offset gound crank

I've noticed some smokin deals on Ebay for Carrillo rods. Unfortunately most are 2.0 or 1.88 rod journals. About how much strength would be lost offset grind the 3.48 stroke GM 5140 non-nitrided crank i have to 3.68 with a 1.88 journal. Anybody done this with good results?

I believe that winston cup engines use small journals these days - probably right down in that size range...

The key is having the crank PROPERLY ground. When they turn it down, make sure they give it a good radius at the edge (or course, you'll have to get the chamfered bearings to go with this) That radius gives the crank much more strength, and is why a properly-done .03-under crank should be stronger than stock...
I'd talk to some of the dirt-track or heavy bracket racers in your area if you don't know a really good machine shop already.

Of course, now that you've got a custom stroke, you'll also need custom pistons as well http://web.camaross.com/bb/wink.gif

The problem you'll have is alot of the cup stuff for sale is the older rods (not usage just date) and they are alot heavier. some of the 2.000 inch rods will weigh as much as 690 to 700 grams which is to heavy for extended use on a stock crank offset ground of not. If you can find the later ones they should be in the 560 to 620 gram range. The 1.880 is the honda size rod journal. If you can't find the lighter ones I'd pass unless you have a good crank. You probably wouldn't save much money by the time you offset the crank and speend more for pistons. Crower sportmans rods have came down in price alot you should be able to get a new set for $450.00. I've used alot of them and have never seen one fail even in engines exceeding the hp and rpm recomended for the rod. I have several in my own limited engines for 5 years and every freshening the rods are checked and haven't needed to be resized yet. This are in 620-650 hp 8,000 to 8,700 rpm engines but they all have light pistons and pins around (400- 440 gram pistons and 103 gram pins). This significantly improves the strength of the rod at rpm. I'd use the crower rod and forget the oddball stuff it will be cheaper in the long run.

Honestly, in an engine you want some longevity out of, I wouldnt ever go with a honda/bmw sized journal. Sure, lower bearing speed, but there just isnt enough surface area. As far as the Carillo rods from teams.. those bastards seem to last bout forever, but that race stuff uses small rodbolts to save weight, so be sure you go with good ones if you try this out. The rod/piston weight, i wouldnt think it was really enough of an issue to worry about.

Honestly, I think you should do what taylormade said... everyone wants to say they have carillo rods, but go the cheaper/easier route & youll have less problems & more longevity outta it methinks.

Rather than start a new thread let me add another question here.

I am looking to offset grind a stock LT1 3.48 crank. I have a machine shop I feel is very competent (have built half a dozen reliable engines with them to date with no "issues") so they can do the grind right.

How much hp/abuse can a stock cast offset crank withstand? (Looking to shift at 6300rpm with most of the power in the 5500-6300 range. Also looking at about 475-500hp range NA with a progressive N2O system to be added as needed at the track.)

BBB

Originally posted by BBB
Rather than start a new thread let me add another question here.

I am looking to offset grind a stock LT1 3.48 crank. I have a machine shop I feel is very competent (have built half a dozen reliable engines with them to date with no "issues") so they can do the grind right.

How much hp/abuse can a stock cast offset crank withstand? (Looking to shift at 6300rpm with most of the power in the 5500-6300 range. Also looking at about 475-500hp range NA with a progressive N2O system to be added as needed at the track.)

BBB

IMO, 475-500 and 6300 would probably be the upper end of safe. If you add N2O, I think you'll soon be running over your own crank. If you must use it, go stronger on the crank and rods first.

As strong as Cup rods are, if used they are not a good buy, IMO. A typical race is over 1,000,000 engine revolutions under power. Metal remembers every time it was ever stressed, especially if those stresses were substantial. That's why they are changed before they reach the end of their useful life.

I did cylindrical grinding for many years in an industrial marine machine shop, and the offset crank grinding is a fairly normal proceedure. The smaller journal surface would actually decrease rotational friction, but a slight imbalance due to the offset may cause some problems. How strong is a Cup rod, you ask. Around 270,000psi which is extremely strong. Here is the material and description of a Cup rod:
ARP®3.5 (AMS5844)
"While similar to Inconel 718, these super-alloys are found in many jet engines and aerospace applications where heat and stress attack the life of critical components. The high cobalt content of this alloy, while expensive delivers a material with superior fatigue characteristics and a tensile strength in the 270,000psi range. The immunity to hydrogen embrittlement and corrosion of these materials a significant design consideration. These materials are primarily used in connecting rods where extremely high loads, high RPM, and endurance are important factors, such as: Formula 1, Winston Cup, and CART applications."
I had the displeasure to machine Inconel several times...and it is a tough material to say the least. Stellite, high-level 400 series stainless, and heat-treated 4340 were some of the "toughest" materials that I machined. To finish them, they generally have to be ground. I would say that the Cup rods would withstand anything that you could throw at it, even when taken out of service prior to their useful life. But there are other issues that may not make the swap cost effective (i.e. turning and rebalancing the crank for one)...

Originally posted by CAJUN-Z
ARP®3.5 (AMS5844)
"While similar to Inconel 718, these super-alloys are found in many jet engines and aerospace applications where heat and stress attack the life of critical components. The high cobalt content of this alloy, while expensive delivers a material with superior fatigue characteristics and a tensile strength in the 270,000psi range. The immunity to hydrogen embrittlement and corrosion of these materials a significant design consideration. These materials are primarily used in connecting rods where extremely high loads, high RPM, and endurance are important factors, such as: Formula 1, Winston Cup, and CART applications."
I had the displeasure to machine Inconel several times...and it is a tough material to say the least. Stellite, high-level 400 series stainless, and heat-treated 4340 were some of the "toughest" materials that I machined. To finish them, they generally have to be ground. I would say that the Cup rods would withstand anything that you could throw at it, even when taken out of service prior to their useful life. But there are other issues that may not make the swap cost effective (i.e. turning and rebalancing the crank for one)...

Good info.

Are you saying that AMS5844 material is used to make the rod itself or just the rod bolts? It's a popular high-end aerospace bolt material; the shuttle is full of it. I believe it's non-magnetic, and I thought I heard that Cup rods needed to be made from a magnetic steel. I'd really like to know.

Those nickel/cobalt/chromium/molybdenum alloys are VERY difficult even to grind.