Questions on how to mod a crankshaft open b

Check here for the latest and greatest engine modifications.

Moderator: hbartel

Post Reply
User avatar
o1moregil
Posts: 688
Joined: Tue Sep 27, 2005 4:12 pm
Location: Midland Texas

Questions on how to mod a crankshaft open b

Post by o1moregil »

I'm trying to get a little more power on my 25's, my os fx's are fearly new and are tac'n at 1780 and some at over 1800 with a 9x4 MA prop header and a can , I have been reading on the turbo cranckshafts that novarossi has on there engines, and I am wondering how does this crank help on the performance?, what does this do? has anybody tried turbo'in a regular crankshaft?


heres a picture on a turbo crankshaft of a novarossi
http://www.planethobby.com/image.php?type=P&id=556

[:p]I just like how flying open make my heart rate go up[:D]
Lee Liddle
Posts: 3330
Joined: Thu Jun 20, 2002 10:30 pm
Location: USA

Post by Lee Liddle »

Gil, the cut out on the left side of the crank counterweight area seems to be to reduce drag. That is the "leading edge" of the counterweight part of the crank when it is rotating. It may also serve to "scrape any fuel mixture in that area and throw it back and up, helping it to enter the ports.

The other cutout which comes out of the center hole does two things. One thing it does is to "throw" or "sling" fuel out of the crank. Also, when the crank pin is at bottom dead center the connecting rod blocks fuel from coming out of the crank hole. This cutout helps eliminate the point at which the rod blocks the fuel.

The best thing that you can do to increase rpm is to take the crank out of the engine and increase the intake hole in the crank about 1/16" on both the opening and closing side. No more than 1/16". This will increase the length of time that your crank allows fuel and air to enter the engine. It`s like putting a higher "lift" camshaft in a car engine.

This should give you over 19k. But be careful or you may blow the engine up. I`ve found that the OS connecting rod isn`t good for much more than that without breaking.
User avatar
o1moregil
Posts: 688
Joined: Tue Sep 27, 2005 4:12 pm
Location: Midland Texas

Post by o1moregil »

thanks Lee , very clear explanation, I have never tried modifying an engine (other then the can and pipe), I will open one and I'm going to give it a shot. I might tell buddy Bruce to fabricate me a Venturi (another thing i'll like to try out), he has a small machine shop in his garage
Hat Trick
Posts: 1540
Joined: Thu Mar 15, 2001 6:58 pm
Location: USA
Contact:

Post by Hat Trick »

Venturi and opening up the hole in the can will usually get you to 19K easily.
Captain America
Posts: 1009
Joined: Tue Aug 09, 2005 2:33 pm
Location: Middle of f'n nowhere

Post by Captain America »

If you run a pressure bladder...
combatgoblin
Posts: 244
Joined: Sun Jan 08, 2006 11:20 am

Post by combatgoblin »

What tool do you use to shave the crank?
User avatar
o1moregil
Posts: 688
Joined: Tue Sep 27, 2005 4:12 pm
Location: Midland Texas

Post by o1moregil »

Don, I Used a dremel and a grinding bit, then I smoothed it out with a finer grit, then polished it.
Steve108
Posts: 9
Joined: Wed Apr 13, 2005 5:42 pm

Post by Steve108 »

Is the cutout around the center hole timed? I have several os 40 la's that I have been playing around just to learn some things. Maybe I'll give this a try.
User avatar
o1moregil
Posts: 688
Joined: Tue Sep 27, 2005 4:12 pm
Location: Midland Texas

Post by o1moregil »

Image
User avatar
o1moregil
Posts: 688
Joined: Tue Sep 27, 2005 4:12 pm
Location: Midland Texas

Post by o1moregil »

Image
User avatar
o1moregil
Posts: 688
Joined: Tue Sep 27, 2005 4:12 pm
Location: Midland Texas

Post by o1moregil »

Image
User avatar
o1moregil
Posts: 688
Joined: Tue Sep 27, 2005 4:12 pm
Location: Midland Texas

Post by o1moregil »

I found this article on the web a while back, same thing with aircraft engines, I might mod anothere one and add a custom head that Bruce made for me, the head is a copy of Doc. Evils 25 fx heads with a Nelson Plug, they scream!!
Post Reply