What size clutch would be recommended for use with a blown flathead motor? 9", 10", or 11"? Estimating my build to be about 220 HP, so it is a upper mild to medium performance 276 ci motor using 400 jr. cam 390 Holley, ported, and 8CM heads. Thanks, Roger
I stick my neck out and say 9". Be sure to get a good pressure ("modern") plate. The reason for this is to keep the rotating m*** as low (light) as possible. A lightened flywheel is a good thing to have, makes a big difference on a flathead
Weight of vehicle is main determinant...9" typically for very light. move up to 10 if nervous. 11 if building a dumptruck. BUT you don't say what engine you have. Early and late give you different sets of possibilities for clutch sizes with stock flywheels, Aftermarket wheels might need special order for what you want. Early and late wheels do not interchange comfortably.
With any blowen flathead, you will blow right by a 9" cover and disc, like a slipping auto. We use a 10" and your choice Iron, Steel or Alum flywheel relative to the weight of your ride. A Mc Cleod works excelent for the 10" type applications , blown or otherwise. Any questions feel free to give us a call at 1-818-248-2347 ask for Mike or Max Sr. Thanks Max Sr.
Thanks for the replies. It is an 8BA. The car will be in a stripped down Model A roadster so I am guessing the wieght would be about 1800 lbs. Roger
I run the 11" in my 28 roadster with a mild 8ba motor. been going for about 17 years now same clutch.
Is the weight difference really that great between 10" vs. 11"? Reason I ask is I have a new Weber aluminum flywheel with their street version 11" clutch and pp. The flywheel is drilled for both 11" & 10". If 10" is a good compromise, I'd consider switching.
It's quite a chunk of steel, and most have very stout springs...the one I once used seemed to slow engine revving noticeably. I think I have a loose 10 you can weigh. 10" drilled stock wheels for a late flathead are rare...taxi, police stuff. Common are 9 1/2 (not easily compatible with early trans) and 11", totally compatible, so the 10 requires drilling or aftermarket wheel. Early engine wheels are common in 9, 10, and 11. An alternate late stock wheel choice is the Merc B&B, two versions depending on what size throwout, early or late Ford.
I've toyed with using an earlier 9". I have one of the 9" flywheels with the large "lip" (for lack of correct terminology). I thought of machine the lip down to reduce weight. The difference in weight between the 9" vs. the 11" is absolutely noticable by just picked them up. The 9" seems frail in comparison. Sorry, I didn't mean to hi-jack the thread. I should have PM'd Bruce that question.
I'd run a 10" clutch on that engine - with either an aluminum flywheel or a lightened steel one. You're running a T5, so you have a low 1st gear and you're in a light car - so you don't need a huge amount of flywheel weight. If you're looking for buy the parts new - then contact Mike or Max at H&H, they are good folks and can take care of you.
If you have access to a rebuilder, you have another variable...Long plates can run 6 or 9 springs, and springs come in different tensions. The 9" came at least in p***enger and tractor versions...and the 11 came in my experience with insanel stiff springs.
I always try to get a clutch rebuilder to build to spec both clutch & pressure plates. It rarely costs any more than big box stock parts. Can be tricky if you're not local to the place though - check yellow pages for the big truck repair shops & find out who they use for brake/clutch relining. As Bruce mentioned, they can "tune" your pressure plate to whatever you want/need.
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