Increasing Torque

[342Four]

mathematically what you have said there is correct

but you have forgotten to explain some stuff

1st re potential energy with lightened flywheel:

because there is a less mass to spin, the gain in potential energy is less, which means that there has to be more throttle to increase the spin of the flywheel to match the same potential energy of the stock one (for example 3500rpm lightened PE = 3000rpm stock PE)

this is part of why more throttle is needed

2nd re linear kinetic energy with lightened flywheel:

there is no change in linear kinetic E as mass of the flywheel has nothing to do with it

3rd re rotational kinetic E:

indeed the rotational inertia is less due to less mass, but as a consequence higher revs are needed to match the equivalent rotational inertia of the stock flywheel

so what it means is that you have interpreted the data wrong

the most important thing is rotational inertia, although PE will affect it

because there is less mass to deal with, the PE and RI will be less at the same rpm, therefore an increase in RPM is needed to have the same equivalent PE and RI of the stock flywheel

On an aside tho, the lightened flywheel may make it easier to climb the hill, as going up a hill is a change in momentum, and with the less PE and RI, it makes it easier to change that forward momentum to an uphill momentum

[HolyEvil]

interesting read.. I'll try to glean all the knowledge off here and hopefully realise what can help in my acceleration (whether from start or rolling)

please keep discussion and keep suggesting what other stuff we N/A drivers can do to improve acceleration in the low speeds...

p/s-would a lighten flywheel help a auto car? (me have auto car)

cheers..

Edited April 5, 2007 by HolyEvil

[noone]

If you have an auto u have no flywheel, lol, u have a torque converter

have you considered a hi-stall converter matched with a good cam and tune They are bound to give some assistance in launch of the line. The basic Idea being to stall the car up at higher revs where it is making more power torque and if grip permits quicker launch's follow

Most auto Drag cars use modified converters talk to a decent auto shop an they may be able to advise.

And yeah some interesting Stuff in this thread

Edited April 5, 2007 by noone

[Eug]

interesting read.. I'll try to glean all the knowledge off here and hopefully realise what can help in my acceleration (whether from start or rolling)

good to see that not everyone on this forum is a 13y/o school kid on holidays!!! although some may act like it hey

If you have an auto u have no flywheel, lol, u have a torque converter

exactly what i was going to say...

some of the auto drivers on this forum have had something done to their valve bodies to make it shift harder (or something) - don't quote me on it. a mate had his sent down somewhere in melbourne? to a place called MV Automatics or similar. quite a nifty mod.

[Cubes]

A longer stroke is a big no-no if you want an engine to rev. So if you're chasing outright power (especially with a NA engine) then you want something with a short stroke. But if you want something to pull boats or carry a family, you'd buy something with a long stroke (like those old Holden V8s)

Thats correct if you simply stroke the motor out and don't make changes to head airflow (cams/inlet) to allow for the greater airflow potential the bottom end is able to provide.

Make changes to inlet tuning (runner length & plenum volume to suit the larger capacity) and cams; the larger motor will make considerably more every day usable power.

The rb30's stroke is not considered long. Its rod to stroke ratio is perfect for making big high rpm power and mid range torque. Interestingly enough the rb20 is next in line, then the rb26 then rb25.

My vote goes with a well sorted cam + auto + stall converter.

[HolyEvil]

If you have an auto u have no flywheel, lol, u have a torque converter

have you considered a hi-stall converter matched with a good cam and tune They are bound to give some assistance in launch of the line. The basic Idea being to stall the car up at higher revs where it is making more power torque and if grip permits quicker launch's follow

Most auto Drag cars use modified converters talk to a decent auto shop an they may be able to advise.

And yeah some interesting Stuff in this thread

haha no wonder all the pictures i've seen like in carbibles when i'm reading up on engines have flywheel with clutch in it =D

oh yeah.. i'm actually not talking about launch (ala burnout stuff), but like as the light turns green.. what to mod to make my car accelerate faster.. mostly looking things at the lower end of the scales.. increasing 0-80 time perhaps.. stuff like that..

and i'll read up on whether those converters would be good for me =)

cheers

[HolyEvil]

some of the auto drivers on this forum have had something done to their valve bodies to make it shift harder (or something) - don't quote me on it. a mate had his sent down somewhere in melbourne? to a place called MV Automatics or similar. quite a nifty mod.

hmmm can u find out more about this?? it sounds interesting...

cheers eug!!

[HolyEvil]

My vote goes with a well sorted cam + auto + stall converter.

the cams as in inthe intake cams? ..I've always wondered when people change the cams.. what does the changed cams affect.. they are the same in size yeah?

all these stuff... great to read..

cheers mate

[Eug]

hmmm can u find out more about this?? it sounds interesting...

cheers eug!!

Mike from MV Automatics calls it a "stage 2" shift kit - basically he modifies the valve body to make it shift harder. I'm not too technical on how it works, etc. because I don't have an auto and never driven one.

try this link: http://www.skylinesaustralia.com/forums/in...mp;hl=shift+kit

[scathing]

My new car is due to be unloaded Monday. When it gets to the workshop I am going to fit a lightened flywheel - and use less throttle getting up the hills around home!

OK, so your future car will have a lightened flywheel.

But, when you made the above posts, have you ever drive a car with its stock flywheel and then a lightened one to compare the difference? Were speaking from personal practical experience when you made the assertions, or not? Even in the future, if you get the car and make the change immediately you'll have no idea what the car was like with the OEM flywheel so you'd still lack the experience to make an informed comment.

I guess everyone who's ever made the change is wrong when they say the car needs more throttle at low RPM to maintain speed up hills. I guess everyone else on the planet must be experiencing a psychosomatic loss of low-end torque.

Like I said, I drove my car around with the stock flywheel for around a 3-4 months without any other mods before installing another flywheel half its weight (and made no other changes to the car with the flywheel install) and now around town I sometimes need to grab 5th on hillls the car would used to happily pull 6th while going up. Once I'm up in the middle of the rev range any differences aren't noticable, but when I've got the engine turning over at 1500RPM I can definitely notice the loss.

[djr81]

mathematically what you have said there is correct

but you have forgotten to explain some stuff

1st re potential energy with lightened flywheel:

because there is a less mass to spin, the gain in potential energy is less, which means that there has to be more throttle to increase the spin of the flywheel to match the same potential energy of the stock one (for example 3500rpm lightened PE = 3000rpm stock PE)

this is part of why more throttle is needed

Well you are right in the sense that you need more throttle to achieve more rpm. I don't think that is much of a surprise to anyone. With a lightened flywheel you certainly don't need more throttle to achieve the same rpm, which is the point, really.

2nd re linear kinetic energy with lightened flywheel:

there is no change in linear kinetic E as mass of the flywheel has nothing to do with it

Yes there is. Just because it goes round (at right angles to the direction of travel) doesn't mean you can ignore its effects in a straight line, ie it still acts as mass.

3rd re rotational kinetic E:

indeed the rotational inertia is less due to less mass, but as a consequence higher revs are needed to match the equivalent rotational inertia of the stock flywheel

Well if you re-read what wrote you will see I was describing a situation where the car is accelerating in gear - the dumped clutch off the line is slightly different & I described that differently. What you are saying in item three is correct for a start and or a gear change.

so what it means is that you have interpreted the data wrong

the most important thing is rotational inertia, although PE will affect it

because there is less mass to deal with, the PE and RI will be less at the same rpm, therefore an increase in RPM is needed to have the same equivalent PE and RI of the stock flywheel

Well I don't think I did, but anyway. As I explained there are two distinct situations - ie the clutch dump/start from standstill & then the mashing the throttle when already in gear. With a lightened flywheel you need more rpm off the start to get the same launch (due to lower rotational kinetic energy). This can be seen as more throttle, but it is only sort of more. You still need basically the same throttle position for the same rpm - you just need more rpm.

The second circumstance ie in gear acceleration you definately need less throttle with a lightened flywheel.

On an aside tho, the lightened flywheel may make it easier to climb the hill, as going up a hill is a change in momentum, and with the less PE and RI, it makes it easier to change that forward momentum to an uphill momentum

This can also be characterised as the amount of throttle needed after the clutch has been dumped. I thought this was what the bloke was asking, but I may have misinterpreted it a bit. I think we basically agree with each other. Just placing different emphasis on different circumstances.

Good to see people making sense without resorting to abuse.

[djr81]

OK, so your future car will have a lightened flywheel.

But, when you made the above posts, have you ever drive a car with its stock flywheel and then a lightened one to compare the difference? Were speaking from personal practical experience when you made the assertions, or not? Even in the future, if you get the car and make the change immediately you'll have no idea what the car was like with the OEM flywheel so you'd still lack the experience to make an informed comment.

I guess everyone who's ever made the change is wrong when they say the car needs more throttle at low RPM to maintain speed up hills. I guess everyone else on the planet must be experiencing a psychosomatic loss of low-end torque.

Like I said, I drove my car around with the stock flywheel for around a 3-4 months without any other mods before installing another flywheel half its weight (and made no other changes to the car with the flywheel install) and now around town I sometimes need to grab 5th on hillls the car would used to happily pull 6th while going up. Once I'm up in the middle of the rev range any differences aren't noticable, but when I've got the engine turning over at 1500RPM I can definitely notice the loss.

Let me re-state that. My replacement car (same model etc) will be getting a lightened flywheel attached. Have I driven a cars with different amounts of inertia in the engine. Yes. Do I think the whole world should be on drugs to cope with psychological conditions? Well to be honest sometimes I think it might help.

They weren't assertions. They were statements made off the back of a few simple maths calcs. If I have made a blue with the calcs (& I don't think I have) then fair enough, but otherwise what you are saying & what the maths is saying are two very diferent things. As a rule I trust the data more than the seat of the pants experience. Certainly there have been times where I could have swarn a change was for the better only to have the data tell me different. So I guess we are going to have to agree to disagree.

[MBS206]

Let me re-state that. My replacement car (same model etc) will be getting a lightened flywheel attached. Have I driven a cars with different amounts of inertia in the engine. Yes. Do I think the whole world should be on drugs to cope with psychological conditions? Well to be honest sometimes I think it might help.

They weren't assertions. They were statements made off the back of a few simple maths calcs. If I have made a blue with the calcs (& I don't think I have) then fair enough, but otherwise what you are saying & what the maths is saying are two very diferent things. As a rule I trust the data more than the seat of the pants experience. Certainly there have been times where I could have swarn a change was for the better only to have the data tell me different. So I guess we are going to have to agree to disagree.

djr, I've seen live fed data (From the ECU) telling me that more throttle is being applied to maintain the same speed up a hill.

When I had said earlier you will require more throttle when going up a hill I was meaning that you will require it when cruising, not so much to accelerate up the hill, but to help hold your speed constant

Wheni you get your new car, please fit a stock flywheel, do some datalogging up a known hill in top gear, at a set speed, then fit your light weight flywheel (The only change you make) and do that exact same datalogging.

Tell me what you see in the throttle position part.

As for your calcs, there is something sitting in the back of my mind, that I'm trying to pull forward, it says that your calcs are correct, but there is something that we have not yet taken into account

[342Four]

Well you are right in the sense that you need more throttle to achieve more rpm. I don't think that is much of a surprise to anyone. With a lightened flywheel you certainly don't need more throttle to achieve the same rpm, which is the point, really.

well - actually you do need more throttle. thats the point i was making

choose a certain rpm point with the stock flywheel - do the math calcs ends up with a number (say X)

to achieve X with a different flywheel (in this case lightened) you either have to spin it faster or slower (due to difference in mass)

in this case, a lightened flywheel has to spin faster to achieve X ie more throttle

Yes there is. Just because it goes round (at right angles to the direction of travel) doesn't mean you can ignore its effects in a straight line, ie it still acts as mass.

my mistake - it seemed to me you were talking about the linear motion of the car

a lightened flywheel will decrease around 4kg from a car of 1500kg (or is it lighter), which is like 0.0000001 less KE

Well if you re-read what wrote you will see I was describing a situation where the car is accelerating in gear - the dumped clutch off the line is slightly different & I described that differently. What you are saying in item three is correct for a start and or a gear change.

mmkay - i was talking about a constant velocity, not acceleration

Well I don't think I did, but anyway. As I explained there are two distinct situations - ie the clutch dump/start from standstill & then the mashing the throttle when already in gear. With a lightened flywheel you need more rpm off the start to get the same launch (due to lower rotational kinetic energy). This can be seen as more throttle, but it is only sort of more. You still need basically the same throttle position for the same rpm - you just need more rpm.

The second circumstance ie in gear acceleration you definately need less throttle with a lightened flywheel.

true - 1st situation more throttle is needed, however in the 2nd situation, you will need less throttle to get the flywheel spinning (due too less mass), but most likely slightly more throttle than usual to maintain that rotation (again due to less mass - once spinning, the light flywheel will slow down sooner than the stock one)

the amount of throttle used may be the same or slightly more net wise, with less to start off, but more to maintain constant acceleration (and this is amplified when going uphill - see my conclusion at the end)

This can also be characterised as the amount of throttle needed after the clutch has been dumped. I thought this was what the bloke was asking, but I may have misinterpreted it a bit. I think we basically agree with each other. Just placing different emphasis on different circumstances.

Good to see people making sense without resorting to abuse.

i think we kinda do

at least we both seem to know the math calcs

from my experience (passenger, not driving) and from teh math, a gear change down will most likely occur going up a hill, 1: because there is less mass therefore less RI and PE which leads to 2: going uphill places strain on the motor and due to the less RI and PE, the flywheel will slow down quicker, leading to a downshift to keep engine revs up

On the flat however, a lightened flywheel will need roughly the same amount of revs when cruising, and about the same amount of throttle when accelerating (however this, depending on the driving style, is all relative - one person may use the quicker increase in rpms as a reason to use less throttle, while another may use it to give more throttle - i know what i would be doing )

I hope you can see where im coming from, and hopefully it makes a bit more sense to you

[djr81]

djr, I've seen live fed data (From the ECU) telling me that more throttle is being applied to maintain the same speed up a hill.

When I had said earlier you will require more throttle when going up a hill I was meaning that you will require it when cruising, not so much to accelerate up the hill, but to help hold your speed constant

Wheni you get your new car, please fit a stock flywheel, do some datalogging up a known hill in top gear, at a set speed, then fit your light weight flywheel (The only change you make) and do that exact same datalogging.

Tell me what you see in the throttle position part.

As for your calcs, there is something sitting in the back of my mind, that I'm trying to pull forward, it says that your calcs are correct, but there is something that we have not yet taken into account

Unfortunately you can (especially with turbos, but also with atmo motors with big cams) get large changes in TPS for small changes in torque output & even smaller changes in acceleration going up hills.

Well that is the hard bit, really. Getting a single change made to the car & then testing it under the same circumstances. Even the data logging I have done on the circuit gives large variations in rpm changes (ie acceleration) depending on the ambient temps on the day. As often as not people make more than one change at a time. Certainly that is my plan at present as the workshop is two hours drive away from home.

If your memory comes good please post the results up.

[djr81]

from my experience (passenger, not driving) and from teh math, a gear change down will most likely occur going up a hill, 1: because there is less mass therefore less RI and PE which leads to 2: going uphill places strain on the motor and due to the less RI and PE, the flywheel will slow down quicker, leading to a downshift to keep engine revs up

I hope you can see where im coming from, and hopefully it makes a bit more sense to you

Spot on. I think that there is a bit of that going on.

[Sinturion]

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

Edited April 10, 2007 by Sinturion

[HolyEvil]

Unfortunately you can (especially with turbos, but also with atmo motors with big cams) get large changes in TPS for small

okie..going off topic for the moment.. what's ATMO?

cheers

[Eug]

okie..going off topic for the moment.. what's ATMO?

cheers

atmo is just shorthand for atmosphere/atmospheric, which basically just means naturally aspirated.

[342Four]

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

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)

PPS

hmmm - im quite proud of that - its the first time ive been able to describe it so that it makes sense

Edited April 10, 2007 by 342Four