Should have done very basic research before even building/buying that motor.
Using oem crank and than modified (lightened) on top of that while increasing power output by 50% with higher revs is never good bet.
Like they say, it is not if but when the boom will happen.

 

Maybe, and hindsight is great when you're ££££ down. I'd be interested to know what research would have told me this was a time bomb which would have lasted minutes though? I actually went 250 rpm lower than the advised limit but was assured it was all designed to take it. You expect things to be built properly, and in this case it's my view that a mistake was made and that can't be researched.

The engine is now putting out the same power, reliably, but with a lower rev limit.

 

Nah, he's on a 3 rotor now with variable length intake trumpets. He is building a new engine though for next year, but he'd have my bollocks if I told anyone at the minute, even his missus doesn't know (Although, I think that's so he can hide the bills....)

 

Your only going to get so much power out of so much displacement with only so much RPM. Either displacement, or RPM need to be raised to get a significant difference in power. More RPM is a lot harder on reliability. Displacement is your better bet but that limits your RPM even more. There are things you can do like more compression and larger cams but at a certain point that stuff has diminishing returns and the way the F20/F22 is those diminishing returns happen pretty quick.

 

In all those discussion of engine balance no one ever mentioned what balancer was used.

This was an add-on build that claimed 285 whp. However, not cheap with headers, exhaust, cam, and ITB intake, Most just go to 2.4 for that power, some with a K24 swap. K24 swaps are common in general, they are available virtually as a crate engine. Kits for the K24 to S2k swap are available. Also gets expensive.

Drag cars can produce high revs and power, but for short periods. I have been told that the crank isn't stiff enough for high revs, especially with a stroke. While expensive metallurgy (300M, 4340, cryo treatments) can make a crank stronger (higher yield and tensile strength), it doesn't add stiffness. The problem is the minimal overlap of the crank and rod journals. Many of these large displacement engines have 100mm or longer strokes.

I think the S2k has a block girdle from the factory. Titanium rods, very low compression height pistons (oil ring over the pin, minimize weight, max rod length), short pins can reduce reciprocating weight. Straight cranks are always in rotational balance, the throws offset each other, but unless opposed has a secondary balance issue as the rod angularity is different at the top and bottom of the stroke.

It is possible and common in some areas to sleeve the engine. Darton has MDS sleeves. That lets the bore grow to 90mm. With a 106mm stroke (that is over 4", something expected in a 427 Chevy) the engine can grow to 2.7L. Don't expect 10k rpms.

I've always wondered why no cams use the VTEC to make one 7000 rpm lobe and one 9000 rpm lobe. That wouldn't increase power but fatten the power curve. The reason given for a 2.4L or larger even with a lower limit is the broader powerband,

Note that Ford has 100 hp/L with their Shelby 350...a 5.3L V8 without direct injection. The Ferrari 458 had around 130 hp/L with direct injection. The GT3 is also around 125 hp/L with direct injection.

 

I suspect the reason the balancer didn't come up is that most folks in this discussion may not be aware that some engines (primarily American V8's) are externally balanced with weights on the harmonic balancer or the flywheel/flex plate.

Otherwise the job of the harmonic balancer is to absorb and distribute the dynamic acceleration/deceleration of the crankshaft and valve train between combustion events.

Balance of a crankshaft is different from stiffness. Balancers can reduce twisting stresses on a crankshaft, but not axial/radial stresses.

I've done a bit of study and work on Nissan KA24DE's, a 2.4 liter 4 cylinder with a 96mm stroke (3.78"). It has a "half counterweight" crank design that is fully balanced, but the forces are not all lined up and the crank is known to flex at higher RPM. One of the remedies for folk that want to rev it is a Brian Crower fully counterweighted crank, offered in both stock and stroked versions.

Another attempt to control the dynamics is to reduce the flywheel/clutch weight and increase the weight of the crank pulley, to reduce the end-to-end whipping/bending dynamics.

The F20C and F22C are well ahead of the KA motor, but the same forces must still be reckoned with when raising the rev limits.

 

Only some production engines were externally balanced, virtually no race cars are. It is done when it would be unreasonable to create counterweights large enough to balance the throws and reciprocating weight. The balancers handle torsional vibrations and there are several significantly different designs.,
Valvetrain?
Yes...but that was a different topic. The Honda cranks are strong enough not to break; but they aren't stiff enough to handle very high rpm for prolonged periods.That is because they aren't stiff enough which is the result of small journal diameters with a long stroke.
Inline 4 cylinder engines are in primary balance and are only in secondary balance from balance shafts. Longer rods, shorter strokes, and lower reciprocating weight will reduce the secondary forces. The counterweights just move more of the balance to each crank through. Since many of these cranks are marginal in stiffness, this can be beneficial. In effect, it is putting each cylinder into balance individually.

An interesting setup would be one that stiffens the crank while reducing secondary forces. Maybe a sleeved 90mm bore with an 84mm stroke, 6" titanium rods with very low compression height pistons with short wrist pins. The increased main/rod journal overlap would improve stiffness with the improved angularity and low reciprocating weight would make better at high RPM. The counterweights would further reduce the stresses at the expense of more rotational inertia. It would be an academic exercise since there probably isn't a racing class where it could be used effectively.
Why do you think the F22 is behind the K24? It is a trade off of size for speed...and some production cost issues. Do you have an example of a heavy pulley, other than working as expected in an external balance, being used to reduce "whipping/bending dynamics"?