How to build your own racing connecting rods?

[Hemi Joel]

Hi, I'm going to need custom steel racing connecting rods with a length in the 9-in range. This is for the blown 337 Lincoln flathead for land speed racing. I got a price from Carrillo of about $800 per rod.
So I want to investigate the feasibility of making a couple sets on my own. Has anyone done this? If so, what is the material and the process?
It only has a three and a half inch bore, so I don't think the big end of an aluminum rod would fit through it, plus with a track length of 5 mi, I have heard that aluminum rods aren't the best for land speed racing. That is why I'm planning on using steel.

Thanks, Joel

[chilly460]

Might take awhile...

[frnkeore]

Do you have a good milling machine and a good machinist available?

[Hemi Joel]

Do you have a good milling machine and a good machinist available?

Yes, my son who is my partner in the project is a machinist and has his own Fanuc Robodrill CNC mill in his garage. It is a very accurate and capable machine. He also does all the computerized design stuff like cad cam or something like that. But his experience is industrial and aerospace, he know nothing about connecting rods.

[SSdynosaur]

Before committing to self-production you might ask Crower for a bid. I have "special ordered" 3 or 4 steel rod sets for NHRA racing and find their attention to dimensions and overall workmanship to be exceptional. Not the cheapest, by any stretch, plus, everything ordered during the current economic conditions is going to be a wait but that is common throughout the US industrial complex.

[frnkeore]

Ok, you will have to draw it up first. I'd use H11 or 4340 and you'll have to do some measuring for big end clearance and taper on that end, to be sure the beam clears the bottom of the bore, with the stroke your going to use, too.

You'll need to rough the part and HT, before finish machine work, too.

You'll have to know how your going to locate the cap, hollow dowels or shouldered bolts. Once it's drawn, he should know how to do the machining.
Do a search of connecting rod drawings and you should come up with something start with.

[winr1]

Scat has some flat head rods around 7" for 599.00

Wonder if they could make a 9" rod economically ??

Is a 9" rod factory length for a 337 ??



Ricky.

[machoneman]

A wild thought: could an old radial aircraft engine or even a liquid cooled V engine have similar log rods. Have no idea about who supplies rods for really old aircraft engines but.........

[Gaugster]

Along those same lines....might want to check into any extra long diesel rods. Ideally finding the right length and then could be narrowed etc...??

[428 GALAXIE]

https://www.autoverdi.com/rods

[blykins]

There are several rod companies who will do customs.  Molnar will, R&R, etc.   R&R just made me a full custom set of aluminums for about $1200.   They have the capability to do steel, titanium, and aluminum.

[Hemi Joel]

Thanks for all the great suggestions. I think I screwed up the math on the rod length. It should be 8.25". 12" deck height, 4.5 stroke, 1.5 compression height. If we do make our own, we could 3d print a plastic piston and rod to test fit and clearances.

What do you guys think of switching to a 2.55 compression height on the piston so I could use off the shelf 7.2" BBC rods? Will that be to heavy of piston, or other issues?

[blykins]

I personally wouldn't want a piston that tall/heavy.

[frnkeore]

I might be able to help you with old 6 cyl rods.

Chrysler and Dodge trucks with what was called 251, 253 or 253 eng, had 7 7/8 long rods.

IHC eng called U for tractors and BD for trucks, 269, 282 or 308 had 8 9/16 long rods.

Both have 2 1/8 crank pins. Big end width is 1 3/8 and 1 11/16 for IH

The MOPAR's have 55/64 WP & the IHC has 59/64
 

[cjshaker]

Flathead pistons are typically tall and heavy to start with. That would be a lot of added weight to an already marginal bottom end. And as you mentioned, with bores being so small, a mock-up with a plastic or wood rod would be essential before even trying anything. Personally, I'd be surprised if they fit without hitting the cylinder.

On the radial engines, while they do have long rods, they're only designed to run at 3500 RPM max. I'd imagine you'll be pushing your engine to 5500-6000 with a good bottom end. Well out of range of what radial engine rods are designed to run. I'd be surprised if you could find anything close to correct journal sizes anyway.

You mentioned adding extra crank supports. Are you narrowing the main and rod journals on a billet crank to make room? I'm really curious how you're going to accomplish this. Any way to post pics, or is this a top secret job?