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I have a 1966 327 300 HP 4 speed. My orginal flywheel is casting number 3791021 with a 10 1/2" clutch. I need a new flywheel and am being told that the 11" clutch is the wasy to go. Now the questions --
1) Is there room for the larger clutch/flywheel???
2) Will the starter clear the larger clutch/flywheel???
3) What is the "best" flywheel casting number for this larger clutch???
1) The flywheel used with you 10.4" clutch is a 12-3/4", 153 tooth unit. There is NOT room in your existing bellhousing for the 14", 168 tooth flywheel used with the 11" clutch. To use an 11" clutch you will have to change your bellhousing from the GM #3858403 which you likely now have to the GM #3899621;
2) If you change to the 14" flywheel, you will also have to change your starter to one with a nose compatible with the 14" set-up;
3) There is really no "best" casting number for the 14" flywheel. Several different castings have been used over the years. The current GM PART # for the 14" flywheel is GM #3991469;
4) I do not recommend that you switch to the 14" flywheel/11" clutch. Besides all of the parts changes, there is really no need to do this for your application. Instead, if you need to replace your current flywheel, replace it with GM PART #14085720. This unit will be a direct replacement for your current flywheel. It's a very high quality, nodular iron piece and will serve you very well.
You will not be able to obtain a pressure plate assembly or friction disc from GM as all of the other 10.4" clutch components have been discontinued. For a stock-type clutch, I'd recommend going with a Sachs or LuK unit.
If you have a stock 300 hp 327, I can't think of any reason in the world you would want to go to an 11" clutch. Your stock size clutch was used on all 327's in your model year from the least to the most. I think if you change to 11" clutch, you will have to change the bellhousing, flywheel and starter (nose). I'd also think twice about replacing the flywheel. If it just has surface cracks, it can be refaced.
In addition to the list of parts to replace is the starter brace. It is different between the large and small bellhousing setup. Very few small blocks were ever equipped with the 11" clutch assy and no 327's cars were ever equipped with it. I just did a switch the other way from the 11" clutch to the 10-1/2" assembly because that was the stock setup and I wanted it to be more correct. No way would I change it if I were you.
Yes, no 327s were ever equipped with an 14" flywheel/11" clutch in PRODUCTION. However, MANY small blocks did use this set-up. Virtually all 1969-1981 Corvette small blocks used a 14" flywheel. The exception was 1970-72 ZR-1. Also, virtually all 69-81 small blocks used the 11" clutch. The exceptions were the 70-72 ZR-1s and 78-79 L-48 with 4 speed trans. The latter used a 14" flywheel and a 10.4" clutch. These flywheels were dual-drilled for both clutch sizes.
Beginning with 1984 with manual trans, it was back to the 12-3/4" flywheel with 10-1/2" clutch and that remained throughout C4 production.
I realy should have thought about that before posting. Many higher HP Camaro 350's also used the big clutch while the base 350's used the smaller clutch in the early 70's. The 10.5" was used on Camaro's after the mid 70's. Thanks for the correction.
I guess I missed all the discussion regarding Center Force Clutches. I just installed a Center Force II set up in my car. It's not complete yet so I don't if there are any adjustment issues as of yet. I recall someone stating they had to remove the Center Force throw out bearing and install a different brand to get the adjustment correct. I guess I'll wait and see.
Scott,
I would also recomend a Centerforce II for most street driven Corvettes. I currently run a Centerforce Dual Friction clutch and it feels like it grabs more aggresively than a conventional clutch assembly. Probably overkill for a street car. If this one ever wears out, I will probably go with a Centerforce II from now on.
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