De-Stroking a KA and efficiency minded modifications

[420sxse]

DeviousKA: I saw a reference to a de-stroked setup you built: (...). Did you use the KA rods? What transmission would be aproptiate for an s13? How difficult is it to attach the Altima KA head? Also, when you say the setup is fully balanced, do you meanyou had the rods and piston weight matched?A bit of context for y'all: I'm considering a project with a mind towards efficiency...not only simple fuel economy, but more importantly engine efficiency (volumetric and thermal) and weight savings. Some ideas: de-stroke, PnP, light flywheel, knife edged crank, light crank pulley (can get away with it since the z20 crank is fully counterweighted), insulating the intake plumbing, a small turbo (I know, I know, but they are efficient) for instance. I have heard that I/H/E can increase efficiency. I am also thinking about a carbon fiber hood, light wheels, and perhaps some other minor weight savings (but a full interior). Perhaps aero mods to reduce coefficient of drag but that would be difficult, as I doubt many aftermarket body mods are tested for anything but style. My goal is to increase performance over stock (or at least not degrade it) and increase MPG (SAE 22/27). I have no set power or economy goals...it depends on what balance I decide to strike, but I wonder how much power I could get before I have to sacrifice fuel economy. I bet it isn't much, and economy would depend on how the car was driven. That's one of the main ideas behind the turbo consideration. What do y'all think? Any ideas/concerns?
Modified by 420sxse at 9:45 PM 3/12/2006

[InsanityInc]

Uh... longer stroke is better for daily driving fuel efficiency as far as I know. Also, high volumetric efficiency and high fuel efficiency are impossible to achieve simultaneously (unless you have a diesel engine, of course).

If you use parts such as a larger intake and exhaust, your daily driving fuel economy will increase due to decreased volumetric efficiency under daily driving conditions (also, because a non-CAI will suck in hot air which is very good for fuel efficiency).

[deviousKA]

I have 2 of these 2140cc kaZ sitting on stands waiting for a coulple more g's worth of parts. Im not going to go in depth on their design, it would be to easy for someone else to copy and to claim they created it. I already have enough problems with a few datsun shops and magazine articles that have flat ripped me off design wise, and took all the credit. Im not one to usually say something like this, but in the realm of custom nissan/datsun engines I hold the info tight.

I have said way to much here on nico already, sorry. Im not going to go into my special rod/piston combo, all I can say is that it is primo.

You can find some oem or aftermarket forged datsun rods and some custom forged pistons to go with the setup, just do your research and determine if the characteristics are in line with your plan.

Like InsanityInc mentioned, something like this is far from efficient daily driver wise in a huge 240sx. They are designed for top end and require as much work into the drivetrain as the engine itself.

[91RMKS13]

What transmission would be aproptiate for an s13?

i think the transmission from a silvia or a 240sx would work well in an S13

[420sxse]

Thanks for the input. As far as de-stroking goes, my reasoning was that the decrease in displacement would use less gas as a base, and possibly compensate for the power loss with forced induction. I don't know how sound this theory is, and from the response from InsanityInc and deviousKA...it sounds like it wouldn't be worth it? From a daily driver/economy standpoint, I mean (not necessarily work/headaches involved). I am most interested in methods of increasing thermal efficiency. And according to InsanityInc, I am a bit backwards on my thinking about volumetric efficiency. The non-CAI would increase thermal efficiency (as does warming the gas, using a lower octane rating, and upping the compression ratio). So the bit about insulating the intake plumbing (I was also thinking CAI with it)...would not be good. I should have realized that...cold air is denser...will help HP, but only because more air and fuel can be crammed into the chambers, right? I still need to reaserch and decide what I want to risk as far as potential detonation issues, as increased thermal efficiency leads down that path. I am still reading and considering options (both turbo and N/A). I am far from beginning a project. I am just thinking in writing about possibilities. Also, I know this is the N/A forum, but I wanted N/A views on these issues (knowing that adjustments must be made if I do decide to turbo).deviousKA: I understand completely. Thanks for all the info anyways. I guess I'll just have to read up some (a lot) more. I'll have to look up those articles j/k. People who steal the ideas of others often don't translate those ideas well.

[InsanityInc]

Thanks for the input. As far as de-stroking goes, my reasoning was that the decrease in displacement would use less gas as a base, and possibly compensate for the power loss with forced induction. I don't know how sound this theory is, and from the response from InsanityInc and deviousKA...it sounds like it wouldn't be worth it? From a daily driver/economy standpoint, I mean (not necessarily work/headaches involved).

Using more gas isn't why larger engines get worse economy. To achieve the desired acceleration for street conditions, larger engines generally aren't using their greater capacity. The reasons are a few fold. First and foremost is just reciprocating losses. You have 8 large pistons as opposed to 4 small ones, that takes more power.

The other reason is less recognized by people, but is a very important one, is simply that for a given volume of gas, a larger combustion chamber will have a lower compression pressure. This is simply because if you compress 1 mole of oxygen into an 80cc combustion chamber at a given temperature, the pressure will be SIGNIFICANTLY lower than the pressure of 1 mole of oxygen in a 30cc combustion chamber. And as you've stated (and is common knowledge) compression pressures have a very direct relationship to fuel economy. However, combustion chamber volume is far more dependent on engine BORE than engine stroke.

Therefore, the two main reasons why larger engines are less efficient are not addressed when destroking an engine. Your reciprocating losses are basically the same, and the combustion chamber stays the same size.

Quote »So the bit about insulating the intake plumbing (I was also thinking CAI with it)...would not be good. I should have realized that...cold air is denser...will help HP, but only because more air and fuel can be crammed into the chambers, right?[/quote]Exactly. Cold air is denser. However, for efficiency dense is very bad, because it means your pressures are lower for a given amount of air.

[pregmantis]

I agree wit you on the parasitic losses of bigger, heavier ratating mass but I dont think thats why bigger engines use more gas. I would think they use more gas because they pull in more air/FUEL mixture.

[420sxse]

Using more gas isn't why larger engines get worse economy. To achieve the desired acceleration for street conditions, larger engines generally aren't using their greater capacity. The reasons are a few fold. First and foremost is just reciprocating losses. You have 8 large pistons as opposed to 4 small ones, that takes more power.The other reason is less recognized by people, but is a very important one, is simply that for a given volume of gas, a larger combustion chamber will have a lower compression pressure. This is simply because if you compress 1 mole of oxygen into an 80cc combustion chamber at a given temperature, the pressure will be SIGNIFICANTLY lower than the pressure of 1 mole of oxygen in a 30cc combustion chamber. And as you've stated (and is common knowledge) compression pressures have a very direct relationship to fuel economy. However, combustion chamber volume is far more dependent on engine BORE than engine stroke.Therefore, the two main reasons why larger engines are less efficient are not addressed when destroking an engine. Your reciprocating losses are basically the same, and the combustion chamber stays the same size.

First, the point about extra mass/moving parts; yes. However, the assertion that more cylinders don't induce more air is ridiculous. How the hell can a 5L V8, for instance, not generally take in more than a 2.4L I4? What you are saying in the second paragraph, I take it, is that the engine is most efficient at WOT, but not necessarily most economic. That the compression ratio drops under normal driving conditions, because the plate in the TB restricts the air...the cylinders do not fill up to their full capacity. Therefore the C/R drops. Are you suggesting this loss of compression wouldn't be true of any engine? Also, ignition timing is not constant these days, so I am not buying this. With less throttle, the E.C.U. simply needs to ignite the mix closer to TDC to achieve more compression. Further down under WOT to decrease compression. I suppose it's possible the degree of latitude isn't enough to fully compensate. I see your point about the combustion chamber staying the same size, though.

[InsanityInc]

First, the point about extra mass/moving parts; yes. However, the assertion that more cylinders don't induce more air is ridiculous. How the hell can a 5L V8, for instance, not generally take in more than a 2.4L I4?

Because you have a magical little device called a throttle body. You get to control how much air goes into your engine. A 427 at idle pulls less air than a geo engine at WOT.

Quote »What you are saying in the second paragraph, I take it, is that the engine is most efficient at WOT, but not necessarily most economic. That the compression ratio drops under normal driving conditions, because the plate in the TB restricts the air...the cylinders do not fill up to their full capacity. [/quote]Exactly. In general, bigger engines aren't making more power under daily driver conditions, for a given vehicle weight anyway.

Quote »Therefore the C/R drops. Are you suggesting this loss of compression wouldn't be true of any engine?[/quote]No, I'm just saying it's a much greater drop for larger engines, hence the worse economy. The same amount of air in a larger cylinder produces less pressure, that's just a scientific fact.

Quote »Also, ignition timing is not constant these days, so I am not buying this. With less throttle, the E.C.U. simply needs to ignite the mix closer to TDC to achieve more compression. Further down under WOT to decrease compression.[/quote]Now you're mix and matching terms. I'm talking about COMPRESSION pressure. The pressure BEFORE the mixture is ignited. Ignition timing can only affect combustion pressure, which does have an effect on economy as well since the flame front compresses the remaining mixture as it travels, but initially all the pressure comes from mechanical compression.

Besides, think about it this way:

If you could easily control compression/combustion pressures to whatever you wanted with ignition timing, then why would engines be made with higher/lower compression pistons? Igniton timing can only do so much.

[InsanityInc]

I agree wit you on the parasitic losses of bigger, heavier ratating mass but I dont think thats why bigger engines use more gas. I would think they use more gas because they pull in more air/FUEL mixture.

So you drive at WOT all the time then?

[UK-SRi]

You lose your licence quicker....

Mike

[InsanityInc]

You lose your licence quicker....

Mike

Poor license economy?

[420sxse]

Because you have a magical little device called a throttle body. You get to control how much air goes into your engine. A 427 at idle pulls less air than a geo engine at WOT.

Be this as it may...let's compare apples to apples. My point was: Doesn't a 427 at idle pull more air than a Geo engine at idle, and a 427 at 2K RPM pull more air than a Geo engine at 2K RPM?

In general, bigger engines aren't making more power under daily driver conditions, for a given vehicle weight anyway.

At WOT, a stock LT1 is putting around 130hp to the wheels at 2.8K RPM (in a '97 automatic Camaro). A KA24DE at WOT puts about 70hp to the ground at 2.8K (in an s13). I would have thought that similar differences would be seen at partial throttle, but I could easily be wrong.

...I'm just saying it's a much greater drop for larger engines, hence the worse economy. The same amount of air in a larger cylinder produces less pressure, that's just a scientific fact.

I understand what you are saying about what happens when a given amount of air is compressed in different sized chambers, and there can be no debating that point...you are correct...but is that amount of air consistent at any given point of the RPM range between a V8 and an I4? I will have to think about what you say about the greater drop in compression for larger cyllinder sizes. It's been a while since Chem 161.

Your reciprocating losses are basically the same, and the combustion chamber stays the same size.

I get what you are saying here, and agree. I also think I see why a longer stroke might benefit economy now that I think about it. I forgot to mention that. I'm not really considering de-stroking now thanks to you and DeviousKA.I do admit that I'm not incredibly knowledgable, and am still deep within the learning process. Please forgive my ignorance. I was posting this topic to get some ideas and corrections of mine. Thanks for the responses.

[Edub1]

Internal combustion engines are most efficiant (work wise) when they are working their hardest and least efficiant when they are not. The trick is a to use a small very high compression, hard working motor to achive this.

You want efficiant, have a look at a 1L motor from a crotch rocket.

Put something like that in your car and you would have a quick 40MPG 240

[InsanityInc]

Be this as it may...let's compare apples to apples. My point was: Doesn't a 427 at idle pull more air than a Geo engine at idle, and a 427 at 2K RPM pull more air than a Geo engine at 2K RPM?

Not necessarily. Depends on the throttle position.

Quote »At WOT, a stock LT1 is putting around 130hp to the wheels at 2.8K RPM (in a '97 automatic Camaro). A KA24DE at WOT puts about 70hp to the ground at 2.8K (in an s13). I would have thought that similar differences would be seen at partial throttle, but I could easily be wrong.[/quote]Yeah, at an EQUAL throttle position. But if you want to accelerate with 70hp worth of power, you aren't going to be at WOT in the LT1. People accelerate around town with a fairly equal amount of power (usualy only about in the 20-40hp range). If you have a bigger engine, you simply don't apply the gas as hard to reach that level of power.

Quote »I will have to think about what you say about the greater drop in compression for larger cyllinder sizes. It's been a while since Chem 161.[/quote]It's a lower pressure, specifically.

PV=nRT

All things constant on the right, if V is bigger, then P must be smaller.

[pregmantis]

edub, I would think that if you put a motorcycle engine in a 240 it would be very slow and eat alot of gas....it would prob detonate itself to death

[Edub1]

Well, considering that these motors make about 185HP I think you'de be ok.

Mainly, It's an example. The general concept of fuel efficiancy involves making an engine as small and powerfull as possible.

It's the same thing as building for performance. In fact, top fuel dragsters on a HP Vs fuel basis are far more efficiant than anything on the street. Jet engines are even more fuel efficiant. If you could match that efficiancy, you would have 250HP from a 0.25L motor. Only it wouldn't be streetable, of course.

There are issues of practicality here but the point is that raising the eficiancy of a motor is the same for fuel efficiancy and for power. The difference is that for fuel efficiancy you use the smallest possible motor. Hence my crotch rocket analogy.

[InsanityInc]

It's the same thing as building for performance. In fact, top fuel dragsters on a HP Vs fuel basis are far more efficiant than anything on the street. Jet engines are even more fuel efficiant. If you could match that efficiancy, you would have 250HP from a 0.25L motor. Only it wouldn't be streetable, of course.

There are issues of practicality here but the point is that raising the eficiancy of a motor is the same for fuel efficiancy and for power. The difference is that for fuel efficiancy you use the smallest possible motor. Hence my crotch rocket analogy.

You're confusing fuel economy and chemical efficiency. The CHEMICAL efficiency of a turbine engine is better than an otto cycle engine. The CHEMICAL efficiency of an otto cycle engine is best at WOT.

The FUEL economy? Both ridiculously low. Just look at rotary engines. Since they're only 1.8L, they should get really great fuel economy, right?

Wrong. They get **** for fuel economy.

Here's a tiny, tiny turbine:

http://72.14.203.104/search?q=...&cd=7

Produces 17.62lbs of thrust.

Fuel consumption? 200g/min. That converts to 26 lbs/hour, or 4.16 gallons per hour. Let's say that SOMEHOW that 17.62lbs of thrust managed to get you to 60 miles per hour. That means that your fuel economy would be 14.4 miles per gallon.

Terrible economy. In reality, it would likely be even worse because I doubt 17.62 lbs of thrust is going to get you anywhere NEAR 60mph. Probably closer to 20mph, at which point you're getting 4.8mpg.

Case in point: maximum chemical efficiency DOES NOT equal maximum fuel economy. There are diminishing returns. Essentially, if you're burning more gas to get more chemical efficiency, you're going to lose out on economy VERY quickly, because the additional gas burned will outweigh the economical gains.

[Edub1]

There are generally two reasons people post on these borads. One, is to exchange ideas. The other, is simply to engage in verbal arm wrestling. It is clear to me that you are here for the latter.

I do not mean this as an insult in any way. It is just an observation.

I have noticed that you speak of concepts that suggest that you have some technical knowledge. However, it seems that for some reason the concepts of which you speak tend to be missapplied and conveluted. Again, I don't mean this as an insult. I am just a little curious as to how this happens.

My guess is that you are so hyper focused and so intent on proving others wrong that your brain enters some sort of "constructive processing" in which you see imagined scientific support for your arguments and become incapable of comprehending the other persons point.

The points I raised in the above post are factual - this should be obvious. I'm not going to try to convince you of this because I know it would be futile.

Let me reiterate that this is not an insult or a personal attack. I'm just trying to make you aware that many of your arguments sound completely conveluted and irrational to those of us who with technical knowledge.

If I'm right, and you do in fact understand the concepts of which you speak - slow down, relax and try to give some thought to what others are saying. This is not a competition. We are here to exchange ideas, not to engage in verbal arm wrestling.

[InsanityInc]

If I'm right, and you do in fact understand the concepts of which you speak - slow down, relax and try to give some thought to what others are saying. This is not a competition. We are here to exchange ideas, not to engage in verbal arm wrestling.

It's very simple, really.

Drive around at WOT all the time. Does your gas milage get better, or worse?

Chemical/Thermal efficiency is NOT 1:1 with fuel economy in a gasoline engine.

See, you add more air, this obviously increases the pressure in the cylinder which is a good thing. Unfortunately, in order to avoid knock you have to put more fuel into the cylinder so you aren't running incredibly lean. Therefore, unless the thermal efficiency gained outweighs the larger amount of gas you're using (hint: it doesn't), your fuel economy will go down even if your thermal and chemical efficiencies go up. And this doesn't even take into account reciprocating losses and whatnot, which further decrease economy at larger cylinder volumes.

In a diesel engine, you don't have the lean burn problem anymore really, due to the advent of direct injection. This is why diesel engines are not throttled. Since you don't have to add more fuel to go along with the air, you get better efficiency by running at WOT.

Honestly, just drive around at WOT and see if your fuel economy improves. According to you, it should.

[Edub1]

I'm not going to get into a debate on this - it's real simple.

An internal combustion engine is most efficiant when working its hardest.

"Efficiant" means the amont of work done vs the amount of fuel used.

Increasing performance and increasing efficiancy are one in the same. For efficiancy, a smaller, better performing motor is used. For performance, a larger one.

Of course a given motor will use more fuel under WOT but it is doing more work.

Think of it this way - for two motors of the same design, doing a given amount of work, the smaller, harder working of the two will do said work using less fuel.

This is an irrefutible fact. There are no two ways about it. If you stop and think about it for a while you will see that this is so. If you are simply intent on winning an argument you can go ahead and invent a non-sensical, contradictory theory.

I'm not going to waste time trying to convince you that 2+2=4.

[420sxse]

Depends on the throttle position.

Yeah, OK, I should have seen that one coming. I should have said "all else being equal, the engine with the larger displacement will use more air and fuel to attain a given performance level". "All else" includes stroke. I do understand that de-stroking an engine will not necessarily increase economy due to factors other than raw displacement.

PV=nRT

My contention (however poorly stated) all along has been that in an internal combustion engine, due to design and function considerations, as V (volume), increases, so does n (a convoluted measurement of mass in grams). The throttle body is probably a lot bigger on an LT1 than on a KA. This is just my version of common sense speaking to me. Talking about the difference between 1 mole of air/fuel mix (at a given ratio ratio) in a 5.7L engine vs. 1 mole of air/fuel mix in a 2.4L one is all well and good, but this is going to happen when there is a wide variance between throttle positions. Now, suck for both banks on that LT1 through a KA throttle body and I agree with you completely.Stock TPI/LT1 48mm Throttle Body w/o airfoil -- 783.0 cfmStock TPI/LT1 48mm Throttle Body w/ airfoil -- 821.9 cfmDoes anyone know what a KA24DE TB flows wide open?

Put something like that in your car and you would have a quick 40MPG 240

It gets 40mpg in the tiny motorcycle? Imagine the weight difference. It'd also be pretty flaccid, torque-wise.

Of course a given motor will use more fuel under WOT {but it is doing more work}.

Hence the part you alluded to about getting the engine small enough to do the amount of work you want at WOT. This would be hyper-impractical in a street car, because it would be impossible to vary your speed much, among other things. If the engine was optimized for around town driving, one couldn't travel more than 25-35 MPH. Acceleration would be a *****, too. But it would be economic to drive around town with that screaming little engine. And everyone telling you to get a new clutch would get old.Now, if one could synch up many teeny-tiny little engines, so that varying numbers were running at any given time at or near WOT, THAT would be interesting. Insanely complex to execute, though.I think most of this makes sense, but I just got off a 12hr shift at 7am, and my brain hurts, So it's probable that I didn't think some of this out well. I'm going to bed instead of doing that.

[InsanityInc]

I'm not going to get into a debate on this - it's real simple.

An internal combustion engine is most efficiant when working its hardest.

"Efficiant" means the amont of work done vs the amount of fuel used.

Increasing performance and increasing efficiancy are one in the same. For efficiancy, a smaller, better performing motor is used. For performance, a larger one.

Allow me to say this one more time for you, because you seem to have missed it the other 5 times I said it:

Economy

And

Efficiency

Are

Not

The

Same

Thing.

[InsanityInc]

Yeah, OK, I should have seen that one coming. I should have said "all else being equal, the engine with the larger displacement will use more air and fuel to attain a given performance level".

Yeah, it will. But the REASON it uses more fuel is due to the lower thermal/chemical efficiency at any given CFM due to the lower cylinder pressures, and the increased reciprocating losses. It simply takes more fuel to put out the same power.

[Edub1]

Moderator - please delete this thread.

There is to much disinformation here and I'm afraid that it might make people stupider.

[InsanityInc]

Moderator - please delete this thread.

There is to much disinformation here and I'm afraid that it might make people stupider.

The only misinformation is coming from you. Seriously, go drive around at WOT all the time and get back to me on your fuel economy.