Engine/Transmission (1994 - 1998) Clutches 101

[TWafer]

OK, I guess I’m done making mods for the time being. I turned the timing up to 15. It did reduce EGTs but there seems like a very noticeable drop in low end torque, still I’m going to leave it there till I get a new clutch, then I may drop it back a bit to regain some.

I cant afford a clutch now but would like to figure out what one I might want so I know how much I have to save up. I’ve been reading about the SBC clutches but am somewhat confused. I think I basically understand the differences between the O, OFE & FE. O being the smoothest and lowest capacity, FE being the strongest and grabbiest (is that a word?) and the OFE somewhere in between. Id like to have the best of both worlds of course but given the mods I’ve done and how I use the truck Id probably settle for the OFE unless you guys convince me otherwise. I am confused as to what size I would want 12” or 13”. Apparently 12” is the stock size for my truck. Is the 13” just for the 6 speeds or will it replace mine too? I see mention of replacing the flywheel for the 13”. Is that what I would have to do or is there more to it than that even?

Tim

 

[Andy Redmond]

See insertions. .

OK, I guess I’m done making mods for the time being. I turned the timing up to 15. It did reduce EGTs but there seems like a very noticeable drop in low end torque, still I’m going to leave it there till I get a new clutch, then I may drop it back a bit to regain some.

Turn in the pre-boost fueling screw at 1/2 turn increments to see if it wakes up the bottom end a bit again. You might experiment with different afc positions and the AFC spring tension.

I cant afford a clutch now but would like to figure out what one I might want so I know how much I have to save up. I’ve been reading about the SBC clutches but am somewhat confused. I think I basically understand the differences between the O, OFE & FE. O being the smoothest and lowest capacity, FE being the strongest and grabbiest (is that a word?) and the OFE somewhere in between.

How much is your ultimate hp goal? You are likely safe with the OFE as it is over engineered for many bombers.

Id like to have the best of both worlds of course but given the mods I’ve done and how I use the truck Id probably settle for the OFE unless you guys convince me otherwise. I am confused as to what size I would want 12” or 13”. Apparently 12” is the stock size for my truck.

The 12" is fine, but if you tow go with the 13"

Is the 13” just for the 6 speeds or will it replace mine too? I see mention of replacing the flywheel for the 13”. Is that what I would have to do or is there more to it than that even?

The 13" is a redrilled flywheel that has the bolt pattern for the p. plate out closer to the outside diameter. The clutch center is stronger. You can also spec a roller bearing, kevlar bushing or oem pilot bearing design depending upon the input shaft nose condition.



Most vendors charge a healty core fee to assure getting a flywheel back. A new flywheel is about $350 from Cummins. You would have to have a machine shop redrill it so the 13" Southbend will mount.



SB also offers the 12 or 13" clutches with the 1 1/4" input shaft vs the 1 3/8" used typically with the NV5600 6 spd.



Good luck

Andy