Lightweight flywheel performance

[treynor]

I finally got my LTW Aluminum flywheel installed last Friday. As is my wont, I attempted to get objective performance data on the flywheel. However, I was stymied at my initial attempts:

Before install, I took G-tech readings in 1st and 2nd gear to measure acceleration. 1st gear should show a larger increase, but 2nd gear was more consistent, with peak showings of .60 - .62g at around 4,500 RPM.

After install and 100 miles of clutch break-in, I again attempted to get readings. However:
1) With the new flywheel, WOT spins my stock tires in 1st gear every time.
2) 2nd gear recorded similar peaks of .60g.

So... the best I can offer is the objective fact that my rear tires now break loose in 1st just above 4,000 RPM at WOT, suggesting substantially more delivered RWHP in that gear.

Subjectively, throttle response is improved in gears 1-3, acceleration in 1st is quite a bit a quicker, acceleration in 2nd is at least more immediate, and the engine revs considerably quicker when the clutch is disengaged.

All in all, an excellent mod.

obVendorPlug: Flywheel obtained from Hennessey as part of the Venom Power Pak; installation performed at APEX Motor Sports in Santa Clara.

 

[JonB]

Thanks Ben ! Your objective reports are certainly a benefit to those considering these mods.......And an AL flywheel has gotta be right up there with 3.55 gearset as a great seat-of-pants and bang-4-buck mod. Warranty friendly, too!

 

[SoCal Rebell]

Throttle response is much quicker with an aluminum flywheel, I think it works GREAT in conjunction with the 3.54 gear,


BTW Ben I dragged this weekend at Carlsbad, best run I could muster was a 12.3 @ 118.4, I did cut a .501 light though.

 

[Bill Pemberton Woodhouse]

We recently sold George Ciamillo's MGW Ltd, RT-10, and he had the flywheel installed in his car. I didn't even want to sell the car, I just wanted to do test drives. Like Ben, it has a great seat of the pants feel to it. I am not a big proponent , like Jon B , of the gears, so I would rank this right up at the top for inexpensive, fun mods.

 

[treynor]

I've had several people mention the idea of addings gears to my car. On stock tires I'm already traction limited through 50 mph, so for street driving, I think they'd be a negative, as the rear end would come loose that much more quickly. On the dragstrip they'd be a positive IF I could still clear the traps in 4th gear. On a roadcourse it'd be a wash, or be course-dependent.

SoCal, I'll be interested to hear your impressions of the 3.54 gears if you go the heads/cam route. You're probably at the ragged edge of traction right now in 1st...

Cheers, Ben ('01 RT/10, 515 RWHP / 525 RWTQ, http://www.treynor.com/ViperMods.html)

 

[Dion Fisher]

I have 3:55 spicers in my car and have had no problem with "unwanted" wheel spin.. I have done a couple mods including a NOS 5180 system which I also have often used on the road course with AWSOME results down the straights, up hills, and in the wider corners..

I am netting a mild 539 rwhp and 588 ftlbs torque on the squeeze I think it all has to do with how the power is applied ie; the thing with the toes attached to it attached to the right leg..

I did just purchase a aluminum flywheel and will install it before August 10th for my next track day, that should make things interesting

 

[Dion Fisher]

I can't argue with that, the torque multiplication of using a larger dia. ring gear x awsome instant power can be a tire melter..

 

[Motor City Mad Man]

Has anyone here ever dynoed a Viper after installing an aluminum flywheel to see if there is an increase in rwhp. I know that the HP at the flywheel will not increase, but I would think with a lighter weight flywheel the driveline loss would decrease and result in a higher rwhp number. I had my aluminum flywheel installed a few months ago and am very happy with the change. I plan on adding some high flow cats and dynoing it again this fall.

 

[Tom and Vipers]

Sean,

...a comment on alum flywheel "driveline loss."

The dyno is a flywheel also. Your engine has to accel 2 flywheels during a dyno run.

If the engine flywheel weighed 3000 lbs, virtually all HP would be consumed accelerating that flywheel and hence no rwhp.

Conversely, if the engine flywheel was 0 lbs, all HP would be applied to the dyno flywheel.

Of course, this applies if the dyno pull is an inertial type.

For steady state dyno numbers, there is no accel and hence therer is no HP difference with different engine flys.

Most Dynojets simulate a 2nd gear run during which accel is great. In this case, there should be a HP increase with AL fly, however, I don't think i would call this a drive line Loss. Losses are usually associated with friction.

Actually, if you want to get higher HP ratings from your Viper, try a dyno pull in the next higher gear. The accel rate will be slower, eng fly effects will be reduced and your exhaust may heat up more producing higher flow thru engine.

 

[treynor]

Yes and no. Dynojet runs are typically done in whichever gear is 1:1 on the car being dyno'd, as this yields the lowest driveline loss. Dynoing in lower gears typically yields less power because of (a) driveline inefficiency, (b) flywheel inertial losses and (c) wheelspin Dynoing in higher gears also typically yields less power because of (a) driveline ineffeciency and (b) rolling friction from the tires on the dyno drum. On the Viper, 4th gear is typically used for dyno runs on a dynojet.

If you could run a successful dyno pull in the low gears on a dynojet dyno, a back-to-back comparison between a car with a normal flywheel and a car with a lightweight flywheel would show a substantial boost to 1st-gear HP and a small boost to 2nd-gear HP. The degree of the boost obviously depends on the rotational intertias of the two flywheels. In fact, since in each case the flywheel must be spun from ~2000 RPM to 6000 RPM, if we knew the rotational intertia of each (or even their weight) we could calculate how much power is absorbed by spinning up the flywheel.

How about it -- anyone have weights for the stock and McLeod flywheels?

 

[Serious Eric]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by treynor:
Dynojet runs are typically done in whichever gear is 1:1 on the car being dyno'd, as this yields the lowest driveline loss. Dynoing in lower gears typically yields less power because of (a) driveline inefficiency, (b) flywheel inertial losses<HR></BLOCKQUOTE>

Dyno pulls are typically done in 4th which is 1:1 on the viper as it is in many other cars. Reason 1:1 produces lowest driveline loss is that it's a direct drive through the trans ... all other gears deliver power through the cluster gears which creates significantly higher frictional losses. Flywheel inertial losses should be same for all gears. The engine/flywheel combo has to accelerate from the same initial RPM to the same final RPM during a pull regardless of what gear the trans is in, so I think that's a wash. Another problem with lower gear pulls (and for that matter higher differential ratios), is that the pull goes much faster. Time to accelerate to final RPM is less and that may be a problem for the RPM-step sampling of the dyno.

Do agree with tomatper that lighter flywheel should yield greater engine/flywheel Hp.

 

[treynor]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>The engine/flywheel combo has to accelerate from the same initial RPM to the same final RPM during a pull regardless of what gear the trans is in, so I think that's a wash. <HR></BLOCKQUOTE>

Actually, it turns out not to be a wash because, although the engine/flywheel has the same change in rotational energy during the pull, the elapsed time of the pull becomes longer as you go up through the gears, and thus the HP lost to spinning up the engine & flywheel is amortized over a longer period and has less effect on the final result. For the same reason, the performance effect of the light flywheel on the street is most apparent in low gears.

 

[Serious Eric]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by treynor:
Actually, it turns out not to be a wash because, although the engine/flywheel has the same change in rotational energy during the pull, the elapsed time of the pull becomes longer as you go up through the gears
<HR></BLOCKQUOTE>

Yeah, good point ... I think you're right.

 

[treynor]

FF,
I don't want to oversell this mod. The difference isn't night and day like NOS; it's noticeable in the lower gears and on rev-matched downshifts. 1st gear feels substantially quicker (butt dyno sez 5-10%) and 2nd slightly quicker.
With your horsepower, I'd shy away from changing the rear end ratio. Losing traction consistently in 1st is a PITA.

 

[Richard K]

Okay, in terms of installation, a flywheel is one of those that I won't try on a weekend in the garage. What kind of time/cost (hours and dollars) can I expect a dealership or shop to charge for this swap. Thanks - Richard

 

[RickV2K]

i bought the fw/hd. clutch combo from Jon B and he almost guaranteed they wouldn't need balancing, and once again ...he was right. now......for those of you that can afford to mod your car the way you'd like i'd suggest you go out and do the fw/clutch thingy...along with the 3.55 gears. now....always remember...this is just one persons opinion. i don't need to justify what or why i did it. you're all big boys now. so......IF...it doesn't break your bank &lt;----- then go out and do it. you won't regret it but.......it might take you awhile to learn how to launch your car again.
you can get ahold of Jon B for pricing. enjoy.

 

[9 seconds]

FastFreddie,
While checking around today, I found out that the 3.45 is a Corvette part. You can get it from GM. TNT also has installed several of these. Check with the Corvette forum guys. I bet they can tell you where to get a good deal.

PS. Let us know if you find one.

 

[Tom Welch]

Break in period for new clutches:

Gents,

Be advised that the correct break in for new clutch/pressure plate/flywheel combos is 500 miles with no burnouts or hard launches. This will avoid the possibility of "hot spots" on the flywheel and pressure plate that reduce clutch grip.

Just some $ .02

Tom
Http://btrviper.com