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This crank might be the best mod in the world...., but being we have the "knife edged" crank and "bullnosed" crank, I feel this one deserves it's own moniker.
Yeah, it is 'unique' for sure. Was told it is balanced out. Not sure what kind of harmonics would be created by this unique approach to reducing the counterweight...
Yeah, it is 'unique' for sure. Was told it is balanced out. Not sure what kind of harmonics would be created by this unique approach to reducing the counterweight...
Well, I studied up on the 1980's 190e Merc/Cosworth because it helped to understand the philosophy they used vs the original 16V 944S.
In one version, they took 4 of the counterweights completely off.
Wanna say the engine redline was 8000-8500 but with our engines, you'd better have dry sump to venture into that territory.
This is a fully lightened S2 crank I've been running it for about 7 years 8,000 miles no issues just saying you can really tell the difference in the way the motor picks up revs
Originally Posted by Jay Wellwood
Looking for feedback from the collective brain trust here.
Question - does the cutoff counterweights as shown in the attached pic cause anyone here to cringe or wince?
Application - 3.1L stroker motor project. Crank from an S2 3L to be offset ground to 92mm with shoulders and nitrided.
This is a fully lightened S2 crank I've been running it for about 7 years 8,000 miles no issues just saying you can really tell the difference in the way the motor picks up revs
I'd consider it vs the negatives on a turbo'ed engine.
The mission is to get it into the boost onset threshold asap.
On an NA engine, at some point, the inertia loss of the crank when lower in the revs at slower corners will probably hurt more than help.
I used to race a nitro 2 stroke RC hydroplane.
Engine was 1 cubic inch and made 7.2 hp at 19,000 revs.
You have to launch these into the water with a forward motion and 10k revs or they just die on launch.
Already a race engine, the parts are lightened further to run at front of pack.
When going through the turns, the engine drops 3K revs because there is not enough inertia to keep it at peak vs the work load.
I would have a question if you are losing cooling from the counter balance not splashing through the oil in the pan.
Originally Posted by 951and944S
I'd consider it vs the negatives on a turbo'ed engine.
The mission is to get it into the boost onset threshold asap.
On an NA engine, at some point, the inertia loss of the crank when lower in the revs at slower corners will probably hurt more than help.
T
Curious as to this statement. This maybe true if you have the clutch in and are coasting through the corner, but I do not understand if the engine is connected to the transmission and you are driving through the corner as the rpms are influenced by the transmission/wheel speed. On lightened engines I have been involved in the issue is getting rolling and pit speeds, where you benefit from a heavier rotating mass for inertia. I will agree that you could have a debate on the benefits of a lightened engine, if any. One of the theoretical benefits is due to the lower rotating mass the engine can get up to higher rpms quicker.
Well, I studied up on the 1980's 190e Merc/Cosworth because it helped to understand the philosophy they used vs the original 16V 944S.
In one version, they took 4 of the counterweights completely off.
Wanna say the engine redline was 8000-8500 but with our engines, you'd better have dry sump to venture into that territory.
T
read something interesting about this recently, that 2 counterweights instead of 1 per journal mostly just lets you get the required "balance mass" in a smaller diameter package (block clearance concerns).
I would have a question if you are losing cooling from the counter balance not splashing through the oil in the pan.
Oil in liquid form, you can rule out the front half of the crank "splashing" because that part of the pan is basically oil return.
I would guess there's 2 quarts or less in the sump with our engines running at anything past 3000 rpms, the crank weights would scarcely touch this oil.
Oil in a mist/cloud form is another story.
How much cooling effect this would have is open for interpretation but I would guess, in an infrared spectrum, the crank main and rod journals would show to be way hotter that the counterweights. That's where this oil would have just come from, so, it's cooling effect....?
Originally Posted by rlm328
Curious as to this statement. This maybe true if you have the clutch in and are coasting through the corner, but I do not understand if the engine is connected to the transmission and you are driving through the corner as the rpms are influenced by the transmission/wheel speed. On lightened engines I have been involved in the issue is getting rolling and pit speeds, where you benefit from a heavier rotating mass for inertia. I will agree that you could have a debate on the benefits of a lightened engine, if any. One of the theoretical benefits is due to the lower rotating mass the engine can get up to higher rpms quicker.
Inertia could be substituted by "momentum", it's the engine's resistance to slow down vs the work load.
It stores energy.
The weighted parts do not want to slow.
You lighten everything reciprocating and you reduce this resistance.
An example, you ever cut grass with a self propelled push mower and it's cutting along at a set speed.?
You come to a high patch and the engine slows, slows more and almost kills.
The combination of the engine's power output + momentum of the weighted parts could not overcome the load.
Now, take hat same mover and bolt a 10lb flywheel to it and chances are, it'll cruise right on through.
In the adverse, take 1/2 the weight off the crank and it won't get as far as the stock engine.
I read a paper once that stated that without the inertial power storage of a flywheel, a single cylinder engine (because it has no other firing opposing cylinder) could not run past the combustion stroke. It would not be able to even run long enough to make it to exhaust stroke.
Reducing the crank to a smaller diameter, center of rotation would have the same effect.
read something interesting about this recently, that 2 counterweights instead of 1 per journal mostly just lets you get the required "balance mass" in a smaller diameter package (block clearance concerns).
It's interesting that if I remember correctly, the Cosworth/Merc crank took off the center sets of counterweights and left the end cylinder weights intact.
I asked Michael Mount about this once because his business card reads 'Porsche/Cosworth' but I think it was more because it was lost in multiple points of conversation and he just forgot to reply to this point rather than a lack of experience or formed opinion on it.
Seems that it would be a torsional force nightmare.
If you are into the 16V, and I know you are, find all you can read on that Cosworth/Merc 190e engine, it's pretty interesting since they were from the same era, that even with the force of Cosworth helping Mercedes along with development, the 944S 2.5 16V by comparison is still pretty impressive.
I actually bid on (just missed) a Cosworth?Merc 190e header to measure it and see if it could be adapted to the 944S engine.
It has square/flat exhaust port interface.
04-16-2019, 10:03 PM
Crankshaft Opinion
