Mike B

I'm looking for experience / opinions from anybody who has went this route...It would seem to me that they should both go together...Ideas... <img src="graemlins/drink.gif" border="0" alt="[cherrsagai]" />

David Floyd

I think they should go together and John at Speed Force Racing is doing this to my new 2.8 ltr engine.

<img src="graemlins/burnout.gif" border="0" alt="[burnout]" /> <img src="graemlins/burnout.gif" border="0" alt="[burnout]" />

John Anderson

Probably one of the best mods you can apply to an engine.

Both are very heavy from the factory to produce a silky smooth ride. By shaving the weight, you can have a car that revs extremely fast, builds load faster and makes boost come on super fast.

I'm running our 2.82 Liter (the same engine I'm building for David) with a Garret T66 Ballbearing turbo, with number * hotside and a "P" trim turbine wheel. My car makes 5psi boost with that huge turbo (won't even fit with a regular drop bracket in the car, or the intake manifold, I'm using an SFR intake manifold) at only 2800rpm starting from a lug in fifth at 2000rpm!

A large part of this is due to the reduced weight of the motor! It reves like you can't belive, just TOUCH the throttle and its at 5k! Faster thatn most high compression modified NA's!!

In short, DO IT!

Bri Bro

I concur; it makes the boost come on stronger...but to quote Danno "power is additive".

Danno

ADDICTIVE as crack! Some of you are already mainlining the stuff, I know....heh, heh...:

<a href="http://www.nsxfiles.com/sears_point_2000.htm" target="_blank">http://www.nsxfiles.com/sears_point_2000.htm</a>

SoloRacer

Out of curiosity = what about balancing of the engine? I would imagine that after lightening parts such as the rods, pistons, crank, flywheel, etc. that you would have to get the engine balanced. Would this include the harmonic balancer as well? What about the balance shafts? Do they have to be changed as well? From what I understand, the balance shafts are there to negate 2nd order harmonics. Are 2nd order harmonics changed when you lighten parts?

Mike B

Good questions Solo Racer...I'm also wondering if there are any downsides...What about going to an aluminium flywheel over lightening the stock one...

Danno

Out of curiosity = what about balancing of the engine?

Yeah, I was wondering how it is possble to remove 10-15lbs from the crank and maintain balance? I'm assuming a couple of things here are true in the stock configuration:<ol type="1">[*]the crank itself is balanced, put it on V-blocks and it will stay in any rotation[*]the crank + pistons + rods are also balanced as a complete assembly. so if you put the crank and all the pistons & rods on, then lay it down on two V-blocks, the assembly can be rotated to any angle and it stays?[*]the crank+piston+rod are balanced per journal. That is, if you take each rod-journal and its rod+piston and the two adjacent crank-journals + counter-weights, that all of these are in balance as well[/list=a]If these assumptions are true about the stock engine, how can you remove weight from the crank and maintain balance with the stock rods & pistons? Sure, you can remove 0.5lbs from each rod & piston with aftermarket parts, but that's only 4lbs savings total, meaning you can shave 4lbs off the crank counterweights.

But take 10-15lbs off the crank? Ok, so conditions #1 & #2 can still be true but no way #3. Sure you can achieve balance by canceling two adjacent sets of rods+pistons with each other. And that's going to add torsional stress on the crank since each rod+piston is no longer fully balanced by the opposing counterweights, but rather by the next rod+piston down the crank.

What's the story here?

Mike B

Hmmm...The downside rears its ugly head...

On a side note I see Danno has but four more posts to reach 1000... <img src="graemlins/drink.gif" border="0" alt="[cherrsagai]" />

David Floyd

I'm sure John will fill us in on the balance question.

I do know that he is deleting my balance shafts,using JE pistons and Pauter rods with 16 lbs off the crank and 8 lbs off the flywheel with a 106mm bore, this is the same setup as his engine with no problems.

<img src="graemlins/burnout.gif" border="0" alt="[burnout]" /> <img src="graemlins/burnout.gif" border="0" alt="[burnout]" />

OZ951

From a complete non expert - Looking at the crank it seems that the pistons & rods balance each other out to a large extent since 1 pair of pistons travel in the opposite direction to the other pair and they are separated by 180 degrees. Of course this wild arsed guess could be competely wrong too

I would imagine that one downside to the lightened crank/flywheel would be a greater tendency to stall as a load is applied to the engine (as you let out the clutch & pull away in first gear- based on the assumption that less rotating mass will mean the engine will slow more quickly as a load is applied, if the revs are not kept up that is.)

I am interested to know how the smootheness (vibration) of the engine will be affected by the crank/flywheel mods.

I am also interested in knowing (quantifying) what change in HP/torque results from these mods.

Wayne

86944turbo

4 cyl. engines require very heavy counterweighting due to the fact that there is 180 degree pulse seperation. Knife edging reduces the weight and is not the proper shape. Better to use a symmetrical airfoil shape. That would require a new crankshaft forging. Knife edging only shows an improvement at high revs. These 4 cyl. don't rev much past 7000, and that's not high revs.

Fen

OK, first apologies for resurrecting such an old discussion, but this interests me and "search is my friend".

I read everything I could find on crank lightening and balance shaft deletion last night (hell, it was New Year's Eve, what else was there to do? I have been in bed all week, sick).

I have picked this post to quote as it seemed to sum up my biggest concern that might prevent me from lightening the crank and removing the balance shafts. BTW my car will be a toy, used on track, for fun on the road and travelling to / from the track but not to get to work / go shopping.

I thought about this and came up with 2 questions that I'd appreciate thoughts on - I don't expect a definitive answer on this subject!

I respect Danno's knowledge and understand his thinking BUT, in any engine and at any given time one of the 4 pistons is either:

Rising against the resistance of compression, thus creating an opposite reaction against the crank that is not balanced by weight anywhere else, or

Being pushed down by the huge force of combustion, again creating a large unbalanced force on the crank. This latter must be WAY more than any weight imbalance, suggesting that balancing journals in pairs would not cause a problem. Comments?

Secondly the crank counterweights can only exactly counterbalance the rod/piston at two specific points in the rotation, because they move in a circle and the pistons reciprocate in a fixed plane. Again I suspect that this suggests the balance of crank against pistons is less crucial.

I am happy to agree Danno's assumptions regarding the factory balance (albeit I doubt it's done to a very high tolerance) so I further assume that the balance shafts are designed to oppose vibration caused by the crank counterweights movement outside the plane of the pistons' movement, therefore taking a fair amount of weight from the crank will result in an imbalance of that magnitude between the new crank and the balance shafts. At some level of weight reduction that imbalance would actually be less if the balance shafts were not there at all.

The above is complicated because changing the weight of the crank will change the harmonics and create an imbalance there too...

TurboTommy

The technical aspect of balancing, I cannot comment on and is a topic by itself.

What I do know is that lightening rotating mass has no affect on power output or when the turbo comes on. Power comes from the turning force of the crankshaft (torque), and a different weight crankshaft or flywheel has no affect on this. The ability of a car to accelerate is opposed by load. Heavier rotating mass is part of this load but is very minmal compared to the weight of the car, taller gearing, or aerodynamic drag. The weight of the engine rotating mass plays more of a part when the rest of the loads on the car are minimal (reving from idle and/or low gears). I'm sorry, but I think it's an exageration when you get talk of a vastly better performing engine with lightened flywheel, etc.

Andrew Wojteczko

a known formula that can be used is
Torque out = Torque in - (Inertia * alpha)

This clearly shows that the less inertia, the less reduction in output. So yes, reducing weight off the rotating mass can make a difference in output. Especially when it is before the transmission, before a reduction of at least 4:1.

So, no, performance gains from reductions in inertia are not an exageration by any means.