Dad wants to build a 360 stroked to 408. Will be an all out race motor, but on the milder side. 11.5:1, won't be spun past 6500 and will have around a 600 lift solid cam. At what point do you guys start using an H beam rod over I beam? At a certain rpm, higher compression?

Just my opinion:
oem/aftermarket I beam.....ok for mild performance build.
h-beam.....great high performance rod, would guess its in 90% of all 9-10 second bracket race style engines.
Billet (steel/aluminum/titanium)I beam...best in my opinion for builds beyond that 9-10 second range.

When I think of a race 11.5 to 1, 408 build, me thinks of a 4340 crank and h-beams.

no science , all gut here.

Lots of different opinions on this one. Either I beam or H in 4340 would be good for build you mention. Just be sure they are from China. The main thing with 4340 steel is in the heat treat. Very critical for max strength. Myself I prefer the I beam. Just my theory that the H beam will carry oil. On the sides where milled out.

Chocolate or vanilla?

Are you wanting SB stock type rod and wrist pin end rods? If so either one will work
I'm going to build a old time offset stroker 360 motor cast crank with SB Chevy 2.00 rod journal sizes and probably use a set of Speedway 6.125 long small journal Chevy I beam rods
Lots of choices when starting a new build, take your time and check out every choice out there before deciding

I'd lean to the safer side, H beam.

Will be an all out race motor, but on the milder side. 11.5:1, won't be spun past 6500 and will have around a 600 lift solid cam.

Thats just a good street build, id not be afraid of the light scat I beams, they are proven.

Over 7k id use H beams.

I used to use forged cranks and H beams in every build until I realized a simple 500-550 hp stroker is no harder on a cast crank and I beams. 600-650 area all forged.

Id rather use a cast kit and pay for good machine work on the block then use a forged kit on so so block prep.

The only time id use all forged in a 6500 rpm motor is if it had a power adder or T brake.

Your 11.5 comp with al. heads is peanuts. A pump gas build as well.

At the moment leaning towards the scat rotating kit P/N: 1-48033BI. Should be right around 11.6ish to 1 or so depending on how thick of a head gasket we end up putting on it. I think the rods would be the weakest link, but with the lower rpm and still not a ton of compression they should handle the job okay. A plus with the I beams is they should only require minimal or maybe no clearancing.

in my opinion, the lower the rod angle the more likely i'd choose an h-beam rod. I think the weak link will be the main caps.

H is obviously stronger, which is why almost no OEM use them.

SOS on this rod stuff on a low power build, that kit number the op posted is perfect imo, even a bit of overkill there.

The majority of us on this site will not hurt a I or H beam thats been mentioned unless there is another failure to prompt a rod failure. Even with the base 8740 rod bolts. Many use the 2000 series bolts because they are idiot proof at our power levels.

The only thing ive seen wear in the china based rods have been the pin bushing and that was on a road racer on and off to 7500 to 2000 over and over.

I always use Pro Gram main blocks and studs for any SB over 6700. There's a lot of walking going as the motor revs.

Either shaped rod will be fine. Pick one that's rated for your intended use (which comes down to cross section), and don't worry so much about the shape. I wouldn't be worried to use the Scat I-beams at all on your build.



Actually it's not strength related at all... it's the manufacturing cost/ease that pushes us (FCA) towards powder metal I-beams more then anything.

Since the big/small ends are in the same direction as the I-shape, they can be easily formed, and VERY close to final shape which minimizes the machining costs. Even the hellcat rods are formed this way.

https://www.youtube.com/watch?v=azGg68B-Glk

Actually it's not strength related at all

NO, really?
Should I have used the [sarc] tag?

Widmer made some very interesting comments w/r/t beam shape 20 years ago specifically where in the power stroke gas pressure spikes, different between NA and turbo...

SCAT I beam rods will work just fine in your combination. I used the SCAT I beam rods in my 470/240 engine which makes 700 hp at 7000 rpm. I have over 100 dyno pulls on that engine and now it is going into the Duster for some drag racing. Here is a picture of the rotating assembly in that 470. I used a superlight SCAT crank, the I beam rods and some custom pistons.

Someone pointed out to me recently that they'd never seen an eagle rod break. After thinking about it, I had to admit I hadn't either. Meaning the beam fail. I've seen spun bearings, and seized pins destroy stuff, but never once just a rod failure from eagle..I have seen them in power I'd sweat premium rods over time too.

Just a thought on how hard it is to break, even a low end aftermarket rod when properly installed, and fed oil. Clearance, oil, and tune are probably responsible for most all rod failures imo.

A friend of mine, 10.5 outlaw heads up racer BB Ford NOS high RPM(9800 RPM shifting) motor, pulled two of their BB Chevy 6.800 long rods apart with the L19 bolts years ago

I was just going to mention Dougie and Jason Pettis about this exact same thing.............

Got a 360 stroked to 408 with scat 4340 I beams..nothing to grind...lighter weight...shifts at 6500..traps 6900.

Got a 2nd 408 ready to go in another car same set up..