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Horsepower/rpm limit for stock, cast 454 GM crank.

General engine tech -- Drag Racing to Circle Track

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Postby Alan Roehrich » Fri Oct 17, 2008 7:05 am

Torsionally, a cast crank is stiffer, and will absorb less torque, until it yields.

We ran cast cranks in our 454 based bracket, Super Gas, and Super Comp engines for over a decade, at nearly 700HP, at 7500 RPM. We broke ONE. It had a cheap balancer on it, and two wrist pins had seized on the same journal. It had about a thousand passes on it, or more. It was straight out of a station wagon engine, we used the whole engine, cast crank, two bolt main block, 3/8" rod bolt rods, oval port heads and all. Of course, there was a lot of work in those engines, with LS-7 pistons, big valves, porting, big flat tappet or roller cams, etc. We had a 1/2 dozen of them, and one killer 454, with a steel crank, 7/16" dimple rods, 4 bolt main block, and 990 rectangle port heads.
Last edited by Alan Roehrich on Fri Oct 17, 2008 7:24 am, edited 1 time in total.
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Postby Lazy JW » Fri Oct 17, 2008 7:12 am

n2omike wrote:I heard Bob Glidden quoted saying that a cast crank will make more horsepower than a forged unit.


I too remember from about 30 years ago that Bob Glidden had a preference for nodular iron cast cranks.
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Postby CNC BLOCKS » Fri Oct 17, 2008 7:26 am

Alan Roehrich wrote:Torsionally, a cast crank is stiffer, and will absorb less torque, until it yields.

We ran cast cranks in our 454 based bracket, Super Gas, and Super Comp engines for over a decade, at nearly 700HP, at 7500 RPM. We broke ONE. It had a cheap balancer on it, and two wrist pins had seized on the same journal. It had about a thousand passes on it, or more. It was straight out of a station wagon engine, we used the whole engine, cast crank, two bolt main block, 3/8" rod bolt rods, oval port heads and all. We had a 1/2 dozen of them, and one killer 454, with a steel crank, 7/16" dimple rods, 4 bolt main block, and 990 rectangle port heads.


Its hard to believe that a cast crank is stiffer then 4340 cranks, All the cast cranks I have drilled when balancing are like drilling butter compared to a good forged 4340.

Its hard to beleive Callies, Crower, Kings, Lunati ETC have been making the wrong cranks LOL.

Maybe the Cup teams are using cast cranks now LOL.

I have seen better results with forged cranks then I have seen with cast cranks.
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Postby Alan Roehrich » Fri Oct 17, 2008 7:45 am

Carl, don't be daft, it has NOTHING to do with toughness, or hardness. Cast cranks are not heat treated like the forged cranks you're talking about. No one is suggesting that anyone actually go out and find a cast crank to use in a high end race engine. Cast cranks do not flex, until they BREAK. They WILL break before a forged crank, no one is saying they are better. All anyone is saying, and people a LOT smarter than I am have said it for years, is that up to the yield point, cast cranks are STIFF, and resist bending more than forged cranks.

The ULTIMATE YIELD point of a quality forged steel crank is FAR GREATER than the ULTIMATE YIELD point of a cast crank, NO ONE disputes that. A cast crank won't twist, it will BREAK. A forged crank will twist, many times, and return.
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Re: Horsepower/rpm limit for stock, cast 454 GM crank.

Postby keithnh » Fri May 03, 2013 6:25 pm

Anyone ever push a 3.00 stroke baby LT1 cast crank to test durability at various operating ranges? I am putting together a 302-alike sbc in an 89 block with a roller cam(CC 268 Magnum solid), medium high CR (10.75) and fastburn(aluminum) heads. A peppy grocery getter in a light car I would like the operating range to extend to just below where the cam HP peaks @ 7500 ... which is where the rev limiter will be set. I will not use above 6000 rpm on a day to day basis but every once in awhile Ill want to drop her into 2cnd at 65 and see if I can make the nose rise till I get that balsa wood feeling. Trying to watch my p's and q's on things that could affect detonation flat-tops, zero deck, no sharp edges, and possibly top-coating pistons. The 3.00 stroke should be less of a strain on the crank as the stack speed is slower per revolution than 350 ... I am trying to keep the stack weight .... piston pin rod rings .... weight to a minimum and am now at 600+145+638+41=1424gms. I will be milling off some .025-.035 of the piston top for zero deck which will lower the weight a little more. Have the right CC Ti retainers and the fasties have sodium filled light valves. Trying to do this fairly economically and havent spent a billion yet. The Mahle hyper 350 pistons look strong .150 above top ring groove, Scat 4340 6.0 I-s are not real heavy and should be strong enough. Everyone keeps recommending I buy a forged crank but I have chosen to nitride this factory recon 10/10 cast crank and see what happens. I want to do the same with some Poncho cranks on other projects and am experimenting abit with the Chebby. Everyone of course always says to go for more stroke not less as well but I have made my decision on that. If this engine really turns out nice I may put FAST TBI and accessory super down the road apiece and really check out the cast crank :)
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Re: Horsepower/rpm limit for stock, cast 454 GM crank.

Postby Truckedup » Fri May 03, 2013 7:04 pm

Helped my son in law build two blown 454's for his boat. 2 bolt block,cast GM crank ,GM forged pistons and rods ,roller cam,Merlin heads,GMC clone blower..Set ups like this usually make 550-600 hp at 4600 rpm for boat use .....The engine lasted a whole season typical heavy throttle boat abuse,extended time at 4500 rpm with wide open throttle .Ready for more abuse....We are just hillbilly mechanics....I think if the engine reved over 5500 rpm their life would be a lot shorter.
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Re: Horsepower/rpm limit for stock, cast 454 GM crank.

Postby rally » Fri May 03, 2013 7:38 pm

I used a factory cast 396 crank in my 70 Nova SS Drag Car 396 ci engine years back. Never had an issue. It was spun 6500 RPMs max all its life. I still have this crank on my shelve, its standard and still looks great. I wouldnt be afraid to use it again in a BB Chevy bracket engine.
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Re: Horsepower/rpm limit for stock, cast 454 GM crank.

Postby rally » Fri May 03, 2013 9:00 pm

Also a good cast crank will support a 600 horsepower engine. To be on the safe side anything above 600 horsepower i would recommend a forged crank.
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Re: Horsepower/rpm limit for stock, cast 454 GM crank.

Postby pdq67 » Sat May 04, 2013 1:44 am

I thought a good machinist used a 5 pound hammer on a crank to straighten it because he flat knew what he was doing.

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Re: Horsepower/rpm limit for stock, cast 454 GM crank.

Postby lorax » Sat May 04, 2013 2:54 am

Whole lot of 427 Ford HR and 351 Clevelands won a lot 500 mile nascar races with cast cranks, while the Chevys and Mopars used steel cranks. Don't remember too many of the Ford cranks laying on the track.
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Re: Horsepower/rpm limit for stock, cast 454 GM crank.

Postby keithnh » Sat May 04, 2013 7:20 am

Pretty sure my 302-alike will not approach 600 horses .... even though Comp Cams Cam-Quest 6.0 says it will. Think their numbers are a little(or a lot :) ) inflated ... I did punch in exact flow numbers, valve size and displacement tho. I watch the curves on the cam HP and torque and found the solid roller 268 magnum to look very nice with even HP rise all the way to 7500. Peak torque was at a lower rpm than hydraulic roller and slightly more. Has a moderate lift of .525 which is right about(just below) where fasties "flat-line" supposedly. The CC rep said it was a great choice for exactly what Im doing and that the ramps would have a positive effect on my being able to use pump gas in the 10.75 range. I did want to do my own calculations on dynamic CR to add to my build notebook. Hopefully I will be able to afford a dyno when done to see how it compares to the CC estimates. I will report it here if I do. Want to get each element done with care ... learn a little as I go. Took the cast crank I bought at Autozone to the machine shop to see if it was junk and they said no, it is a straight factory 10/10 baby LT1 crank that will most likely take whatever I can give it, they get from the same grinder sometimes. I had them do their trademark oil passage upgrade and polish. They could send it to nitride but I wanted to hand deliver and meet the guy, will be soon. Trying to figure out what the best "sequence of events" is to get the best result and found this @ treatallmetals.com

For minimal distortion
1 Quench and temper to specified core hardness
2 Rough machine
3 Stress relieve
4 Finish machine
5 Nitride
6 Lap or lightly grind as necessary

For maximum machinability
1 Rough machine
2 Quench and temper to specified core hardness
3 Finish machine
4 Nitride
5 Lap or lightly grind as necessary

I think quenching and tempering are done at the foundry ... dont know how you would machine before thats done unless you do while its still hot at the foundry. Stress relieving is done by shotpeening ... possibly a step I have missed, maybe one I can add now ... I will have to polish again at least I think. Wanted this to be a viable process check I can complete in the future and expect similar results. I wanted to do a hardness check before nitriding, will see if the nitrider can do that although I would like to know how myself, something else to add to the notebook. I believe the crank "grows" slightly with a nitride and would affect bearing clearances possibly. There might be more advantageous bearings to use at a specified clearance once a crank is nitrided although I dont know that yet.
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Re: Horsepower/rpm limit for stock, cast 454 GM crank.

Postby digger » Sat May 04, 2013 7:31 am

cast iron is not as stiff as steel for the same geometry this is shown by the Elastic Modulus, if it is stiffer it is because it is of different geometry nothing to do with the material. it also flexes like every other material. nodular cast iron has a suprisingly high amount of ductility (permanent stretch before fracture) can even be higher than 4340 but gray iron on the otherhand has a mere fraction of the capability
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Re: Horsepower/rpm limit for stock, cast 454 GM crank.

Postby twl » Sat May 04, 2013 7:34 am

I would say,

Magnaflux
Shotpeen
Shaker Table
Cryo-cycle
Nitride
Straighten and turn .010" under.
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Re:

Postby wjnielsen » Sat May 04, 2013 9:27 am

Lazy JW wrote:
n2omike wrote:I heard Bob Glidden quoted saying that a cast crank will make more horsepower than a forged unit.


I too remember from about 30 years ago that Bob Glidden had a preference for nodular iron cast cranks.
Joe

Question: was the iron in the Ford cranks that Glidden ran the same as the iron used in other brands? I seem to remember reading an article from the late '70's featuring a P/S racer (either Nicholson or Glidden) who said that the cast iron in those Ford cranks was so tough you 'could barely grind on it'.

Also, I've been told that cast iron tends to dampen vibrations slightly better. That makes sense to me - a steel piece seems to have more lasting 'ring' to it when you tap it with a hammer.

-Bill
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Re: Horsepower/rpm limit for stock, cast 454 GM crank.

Postby Erland Cox » Sun May 05, 2013 10:49 am

I thought that cast iron flexed less than steel and canceled out vibrations.
Has anyone seen a steel mill or lathe?

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