H vs I-beam rods

[JGC403]

So the plan is to build a 400 based 470 stroker for my '68 Barracuda. I want to start collecting parts for the project. Car will be mostly a street car, but It will see some track time.

Light rotating assembly is the plan.

For connecting rods, what would be better for my build? I used H-beam rods in my 408 and they are heavy compared to factory I-beams. They say H-beams resist twisting better, I personally have never seen a twisted connecting rod either. The factory used I-beam rods and they lived.

With a 400 block and a 3.915" crank the piston will be a lot lighter than a factory piston. So with less mass to control an I-beam should work. Is what I'm thinking.

Is it worth going to a chevy rod journal size and piston pin? Wanted to keep the 440 length rods, but if I can't find a stroker crankshaft with Mopar sized rod journal I will have to get shorter chevy rods.

Just started looking and there isn't as many I-beam connecting rod options as there are in H-beam. and the I-beams that are out there aren't cheap, even the chevy ones.

I had seen an article on some engine build, and found out about inboard piston pins thought those would be cool.

 

[goldduster318]

That seems like a strange comment that the H-beams were heavier in your small block as compared to the stock rods. I did my 340 and went from the stock 340 rods which were 760g or so to K1 H-beams at 656g.

Sure, i-beam rods can work out great for you, it just depends on what power you're making. My experience with the K1 h-beam rods was quite good. They needed no additional work. Bigtime overkill, but I didn't want to take any chances.

 

[moper]

A high quality I beam is lighter and stronger than any H beam. Offset pins don't mean much - especially given the taller piston you're using. As far as the rod length, for me it depends on the head choice. I like a longer rod with a smaller port head with the goal being a bigger torque number at a lower rpm point. If the heads are sized bigger, I like a shorter rod because the engine will "get up" into the heads faster and will make more horsepower.

 

[JGC403]

That seems like a strange comment that the H-beams were heavier in your small block as compared to the stock rods. I did my 340 and went from the stock 340 rods which were 760g or so to K1 H-beams at 656g.

Your right, guess I should of looked at my notes from the 408. Mine was a Magnum 360, so the Magnum rods were around 744g. But still aftermarket I-beams should be lighter than aftermarket H-beams.

 

[Bigdummy]

I'm building a 470 with H beams and ross pistons ,mild solid roller ,and Trick flow heads.im using Short rods for street would use long for strip.I plan on shooting 150 shot on it .H Beams are cheaper than strong I beams.I bought my rods and Pistons off Flatlander racing.Bought MRL heavy duty lifters for a longer life span

 

[moper]

There are also some variences in the H beam weights so look around not only for pin size but weights. The rod weight is much less important than the piston and crankshaft (individually) weights. IMO, chevy pin size is just a win/win/win in terms of price, availability, and performance.

 

[AndyF]

SCAT 6.700 long I beam rods are $367 at Summit and they'll work just fine for a 470 low deck engine. Use a 3.91 crank with 2.20 pins, the SCAT I beam rods and a shelf piston from Diamond (or JE, SRP, Mahle, etc.) and you'll have a nice combo. If you go with the new Trick Flow heads you should be able to make roughly 600 hp without too much work and it should last a long time.

 

[Ottmundr]

Here is an interesting article in response to your question.

http://www.enginebuildermag.com/2008/09/connecting-rods-so-many-choices/

That being said, I wouldn't take just ONE source as the end-all, be-all of truth in engine building, and certainly not in engineering. I would look for other sources that can confirm or refute the conclusions in the article.

If other reputable sources also state that it's a good idea to use specific cross section connecting rod for YOUR application, then go for it.

What I got from this article was H-beam for low RPM/torquey engines, and I beam for high RPM/horsepowery engines.

Keep in mind that the part quality can make a difference, so an optimum design of inferior metallurgy or quality control can screw you.

 

[AndyF]

The 6.700 long rod works really well with a 470 since it gives you a bunch of 1.320 CH pistons to pick from. Diamond, SRP, Ross and ICON all have pistons on the shelf for that combo. Or you can go with the slightly shorter 6.535 rod and use a Mahle or Autotec piston. In either case you want the BB Chevy pin on the crank which means you'll need a Molnar or SCAT crank.