SPEC Flywheel
Thread Starter
Instructor
Joined: Apr 2011
Posts: 218
Likes: 16
From: Littleton CO
SPEC Flywheel
OK, so here is a picture of my new SPEC xtra mass flywheel vs. my old dual mass from the crankshaft side. I am curious about the counterbalance weight. The center of the mass is definitely correct, but it looks like the distribution is quite a bit more spread out on the DMF. Does this make a difference? Does the back of this SPEC xtra mass flywheel look like the ones other folks have mounted? Thanks!
--Calvin
--Calvin
Last edited by calvinlc; Aug 30, 2011 at 11:27 PM.
Burning Brakes
Joined: Nov 2010
Posts: 1,006
Likes: 2
From: Spartanburg South Carolina
What you have there is correct in terms of looks on the backside. Is your motor internally or externally balanced? If it's internal then your flywheel and dampner should be neutral balanced with no weight. If external then you want the weight
Race Director
Joined: Nov 2003
Posts: 12,221
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From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
C4 of Year Winner (appearance mods) 2019
As long as the mass of the new FW is the same as the older, spread-out weight, I'd think they'd end up balanced the same.
I don't believe the physical size/shape matters. Only the exact position of the center of that weight. (IOW, the balance points of the weights would have to sit at the exact same position on the FW.)
It's hard to tell from your pic. Is the new counterbalance weight look as heavy as the older, thinner weight? Is it quite a bit thicker?
IIRC, Bill Boudreau said the counterbalance was only about 30g. That's not very heavy. I was actually surprised by the size of the old DMF weight after he passed on that info to me. I wondered if it was supposed to be 30oz.
Looks like a well-made piece. One where it could be used on ext and int setups. Is it the same thickness? How does it compare in weight?
Thanks!
I don't believe the physical size/shape matters. Only the exact position of the center of that weight. (IOW, the balance points of the weights would have to sit at the exact same position on the FW.)
It's hard to tell from your pic. Is the new counterbalance weight look as heavy as the older, thinner weight? Is it quite a bit thicker?
IIRC, Bill Boudreau said the counterbalance was only about 30g. That's not very heavy. I was actually surprised by the size of the old DMF weight after he passed on that info to me. I wondered if it was supposed to be 30oz.
Looks like a well-made piece. One where it could be used on ext and int setups. Is it the same thickness? How does it compare in weight?
Thanks!
Last edited by GREGGPENN; Aug 31, 2011 at 01:03 AM.
Thread Starter
Instructor
Joined: Apr 2011
Posts: 218
Likes: 16
From: Littleton CO
So the volume of the two weights is very close - within measurement tolerances for odd shapes. The SPEC weight should be about 10% heavier because it is about 10% less radius for the center of mass and that is what is really important is in-oz, so to speak. Assuming the density of steel, the weight is approximately 4.8 oz, and if we multiply by a radius of 5 inches we would get around 24 in-oz. In looking on the Centerforce website they spec a weight of 23.4 in-oz for their flywheels, so I tend to believe that is the right number. The SPEC mass is including the bolts is 152 grams, or 5.35 oz. It has a center of mass about 4.5 inches from the center, which gives it about 24.1 in-oz of imbalance. All of these seem to be consistently lining up, so as long as the distribution of mass only being over a length of 2.5" of arc as opposed to 7.5" of arc like the stock DMF is OK, this should check out well.
Advanced
Joined: May 2010
Posts: 62
Likes: 0
From: Mulvane Kansas
The SPEC flywheel shown is identical to the one I installed. I was rebuilding the engine at the time and had the rotating assembly checked by the engine builder. There were no issues with the flywheel balance. As mentioned before, this is for and EXTERNAL balance engine.
Melting Slicks
Joined: Jul 2006
Posts: 2,151
Likes: 0
From: Strongsville Ohio
I bought and installed the exact same flywheel. I didnt touch anything and just put her right on. She is as smooth as silk. Glad I went with the xrta mass. It still clings around a little but not that bad
Race Director
Joined: Nov 2003
Posts: 12,221
Likes: 446
From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
C4 of Year Winner (appearance mods) 2019
The SPEC flywheel shown is identical to the one I installed. I was rebuilding the engine at the time and had the rotating assembly checked by the engine builder. There were no issues with the flywheel balance. As mentioned before, this is for and EXTERNAL balance engine.
Hmmmm.......
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Thread Starter
Instructor
Joined: Apr 2011
Posts: 218
Likes: 16
From: Littleton CO
Although, when I was making measurements last night I was thinking about this, not because I wanted to do it, but just as an academic exercise. The balance may still be very slightly off as the bolt holes are open if you just remove the weight and bolts altogether. I would think if you wanted it true 0 balance you would probably need to put 2 of the 3 bolts in to get about the same mass, i.e. 2 bolts with heads is probably very close to 3 holes of material removed. The bolts are 9 grams each, BTW.