I'm looking at a nice 355 for sale, but I've got this 400 crank sitting in my garage and I wouldn't mind throwing an extra 23 cubes into the motor. I'm just trying to see how much work it would be to do this.

I'm figuring the ideal situation would be just to drop the oil pan, removing mains, removing rod bolts, removing oil pump, and just dropping the crank out and sticking the new one up there with some new bearings (if necessary you tell me) and some various gaskets and bolt everything back up and be on my way.

Can I do it like that?

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1990 GTA
-355 carb'd, Richmond 4.10, Auburn posi, Eibach Pro-kit, Koni adjustables all around, Alston SFC's
-150 nitrous shot
-Leather!
-Stereo details coming soon

 

No. Since the 400 crank has about ¼" more stroke than the 350, the pistons will try to go about 1/8" past the top of the block. I doubt that your engine will produce its full power potential under these circumstances.

However, it would be possible to put a 350 crank back in your 350, without pulling the rods and pistons. People do that all the time, even with the motor still in the chassis.

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"So many Mustangs, so little time..."
ICON Motorsports

 

wait a minute...i don't remember people needing custom pistons for 383's? don't they still use 5.7" rods?

 

well you should try it sometime and post the results.

 

i appreciate you're worthless post...I was actually trying to figure this out since RB's response didn't contain all the information to satisfy my brain.

 

Long rod 383's use pistons with a higher wrist pin. The 400 crank will also have larger journals I believe, which would have to be turned down in any case.

 

These are the different specs:

400: Stroke 3.75", uses 5.565" rods, 2.10" rod bearings, and 2.65" main journals

350: Stroke 3.48", uses 5.70" rods, 2.10" rod bearings, and 2.45" main journals

By just looking at the length of the rods and the crank throw, you can see it won't be as easy as just swapping cranks. If you opt for 5.7" rods, you still need new pistons. Which will be shorter than 3.48"/5.7" pistons. Plus the clearancing of the block. You could use the 400 rods and 350 pistons, but then you'd have to re-balance the assembly. Which means pulling out everything.

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George P. Lara
1984 Z28
SCCA, SCFB, SC3GFB

 

Here's the details:

The SBC deck height is 9.025 nominal. There is usually .035" more or less of deck clearance in a factory motor. So, the sum of ½ the stroke (the "height" of the crank throw, from main journal center to rod journal center), plus the rod length from big end center to wrist pin center, plus the piston height from wrist pin center to the top, must equal about 8.99" (9.025" minus .035").

350 stroke = 3.48"
350 rod length = 5.7"
350 compression height = 1.55"

½(3.48) + 5.7 + 1.55 = 8.99"


400 stroke = 3.75"
400 rod length = 5.565"
400 compression height = 1.55"

½(3.75) + 5.565 + 1.55 = 8.99"


So far everything fits.

Now what you are proposing to do is to take a 400 crank and attach it to a set of 350 rods and pistons.

400 stroke = 3.75"
350 rod length = 5.7"
350 compression height = 1.55"

½(3.75) + 5.7 + 1.55 = 9.125"

((insert buzzer sound here))

The pistons will stick out of the block somewhere between .100 and .125", and will smack directly into the head.

Plus, there is the minor detail of main journal diamter, as George pointed out. A 400 crank's main journals aren't the same size as a 350.

The way to build a junkyard 383 is to take a 400 crank and turn its mains down to 350 size, use 350 pistons, and 400 rods. As you can see by the above equations, the moving part height is identical to the stock height, since the 350 and 400 pistons have the same compression height.

¿Comprendé?

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"So many Mustangs, so little time..."
ICON Motorsports

[This message has been edited by RB83L69 (edited June 20, 2001).]

 

je ne comprends pas...



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60 Ranchero - Project ( Money Hole )
85 Sport Coupe LG4 - Daily Driver 14.82 @ 91.1
Reader's ride -> My Ride

Just another Hot Rod kid, or thats what they all tell me.
Livin' the Stereotype

 

Et pourquois? Etez-vous bête?

------------------
"So many Mustangs, so little time..."
ICON Motorsports

 

Everyone seems to forget the Flywheel and harmonic balacer is different in a 383. You also may have some possible machine work to do to keep the crank from hitting the cam. I would suggest you don't do this unless you have check clearences very well. I have had mine pro-built and balanced.



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1987 Firebird Formula
305 LG-4
GM Vortec heads 2.02x1.6 valves
Crane CompuCam 2030
700-R4 Trans
4 barrel quadrajunk remained by holley (this carb stinks!!!)
edelbrock performer intake
Hypertech Thermomaster Chip
Open Element Air Filter
No Cat with Straight pipe (Dynomax muffler rusted apart and fell off probably could not stand the heat )
Accel H/P Coil

- Soon to be installed
383 stroker (built and ready)
NO MORE COMPUTER CRAP
700R4 Lockup kit
Edelbrock TES
True Dual exhaust or 4 inch single pipe to dual 2 1/4"
Stall convertor

 

Sorry for reading this now, but I appreciate all of the information. Somehow in all of my readings of this board I missed out on this discussion...

Since I have to get new forged dished pistons anyways for a winter buildup can I buy or have them custom make .030 over -22cc dished pistons that will work with a 3.75" stroke with 5.7" rods?

I just always remember people saying how much the 400 rods suck, but are they ok in 350 blocks?

 

Je ne pas bete, Mais je suis stupide beacoupe le temp.

Oui, je comprende.



------------------
60 Ranchero - Project ( Money Hole )
85 Sport Coupe LG4 - Daily Driver 14.82 @ 91.1
Reader's ride -> My Ride

Just another Hot Rod kid, or thats what they all tell me.
Livin' the Stereotype