Limiting factor for RPMs?

[TC]

How about weedeaters made by Honda?
Wouldn't they kick the world's butt like, seriously major?

Just because I'm saying shorter stroke doesn't mean I'm saying smaller cubic inches....... Like I said a ProStock motor uses a 3.6" stroke, that is pretty close to a chevy 350 stroke, but they have 500ci's.......... There has to be a benefit to them running that short of a stroke, or they'd do like everyone else and run a 4"+ stroke and a smaller bore........And I call BS on the Valve Shrouding fantasy.......

[squirrel]

This is all about TIME, because the faster(quicker) everything spins, equates to you getting down the quarter mile faster..........

The Shorter stroke has less distance to travel per revolution which allows the engine to see higher rpm's in a shorter period of time.....

I was reading about the Crusher Camaro, which has a blown, stroked big block int it, and runs about a half second quicker than my 55 which has a standard size blown 454.

Prima facie evidence that a longer stroke makes a car quicker in the quarter mile.

[TC]

I was reading about the Crusher Camaro, which has a blown, stroked big block int it, and runs about a half second quicker than my 55 which has a standard size blown 454.

Prima facie evidence that a longer stroke makes a car quicker in the quarter mile.

Weight??, Gearing??, HP output??, ya there are other factors........

I still think the ProStock guys run that short of a stroke for a reason.......

[squirrel]

I'm sure they have a good reason, maybe Scott could ask what it is, for you?

[dieselgeek]

It's amazing that you people can't grasp this concept........ It's about the acceleration at which the crank spins,

A crank doesn't spin "at Accelleration" - it spins at a Velocity, usually called Revolutions per Minute. "Accelleration" is the rate of change of velocity. How ironic that you tell "us people" that we can't grasp a concept, while simultaneously showing that you do not know the difference between Acceleration and Velocity.

a longer stroke requires more power to complete one revolution

Huh? that makes no sense. What do you mean "requires more power" - are you saying that it takes more power to turn the engine by hand? otherwise it makes no sense if you're talking about a running engine. No idea what you're thinking here but you should learn to use the right terms IMO.

This is simple physics...........

which you do not grasp.

This is all about TIME, because the faster(quicker) everything spins, equates to you getting down the quarter mile faster..........

Wrong again, Alex. Let's compare two cars, same total weight, one has a 2700rpm Cummins Diesel making 900hp at the wheels, and the other has a 9000rpm smallblock chevy making 500hp at the wheels. All else being equal, the 900hp Cummins is going to get down the track spinning lower RPM than the Chevy spinning a high RPM, provided both cars' chassis are set up to apply their respective power to the track.

The Shorter stroke has less distance to travel per revolution which allows the engine to see higher rpm's in a shorter period of time.....

The RPMS that an engine "sees" is based on a number of factors you are skipping over in your oversimplified and confused Expert Lesson. An engine sitting in neutral revs a lot faster than an engine that's in 5th gear with a manual transmission rolling down the highway.


I wish I could help you understand better but, that's appraently not going to happen. I *do* understand what argument you are *trying* to have about stroke and RPM, and I know from working with top engine builders why certain engines are set up with the short stroke, but since you didn't ask politely I'm not going to waste the bandwidth on this forum trying to explain it to you.

[dieselgeek]

I'm sure they have a good reason, maybe Scott could ask what it is, for you?

Been through this with the Chrysler guys and the Hemi 99. I understand. It's really simple.

[TC]

DG you just don't get it, that's ok, I don't think I can explain it any better than I have, I'm sure others understand my concepts.....Which is all that really matters..........

[TC]

Been through this with the Chrysler guys and the Hemi 99. I understand. It's really simple.

That's it, no explanation??, just it's really simple??....... You don't know Jack.........If you did you'd have more to say than that.......

[dieselgeek]

DG you just don't get it, that's ok, I don't think I can explain it any better than I have, I'm sure others understand my concepts.....Which is all that really matters..........

What don't I get? that Velocity is not the same as Acceleration? It's kinda difficult to get "Your Concepts" when you can't explain them logically.


OR if you are saying I don't get why some engines have short strokes, well - that's your opinion and we know what that's worth.

[dieselgeek]

That's it, no explanation??, just it's really simple??....... You don't know Jack.........If you did you'd have more to say than that.......

Nobody asked and I am not the kind of prick that just launches into a "here's why it works" like someone else here. Meanwhile, I make sure I understand why something works the way it does, or I simply say "I don't know for sure" and then I don't look like... well... what we have here.

[TC]

Don't take my word for it.....

Oversquare or short-stroke engine

An engine is described as oversquare or short-stroke if its cylinders have a greater bore diameter than its stroke length - giving a ratio value of greater than 1:1.

For example an engine which has 100 millimetres (3.94 in) bore and 80 millimetres (3.15 in) stroke has a bore/stroke value of:

100 mm / 80 mm = 1.25:1

An oversquare engine allows for more and larger valves in the head of the cylinder, lower friction losses (due to the reduced distance travelled during each engine rotation) and lower crank stress (due to the lower peak piston speed relative to engine speed). Due to the increased piston- and head surface area, the heat loss increases as the bore/stroke-ratio is increased excessively. Because these characteristics favor higher engine speeds, oversquare engines are often tuned to develop peak torque at a relatively high speed.

The reduced stroke length allows for a shorter cylinder and sometimes a shorter connecting rod, generally making oversquare engines less tall than undersquare engines of similar engine displacement but wider and longer (for engines with vertical cylinder axes).

By changing the crankshaft and modifying the connecting rod(s), piston(s) and/or engine block an engine can be "de-stroked". This reduces the displacement and consequently the torque of the engine, but can allow it to run at higher speeds and in fact develop greater peak power.

http://en.wikipedia.org/wiki/Stroke_ratio

[OldMachinist]

TC why don't you and your buddy Rick build engines with your concepts incorporated and show us all we don't know anything. How about starting with a 2" stroke that should be really killer in your Monte.

[dieselgeek]

that link you quoted from wikipedia does not say the same thing you've been trying to say, so does that mean you've changed your mind? if not then what's the point of quoting something else especially when it's different from your claims 15 minutes ago?

[chevy3100truck]

Don't take my word for it.....



http://en.wikipedia.org/wiki/Stroke_ratio

no one ever argued that a short stroke motor isn't capable of higher sustained RPM, however the wiki you just posted has nothing to do with your idea about "rpm faster" . Acceleration & Velocity are two different things, but I guess your brilliant physics mind can't figure that out.....

the article also notes that larger bore allows for larger valves, but isn't that part of the "valve shrouding fantasy" as you put it earlier??

but I guess we should all just accept that Rick Santos only used to win because his car would "rpm faster" than the competition....... I'll go get that little honda S2000 motor out now cause it should dominate the world......

[BigBlockMopar]

"The closer a crank's rotating mass is located to it's centerline, the easier it can accelerate."