So, what's the best rpm, you think, for engine longevity? Depends on throttle? Just go by feel? Seems like at low speeds/low gearing, the engine can lug down lower than during highway riding. It seems as though there is an upper limit to gearing, whereas the amount of load/work demanded at high speeds places limit on how tall the gearing can be without causing perpetual lugging. Ya gotta wind the throttle so much that you'll beat the bearings out of the poor thing if ya gear it too tall. I gather that the Honda Rebel folk talk about that problem especially. I gather you have to keep those things wound up.

I wonder if you can gear one tall enough to lug going downhill 80 mph.

Seems as though below 3000 in the higher gears generally = lugging. Even then, if you give it much throttle, you should be around 3400 at least (around peak torque).

However, you would think that it should run lower than that, given it's stroke length. There's no winning! Drag it down and lug, or rev it up and blow! We have such a wide torque curve, but should we use it? Is it better to feel it shake or wring its guts out?  

I've read on this forum to let it rev a little, and that seems alright for the higher speeds/loads, but that stroke length leaves some questions.  

I guess I'm overthinking this a little. After all, I can instinctively tell approximately where the bike should be running by feel (vibration/sound/throttle response).

I wonder if I don't keep it revved a little higher than necessary. Sometimes it has a hidden store of low-end torque I don't always utilize. But then, as some of the Harley people might agree, just because you have the torque, doesn't mean it's healthy for the engine.

I'd just like to get a better idea of precisely where I should sit. I've read that the science of bearings is pretty complicated. They have a sweet spot where friction is lowest. Above that, and the friction increases quickly (I assume fluid friction). Below that, the oil film breaks down, and metal-to-metal contact begins, also increasing friction. Of course, load complicates everything. I think this is partly why you need a higher engine speed to support higher loads: to support the oil film. I think I am referring to hydrodynamic bearings.

I'll post a link. I haven't read it very much, so I might have missed some things.
http://www.epi-eng.com/piston_engine_technology/engine_bearings.htm

I wonder if I should stay around 3500-4000 at all times at highway speeds, or should it be okay to gear up to 5th gear at 45mph or something? I've noticed that I can sometimes do that if I'm taking my time. Should the engine smooth out completely, or should there be some putt-putt left? should I be able to feel the pulses? I tend to lean toward the smooth side in the long run. Low rpm+low load=smooth. High load+high rpm=smooth.


I noticed that the ol' Subaru supposedly doesn't reach peak torque until in the 4K's for some reason, but I usually highway cruise in the 2-3K range. V8's seem especially known for cruising low on their torque curves for economy's sake. It seems as though the max efficiency/peak torque thing is not necessarily a hard rule. However, cars usually don't have the wind resistance of motorcycles. Trucks, on the other hand-- especially the older, boxier (and perhaps better looking ) trucks-- I wonder.


Seems as though 1st gear seems happy around 15 mph; 2nd is best around 15-25 (around 20); I like to try 3rd on the city streets to cruise easy. 25 in second starts getting a little busy. However, 2nd is really too far from 3rd, and so 3rd almost lugs at 25. It's probably best 30-45.I like to go to 4th at 45, I think. 4th is happiest 45-55. It probably pulls 40 okay. . 5th is best around 55-60 mph for pulling. If you're taking it easy, It seems comfortable at 50. You might go to 45 if you're light on the throttle.

Be aware that my gearing is a little shorter than many of you because I have a worn 140/80 rear. Speeds are indicated, not actual. Of course, it's just a guess anyway. No need to be so OCD about it.

If I go strictly by the chart of actual speedsat, say 3400 rpm, I get the following numbers (from Gearing Commander).

1st: 19.3
2nd: 28.5
3rd: 39.4
4rth: 47.1
5th: 50.9

It seems that, on the average, I probably drive at (higher gears) or a bit below (lower gears) torque peak EXCEPT in 5th gear, and this is partly (only partly) because it is the last available gear. The other reason is that the four lane seems more demanding for some reason It seems that right around highway speed, demanded throttle opening seems to get high. Is it just me, or does anything above 50 mph take alot of throttle?


Would different gearing have any effect on engine longevity?


Any thoughts?

Look at my previous post, I've been working on it.

(That's not saying I didn't at least wonder about heating issues, or worry about the fact that I needed an oil change) That was before the spacer mod, too .

The flywheel is a rotating mass that helps to maintain inertia, and smooth out the engine pulses.  The crankshaft doesn't run at a constant speed as the engine is running....and the tachometer shows an average rpm and not the constant variations.  When the engine hits the power stroke the crankshaft gains speed, and then at the bottom of the stroke the engine begins the exhaust stroke and the crankshaft begins to slow a bit, then during the intake stroke it slows a bit more.....and during the compression stroke it slows the most.  The speed variations are the largest at lower rpms, and as the engine speed increases the variations are smaller.  In the early days of the internal combustion engines the speeds were very slow and often were only a few hundred rpm, and they would put really heavy flywheels on engines that were used to make electricity - so you wouldn't see the lights go "bright, dim, dimmer, dimmest - bright, dim, dimmer, dimmest" as the engine went through the power strokes.

The Savage is a pretty big single, and it has a lot of rotating mass in the crankshaft, flywheel, rotor, and counter balance shaft.  All of those rotating pieces have to accelerate or decelerate in order to change the speed of the motorcycle when you use the throttle or brakes.

Making the flywheel lighter will result in a bit faster acceleration - but it also allows for quicker changes in the engine rpm in a potentially negative way.  The clutch, transmission, belt and rear hub will see larger pulses coming from the crankshaft drive gears, and they may not be able to dampen those larger pulses properly.  On multi-cylinder engines the variation is crankshaft speeds is made smoother as there are multiple cylinders firing on each revolution.

Lightened flywheels are used by drag racers, motocross bikes,  road racers.....folks that need to be able to accelerate quickly and the engine are generally tuned for high HP and run high rpm.  Heavy flywheels are used on low speed engines, trials motorcycles, tractors, touring bikes and cruisers that operate at low rpm and need smooth engine operation.  Light flywheels do not make or HP or allow and engine to spin at higher rpm - heavy flywheels to do not make torque (they do however make the engine a bit harder to stall at low rpm as the engine has more inertia).

So.....for the Savage engine their is very little to be gained on a stock engine by making the flywheel lighter.  I would guess that a small amount of weight might be removed with problem - but the gain in acceleration might be offset by a loss of smoothness in operation.  One of the first things that Yamaha, Suzuki, Honda, KTM and other bike builders do when they take a sport bike engine and adapt it to use in a Sport Touring bike - is to increase the rotating mass and use different camshafts and smaller valves to make the engine smoother.

Youzguyz has over 140,000 miles on his stock Savage motor, and the engine have never had the cylinder head removed or done any work to the piston, cylinder or crank.  He has done the normal cam chain, and other maintenance as parts have worn - but he has proven that the stock engine is durable during normal touring around Texas.

The modified engines with Wiseco pistons, bigger cams, ported heads, different carbs, etc. on this forum are all made to increase HP and torque within the 1,000 - 6,500 rpm speed of the Savage engine - as the big single stops making HP as the rpm goes over 6,500 rpm.  It is important to realize the big single will never make a lot of HP, as the formula for HP is torque x rpm.....and the rpm on the Savage engine is limited.  So far I really don't know how long a modified engine will go before it wears out....mine has gone about 7,000 miles since the addition of the Wiseco and cam.      

 

Is the Wiseco piston heavier than the original?


Also, I wonder if there isn't something to be gained by adding flywheel weight

that would be dependant on many factors, which you need to be an engineer to really understand
an engineer designed the flywheel for the S40, and I'm not one, so I'll stick with the stocker

I've noticed my 2001 savage has no problem going 75.... but it starts pushing oil out of places and makes a mess.
I have been driving it locally at 65 and under and no oil leaks.... so maybe compression does have its effect on higher revs vrs oil usage...

Dave wrote on 01/04/16 at 08:03:05:



Hmmm.... an opportunity for increased flywheel weight? Or not?