increasing power of a naturally aspirated engine

[Fleet 500]

I don't like that idea. What you end up with is a heavy engine with big displacement and low power/liter. Case and point - Most of the American cars.

The existing engine can always be bored to increase displacement. That way, you can add more cubes without adding weight.
From what I've read (books on how to increase horsepower), installing a set of headers is just about the single best way to increase horsepower.
After that, I would go with an aftermarket/high performance cam and a bigger carb.
And putting on a set of lower (higher numerically) rear gears, while not adding any horsepower, would help acceleration quite a bit (like going from 3.23s to 3.91s).

[Cyco]

The existing engine can always be bored to increase displacement. That way, you can add more cubes without adding weight.

A bigger bore will require bigger (and therefor heavier pistons) which require heavier con rods to hold them in place which requies a stiffer (heavier) crankshaft so that doesnt flex which will require bigger bearings...........

[johnnynumfiv]

It's called aluminum

[Matra et Alpine]

I am not quite sure if you are talking about eigther making the ports bigger or smaller? However I did give a rough description of how the power curves changed on my engine after treatment. and I wouldn't say 90% was wrong more like 40% of what they thought!

*I* was quoting a comment from David Vizard himself.
I'll let him know you think he's wrong about what he said about what he wrote

In my experiance a well set up Dyno will be far more accurate then a flow bench unless you are talking about something else???

"flow bench" doesn't translate to tehis sindde of the pond.
If you mean a proper ENGINE test bed dyno then it is WAY MORE ACCURATE than any wheel dyno.
Wheel dynos are only ANY use for comparative tests.
They are HORRENDOUSLY inacruate for absolute measurements of engine power.
Even power at the wheels has a high degree of variability

if you are referring to one of the 8 phases I mentioned called Intake Overlap then you misunderstood the meaning. Intake Overlap is the very short time where the exaust is closing and the intake is opening. Almost every Otto cycle engine has this phase! and it has nothing to do with the miller or atkinson cycles! This phase is pretty important when it comes to getting the most out of your engine!

Yep, BUT once you extend the overlap then it isn't an Otto cycle anymore
Hve you checked what miller and Atkinsons cycles were and why the differed from Otto in it's day and WHY modern Otto are actually closer to them than they are to Otto in areas of the rev band. See Otto isnt' the ONLY way to make a ICE work and with VV timing an Otto stops being a "pure" Otto.

[KnifeEdge_2K1]

It's called aluminum

you cant use aluminum for the innards cuz aluminum pound for pound is about just as strong as steel, it's 1/3rd lighter but only 1/3rd the strength

the reason you can use aluminum for chassis in cars and bikes is cuz you can change the strength of the tubing by increasing diameter and hollowing it out, that's what they do with mountain bikes but im not so sure about cars although its prolly something similar

[Fleet 500]

A bigger bore will require bigger (and therefor heavier pistons) which require heavier con rods to hold them in place which requies a stiffer (heavier) crankshaft so that doesnt flex which will require bigger bearings...........

Well worth it. One of my car friends bored out his 340 Mopar engine to 365-cu-in and, along with a cam and headers, has dynoed at 420 horsepower and 450 lbs-ft torque.

[Alastor]

you cant use aluminum for the innards cuz aluminum pound for pound is about just as strong as steel, it's 1/3rd lighter but only 1/3rd the strength

I disagree for many commonly used Aluminum and Steel alloys the Aluminum has about 2/3 the strength of its steel counter parts. Therefore it requires the part to be 1.5 times larger to achieve the same strength, but since it has 1/3 the density the overall weight is about ½ that of an equivalent steel part.

Obviously there are always exceptions, but for many applications a reduction in weight can be obtained by substituting steel for aluminum.

[KnifeEdge_2K1]

I disagree for many commonly used Aluminum and Steel alloys the Aluminum has about 2/3 the strength of its steel counter parts. Therefore it requires the part to be 1.5 times larger to achieve the same strength, but since it has 1/3 the density the overall weight is about ½ that of an equivalent steel part.

Obviously there are always exceptions, but for many applications a reduction in weight can be obtained by substituting steel for aluminum.

size is the whole issue here, you would need a conrod 3 times the size of a normal one if you were to make it with aluminum, im pretty sure that won't fit

[KnifeEdge_2K1]

you can see what im talking about when you look at the tubing used in mountain bikes, steel bikes have tubing that's alot smaller in diameter then alum bikes, as you can imagine that's ok on a bike as long as the tubing doesnt exceed a certain diameter but inside an engine you dont have that much room, titanium is a much better alternative

[johnnynumfiv]

If you used forged pistons, do they need the bigger con rods? I've seen milled aluminum con rods before, they are just chunky looking.

[KnifeEdge_2K1]

the strength of the conrods is directly proportional to how high you can rev, the stronger ur rods the higher u can go

[hightower99]

"flow bench" doesn't translate to tehis sindde of the pond.
If you mean a proper ENGINE test bed dyno then it is WAY MORE ACCURATE than any wheel dyno.
Wheel dynos are only ANY use for comparative tests.
They are HORRENDOUSLY inacruate for absolute measurements of engine power.
Even power at the wheels has a high degree of variability

A flow bench is a device that measures the air flow through the head. I thought you were talking about that now I know that you are talking about strapping the engine to a bench dyno. Yes I agree that bench dynos are more accurate but a well set up dyno that takes the measurement from the wheels isn't too bad at all. (too many people don't take the time required to set a wheel dyno properly) the accuracy can be as good as 95% and that is good enough.

Yep, BUT once you extend the overlap then it isn't an Otto cycle anymore
Hve you checked what miller and Atkinsons cycles were and why the differed from Otto in it's day and WHY modern Otto are actually closer to them than they are to Otto in areas of the rev band. See Otto isnt' the ONLY way to make a ICE work and with VV timing an Otto stops being a "pure" Otto.

well todays motors are not "Pure" Otto cycle motors but they certainly don't use the Miller or Atkinson cycles. It is only a few engines (Mostly race cars) with cams set for large overlap that come close. I know that the Otto cycle is not the only way to get an ICE to work you have mentioned the Miller and Atkinson cycles but there are also the "Leonardo" or compressionless cycle, Two stroke cycle, Diesel cycle(2 and 4 stroke), the Carnot cycle, and of course Bourke's "improvement" of the Otto cycle. I think of the Wankel as using the Otto but many call it a Four-phase cycle. this is not all of the cycles that have been used in ICEs succesfully.

[Matra et Alpine]

well todays motors are not "Pure" Otto cycle motors but they certainly don't use the Miller or Atkinson cycles.

When you look at some of the variable valve modern setups some of them are MUCH further away from Otto
Saab SCC was reportedly allowing 70% of the chamber to be exhaust gasses in low torque conditions !!!

[hightower99]

but even that engine was designed by looking at the Otto cycle even though they use 70% exaust filling in low torque conditions doesn't mean that they are using the Miller cycle or the Atkinson cycle they are trying to improve low torque milage...

granted that it does start to step closer to Atkinson and miller cycles...

[Matra et Alpine]

granted that it does start to step closer to Atkinson and miller cycles...

Which brings us back to the first point
In that condition an engineer would NOT describe it as an Otto cycle
Jsut demonstrates the difficulty of assigning names to the differing cycles when they were clearly vastly different in construction. Variable valve timing with steppers was something Otto, Miller or Atkinson or all those other could'nt have foreseen. SO they built with radically different layouts to make it work that didnt' LOOK anything like Otto.