Is there any advantage to long stroke short bore engines from a performance standpoint...

The flywheel storing energy, the firing of another cylinder, and, yes, the length of the crank throw.

So the longer crank arm is working as just another inertial battery. Well, that explains a lot.

Since so far Veeky Forums has had a few people answer questions quickly, why hasn't anyone used diesel's mechanical fuel injections with petrol engines (before electronic fuel injections)? And if there were such a thing, why didn't it took off?

>small inlet size reduces total volume that can be moved

Relatively, damn glad you acknowledged piston acceleration (never figured I'd see someone on Veeky Forums who understands it), though- But while sheer flow is important there's a reason the crazy tunnel ports of old went the way of the dodo, charge velocity at the port. When you deal in an extremely short of period of time like a high-RPM combustion event, the window for packing the cylinder gets smaller and smaller so port shape and relative size to optimize that velocity plays a big role.

You're spot on with your shit, just figured I'd chime in on a caveat.

It was an option in a variety of situations, but it wasn't super reliable nor particularly good for mileage. The top of the line chevy v8s in the 60s had mechanical injected options, for instance.

Fresh fruit juice

Mechanical injection has totally been used on gas engines, it's just that it's really only good on gas engines for WOT since it's pressure sensitive to the RPM of the engine. Diesels can get away with it because they don't mind not running at a stoichiometric AFR (they can go to some ridiculous 70:1) whereas in a gas engine things get dicey at 15/16/17:1

SBC Hilborn stack injection usually run on a sprint car, for instance.

waybuilder.net/sweethaven/MechTech/Automotive01/?unNum=1&lesNum=3&modNum=1
a foot pound of work is different from a foot pound of force
I had used the wrong terms

Right, i forgot. Fuel pressure plays a big role so its better to use something electronic that keeps pressure regardless of RPM. I beat myself for not thinking about that before (studying to be a car mechanic).

But what about performance? i mean, counting on the RPM issue of pressure, wouldn't mechanical fuel injectors provide higher performance and maybe reduce crank walk/misfire at high temps?

For all out wide open performance where getting as much fuel to the engine is your concern, mechanical injection excels, they use it on top fuel dragsters and nitro funny cars to this day. As far as RPM? Well that's not really something fueling has a whole lot of sway over, nor does fueling have anything to do with crank walk. And when you say misfire do you mean detonation or knock? Because misfire is failed ignition, like fouled plug (which mechanical injection would probably exacerbate) or burned plugwire, plugwires arcing to something or a dead plug. Detonation has to with timing and the quality of your gas first and foremost. Yeah if a carb isn't tuned right and the bitch goes lean, THEN that can result in detonation, but pissing enough fuel usually a problem carbs run into.

>quality

Octane is what I meant.

thanks for the input
I still don't quite understand mass flow and timing events in detail

>tunnel ports
wrljet.com/fordv8/tp302.html
I had wondered how a push rod operated engine can get the most out of being cross flow

What i meant is that even without the spark plug the engine could get hot enough (specially in a race car) that the carbed mix could help make the detonation happen before the spark plug acts. Mechanical fuel injection (or nowadays, electronic) would prevent that.

So top fuel and funny cars carry mechanical fuel injectors on petrol? that's news to me. Thanks for the info, user. You made me happy.

>timing

There's a lot of theory that goes into but it's all just trying to achieve the most complete and fastest burn of the fuel air charge. "Advance" is just anticipating when the piston is at TDC (the most advantageous time to light the charge off) and SORTA hoping it goes off at the right time. When you advance timing you tend to make more power because you're giving the charge more time to burn, taking advantage of as much of the potential energy as possible.Advance the timing too far and you can be trying to light the charge off when it's coming from BDC, you'd actively be fighting the piston or even push the burning charge back out the intake because the valves aren't closed when the spark is triggered. You can sort of think of advancing timing like leading a shot with a gun. Retarding the timing logically goes the other direction and is usually a measure to prevent against uncontrolled ignition in nitrous or forced induction vehicles. "Base timing" is just the timing of the engine at idle- So if someone says a car has "23 degrees advance base timing" it means the plugs are firing at 23 degrees of crankshaft rotation BEFORE TDC (0 degrees of crankshaft rotation). "Total timing" is the maximum advance that a system controlling ignition timing allows it to reach. They make the timing advance as RPM increases because everything is occurring faster and faster and (like with the gun analogy) you have to lead your target even further

A lot of the confusion surrounding timing can come from "timing curves" which are just how quickly total advance comes in, in what way- On old distributors this would be controlled through weights and a diaphragm hooked up to engine vacuum to read load and it would advance the system accordingly. Different weights change how the timing comes in, smaller ones will change timing quicker but not hold as long, heavier weights let the timing come in slower and there's a million opinions on it and it's more something informed by personal experience and what works with what you're familiar with.

>What i meant is that even without the spark plug the engine could get hot enough (specially in a race car) that the carbed mix could help make the detonation happen before the spark plug acts

That's detonation, or preignition, or knock, or spark knock- Depends on who you talk to.

>Mechanical fuel injection (or nowadays, electronic) would prevent that.

And eh, no, not really. I could see your train of logic, like it might more evenly cool the combustion chamber, but it's really not the case. Octane (octane just being the stability of the gas, how resistant it is to auto-ignition under heat and pressure) of your gas and timing have more to do with that. There's also sometimes cases where a carbon buildup can get white hot and cause detonation.

And top fuel dragsters run nitromethane, funny cars USUALLY run methanol but sometimes run nitro.

Sheit, you're studying to be a mechanic? Fuck that, should be an engineer, you're brighter than 90 percent of the fucks I went to school with.

Higher comp, more torque.
Can't rev as high though.

I think you're thinking more along the lines of a direct injection system.

It's been done in a couple of cars, look up GM's LNF engine, it uses direct injection.

Thanks. But i dont want to study 6 years of pure theoretics. The funny thing about studying 3 years to learn how to work on cars its that i actually get to actually work on cars.

Even if i spend most of my time working on fixing the suspension of an old VW Beetle, i would rather have more of a hands on experience rather than going full EngineeringExplained (i actually like that guy and mean no disrespect) and becoming some sort of genius on math and physics and have no experience touching a car.

My class likes to mock me because i like to understand in a physics way how shit works, or how atoms behave in an electrical current or system, but i just like understanding how something that you were told "it just works" comes from a lot of very easy to understand little things being placed together using physics, magnetism and electronics, and the such.

You can easily achieve high compression with long strokes.

Dont know if its just you americans but it seems like you all forgot that replacing head gasket for aftermarkets really help with compression for higher performance or for a bolt on turbo

6 years for being a Bongland engineer, huh? 4 years for me stateside, until a company wants to pay me to get my Master's. Wasn't actually as much theoretical as you might think, I got to do a lot of hands on design and implementation shit and was always staunch on getting involved with automotive shit. But that could just be a us and specifically my school thing- I dig it, though, to each their own. Hell, the greatest mind in automotive history didn't have anything more formal than a tenth grade education.

And GM's High Feature V6, and a bunch of Mitsubishi engines dating back to the '90s, and Mercedes had it on one of their engines in the '50s.

It's been done on a lot of engines, but only in the last 15 years or so is the technology getting mature enough for it to be reliable.

TORQUE = FORCE x Perpendicular distance of force from the axis of rotation

Longer stroke means bigger distance, thus generating more force. This is the reason why rotaries have low torque output their "cams" are close to the axis of rotation

I just said that longer strokes are better for compression.

I don't know where you got it in your head that I'm an American or said anything about turbo's.

I had a head gasket failure that ripped up the cylinder liners and heat damaged a few other parts
so In the process of fitting new parts I thought to up the performance but it is all mechanical and ohv
the lazy part of me just wants to swap in an ohc or fuel injected engine but that seems unfulfilling

Thats why they rev high

curriculum.vexrobotics.com/curriculum/mechanical-power-transmission/gear-ratios
it concentrates not only force but moment too
mostly observable in the brake and clutch lever
but also the hydraulics system in that a large volume of fluid in the master cylinder moves a small volume in the slave
petrol engines also depend on a differential in forces all be it one of heat and pressure

it does not work quite the same as leverage
but does depend on a sort of ratio

>TORQUE = FORCE x Perpendicular distance of force from the axis of rotation
Indeed
>Longer stroke means bigger distance
Yes, but you have a smaller piston wich generates less force.
Also rotaries have much torque for their displacement, a 13b renesis has abou 170 nm/L or about 100 ft/lb per litre displacement.

Is it possible to have a strokerkit and decently high revs?

If you're stroking (lol) you might as well use the best materials for the bottom end.
360 mopar stroked to 408 will still run to 6k.
The real question is whether or not you'll be making any power or if the valves will be floating.

If you increase the stroke, the pistun has to travel a higher distance, if you rev a engine with high stroke high you will have extreme piston speeds.
If you exceed aa certain speed the oil film will no longerlubricate the piston properly.
Also the crankshaft would be stressed beyond its limits.

>their displacement
???
hemmings.com/magazine/hsx/2008/04/How-Big-Are-Wankel-Engines-/1610620.html

Is there any calculation i can use to calculate where i should put the redline? The engine is a volvo b23 btw

And side loads on the piston. Those increase with stroke

If you would calculate it in a completely different way than anyone else you could call them as big as you claim.

Can't help you there, maybe another user can chime in. I think it's a good rule of thumb to just knock 1k off the current red line. Could be more or less.

also tensile and compressive loads
I just feel it is being misrepresented

Calculate the current piston speed at redline, calculate the rpm your stroked engine would have at the same piston speed.
This calculated piston speed is safe, you could go a bit higher if you do that you would increase the stress on the engine.

And this is why forged internals are a thing.

Mo' strength, mo' speeds.

It is the amount of space the piston displaces in the houseing, the problem is the completly different way a wankel is constructed.
Only if you keep the piston speed in a sane level.

eh....... that's not 100% correct.

Work is torque x amount force over time.

A longer stroke doesn't exactly mean all is good, although expanding gases work better with smaller bores as stated previously, those kind of things can result heavier for the expanding gases to push and a bigger stroke doesn't always mean more force.

The bore/stroke ratio doesn´t change the torque at all, my sub square na econobox gets 93Nm/L or about 69ft/lbs per litre displacement.
A na oversquare wouldn´t get significantly more.

everything changes torque, my friend.

Combustion engines design is complex because fuel and air can behave quite weird changing the parameters a little bit

Bearing & piston skirt wear at the lower points in the stroke
Harder to make it rev high (not that it matters)

Yes it is. That's the reason why you measure it in newton meters or lb-ft.
If you apply force equal to 1 newton on a stick with length 1 meter which is anchored on the other side you will aplly 1 Nm of force

Thats why I wrote "significantly", show me one naturaly aspirated engine with much mure than 93 Nm/L displacement.

If it would inrease your torque it would get more energy out of the same amount of fuel.
If that would be possible econoboxes would run insanely long strokes.

insanely long stroke would have more friction loss
and having a shitload of torque isn't always great since it stress every component more

That's the idea behind the "atkinson" cycle Toyota uses in the Prius engine.

It will have higher torque values but the fuel economy may be worse due to higher friction. Also to maintain the torque through the whole revolution of the crankshaft you will need more power which means more fuel

The atkinson/miller engine has a high symetric compression ratio, not a high stroke.
The idea behind the atkinson cycle is to have a higher expansion than compression ratio.
>higher torque values
Show me one NA engine with long stroke that has significantly more torque per litre than my NA undersquare econobox engine.

K20A
With 86mm bore and 86mm stroke have 100 Nm/l

Wich isn´t much mure than my econobox.

Also that isn´t a long stroke, its a square.

More gears create more complexity, and more points of failure.

>more gears
Nope, just other gear ratios.

>muh torque
at low rpm you do not have to worry about friction and balance as much
also oil starvation is a problem with high rpm

We get that you took high school Newtonian physics.
That concept is not complex enough to relate to an ICE.
Nice try though.

Second year STEM student. I am simplifing it to this extend because 75% of the anons here are underage

long stroke is mostly shit for performance, although it can mean you can run flat top pistons and still have good compression

maybe this shit I threw together in paint helps

forgot image

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IDK, my 4cyl yj runs at a way lower rpm then my friends 4cyl 4runner that has a much shortter stroke and it's pretty noticeable the power at lower rpms, regardless of the fact that his is a 2.7lt and mines only 2.5 they 2.5 with a longer stroke is more powerful on low end, while the short has way more top end and can just keep going.

I get it. But it isn't about one vs the other. Remember. Travel/track vs Torque. Long strokes might be able to move the crank at high speeds easier (removing the valve float and friction losses) but that means that its gonna need to go at a higher RPM to deal with the same amount of HP.

You won´t gain anything with a long stroke, your torque will allways be around 100Nm per litre displacement.
You could only change the specific torque by forced induction.

>You cant put torque without creating work.
Oh dear...
Do you know what differential equations are?

...

SHORT strokes are key when it comes to moving the crank at high speeds. That's why sportbikes that rev 14k+ usually have a bore about 50% greater than the stroke.

Mostly correct and a good rule of thumb. But very large bore relative to stroke allows for bigger valves than a more narrow longstroke bore (more surface area), so in very high revving applications you will see higher numbers.

Indeed, short strokes are capable of high rpm.
I just wrote you wont gain anything in a long stroke.
But you won´t gain torque in a short stroke either, you will just be able to keep the torque up to higher rpms and therefor have more power.

No, this is horsepower.

Torque is force x Perpendicular distance of force from the axis of rotation. Given that the force is applied in a 90 degree angle on the axis of rotation.

This would be ideal for sportbikes. But for any engine thats gonna operate under heavy load, having a strong torque pull from a long bore is more important than beeing able to maintain power over a large rpm band.

The piston and other internals are more stressed in a long stroke than in a short stroke.
Also the short stroke can have the same low end torque as the longstoke.

In this case, the bore has to be euqually as large as the stroke would be. I dont think this is ideal, especially not in a diesel engine where the long stroke is essential for the fuel burning process.

That's like saying a petrol can have the same low end torque than a diesel. yes. "it can", but the point is proven.

Just like Diesel is able to provide more torque at ignition than petrol, small bore engines are easier at expansion by the ignition. and due to the lenght of the crank arm, while they have issues at higher RPM since there will be more movement inside the engine, the piston will be able to move the crank with more torque easily.

Valve float and friction of the internals are not a base issue of the core principle of bore vs stroke in displacement, but problems with the way internal combustion engine is made. Shorter crank arm will allow for the engine to work at higher RPM easier, and ALSO higher bore rather than stroke will reduce valve float and also allow for higher RPM, but long stroke does provide better power in the end. That being said, in nowadays tech, having a bigger bore than stroke for a performance engine or your tuned up shitbox is just common sense.

Oversquare is less thermally efficiency than undersquare.
Oversquare is less tolerant to ignition timing before knocking.
Undersquare has mechanical advantage vs oversquare at the crankpin.
Oversquare can fit larger valves relative to cylinder disp.
Oversquare is usually accompanied by longer rods and better rod/stroke ratio.
Undersquare exposes combustion flame front to less surface area than oversquare (surface to volume ratio) thus less cooling/quenching = better burn and efficiency.
Undersquare has higher piston speeds and longer travel per stroke, thus piston speed and acceleration will be primary limiting factor, nevertheless the piston will be smaller and lighter.

The Ideal bore/stroke ratio for a gas engine is a bit undersquare, for diesel it is square or a bit longer to create a better burning chamber at high compression ratios.
A diesel engine of the same sieze as a petrol engine will have less torque since it can´t burn the air copletely while the petrol engine does that, assuming both are naturaly aspirated.
>due to the lenght of the crank arm, while they have issues at higher RPM since there will be more movement inside the engine, the piston will be able to move the crank with more torque easily
You forget about the lower piston surface eich will lead to a lower force to begin with wich cancels out the longer crank arm.
You won´t find a 4-stroke engine without forced induction capable of much more than 100Nm.

>Oversquare is less thermally efficiency than undersquare.
It may be a little bit more thermaly efficient, but it looses that tiny bit in higher mechanical losses
>Oversquare is less tolerant to ignition timing before knocking.
Knocking occures if you run fuel with to low octane rating, modern ECUs can compensate that with preignition.
>Undersquare has mechanical advantage vs oversquare at the crankpin.
Indeed.
>Oversquare is usually accompanied by longer rods and better rod/stroke ratio.
Indeed, but the side forces per surface area on the piston are stll higher than on a undersquare.
>Oversquare can fit larger valves relative to cylinder disp.
Indeed, wich is why they tend have better high rpm performance.
>Undersquare exposes combustion flame front to less surface area than oversquare (surface to volume ratio) thus less cooling/quenching = better burn and efficiency.
That is basicly point one.
>Undersquare has higher piston speeds and longer travel per stroke, thus piston speed and acceleration will be primary limiting factor, nevertheless the piston will be smaller and lighter.
The Piston might be lighter, but the crankshaft and conecting rods will be heavier.

No

>It may be a little bit more thermaly efficient, but it looses that tiny bit in higher mechanical losses
What do you mean mechanical losses..Friction? There is less friction with a smaller bore, piston and rings, but a longer stroke so can break it even, but again the undersqaure is (should be) turning less RPM for the same HP. And that's all well before we consider the thermal efficiency by surface cooling, which is superior.
>Knocking occures if you run fuel with to low octane rating, modern ECUs can compensate that with preignition.
Yes, basic. With a larger bore, the combustion chamber is larger and flame speed higher. Undersquare requires as much as 10° more advance than does an equal displacement oversquare.
>Indeed, but the side forces per surface area on the piston are stll higher than on a undersquare.
Yes, side loading is worse for undersquare with the same deck height. I don't like low rod ratios, that's one reason why. Some manu's do a proper job and increase deckheight and rod length for a better rod ratio. Some don't.
>The Piston might be lighter, but the crankshaft and conecting rods will be heavier.
That's okay since the crank is rotating mass, the rod generally not much heavier as only the beam is extended (and only by a few mm usually)

Each one has it's place but it's no wonder production car manufacturers choose undersquare configs mostly, because efficiency and drivable torque.

Checkd

> less friction with a smaller bore, piston and rings, but a longer stroke so can break it even
Nope, the piston sieze grows by square while the displacement grows cubic, so you would still have more friction.
>less RPM for the same HP
Since it can´t generate more torque than a undersquare it won´t produce more HP at low RPM.
both types of engine will get you about 100Nm/L.
> Undersquare requires as much as 10° more advance
Wich is why some manufacturers use 2 sparkplugs, also that isn´t knocking.
>loading is worse for undersquare
It isn´t, since you have a larger piston area taking the force wich is actualy simmilar, but it is depending more on the conecting rods.
>the rod generally not much heavie
It will have more side movement and will be heavier wich will result in higher forces, als the small piston can´t take as much force as the bigger one.

>point 1
Reminder: piston ring friction is the primary source of friction in an ICE
>point 2
Undersquare engine will produce more HP at a lower RPM than oversquare, not the other way around. I didn't imply the latter. Therefore less ring lapping and associated losses.
>point 3 - (2 spark plugs)
That's not a standard practice- at all, and doesn't help with knock threshold. More advance on the undersquare not only allows more burn time around TDC for better combustion, it harnesses more heat before it can be wasted to conduction.
>It will have more side movement and will be heavier wich will result in higher forces, als the small piston can´t take as much force as the bigger one.
Oh, you were doing good until this one.
Larger pistons don't take higher forces better than smaller pistons, that's not even a general rule. Larger pistons require more and larger gusseting. That and the basic fact that they're bigger makes them heavier as well.
Oversquare needs the longer, heavier rod, not undersquare.
With displacements equal:
High rod angularity means a shorter, lighter rod and smaller lighter piston.
Lower rod angularity means longer, heavier rod and wider heavier piston. I hope that's what you were saying...

>piston ring friction is the primary source of friction in an ICE
Indeed, but if the piston ring gets almos insignificantly smaller and the distance it travels grows significantly you will gain friction.
>Undersquare engine will produce more HP at a lower RPM than oversquare, not the other way around. I didn't imply the latter. Therefore less ring lapping and associated losses.
Undersquare means lower stroke than bore, you cant produce more than the ~100Nm a undersquare produces.
>not a standard practice- at all
On cylinders over 500cm3 it isn´t unusual, on smaller ones the benefit usualy isn´t significant at normal rpms.
The knocking tendency is the same on both systems, assuming you have the same fuel, compression ratio and manifold pressure.
>Larger pistons don't take higher forces better than smaller pistons
The oil film will be under a lower stress when the sideforces are pushing on a higher surface, wich results in lower wear.
>Oversquare needs the longer, heavier rod, not undersquare.
wich generates more sideforces on a smaller piston.
Wich is why short strokes are popular, since the lower side forces go to a higher surface.

you guys crack me up

pic related is you