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I've looked all over the forums and interwebs and can't find an answer to this question. Are flywheel and clutch bolt patterns important?

I have a 351w I'm putting into a 68 mustang mating to a TKO. I know the 351 needs a 157t 28 oz imbalance. Centerforce, for example has 10.5 and 11 inch flywheels and clutches. But for 64-80 they use a #4 or #2 bolt pattern and 86-95 a #7 bolt pattern. Is this important? Why the differentiation? They have the same 28 oz imbalance and weight (23.3 lbs). Can I put the "86" in my 68. If not, why?

BTW I'm using a Lakewood scattershield.
 

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On the older 157 tooth flywheels they used either a 10" or a 10.5" clutch only. I think, not sure but I think even the larger 164 tooth flywheel still only had a 10.5", I'm not sure. But the later flywheels from the 80's used a "metric" bolt pattern as well as dowels. They will not bolt up to the "vintage" flywheels.

Just make sure you have the correct flywheel for the bellhousing and starter you have. A 157 tooth flywheel will fit in a 164 tooth bellhousing but there's no combination of starter that will work at least on a factory bellhousing. Obviously a 164 tooth flywheel will not fit in a 157 tooth factory bellhousing.

On starters, there's a ton of confusion here in catalogs. For some reason for vintage Fords they list starters for either automatic or manual applications. This is so wrong! The automatic starter is a 157 tooth flywheels. The manual starter is for 164 tooth flywheels. Of course 157 tooth and 164 tooth flywheels both came in manual or automatic transmissions. The difference between both starters is not the drive tooth count, both are the same but the length of the snout. On 157 tooth flywheels the ring gear is set back about 3/8" and the 164 tooth flywheel's ring gear is flush with the engine side of the flywheel. If you put a 164 tooth starter on a 157 tooth flywheel, it will not engage. A 157 tooth starter on a 164 flywheel will grind.

FYI. I'm putting a GT40P into my 66 Mustang. I bought a billet PRW flywheel that is SFI rated. Besides having a SFI sticker and bolt on balance weight, so it can be used for 0, 28 or 50 oz balance but it is also drilled for every clutch bolt pattern, vintage and metric with dowels. PRW claims that just about every engine builder in the Engine Master series uses PRW. I thought that was a lot of advertising hype. Steve Dulchic who is the editor of Engine Master magazine hangs out on another forum I hang out on. I contacted him and he verified it. He told me that was true that just about everyone uses them. He said he hasn't heard of any complaints from any of the engine buillders. He followed up saying while he has never used one, he wouldn't hesitate to use one. It was about $230 delivered to the door.
 

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It's not difficult to drill and tap holes in a flywheel to fit whatever pressure plate you want to run, I've done several. I've fit metric pp's to old flywheels and old pp's to newer flywheels. The pp's are supposed to be zero balanced so that's not an issue. Just take your time to locate and drill the new holes using the pressure plate as a template. I'm currently running an old pattern pp on a 5.0 flywheel with a T5. Just had to remove the locating dowels and counterbore the new bolt holes so they could accept the shoulder bolts that were used to locate the old pp's..
 
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