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Topic: Can my driveline handle this?

in Forum: C3 Driveline Components


Can my driveline handle this?

Posted: 7/28/05 11:08am Message 1 of 6
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Edgewood, KY - USA
Joined: 10/26/2003
Posts: 339
Vette(s): 1981, Black/Black, Engine bumped to about 400HP.Ext/int mostly stock.

I currently have the original 350, THM 350 tranny, rear-end, etc. in my '81.  I would like to bump the power up to around the 350 HP & 400 ft.lbs. ballpark, to give it the engine that "nature intended".  My plan is to pull the engine this winter and either put in a crate engine or add Hi-perf intake, heads, cam, headers, dual exhaust and maybe modern "high-multiplication-factor" torque converter and non-computer carb and distributor.  I will choose components designed for low-RPM torque, in the 1500 - 5500 RPM range.

Now... I've asked many questions related to the engine options and feel like I understand the pros and cons.  My next questions are related to whether the existing driveline can support that level of power, from the stock engine bottom-end all the way to the spindles:

Can the stock crank, rods and pistons handle that output, given the low RPM aspirations?

I have heard the THM 350 designation means it will only handle 350 ft.lbs. of torque reliably.  True?  Can it handle my planned engine without upgrades?  If not, anyone know the weak points of it that need to be replaced?

Does anyone know the torque multiplication factor of the stock '81 torque converter?  Can I assume that is considerably less than the modern ones with a factor of 2.5, or were they already getting better by '81?  Also, wouldn't the converter with higher torque multiplier just put that much more torque through the tranny and driveline, effectively putting more strain on it than with my old converter?  Does this rule out a modern torque converter for me, if I hop up the engine as described above?

Lastly, do you see any issues with the strength of the rear-end in the situation I've described?  Any portion, such as differential, half-shafts, U-joints that would require beefier replacements?

Thanks for all your help!




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Can my driveline handle this?

Posted: 7/28/05 11:16am Message 2 of 6
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Kendall Park, NJ - USA
Joined: 3/9/2005
Posts: 789
Vette(s): 1981 - 59 Beige over Cinnebar leather. Edlebrock top end, 2200 stall w/shift kit, 3:55s, Mufflex maniback exhaust, nice stereo, 16 in AREs w/BFGs
Just a heads up.  The 81 is not a TH350, Its a TH350C.  I had some minor massage work done to my L81.  Im at about 240hp up from the 190.  Both the shift kit, and the Torque converter amonst other stuff were not compatable....  Hope this saved you some head aches...


Can my driveline handle this?

Posted: 7/28/05 11:23am Message 3 of 6
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Edgewood, KY - USA
Joined: 10/26/2003
Posts: 339
Vette(s): 1981, Black/Black, Engine bumped to about 400HP.Ext/int mostly stock.

Actually, for any other auto '81 owners watching the thread, the parts catalogs don't usually list shift kits and torque converters for the 350C, BUT that doesn't mean they don't have parts/kits for them.  Summit told me they just can't list every specific tranny variation in the catalog.  I was able to order a Transgo shift kit from them that is specifically made for the 350C.  I haven't started calling about a torque converter yet.  




Can my driveline handle this?

Posted: 7/28/05 5:52pm Message 4 of 6
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Duncanville, TX - USA
Joined: 11/8/2003
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Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas
The designation "350" has nothing to do with how much power the trans will handle. The newer tran's are labled as such, but not the older ones. A well built 350 will handle anything you throw at it.
As far as torque multiplication factors, I've never seen any data on one(350). Torque converters multiply the torque that is provided, and different converters will work different. The same t.c. will work differently in a different car, with a different engine. I've used Chevette converters behind big blocks in drag cars before! As far as putting more torque thru the driveline, you have to realize, the convertor doesn't actually make torque, the engine does. The convertor will only "multiply" that torque up to it's theoretical "stall speed", after which, the 'multiplication' factor no longer exists. It's basicaly one-to-one after that. HP/aftermarket t.c.s are simply better built, with some modifications to the turbines and stators to give higher stall speeds, which is meant to put the engine into it's 'power band' at takeoff.
I think the stock driveline in a 'Vette will handle the increase you're looking for with no problem, providing it is in good condition to begin with. I think the biggest weak-link in your car would be the half-shafts, not the trans or diff.


Joel Adams
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Can my driveline handle this?

Posted: 8/2/05 4:50am Message 5 of 6
Former Member
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Edgewood, KY - USA
Joined: 10/26/2003
Posts: 339
Vette(s): 1981, Black/Black, Engine bumped to about 400HP.Ext/int mostly stock.
Thanks guys.  Any opinions on whether the factory '81 bottom end can handle these top-end upgrades?  Also, what needs to be done to the half-shafts?  Is it the actual half-shafts or the U-joints?  Can I replace with those for an earlier year big-block vette?


Can my driveline handle this?

Posted: 8/2/05 6:24pm Message 6 of 6
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Duncanville, TX - USA
Joined: 11/8/2003
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Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas
The low compression on your '81 is going to be the biggest problem. Putting a big cam in it may not give very good results without bumping the comp. ratio up a bit.
You can still go with a modest cam, a good set of heads & intake and have a stouter engine than you do now. Talk with some cam people, and get their recommendations. That's really the best way to go.
As far as your half shafts, I think you should have the large diameter shafts now. Is that true? Is so, then I would recommend a using a good u-joint, one without the grease zerk. Some say it doesn't matter, that the greasable ones are OK, but, imho, the solid u-joints are stronger. my 2c


Joel Adams
C3VR Lifetime Member #56    

My Link


(click for Texas-sized view!)
             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

in Forum: C3 Driveline Components


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