Sheared flywheel bolts - need to worry about this?

[turbokinetic]

This is sort of off topic because it is about a FWD engine but you guys may have some ideas!

I'm running a 3.8 SFI Turbo engine, FWD with a 4T65EHD transmission. The 3.8 has the stock FWD chankshaft and driveplate with six 7/16" fine-thread bolts holding the driveplate on.

I have upgraded the bolts to grade 8 (factory had grade 5).

Someone has expressed concern that the flywheel bolts may shear off, since the bolt circle is so small on the FWD crank versus the RWD crank they are used to working with. The late model FWD 3800 has a larger bolt circle at the flywheel.

I know some of the newer 3500 and 3900 60° engines have been turbocharged and are surely putting out at least as much torque as I am, and I beleive they ahve the small bolt pattern.

Has anyone had driveplate failures or sheared bolts?

I am installing a fully built transmission now and plan to turn the boost up but don't want to shear the bolts! With the old trans at 15 PSI, the car was very fast, and would overwhelm the transmission. This trans will hold the torque and put the stress on the driveplate bolts.

Engine specs:
Roller cam 3.8 SFI block
Comp 258HR cam
Sealed Power forged pistons - stock C/R
Ported heads, intake and exhaust manifolds
Turbonetics GTK450
Air to air intercooler with 2.5" air pipes
3" exhaust from turbo back.
60# Seimens Mototron injectors
Code59 speed-density ECM

Thanks in advance,
David

 

[liv4gnz]

there is nothing stronger than grade 8 available lol had to say it

 

[mikestertwo]

I don't think you have anything to worry about.

 

[turbokinetic]

Thanks guys - I didn't figure that would be a problem but after the horror story I was given, I wanted some reassurance!

Actually - there are stronger bolts than an SAE grade 8. They are special purpose hardware, rated by tensile strength instead of a "grade." ARP is an example of a company who sell bolts that are stronger than grade 8.

I've read that the bottom end of the 3.8 is good for 500 HP and I plan to push this to 500 HP if it will do it!

Got the trans in and bolted up - will try to get the rest of it buttoned up tomorrow.

David

 

[bmackinnon]

Hey David! How's that bad-boy runnin'?? Apparently good enough that the stock 'HD' trans couldn't stand the heat?? Please update your thread in the Hybrid section, and tell us about the new trans, driving experiences, tuning updates, etc... :biggrin:

 

[turbokinetic]

Hey David! How's that bad-boy runnin'?? Apparently good enough that the stock 'HD' trans couldn't stand the heat?? Please update your thread in the Hybrid section, and tell us about the new trans, driving experiences, tuning updates, etc... :biggrin:

Will do!
David