I am finishing up my 383 LT1 motor, and have purchased a new Steel flywheel Street Twin. I was unaware of the huge weight difference between a stock clutch and flywheel assembly, vs the Street Twin.

Stock weight (flywheel/clutch disk/pressure plate)= 42 lbs.
Street Twin (steel flywheel/both clutch disks & separater/ pressure plate)= 56 lbs.

I am concerned about increasing the rotating weight of my setup by 14 lbs.
Not to mention the added 5 lbs. heavier than stock fluid damper.
But honestly do not know how much this will hurt or help my set up?

This is a daily driver 96 Formula 6 speed 383 with a GM 847 cam and LE ported heads and intake...etc

I called and talked to McLeod tech person before purchase and discussed going aluminum or steel flywheel.
The aluminum flywheel is 6 lbs. lighter.
I was advised for a street driven car as heavy as these f bodys are to go steel flywheel.

Guess my questions are, what to expect with a heavier rotating assembly on the street..track?

Slower to wind up?

Easier on the street due to the higher rotating inertia?

How much hp did I loose adding 19 lbs. total added rotating weight?

This thing is going to be like a stump grinder...turn it off and it will take 5 minutes to wind down..ha ha...geeez.. I hope not!!!

Thank you,
Keith

 

It would be hard to quantify. The change in hp will vary with the method of measuring. There is likely a very small (hard to measure) decrease in real world performance (accelerating the car vs. a dyno). Don't lose any sleep over it unless you are in a heads up racing class where hundreths or thousanths of a second are the margin of victory. It may launch harder and accelerate marginally slower after the launch.

Rich

 

Thanks.
No I will not loose any sleep haha..., but do want all the performance I can get, and thought a heavy flywheel is going against the grain.

It may help smooth out the drivability some.

I realize McLeod must know their stuff, and I did post the same questions at their forum with no response yet.

You can understand my wondering about more rotating mass.
I just want to understand why McLeod added almost 15 lbs. to their flywheel over our stock one?

Thanks again,
Keith

 

I've ran both, and if there is any difference at the track, I didn't see any. But I normally leave around 5 grand. It did take a while to get the steel broke in. It wouldn't be unusual for me to spin the tires at a signal light with no effort, due to the extra rotational mass. Once I got it broke in ( stuck in stop and go traffic coming up the hill for two hours ) it worked perfect. I now run the aluminum flywheel, and it broke in right away. Aluminum is closer to stock weight clutch assembly, and it revs quicker, but 60 fts and speed at the track haven't changed that much.

 

So why the change from the steel to the aluminum?
The aluminum cost more.. not much, but more.

There is a 6 lb. difference (between the aluminum and steel street twin) according to the McLeod tech I spoke with, even with that and knowing I added a fluid balancer that weighs aprox 5 lbs. more than a stock harmonic balancer, the McLeod tech still recomended the heavier steel flywheel...which I bought per his recomendation.

His reasoning was it would improve the "street maners" of my heavy car. I was asked the weight of my car, and never having it weighed as of yet...I guessed at the curb weight advertized...3400 lbs.


Thanks for the replies,

Keith

 

Your crank and bearings sure know the difference, anytime you can "lighten the load" your engine will be happier and live longer. Old Schoolers loved the massive weighted flywheel when they ran torqueless 283's and 327's.

 

Good point.
I had not thought of that.

The McLeod techs must be old school...haha
The LT1 motor has better torque than those earlier motors for sure, except maybe for the L98 350 TPI motors.
My son had an 89 Camaro that we put an 85 Corvette L98 automatic in, then did a 6 speed swap and had to buy a flywheel to adapt the L98 to the LT1 trans/clutch set up.
McLeod had the flywheel we needed. It was a heavy monster too, also very expensive at $450 or so.

Thank you for the replies,
Keith

 

I think this is a great question. I run the steelwheel and it will rip your teeth loose. I'm thinking that the lighter flywheel is the way to go with these cars. People pay serious money for the lighter cranks for a similar reason.

Do the alum. wheels hold up to the stress as well. Heat tranfer is probably better?

I'd be curious to hear if anyother opinions or test results for sure!

 

I run a spec_3 13# alum on a 97 LT1 383 - D1. Car is setup for a street/ road corner. I went for the lightened fly for faster rpm_rev/ unit time. I does take a bit of skill slipping the clutch due to reduced inertia. B.

 

As a rule, the road course applications call for the lighter assy to allow for quicker revs since you are already running at speed.

A drag strip application likes the heaver steel due to the stored energy a heavier mass releases at launch.

 

I agree, in general. Of course, it's always a matter of degree. As far as the street, within the parameters here I vote for the heavier flywheel for ease of driving in start/stop situations. Having tried both, I find it quite a bit easier to drive with a steel flywheel and a big cam. If it's a small cam, maybe the Al flywheel would be better.

Rich

 

For once, I’m going to disagree with Rich using the surgeons excuse….. “In my hands.”

Seems like I’ve owned about every clutch combo you can own for a LTx car and the dyno sheets never seemed to show any difference in any of them. Had people whom I trust tell me they see more power on the dyno from lighter flywheels, but my car never seemed to respond one way or the other. Don’t know what to say different!!

Regarding “launches” or “road race acceleration out of corners:” Kinetic energy vs raw power seem to be a bit of a yen and yang deal. If you make enough power…… the kinetic energy really doesn’t matter much outside of a textbook. You still need to hook.

Know what I mean!... Dog. You launch at 4000 rpm with a heavy clutch assembly or you launch at 4500-5000 with a lighter one. You accelerate a bit slower with a heavier one (not real sure if it really works that way) and the energy carriers you stronger though the next gear or you accelerate quicker with a lighter assembly and loose some in the next gear. (not real sure if it really works that way)

Sounds like a wash to me. Except the heavier one is stronger……well, maybe. Maybe not.

 

Give your engines a break, run the lighter flywheel, your bearings and general engine happiness will thank you. The lighter the better when it comes to rotating mass, you'll never see a race team add unneeded weight especially if it doesn't affect duability.

 

On a street car and the rpm the cars typically see, I seriously doubt you see much effect one way or the other. Now if your NASCAR running 9500 rpm and you only need the engine to last 500 miles....... every single little bit helps. The people on this list are not quite up to that standard, yet. Think the recommended block service interval on the new LSx motors is 300,000 miles if that says anything.

Again, from experience with weekend toys: I've simply not seen anything one way or the other that really stood out.

 

I wouldn't think so with the LTx stuff......its not that big of a diff in my opinion. All of it is heavy even the aluminum flywheels.....it not like they are only 15 pounds or something