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As I recall the argument was being made that the stock unit was lighter but I thought it was RB that said this about the S-10 clutch on the modified stock flywheel being lighter....? I was surprised at the time....

The weight change per se has no benefit unless you want to get weight off of the car. How much benefit is 1 added HP in 2nd gear to the user? (Do the math.) And what disadvantage is it? In rallying an RWD car, a heavy flywheel has some advantages:
  • It is a damper on the driveline to help prevent a lot of erratic wheel spin as you try to accelerate over a rough, loose surface
  • Diving into downhill corners, a heavy flywheel is VERY useful; downshift and dump the clutch just as you throw the car sideways into the corner and the shock to the drivetrain breaks the rear wheels loose very nicely and helps you get the wheels slipping for steering control. Can't do that with a wimpy 10 lb AL flyhwheel....
So the benefits or detriments should be the focus IMHO, not the weight per se. Light is not superior in all situations.
I certainly can't argu with your pass rallying experience where a heavier flywheel has shown to have its advantages. But we are not building rally cars. These are street cars, and it's well documented that a lighter flywheel frees up the engine's revability and will permit faster acceleration in the first 2 gears.

Anytime rotating mass is removed performance will go up.

My engine reved up MUCH faster on the test stand with the aluminum flywheels vs the stock. Very obvious something changed.

I switched my rear tires on my atv to match my skinny fronts. It shed 20lbs of rotating mass on the rear axle. The atv gained noticible performance and acceleration.

I removed the heavy 3 lbs starter ring gear off my snowmobile primary clutch. The 700 triple 2 stroke now revs up faster then before. Did the same to my brother's 600 triple, same results.

Same applies to crankshaft, and other engine internals, flywheel, and other driveline components, wheel and tire combination etc......

Shed rotating mass = better acceleration...
 

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Opel Rallier since 1977
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Hey Vincent,

I am right there with you on the effect of lighter rotating mass. I did a spreadsheet a couple of years ago to compute the HP going into the whole rotating mass of the engine plus flywheel and clutch (or TC and auto trannie mass) of a small block Mopar drivetrain as it revs up. That is how I have some clue on the HP change to the rear wheels here.

IMHO the question is "What is 1 HP at the rear wheel worth?" Doing the math... that is the approximate gain at the rear wheels in the lower gears. Probably worth a lot in road racing.. 1 more HP coming off the slow corners and that ends up at what? 1/4 to 1/2 car length to the next corner? That is worth a TON in road racing, not due to the HP per se, but due to your improved positioning into the next corner. $400 there is very well spent.

Is $400 for 1 HP worth it to someone cruising on the street? That becomes very questionable. For the OP, I think he has said it is a lot of $$ for now. So that value judgement has been made.

Revving faster on the stand is not of much meaning; the possible value is in how much faster it revs in the car, with the combined rotational mass of the drivetrain plus the linearly accelerated mass of the car. The mass changes in the snowmobile clutch or the the ATV wheels gives a different mass acceleration of the vehicle versus so many lbs off of an Opel flywheel. (And we don't know the tire diameter difference if any for the ATV, which is effectively a gearing change....) So yes there is an effect. But how much, and what is the value, and what are the downsides? Flywheel weight is also used to smooth out driveline impulses from the engine, and lowers the tendency for the car the jerk along with a manual trans in 1st gear at very low speeds. Is that smoother operation of value to the user?

As usual for the value, 'it depends'. I know that folks want to gravitate to absolutes: this or that is always better. But it really is not that way for this stuff. The value to the application and the user is what we ought to consider, IMHO.

I see this all the time over in Mopar-land. The drag-racers have only one view: more peak HP, regardless of what it costs you in low RPM torque, driveability, fuel mileage, etc. A few of us on FABO have made some real progress in getting a broader view of different applications and parts choices on the Small Block forum. (The Big Block guys are hopeless LOL.) Best drag race parts is not the way to build a good street crusier engine. Application drives design. IMHO....
 

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IMHO the question is "What is 1 HP worth?" Do the math... that is the approximate gain at the rear wheels in the lower gears. Probably worth a lot in road racing.. 1 more HP coming off the slow corners and that ends up at what? 1/4 to 1/2 car length to the next corner? That is worth a LOT in road racing, not due to the HP per se, but due to your improved position into the next corner. $400 there is well spent.

Is $400 for 1 HP worth it to someone cruising on the street? For the OP, I think he has said it is a lot of $$ for now. So that value judgement has been made. If it was $4 for 1 HP, no-brainer; do it! LOL

Revving faster on the stand is not of much meaning; the value is in how much faster it revs in the car, with the combined rotational mass of the drivetrain plus the linearly accelerated mass of the car.

As usual for the value, 'it depends'. I know that folks want to gravitate to absolutes: this or that is always better. But it really is not that way for this stuff. The value to the application is what we ought to consider, IMHO.
All good bud. I enjoy these debates as is the point of these forums, to share our thoughts and experience on commun subject. We won't see this topic in the same light today, but who cares right?

Always appreciated your knowledge and wisdom. Thanks chiming in and have a good weekend.
 

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Opel Rallier since 1977
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Yep, and I have learned and changed my views as time has gone on since I started into this car stuff 47 years ago with my first car. We all start at different points in time, have different backgrounds, get different exposures and get different interests. You won't see me commenting much on the details of Opel head flow. I got a snootful of cast iron powder in 1975 porting my first set of heads (Ford 351C), and if RallyBob has the data, I am happy to learn from him and be a lazy bum in that department LOL.
 
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