Engine builders

[pontiacvince]

Question for the engine builders.
Would you rather have a 3.75 stroke, short rod engine with heavy pistons and 5/64 rings vs. a 3.48 stroke, 6.00" rod with shorter piston and thin ring pack???
About 25 c.i. difference.

[Dashman]

Performance wise, the larger displacement results in more horsepower. The longer stroke results in more torque. However, I believe that there is longevity with a 6" rod. It would be great if the small block deck height was at least 0.25" taller, and one could have the best of both worlds.

I blueprinted a 6.0" rod, 355, that went about 125,000 miles in my '81 K20. It was still strong before it slipped out of 3rd, over revved, and broke off a dime size piece of short piston. I'd rather do a 5.85" rod with a better piston height and ring grouping.

[HO455]

Originally Posted by pontiacvince

Question for the engine builders.
Would you rather have a 3.75 stroke, short rod engine with heavy pistons and 5/64 rings vs. a 3.48 stroke, 6.00" rod with shorter piston and thin ring pack???
About 25 c.i. difference.

I'd go with the 3.75 stroke with the longest rod and short piston height. And of course, the thin ring pack.

It all depends on the application. Most folks would never notice the thin rings and they might notice the piston weight differences only if they drove the two engines back to back in a lightweight race car.

In the average truck usage the longer stroke and higher CID should have a better torque band which is what you want. The piston weight and ring pack might help fuel mileage in a perfect world.

[72SB]

383, 6" rod, short piston, all forged...running strong for 50k mi now

[pontiacvince]

Thanks guys. I've been doing some research on the whole "long rod vs. short rod" discussion and from what I gather, the long rods (higher rod/stroke ratio) are better at mid - high RPM and the short rods are better for torque/low RPM. Plus the added stroke/cubic inch addition of the 3.75 crank will be my choice over the 3.48/long rod.

[oneshotkyle]

Motortrend/engine masters did a BBC long rod vs short rod dyno comparison on a episode. It pretty much did barely anything as far as power.

[PbFut]

I think you will feel and like the torque of the shorter rod longer stroked engine. Shorter rods increase side load of the piston on the cylinder but it is trivial as it relates to longevity of the motor for most enthusiasts. We keep our oil fresh. Cubes and stroke is what you want in a truck.

[MikeB]

Originally Posted by oneshotkyle

Motortrend/engine masters did a BBC long rod vs short rod dyno comparison on a episode. It pretty much did barely anything as far as power.

Exactly. Any measurable difference would probably be within the margin of error between the two dyno runs. Now, if you're building a 16,000 RPM F1 engine, that's another story!

And the only reason to build a 355 instead of a 383 would be budget considerations, like when you already have a good 350 crankshaft, damper, flexplate/flywheel, etc.

My preference would be a 383 using 5.7" rods. Something I don't like about 6" rods is the oil ring pack running through the piston pin bore. Maybe that's not an issue, but it just goes against the grain (and my brain).

When I worked part time for an engine shop, most of the 383s we built used 5.7" rods, some making well north of 450hp on a dyno.

If you do go with a 383, be sure to read all you can find about relieving the block to clear the rods. Also, make sure to use the proper rods like these to clear cam lobes.

https://www.scatcrankshafts.com/prod...rods-arp-7-16/

And I'd recommend buying a balanced assembly from SCAT or Eagle.

[oneshotkyle]

No replacement for displacement