340 to 372 c.i.

[replicaracer43]

So what's the HP and torque difference going to be if the parts are all the same 372 inch to your run of the mill 360 .030 over 365" . Maybe 5hp and what 10' pounds of touque ? Doesn't seem worth the effort unless you have all the parts, and you can have it all machined and balanced for much cheaper than the going rate!

Agreed.....and I personally would rather have a .020 or .030 over 360 block, than a max bored 340 block at 4.100..... this type engine was built back when there were few piston choices.

 

[Fast340cuda]

I'm running a .020 over 340 block with a 3.58 stroke 4340 forged MP crank. Rods are standard length with .060 over SRP 360 pistons, combo only needed basic machine work and balancing. Love this combo, it dropped almost 2 seconds off of my ET from the x headed 340 that was previously in the car.

 

[EL5DEMON340]

I'm running a .020 over 340 block with a 3.58 stroke 4340 forged MP crank. Rods are standard length with .060 over SRP 360 pistons, combo only needed basic machine work and balancing. Love this combo, it dropped almost 2 seconds off of my ET from the x headed 340 that was previously in the car.

You didn't get two seconds from the crank change LOL

 

[ir3333]

340 to 372 with appropriate pieces could drop 2 seconds

 

[rmchrgr]

340 to 372 with appropriate pieces could drop 2 seconds

I think a bunch of other stuff would have to had been changed as well - converter, gears etc.

Either way, I'll say it again, it's a good combo, at least on paper.

Just to add, a 'stroker' 340 is going to be a different animal than a .060" over 360. Though it's only a small advantage, the 340's smaller main bearings will rev quicker and produce less friction which = free horsepower. It's just a better foundation.

If you think about it, a 340 is more race-inspired. I mean, R blocks are based on 340 architecture, no? During their production run, 360s offered little in the way of performance and were essentially designed for trucks and heavy cars. Of course they can be built to do whatever you want them to do but at the street/strip level we are talking about using production blocks, I believe the 340 is best.

 

[fratzog lover]

Maybe the 340 was tired and out of tune?

 

[Fast340cuda]

You didn't get two seconds from the crank change LOL

Agreed, just sharing my experience between a 340 and 372 CID small block. I also changed to a small solid flat tappet cam and Unported edelbrock heads, everything else stayed the same. These are both 91 octane pump gas motors.

 

[replicaracer43]

I think a bunch of other stuff would have to had been changed as well - converter, gears etc.

Either way, I'll say it again, it's a good combo, at least on paper.

Just to add, a 'stroker' 340 is going to be a different animal than a .060" over 360. Though it's only a small advantage, the 340's smaller main bearings will rev quicker and produce less friction which = free horsepower. It's just a better foundation.

If you think about it, a 340 is more race-inspired. I mean, R blocks are based on 340 architecture, no? During their production run, 360s offered little in the way of performance and were essentially designed for trucks and heavy cars. Of course they can be built to do whatever you want them to do but at the street/strip level we are talking about using production blocks, I believe the 340 is best.

While the 340 DOES have smaller main bearings, the difference in friction between the two is meaningless...the engine deffinatly isn't going to rev faster due to the main bearing size. If you think about it, a 360 has a lighter piston than the 340, and the cast crank is lighter than the forged 340 one. The crank rides on a film of oil, not the bearing surface. a 340 with a 3.58 stroke crank is NO better than a 360.....

 

[sbmmustang]

help me with this math...
3.58 stroke crank (360) turned down to 340 journals
What compression height (pistons) is required for zero deck?
..who have built a 372....pros/cons?

Why not just do a 4in stroke for the same money?
More cubes(416) same price?

 

[Abodybomber]

Brian Earle, you wish...someone , I know( Should have kept, the Dart)...

 

[rmchrgr]

I considered a 372" combo for a while but ultimately decided on a 4" crank/416" combo. For a street machine, it's really a no brainer. Like mentioned already, same money, more cubes, more torque, more everything.

I used a BPE 4" crank with 2.100 rod journals and 6.125" Scat rods, dished Diamond pistons @ zero deck, RHS heads with CNC port by IMM. Compression should be around 10.2-10.3:1. Looking at a 251 @.050" solid FT cam. Should be north of 525hp.

It's a light rotating assembly for sure. I can't recall exactly what it was but the bob weight was under 1,100 grams. The pistons probably weigh like half of what the stock-type 340 slugs weigh.

372" is a good combo but probably more suited to a race-only application.

 

[gliderider06]

I have been toying with this idea as well. from what I have priced, it seems that it is cheaper to build a 3.58 stroked 340, than a 4.00" stroke motor, unless I have been looking in the wrong places. a stock 360 crank can be turned down, use 360 pistons and rods.
what I have seen a 4.00" crank rods and pistons are well into the $1,000 range, where the 3.58" is half the cost. Am I looking into the wrong places for buying parts?

 

[70aarcuda]

416-372=44 cu inch less also...

you can buy a scat 3.58 stroke 340 main crank for the same price as a 4.00 stroke crank...rods are the same price .....you can save a few dollars using kb107 pistons on the 372 vs forged pistons for the 416......

price the cost of cutting the crank....?

 

[rmchrgr]

I have been toying with this idea as well. from what I have priced, it seems that it is cheaper to build a 3.58 stroked 340, than a 4.00" stroke motor, unless I have been looking in the wrong places. a stock 360 crank can be turned down, use 360 pistons and rods.
what I have seen a 4.00" crank rods and pistons are well into the $1,000 range, where the 3.58" is half the cost. Am I looking into the wrong places for buying parts?

The cost is the same dude.

Are you looking at forged pieces or cast? Cast cranks generally are around half of what a forged crank would cost. Just about all the cast cranks I looked at regardless of brand or stroke were under $400 while any forged one was over $700.

Cast/hyper pistons are also ridiculously cheap compared to forged. Just about any brand-name forged piston set will be over $750.

I ultimately decided to build a 416" stroker instead of a 372". Unless you want to run a higher rpm with the shorter stroke, there is is no logical reason not to run a 4" crank, especially if it's for a street machine. I was intrigued by the idea of a "372" but the more I thought about it, the less hp/dollar sense it made. 4" crank strokers can make over 500HP so easily these days, why limit your displacement just to be different?

I went with a forged, 4" stroke crank from Rod Bloomer/BPE. It is an 'import' piece but still a quality part for a decent price. It has 2.100" rod journals to run generic rods with .927" wrist pins.

BPE has several flavors of crank/stokes to choose from including 4.25" stroke. He also has a deal where you can have 'custom' pistons made for your combo which are the same price as a shelf set. Give him a call, he is good to deal with.

 

[dwire67]

I have a 372 cu inch 340 in My Dart, Brian from IMM built it. It is a pump gas motor with W2 heads , it runs outstanding I have gone 11.30 @120 mph in 3100 lb Dart
It has Scat LW 3.58 stroke crank it has 2.124 rod & 2.499 main

 

[Locomotion]

340 to 372 with appropriate pieces could drop 2 seconds

With the "appropriate pieces" you could drop 2 seconds going from 372 cubic inches to 340 as well!

 

[gliderider06]

What made me think of this is that I already have 360 crank/rods. My 340 block only needs .020 to clean it up. it seemed like a cheaper way to go, for me that is.

 

[replicaracer43]

What made me think of this is that I already have 360 crank/rods. My 340 block only needs .020 to clean it up. it seemed like a cheaper way to go, for me that is.

Not sure how its cheaper, you can probally get a 360 bare block cheaper than the cost to make such a big cut on the main journals.

 

[RustyRatRod]

this is always controversial but the square bore / stroke 318/390,408 and 416 make a lot
of torque but do not like to rev quickly.
the 372 - 377 could produce good torque,be quick revving and more efficient.
...oh oh, now i've started it!

I would be willing to bet money that you could not tell the difference in how fast two engines revved side by side with different strokes.

 

[pishta]

Yeah, LA bearing size have jack to do with rotational drag as they are all hydro-wedge liqued bearings that require almost no force to turn when "rolling" on the oil surface. Bigger bearings were probably due to the cast cranks weakness over the forged piece of the 273-340 and the torque the motor was creating (and the stuff it was powering) was possible approaching the now cast cranks design parameters. Smaller bearings just seem like spending $100 on a 1hp gain and losing meat in the crank....but now you can use $$$ Honda bearings for your Mopar!