C4 Tech/Performance L98 Corvette and LT1 Corvette Technical Info, Internal Engine, External Engine

flywheel options

 
Old 04-13-2019, 12:32 PM
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bud40oz
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Default flywheel options

i have been thinking of building a 406 and putting it in my 91, just not sure what i could use for a flywheel. it would be a 2 piece rear main instead of 1 piece and i don't think the flywheels interchange with bolt patterns. Then i don't know if i would run into clutch problems also.
anyone who has done this before with a zf 6 speed? , i would like to talk with you..
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Old 04-13-2019, 12:45 PM
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dizwiz24
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Originally Posted by bud40oz View Post
i have been thinking of building a 406 and putting it in my 91, just not sure what i could use for a flywheel. it would be a 2 piece rear main instead of 1 piece and i don't think the flywheels interchange with bolt patterns. Then i don't know if i would run into clutch problems also.
anyone who has done this before with a zf 6 speed? , i would like to talk with you..
i really like my fidanza lightweight aluminum flywheel.
some people worry about extra noise, but a thicker zf countershaft shim and a sprung hub clutch (which stock disks arent) will solve 90% of the noise problems.

IMHO its just low hanging fruit to drop 26 lbs of intertia rotating mass from the driveline.
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Old 04-13-2019, 02:29 PM
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cuisinartvette
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FW are made for different patterns may need to call. Know they make them for 2pc rear main engines not sure about the other, Id imagine they do.
What gear are you running? For a street car I dislike super light FW and puck type clutches they are a pain, can chatter etc. That inertia of a heavier or mid weight makes all the difference in the world on shift recovery and launching. Road course guys love em for obvious reasons...others do it so they can sit in the driveway and rev it quicker (so what)
An SFI rated one is highly recommended.

If you have enough tq and gear the light ones are much easier, doesnt seem to be so much of an on/off switch.

Last edited by cuisinartvette; 04-13-2019 at 02:42 PM.
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Old 04-13-2019, 02:36 PM
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mtwoolford
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Check with SPEC, they have a wide variety of flywheel and clutch combos. Plan on buying a new oil pan to match up with the earlier 2 piece rear main seal block. A lot of clutch problems can be diagnosed before the transmission is installed if you leave the pilot shaft (clutch installation tool) in the clutch disc / pilot bearing and have someone depress the clutch pedal to ensure that the pressure plate disengages. Also rotate the crank / flywheel and observe that there is no interference with the bellhousing.or clutch fork...unlikely, but there have been several threads on this very problem; the common denominator seemed to be the use of a incorrect height fulcrum stud for the clutch fork...I believe there are three different heights available if the LT5 is included. The throw on the clutch fork / throwout bearing can be increased by using a thinner spacer between the clutch master cylinder and the firewall. Just my opinion, but with the large cubic inch stroker you're contemplating, I'd use SPEC's "heavy" billet steel flywheel and put all that spinning inertia to work for you....just my opinion., I know a lot of guys love 12 lb aluminum flywheels. On my LT4 350 I used a SPEC 22 lb "lite" billet steel flywheel and a stage 3 plus clutch with a thinner spacer (roughly half the thickness of the oem piece) between the clutch master cylinder and the firewall. DOT 5 silicon based brake fluid in the clutch system worked wonders too. good luck
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Old 04-13-2019, 02:45 PM
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MT so on a non adjustable ( I use a 90s era F body slave/T56) that is the best way to increase throw? Always had an issue with that and sometimes get notchy shifts
only other way seems to be to make a cup shaped spacer in between the rod and fork by the trans. There is only .030?? gap where its fully disengaged, my one gripe about this thing.
Should be buttery smooth....even took a brand new trans apart thinking it had a synchro issue. Not.

Wait wouldnt spacing the slave from the firewall do the opposite? Heard there is a spacer or shim that can be put behind the flywheel not to sure if thats safe or not. Opinions?

Last edited by cuisinartvette; 04-13-2019 at 02:46 PM.
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Old 04-13-2019, 03:12 PM
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Yeah I dont have a puck type (the fan blade looking) clutch. Those are light, but on/off like a switch.

tough to feather clutch and back up a hill for example, without stalling

i run spec stage 3+ clutch. Its more disk like and sprung hub.

in traffic, the lighter flywheel makes the car easier to stall. Stop and go traffic is more difficult. Drag launches are a little trickier, its more on/off and difficult to slip the clutch.
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Old 04-13-2019, 06:53 PM
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mtwoolford
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Originally Posted by cuisinartvette View Post
MT so on a non adjustable ( I use a 90s era F body slave/T56) that is the best way to increase throw? Always had an issue with that and sometimes get notchy shifts
only other way seems to be to make a cup shaped spacer in between the rod and fork by the trans. There is only .030?? gap where its fully disengaged, my one gripe about this thing.
Should be buttery smooth....even took a brand new trans apart thinking it had a synchro issue. Not.

Wait wouldnt spacing the slave from the firewall do the opposite? Heard there is a spacer or shim that can be put behind the flywheel not to sure if thats safe or not. Opinions?
My car is a 96 LT4. This is from an email to Bill Bourdeau, aka ZFdoc, for which Bill replied "Nice effort to visualize physical goings on of the clutch hydraulic system"

"I now understand how the clutch pedal arm / clutch master cylinder work:

(1) the clutch pedal spring rotates the pedal arm towards the driver;

(2) The clutch pedal is pinned to the clutch master cylinder rod and the rod is pulled outwards toward the driver until a shoulder on the rod end inside the master cylinder hits a retainer on the (driver side) end of the clutch master cylinder;

(3) the operating piston is kept in contact with the master cylinder rod by a spring at the forward end of the master cylinder bore pushing the operating piston rearward into the operating rod.

The effective stroke of the piston is determined by how far the clutch pedal can be pressed down; normally the pedal travel is stopped by the floor /rug. Thinning the spacer between the clutch master cylinder and the firewall moves the clutch pedal up and away from the floor /rug, increasing the distance the operating piston in the clutch can travel with an increase in the volume of fluid displaced and available to operate the slave cylinder.

When I mocked up the whole assembly on a work bench, I found:

(4) The piston in the master cylinder has a maximum available travel of 39 mm

(5) with the oem spacer, maximum travel of the operating piston was only 16 mm.

(6) with no spacer at all, the maximum travel of the operating piston was 30 mm.

In the car, I found that a spacer approximately one half the thickness of the oem spacer yielded the best results; This had an added benefit of bringing the clutch pedal even to the brake pedal. Bill recommends a throw out bearing travel of 0.290" - 0.315"; is yours anywhere near that? My ZF with a SPEC clutch and all new throwout bearing, clutch fork and stud and slave cylinder measured out at 0.190" to 0.210" with the oem spacer and with the aforementioned half thickness spacer 0.285"; I honestly can't say why, but the clutch in my car works way better with DOT 5 silicon based fluid; others have reported similar results.

Hope this helps; MT

Last edited by mtwoolford; 04-13-2019 at 06:59 PM.
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Old 04-13-2019, 07:09 PM
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Interesting and thanks. I can now solve a sometimes notchy feeling trans without overextending/blowing the slave...done that a few times.Sure is a fine line between engaging/not and blowing the darn thing. Firewall flex may play part too...back on topic.
Thanks again
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Old 04-13-2019, 07:31 PM
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Kevova
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Stock 400 sbc is external balanced. Flywheel options maybe limited. You will also need correct balancer. 400 also uses larger diameter main bearings. If you go with aftermarket internal balance crank might as stroke it to a 421-434.

Last edited by Kevova; 04-13-2019 at 07:32 PM.
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Old 04-13-2019, 09:14 PM
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my son was born in 1994 and this happened before he was born. back when i got pretty serious about racing my 89 6-speed, i bought a gm 4-bolt main block which accommodated the factory roller lifters and 1-piece rear seal. then i bought an aftermarket 2-piece steel crank and used this in the gm block but did not use the 1-piece adapter. then i purchased a mcleod twin disk clutch with their aluminum flywheel and hydraulic t-o bearing. we set up the t-o bearing similar to what the c5 and c6 guys do for travel and clearance. never had any issues and i pretty well beat the snot out of it and it came back for more.
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Old 04-14-2019, 11:58 AM
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Tom400CFI
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Originally Posted by Kevova View Post
Stock 400 sbc is external balanced. Flywheel options maybe limited.
Easy fix; take the FW to a machine shop w/a 400 flex plate for reference. Have them machine OFF metal from the opposite side (of the counter weight) until the balance matches the flex plate.
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Old 04-14-2019, 01:41 PM
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Originally Posted by Tom400CFI View Post
Easy fix; take the FW to a machine shop w/a 400 flex plate for reference. Have them machine OFF metal from the opposite side (of the counter weight) until the balance matches the flex plate.
just my opinion, but I always try to balance the entire rotating assembly, pistons, rods, crank, flywheel, as a unit, especially when a bunch of non oem pieces are going together.

More specifically, with flywheels and the ZF trans, assuming the balance issues are dealt with, the issue with the pull type clutch used in conjunction with the ZF was that the ZF clutch sat too far to the rear, so and early cure to replacing the oem dual mass flywheel specific to the ZF with a one piece flywheel (usually from a F body) before aftermarket flywheels became available, was to take an oem one piece flywheel and machine off 0.095" from its face. I think this could be one possible way of adapting a flywheel meant to go on a two piece rear crank shaft to the ZF trans / clutch.
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