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View Full Version : lightweight flywheel-do or don't



trfourtune
03-16-2006, 10:30 AM
for a hot street car, 1962 tr4, autocross car, should i use a 10lb,20lb, or stock 20+ something pound flywheel?? 290deg cam,10:1 comp,dellorto's,headers, etc, typical lead foot. how many revs do you need to launch a 2200lb car with a 10lb flywheel and stock tr4a/tr6 clutch?
rob

GB1
03-16-2006, 10:46 AM
For my hot street car (with similar mods) I have been told that by removing 25-33% of the flywheel weight is the appropriate amount.

kennypinkerton
03-16-2006, 09:03 PM
If you buying from a catalog, and only have 10lb and 20lb to choose from, go with the 20lb'er. A super light flywheel will cause bad idling problems.

Basil
03-16-2006, 09:24 PM
I've heard that lightening the flywheel can increase HP but at the expense of torque, is that true?

kennypinkerton
03-16-2006, 09:34 PM
Flywheels are designed to keep turning the engine until the next cylinder fires. Lightening a flywheel reduces rotating weight, and allows an engine to build rpms quicker... and free's up HP wasted on spinning that heavy flywheel. It won't effect the HP or torque of the engine, but make it too light, and you have problems with idling. That's been my experience around the racing stuff. You have to modify the fuel, idle speed, and ignition at idle to keep 'em running with a super light flywheel. And they are way easier to stall on take off.

Bugeye58
03-17-2006, 05:31 AM
Kenny, when racing, the last thing I care about is the idle characteristics. When I hit the pedal, I want the engine to spool up NOW.
Jeff

WhatsThatNoise
03-17-2006, 06:48 AM
Rob, What is your rear end ratio & are you running the stock transmission?

IMHO, your best bang for the buck is a LSD & good tyres. Also, tighten up that front end.

(or have you done that already)

For Auto-x its handling you want first..Power is secondary.

DrEntropy
03-17-2006, 07:31 AM
[ QUOTE ]
Kenny, when racing, the last thing I care about is the idle characteristics. When I hit the pedal, I want the engine to spool up NOW.
Jeff

[/ QUOTE ]

That li'l pump motor will DO that?!?!

Amazing. /ubbthreads/images/graemlins/jester.gif

WhatsThatNoise
03-17-2006, 08:17 AM
He said "spool up"

Must be a sewing machine motor.

MGAdams
03-17-2006, 08:29 AM
Of course there is a down side to lightening ... they can go from this;
https://www.imagestation.com/picture/sraid202/pbfb18190d770db66dcafbb7892f9c750/efcf5f2f.jpg

to this;
https://www.imagestation.com/picture/sraid202/p136005b322141df364fa063474c634bc/efcf5f30.jpg

This was in a lot of "spares" i purchased from a previous owner ... I think it was from shoddy installation and over-torqued bolts. I am using a lightened steel flywheel.

Mike

WhatsThatNoise
03-17-2006, 08:52 AM
Yipes........

< covers eyes >

I put one of those 10 lb aluminum jobbies in the Elva.

Hate to have ta try putting it back on while driving.

DrEntropy
03-17-2006, 08:59 AM
...or gather up the pieces of yer legs... gah!

ChrisS
03-17-2006, 10:14 AM
When looking at a flywheel weight alone does not tell you if the engine will spool up faster. The material and location (shape) of the weight is important. I donít remember my physics that well, but there is a term called Radius of Gyration (general abbreviation WR2) which describes the inertia characteristics of a given shape, i.e. a solid disk or a hollow wheel. Each shape has a different formula for calculating WR2 but essentially W is the density of the material, and R is the radius (the differences in the formulas are essentially the volume calculation). The time required to change the speed of the rotating object is something like

time = (WR2 x Change in RPM) / (308 x torque)

for steel W = 490, for cast iron W = 450, and for aluminum W = 165

If we say that the engine torque is what it is and we want to rev the engine faster, then we need to make WR2 smaller. If you buy an aluminum flywheel with the same shape as a steel one WR2 is reduced because W is 165 instead of 490, if you cut down the outside radius on an existing steel flywheel WR2 goes down because R is smaller. Now we canít really do that because there is the ring gear that we need to start the engine, but if we take away weight at the edge of the flywheel we will be helping. For example, on a spridget flywheel if the material forming the slight step between the pressure plate and the ring gear was removed it would have a greater impact than if an equivalent weight were removed by simply shaving the friction surface.

Sorry for the long post, Iím just trying to point out that if someone is planning on lightening a stock flywheel, the further from the rotating axis that the weight is reduced the more impact it will have on getting the engine to rev up quickly.

kennypinkerton
03-17-2006, 10:52 AM
Hmmmmm... Even though this was just a clutch failure, I'd imagine a flywheel failure could do the same thing...
https://www.chicagolandmgclub.com/photos/gearbox_reb/mga_gbx_broke.jpg

Don't they sell shield to save your legs in an event like this?

Nunyas
03-17-2006, 03:55 PM
I dunno if they sell those shields for our cars, but fabricating a thicker firewall and trainy tunnel ought not be too difficult assuming you have all the tools necesary to build a racer. If I'm not mistaken, some race orginizations have a trainy tunnel thickness requirement. At least, I recall hearing about it... unfortunately I can't recall what type of racing has the requirement.... maybe drag racing?

Bugeye58
03-17-2006, 05:57 PM
Chris, thanks for the clarification on flywheel lightening. I currently run properly shaped aluminum flywheels, and have a steel spare that was lightened in the correct manner.
Scattershields are REQUIRED for most SCCA classes, and all other forms of road racing that I'm familiar with. The SCCA rule reads "Scattershields or explosion proof bell housings shall be required on all cars (except Showroom Stock, Touring, and Improved Touring) where the failure of the clutch or flywheel could create a hazard to the driver.
Minimum material specifications are:
.125" SAE 4130 alloy steel.
.250" mild steel plate
.250" aluminum alloy.
NHRA or SFI approved flexible shields.
I run a .375" 2024 aluminum shield in the plane of the clutch/flywheel rotation.
Oh, and Doc, the 948 wasn't a pump motor. That was the Coventry Climax, and they won't even let me think about it!
Jeff

GB1
03-17-2006, 07:00 PM
Good thing it was on the starters side!

DrEntropy
03-18-2006, 12:03 PM
HeHe... 'k, Jeff. I'll try an' keep 'em straight.

Too bad it'd (the Coventry unit) be "recognisable" at a glance. You ~could~ consider an Elite for racing... ack! On second thought, noooo...

mjamgb
03-18-2006, 01:40 PM
Scattershields are avilable but a scatter blanket (typically Kevlar/aramid blend) is easier to install and much lighter! Try drag racing outlets (like Summit) for products.

jlaird
03-18-2006, 01:43 PM
Modified drag racers at some point require a shield.

trfourtune
03-20-2006, 01:27 PM
hi,
i am planning to use the stock rear end 3.7:1 with a phantom grip lsd and a w58 toyota supra 5-spd. yes, major suspension mods in the works. most of this is still in the works (planning, designing, reasearching). i already have adjustable front and read anti roll bars. 1" front, 5/8" rear. these are the rally/road revington tr antiroll bars from england. i have not decided on how soft to run the front and rear springs yet. revingtons' package with these bars are 450# fronts, 160# rears with 5.5" ground clearance.
i understand however that i would get better GRIP with softer springs, however bottoming with a tr4 becomes an issue with soft springs in a fast, rough road condition.
rob

WhatsThatNoise
03-20-2006, 02:19 PM
My thought was....

The lower your 1st gear is, the lighter your flywheel can be.

I don't know what the stock ratio is on a TR4 or what it will be after you put the Supra 5-speed in. (tires can influence your choice also)

BTW..Phantom Grips destroy differentials. They are total crap and the company that produces them should be burned to the ground.....END OF STORY

aeronca65t
03-20-2006, 02:55 PM
[ QUOTE ]
My thought was....
The lower your 1st gear is, the lighter your flywheel can be....

[/ QUOTE ]

Probably true if you mean "geared lower" (which is numerically higher).
But most folks looking at light flywheels are also interested in close-ratio gearboxes (which means that first gear isn't so "geared down" and is numerically higher).
And many race motors have less torque at low RPMs, which makes things even worse.

There is no real solution to this....other than careful slipping of the clutch to get rolling.

By the way, I lightened my steel flywheel by carefully removing material from near the outer diameter (where it makes the most difference). I used big radius blends on the cuts to reduce any stress concentration.
I only took off about 3 pounds, but I think it helps acceleration a bit (and it was free /ubbthreads/images/graemlins/cool.gif )

I use a thick piece of cast-off Lexan as a scattershield.

I've heard very mixed reviews about the Phntom-Grip limited slip diff modification.....some of the front-drive guys I know have complained of rapid spider gear wear.

trfourtune
03-20-2006, 02:57 PM
phantom grips are crap?
really. i didn't know that. are they more like a locker that snaps in and out?
rob

trfourtune
03-20-2006, 03:01 PM
hi,
i wouldn't use lexan. i doesn't x-ray very well when it is imbedded in your leg or fragments are in your leg. 4340 is the stuff.
rob

trfourtune
03-20-2006, 03:03 PM
oops! /ubbthreads/images/graemlins/blush.gif
4130
rob

WhatsThatNoise
03-20-2006, 03:34 PM
[ QUOTE ]

Probably true if you mean "geared lower" (which is numerically higher).
But most folks looking at light flywheels are also interested in close-ratio gearboxes (which means that first gear isn't so "geared down" and is numerically higher).
And many race motors have less torque at low RPMs, which makes things even worse.


[/ QUOTE ]
YES.......All true......I should have been more specific.
My own situation (Auto-X & fast road use) MGA 1622 engine 10 to 1 compression

270 degree cam----11 lb Flywheel-----3.73 rear end-----1500 lb car (wet+me)----MGB heavy duty clutch---Tran-X LSD(clutch type)

The standard box has 3.64 2.21 1.37 1.0
The close ratio box 2.45 1.62 1.27 1.0

Street tire launch (standard box) 3000 rpm (C/R box) 4000 rpm

While the standard box is easy to drive (feels stock) on the street, the C/R box requires some slippage.
The Elva has gobs of low down torque & is out of it's cam @ 6400 rpm's
I don't know the hp or torque.

WhatsThatNoise
03-20-2006, 04:09 PM
Rob,
Check out..... https://www.grmotorsports.com/board/viewforum.php?f=2&sid=0c1ba8f4709f705ee050041a0261 25a3 & search Phantom and Grip

For a 2200 lb, RWD car many people recommend a Quaife LSD

I know they are $1500.00
If it makes you feel any better......I'm broke too. /ubbthreads/images/graemlins/jester.gif

mjamgb
03-20-2006, 04:19 PM
I got my quaife from a fella running an Elva Courier... He said it made him nervous in high speed sweepers but I've had no issues whatsoever. Perhaps he didn't have it well set up, I dunno.
Yeah, I got it for $1K ten years ago!

WhatsThatNoise
03-20-2006, 05:36 PM
What I heard is that light cars like Elva, Sprite, Turner etc. have very sensitive butts & wiggle more.
(They like smooth clutch packs)

Heavier cars MGB, TR 2-4 & AH are not so much disturbed by the operation of the torque sensing mechanism.

(The great thing about Quaife is that they are guaranteed INDEFINITELY to who ever manages to blow it up)

Also...You don't have to periodically replace clutch packs, goof around w/ ramp angles or be a chemist to properly figure out how much "slip" juice to add.

Matthew E. Herd
03-20-2006, 07:05 PM
Really?? Quaifes are guaranteed for the life of the unit? That's amazing! Makes their $1350-1500 prices seem like a decent investment.

WhatsThatNoise
03-20-2006, 07:25 PM
Quaife America Torque Biasing Differential Lifetime Warranty: Quaife America warrants each new Quaife ATB Differential against defects in manufacture, material, workmanship, and wear-out when used in the vehicle application for which it was originally designed, on any motor vehicle, under any and all operating conditions, including racing, for as long as the original purchaser, or any subsequent purchaser owns the differential

<font color="red"> I click &amp; pasted the above from thier website.

DrEntropy
03-20-2006, 08:41 PM
Dave wrote: [ QUOTE ]
What I heard is that light cars like Elva, Sprite, Turner etc. have very sensitive butts &amp; wiggle more.
(They like smooth clutch packs)

[/ QUOTE ]

Find an Elan driver with the original donut-type rear axles and try that out. Smooth... Hahahaaaaaa! "Snap!... SPROING!" sometimes followed by: "SH*T!"

Simon TR4a
03-21-2006, 11:42 AM
Rob, I don't know what ratios are in the 5 speed box, but obviously a numerically high first gear ratio gives scope for a better launch, so makes lightening the flywheel more practical.
I feel this is not necessary for this type of event, however, as two things will help you do well: your driving ability and grippy tyres.
The tyres must get up to temp quickly, so if allowed by the class rules get Hoosier Autox, and if you have to have street legal tyres get the fattest, stickiest ones you can.
That and driving ability will make much more difference than spending a lot of money on engine development.
A limited slip diff is also going to help a lot, (remember you should break in a new lsd by driving around in figure 8s in an empty parking lots), and getting the best alignment and suspension settings will be very important; again more so than power. (Some toe-out at the front helps pull the car into the corner.)
All this is just my opinion, but the bottom line is I would not mess with the flywheel.
Cheers, Simon.

Matthew E. Herd
03-21-2006, 10:48 PM
I didn't mess with mine, and I feel it's a much easier car to drive than my buddy's MR2 with lightened everything. It's obviously not as fast, but it's still quite peppy. I don't feel that the added mass is a real killer, but rather helps with making a solid launch (without stalling). It does make you slightly slower, especially in the lower gears, but I feel this is negligible.

jfslenes
03-31-2006, 11:31 PM
Hope I don't repeat too much. Yes, go with lighter flywheel. But go with factory made if possible, just for accuracy, quality, etc.

You'll notice 3 things:
1. You'll kill it the first few times you begin to release the clutch. The engine has less rotating mass to keep on rotating.
2. It will spool up faster, yeah team!
3. The converse also applies. Your brakes don't have to slow the motor, compression will help you slow. Brake later (not at all), yeah team again!

WhatsThatNoise
04-01-2006, 02:04 AM
For the record.......Go for it.

Get the 2 pound flywheel &amp; everything else.

Later, if you discover the car is undrivable, you can adjust from there.

You have more than enough opportunity to be practical &amp; responsible in the decisions you make daily.

Can you tell I just got back from the pub? /ubbthreads/images/graemlins/grin.gif

DCM
04-01-2006, 09:34 AM
I lightened mine from 22 lbs to 15 lbs.
The engine has about 10-1 c.r. a slighty better cam, 7 degrees of cam advance, ceramic coated header, roller rockers, high flow stainless steel valaves, etc.
I keep the revs limited with a Pertronix Second strike to 6500 rpms.
All of this adds up to a very reposnive engine. But, the 7 degrees advance at the cam limits the power curve to max. at about 5000 revs.
Oh it will go to the red line, but especially in 3rd and 4th gear slowly.

trfourtune
04-03-2006, 01:24 PM
well,
i talked to jack drews "uncle jack". he said that was one of the first things he'd do. he said it's in the top 3 mods that make the most difference to a tr4 motor. Darryl uprichard of racetorations said he would not shave much off a stock flywheel because of safety, but would go with a purpose built lightweight. i put the stock flywheel with ring gear on the scale, get this, a WHOPPING 30 LBS"! i would be taking 8-9 lbs off to get to 20 lbs. pressure plate 12 lbs, friction disc 2 lbs. best price on lightweight flywheel from ts import auto $335. i think i'll go for it when dollars available
rob

Super 7
04-08-2006, 11:40 PM
I had the flywheel cut down in my Street / Autocross Cortina from like 23 lb to 14 and change. It needs a slightly faster idle than before, and I stalled it a few times at first. It picks up revs quicker than before. all the weight was removed pretty much from the outside BTW

Its cheap and it works.

WhatsThatNoise
04-09-2006, 05:59 AM
[ QUOTE ]
i think i'll go for it when dollars available
rob

[/ QUOTE ]
/ubbthreads/images/graemlins/thumbsup.gif
Get the ARP bolts along with their special sauce.
Don't use lock tabs (if that was original)
Remember that aluminum expands &amp; contracts more than steel so this requires perfectly torqued/stretched fasteners.
(This means a CALIBRATED Mac, Snap-On or equivalent quality torque wrench)
Read the instructions about proper torquing technique.

There is a lot of hostility in a 6000 rpm flywheel. /ubbthreads/images/graemlins/grin.gif

Alan_Myers
04-15-2006, 02:49 AM
[ QUOTE ]
Get the ARP bolts along with their special sauce.
Don't use lock tabs (if that was original)
Remember that aluminum expands &amp; contracts more than steel so this requires perfectly torqued/stretched fasteners.
(This means a CALIBRATED Mac, Snap-On or equivalent quality torque wrench)
Read the instructions about proper torquing technique.


[/ QUOTE ]

Hi,

Add to the excellent suggestions above...

On a TR4, drill and tap to increase the number of flywheel bolts from the stock 4 to 8... especially if using an aluminum flywheel.

/ubbthreads/images/graemlins/cheers.gif

Hap Waldrop
05-20-2006, 09:13 AM
On our Spridget race cars we use light flywheels, either alloy or steel nrmally around 8 pounds, in no way would I recommend this for the street, most common compliant is the car is hard to get going from a dead start, not a concern for a race car. On tranny gearing my first gear in my racing gearboxes is 1.60 or 1.65, which allows me to use first gear on the track in the slower corners.

tony barnhill
05-20-2006, 11:59 AM
Hap - glad to see you made it over here...don't forget, I still want an aluminum flywheel for the MGB GT that I'm gonna convert back from V6 to original for HSR after the GRM Challenge.