Lightening a crank

[The S is Silent]

I've got an na engine sitting in the horizon at home that is currently busted, and thought about trying some stuff out. I basically want to make an autocross car out of it.

I want to be able to rev the crap out of it, so i'm going to go with the lightest engine assembly I can find. Lightweight rods, lightened or aluminum flywheel, and a lightened crank.

Now, here's the question. How successful would it be to drill out material from the rod journals and trim down the counterweights. Would this completely destroy the integrity of a cast crank. 100 hp isn't too big a load on it, so I think it is doable, I just want to know some oppinions. How much will weight dropped help to increase my rev limit.

Any thoughts or comments will be appreciated. This was just something I was thinking about on the way home today.

[marcoze]

Trimmin counterweights = No longer acting as counterweights. Very unbalanced.

[The S is Silent]

Drill out material from the rod jounals, and take the same amount of material off the counter weights.

[marcoze]

sounds possible. Maybe try some aluminium rods?

[yogurtslinger]

Quote:

Originally Posted by marcoze Trimmin counterweights = No longer acting as counterweights. Very unbalanced.

which is why you have to have it re-balanced....

I thought about *knife-edging* my crank but, it was too expensive for my taste and not that great on the heavier cars like the G and J bodies.. I think clickhere33 had his crank knife edged, might wanna give him a pm and ask him. The cast crank should easily handle being knife edged and should easily handle almost anything you could throw at it.. hell, some guys are using cast cranks and making over 350 horspower daily...

Bryan

[shelbyplaya]

try talking to garret.. he's got a crank thats been grounded down to nothing.....

[Reaper1]

I know of a guy that used to race circle track with our engines. He built a few engines that he hacked the counterweights in half then had the whole mess rebalanced....quite interesting. I almost did it myself, but the custom work the journals took long enough without ahveing to worry about that headache. What sucks is I have this nice crank, rods, and pistons all ready to go in this block....along with main cap studs ect., but I still need other stuff to make it all "right"...and now my "ubermotor" plans have completely taken a new direction....so these parts are now just sitting......arrrgghhhh!

[igotaneed4speed]

knife edging a crank on one of our motors is good for at least 20-15 h.p if used with a good pan and screen. Throw a dry sump and ull pick up 40 or more with the combo... no windage is more power

[The S is Silent]

What is a dry sump oil system? It came up in the thread about the new Vette, and now.

[89acclaim]

This should help. http://auto.howstuffworks.com/question331.htm There is also a write-up in the mopar performance book. Hope this helped.

Daniel

[The S is Silent]

Thanks for the link...sounds a little complicated for use on a junkyard car

[Putter]

Remember the weight that limits rpm is the rod/piston...thats what you have to start and stop all the time, and if you're really really going to turn a motor, start looking at rod angle ratios and maybe think about different pin height pistons and longer connecting rods with maybe an underground crank thats been offset... now we're talking $$$

[mr_v8horsepower]

My last v/8 stroker crank had to have 3/8 in. cut off the counterweights just to clear the bottom of the pistons. They then added 6 sticks of Mallory metal to the c'weights to rebalance the crank at $50 per stick. It ain't cheap!!
Good side of it was the weight was added closer to the centerline of the crank which keeps the flywheel effect down and the crank spins quicker, just like an ice skater when they pull their arms in while spinning.

[89acclaim]

You could try using rods form the 2.5 tall block with milled down 2.2 turbo pistens. Like what 22dodge talkes about in 2.2/2.5 stuff I've done

Daniel

[The S is Silent]

Yeah, its the longrod motor: 2.2 crank in a tall deck block while using the longer pre-CB 2.5 rods and milled 2.2 pistons.

It is definitley an option. Finding the talldeck blocks is becoming more difficult (or so I have heard).