Flywheel size vs Bellhousing

[reeltales]

I have a 71 C10 that I am converting from the 250 I6 to a 327 sb. I plan to use the I6 motor mounts and Bellhousing. The original tranny was a 3 on the tree which is being changed to a Muncie M20. The clutch disc that was in the truck is a 10". I would like to go to the 10.5" or even an 11".
The question is will the I6 style Bellhousing be able to use the larger Flywheel and still allow the starter to bolt to the Bellhousing? Are the larger Flywheels the same diameter and just have the pressure plate holes drilled in a different spot?

[reeltales]

I did check my current flywheel is a 168 tooth 14", not sure if that will help with answers. Or would I be OK just to find a new 10" clutch? they see to be harder to find.

[Grumpy old man]

I just did mine recently , originally a 6 I changed the 6 cross member to the V8 so I could mount the V8 in the front holes and still use the 67 bell housing to mount a M-22 Muncie . I used all new parts from Summit . 11" clutch , You need to double check the input hole on your bell housing to make sure it matches the input size of the M-20 you may need a spacer to have a good fit . you can't rely on just the mounting ears for support , Mucie's are famous for the ears cracking without the proper bell housing to trans clearance .


https://www.summitracing.com/parts/PIO-FW100

https://www.summitracing.com/parts/PFT-MU5473-1B

[reeltales]

Looks great. I was under the impression that if you moved to the front frame holes and changed the crossmember, you would have to also change Bellhousings. Does the new v8 crossmember mount a few inches in front of the old I6 which was removed?

[Grumpy old man]

yes the V8 cross member fits the frame further forward , many guys just use the 6 position to drop a V8 in it's the fast / cheap way out . If you just want to have a V8 to go blasting around in it's fine . To go V8 correctly you'll need a cross member , drive shaft , engine perches , a better radiator , a fan shroud , and if you want to do it while the cabs still on the frame well good luck cutting and removing all the rivets from the old cross member and fitting the V8 cross member in . I did mine on the bare frame . It all depends on what your trying to have when it's done . and how much you plan on dumping into the truck .

[Grumpy old man]

Muncie's and 4 speed Hurst floor shifters aren't cheap . about $2,500.00 should cover it .

[reeltales]

I found a guy who rebuilds and sells the M20 for $750. He has been doing it for 20+ years. The truck is currently stripped down to the frame so grinding the rivets would not be too hard. I currently have the SBC engine stands but do not have the SBC Engine Cross member, or the longer driveshaft, Fan Shroud etc.

The truck is just going to be used by my wife to enjoy and drive some (but not a daily driver). This is why I was leaning toward using the I6 mounts because of the reduction of cost. The problem I have now is the I6 clutch disc was 10" which I think might be too small for the 327 that I have built.

[Steeveedee]

Originally Posted by Grumpy old man

Muncie's and 4 speed Hurst floor shifters aren't cheap . about $2,500.00 should cover it .

I sold my '64 Impala convertible with its SHP 327, close-ratio Muncie and 3.91 posi for $2000 in '82 because my wife didn't want to have to drive a manual transmission car. The guy that bought it new did so to race it. It had only a radio, rear seat speaker and a tach as options beyond the speed parts. Manual steering and brakes. I'm having a sad moment, thinking about what that would bring now.

[Mike C]

From a performance standpoint, the motor mounted in the 6 cylinder position should have a pretty significant effect on weight distribution with it mounted much further to the rear and lower. It also allows for EASY routing of the 2 1/2” performance straight dump repo Corvette exhaust manifold piping. Both of which I would choose for a street truck.

[Grumpy old man]

Originally Posted by Mike C

From a performance standpoint, the motor mounted in the 6 cylinder position should have a pretty significant effect on weight distribution with it mounted much further to the rear and lower. It also allows for EASY routing of the 2 1/2” performance straight dump repo Corvette exhaust manifold piping. Both of which I would choose for a street truck.

In the correct V8 position there is plenty of room for 2 1/2" straight dump rams horn manifolds even with manual clutch linkage and by tucking the exhaust thru thr rear cross member cleans up the bottom of the truck along with a rear mounted fuel tank to help with weight distribution .

the wheel base of a 67 short bed and a 67 Chevelle are both 115" and the weight for both is in the 33-3400 lb range giving a drop on the truck and other mods they should be very close performance wise .

[weim55]

To address a couple of issues with your swap and questions:

Your muncie 4 speed is going to have a smaller input retainer size than the hole in your truck bellhousing. I believe Advance Adaptors will have the conversion bushing you will need to make the swap.

If your V8 is a typical warmed up small block with no intention to race (just a street driver) no problem on the 10'' clutch. Back in the day when these trucks were still coming through the shop as daily driven work horses I upgraded ALL my clutch jobs to a 12" clutch assembly, 6 cylinder, small block or big block. The 12" assy had about a 20-30 dollar price difference so it would be silly not to upgrade. Still a diaphram pressure plate, still a nice light pedal pressure. All the bellhousings will accept the larger clutch assy. and all 67-72s use the larger 168 tooth flywheel reguardless of engine.

Yes, your original 6 cylinder flywheel is the larger 168 tooth version that will accept larger clutches. Same flywheel will work on any two peice main seal 6 cylinder or V8 except for the factory 400 or 454 V8.

Steve weim55 Colorado

[reeltales]

Steve, is it possible that GM had a Flywheel just for the 10" clutch? The one I have has a bolt pattern for the Pressure plate that is less than 11". I am not sure even a 10.5" clutch would fit between the pressure plate bolts. It appears that some of the flywheels I have see have the pressure plate bolt holes very close to the outside edge of the flywheel.

[weim55]

I don’t know the year to year specifics for flywheels the way some guys on the board would. I never remember having to replace a fly wheel on one of these trucks to install the larger clutches. I’d be willing to bet the flywheels even have the same casting numbers but are drilled differently depending on the original clutch application . Flywheels for the larger clutches are very common so you would have no difficulty finding one. If you want to keep cost down certainly no issue to run the smaller clutch on your 327.

Steve weim55 Colorado

[Jcfcamaro]

I have a real nice 10in flywheel which I believe they call it a 10.5. A few years ago I was building a new motor and took all my parts to the machine shop and got the 10.5 mixed up with the 11in one I was planning on using. Didn't figure it out until he had already surface ground and balance it. It's been sitting ever since. I'd make you a good deal on it but its heavy for shipping. Also look for a casting number 403 bell housing there pretty cheap and see them all the time for sale .

[reeltales]

I talked to a friend who thinks he has a GM 14" at his shop. If so I will resurface and use that one, otherwise the aftermarkets should work. Still up in the air with respect to use the front holes or back for engine mounting. I have all the parts for the back holes and only a few parts for the front mounts (have the sbc engine perch's but missing the v8 bell housing crossmember and longer drive shaft.)