Non CW cranks?

Rick_Eberle · Post by **Rick_Eberle** » Sun Jul 23, 2006 9:47 pm

I noticed that Jake sells a non counterweighted 78mm crank. It's cheaper, and I would assume lighter than the cw version, so what's the catch? What would a non cw crank be useful for?

MASSIVE TYPE IV · Post by **MASSIVE TYPE IV** » Mon Jul 24, 2006 5:08 am

And we use them quite often as well, especially for road course engines..

The TIV is NOT like a TI that needs a counterweighted crank to keep the case alive with higher RPM. The TIV case really doesn't care about any of that stuff like a Type 1 and as long as the entire dynamic mass is balanced there are no ill effects of a non counterweighted crank.

A good example of this are my FP Road Race engines, we removed the counterweights to reduce mass and picked up speed on the course, the longevity of the crank and case was not effected! Now we lighten those non C/W cranks a good 3-4 pounds and the issues still are not noted even after a full race season of 7-8,300 RPM (12 races @45 minutes each)

I used a lightened crank in "The Mighty Spyder" and it makes power to 8,000 RPM!

I'm building a 2270 for my 912E and it will be getting a non C/W crank-

914fan · Post by **914fan** » Mon Jul 24, 2006 12:06 pm

I have read on several v8 boards about loosing driveability with a lightened flywheel. ( yeah I know water pumping POS) Something about it reducing the total reciprocating mass and increasing stalling. With the extra weight of extra pistons, rods, etc. that sounds strange. My question is how light is to light. Jake, you posted that you have lightened light cranks by a further 3-4lbs, on a f-prod RACE engines. I assume that many other things were lightened for this app. So how light can you go with everything and not get driveability issues? This is in referance to street vehicles.

Could a lightened crank, rods, flywheel, with DTM (IE no crank fan) be streetable? If so whats the V8 peoples problems.

MASSIVE TYPE IV · Post by **MASSIVE TYPE IV** » Mon Jul 24, 2006 12:12 pm

Its according to how you drive, the gearing and how heavy the car is.. Our F prod engines don't start making power till 5,000 RPM and must get off the corners as soon as possible, so their parts can never bee too light. One of them uses a 2.5 pound chromoly flywheel with a 3 pound tilton clutch pack for a pressure plate! That engine has a rotating mass less than 1/2 the original weight..

If the engine has big torque and is designed for the correct RPM range and it goes in a lightweight car it's hard to go too light..

It's never light enough for me!

A v8 engined car weighs a hell of alot more than a VW, so the problems are worsened... Plus most of those guys are weenies that don't drive hard enough to even need lightweight parts!

914fan · Post by **914fan** » Mon Jul 24, 2006 12:27 pm

You rock Jake. That was funny. I allways thought that is was wierd that double or triple the power of us and they have problems. I usually look at the Cobra, Gt40, and Corvette forums. Those cars are not usually 2-3 times hevier than a 914 at 2300#s. So it must be the drivers, or lack of I guess.
So A 2270 (96X74?) could be lightened very far for use in a bug, but not as much for a 914 due to increased weight. Assuming "normal legal street" driving, pulling to around 6K. Or with the longer stroke, and increased torque, would it not matter?
I have allways read that a lightened assembly does not make more power. It only allows for faster rpm increases. That has allways sounded like BS. Do you see diferences in power with ligtened parts? I would assume that you might lose some low end torque in the first 1000 RPM, but that overall the power would be higher.
Thanks for the info.

HAM Inc · Post by **HAM Inc** » Mon Jul 24, 2006 12:34 pm

If you don't like speed shifting then the light wt. crank and flywheel will make shifting more awkward due to the rpm drop between gears.

I have always been amazed at the number of people out there who install a counterweighted crank and a lightened flywheel in the same engine.

For competition the lighter the better.

914fan · Post by **914fan** » Mon Jul 24, 2006 12:40 pm

With the H4 engine why would you need a CW crank. Dosent the opposite piston / rod balance out, and in effect Counter Weight your assemble.

I know in V and Inline configurations a CW crank is benificail, but I dont see the benifit in our engines.

HAM Inc · Post by **HAM Inc** » Mon Jul 24, 2006 1:02 pm

I've never seen the need for them in any of my experiences. Back in the 70's and 80's the T1 race engines my dad built (and won a couple hundered races with) ran 13.5-14.0:1 compression with non-counterweighted cranks and we never had any problems.

I believe that many of the center main issues blamed on non- counterweighted cranks are actually related to tuning issues. T1 cases are not as hardy as T4 cases and do not tolerate detonation very well.

MASSIVE TYPE IV · Post by **MASSIVE TYPE IV** » Mon Jul 24, 2006 1:09 pm

Correct dynamic balancing is also the key... Thats why I spent the bucks to get the best damn machine on the planet.

HAM Inc · Post by **HAM Inc** » Tue Jul 25, 2006 6:51 am

Jake's right, if the entire reciprocating and rotating assembly is balanced correctly, and the powerplant is well tuned the case will hold up just fine without a counterweighted crank.
Counterwt. cranks have there place, but it sure isn't in Road racing, AX or any application where corner exit acceleration is critical.

MASSIVE TYPE IV · Post by **MASSIVE TYPE IV** » Tue Jul 25, 2006 7:19 am

Part of "Balance" is combustion chamber volumes, deck heights and port volumes as well as cam specifics being correct..

I believe thats one reason why TI engines in stock form pounded cases so bad, the chambers and deck heights were all over the place from the factory..

Len measures volumes in tenths of a cc....