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I bought a M21 to put in my 76. I need to get a bellhousing and clutch kit, but I'm not sure on proper size. Most sites I've checked out call for a 10.5" bellhousing with 10.4" clutch and 153 tooth flywheel, but they also state for a 3spd. I was thinking more along the lines of going with an 11" setup, but I'm not sure at this point what will or won't work since. Does anyone know if I have to use the 10.5" or will the 11" be fine? It's only a half inch difference, but that's alot considering right now I have a TH350 in it and it's tight against the floor hump.
Any information will be helpful.
 

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The 68-70 Nova used an 11" on the BBC cars. The SBC cars used the 10.5". So if you are running a SBC I would think the 10.5" would be right. On the same note the more surface area you have the more grip you'll get on launch. So I don't "think" you can really go wrong with either.
 

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Greetings,

Definitely go with the bigger bellhousing and clutch setup. Yes it is more money, but well worth it. You can find the BBC bellhousings (the casting ends in 621) all over eBay and other places.

Jason
 

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Are they really paying big dollars for an origional? I have one that I was planning on using, but if I can get enough out of an origional to buy a new one I might go that way since my car isn't going to be close to stock.:D
 

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I have seen auctions top $350. Right now if you do a search for "621 bellhousing" it will result in either high priced ones in good shape or damaged units for $100+ . I have an original that came from a 66 El Camino and a Lakewood scattershield for the Nova. The original will be hung on the wall, it was removedwhen the car was almost new and is in excellent shape.
 

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What is an 11" bellhousing I mean where is that measurement from where is the difference from 10.5".
 

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The 11" refers to the size clutch assembly. Here is a link to a photo showing the difference in the 2 bellhousings. The most obvious feature is the starter bulge. Now to confuse even more there are differences between passenger car and truck bellhousings as shown in this photo The difference in the center hole is about 3/8" different and if the truck unit is used with a car transmission it will not center properly and usually cause damage to the clutch and/or transmission
 

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Those pics are great I knew about the clutch assemblies being different sizes,but no idea about bellhousings.I just bought use M21 with 752 bellhousing guy said it was from BB Chevelle 66-67 from the pics posted it looks like it is for BB.Thanks now I know what to look for.
 
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