SB Dodge Engines Which do you prefer?

[WileERobby]

360. Without question.

 

[monaco66coupe]

I wanted to mention just for fun I was visiting another crazed mopar truck nut friend that has seven 60/s to 70's trucks, and one 5500 Dodge 1969 dump truck, with a lowly 318 engine in it!
He says it pulls it carries a 10k load all day! no sweat!


not very fast though!!!!

 

[MoparLeo]

Go with the 72 360 combo. The 360 was always under appreciated and given a bad wrap that it did not deserve.
Longer stroke than the 273/318/340 means low end torque. Which is what moves your car down the road. Everybody wants a stroker.
HP means much less tan torque. 340 is nice if you like to keep her wound up. Lower rpms means less engine stress. And that is a very good thing.
Externally the oil pan is the main difference between the engines because of the longer stroked crankshaft.
They are rugged engines. Designed for trucks as were the 5.9 Magnum and the Gen III 5.7 Hemi.
Click on the links on my post # 3 for all the things that are common as well as different between all these engines.

 

[4406bbl]

My preferences stem from "what do I want to accomplish?". For starters, regardless of the recipe, I have found that the older LA blocks are far stronger than the later Magnum versions. My trusted machine shop didn't have a torque plate for the LA engines. I asked why, and the reply was that they (older LA engines) are so robust, they couldn't see a difference when one was bored with the torque plate versus one without. HOWEVER, if one were to machine a Magnum block, he/she should not only use a torque plate, but also bolt on motor mounts, alternator bracket, PS bracket, water pump, and anything else that could possibly distort the block... because it will!! My machinist's opinion is that the Magnum blocks are rather flimsy compared to the older LA blocks. This means regardless of the package, I prefer the older LA blocks.

Casting numbers will terminate with a -Xx number. For example: when a new sand cast was created, the dash number was -1. After a block or 5 was cast, one of the cylinders would collapse and they would have to replace that portion of the casting. The dash number then became a -2. I've seen -17 on a block I sent to the recycle yard. So after 10 or so "fixes", statistically none of the original cylinder spacing is preserved in the casting this block was made from; the cylinder wall is much thicker at the 4 O'Clock position than the 10 O'Clock position. This is referred to as 'core shift'.

Moving on to the cylinder heads, I ported dozens and dozens of heads for both foreign and domestic applications, ranging from 1 to 10 cylinders, 2-valve and 4-valve per cylinder. What I can tell you is that flow numbers usually don't tell you how the head will perform in YOUR intended application. I am not the least bit partial to the older LA heads with open chambers. There's too much power left on the table without the squish pad. The only LA head I can like is the late 80's 318 "302" casting with the swirl port combustion chambers (and a squish pad). Up one notch from that is the production Magnum heads. Frankly, I've seen where independent speed shops have flowed 340 X heads and Magnum heads (with smaller valves) and the Magnum heads flow better!

Velocity is king when it comes to getting the most from the air and fuel the engine ingests (BSFC on your dyno report). High velocity helps promote vaporization of the fuel and homogenization of it with the air charge. (There is a Ford Variable Venturi Carburetor patent I absolutely love that references the ability of Mach 1 air velocity -- the speed of sound -- to obliterate fuel droplets in an incoming air stream and convert them to a vaporous element.) Therefore, the ideal port size is one that chokes right about where you want to make the most power. Anything more than that and the port gets 'lazy'. Valve lift should support port flow. In other words, if you have a head flowed on a bench, maximum flow numbers should occur at or slightly below where your cam opens the valve. Aftermarket camshafts make more power because the factory cam maxed out flow past the valves before the port itself maxed out; low flow AND low velocity.

Next is bore to stroke ratios. It is commonly accepted that longer stroke engines make better torque at lower RPM, while shorter strokes are able to scale higher RPMs. Shorter stroke equates to slower maximum piston speed at any RPM. This is great if you're targeting 7500 RPM. However, the laws of fulcrum arm physics dictate that a longer stroke can impart more force on a crankshaft than a shorter throw (stroke) crank. However, this increases max piston speed at 90 degrees ATDC.

If I were building an engine for the 1/4 mile (or other high RPM racing application), I'd probably use a 340 with a relatively short stroke (3.31") and large bore (4.040"). This affords higher RPM, which is good for high-end HP.

If I wanted decent throttle response and great fuel economy in a street vehicle, I'd probably go for a 360 (3.58" stroke and 4.00" bore) or even a 225 (4.125" stroke and 3.40" bore) due to the longer stroke.

Add to the consideration the stroker packages like the 408. The longer stroke makes for delightful throttle response on the street. At lower engine speeds, piston velocities are reasonable. Yet, consider Chrysler created custom engine packages for sanctioned racing where they opted to de-stroke a popular engine to meet maximum displacement rules versus using a block with a smaller bore and then designing a longer stroke. Examples include the 305 AAR package (de-stroked 340), and the 80's era 2.0 liter de-stroked 2.2.

Modern aftermarket heads usually have excellent port biasing combined with combustion chambers that promote in-cylinder activity. Usually they also utilize the thermal conductivity properties of aluminum, which provides for higher compression ration and/or more boost. These heads almost always target high-RPM applications with "generous" ports and large valves. For certain applications I would favor the "302" casting 318 heads just to capitalize on the smaller ports & valves, combined with the swirl port combustion chambers.

What are you wanting to build??

I would question that machine shop a little...la blocks distort a bunch with a torque plate. The 2 magnum blocks I had sonic tested were thicker and more consistent than the early block I had, all cylinder walls over .200 except one minor thrust was .190. I don't know where they came up with bolting motor mounts and alternator on, that's a ford small block issue. There are quite a few turbo 360 magnums over 700 hp and they are not losing blocks.

 

[66 Sat]

One thing that's always bugged me about the 360 is the external balance.
Why is it externally balanced and not internally like the 318/340? Was it a cost issue or some mechanical reason?
I read up on external v internal and it said internal is much better for engine longevity if making big power.
It just annoys the perfectionist in me.

 

[4406bbl]

Longer stroke and cast crank made the external balance necessary. Cost saving was a big issue too.

 

[Sparky Anderson]

I have had them all, none are bad, but flat out power, you can't touch a 340 motor with a aftermarket cam, high stall converter and 3.91 or higher gears. I have seen many cuda's with big block get beat by a cuda running a 340 in the quarter mile. Go with a 360, cheaper to build.