Limiting factor for RPMs?

[squirrel]

I'm not debating that I know there are variables when it comes to the car, this is just about the motor and how stroke has an effect on how fast(quickly) an engine RPM's.....

But what you fail to see, is that NO ONE CARES how fast an engine "RPM'S". It has nothing to do with anything.

[BKBridges]

Back to the thread...
Mopar small blocks like to rev. IMO 7K isnt out of the question for a stroked small block with a forged crankshaft and a well set-up stock oiling system with aftermarket windage tray and deep baffled pan. With additional oil system mods well described in the literature +8K revs are possible. Big block Mpars need a bit more oiling system work to keep the back rod journals happy at high RPM... Neither has 4 bolt mains "stock" so there is some weakness there (unlike the G2 Hemi) I do know for certain that even a Dick Landy built Big block with oiling mods doesnt like 8000 rpm for very long.

[jcharliem]

...what you need to get through you thick ass skull is this is about "TIME", the TIME it takes the crank to make one revolution...

This is becoming so comical. What am I missing?... I thought a long-stroke mill takes the same amount of "time" to rotate one revolution as a short-stoke mill if they're operating at identical rpm's? While you'll have different bearing speed... the "time" is the same.

Boys and girls... again this is what happens when you're self taught and the teacher doesn't know shit. TC logic and theories = Clown.

[dieselgeek]

This is becoming so comical. What am I missing?... I thought a long-stroke mill takes the same amount of "time" to rotate one revolution as a short-stoke mill if they're operating at identical rpm's? While you'll have different bearing speed... the "time" is the same.

Boys and girls... again this is what happens when you're self taught and the teacher doesn't know shit. TC logic and theories = Clown.

... or maybe you and me and Randal are just too dumb to follow TC's cutting edge theories. You know he hangs out with guys who make dragsters go 300mph right?

[TC]

This is becoming so comical. What am I missing?... I thought a long-stroke mill takes the same amount of "time" to rotate one revolution as a short-stoke mill if they're operating at identical rpm's? While you'll have different bearing speed... the "time" is the same.

Boys and girls... again this is what happens when you're self taught and the teacher doesn't know shit. TC logic and theories = Clown.

Never mind, you are so far off kilter from what I'm trying to say, that no matter how I explain it your never going to understand it..... I'm figuring your feeble mind can't grasp the concept.......

[squirrel]

Never mind, you are so far off kilter from what I'm trying to say, that no matter how I explain it your never going to understand it..... I'm figuring your feeble mind can't grasp the concept.......

Seriously...what ARE you trying to say?

[TC]

Seriously...what ARE you trying to say?

It's all about the acceleration of the crankshaft, how quickly it turns to reach a certain rpm and since a short stroke has less of a distance to travel it will spin faster than a longer stroke when equal forces are applied to the pistons....... Basically the shorter stroke will peak rpm's faster because it has a shorter distance to travel....... A longer stroke requires more power to complete a rotation in the same amount of time as a smaller stroke needs......

The rod journals spin in a circle, it takes time and energy to get around that circle if you increase that circle you increase the distance that needs to be traveled around that circle and the only way to not increase the time it takes to get around the circle is to increase the speed at which the circle is traveled, and to increase speed you need to increase the energy spent.......

Basically saying that a 350 can rpm faster than a 454.........

Or at least that is how I see it.........

[38P]

Rev it up!

Most certainly, the acceleration and deceleration of any mechanical drive "system" (i.e. engine reciprocating assembly, flywheel/flexplate, clutch/torque converter, transmission, driveshaft, differential, axles, wheels and tires) is going to be materially affected by the mass and inertia of parts, the torque imput, and the resistance to work (mass of the car, aerodynamic loads, traction, etc)

With that in mind, an engine with heavy parts and lots of "inertia", such as an old long-stroke racing engine of the 1930s, likely consumes more power in accelerating its own reciprocating mass and thus has relatively less "surplus" torque for acceleration than an engine with lighter, lower inertia parts. This same theory somewhat underpins lightweight flywheels, smallish Honda bearings, aluminum rods and other mass/inertia reductions.

The early sale pitches for Kettering-style V8s in historical hot rodding literature often discussed how much quicker relatively short-stroke OHVs "reved" than undersquare flatheads. Of course superior breathing and higher specific power had more to do with this than bore and stroke. But certainly anyone who has experienced a DOHC F1 mill or even a modern sport bike likely has a developed appreciation for how quickly an efficient low-inertia engine can gain rpm under optimal loading conditions.

Obviously stroke is only one factor. And considering how long the long vs. short stroke debate has raged (50+ years), it likely will not be resolved with another "wee match" on BS.

[38P]

EVERY guy wants to build a high RPM engine, some even try, 90% of them give up because they can't figure out all the little hurdles to overcome, and since no one talks about those in magazine articles or advertisements - well, those guys never find out until it's too late.

I hesitate to mention that there are a fair number of "high-rpm" OEM engines for sale with a payment book and a warranty, such as the BMW M3 V8 and the Boss 302 . . . .

[TC]

Most certainly, the acceleration and deceleration of any mechanical drive "system" (i.e. engine reciprocating assembly, flywheel/flexplate, clutch/torque converter, transmission, driveshaft, differential, axles, wheels and tires) is going to be materially affected by the mass and inertia of parts, the torque imput, and the resistance to work (mass of the car, aerodynamic loads, traction, etc)

With that in mind, an engine with heavy parts and lots of "inertia", such as an old long-stroke racing engine of the 1930s, likely consumes more power in accelerating its own reciprocating mass and thus has relatively less "surplus" torque for acceleration than an engine with lighter, lower inertia parts. This same theory somewhat underpins lightweight flywheels, smallish Honda bearings, aluminum rods and other mass/inertia reductions.

The early sale pitches for Kettering-style V8s in historical hot rodding literature often discussed how much quicker relatively short-stroke OHVs "reved" than undersquare flatheads. Of course superior breathing and higher specific power had more to do with this than bore and stroke. But certainly anyone who has experienced a DOHC F1 mill or even a modern sport bike likely has a developed appreciation for how quickly an efficient low-inertia engine can gain rpm under optimal loading conditions.

Obviously stroke is only one factor. And considering how long the long vs. short stroke debate has raged (50+ years), it likely will not be resolved with another "wee match" on BS.

I wish I could be as good with words as you are Speedy....Well Said........

[dieselgeek]

A longer stroke requires more power to complete a rotation in the same amount of time as a smaller stroke needs......

Absolutely incorrect. You can't state that. The longer stroke requires MORE DISTANCE TRAVELLED but you can't say it requires more force. FOr the ninth time, it's getting old telling you how this all works. THe issue with you and the rest of us here is MOST DEFINITELY NOT that your "theories" are advanced or out of the box - the issue is that you base these ideas on incorrect understanding of physics. Of course your ideas sound awesome - because you never bothered to learn the Basics first... newsflash, that does NOT make you smarter than everyone else here. In fact quite the opposite is true.

The rod journals spin in a circle, it takes time and energy to get around that circle if you increase that circle you increase the distance that needs to be traveled around that circle and the only way to not increase the time it takes to get around the circle is to increase the speed at which the circle is traveled, and to increase speed you need to increase the energy spent.......

No mention that the longer stroke has more leverage on the crankshaft, thus makes more torque per energy spent pushing on the piston? LAME.

Basically saying that a 350 can rpm faster than a 454.........

You can't state that in general either. And WHO GIVES A SHIT which engine can "free rev" faster? meanwhile, what about the hundred other factors you are leaving out? rotating assembly mass? You keep talking about "rpm faster" but you have yet to state where and when this would benefit anyone. You aren't even making any kind of claim that can be discussed or debated...

Or at least that is how I see it.........

And you see it wrong, period. No ifs ands or buts, no "we don't understand" - you do drugs and it screws up your brain, and these lame ideas are the result. It's not us - it's you. Period.

[dieselgeek]

And for the love of God:


Warning!!!!!! This Member is 75% of the time thinking of theories that do not coincide with yours and are generally outside the box, 25% of what he says is along the main stream of what other people think, it is not that he disagrees with you, it's that he thinks differently than you........


Let me add this.

WARNING! That member doesn't know the meaning of the word "theory" either.

[squirrel]

It's all about the acceleration of the crankshaft, how quickly it turns to reach a certain rpm and since a short stroke has less of a distance to travel it will spin faster than a longer stroke when equal forces are applied to the pistons....... Basically the shorter stroke will peak rpm's faster because it has a shorter distance to travel.

I guess if you're trying to get a crankshaft spinning as quickly as you can, then this might be worth discussing.

Longer stroke = more intertia in the crankshaft that you have to get moving
Longer stroke = more distance the pistons and connecting rods have to move
Longer stroke = more torque available on the crankshaft (due to the longer "arm") to get it moving

How about if you put some numbers on it? Do you know how to calculate the moment of inertia of a crankshaft?

[Bob Holmes]

Well, I guess I'm weird. I want the lowest "revving" engine that will get me to my goals.

I don't make enough money to want to rev the wee out of an engine.

[38P]

Don't have the formula handy, but this one

reads how I recall it:

http://www.thecartech.com/subjects/auto_eng/car_performance_formulas.htm

meq = equivalent mass of rotating parts [kg]

= [ Iw (1/rw)2 + Ip hf (if /rw)2 + Ie ht (if ig / rw)2]

where:

Iw = polar moment of inertia of wheels and axles ≈ 2.7 [kg m2]

Ip = polar moment of inertia of propeller shaft ≈ 0.05 [kg m2]

Ie = polar moment of inertia of engine ≈ 0.2 [kg/m2] + polar moment of inertia of flywheel and clutch ≈ 0.5 [kg m2]

hf = mechanical efficiency of final drive

ht = mechanical efficiency of transmission system (hg x hf)

ig = gearbox reduction ratio [ig1 or ig2 or