Increasing Torque

[Eug]

a little long winded, but nicely put Ashley.

[MBS206]

If your memory comes good please post the results up.

I will do... Will have to speak to a few more of the guys that deal with that sort of stuff day in, day out at work...

[HolyEvil]

Had another thought.. would piggy back ECUs like E-Manage http://www.skylinesaustralia.com/forums/in...154016&st=0 help? is there any benefit for a N/A to have a piggy back ecu or a proper standalone aftermarket ecu?

cheers

[Eug]

turbo cars respond better to mods.

NA cars, not so much - gains would be around the 10-15kw territory. basically all you can do is lean out the fuel mixtures and dial in a little more timing.

that said, i've just bought a SAFC to clean up my air fuel ratios...

definitely NOT a bang for buck mod - but definitely helpful.

[mokompri]

i agree with djr.. in simple terms, with a lighter flywheel there is less rotational mass to move, thus meaning it requires less energy/power/throttle to spin. with everything else constant, this means there is less mass for the engine to deal with pushing the car up the hill, this means less throttle required. now where a heavier flywheel WOULD help on the uphill, would be if you were simply coasting up and NOT applying throttle, because you have more stored energy to use up, your car has more momentum/inertia and i think this is where people are confusing seat of pants results with whats really happening.

under a certain rpm the car wont be making enough power to accelerate uphill, and will continously lose rpm, and so requiring a downshift, because there is less momentum/inertia, rpm's will drop faster and therefore you will need more throttle and rpm to keep yourself in the usable rpm range after you clutch it in and change gears. so a heavier flywheel also helps changing gears on the uphill. but this shouldnt be confused, with how much energy/throttle is required to move the car at x rpm on a certain hill, the lighter flywheel will always require less.

Back on topic:

In theory a longer intake pipe should give you more down low, at cost of top end power - and vice versa.

You could start to experiment with variable intakes - eg having valves to open and close to direct air through different routes/distances depending on your throttle/rpm, but that starts to get quite tricky

I believe the width of your exhaust pipe would give you similar changes - eg, smaller exhaust would give you more low power at the cost of top end.

edit: I might be a bit mistaken on this, i have to do some more reading about it

not necessarily, it doesnt hold true as an absolute statement. a longer intake *can* give better intake velocities up top which will increase VE (sometimes over 100%), giving more power. theres a balance between restriction and length which has to be made, but its quite easy to reverse the logic of what you have said in a proper setup.

to my knowledge, with exhausts its a case too small or too big

there is a size that is too small and will restrict power across the rev range (most often the case with factory exhausts systems - the manufacturers wish to keep the noise/vibration/fumes down so as to pass all the necessary tests sufficiently

this is a case of the exhaust being too big a restriction on the engine - ie try blowing through a straw - ur lungs (the engine in this case) have too much gas to force out of the straw, and no matter how hard you try to force it thru, the force of the air out of the straw is pretty much constant)

there is also a size which is to big and will rob power across the rev range (there is not enough backpressure in the exhaust and as a consequence the exhaust gases cool too quickly and just 'sit' in the exhaust pipe

try blowing through a piece of PVC stormwater pipe - your lungs (the engine in this case) run out of gas to push out the end of the pipe - try it, the force of the air coming out the end is barely anything)

Then there is the right size - the pipe is not too small that it restricts heaps, and not too big that it robs; it scavenges - drawing exhaust gases out of the chamber, but having enough pressure to not stagnate and condense in the pipe (think of a didgeridoo - when you blow through it, its not too restrictive, not too big, and resonates which demonstrates a scavenging effect (a high pressure wave is created when the exhaust port closes, then a low pressure wave is created as the port opens, and so on, these pockets of high and low pressure create that scavenging effect), which is very similar to the sound waves created when a didgeridoo is played)

hope i got that right and i hope that makes sense

PS

the right exhaust size is generally not one size, but over a range

then - the smaller the size in the range, generally the better it is low down (up high it just doesn't flow enough and so becomes restrictive); the bigger the size in the range, generally the better it is high up (it is too big @ low rpms as its not flowing enough - high rpms the scavenging affect works well)

i have to strongly disagree. with exhausts, its a matter of attaining the least amount of restriction, after the 'tuned' extractor section of exhaust. backpressure by definition is something that pushes against the cylinder coming up to TDC, and causes a loss of power, this is simple physics, backpressure is not desirable, EVER (not counting 2 strokes ). the velocity is simply a side effect of pressure in the exhaust, so if the gas is just 'sitting' there, it means there isnt that much pressure in the exhaust relative to its size, BUT this isnt a bad thing, it just means there is low backpressure, which

is GOOD.

in extractors, backpressure is also not desirable, but there needs to be a balance struck with velocity for pulse *timing* and an acceptable amount of backpressure. the *net* gain for power may require some back pressure to exist, to get the right velocities, but this is a side effect and not something that you aim for.

backpressure being 'needed' for power is old school

[342Four]

out of curiosity then how do you explain a lose of power on a hyundai excel after a 4 inch CAT back exhaust was added

ive seen the results(on the excel)- and had seat of the pants experience (on various other small engined cars) that have had big CAT backs put in place - and they suck big time

have a read of some autospeed articles if you can get your hands on some

www.autospeed.com.au

they know what they are talking about theoretically (well, most of the time) and test it out too

[MBS206]

That's one quite simple.

You actually DID increase backpressure with doing that.

How you say? It's straight through

Quite simply, enlarge the pipe size, gas velocity slows dramatically, manages to cool, and condense, which means it slows even more.

And before you all say (But the exhaust gas is always hot at the exit) exhaust temps as they enter the exhaust are over 400degrees celcius (neasured) at idle.

So larger pipe, makes gas cool more and slows it, cool gas is more dense (Takes up less space) therefore it condenses more and slows, which makes it harder to push the gas out.

[djr81]

That's one quite simple.

You actually DID increase backpressure with doing that.

How you say? It's straight through

Quite simply, enlarge the pipe size, gas velocity slows dramatically, manages to cool, and condense, which means it slows even more.

And before you all say (But the exhaust gas is always hot at the exit) exhaust temps as they enter the exhaust are over 400degrees celcius (neasured) at idle.

So larger pipe, makes gas cool more and slows it, cool gas is more dense (Takes up less space) therefore it condenses more and slows, which makes it harder to push the gas out.

You are correct - up to a point.

What you have neglected to mention is that as the gas cools an increase in density means it sees a DECREASE in volume. So measured in cfm (or whatever units people prefer) there is much less VOLUME of gas to be removed. In an exhaust the velocity of the gas is proporional to the volume of gas. The result of the lower gas velocity & the lower volume is that there is a lower pressure differential needed to push it out the back, that is back pressure drops. The effects of a reduction in volume (driven by temnperature change) is much more influential on pressure drop than the effects of an increase in density.

I am not going to post up the calcs for this, I am sorry but they are complicated at best & not really of much help unless people wants to spend hours studying fluid dynamics & compressible flow. But the short answer is the more temperature you can dump out of your exhaust gas the less back pressure you will see.

Edited April 13, 2007 by djr81

[mokompri]

out of curiosity then how do you explain a lose of power on a hyundai excel after a 4 inch CAT back exhaust was added

ive seen the results(on the excel)- and had seat of the pants experience (on various other small engined cars) that have had

big CAT backs put in place - and they suck big time

have a read of some autospeed articles if you can get your hands on some

www.autospeed.com.au

they know what they are talking about theoretically (well, most of the time) and test it out too

i cant comment on a car i dont have personal experience with.. but i can name an n/a 2L silvia that went from 2.5" to 3" cat back and gained everywhere in the rev range, how do you explain that? you cant and theres no point in trying because you know nothing about the car other then the small bit of information i have given you.

but heres some food for thought. alot of carby cars can easily lose power after swapping to a higher flowing exhaust. the reason for this is quite simple, fitting a higher flowing exhaust changes the breathing characteristics of the engine, often to a point where the mixtures set by jetting on the carby are no longer optimal for the new 'setup', this caused a loss of power. of course re-jetting and retuning of the car, would then see an increase in power from its previous state. Another example is the late model wrx. the ecu of these cars did not cope well with changes to the airflow of the engine, and as such what would happen is after fitting an exhaust people found no gain up top. how do you explain that ? turbo cars always gain from a more free flowing exhaust dont they ? well its simply because the ecu noticed the increase in airflow and thinks there is something wrong, and does the equivalent of a nissan 'rich and retard'. with ecu tuning, these problems are all solved. im not saying this is what happened in that circumstance, but im saying your lacking information and im certain that a 'lack' of backpressure wasnt the problem.

i think YOU should be the one reading some autospeed articles, i actually have had a subscription for quite some time and know that they take the same position as i do in regards to backpressure in exhausts.

That's one quite simple.

You actually DID increase backpressure with doing that.

How you say? It's straight through

Quite simply, enlarge the pipe size, gas velocity slows dramatically, manages to cool, and condense, which means it slows

even more.

And before you all say (But the exhaust gas is always hot at the exit) exhaust temps as they enter the exhaust are over

400degrees celcius (neasured) at idle.

So larger pipe, makes gas cool more and slows it, cool gas is more dense (Takes up less space) therefore it condenses more

and slows, which makes it harder to push the gas out.

as djr pointed out, backpressure reduces from a temperature reduction. here are the common gas laws

V = kT

P = kT

PV = k

V = volume

P = pressure

T = temperature

k = a constant of proportionality

you can see that, with a reduction in temperature, with a fixed volume (which is the exhaust pipe, because the gas will always fill it), you get a reduction in pressure/backpressure. theres no 2 ways about it. a pipes capacity to move mass is whats important, because each combustion cycle produces the same amount of mass, what changes is only the temperature and density. yes, energy is lost by loss of heat which slows down the gas, but this is outweighed by increased mass the exhaust can flow due to the colder gas, this is shown by this equation: speed = kinetic energy^0.5 (the kelvin temperature is directly proportional to the kinetic energy of a gas). no matter what numbers you plug in, you will always get more mass of gas flow with a lower temperature, which gives less backpressure.

[Cubes]

Why not shove a turbozet in the rear muffler 'suck' the exhaust gas out that improves scavenging from the umm... turbo.

Fully hektic. Hey it could work.

[342Four]

good thinking cubes

ohh - it seems an ecu reset or re-jetting seems to be the answer then often

but surely there is a 'too big' size for an exhaust (pulse width and scavenging have an affect on power and too big would reduce that surely)

[mokompri]

good thinking cubes

ohh - it seems an ecu reset or re-jetting seems to be the answer then often

but surely there is a 'too big' size for an exhaust (pulse width and scavenging have an affect on power and too big would reduce that surely)

scavenging occurs in the 'tuned'/extractors part of the exhaust, and yes as i already mentioned it is more important to have properly timed pulses over all out flow. the cat-back however has no effect on scavenging, the more free flowing the better.

[Eug]

this is all starting to lead into technicalities...

while justification, numbers and calculations is good and all - what it comes down to is what is good and works. so get listing!

- i've heard that the pros for a lightened flywheel outweigh the cons (however this is 'apparently' not the case for drag racing turbos)

- any sort of reasonably sized exhaust and extractors will work better than standard

anything else?

[ignuz]

this is all starting to lead into technicalities...

while justification, numbers and calculations is good and all - what it comes down to is what is good and works. so get listing!

- i've heard that the pros for a lightened flywheel outweigh the cons (however this is 'apparently' not the case for drag racing turbos)

- any sort of reasonably sized exhaust and extractors will work better than standard

anything else?

Rip out the back seat, and all the junk in the boot (including the spare wheel)

[Eug]

Rip out the back seat, and all the junk in the boot (including the spare wheel)

hahaha yes nick...

i did that for about 3 months; the road noise, exhaust noise, and lack of rear seats made things quite uncomfortable.

like my trimmings too much - that said, there was a noticeable improvement.

[342Four]

heck - for the drags take everything out

your spare tyre, jack, winder, nut remover thingo, the carpet covers would equal about 20-30kg of weight plus

then if you want to get really serious you could take out the rear seats and the passenger seat

[MBS206]

heck - for the drags take everything out

your spare tyre, jack, winder, nut remover thingo, the carpet covers would equal about 20-30kg of weight plus

then if you want to get really serious you could take out the rear seats and the passenger seat

Why? There's no fun in that at all! You won't know what time you really do in "street" trim.

Unless you only want to have a "time" that the car "can" run, if it is lighter...

At the drags, leave in exactly what you have in on the street. Then you'll know what the car can do on the street, plus, you don't have all that time and effort taking it out, and putting it back in.

[SKiT_R31]

Why? There's no fun in that at all! You won't know what time you really do in "street" trim.

Unless you only want to have a "time" that the car "can" run, if it is lighter...

At the drags, leave in exactly what you have in on the street. Then you'll know what the car can do on the street, plus, you don't have all that time and effort taking it out, and putting it back in.

^^ aggree'd

but, if its a club drag day etc, and its possible, it doesnt hurt to do both, run in full trim - then start taking shit off the car and see how fast the car can go