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Old 06-28-2002, 07:23 PM   #1
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SB Chevy 400 Flywheel

I have a 400 engine and want to bolt it up to my T-5 tranny. Problem: My trans uses a 10.4" diameter flexplate and the only flywheels I can find are made for 10.5" flexplates. Can someone please tell me where I can find a flywheel that will work for my application?

The flywheel also has to have a 153 tooth ring gear. If there isn't a 400 flywheel that fits these requirements, I'd be grateful if someone could tell me where to find a 350 flywheel that does. They make a bolt-on external balancing plate to make the 350 flywheel work on 400's.

Note: The 400 has a 2 piece rear main seal - 3.58" crank bolt pattern.

Please help me out. This is the only obsticle keeping me from dropping the 400 into my '91 Firebird!

Thanks

Last edited by wingnut; 06-28-2002 at 07:36 PM.
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Old 06-28-2002, 09:01 PM   #2
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www.centerforce.com lists a 400 flywheeel like you described.
153 teeth, 2 bolt patterns. Probably 10.4" and 11"
But it will set you back about $350+
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Old 07-01-2002, 07:40 AM   #3
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What you need to do is either get the CF flywheel mentioned above; or get a 83-85 305 flywheel and take it to your local balancing shop and have them "unbalance" it to 400 specs. I did the latter for my 400.

You will also find that your starter won't bolt up to the 400. Furthermore, no starter that will work with a 12" 153-tooth ring gear will work, because if there was a bolt in the inner bolt hole of the pattern in the block, it will go right through the middle of the starter drive. It is not possible for any starter whatsoever to work, unless someone finds a way to have a bolt with an offset in the middle. Get a machine shop to drill the hole you need before you put the motor in the car, it's alot easier then, if you don't have good measuring tools and a drill press it's best left to professionals, its exact location and properties are critical.

FWIW, I used the flywheel as described above on my 400; drilled the special hole in the block; and I'm using a CVR mini-starter, becasue the stock POS is entirely too weenie to turn a 400 over.
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Old 07-01-2002, 08:25 AM   #4
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Or simply get a Tommy Johnson Motorsports mini-starter like I did, which has a 400 bolt pattern and bolt it up....for like $115. Well spent money, IMHO.

(No, I don't have the web address, just do a web search)
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Old 07-01-2002, 06:49 PM   #5
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Check out the starter for an '87 IROC w/5.7L. It shoud have the
right spacing and bolt pattern for use with the 153 T. flywheel.
The one I installed had a large frame like the older 350 starters.
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Old 07-03-2002, 03:54 AM   #6
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What RB says is correct. You need an 83-85 flywheel for it. That's what I'm using for my T5.

p.s. And RB congrats on the fact that you know the difference between "its" and "it's". Seems like 99% of this board doesn't ! lol
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Old 07-03-2002, 04:53 PM   #7
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Quote:
Originally posted by RB83L69
get a 83-85 305 flywheel and take it to your local balancing shop and have them "unbalance" it to 400 specs.
Why a 305 flywheel? Why not a 350 flywheel? I have an external balance plate, made to bolt onto a 350 flywheel.
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Old 07-04-2002, 08:45 AM   #8
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Because 350 flywheels are 14" 168 tooth, and the starter for them won't fit in the bell housing.

I've been there and done it, along with I have long since forgotten how many other miscellaneous motor swaps. Not to be a jerk, but this question gets asked with astounding regularity, and every time I give the same answer, and every time somebody who has never done the swap tells all about how this or that or the other thing should work, or how they've heard something or other from somewhere they think, or some other foolishness that makes it sound easier... and every time the real doer of the deed (as opposed to the armchair motor builder) bites off on the BS, they discover the truth, the hard and expensive way.

If you follow the instructions I gave you, everything will bolt up, work perfectly, and cause no trouble. You'll get it right the first time and you won't be laying up under an assembled car, all PO'ed because you can't get a starter to work on it. That especially goes for making sure the right hole is drilled in your block: do not fall for the line about how this starter or that one "seems like it ought to work" without adding the late-model hole, IT WON'T HAPPEN.

The "pork chop" weight might work, and in fact does sometimes; but IMHO it is merely a substitute for doing it the right way. I usually pay about $25-$30 for the balance shop service, and never have to worry about it again; and the flywheel remains in the stock location that way, so you won't have to post again later about how your clutch doesn't work right, about how the throwout bearing is the wrong one, about adjustable ball studs, etc. etc.

Trouble-free the first time is good.
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Old 07-04-2002, 09:01 AM   #9
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AMEN! I followed his advice by SEARCHING the boards first, and it worked right the first time, with no headaches! Listen to the man and you won't be sorry
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Old 07-05-2002, 08:25 AM   #10
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Thanks for the advice. For the record, I did perform several searches on this topic before I made my initial post. I saw the "use an un-balanced 305 flywheel" advice. I just don't want to use a 305 flywheel on an engine that will be putting out far more power than it was intended for.

Not to sound ungrateful, but I will be using an aftermarket 350 flywheel with the 400 balance plate. Several companies make them in the 153 tooth variety. And FYI, a stock 350 flywheel is thicker/heavier than a stock 305 flywheel.

Thanks for the replies.
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Old 07-05-2002, 09:33 AM   #11
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Your car will be faster with a lighter flywheel; the GMHPP one for instance is the same as the stock 305 L69 one. And you really don't have to worry about the engine's power breaking the flywheel; there are other far weaker things that will protect it.

If what you have is an aftermarket one, then it's not a "350" one as such; it's really just a 12" 153-tooth one for 262/265/267/283/302/305/307/327/350/366/396/427. It could just as easily be called a "305" one or a "267" one or a "396" one.

The "pork chop" weight shifts the flywheel rearward by the thickness of its flange. It's luck of the draw whether it will cause clutch problems; if it does, its symptom will be that the clutch won't engage fully, because the throwout bearing may not be able to move rearward far enough to get out of the way of the diaphragm to stop pressing on it. Your odds of immediate success will improve by having your aftermarket flywheel "unbalanced", just as they would with a stock one.
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Old 07-05-2002, 09:52 AM   #12
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I assumed that the weight was to be bolted to the rearward surface of the flywheel (did not come with instructions). Are you sure that it's supposed to go on the forward surface?

Yes, the aftermarket flywheels are made for "small block chevy", not specific engine sizes. I was trying to make a point that a stock 305 flywheel is thinner/lighter than a stock 350 flywheel.

As for my car being faster with the lighter flywheel, that depends on the application. A lighter flywheel is prefered for road racing, as it allows the engine to rev quicker. However, my car will be used exclusively for (1/4 mile) drag racing. A heavier flywheel will make the car launch better, as it will have more inertia.
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Old 07-05-2002, 10:44 AM   #13
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Most of the ones I've worked with were designed to go between the flywheel and the crank... although, if it's small enough to fit within around the clutch disc and all that, it might work on the rear of the flywheel...

The problem with a heavy flywheel is that as the motor RPM accelerates, more energy is required to spin up a heavy flywheel than a light one. That slows down the rate at which the motor can rev up. If you think about going down the 1320, the motor has to spin from some low RPM (whatever it drops to after launch) and trap RPMs, even though it speeds up and slows down several times, the net RPM change is from launch to traps; any reduction in how fast it revs between those 2 RPMs, adds to your ET. Expect an added tenth for every ten pounds, at least. I haven't heard of any car at all going faster with a heavy flywheel for nearly 20 years now, not even the old 283/sled combos that used to be set up that way. Nowadays everybody lightens them up as much as they can. Lighter driveshafts, lighter wheels, etc. all have a similar effect.
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Old 07-05-2002, 10:44 AM
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