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MG TD TF 1500 - XPEG Flywheel

TF XPEG 1500CC Engine Rebuild is now full steam ahead and my engine builder asked me about weather the flywheel should be lightened. What are people's thoughts on this. I did a search on the archives but couldn't find anything (will try again as there must be somthing). All help would be much appreciated.
Thanks Darryl

D Lamb

Just found lots in the archives but still not sure after 30 mins reading if it's a yes or a no...
D Lamb

Yes...
I realize this is for the early flywheel but your machinist can adapt to the XPEG - http://www.mg-tabc.org/library/BG_flywheel.htm
Gene Gillam

You can safely remove 8# from your later type flywheel, down from 24# to 16#. Adapt the diagram supplied by Gene.
Len Fanelli

Thanks Guys what's the effect and advantage of lightening the flywheel.
D Lamb

Lightening the flywheel - which I recommend - gives faster throttle response - the engine spins faster since there is less mass to get spinning. The downside is that when moving from stop, the clutch needs a bit more feathering since with a lighter flywheel there is less momentum to keep the engine from bogging down. Not really a problem in my book.

Tom Lange
MGT Repair
t lange

I would think the answer depends on the intended use of the car. Lightening the flywheel increases engine acceleration but also affects negatively the clutch action. A great idea for competition or a steady itinerary of hard sporting use but not of much benefit for a street application.
TDs and TFs aren't terrifically tolerant of over-revving and the clutch has a grabby reputation already. I'd prefer street driveability myself, but that's just my opinion.
T W Moore

I have a B&G window flywheel that the racers are fond of. I run Len's roller lifter cam and LOVE the throttle response. I would like to report that my 90s Toyota pick up was terrible with stalling from a stand still (about as non spotty as you can get). My TF just doesn't have that problem. Truthfully I did not note a large difference between the old set up and the lightened flywheel. My guess is that the xp*g engine just has a lot of low end torque despite what you do with the flywheel so you might as well reduce the rotating weight.

Alex
Alex Waugh

Tom Moore and Tom Lange,

Using Bob Grunau's diagram (been around a long time), I removed only 4 pounds and I did notice better throttle response.

However what really made a difference was the polishing of the rods and a careful static balance of all reciprocating parts. I even played "the shell game" with all the small bits, 'till I got every rod/piston assembly exactly alike. I then dynamically balanced the lightened flywheel and clutch (but not the friction disk), crank and pulley.

THEN, I really got the benefits of the lightened flywheel. Clutch take-up was very smooth and the throttle response seemed to be even better (but maybe an illusion, too), but I've been pretty happy with the whole set-up.

... a lightened flywheel - highly recommended.

Gord Clark
Rockburn, Qué.
Gord Clark

The flywheel on my XPAG was reduced in weight by about 28% by a well known race engine builder locally. That was as far as they felt was safe. The clutch action is absolutely normal and good now that I have adjusted it correctly. The engine revs freely. I also had the crank, pulley and clutch balanced at the same time.
Dave H
Dave Hill

You can easily remove 4-6 pounds from the flywheel without a noticeable negative effect on the clutch, and gain a slight improvement in throttle response.
Steve Simmons

As long as you don't overdo it I agree with the opinions above. Lighten it 4 to 6 pounds ... but no more than 8 pounds for street use.

Two points I would like to add. Firstly, removing weight close to the centre lightens the car but not much effect on the rotational inertia. Removing weight close to the outside/periphery lightens the car AND reduces rotational inertia significantly more. Secondly, a light flywheel gives more improvement in throttle response in lower gears (e.g. first) than higher gears (e.g.top).

Bob Schapel
R L Schapel

I understand the increase in run-up to high revs while the engine has no load on it. Isn't that gain overwhelmingly overshadowed once you start to let out the clutch? Aside from a 800hp race car in drag race where you might need to get up to 4000 rpm a tenth of a second faster before dumping the clutch, what's the point in our application?

I'd like to see some data on the difference in acceleration when shifting in normal traffic with the rpm's going from 2000 to 4000 before proclaiming that shaving 6 pounds off the flywheel is a good idea.

Does anyone know of any evidence that in a 1900 pound car with a 47hp engine there is any benefit to lightening the flywheel 6 pounds?

No mention of lightening the pressure plate or cage?

I'm thinking putting a few more pounds of air in the tires to reduce rolling resistance, only filling the gas tank half way or getting the Mrs to lose weight will make a bigger impact towards whatever minor improvement in acceleration can be had, and each is totally reversible.

.....
MAndrus

MAndrus - sorry to hear that your car is so down on HP; no wonder you are concerned. You should have at LEAST 54.4 HP.

Under most circumstances I listen closely to racers and their experience. If they say (as they do) that a lightened flywheel improves acceleration with very little downside, then I listen. My cars feel more nimble and 'throwable' with the lightened flywheel.

Tom Lange
MGT Repair
t lange

Tom, I know you didn't mean to be condescending to those of us who still run them the way they were designed, but only under perfect conditions at sea level with a new factory engine and a room full of engineers and perfect fuel, maybe it's 54.4hp at 5,200rpm.

The actual HP from 1,000 through 3,500-4,000 (the range at which most of us accelerate and shift) will be greatly less than 54.4hp. Every engine's performance graph on a dyno is curved, and the curve is usually incredibly severe. In the lower ranges, HP can easily be half or less of it's maximum. At 3,500rpm it's more likely to be about 35hp. My 47HP figure was being generous... OK?



So, before I spend $100.00 or so to have my flywheel lightened and re-balanced, I'd like to know: What HP or torque gain has been measurably realized by shaving 6 to 8 pounds off the flywheel? 2 percent while accelerating from 4,000 to 5,500 rpm? 5 percent from 1,000 to 2,500 rpm? 10 percent across the board? If it's significant I'll consider it carefully.

Also, you're lessening the effect of a heavier flywheel's inertia between power strokes. What effect will that have? Please don't say none. Manufacturers wouldn't build cars with heavy flywheels if they didn't have to, and a significant undamped repeated change is speed can understandably destroy an engine.

MAndrus

MAndrus....

http://www.uucmotorwerks.com/flywheel/how_a_lightweight_flywheel_works.htm

There are many of us who have had it done when our engines were out of the car and appreciate the perceived change in acceleration, I say "perceived" because I'm sure most, like myself, haven't had it on a rolling road to find out if there truly is a difference.

If you don't see a need to do it to your flywheel then fine, don't do it.
Gene Gillam

I doubt that a lighter flywheel would show any improvement on a rolling road because that measures power at constant revs. But think about where the engine's power is used. When accelerating on the road, portion of the engine's power is used to accelerate the car but portion is also used accelerating the flywheel. Lightening the flywheel results in a higher portion being available to accelerate the car. The factory flywheel weight is a nice compromise between a heavy flywheel (to reduce the chances of stalling when letting out the clutch) and a light flywheel (to make the car accelerate faster). There is nothing wrong with keeping a standard flywheel but some of us prefer to get a bit more performance from our engines. Having said that, my own race TC has a light flywheel but it is not super light.

A light flywheel also results in revs dropping more quickly when de-clutching between gears. This facilitates faster gear-changes.

Bob Schapel
R L Schapel

MAndrus - I never intended to be rude or condescending; I completely agree that the power of an XPAG differs all along the RPM band. I believe in small power improvements that cost little, except for effort: I lap in valves after a few thousand miles, I make sure my engines are completely balanced, I run 1-1/2" carbs on bigger intake and exhaust manifolds with matched ports, and lighten the flywheels of all the cars I own and build by 6-8#.

The trouble is that nobody ever does ONE thing to improve their engine and put it on a rolling road, then the next, and the next. I doubt balancing puts forth much more power, but the decrease in vibration allows the engine to be used more vigorously, which seems to translate into more power. Matching ports can't make more than 1HP difference, but it makes me feel that the engine breathes better. How much difference can the bigger exhaust manifold really make? Dunno, but I always use them on my engines.

For me, most MG matters are pretty much seat-of-the-pants engineering; I have NO empirical evidence to show that ANYTHING I do yields a more powerful engine. I DO know that my rough but stock green TD with the above mods and probably 50,000 miles easily out-accelerates my 5,000-mile red Mark II with a Moss forged crank, Crane cam and Crower forged rods - an $8,000 engine built by an excellent shop. The green one is the one all my friends want to borrow to take their wives or girlfriends out on dates, because it just FEELS better - lighter, more nimble, more Fun.

Like so many things, it works for me, whether it can be proven or not, so I'll just keep on doing it. Like most things in life, we do what we think is right.

Sorry if I offended anyone - it was not my intention.

Tom Lange
MGT Repair
t lange

Hi MAndrus,

"Does anyone know of any evidence that in a 1900 pound car with a 47hp engine there is any benefit to lightening the flywheel 6 pounds?"

I lightened my flywheel by 6 pounds and the engine was definitely quicker through first gear than it was before. No other changes other than a new clutch disc. My car (TC) is more powerful than stock so improvements may be more pronounced. Did the same type of flywheel work in a supercharged B engine and again (with no other changes), a noticeable improvement. Nothing night and day, but slightly faster acceleration and quicker throttle response.

"Manufacturers wouldn't build cars with heavy flywheels if they didn't have to"

They build the flywheel at a weight that is a balance between economy and performance. If all our roads were straight and 50 miles between exits, they would probably install 200 pounds flywheels. Just get the car slowly up to speed and shut the engine down for a while. ;) Flywheel weights are matched to the intended use of the vehicle, with the average driver behind the wheel. I'm not an average driver, so I've modified mine for better response. The factory only chose 22 pounds (that's stock weight by the way) because that matches the average customer's needs. They did not use stock flywheels in their performance and race cars.

Ever see the flywheel on a farm tractor? Big sucker, to maintain engine momentum on rough ground.
Steve Simmons

I would reckon the tractor would use its flywheel mass for the pto shaft, one of the benefits mentioned in the past I think is less torsional force on the shaft.
mog

Does anyone know the total weight of the flywheel, cage, pressure plate and clutch plate.. the entire spinning assembly?

22 pound flywheel plus perhaps another 18 to 25 pounds?

Has anyone also lightened the cage and pressure plate?

....
MAndrus

Thanks guys lots here to discuss with my engine builder. Appreciate all your comments.
D Lamb

Darryl,

Manley Ford sells a nice setup for the Brown & Gammons flywheel. More of a modern clutch, but it works very well. It's quite smooth - I've noticed no problems from the lightened clutch.

Jim

Manley's site:

http://www.freewebs.com/manley776/apps/photos/album?albumid=8596948
J Barry

Jim,

I bought a similar setup but ended up selling it to a vintage racer. It was a bit abrupt on take up for me and I couldn't get used to it. If I remember correctly the flywheel weighed about 7 lbs.

Gene
Gene Gillam

Gene,

That's interesting. So far - and I'm still on the break-in oil - we have quite a smooth clutch with the B&G flywheel. I bought a pressure plate as per Manley's instructions, but it had straight "fingers" versus the curved ones that Manley uses. Because of that, I had to source a different throw-out bearing with a curved face. Using a flat bearing face with flat fingers would probably give a sudden clutch engagement.


Jim
J Barry

Unless you are racing the car.... Save your money. Regards, Tom
tm peterson

So, have we come full circle that a somewhat standard lightened flywheel gives better performance with little down-side, that the heavily-lightened flywheels are probably TOO light for a street car, and that modifications like engine balancing add up?

Tom Lange
t lange

Thanks Tom for summing up. Think that's where I am.
D Lamb

That's the gist of it. Although some people do like a super light flywheel. Beyond driving style, it probably depends also on how you plan to use the car. In city traffic I doubt anyone would enjoy a 7 pound flywheel, while being the only person on a winding canyon road, everyone would probably want one.
Steve Simmons

This thread was discussed between 06/08/2015 and 12/08/2015

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