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Flywheel in auto-x=the suck even more

Old 09-25-06, 10:41 AM
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Flywheel in auto-x=the suck even more

A lightweight flywheel gets my vote for most useless and counterproductive mod for SOLO use. The 7 already doesn't have enough low end grunt, and a lightened flywheel makes this problem more pronounced as revs drop incredibly low for tight corners. I will run my current set up for the remainder of the season, and will upgrade the suspension this winter in an effort to carry more speed through the corners and drop my revs less.
I can understand why the flywheel would be good for track, but for auto x the courses don't reward the top end power of our cars enough.
I base this on driving other vehicles on the same courses. Miata's seem to have more low end grunt than my 7, shooting them out of slow corners quicker. While they don't have the top end power, I rarely get into the top end power on any course. I also had the pleasure of driving an SRT-4. What it lacked in steering response it made up for in a quick spooling turbo (lag was not noticeable) and low end power. I can go faster with these cars than with my 7.
I'll try some negative camber and a stiffer suspension. Maybe I'll even swap flywheels back out. I've even thought of purchasing a miata. I feel I max the car out at events, but when I drive a miata I could shave even more time off. It may be time to reserve the 7 for track duty and purchase a miata for auto x. I'll see if suspension adjustments can counter act the lack of low end torque. I think my light flywheel made a problem for our cars even worse on those tight courses.
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Old 09-25-06, 02:38 PM
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Shouldn't drop any lower than with a normal flywheel unless you are going slower. And it should also accelerate quicker(lower or high rpms), due to less rotational mass.

The only thing I see happening is when you let off the gas it slows faster, but that just means if you let off to slow down, and not use the brakes, just wait a few more feet.
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Old 09-25-06, 02:44 PM
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lightweight flywheel does lose a bit of low end grunt in the low rpm range

a heavier flywheel stores more rotational inertia in low rpm situations, helping the car get going at low speed / low rpm (like going from a dead stop).

solution -> low speed, low rpm 2nd gear corner; downshift to first.
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Old 09-25-06, 03:05 PM
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maybe that course design was more of a problem for your gearing...

look into a higher (shorter) rear end gear like a 4.3 or something near 4.9ish to get more (relative) torque out of your motor... (torque relative to mph). you will notice huge differences in low end powah with a much shorter final drive.

I think the major benefit of a light flywheel is the more rapid throttle response which helps you modulate the throttle and smooths out shifts in the quick timeframes of racing.

I had a light flywheel on my short gear'd GSR swapped Civic and it was an autocross monster... the light fly (8# compared to 17#) and shorter final drive (4.9 compared to 4.4) were my two favorite mods.

if you dont want to swap rear gears you can run 15" or 16" wheels with lower overall height tires to gain similar gearing advantage... thats one reason some Miatas on 13x9's feel like they have torque... those short tires provide shorter gearing. an FD on some 15x10 or 16x10 superlight RealRacingWheels would be sick. I have some 16x10's from them and theyre almost single digit in weight. kumho makes 275 wide Rcomps in 16 too.

Last edited by owen is fat; 09-25-06 at 03:09 PM.
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Old 09-25-06, 03:31 PM
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Once you launch a car from a dead stop and get it moving(drag racing) the heavy flywheel is not helping you go faster. The flywheel only can give back the energy it has if it is moving and the car is not. Rev it up and dump the clutch and thats all you get. The flywheel then becomes another thing to accelerate before the power can make it to the ground and move the car.
Unless you are trying to make up all your time on course with a pro-stock style launch leave the light flywheel in there. It does more for you than light wheels.
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Old 09-25-06, 06:25 PM
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Exactly what jgrewe said. The only time the flywheel+engine has more rotational energy then the rest of the drive line is when the clutch is disengaged. When the clutch is engaged the whole drive train from the rotors and e-shaft all the way back to the rear wheels, plus stuff that we donít need to talk about, can all be considered part of one spinning object that the engine is working on. If you take weight out of the wheels, drive shaft, axle(s), you are reducing the rotational inertia which makes it easier for the engine to spin the whole system. Also rotational inertia and energy are not to be confused as the same thing even though they are linked together.

BUT my roommate did just bring up a good point. The heavier drive line you have the less you will be slowed down up hills, because of the stored energy. And the heavier a flywheel you have the more energy you can store at a specific rpm, for drag launches in low torque cars. An auto-x course should not be on a hill and you only launch once so it wont matter when compared to the gains in acceleration due to decreased rotational inertia. Hell the TINY bit of time you would gain up hills would be negated by the time you lose coming back down them and on flat surfaces.

Lightened flywheels are ONLY useful in any kind of course with turns. And with higher torque cars in drag races as well. Oh and in city driving with lots of stop go ish.

YAY phyics
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Old 09-25-06, 06:30 PM
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Originally Posted by aznpoopy
lightweight flywheel does lose a bit of low end grunt in the low rpm range

a heavier flywheel stores more rotational inertia in low rpm situations, helping the car get going at low speed / low rpm (like going from a dead stop).

solution -> low speed, low rpm 2nd gear corner; downshift to first.
Put away the crackpipe, man!

A lightweight flywheel increases acceleration EVERYWHERE.

A heavier flywheel makes it easier to pull away from a stop if you are lazy about driving and let out the clutch before applying any throttle. Once the clutch is engaged ALL vehicle acceleration is coming from the engine, and the flywheel only serves as a parasite on acceleration.
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Old 09-25-06, 08:57 PM
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Originally Posted by owen is fat
maybe that course design was more of a problem for your gearing...

look into a higher (shorter) rear end gear like a 4.3 or something near 4.9ish to get more (relative) torque out of your motor... (torque relative to mph). you will notice huge differences in low end powah with a much shorter final drive.

I think the major benefit of a light flywheel is the more rapid throttle response which helps you modulate the throttle and smooths out shifts in the quick timeframes of racing.

I had a light flywheel on my short gear'd GSR swapped Civic and it was an autocross monster... the light fly (8# compared to 17#) and shorter final drive (4.9 compared to 4.4) were my two favorite mods.

if you dont want to swap rear gears you can run 15" or 16" wheels with lower overall height tires to gain similar gearing advantage... thats one reason some Miatas on 13x9's feel like they have torque... those short tires provide shorter gearing. an FD on some 15x10 or 16x10 superlight RealRacingWheels would be sick. I have some 16x10's from them and theyre almost single digit in weight. kumho makes 275 wide Rcomps in 16 too.
thanks for the advice. I just got a new wheel and tire package this summer. It's in my sig. i'm happy with how the car responds to my steering inputs, so I don't want to change that (not broke, don't fix). If a suspension upgrade and negative camber don't fix the problem I'm having, I'll try the gearing.
I hate downshifting to first on anything but complete 180 turns. It seems like fine control goes out the window downshifting into that gear. I think in the turns I was complaining about it may have been counterproductive.
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Old 09-25-06, 09:05 PM
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I don't see how any flywheel will "drop the rev" for a corner. Your motor will be turning a given rpm for a given gear at a given speed no matter what.

What a light flyweel WILL do is low the revs to come quicker as you accelerate... and as a result will also let the revs drop quicker when you let off the gas and put in the clutch. THERE may be your problem. If you're having trouble matching revs when downshifting then you may need to adjust technique, but a ligh flywheel shouldn't be making you slower.
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Old 09-25-06, 09:13 PM
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downshifting to first on very tight 180 deg turns seems counterproductive. but if it a turn around one cone in the end you might just want to use first to whip the rear around and get it pointing the correct direction.
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Old 09-26-06, 09:58 AM
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Originally Posted by ikari899
downshifting to first on very tight 180 deg turns seems counterproductive. but if it a turn around one cone in the end you might just want to use first to whip the rear around and get it pointing the correct direction.
That is what I was reffering to. I didn't mean bigger multiple gate 180s. I agree that downshifting there would be counterproductive.
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Old 09-27-06, 12:59 AM
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Originally Posted by ikari899
downshifting to first on very tight 180 deg turns seems counterproductive. but if it a turn around one cone in the end you might just want to use first to whip the rear around and get it pointing the correct direction.
I recently discovered the benefits of down shifting to 1st gear for 180s at my last race. On a 35 second course I dropped nearly 2 seconds off my time. Cornering ability actually improved with the downshift, and minimized my usual problem of "pushing" through the turn. Here's a video that shows the results: http://youtube.com/watch?v=MuzeHxIXy...elated&search=
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Old 09-27-06, 02:29 PM
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I shift to 1st for hairpins. For bigger 180 turns I lose just enough revs to **** me off yet not enough to warrant a downshift. I'll see if I can hook up a camera next time to show what I mean. If I could just carry a little more speed through the corner I'd be fine.
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Old 12-26-06, 03:40 PM
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I had a similar problem with hairpin turns and was compounded by the fact that my airpump wasn't working which killed any low-end torque.

I found that downshifting to 1st before I entered the turn allowed me to concentrate on getting through the turn and out at a higher RPM, generally taking off ~1.5 seconds versus leaving it in 2nd.
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Old 12-28-06, 04:04 PM
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Larz depending upon the class you are going to run in will dictate what you can and cannot do. If you have a aluminum flywheel you are already running in ASP. With the right mods, you really only need to go to 1st on a few corners. If you are running in SM2 then change the gears to 4.7 and if you can have brian at BNR build you a set of turbos like Allan Densmore has. You will never have a lag problem again. You can then leave it in 2nd and spin the tires at will.

Allan
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