Forged Crank

Mr.Spool

Well-Known Member
Joined
Nov 6, 2006

Mike T

Well-Known Member
Joined
May 3, 2013
In my experience the stock crank will begin to flex somewhere around the 500 hp mark. This has also been the experience of most that I've discussed it with. It shows up as a diagonal pattern in the main bearings. At what point does it actually break IDK.

I would be comfortable using a stock crank up to 500 hp. If it needed machine work I would consider putting that money towards a forged crank.
 

Mike T

Well-Known Member
Joined
May 3, 2013
I've always felt that an 1/8 mile car has a better chance of surviving. Any problem I've ever had was back half (street or strip)
 

SCOOBY DOO

I'M NOT A MONSTER, I'M JUST AHEAD OF THE CURVE!!!
Joined
Feb 18, 2007
Grumpy used a 20/30 stock crank and ran bottom 10's for years and a best of 9.98 at 138 with it. Bison ran some silly HP though the stock short block in his blue car.
 

Mike T

Well-Known Member
Joined
May 3, 2013
I know people who have had good success as well. Most have acknowledged evidence of flex at teardown. It really isn't evident with aluminum bearings but multi-layered bearings show it very well
 

SCOOBY DOO

I'M NOT A MONSTER, I'M JUST AHEAD OF THE CURVE!!!
Joined
Feb 18, 2007
I know people who have had good success as well. Most have acknowledged evidence of flex at teardown. It really isn't evident with aluminum bearings but multi-layered bearings show it very well
Something to note. On my final freshen up of my stock short block, my engine builder torqued the main caps and the crank seized. It wouldn't spin once it was torqued to spec. The crank was checked for straight ahead of time when it was sent out and only needed a quick polish. Now, either the block had flexed or the caps distorted. An align bore sorted it out. The other problem I had with a .030 over block was I went into the water jacket in 3 different cylinders. Had two cylinders sleeved and rebored. The third time I tossed the block and went to my back up standard bore short block. If I did it all over again I'd get a block that was as close to standard bore as possible. Racing every weekend finds weaknesses. These engines are durable, if built correctly and zero KR.
 

Mike T

Well-Known Member
Joined
May 3, 2013
The flex would be no different using aluminum or multi-layered bearings. The multi-layer bearing due to the different coloring of the layers makes it much easier to see.
 

Mike T

Well-Known Member
Joined
May 3, 2013
I think guys may be picturing a crank moving all over the place when in reality we're talking the thickness of a hair. With .002 bearing clearance it doesn't take a rocket scientist to see that there's no room for flex.

Ultimately the oil wedge determines wheather the crank contacts the bearing or not.
 

Mike T

Well-Known Member
Joined
May 3, 2013
I honestly don't even have a guess as to how much deflection may be taking place at the rod throws
 
Top