Grinding a cast 3.48" crank to 2.00" rod journal?

[Raybo]

Due to the rules we have to use cast cranks. I want to build this as an experiment but I am unsure if it will weaken a cast crank too much. Anyone done it? Dirt oval 6500-7000 rpm

[maxracesoftware]

Due to the rules we have to use cast cranks. I want to build this as an experiment but I am unsure if it will weaken a cast crank too much. Anyone done it? Dirt oval 6500-7000 rpm

NF = Nodular Forging cast-crank
a NF cast-crank will Ring a little if you strike the Counterweights , sort of like a Steel crank, but duller + ring duration will be a 3rd the duration

a plain cast-crank will sound like a dull thud , almost like a cracked Steel Crank


are you asking about both Rods and Mains ??

never did a cast-crank that way

all the Chevy OEM Steel cranks i had were medium Rod Journals ground down to small Rod Journal size on Rods only

You will find more HP doing other things/mods than grinding Rod Journals -0.100" down
especially on a lower RPM Range Engine .

[Raybo]

only grinding rod journal. These are stock replacement eagle or scat cast cranks.

[maxracesoftware]

only grinding rod journal. These are stock replacement eagle or scat cast cranks.

Still you will find so much more HP doing other mods .

i'd only attempt this if i had first maxed-out every other part of the Engine combination .

[fordified]

I ordered directly from Scat and had them grind a 2.00 journal on a forged Ford crank. They may be able to do that on a cast crank. It wasn't cheap since it was considered a custom order but it did include a no-hole shaved counterweight balance.

Larry's right. For the extra cost, you could probably buy a different camshaft or two or any number of other modifications that will be money better spent.

[Raybo]

This is for a very strict set of rules on a dirt oval. Cam lift and vacuum rules, I feel like Ive maxed out my ring package and cam package. Just looking to drain some more juice from the turnip.

GM forged cranks are getting tough to find.

[Ron Miller]

Back in the days "1980's" guys around me were building the sbc 415 combo. This was using the factory 400 cast nodular crank. The rods were turned down to 2" with a very large radius and the stroke offset was +.090. Some guys even went as far to have the cranks gassed nitrided. One combo was using a small hit of Nos 125hp. This 415 sb was a daily driver to.

[Walter R. Malik]

only grinding rod journal. These are stock replacement eagle or scat cast cranks.

Still you will find so much more HP doing other mods .

i'd only attempt this if i had first maxed-out every other part of the Engine combination .

Horsepower and vehicle acceleration are two completely different things, Larry.

Lighter rotating weight anywhere in the drive line will accelerate faster.
In most cases it might only be a fender length which is sometimes enough.

To answer the OP's question, I have gone to Quad 4 / Honda journal size in some oval engine situations, (usually 2 barrel rules), and seen a direct difference with a greatly reduced bob weight. Everything can get substantially lighter; the big end of the rod, the bearing and the journal.

However, if he is limited to O.E.M. production rods he would need to be very creative, as long as it doesn't need to be a Chevrolet V8 rod.
Like using an Ecotech 2.0 liter rod.

[Raybo]

2 bbl rules here. Have to use a chevy 5.7 rod can be eagle or scat. Looking in catalog it shows 2.00 rods weigh 40 grams more, so Its the same forging just machined smaller.

[Walter R. Malik]

2 bbl rules here. Have to use a chevy 5.7 rod can be eagle or scat. Looking in catalog it shows 2.00 rods weigh 40 grams more, so Its the same forging just machined smaller.

As long as the rules don't say "Chevrolet V8" rods, the Eco-Tec is a Chevrolet.
O.E.M. 2.000" journal rods with 11/32" bolts certainly do NOT weigh more; aftermarket, probably.

The real issue is that you possibly don't wish to take the rules writers to task about "exactly" what they wrote.

[Dave Koehler]

2 bbl rules here. Have to use a chevy 5.7 rod can be eagle or scat. Looking in catalog it shows 2.00 rods weigh 40 grams more, so Its the same forging just machined smaller.

Glad you noticed that. It kinda negates any rotating weight you might have removed.
In this case I would be tempted and not afraid to pick and choose some OEM rods.
Pull out all the time honored tricks and methods to get them up to snuff.
I would also look into how light of a piston and pin package I could acquire.

Did a few cast crank combos in years past.
Stroke check each candidate before going forward.
Mag of course
Remove casting flash and deburr the snot out of it.
Shot peen. If you can't get the real thing done, put it in a blaster and hammer it.
As I recall I would take the rods down to +.015. Do the shot peen thing and then finish grind.
low heat nitride
Large radius
Going that far under allows you to set the stroke exactly on each and correct any indexing that you can.
If you have a light package and use the 350 crank (not 305) you should have enough material that you could radius the leading edge of the CWs.
If enough weight has to come out of the crank I would turn down the CWs to get close to finish balance and wrap it up.

[fordified]

only grinding rod journal. These are stock replacement eagle or scat cast cranks.

Still you will find so much more HP doing other mods .

i'd only attempt this if i had first maxed-out every other part of the Engine combination .

Horsepower and vehicle acceleration are two completely different things, Larry.

Lighter rotating weight anywhere in the drive line will accelerate faster.
In most cases it might only be a fender length which is sometimes enough.

To answer the OP's question, I have gone to Quad 4 / Honda journal size in some oval engine situations, (usually 2 barrel rules), and seen a direct difference with a greatly reduced bob weight. Everything can get substantially lighter; the big end of the rod, the bearing and the journal.

However, if he is limited to O.E.M. production rods he would need to be very creative, as long as it doesn't need to be a Chevrolet V8 rod.
Like using an Ecotech 2.0 liter rod.

I thought it has more to do with a reduction in bearing surface than weight. A friend went from a 2.100 crank pin to a Honda. It didn’t show a difference on the dyno but it did pick up at the track. I would have to believe that weight reduction would have helped acceleration like you said.

[Krooser]

My Chevy buddies built many cast crank SBS's at around 500-550 HP back in the 70's-80's. They would run them two season on dirt and sell them o the street crowd after they were done. Can't say I remember many failures.

I ran nodular iron cranks in my Cleveland s and never had a failure in 5+ years.

[lefty o]

only grinding rod journal. These are stock replacement eagle or scat cast cranks.

Still you will find so much more HP doing other mods .

i'd only attempt this if i had first maxed-out every other part of the Engine combination .

Horsepower and vehicle acceleration are two completely different things, Larry.

Lighter rotating weight anywhere in the drive line will accelerate faster.
In most cases it might only be a fender length which is sometimes enough.

To answer the OP's question, I have gone to Quad 4 / Honda journal size in some oval engine situations, (usually 2 barrel rules), and seen a direct difference with a greatly reduced bob weight. Everything can get substantially lighter; the big end of the rod, the bearing and the journal.

However, if he is limited to O.E.M. production rods he would need to be very creative, as long as it doesn't need to be a Chevrolet V8 rod.
Like using an Ecotech 2.0 liter rod.

if you've ever lost a drag race by .001 seconds, a fender length is plenty.

[rustbucket79]

only grinding rod journal. These are stock replacement eagle or scat cast cranks.

I’ve had 3 broken cast replacement cranks from one of those companies, all were dirt oval applications. Do not go down this path. I would use a GM crank, not sure you’ll find a gain, sure you should have the crank magnafluxed every season.