318 4" bore 3.58" stroke(360)

-
CordobaDart

CordobaDart

318 SLANTMAN
Joined
Nov 26, 2011
Messages
226
Reaction score
30
Location
Wabasso, Minnesota
I was not planning on building this engine but am commited now. While visiting a cousin who has a few Mopars himself, he gave me a crank and pistons that was not going to get used anymore. A 3.58 eagle cast crank that was used in a 340 in good shape. Then I got ideas in my head...

A 70 318 has been lurking around my storage of parts for 8 years had pitting and wear in the bores. I would like to do a fun street build. I have a few 360's laying around in the garage that are good low mileage ones, but figured, why not use this otherwise not going to be used 318 and free 3.58" crank? The casting of this crank does show imperfections(bubbles in the counterweights) but was run successfully before someone yanked it for a 4" stroke crank.

Got the block zero decked/bored to a set of kb107 standard bore pistons. I am thinking of doing a partial fill of hard block just up to the top of the frost plugs but am on the fence with that. I will update this as I slowely work on it and collect parts. The goal is to have the rotating assembly in by the end of summer. Heads/cam will come later (probably over winter). I was going to run the factory 318 full float rods but they need to be resized and the crank was balanced to lighter scat rods and some 4.070 kb107's when it was in a 340, so I do not want to pay for mallory metal, so I will get different rods. I know it is a gamble of a build, just thought I would share, maybe in the future I can use this as a what NOT to do thread. Haha
IMG_20160522_094248.jpg
IMG_20160616_234025.jpg
IMG_20160616_234051.jpg
 
a lot of us guys don't like to hear this but that combination has been the Corvette main base engine for a long time.
3.90 bore / 3.66 stroke....there is a reason GM engineers settled on this this platform.
...Should be a terrific combination for an A body with near perfect hp / torque balance
and be very fast.
 
Hensley Motorsports has been hoggin out 318s to 4 plus inches for thirty years. They don't hard block anything.
 
RustyRatRod said:
Hensley Motorsports has been hoggin out 318s to 4 plus inches for thirty years. They don't hard block anything.
Click to expand...

Thats right, and so have i, half that long though.
No need to block fill unless you plan on turning rpm's higher than that crank will handle to begin with.
Where are all those nay sayers now? ;)
 
That's what I did too. I bought a 340 block and had a 360 crankshaft that came out of my brother in laws van.
Have fun and it should run really strong!
 
don't thing you could push a 318 bore to 4.07 without it being a hot running motor , how thick are the cylinder walls ? did you do a sonic test on the cylinders walls ? if it can go that , i'm thinking on some 340+.04 pistons in stock , a 318 block lower end in stock . same crank stroke , same length rod , same pin size . todays gas would be shaving the tops on the pistons . well whats anybody think ?
 
pomonamissel said:
don't thing you could push a 318 bore to 4.07 without it being a hot running motor , how thick are the cylinder
walls ? did you do a sonic test on the cylinders walls ? if it can go that , i'm thinking on some 340+.04 pistons in stock , a 318 block lower end in stock . same crank stroke , same length rod , same pin size . todays gas would be shaving the tops on the pistons . well whats anybody think ?
Click to expand...

This block got bored .090" over to 4.00". The 340 that the 3.58" crank was in had a .030" overbore so it had 4.070" pistons. I believe it was 372 cubic inches. Where this build will be 360. But with a far lighter rotating assembly than a stock 360.
 
thanks for the clearing that up , did you have to do some work on the pistons to clear the counter weights of the crank ? and what c/r are you running , did you have to cut the tops of the pistons ?
 
ir3333 said:
a lot of us guys don't like to hear this but that combination has been the Corvette main base engine for a long time.
3.90 bore / 3.66 stroke....
Click to expand...
It's not the same combination.
4.00 - 3.90 = .100 difference
3.66 - 3.58 = .08 difference
While not a lot of difference in your hand, it is a lot, a real lot in car terms and machining.
You like to post this. Perhaps a Chevy is more your speed? LMAO
 
rumblefish360 said:
It's not the same combination.
4.00 - 3.90 = .100 difference
3.66 - 3.58 = .08 difference
While not a lot of difference in your hand, it is a lot, a real lot in car terms and machining.
You like to post this. Perhaps a Chevy is more your speed? LMAO
Click to expand...

i do like some chevy's but prefer Mopar.
The only Chev i like well enough to buy would be a '55 2 dr post.
 
FWIW, don't forget that you'll have only the 2.5"-diameter main journals in that 318 block, rather than the 2.81" journals that the 360 had.

Maybe the 2.5" crank journals will be fine, though. When the Chrysler engineers designed the 360, they intended it to be a real fire-breather with free-flowing heads that would kick the Chevy 350's butt, and that's why they increased the main bearing diameter. However, then the smog laws kicked in, so the 360 engine could never be developed to generate the amount of power that the Mopar engineers had originally intended.
 
pomonamissel said:
thanks for the clearing that up , did you have to do some work on the pistons to clear the counter weights of the crank ? and what c/r are you running , did you have to cut the tops of the pistons ?
Click to expand...

I have not gotten that far yet! Ha, but I want to shoot for 9.5-1 to 10-1 compression. Being that the bore is 4.00" now, it has 360 pistons(kb107's) to work with the 360 stroke, so no piston shaving. Once I figure what heads I will run and find my compression out, then I will cam it to make it run on pump gas. The KB 107's are are a pretty tall piston, the machinist told me that by the time he got close to zero deck, the taper in the deck was finally gone. So now it is straight, not sure what my deck height is specifically though. It was last minute that I had my friend take it with him when he brought his 360 block in to get it ready to go 408 stroker.
 
Last edited:
Bill Crowell said:
FWIW, don't forget that you'll have only the 2.5"-diameter main journals in that 318 block, rather than the 2.81" journals that the 360 had.

Maybe the 2.5" crank journals will be fine, though. When the Chrysler engineers designed the 360, they intended it to be a real fire-breather with free-flowing heads that would kick the Chevy 350's butt, and that's why they increased the main bearing diameter. However, then the smog laws kicked in, so the 360 engine could never be developed to generate the amount of power that the Mopar engineers had originally intended.
Click to expand...
Yes I hope that this cast steel crank I got holds up, I hear the Eagle cast 4.0" cranks don't hold up so well. But of course the price was right.
 
Post bore the machinist did check a cylinder or two with the sonic checker for fun, even though I did not ask for it, he found .145 to .1" wall thickness, so yes this build is a gamble, but hey, you only live to build wierd things once. The machinist is a mopar guy and has a Super Stock 65 valiant with a 273 rocking a slight offset ground aftermarket forged crank, custom pistons, and extremely worked over 302 heads backed by a 4 speed, picture on the office wall shows it doing a decent wheelie, awesome, I believe he runs in the 10's in the quarter and heard he spins it well past 8k rpm :) He was the only guy in my area with a sbm torque plate, so I was happy to pay more to go to him.
 
RustyRatRod said:
Hensley Motorsports has been hoggin out 318s to 4 plus inches for thirty years. They don't hard block anything.
Click to expand...

Wow! I hope mine holds up to street use with an occasional pass at the 1/8th mile track down the road, never raced before though, so time will tell. This block is a "4 ear" engine mount block if that means anything. Probably not.
 
MOPAROFFICIAL said:
Thats right, and so have i, half that long though.
No need to block fill unless you plan on turning rpm's higher than that crank will handle to begin with.
Where are all those nay sayers now? ;)
Click to expand...

I don't want to push this one much past 6K. Time will tell though. The msd box in my Dart has a 6400rpm Rev pill in it now and I have accidently bounced off that with my current 318. Oops.
 
I probably never would have done this build but have been feeling brave since my dad survived an open heart surgery for a massive aortic dissection on May 1st. He was 5 blocks away from the Sanford Heart hospital doing a charity concert at a church in Soux Falls when he started having heart attack symptoms. No ambulance ride, they took him straight there, Doctor had not seen one as bad as his. If he had been home, he likely would have had a 20 minute ambulance ride to the local hospital only to be airlifted to the nearest heart place, likely would not have made it. He seems on his way to a full recovery, helped him recharge the A/C on his 91 dodge truck yesterday, so I am not taking one day for granted. Having a great father's day with him:)
 
File fit my rings on Sunday, .026" top ring, .022" second. am torn between scat and eagle rods though. This engine will be used on the street, but I would like to spin it to 6500 rpm on the back roads on occasion.
 
Bill Crowell said:
FWIW, don't forget that you'll have only the 2.5"-diameter main journals in that 318 block, rather than the 2.81" journals that the 360 had.

Maybe the 2.5" crank journals will be fine, though. When the Chrysler engineers designed the 360, they intended it to be a real fire-breather with free-flowing heads that would kick the Chevy 350's butt, and that's why they increased the main bearing diameter. However, then the smog laws kicked in, so the 360 engine could never be developed to generate the amount of power that the Mopar engineers had originally intended.
Click to expand...


This is not correct.

Chrysler used bigger Maine because they KNEW they were going cheap and going to use a CAST CRANK. They wanted to increase overlap.

It's not a speed secret. It's stupid really. The aftermarket has been using smaller bearing diameters for years to keep bearing speed down.
 
"Chrysler used bigger Maine because they KNEW they were going cheap and going to use a CAST CRANK. They wanted to increase overlap."

Interesting point, Yellow. But could you explain what you mean by "overlap" in connection with a crankshaft? I am not following you there. Thanks.
 
Bill Crowell said:
FWIW, don't forget that you'll have only the 2.5"-diameter main journals in that 318 block, rather than the 2.81" journals that the 360 had.

Maybe the 2.5" crank journals will be fine, though. When the Chrysler engineers designed the 360, they intended it to be a real fire-breather with free-flowing heads that would kick the Chevy 350's butt, and that's why they increased the main bearing diameter. However, then the smog laws kicked in, so the 360 engine could never be developed to generate the amount of power that the Mopar engineers had originally intended.
Click to expand...

...or they could've increased the bearing diameter for longevity especially in truck applications where heavy loads are ever present...but even that's a stretch. Only Dodge knows how many full size pickups ran for 200K miles any beyond with the modest little 318 and never exhibited any issues even with the smaller journal size.

Beyond that, the standard journal size will not affect the longevity unless he starts spinning it too high for the oiling system to keep up, or higher than the crank can live. In short, the block itself is puh-lenty strong.
 
Bill Crowell said:
"Chrysler used bigger Maine because they KNEW they were going cheap and going to use a CAST CRANK. They wanted to increase overlap."

Interesting point, Yellow. But could you explain what you mean by "overlap" in connection with a crankshaft? I am not following you there. Thanks.
Click to expand...
I've never heard that.... I think ....
Crank over lap?
 
Picture the crank from the side. The bigger mains overlap into the rod throw section's throws,
increasing strength in that area. Pontiac also did this in their 421-428-455 engines when the 421
wouldn't last a Nascar race with smaller mains. Hope this makes sense.
 
You must log in or register to reply here.
-

Back
Top