Flywheels Who's running what and why?

[DeaconBlue]

the only difference you are going to see with the fidanza flywheel is that when driving normally (babying the car) your shifts have to be much faster or the rpms drop off to fast to smoothly engage in the next gear. the flywheel lowers the rotating mass of the engine alot and there for makes it rev and fall off alot faster, so with the stock flywheel if you let off the gas and hit the clutch the rpms fall alot slower than with the fidanza. this is the only difference i have noticed. i havent really noticed any gains at all but i sure they are there even if minimal.

Same thing I have said about my car for years - now its even worst with the 3.4L stroker short block since we took 2.2 lbs out of the pistons, wrist pin and rods. Next time the clutch comes out I will most likely install a custom 15.4 lbs billet steel flywheel to make driving on the street and in traffic a bit easier than with the 9.0 lbs aluminum flywheel.

 

[raceguy1969]

put a steel billet 17lb in my car with southbend rally,in my 1990, it works great but brought my mpg's down from 28mpg to about 24.5 on average, never get any better than 24.9mpg now. so i would say resurface the stock one, btw there was NO POWER IMPROVEMENTS with the 17lb

 

[RonPorter]

put a steel billet 17lb in my car with southbend rally,in my 1990, it works great but brought my mpg's down from 28mpg to about 24.5 on average, never get any better than 24.9mpg now. so i would say resurface the stock one, btw there was NO POWER IMPROVEMENTS with the 17lb

Holy "Thread From The Dead"!!

BUT....it's good info for the newer folks.

Never went with a lighter FW in my SHOs, but with a 2.5L turbo Subie engine, the 14# (versus the 28# dual-mass) flywheel was better than the 9-10# FW that a buncha guys regretted for the street.

I would probably still stay with a stock FW on the SHO, although a 17# one sounds good at replacement time.

 

[SHOspazz92]

put a steel billet 17lb in my car with southbend rally,in my 1990, it works great but brought my mpg's down from 28mpg to about 24.5 on average, never get any better than 24.9mpg now. so i would say resurface the stock one, btw there was NO POWER IMPROVEMENTS with the 17lb

You expected more power from a lighter flywheel?

In anycase, I've always been happy with stock. However, I would probably be happy with a 17lb unit. My S/C car has a 9lb flywheel in it, can't wait to get it out.

-Sam

 

[bigblock]

been driving on a 9lb (see sig) for the last 2 years. i prefer it over a stock flywheel. taking off just takes more rpms and gas when letting the clutch out. the only time i had an issue was stop and go driving through sf hills. the flywheel got so hot it stretched the ring gear and then broke the mounting tabs. it also created a lot of heat spots on the insert. had the insert and ring gear replaced by mfg for 100 bux. the clutch was ok so i reused it and that was last year. i was just at the drag strip and it still holds after 8 runs with n20 and drove it home.

 

[intimdatr]

Has anyone got any dyno charts with differing FW's?

 

[raceguy1969]

I didn't know what to expect, but it was a waste of money with a nearly stock sho, but now that I have replies, when do u think rod bearings need to be replaced, mine are stock with 214k and I'm kinda getting paranoid and don't want to wreck a precious motor. and how important are new piston rings and a valve adjustment? Thank you

 

[LOUDSHO92]

I didn't know what to expect, but it was a waste of money with a nearly stock sho, but now that I have replies, when do u think rod bearings need to be replaced, mine are stock with 214k and I'm kinda getting paranoid and don't want to wreck a precious motor. and how important are new piston rings and a valve adjustment? Thank you

I would do rod bearings and valve adjustment now. I had my rod bearings go out just above 200k. The valves should be done every 60k. I have seen some been fine after 60k and others need every valve adjusted. It really depends.

Unless you have blow by piston rings are fine.

 

[zak]

Has anyone got any dyno charts with differing FW's?

SHOshop did do a chasssis dyno test on the 9 lb Al flywheel alone, IIRC it was worth about "3 hp". Please understand that the number isn't "real", just an artifact of the chassis dyno test (where you are estimating engine hp by accelerating a 3500 lb roller that in turn is simulating the car's mass) - an engine makes the same hp for a given RPM whether its got a 50 lb flywheel or a 5 lb flywheel when measured on a proper water brake or other dynomometer. Nonetheless it gives you some idea of the effect of the reduced inertia on engine responsiveness/improved ability to accelerate the car. My guess is it probably also improves fuel efficiency by about 2%.

My 9 lb SHOshop flywheel did improve engine response in gear and in neutral (e.g. shifting, as others noted). Downside is reduced heat capacity (ability to absorb heat) which I learned the hard way getting stuck on the Tappen Zee Bridge for a few hours on a hot day (warped the steel insert, but not so badly that the clutch had to be replaced right away). This also happened to Tom, Vadim's onetime sidekick, while driving a supercharged SHO in Vegas traffic - that flywheel was completely toast. Luckily NESHO was able to supply me with a replacement insert after SHOshop went out of business - thanks NESHO :thankyou:.

 

[intimdatr]

What I was wanting to know was not HP gains but rather Improvements in the power band above 7500 rpm, do the lighter FW make a difference as far as the motor not running out of steam at about 7500 rpm?

 

[Shoaz]

What I was wanting to know was not HP gains but rather Improvements in the power band above 7500 rpm, do the lighter FW make a difference as far as the motor not running out of steam at about 7500 rpm?

No. That's due to the intake being a cork at those RPMs. It only flows so much.

 

[zach44102]

If you have stock cams thats what holds you back in those rpms. I have bbb, lightly ported runners, and stock heads with S2 cams and it peaks at 6900rpm. And wants to rev to the moon. I plan on porting my heads, and really enlarging the intake runners an ports. That should make for some 8000rpm fun.

I have considered getting a shosource 8 lbs flywheel. Not sure if i want though

 

[rubydist]

an engine makes the same hp for a given RPM whether its got a 50 lb flywheel or a 5 lb flywheel when measured on a proper water brake or other dynomometer.

^ This statement is a huge pile of stinking dung.

One does not measure engine horsepower. One measures torque. Accelerating a heavy flywheel takes a bunch of torque. Accelerating a lighter flywheel takes less torque. Therefore, when you put a lighter flywheel on a given engine and test it, the output torque will measure higher. This is because less of the combustion chamber energy is wasted accelerating the flywheel.

From the measured torque, one calculates the horsepower. An engine with higher torque at a certain rpm will therefore have a higher horsepower at that rpm. As a result, an engine with a lighter flywheel will produce more output horsepower. It is a simple math problem.

The reason that one obtains "better performance" and/or "improved engine response" from installing a lighter flywheel is because there is more output torque and therefore more horsepower available at the wheels with the lighter flywheel.


btw, the fact that bigblock's flywheel got so hot it destroyed the ring gear is not the fault of the flywheel, but the fault of the driver who slipped the clutch too much. One does need to be a little better driver to use a 9lb flywheel than the stock, but I have a 9lb flywheel in my daily driver (3.2) and it is no problem (and we have plenty of hills here in CO), even in stop and go driving (my old left knee is the problem in stop and go driving....)

And, the fact that raceguy1969's gas mileage when from 28 to 24.5 is not the fault of the flywheel, but the fault of the driver who is enjoying the improved acceleration that the lighter flywheel gives.

 

[RonPorter]

I didn't know what to expect, but it was a waste of money with a nearly stock sho, but now that I have replies, when do u think rod bearings need to be replaced, mine are stock with 214k and I'm kinda getting paranoid and don't want to wreck a precious motor. and how important are new piston rings and a valve adjustment? Thank you

Valve adjustment is a waste of time & $$$, unless you can't sleep at night unless they are within a thousandth of ach other.

Over alomost 25 years, I have NEVER heard of any valve adjustment being off enough to cause a problem.

None of the few I've wasted $$ to have done mattered at all.

Don't waste your time & $$$, unless you are super-****.

 

[RonPorter]

^ This statement is a huge pile of stinking dung.

One does not measure engine horsepower. One measures torque. Accelerating a heavy flywheel takes a bunch of torque. Accelerating a lighter flywheel takes less torque. Therefore, when you put a lighter flywheel on a given engine and test it, the output torque will measure higher. This is because less of the combustion chamber energy is wasted accelerating the flywheel.

Uh....no.

Once the flywheel is up to speed (achieved quickly at a relatively low RPM), you may actually see "better" torque #s at high rpm from the smoothing effect of all that weight flying.

Don't count on anything from a lighter flywheel on the dyno. It's all a "feel" thing with quicker revs. Plus the downside of quicker dropping revs on shifts.

Just like guys who put big brakes on street-only cars. Only a better "feel", no better braking.......

 

[DrivinhardLLC]

I have done datalogging and GPS testing before after of a 12" diameter, 51 lb stock flywheel/clutch on my Z06, switching to a 5.5" diameter, 8.9 lb stock car clutch. The lower the gear, the more "gain" since the lower gears mechanically allow the engine to rev faster, allowing you to really see the gain in moment of inertia. Any given straight on a road course shows up 1-3 tenths in time to distance (3 tenths on the ones where you are using 2nd and 3rd gear more). Over the course of a lap on a "typical" 2 or 2.5 mile track, it has shown to be around .5 to .75 sec/lap. Pretty dang substantial.

Dynojet testing showed about 20 ft/lbs torque gain all across the rev band. Realize this is an extreme example as it was a 36 lb weight reduction AND the new unit has all the mass packed in a MUCH smaller dia unit, so the inertia gains are enormous.

Something this small is almost unusable on the street, and worthless for drag racing.

One interesting byproduct I didn't expect, was a brake bias change on track. When you let off going into a corner, you no longer have the inertia of a heavy clutch driving energy into the propshaft, so the car "dies" a bit more off throttle and the rear brakes work a bit better since they aren't fighting as much energy in the rotors. I actually changed rear pad compounds to adjust the bias slightly.

 

[dohcsable]

Speaking from experience with the ti, it went from a 20 something to a 7lb.....it revved much quicker, but was alot trickier to drive around. Also really wanted rev matching for downshifts. Also, when it was dynod it didn't gain hp, and didn't lose any torque to the wheels.....but the car a bit quicker.


Hope that helps some.

 

[greenbeanmtx]

Up until my current sho, I've always ran stock flywheels. The prev. owner put a 17lb billet steel unit in with a CM stage 1 clutch and if I have the a/c on, it is VERY hard to modulate from a stand still. Once moving it is a nice difference for rev matching and such. I suspect my issue is more clutch related ( have a new oem ford unit in the box) but this CM has plenty of life left in it so I am just dealing with it.

 

[AREA 91]

Fidanza in the Green Bastard. (This car lives above 4K)
Stock for the Mocha Frost daily driver.

IMHO, split the difference and go with the 17lb!


P.S. Sorry I couldn't make it to the meet Ken.:rainshit:

Bringing this back from the dead.
My green 91+ now has a billet 17 lb flywheel and CM3 clutch kit.
This is a great heavy duty setup. I have not had any problems with this kit.
Multiple nos launches on slicks and it takes every pony. It works so good that I snapped the input shaft in half!

You cannot run an 8-9lb aluminum flywheel with a double diaphram pressure plate!!! You will have high rpm shifting problems.

 

[rubydist]

Uh....no.

Once the flywheel is up to speed (achieved quickly at a relatively low RPM), you may actually see "better" torque #s at high rpm from the smoothing effect of all that weight flying.

Don't count on anything from a lighter flywheel on the dyno. It's all a "feel" thing with quicker revs. Plus the downside of quicker dropping revs on shifts.

Just like guys who put big brakes on street-only cars. Only a better "feel", no better braking.......

As was mentioned earlier in this very thread, the 9lb flywheel made about 5 lb-ft more torque and about 3 more horsepower than stock on the dyno, so you can clearly see the improvement on the dyno. I used to have the graph, but it seems to have gotten lost in one of my computer upgrades...

The fact that a lighter flywheel takes less torque to accelerate is a fairly simple math problem, and if you want, I can bore you with all the details. However, in the interest of time and space, it might be better if you just accepted the truth from someone who can do the calculations and actually knows what they are talking about in this case.

The fact is that "its all a feel thing" is actually measurable.