Stock flywheel - yea or nay? (Clutch experts, assemble!)

"Ramblin Rover - The Vivisector of Solihull" (RamblinRover) 12/05/2013 at 21:05 • Filed to: None

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My current RV8 flywheel is, to put it bluntly, a bit lardy. It's also thicker than it needs to be (probably). See, the idea is to possibly use a stock GM 10.4/26 spline clutch, and that's going to need something specialty anyway. So here's where it gets interesting...

As you can see in the pic, the stock flywheel (at least, the one I have) does have the benefit of being moddable with absolutely no risk to strength whatsoever. Which is a good thing, because its 6-bolt pattern is a fraction over 12", and the GM clutch would be an 11 5/8". I have encountered mention of a Rover friction plate used in a GM 10.4, so one would assume the opposite works, but my pressure plate has severe finger wear, and the GM would presumably mate better with GM throwout parts. So it'd be easy to make a set of holes for a GM 10.4, but how much depth will I gain vs. flywheel thickness loss? Will it be enough?

To explain, the 3.9 clutch *may* be thicker than a GM. So far, I haven't been able to determine, but I may know tomorrow. The stock bellhousing, as found on a Defender, is very very long. It's longer than it needs to be, but it is also accommodating a (definitely) deeper than it needs to be flywheel and a (possibly) deeper than it needs to be clutch. If I compare the existing clutch + flywheel setup to the input shaft of my selected trans, it's right on the edge of what would be acceptable for deep enough into the pilot bushing - the flywheel+clutch push it out. If the GM clutch gains me 1/4" or so it'd be fine, probably, but it still may need a spacer for the bellhousing, as the whole assembly (working together okay) may be too far from the engine even with the largest off the shelf Rover - T10/Muncie bellhousing I can get. Is it recommended, then, to go to another flywheel?

Here's the simplest option: a brand-new aluminum flywheel from the same supplier as the bellhousing. Thinner, already drilled for a clutch *they* provide for an RV8 to GM 26 spline, and matched to the bellhousing. The problem, however, is price. The new flywheel would go for $500-$600+ IIRC, and would require a custom clutch, which in addition to being less easy to support is pricier as well. After all that, an aluminum flywheel would make for much, much faster engine rev on an engine with ITBs, but are the tradeoffs worth it? Is it likely, say, to impact day to day driveability? I kind of suspect it might, but who here has a because racecar flywheel they've DD'ed?

There's a more convoluted option: trying to get a Rover saloon car flywheel from the UK. Middle ground price, thinner (so *probably* wouldn't need a spacer, but might end up that way anyway), not as light as the racey one, but a touch lighter overall. However, as it's a less heavily made flywheel that would still need modification, the devil might be in the details, and it wouldn't be guaranteed to work - even after a costly ship from the UK. In some cases the Goldilocks option really is best, but this one I have severe enough concerns about I'm not sure.

Tl;dr: three clutch options unless I've missed one:

1. Lots of cobbling, but probably quite cheap. May end up dorky, might incur irritation after irritation, but would likely work all said and done.

1a. Find another Rover pressure plate and a Chevy friction plate - probably fuck up depth worse, but ensure no flywheel shenanigans needed.

2. Get it done "right", per wallet rape. End up with becauseracecar-ish build, which might suffer from impracticality and definitely would be expensey over time.

3. Try to go for a "genius" option from the UK, with some risks involved and moderately pricey. Probably less cobbling and might come out to almost the price of option 2 on the front end, but leaves me with Chevy parts like option 1. Also leaves me with an extra flywheel I'd need to sell (as would 2).

3a. See 1a, but with bonus of skinnier flywheel so less emfuckening possible. Might be among the most pricey options, though, and would never ever be able to buy just a clutch kit.

Thoughts?

YSI-what can brown do for you > Ramblin Rover - The Vivisector of Solihull 12/05/2013 at 21:36

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Although, let me ask you this. Is your car a DD?

Ramblin Rover - The Vivisector of Solihull > YSI-what can brown do for you 12/05/2013 at 21:40

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That's the idea. If I'm going to toast any clutches, they might as well be GM clutches, and if I want to be able to lazy-start and resist stall in day to day driving, a heavy flywheel isn't that bad an idea. It's also not completely an impediment to the first 30 feet off the line - wind up, and with a heavy flywheel you can KAPOW. Where it would hurt is mileage a touch (maybe, probably impossible to measure), and actually stepping through the gears to top speed.

Arch Duke Maxyenko, Shit Talk Extraordinaire > Ramblin Rover - The Vivisector of Solihull 12/05/2013 at 21:42

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4. SBC swap

Ramblin Rover - The Vivisector of Solihull > Arch Duke Maxyenko, Shit Talk Extraordinaire 12/05/2013 at 21:45

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4a. NO.jpg, and MaxYenko eats my shorts.

(If I were going for "easy" without emfuckening the weight balance, it'd be a 289 with a Toploader. Genteel and with stacks, however, is the name of the game, that and keeping it column shift.)

YSI-what can brown do for you > Ramblin Rover - The Vivisector of Solihull 12/05/2013 at 21:49

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Well, if you can keep the car from stalling at a light, then I say go lighter. The ability to for the engine to rev faster makes heel toe downshifts 10x easier. Plus when revving the engine it sounds SUPER aggressive.

Ramblin Rover - The Vivisector of Solihull > YSI-what can brown do for you 12/05/2013 at 21:55

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I should have rev-ability to spare, though (8 throttle bodies). 200+hp (perhaps 250+) in a 2400lb car is more than enough any way you slice it, particularly arriving via V8. So, while light would be nice in some respects, I'm not sure it is in enough to justify the costs.

YSI-what can brown do for you > Ramblin Rover - The Vivisector of Solihull 12/05/2013 at 21:57

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What car is this? 2400lbs with a V8?

Ramblin Rover - The Vivisector of Solihull > YSI-what can brown do for you 12/05/2013 at 22:03

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Ford Falcon Ranchero, with the awesomely Superleggara Rover V8 that tips the scales at less than the original engine. 4.2l/262ci, all aluminum and will be bolted to aluminum trans.

YSI-what can brown do for you > Ramblin Rover - The Vivisector of Solihull 12/05/2013 at 22:06

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Holy crap, that sounds amazing!

If your car already revs pretty freely, I see no problem with going heavier. You might lose a bit of MPGs but it will make the car super easy to drive in traffic, but that is just my choice. The rest is up to you!

rabidpenguin > Ramblin Rover - The Vivisector of Solihull 12/06/2013 at 09:53

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For my money and I have this done currently on two of my automobiles, is take the stock flywheel to a machine shop that can machine it down and lighten it. A good shop will work with you on your application. For instance on my DD, they removed a small amount because it was my DD. On my weekend car the shop took off alot more because I wasn't really concerned by how much more difficult it would make the car to drive. When they machine the flywheel, they only take from the rear(engine mating side) so it won't effect the setup of the stock clutch, PP and TOB. It is also alot cheaper than purchasing a new lightened or aluminum flywheel. The downside is that obviously they won't remove as much weight as an aluminum or redesigned flywheel you can purchase and you won't get as big of a performance gain.

Ramblin Rover - The Vivisector of Solihull > rabidpenguin 12/06/2013 at 18:15

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I was just down at the clutch shop owned by a friend of my dad, and that's what we came up with as well. In fact, per lightening it at all, when he heard me mention the ITB setup he got the bug eyes and strongly advised keeping the flywheel as heavy as I was comfortable with to avoid explodeys. I also now have the name of a machine shop to GM pattern and balance the flywheel, and have confirmed that a GM friction plate will operate with no issues, as well as confirming the as-installed finger height of a GM 10.4" pressure plate. All in all, I should be in good shape to proceed.