I'm curious about how many RPM you're turning and was this turned to 2.200" size journals?

What I've been considering is using the 2.375" (Mopar) size journal just because I have the parts to do it already (490 cubic incher). I would be using steel h-beam rods and turning about 6500 maximum RPM. This is a mostly street and occasional strip car. I don't want to put together a ticking time bomb though. That's the last thing I want.

I run a 68 Mustang with a 500cid/PG.

This will be the third season on the offset ground cast crank. The crank was ground by a local shop to 2.200"- it came from the "pile". We use Eagle rods with Arias pistons. The motor is taken apart at the end of each season crank is magged - so far so good. Also use a TCI Rattler - good damper is important.

Only problem we had was the rod caps walked, appears to have been cured by upgrading the bolts per Eagle and using stretch gage.

Made 645HP @ 6250 and 650ft/lb @ 4250, was turning 6,900rpm in the eyes, now converter has been tightened so hopefully that will go down a bit.

We recognize that the crank won't last forever - but we can have a lot of cranks ground for the cost of a steel one. This will likely be the last year for this one. Sure beats tearing truck rods in half with the old 460 combo!

That's nice info.

My thought was with the larger meatier 2.375" journal (and consequently shorter stroke) along with my relatively low RPM 6500 that I may be able to get away with an offset ground crank (with h-beam rods). Mine really would only see the strip maybe 10-20 runs per year maximum.

I am very concerned about getting a good damper, because I feel that could be a key.

I have discussed this subject at some length with Jimmy Fischer at Engine Systems and his rule of thumb is to limit the stock offset ground cranks to a max of 650hp and 6500rpm. He feels the SCAT cranks can handle 750hp.

Anyhow, I have allways wondered just how strong the new "cast steel" cranks really are. They say they are 30% stronger than an offset ground stocker but how does that compare to a stock stroke stock(whew) crank?
Also, how does the new Eagle crank compare tp to SCAT crank given the price is about half? Are they internal or external balanced?

Since I'm new to the BBF stuff too, keep the great info coming!

Thanks,

The Eagle crank is in my yet-to-be-finished first 385 engine build-up. It has ARP main cap studs, ARP rod cap screws and a SFI-approved dampener (I've sprung for the pricey ATI Super Dampener), with the hopes that their extra cost is worthwhile insurance against crank flex/breakage.

If you were to change your gearbox/prop, would you feel 'safe' to take your combo to a higher RPM level - say 6800 or more?

OK - I gotta ask: is a "Mandella" your boat manufacturer's name?

At this time I am not entertaining running this motor any higher. I have already lost one crank to low oil pressure problems(not breakage) so I am somewhat leary at this time. Also, I have noticed that most buildups of stock architecture stroked BBF's have HP peaks right around 6000rpm. My strategy is to add more horsepower but maintain the limit of 6000-6200rpm and increase boat speed by changing the gear ratio. Since these motors are basically modified stockers, I do not want to run them too hard.

A 2.375 bearing has a circumfrence of 7.46 inches which means at 6500 rpm the surface speed of the bearing is approx. 4040 fpm

The 2.2 bearing has a circumfrence of 6.91 inches and a bearing speed, at the same rpm, of 3743 fom which is 297 FEET less than the 2.375 bearing.

It is quite common for BBC racers to use a 2.1 bearing size and most, if not all, NASCAR builders are using tiny HONDA bearings.

Or - When both journals are at the SAME 6500rpms, the heat, wear would be lesser for the 2.2 journal by the 297 ft. or equivalent to 516rpms slower? (297ft/min X 12"/ft X rpm/6.91" = 516rpms).

Which begs to say the smaller the journal the better - less heat, wear, etc; EXCEPT for the trade-off in journal strength. How much stronger is a 2.375" journal vs. a 2.20" journal? -- Depends on what it's made of and how it's conditioned, right? If the same metal/conditioning, the larger is stronger. How strong does it need to be... is like saying 'Do you feel lucky?'

Your math is correct. In order to hit the same bearing surface speed with the 2.2 bearing you would need to turn up around 7017 rpm. As I am sure you are aware, heat from friction goes up in an exponential manner, so any decrease in bearing surface speed is good. Also note that SVO NASCAR blocks use the smaller 351C main bearing size, and the 460 prostock blocks use a much smaller bearing also, though I am not sure what size it is.

You are also right on the money that everything is a trade-off. Either way, I think we have all seen BBC motors making big power with a 2.2 bearing, I don't think the drop in size is a major problem. The Honda bearings I spoke of are sized under 2 inches I believe, and yes the Nascar cranks are top notch, probably by Crower or King.

I believe that Alex can provide some input when it comes to bearing sizes. If I remember correctly he was doing some fiddling around with smaller bearings a while back.

Hopefully that will come down as we got the converter tightened up. With the tire/gear it should be about 6600, SAFER!

Find out this weekend - first race is Saturday.

I have given very hard consideration to the Eagle 4.140" crank like Ryan has. That seems like the most bang for the buck. I am a little concerned that with my pistons I would have to use 6.635" rods (as apposed to 6.700" or 6.800").

My major reasons I was heavily considering the 2.375" journal was so I could use a 6.76" Mopar rod, have a shorter stroke (3.975" easier on mains) and possibly not have to deal with external balancing.

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Originally posted by Mike_R:
I was gone for a week on vacation and came back to find this 460 crank discussion still going on. Good deal. This a subject where you can never learn too much.

I have given very hard consideration to the Eagle 4.140" crank like Ryan has. That seems like the most bang for the buck. I am a little concerned that with my pistons I would have to use 6.635" rods (as apposed to 6.700" or 6.800").

My major reasons I was heavily considering the 2.375" journal was so I could use a 6.76" Mopar rod, have a shorter stroke (3.975" easier on mains) and possibly not have to deal with external balancing.

There are just so many pros and cons either way I go. It's a tough decision, but the Eagle crank is awfully appealing for the price.

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Drink gas haul a$$ American Racing

quote:

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Originally posted by TomP:
I know a guy that has two Boss 429 steel cranks for sale, i think he also has an SFI Damper for one.

[This message has been edited by TomP (edited 05-12-2001).]

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