Technical cast steel crank vs. 4340 moly, Eagle

Budget 36, I'm not sure you realize what breaks cranks. TORQUE breaks parts. Let me tell you what happened to me twice. I know your situation is a little different, but hear me out.

My tow rig is a medium duty C-60 chassis and GVW was 23,000#. When I got it, it had a brand new MD350 Target Master, as shipped with 4-bolt block, a forged crank, cast dished pistons, factory cam, small port heads with small sodium valves, (7:9 CR). I changed to a factory 4 bbl manifold and small Holley 450 cfm, MSD, headers, etc...

This worked pretty good for a long time (70,000 miles) until it broke the snout off the crank right at the bottom of the damper bolt hole. The torque peak was 2800 rpm and that is where I ran it all day long. That one left me in NW Washington State.

Then I built a 383. I bought a $700 forged crank from S_____, my favorite mail order store. That motor had KB flat top Hyper pistons (10:1), bigger SS valves, pocket ported heads, headers, B&M 144 (@ 2# boost), 250-262 XE cam. It ran like a champ, got a best of 7.8 mpg and lasted for 11 years and 110,000 miles, and snapped the crank snout off right at the bottom of the bolt hole. The torque peak again, 2800-3000. That one left me just west of Louisville, KY.

That is the exact reason why marine motors and MD motors come with a forged crank. They both run at or near the torque peak all day long and that causes the max torsional twist in the crank, which eventually fatigues the parts and leaves you in the middle of nowhere.

I should have RPMed the motor a little more and changed the gear to match and saved some parts, but it would cut the mileage quite a bit. RPM doesn't hurt parts as bad as torque, until you exceed the integrity of the parts, which is usually way up the RPM scale.

However, there is a salvation to this dilemma. Drill and tap the bolt hole all the way through the first counter weight and pull it down with a grade 8 or automotive head bolt of the correct length to hold it all together. Then you will find the next weakest link some where else in the forging.

Cast crank... I don't think I would do that unless you don't have the extra 300-400 bucks. Then again, it might work for as long as you need it. Good luck!

So, I put a 427 tall deck in it... GVW is 28,000# and it now gets about 5.5 - 6 mpg on a good day.

If I had to do it all over again, I would have put a Cummins in it!

 

I completely agree on the Cummins part. But I was going to mention that Chevy’s all time workhorse Engine has a steel forged crank. This would be the tough as nails tall deck 366. I’ve seen these 366’s do things they never should have. They don’t make diesel power or diesel economy, but they take a shit ton of abuse. I’ve often wondered about a 366 in a C-30. I suspect they would take a lot more abuse than a 454 from a one ton truck.

 

The 366 was in larger trucks around here, but where the heck would one turn up at?

Didn't they have an extra ring on the piston?

No matter. Compare freshening up a BBC vs SBC before you even consider taking it to a machine shop.

 

I think you have to find a C40 or larger to get high nickel block , forged crank , HD rod bolts and 4 bolt mains all in one package in a truck for sure . C and P 30 had 4 bolt main and all I ever touched had a cast crank , and standard rod bolts . Maybe I never found a good one , I guess .

 

366 was only offered in C-50 and larger trucks. I’ve heard of C-40’s but never seen one or worked on one. 366 did have an extra ring, double roller timing chains, four bolt blocks and forged steel cranks. These engines were built to take anything you could throw at them. They were designed before diesels were common.


Sent from my iPhone using The H.A.M.B. mobile app

 

Yes, 366T and 427T were both MD truck motors, C-50 and up. Both have a .400" taller deck height and 4 ring pistons. Everything was much more durable.

I have run a 366T in a C-60 tandem axle straight truck (30,000# GVW), but they are gutless wonders compared to the 427T. 366's were in a lot of school buses and are dirt cheep, because they are not as much power and only get 4-5 mpg.

427T is another story. They make a very good stroker motor with much room in the crankcase for a long throw. Both 366T and 427T have a 3.760" stroke and are not torque motors. Like a 327 SBC they need to spin up to make power. That's why they are not fuel efficient.

I was going to put a 4 1/2 " stroker and 454 3 ring pistons in mine with +.400" rods, but It was another 2500 bucks. Some times I wish I'd have done it just to see the difference in power and mileage. Maybe a turbo would be good on one instead. Haven't tried that yet.

Another plus is both 366T and 427T are internally balanced and use a zero balance flywheel as most SBC, making an engine swap much easier than a 454.

Here is a neat page of info on both, enjoy... https://www.tradecraftspecialties.com/bbckb#Topic11

 

My buddy had a 73-74 chevy 1/2 ton with the cast-crank 350, Q-jet. One day the crank broke at the front fillet of #1 main bearing. I suspect the truck may have been in a front end collision before he bought it. Still ran but clanked and tossed fan belts.

 

It will work just fine. These are good kits.

https://www.enginekits.com/350-to-383-stroker-kit.html

 

We’re building a 500 caddy.
300/500 @ 2500/2700 rpm
In stock form.

 

I have replaced 3 BBC with 472s or 500 caddy every customer was pleased.

 

I’m hoping I feel the same.
The 500 is going in my short bus with plans of converting into a motorhome.
Really don’t see an advantage $ wise to go diesel for this.
Bought 2 472s for future builds.

Any cam recommendations for a tow rig or keep it stock?

 

I did think about that one time, but I don't know anything about Caddies.

 

Not much different than any other
The caddy received the best material gm offered. The engineers designed a high torque low rpm engine to pull the heavy caddys around.
They usually wear very little. My 500 was well in spec. We polished and rehoned.
They do not like high rpms. But make great pullers. I helped a friend of mine swap out a 350 for a 472 years ago. Went from10 mpg to 15 mpg and pulled much better

 

I met a guy at a swap meet one time that had an old square Winnebago motor home for a hauler. He pulled the 318 out and put in a 472 Cad and went from 7 mpg up to 15 mpg! I thought he was exaggerating a little, but his partner vouched for him.

 

Hope the same happens with my bus.
Caddys are supposed to be fuel efficient for a large engine. The key is the low rpm torque

 

The guys said they pulled a load better and were 3 to 4 better on milage than the 454s

 

That’s what I have heard. I was shopping for a 454 when I found the 500. I like the low rpm torque range of the caddy better than the bbc

 

Do Caddies have a cast crank?

 

Yep. To be correct, its nodular iron. The performance site claims a stock crank can handle 1200hp. The journals are huge. https://www.google.com/amp/s/www.hotrod.com/articles/hrdp-0804-541-big-block-cadillac-v8/amp/

 

Wow! That's impressive!

 

That is good info for the memory bank . 500 cubes is tuff to beat no matter what valve cover it wears .