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351M to 400 conversion

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    Posted: 22-November-2020 at 7:16AM
I'm converting my 351M to a 400 and wanted to verify a few things based on some of the research I've done.
  1. I took a crank from a 400 truck motor.
  2. I am getting the TMeyer 400 pistons to bump compression, using my existing rods.
  3. I read I need to use a balancer and flexplate for a 400 and not 351M because the crank counterbalancing is different? Or is this BS because a 28 oz imbalance is a 28 oz imbalance?
  4. Are the main crank bearing diameters the same for 400 vs 351 crank?
  5. I'm going to use a C6 instead of C4 the car (78 LTDII) originally had. Does the C6 swap out in place of the C4 in terms of fitment to the car?
  6. Does the C6 use the same flexplate as C4?

My block had already been bored 030 at some point, so I'm taking another 010 off to clean up the cylinder walls.

Anything else I'm forgetting?
78 LTD II sports touring package (blue), father original owner
67 Mustang (5.0)
69 Mach 1 428 SCJ Drag Pack
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 72 RS 351 Quote  Post ReplyReply Direct Link To This Post Posted: 22-November-2020 at 7:36AM
You can use any good 28oz balancer and flexplate if the tooth count for the starter matches your trans. The C6 is fine if it's the big block C6.

Everything is the same from the 351M to 400, except the height/length of the pistons, rods, and crank throw. I'm not sure you can use the 351M rods, it's been ages since I saw the rod and piston specs. One of them will work and are similar in strength.

edit' I see the converter four mounting stud pattern can be different from the C4 to C6, I forgot about that too.


Edited by 72 RS 351 - 22-November-2020 at 3:37PM
Don
73 Ranchero "Sport 72 front end", floor shift/console, planning EFI 7000+ rpm 351-4V &4R70W
73 Ranchero GT 351C-4V &4R70W for sale later.
92 Lincoln Mark VII SE GTC, OBDII 347/4R70W
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Lizer Quote  Post ReplyReply Direct Link To This Post Posted: 22-November-2020 at 8:17AM
I'm pretty certain they used the same rods for both 351 and 400. The 400 pistons are shorter. To be safe, I saved the pistons and rods from the 400 I tore down to reuse those rods.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote 72 RS 351 Quote  Post ReplyReply Direct Link To This Post Posted: 22-November-2020 at 9:55AM
Very good, OEM Ford pistons were known for being very long. Those are typically 1.6 inches and longer.

Aftermarket pistons in stroker kits, and modern combinations of rod/pistons are often much shorter, 1.2-1.4" for example. So I'm sure the "shorter" 400 pistons are very reliable in any typical combination. I hope those you chose are a somewhat light weight design.

Some power is in the weight of the assembly, strokers have nice light weight pistons. The Cleveland stroker kit I'd like to consider I have no idea of the details, weights and dimensions. I glanced at the description on eBay, saw the $1500 tag, and just saved it to watch for later.

Your 400 will be great for normal rpm use, and make plenty of torque all the time.
Don
73 Ranchero "Sport 72 front end", floor shift/console, planning EFI 7000+ rpm 351-4V &4R70W
73 Ranchero GT 351C-4V &4R70W for sale later.
92 Lincoln Mark VII SE GTC, OBDII 347/4R70W
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Lizer Quote  Post ReplyReply Direct Link To This Post Posted: 22-November-2020 at 10:01AM
well, what I’m saying is the 400 piston is a shorter piston than the 351 piston, which is how they maintain the same rod length for both. 

The Track Boss pistons Tim Meyer makes bump the compression to 9.2 and essentially zero deck the piston clearance. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Big Bird Quote  Post ReplyReply Direct Link To This Post Posted: 22-November-2020 at 10:55AM
Remove the original valves and throw them away.
Far, far away.
Get one piece valves.
C6 is longer, so you need a shorter driveshaft, Kickdown is different too.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rockatansky Quote  Post ReplyReply Direct Link To This Post Posted: 22-November-2020 at 12:07PM
28oz/in is 28oz/in, the balancers are essentially the same. original 400's came with a heavier mass ring but when those ran out the lighter 35M balancer superceded the other. watch your converter stud pattern, the C6 uses an 11.4"-11.5" circle and most C4's use a 10.5" circle. offset distance from the back of the block needs to be checked also

things the flexplate needs to do right;
overall diameter / tooth count
imbalance weight value
converter stud pattern diameter
offset (needs to match the starter throw / you may need a different starter for the C6)

the trans slip yokes are different also, you'll need a 31 spline yoke as well as a cut & balance job

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Lizer Quote  Post ReplyReply Direct Link To This Post Posted: 23-November-2020 at 6:28AM
Originally posted by Rockatansky Rockatansky wrote:

28oz/in is 28oz/in, the balancers are essentially the same. original 400's came with a heavier mass ring but when those ran out the lighter 35M balancer superceded the other. watch your converter stud pattern, the C6 uses an 11.4"-11.5" circle and most C4's use a 10.5" circle. offset distance from the back of the block needs to be checked also

things the flexplate needs to do right;
overall diameter / tooth count
imbalance weight value
converter stud pattern diameter
offset (needs to match the starter throw / you may need a different starter for the C6)

the trans slip yokes are different also, you'll need a 31 spline yoke as well as a cut & balance job


I'll be replacing the TC so that wouldn't be a big deal, but what is the offset distance and how is that checked?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rockatansky Quote  Post ReplyReply Direct Link To This Post Posted: 23-November-2020 at 11:51AM
this youtube talks about flex offset, he calls it 'depth' at one point. another corresponding offset you might want to explore is how far the crankshaft mounting flange sits away from the back of the block. IIRC not all Ford engines are the same in this regard either and may coincide with the different offsets designed into the flexplates. bottom line at the end of the day, when you mate the engine to the transmission, you need to be able to pull the TC out of the trans pump about 1/4". if there is no 'pull-out' then you're compressing the TC between the flex and the pump, the pump will not survive.

Never Use The Bell Bolts To Pull The Engine And Transmission Together! NEVER!



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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rockatansky Quote  Post ReplyReply Direct Link To This Post Posted: 23-November-2020 at 11:57AM
this article shows the 'pull-out' distance where the studs are not sticking through the flex all the way when the TC is all the way into the pump

https://www.hotrod.com/articles/pit-stop-wrong-flexplate-causes-main-thrust-bearing-failure-302-ford/
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 72 RS 351 Quote  Post ReplyReply Direct Link To This Post Posted: 23-November-2020 at 12:08PM
Ditto. In many examples over recent years, people have discovered their engine failing due to the crank being pushed constantly forward, destroying the thrust bearing, and then the material wipes out all the bearings.

When the engine and trans are bolted together(initial finger tight point), the torque converter should be checked again for a final time. Be sure it slides easily forward and back, the studs should protrude fully and almost go in behind the flexplate. That tells you that the converter is installed fully. If it isn't, the studs may be forced against the flexplate etc, some times people don't check that. The force will ruin the crank quickly, and possibly the trans pump. But the crank is the biggest deal, you don't want to rebuild a new engine, that you just put in.
Don
73 Ranchero "Sport 72 front end", floor shift/console, planning EFI 7000+ rpm 351-4V &4R70W
73 Ranchero GT 351C-4V &4R70W for sale later.
92 Lincoln Mark VII SE GTC, OBDII 347/4R70W
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