

[GlassTop09]

One thing I did hear was it was either a lighter flywheel OR a lighter DS..but not both.

I've never heard or read that. Would you elaborate on why not to use both a lighter flywheel & a lighter driveshaft?

 

[Norm Peterson]

With oem 3.55 rear gears and a lighter flywheel... on paper, say if cruising at 50 mph.... punch it, the car should accelerate a little faster. You are not putting energy into spooling up a heavier flywheel.

Sure, I can see the issues if trying to take off from a stop /drag race. But once its going, acceleration should not be an issue. At the local .4 mile oval stock car track, the cars with the heavier flywheels all ran dead last.

One thing I did hear was it was either a lighter flywheel OR a lighter DS..but not both.

A heavier flywheel helps when you can "steal" some of its rotational momentum and (briefly) turn it into driveshaft torque. Starting from a full stop is where it's worth the most, just to help get the car rolling without stalling it or using excessive clutch slip.


Norm

 

[Pentalab]

Do you have any data to support this or actual experience to surmise this?

The announcer rattled off the only changes between the 24 cars. They were all identical..except the oem heavier flywheel equipped cars..all ran dead last..end of the pack. Same deal on the next 2 races in their series. Then they finally went to lighter flywheels,and started to move well up..go figure.

 

[Pentalab]

I've never heard or read that. Would you elaborate on why not to use both a lighter flywheel & a lighter driveshaft?

I read that here on S197 several times. It was also on the Roush forum. I will do some digging and see if I can find it for you. My best guess is perhaps with both items being light, too much rotational mass has been removed. I have always wondered just how light a flywheel could be made.

 

[Norm Peterson]

It might be possible if too much rotational inertia was removed that the knock sensor might start reading the instantaneous changes in crankshaft rotational velocity (which get bigger as the flywheel effect is decreased) as knock.


Norm

 

[GlassTop09]

The announcer rattled off the only changes between the 24 cars. They were all identical..except the oem heavier flywheel equipped cars..all ran dead last..end of the pack. Same deal on the next 2 races in their series. Then they finally went to lighter flywheels,and started to move well up..go figure.

This part I can understand.....this is the scenario (autoX\road racing or street roll racing) where a lightened flywheel\clutch package has an advantage over a heavier flywheel\clutch package due to allowing quicker revving/faster shifting/faster acceleration & deceleration when the engine HP\TQ output\chassis curb weight is similar to reducing overall lap times where the importance of getting the car moving quickly from a stop isn't critical to the race objectives, as opposed to drag racing (or street light-to-light racing).

 

[GlassTop09]

I read that here on S197 several times. It was also on the Roush forum. I will do some digging and see if I can find it for you. My best guess is perhaps with both items being light, too much rotational mass has been removed. I have always wondered just how light a flywheel could be made.

Since your earlier post I've searched for info on this topic as well & found some only off of other BBS forums to date, not any from other sources where a more controlled study was executed to provide some objective results to either confirm or deny so I would appreciate any information provided.

I have a hard time making the connection between the 2 since the flywheel side (which we really should be adding in the pressure plate's radius\mass as well since this is physically connected to the flywheel to provide a TOTAL engine rotational mass scenario) is directly connected to the engine thus more directly affecting the engine itself whereas the lightened DS is within a connected rotational system between the trans & rear axle which is a part of this system's TOTAL rotational mass which must be seen as a sum (includes clutch disc; trans gearing\shafts; DS; rear diff; both rear axles; brake rotors & wheels\tires) not in part & only will come into play when the clutch disc is fully engaged by the PP in which then becomes ADDITIONAL rotational mass to the flywheel\PP so to separate the DS out of this "system" is a little disingenuous IMHO due to the DS's very small radius in comparison to the flywheel/PP's radius which is magnitudes larger thus is the far larger influencer to the engine's rotational integrity (including acceleration\deceleration) than any of the other "system's" mass......not that it doesn't provide an effect at all.
The reality is these are really 2 functionally different systems that are affected by the same dynamics but in vastly different/differing amounts relative to each other. The only way that the DS side can become a major player in the whole scheme of things is when excessive amounts of rotational mass is artificially removed from the engine side that will then "expose" it once the 2 systems are merged.
This is where the use of an all aluminum flywheel on a V8 engine is IMHO taking it too far as this is pushing it to the ragged edges...if it is not sufficiently counterbalanced on the PP side AND on the harmonic balancer side to maintain protection to the ENGINE's crankshaft so the engine won't self destruct due to excessive harmonics within the crankshaft's structure (especially a cross plane crankshaft such as equipped in these 4.6L Modulars but any crankshaft in general). Using an all aluminum flywheel not properly counterbalanced enough w\ the PP in conjunction w\ a lightened DS is where I can see this might come into more focus....but not w\ a lightened CM steel flywheel/PP combo due to the max weight loss is less than 6 lbs on avg vs OEM...in reality is even less if a performance PP that gives more clamping force is used as they are usually heavier than an OEM PP.

This part I can attest to 1st hand as I am currently running an Exedy flywheel\clutch package (Exedy HP Lightened CM Steel Flywheel, Exedy Single 11" Organic Sprung Clutch Disc, Exedy Mach 500 Stage 3 Grooved PP) along w\ a Ford Performance 1-Piece Aluminum DS & have no issues generally whatsoever.
Now what I've found this combo WILL expose is any other issues that will affect the rotational integrity more acutely while under load (misfires, drastic temperature changes while crankshaft is cold...throw off misfire monitor until crankshaft warms up enough to smooth out the velocity pulses to the CKP sensor so the PCM can determine the difference caused by a real misfire, A/F ratio imbalances, cam profiles more radical than OEM cams, etc) due to less rotational mass overhead vs OEM so engine is more sensitive to this stuff & can be felt/picked up more easily thru the chassis during operation but otherwise nothing else. But the acceleration performance from this total package is worth it's weight in gold!
I have a set of Lunati VooDoo cams installed which even though aren't nowhere near radical but they did change the CKP pulses enough (improved low end TQ output below 2500 RPM's) to show up as false misfires if the crank temp seen thru the ECT was below 80*F during a cold start....verified this past winter using FORScan software monitoring 2 different misfire PIDS (was checking spark plug operation after removing bad dielectric grease from COP springs\boots) in which 1 PID was counting a lot of misfires but the 2nd PID (which counted misfires at low engine load%) was consistently showing no misfires at the same time.
So 1 of them was wrong-can't have it both ways....it showed up when the engine's ECT crossed 80*F during warmup, the 1 misfire PID that was counting the excessive misfires slowed up to almost none to then essentially agree w\ the 2nd misfire PID that was showing no misfires thruout. Fixed this by going in tune & resetting the misfire monitor's min ECT enable setting from the OEM setting of 20*F to 80*F so the misfire monitor wouldn't run until the engine's ECT exceeded 80*F so the false counts won't skew the PCM's cylinder misfire counts since the only other way to fix this is either go back to OEM cams or retrain the NPC misfire monitor thru IDS to the new cams (Ford dealer). Never had this issue w\ the OEM cams during the '18-'19 winter months w\ this same clutch\DS setup prior the cam swap done in July '19 but never had this issue after the swap either until starting in November '19 when the weather started getting cold but until I resolved the few real misfires from the bad dielectric grease (I could feel\hear them) I couldn't see this w\o the FORScan software's datalogging capabilities...… I then verified the rest of them when I found the broken cam follower (using 1 intake valve instead of 2 which unbalanced the #7 cylinder's A/F ratio lean causing firing imbalance relative to the rest of the cylinders thus CKP sensor pulse imbalance interpreted as a misfire on #7 cylinder when it actually wasn't misfiring...….. I do attribute some of this to the lessened total rotational mass of this Exedy package vs the OEM package from a position of observation based off the science but not factual since these cams weren't installed & run on the OEM package thru a winter to get a real comparison.

So if a more radical set of cams are installed along w\ a lightened flywheel\PP combo I can see this cold start scenario getting much worse & setting off false misfire DTC's...….something to keep in mind.

You will generally come out ahead if you install a total flywheel\clutch package from the same manufacturer as these packages are actually designed to not negatively affect engine rotational integrity. You will note that Exedy doesn't offer any other flywheel choices outside of their lightened CM steel flywheel for any of their clutch packages & ALL of their twin disc HP clutch setups come only as a complete package including CM steel flywheel.....there's a reason why that is.....& is 1 of the reasons why I chose Exedy for my Stang when it came time to replace the OEM clutch. All manufacturers build their separate clutch discs\PP's to match up w\ the OEM nodular flywheel\PP package's rotational integrity when used w\ the OEM flywheel unless included in a complete package which is then properly weighted to provide the necessary performance objectives w\o causing damage to the engine\drive train.

My 2 cents concerning this topic...……….

It might be possible if too much rotational inertia was removed that the knock sensor might start reading the instantaneous changes in crankshaft rotational velocity (which get bigger as the flywheel effect is decreased) as knock.
Norm

Yes the instantaneous changes in crankshaft rotational velocity from too much reduction in flywheel/PP mass from OEM will definitely cause the engine's CKP sensor tone wheel\ring to swing too far out of sync & thus can throw off all kinds of things timing related....and w\ these 4.6L Modular engines in particular since the CKP timing wheel is mounted on the front of the crankshaft behind the harmonic balancer instead of at the flywheel end which will amplify the effect even more. May be possible to induce knock but in my mind if that is happening from just a lightened flywheel\PP\DS setup there's some structural damage involved somewhere along w\ it to create the sound freq necessary to set off a knock sensor...……….

Again my 2 cents...…….​

 

[Flusher]

I have some first hand experience with running lightened crankshafts, flywheels, and balancers/dampers. My experience has been primarily with muscle car era V8s, some inline 4cylinders, and the bulk of my experience being with small block Mopars.

GlassTop is right, you have to factor in everything. When balancing rotating assemblies, I would include everything that attaches to the crankshaft, i.e. crank pulley, clutch PP etc. The externally balanced LA-V8 Mopars have the rear counterweight on the torque converter, which could not be balanced with the rotating assembly. Ultimately I started internally balancing with a neutral balanced converter. Any serious effort should be internally balanced.

The only real A-B-A-C testing that i have done was with my 340 Duster @ 3125lbs and I was around 200lbs. I had read a lot about how a heavier flywheel can make your small block car launch like a big block car The factory cast flywheel is 30lbs. When it came time to upgrade the clutch, I installed a McLeod 60lbs flywheel.

What i noticed was, absolutely no change in how the car launched and it would not rev anywhere near as fast as with the 30lbs flywheel. I also lost RPM because I wasn't making enough power to spin the extra rotational mass.

I had McLeod cut the 60lbs flywheel down to 30lbs and the performance came back. After a few months, I started thinking, if some's good, more's better. I couldn't afford an aluminum flywheel, but McLeod cut my flywheel down to about 22-23lbs. I liked the responsiveness of the lightened flywheel and I didn't notice any negatives. Maybe there was a learning curve while trying to casually leave an intersection with a cop in the lane next to me, while trying not to attract attention.

I ran 3.23, 3.55 and 4.57:1 with 27-1/2" diameter tires. In the same scenario, causally leaving after a red light, with a cop in the lane next to me, I didn't notice any difference between the gear sets, while leaving at that low of an RPM.

My next few engines had moderately lightened and knife-edged crankshafts with the same lightweight steel flywheel, so i don't have a direct A-B test, because it was an entirely different combination.

I built some Nissan engines, with my friend, which had drastically lightened crankshafts, flywheels, etc. These were definitely fast revving engines, but didn't make much power, compared to a V8. No disillusions here, that these cars were going to launch like a big block. There were no issues with drivability. What we did notice, in addition to revving substantially faster, surprisingly, when free-revving the engine andin between shifts, the RPM didn't drop as fast as with the heavier components.

I have installed many aluminum flywheels behind SBC/BBC and FE Fords in Cobra replicas, some of which were in the 3600lbs range. Never once did I notice a difference. In fact, I share Carroll Smith's philosophy, run a flywheel only heavy enough to keep the engine from stalling.

I can't say anything about the electronics stated above, that's above my skillset at the moment. I'm impressed with what GlassTop has done in his Lunati Cams thread.

I don't know about the driveshaft. I would like to see some direct A-B-A-B testing, at a drag strip, to see what difference, if any. I don't see the driveshaft making a lot of difference on a dual-purpose car. However, look at the modern racing transmissions in every type of racing today. Every effort has been made to reduce rotational mass, because it takes power to turn that mass. I think a light-weight driveshaft has merit, if not anything else, a slight reduction in unsprung weight. There is just not a lot of rotational inertia in a 3" diameter tube, but it all adds up. I am of the philosophy of, lighten everything including the driver.

Cheers,

 

[Norm Peterson]

My guess about a 60 lb flywheel . . . must have been some "if some's good, more's better, too much is just enough" thinking went into that decision.

But I understand rather well that you can teach yourself how to get away with using less flywheel even with tall gearing ('79 Malibu, 3400-ish lbs, 25 lb flywheel, 2.85 1st, and 2.56's in the axle).


Outside the dragstrip, racing decisions are by nature skewed away from such street driving concerns as easy startup from a stop, minimizing clutch slip, and avoiding any 'necessity' of wheelspin.


Norm

 

[Flusher]

My guess about a 60 lb flywheel . . . must have been some "if some's good, more's better, too much is just enough" thinking went into that decision...

Norm

That was 31 years ago. But that's what the magazines were printing then, so it must have been right. I'm glad George at McLeod talked me out of a 100lbs flywheel.

I went through that learning curve, and now I know for myself.