This is what happens when you get bored on a Sunday............
02-09-2012, 12:52 PM
#64
Drifting
Thread Starter
Member Since: Dec 2005
Location: Dayton, OH
Posts: 1,822
Likes: 0
Received 0 Likes
on
0 Posts
02-09-2012, 12:59 PM
#67
Drifting
Thread Starter
Member Since: Dec 2005
Location: Dayton, OH
Posts: 1,822
Likes: 0
Received 0 Likes
on
0 Posts
02-09-2012, 01:09 PM
#68
Safety Car
Member Since: Jun 2009
Location: Frederick, Maryland
Posts: 3,888
Likes: 0
Received 2 Likes
on
2 Posts
Can someone reiterate the purpose of drilling the lifter trays? Better oil flow? 
Geerookie: What was your reasoning for not going with the 5.5"? Are you trying not to do a button setup?
Geerookie: What was your reasoning for not going with the 5.5"? Are you trying not to do a button setup?
02-09-2012, 01:22 PM
#69
Drifting
Thread Starter
Member Since: Dec 2005
Location: Dayton, OH
Posts: 1,822
Likes: 0
Received 0 Likes
on
0 Posts
Not sure I understand the clutch question......7.25" does use a button flywheel.
The reason for a 7.25" instead of a 5.5" is heat capacity and reliability. The trade off in laptimes between a 5.5" and a 7.25" is insignificant (we did the math
) in a race less than an hour, but the heat capacity/reliability is at least twice as much. That clutch only weighs ~3lbs more than the 5.5". This is an 8-leg Optimum-V compared to a 6-leg 5.5" Optimum-V. This clutch with discs weighs 10.4lbs
02-09-2012, 01:58 PM
#71
Safety Car
Member Since: Jun 2009
Location: Frederick, Maryland
Posts: 3,888
Likes: 0
Received 2 Likes
on
2 Posts
Drilling the lifter trays gives you better drain back so the oil doesn't pool. On an engine that runs at high RPM all the time this will contribute to oil starvation but probably more important is if the oil pools in the lifter cups and the lifters are pounding up and down it will cause the oil to foam which significantly reduces its effectivness.
Not sure I understand the clutch question......7.25" does use a button flywheel.
The reason for a 7.25" instead of a 5.5" is heat capacity and reliability. The trade off in laptimes between a 5.5" and a 7.25" is insignificant (we did the math) in a race less than an hour, but the heat capacity/reliability is at least twice as much. That clutch only weighs ~3lbs more than the 5.5". This is an 8-leg Optimum-V compared to a 6-leg 5.5" Optimum-V.
This clutch with discs weighs 10.4lbs
Not sure I understand the clutch question......7.25" does use a button flywheel.
The reason for a 7.25" instead of a 5.5" is heat capacity and reliability. The trade off in laptimes between a 5.5" and a 7.25" is insignificant (we did the math
) in a race less than an hour, but the heat capacity/reliability is at least twice as much. That clutch only weighs ~3lbs more than the 5.5". This is an 8-leg Optimum-V compared to a 6-leg 5.5" Optimum-V. This clutch with discs weighs 10.4lbs
Will you be driving to the track or trailer it?
02-09-2012, 04:10 PM
#72
Drifting
Thread Starter
Member Since: Dec 2005
Location: Dayton, OH
Posts: 1,822
Likes: 0
Received 0 Likes
on
0 Posts
100% race car now.
02-09-2012, 04:13 PM
#73
Drifting
Thread Starter
Member Since: Dec 2005
Location: Dayton, OH
Posts: 1,822
Likes: 0
Received 0 Likes
on
0 Posts
02-09-2012, 04:27 PM
#74
Safety Car
Is this your first rodeo with a C5 clutch swap? Lets just say that in some cars they put in an off-balanced clutch assembly to bring the engine within spec. If you are lucky enough to have one of these cars (I was) and you install a properly zero balanced clutch setup (I did), you will be greeted with a wonderful new vibration after you get it all back together (boy was that fun).
The older GM service manuals tell you to mark the location of the balance weights on the back of the flywheel and transfer them to the new one (No holes for them on a Fidanza flywheel). The later GM service manuals tell you to not transfer the balance weights and that the clutches come as a balanced assembly.
I pulled the clutch and took it to a driveline shop with my stock stuff. Had the stock stuff spun up and had the new clutch assembly matched exactly to the off-balance on the stocker. Upon reinstallation the vibration was gone.
So... if you have the time it's best to go have the new assembly match balanced to the stock assembly. Or, at least have the stock one checked. If it turns out it's balanced then you're fine. Oh... and lets not even get into all the stories about "zero balanced" aftermarket clutches that aren't.
The older GM service manuals tell you to mark the location of the balance weights on the back of the flywheel and transfer them to the new one (No holes for them on a Fidanza flywheel). The later GM service manuals tell you to not transfer the balance weights and that the clutches come as a balanced assembly.
I pulled the clutch and took it to a driveline shop with my stock stuff. Had the stock stuff spun up and had the new clutch assembly matched exactly to the off-balance on the stocker. Upon reinstallation the vibration was gone.
So... if you have the time it's best to go have the new assembly match balanced to the stock assembly. Or, at least have the stock one checked. If it turns out it's balanced then you're fine. Oh... and lets not even get into all the stories about "zero balanced" aftermarket clutches that aren't.
02-09-2012, 05:11 PM
#75
Drifting
Thread Starter
Member Since: Dec 2005
Location: Dayton, OH
Posts: 1,822
Likes: 0
Received 0 Likes
on
0 Posts
Is this your first rodeo with a C5 clutch swap? Lets just say that in some cars they put in an off-balanced clutch assembly to bring the engine within spec. If you are lucky enough to have one of these cars (I was) and you install a properly zero balanced clutch setup (I did), you will be greeted with a wonderful new vibration after you get it all back together (boy was that fun).
The older GM service manuals tell you to mark the location of the balance weights on the back of the flywheel and transfer them to the new one (No holes for them on a Fidanza flywheel). The later GM service manuals tell you to not transfer the balance weights and that the clutches come as a balanced assembly.
I pulled the clutch and took it to a driveline shop with my stock stuff. Had the stock stuff spun up and had the new clutch assembly matched exactly to the off-balance on the stocker. Upon reinstallation the vibration was gone.
So... if you have the time it's best to go have the new assembly match balanced to the stock assembly. Or, at least have the stock one checked. If it turns out it's balanced then you're fine. Oh... and lets not even get into all the stories about "zero balanced" aftermarket clutches that aren't.
The older GM service manuals tell you to mark the location of the balance weights on the back of the flywheel and transfer them to the new one (No holes for them on a Fidanza flywheel). The later GM service manuals tell you to not transfer the balance weights and that the clutches come as a balanced assembly.
I pulled the clutch and took it to a driveline shop with my stock stuff. Had the stock stuff spun up and had the new clutch assembly matched exactly to the off-balance on the stocker. Upon reinstallation the vibration was gone.
So... if you have the time it's best to go have the new assembly match balanced to the stock assembly. Or, at least have the stock one checked. If it turns out it's balanced then you're fine. Oh... and lets not even get into all the stories about "zero balanced" aftermarket clutches that aren't.
Hmmmm.....I wasn't aware of this on C5's. I haven't had a stock clutch in this car for 5+ years. I took out a Fidanza flywheel and Spec clutch disc and Spec aluminum pressure plate. (read first post with clutch weight savings
)I guess that is what you call dumb luck
As they say, "Ignorance is Bliss"
02-09-2012, 06:22 PM
#76
Racer
The reason for a 7.25" instead of a 5.5" is heat capacity and reliability. The trade off in laptimes between a 5.5" and a 7.25" is insignificant (we did the math) in a race less than an hour, but the heat capacity/reliability is at least twice as much. That clutch only weighs ~3lbs more than the 5.5". This is an 8-leg Optimum-V compared to a 6-leg 5.5" Optimum-V.
) in a race less than an hour, but the heat capacity/reliability is at least twice as much. That clutch only weighs ~3lbs more than the 5.5". This is an 8-leg Optimum-V compared to a 6-leg 5.5" Optimum-V.There is probably more MOI to be gained going to an alum starter ring on a 7.25" vs a steel ring on a 5.5" (it's 1/3 of the total weight, and much bigger dia than the clutch itself)
02-09-2012, 06:26 PM
#77
Racer
02-09-2012, 06:43 PM
#78
Safety Car
From the Tilton catalog,
MOI of a 7.25" sintered clutch & flywheel is 266
5.5" is 154
163 tooth flywheel (OEM size) MOI - 178
153 tooth (need special starter, 5.5" clutch) - 114
110 tooth (for 7.25" clutch, won't work w/o reverse start) - 53
Typical 5.5" sintered clutch MOI - 30
7.25" - 88
Doesn't/didn't the Caddy team run a little flywheel w/reverse starter? (MOI of ~65?)
What did the math show for lap time differences and what numbers did you plug in?
I only felt the difference out of slow turns, but would be interested in the actual #s.
Shifting speed was identical to my RPS, if that figures into your calculations.
MOI of a 7.25" sintered clutch & flywheel is 266
5.5" is 154
163 tooth flywheel (OEM size) MOI - 178
153 tooth (need special starter, 5.5" clutch) - 114
110 tooth (for 7.25" clutch, won't work w/o reverse start) - 53
Typical 5.5" sintered clutch MOI - 30
7.25" - 88
Doesn't/didn't the Caddy team run a little flywheel w/reverse starter? (MOI of ~65?)
What did the math show for lap time differences and what numbers did you plug in?
I only felt the difference out of slow turns, but would be interested in the actual #s.
Shifting speed was identical to my RPS, if that figures into your calculations.
Last edited by RX-Ben; 02-09-2012 at 06:56 PM.
02-09-2012, 06:52 PM
#79
Drifting
Thread Starter
Member Since: Dec 2005
Location: Dayton, OH
Posts: 1,822
Likes: 0
Received 0 Likes
on
0 Posts
I just put a 5.5" 2 disc V drive in a 99 coupe, and I noticed the discs are MUCH thinner than the 2 disc 5.5" V drive that's in my car. The button flywheel seemed to have more offset (deeper dish) to make up for this (ie, I assume the stack height is the same I presume). Not sure if QM changed this up for the LS stuff or what. The unit was slightly lighter than mine.
There is probably more MOI to be gained going to an alum starter ring on a 7.25" vs a steel ring on a 5.5" (it's 1/3 of the total weight, and much bigger dia than the clutch itself)
There is probably more MOI to be gained going to an alum starter ring on a 7.25" vs a steel ring on a 5.5" (it's 1/3 of the total weight, and much bigger dia than the clutch itself)
True. MOI is all about distance from the center.
I have a document written by a guy who did a comparison between Tilton 5.5 and 7.25 and QuarterMaster 5.5 and 7.25 clutches. The QuarterMaster 7.25 Pro being the highest MOI.
The car he was using was a Formula Ford so it was light and the differences should be much more obvious than they would be in our 2900lbs beasts. He took into account gearing, tires, wheels, drag. HP etc.
He did comparisons of no load acceleration and loaded acceleration (real world). The difference in acceleration between the 5.5 and 7.25 was on .02 seconds at 1000 meters.
Obviously the difference was a bit bigger in lower gears at shorter distances but still only about .08 sec.
Takes a much better driver than me to take advantage of that.
Plus remember, that isn't a 2900lb Corvette with an 18" wheel and tire combo that weighs 42lbs!
02-09-2012, 06:57 PM
#80
Drifting
Thread Starter
Member Since: Dec 2005
Location: Dayton, OH
Posts: 1,822
Likes: 0
Received 0 Likes
on
0 Posts
How would the clutch in a '99 C5 be different than the one in your car? Was it Optimum-V compared to V-Drive?
Oh, wait, you have a Pro, correct?
Big differences between all especially if you have a 2 disc rally setup.