engineguyBill wrote: ↑Sat Dec 23, 2017 11:55 am
Not a huge difference between 24# and 30# flywheel, but for a street-driven application the heavier flywheel is the better choice.
Agree with all those who say the difference is slight and the change is for the worse.
engineguyBill wrote: ↑Sat Dec 23, 2017 11:55 amLightweight flywheel is the appropriate choice for a lightweight vehicle or medium weight vehicle with low gear ratio, that is designed to accelerate quickly to very high RPM, like 7500 or more.
But Bill, that's pretty much the example here; Boss 302 with 4.30 gears. But even so, back to point one, most agree, don't go there.
Jack Vines
Studebaker-Packard V8 Limited
Obsolete Engineering
Agreed. BUT it is a "street" car . . . . . . . . . . . The car has to exhibit some manners and finesse when accelerating away from a traffic light, for example. A totally different scenario than running down a race track and rowing through the gears.
Bill
Perfect Circle Doctor of Motors certification
SAE Member (30 years)
ASE Master Certified Engine Machinist (+ two otherASE Master Certifications)
AERA Certified Professional Engine Machinist
If I can do it with a rough and lumpy engine that is barely running at low RPM, with a 9lb flywheel and a puck clutch, and a gimpy left knee that has trained me well to shift clutchless, I'm pretty sure a big 302 in a sub-3000lb car should be just fine.
SupStk wrote: ↑Fri Dec 22, 2017 7:57 pm
The old school recommendation for stick racers was to have flywheels that was 1% of the car's weight. That may still apply to street/strip cars.
My question is, where are you going to find a 6 lb. flywheel for that 600 lb. car?
Mine came in at 7, the 7.25" triple disc carbon clutch adds another 6, the ring gear another 2, but its but it's pretty low inertia and includes a 36-1 trigger pattern. It seems fine in my driveway but its not been out on the street yet.
The same clutch on a 17lb flywheel/ring gear in a 3000lb car was fine. I was nervous because I'd read all kinds of what turned out to be complete nonsense about light weight setups. The clutch will chatter a little if you're not careful but the peddle is honda civic light so very easy to control and much more pleasant to hold down in traffic than even the stock clutch with no real problem creeping along....it definitely grabs faster and more abruptly than the oem clutch but once you know that its easy to deal with. My point is the difference in the clutch feel was all I noticed about driving it when I cut the flywheel/clutch weight in about 1/2.
I guess with a 4.5" clutch setup you could cut the wight in about 1/2 and inertia by 75%...so it would be very close to a 6lb setup
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4.30 gears with a wide ratio Top Loader? I ran the L-88 14lb flywheel for years in my 69 Z/28 302....with 3.70 and 2.20 low Muncie....car weights and motor characteristics should be very comparable.....NO PROBLEM in my book of experience....
I'm my experience a lighter weight flywheel helps with shifting and also to some extent braking. As for take off from a stop how your engine runs off idle is a big factor too. A higher strung engine may need a little more rpm vs a big cube engine that can pull away cleanly at idle speed. I've also noticed you may need a bit more idle speed for a smoother idle.
I have read many threads on this subject but have yet to see anything about the torque vs weight of car.
Im in the process of building a W2 408 stroker solid roller motor for a 69 Swinger which will weigh around 3300#.
1st gear is a 3.09 and rear will be 3.91s.
I am torn between using a stock 32# or lighter 20# (aprox)...
This is a street/strip car and my thinking is that the lighter flywheel will soften my launch but accelerate faster once under way on the strip. On the street I am hoping the high torque of the engine, low weight of car and deep gearing will keep it from being jumpy if I go with the 20#er.
408swinger wrote: ↑Wed Dec 27, 2017 8:03 pm
I have read many threads on this subject but have yet to see anything about the torque vs weight of car.
Im in the process of building a W2 408 stroker solid roller motor for a 69 Swinger which will weigh around 3300#.
1st gear is a 3.09 and rear will be 3.91s.
I am torn between using a stock 32# or lighter 20# (aprox)...
This is a street/strip car and my thinking is that the lighter flywheel will soften my launch but accelerate faster once under way on the strip. On the street I am hoping the high torque of the engine, low weight of car and deep gearing will keep it from being jumpy if I go with the 20#er.
Is my thinking flawed?
You should be running an aluminum flywheel. You don't need all the FW weight.
joe 90 wrote: ↑Thu Dec 28, 2017 12:24 am
Not at part throttle.
Once the car is moving what exactly is the flywheel doing for you other than hindering acceleration? Its job is to very temporarily resist changes in rpm...so it can smooth out the feeling of power from the pulses when the engine fires and that can help keep the wheels spinning but that isn't normally something you're after at part throttle and at full throttle a little higher launch rpm will also work. On a road course lighter is pretty much always faster, at the drag strip lighter/higher rpm launch will cause a bit faster wheel spin which can mean less traction so even though it will accelerate faster once its going the 60ft time may suffer enough that you can't ever make it up....that is the balance you're after when choosing a flywheel I think if a slipper clutch isn't an allowed/practical option.
I'm pretty sure the factory chooses a flywheel weight to make the engine feel smooth because a smooth engine is perceived by most as a sign of quality. I'm not sure is that has any effect on engine longevity. The setups I've gone very light on in the past had very short engine lives but it was the top end not the bottom engine wearing out so I doubt more flywheel would have helped...no idea on a street car but I'll find out if I ever get frankenferrari running well enough to actually drive it.
The cam I will be running is a custom solid roller
248/250 @ .050. , .648 lift on 108 lsa
I really cant visualize what its power delivery or idle charactoristics will be like.
My understanding is that a heavier flywheel transmits more intial energy to the pavement and may tend to worsen traction issues. Whereas a lighter flywheel will lose some energy on clutchdrop thus helping to lessen tire blowoff and driveline shock. But that will be more than made up for in the revabilty of the engine once under way.
This topic is above my pay grade, but i have read that TF cranks can twist over their length quite a few degrees when at full power. I have never heard what amount of torsional twist exists between the FW and say the tire contact patch in other applications. It would seem to me that individual cyl power pulses are rather spikey during the cranks rotation, having a FW to help absorb, and this detail is seldom mentioned, and then have the FW re insert that momentary stored softened power pulse into the drivetrain, BEFORE the pulses reach the remainder of the drivetrain, would seem to be an upside. I thought this is one reason 60-2? inductor ignition timing wheels have an advantage of measuring real time varying crank speed at different points of crank rotation. We all can agree, a FW consumes zero power, it only effects the time frame it is released. I am not disagreeing one bit in the worse case, like road race , up and down rpms, a heavy FW offers few if any benefit, and take everything above with a grain of salt.
my little brother put a much lighter than stock aluminum flywheel in his ford-sedes benz, (Mercedes 280c with a warmed over ford 302) I told him not to, but he did it anyways, and it made it so you cant just let the clutch out like a tractor, but it wasn't bad at all by any means. It sure made it free rev like crazy.
The car is pretty heavy like 3200lbs, the motor is a 302, with stock crank, aftermarket rods/pistons, ported gt 40 heads, Jones, hydraulic roller, ported pro comp dual plane and a 600dp. It didn't take anything away from the car other than needing a few hundred extra rpm with clutch release. I think it helped with acceleration and shifting, and the way it revved...... it definitely sounded bad ass......
