4140 forged vs 4340 forged cranks - race only

[StrokerMcDell]

I've been running a short stroke 74mm 4140 forged crank for a couple of seasons in our buggy.

About 40 x 1/4mile passes to date - inc 24 x sub 11.50s / 2 x 10s  .... slowest of the 40 was a 12.4.

Engine is a 2054cc draw thru turbo and it made a gross 312rwhp (before transmission losses)
Buggy weighs 1400lbs with driver and is rev limlted at 6500.

Question is ... should I start to worry about the 4140 crank ??.. (its also only got I beam rods)

The engine really likes the short stroke but havnt seen anywhere I could buy a 4340 forged 74mm crank.

Is it the case that the grade of steel used is less important than the crank being forged?

Regds
David

[Carsten]

The same old question ;-)

Have a look :

http://cal-look.no/lounge/index.php/topic,11892.msg180644/topicseen.html#msg180644

Still found no answer for me....??

Greets , Carsten

[StrokerMcDell]

Not sure if any of that helps ?

Regds
David

[dangerous]

As far as I am aware the 4140 cranks are not nitrided.
If you are worried you may like to have yours crack tested regularly,
and if OK , have the nitriding done.
Always check the journals after the ntriding.
Generally they stay close to size,
but some cranks will bend, and some will increase in size more at the thicker cross sections.

Our procedure was to always pre grind the crank .003" from size,
 then finish grind after nitriding and straightening.
Common industry practise for production though, is to grind well into the tolerance, then nitride and just polish.(straighten if required).
This may work for you.