360 Crank in a 318?

[Road_Runner]

OK, so I have decided if I swap blocks in the Barracuda I'm going with a 340 block & 360 crank for right at 370 cubic inches.  So does the same crank work in an LA 318 block?  It seems that all the advantages of the longer 360 stroke in the 340 block would still be true in a 318 and I could say it still has the original driveline assuming I also stay with the 904 auto trans.  Anybody know if this is doable?  A good idea?  It seems like this could be a cool combo with the 318!

Thanks in advance, Jim

[femtnmax]

The 318 and 340 use smaller crankshaft main bearing diameter than a 360, so my understanding is the 360 crank will NOT fit into the other engines without turning down the 360 crank main bearing diameters.

[Road_Runner]

The 318 and 340 use smaller crankshaft main bearing diameter than a 360, so my understanding is the 360 crank will NOT fit into the other engines without turning down the 360 crank main bearing diameters.

I think you're right, my main question is that this is a known option for the 340 block, just wondering if anyone has any experience with or knows of anyone who's done this with a 318.  Since doing this to a 340 yields an extra 31-32 cubic inches, if it adds 30 to the 318, that would be a 348 which should be capable of 375-400 HP without being too radical for a semi-daily driver with A/C, PB, etc.

Later, Jim

[Chryco Psycho]

the 318 & 340 blocks are the same size , yes it will fit the 318 block , only the bore is smaller on the 318

[Changin Gears]

I always thought this combo would make a good truck motor,  longer arm for a little more towing torque.

[Chryco Psycho]

Yup , + lighter piston so it would rev quicker too

[Road_Runner]

So how about for a 73 Barracuda?  Could this combo with some good heads & dual plane intake 4bbl and either manifolds or headers yield the 375-400 or so HP I'd like to get?  Again, I would only do this combo if I decide to keep the car 'very stock' vs 'mostly stock'. Mostly stock would be a mostly stock appearing 340 and possibly a 4 speed instead of the 904 auto...

Thanks again, Jim

[Chryco Psycho]

where does that put the ci ? around 355 ?
can't remember the bore of the 318 LOL anyway you are just over 1 HP / Ci which is doable with a good selection of parts

[Road_Runner]

where does that put the ci ? around 355 ?
can't remember the bore of the 318 LOL anyway you are just over 1 HP / Ci which is doable with a good selection of parts

Thanks, gives me an option if I keep the original powertrain.

[73restomod]

You can buy a new cast crank 360 stroke with 318/340 mains and rods from MP for 400 bucks. Scat has a forged and a cast version, and I think eagle may make one as well. You can run 2.02 valve head, just notch the bore a little to prevent shrouding. HRM built a 400 horse 318 some time back. The build is still online. My guess is 375-400hp with a 360 stroke would be easy mode, as long as the heads are up to it.

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[Chryco Psycho]

But why spend all that $$ & still have a cast crank ?

[73restomod]

I can see your point, but modern cast crankshafts, they are not your daddy's cast cranks, as the saying goes. Most can easily and reliably handle 400-425 horsepower, the scat version is $377. The Mopar version sells for $410. You can get them forged as well but the price is higher, way higher. If you shop around you can find them for under 350 easy. Scat, eagle, and mopar all rate their cast cranks at 500hp. Ohio crankshaft has a forged version for 615. Piston selection is easy, most early 318s will easily go to a 4 inch bore, and still have meat left for an overbore.

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[PlumCraZRT]

Assuming you get a 4" bore out of it, you're back at a 360.  Is it worth buying a custom crank to get a 360?  With a 360 stoke and the stock 318 bore (3.906"), you're at 343 cid.

If you go that route, I would rather just get a stroker kit with custom pistons and get 390+ cubes. 

[73restomod]

Hensley performance does them as a crate motor, only they add the 4 inch stroke for a total of 402 cubes. You can only overbore the pre 76 years this amount, although some claim to have gone .120 over on leanburn era 318s without issue. Every cylinder must be sonic checked thoroughly, but its do able.  @ .040 over you have a 3.95 bore and the cubes add up to 349. To me a stroker comes down to the heads and intake. Unless your gonna slap some indy heads on it, most aftermarket heads out of the box just drop in efficiency per cube too quickly. Example, a motor makes 1.25 hp per cube at a stock displacement combo, then you stroke the same combo, and it drops to 1 hp per cube. Sure its bigger, but how much did you really gain? If it was a 300 cube motor it would have 375 hp; stroke the same combo to 390 cubes and it only makes 390, because the intake architecture is meant for a 300 ci motor. A great example are the blueprint 408 crate motors, it only makes 375 horse, torque is good, but not where it needs to be for a motor of that size. Its too much for the magnum heads, and realistically its too bottle necked to make much more than a hp per cube. More is better in my book too, until you hit diminishing returns. Another great example of this is the 73 340 versus the 74 360. They used the same camshaft, intake, heads, exhaust, etc.; the 360 for its 20 extra cubes only beat the 340 by 5 hp, and lost 5 ft lbs of torque.  That means the 360 was already 5% less efficient at making power with the same architecture as the 340 it replaced. At that rate if they had gone to 400 cubic inches it would have been 15% less efficient, likely more if you account for diminishing returns.



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[bad440]

The 1974 360 had 245 HP up 5 from the 340 but the torque increased from 295(340) to 320, the difference was quite noticeable, as well as quicker than the 340. I have road tests of the day which indicated the 360 Duster was turning 14.6 in the quarter, 340's in '72-'73 were 15 second cars(all this with 8.4 compression). I know this as I still have my 1974 Challenger Rallye 360.Those 74 360's were impressive for the day, same HP as LT1 Corvette or Z28 but quicker as well as more torque.