Hello, I'd like to know if I can use a BOSS 351 flywheel D1ZX-6380-AA with a 351C 4V engine? I am converting my car from auto to a 4 Spd Toploader and I have the above flywheel. However, I am not sure the balancing of this flywheel is the same as that of a Cleveland flywheel. I realize the Boss engine is very similar but there might be balancing weight considerations. Part books show two different flywheels for these engines and there are no indications they are interchangeable. Since this is a potentially hazardous combination please only answer if you know for a fact that flywheel can or cannot be used with this engine. Thanks,

 

The balance is the same.

 

As long as it is a Cleveland based Boss it could have a larger clutch than the 4V or 2V so it would require the corresponding parts. So it wont bolt in with what would be an existing clutch and pressure plate. The difference would be having to use an 11 inch clutch instead of a 10.5 inch clutch. Not sure what size they had since all my Clevelands are automatics.

The only real difference between the BOSS351 and a 4V is the cam, adjustable rocker arms, and the BOSS had an aluminum intake. The bottom end is pretty much the same stuff, but should have 4 bolt mains. I have a couple non BOSS 4 bolt main blocks so it isnt that much difference. The BOSS had closed chamber heads but then so did the 70 4V and the BOSS 302, but the 302 had much smaller chambers since its 50ci smaller.

 

IIRC, the BOSS 351 used the same 10.5" clutch as other 351s, and indeed, the 390.

 

This is a 164 tooth 11" flywheel. I thought that's what all Cleveland engines used (except for some 351's that may have been fitted with the 157 tooth 10'5" 302 flywheels by changing the counterbalance weight to adapt the T5 transmissions' smaller bellhousing).

However, what I am really concerned about is the fact that stock Clevelands are externally balanced (my engine has been rebuilt but I doubt it has been internally balanced). Thus the flywheel act as counterweight to keep the engine running smoothly without vibrations. Since the Boss engine has different internal parts which can affect balancing, there lies my concern.

Both engine (Cleveland & Boss) have a different flywheel with a different part number (C6TZ-6375C for all 351 Cleveland and Windsor, D1ZZ-6375B for Boss 351 only as per the 1974 Chilton). The Hollander Interchange manual also shows a different flywheel for these engines). They are both 164 tooth 11" yet don't have the same part number. Why?

I've heard something about the Boss flywheel having higher grade iron but nothing definitive. If that's the case then the better. But what about the counterbalance weight? I just want to avoid my ignorance making a potentially serious (read dangerous) mistake. If you know that I am wrong about something please do tell me.

Why do I want to use that flywheel you may ask? This is a driver I have decided to turn into a Boss 351 clone. I have many actual Boss parts (such as trans, bellhousing and flywheel) that I want to put on the car as I build it, but I know that switching from a flex plate to a flywheel is more than a fitment issue. Any good advice would be greatly appreciated. Thanks

 

The deed is done. Successfully converted to a 4 Spd Toploader from a C6. The power gets to the ground better, making the car feel lighter (it is in fact lighter by about 100 lbs) and fun to drive. To answer my own questions after more research, turns out the engine/flywheel balance is indeed the same with all 351C engines whether they're Boss or Cobrajet. There was really no issue there. Everything fit like a glove (except for the driveshaft and trans mount of course). Hopefully this will benefit someone else someday. Cheers,

 

I am curious on what you found out. I am dropping in a 351c into my 67 Mustang with a 4speed toploader and I have a few questions for you. Did you use the 157 tooth flywheel? What size clutch? What was the problems with the toploader and drive shaft fitment?

 

I used an 11 inch clutch with an OEM 164 tooth ring-gear/flywheel just the same as an original 71 Boss (I think the same as all 351C except the boss has a stronger flywheel - that's my understanding ayway).

The driveshaft is longer with a 4spd than with a C6. But since your car is a 67 my specific measurements probably don't apply. One way to do it is to put everything together and then have a driveshaft fabricated to your spec.

Something else to watch for is the starter motor. The manual trans starter has a shorter head. Here are some part numbers I used that can get you started (the suffix indicates manual or auto trans.):

C5TF-11001-A (Standard Trans)
C5TZ-11002-D (Standard Trans)
D5TF-11001-DA (Standard Trans)
Other Part Number: 3132

C2TZ-11002-B (Auto Trans)
Other Part Number: 3124

Hope this helps,