When to change gear.....

[gulzar]

hi guys been doing some reading and need to add ive driven severel vag 1.9 tdi and 2.0tdi engines even those with dsg. seats, golfs mark 4 and golf mark 5, passats.,
100bhp. 130bhp, 150bhp remapped to 160 bhp and also bmw 320td remapped by dms. not going to comment on the beemer as not quite relevant to this post.

its important to know that what makes these tdi's quick is the torque they create. changing gear to get moving quickly requires you to change gear just as the peak power is reached. in first second and third gears this is about 4000rpm unless mapped obviously.4th 5th,and 6th can be strung out. its all about riding the wave of torque, and unfortunately if you rev them to the redline in the early gears you can notice the pull just die off. so important to change just as you feel the maximum pull achieved as the next gear will create that same shove into you seat. you fall staright back into the torque wave band.

as far as the panda is concerned its engine is different, what works for the panda might not work for the vag tdi's.

in the vag tdi's economy drive as stated is change by about 2000-2500rpm. on a remapped tdi you can just let them go for the limiter.

revving them to the redline will not harm but isnt very productive in the first three gears on a standard car.

gulzar

thats just my experience and opinion though.;-)

 

[uzi_cupra]

hi guys been doing some reading and need to add ive driven severel vag 1.9 tdi and 2.0tdi engines even those with dsg. seats, golfs mark 4 and golf mark 5, passats.,
100bhp. 130bhp, 150bhp remapped to 160 bhp and also bmw 320td remapped by dms. not going to comment on the beemer as not quite relevant to this post.

its important to know that what makes these tdi's quick is the torque they create. changing gear to get moving quickly requires you to change gear just as the peak power is reached. in first second and third gears this is about 4000rpm unless mapped obviously.4th 5th,and 6th can be strung out. its all about riding the wave of torque, and unfortunately if you rev them to the redline in the early gears you can notice the pull just die off. so important to change just as you feel the maximum pull achieved as the next gear will create that same shove into you seat. you fall staright back into the torque wave band.

as far as the panda is concerned its engine is different, what works for the panda might not work for the vag tdi's.

in the vag tdi's economy drive as stated is change by about 2000-2500rpm. on a remapped tdi you can just let them go for the limiter.

revving them to the redline will not harm but isnt very productive in the first three gears on a standard car.

gulzar

thats just my experience and opinion though.;-)

makes perfect sense, what i was trying to say too...

 

[techathy]

Sounds great but to increase torque by 25% (a noticeable torque drop) you increase the ratio by 30% (a not uncommon ratio increase) ends up in a net acceleration loss. You'll find that the lower gears are typically the ones that holding onto the revs beyond peek power becomes more advantageous, as typically gears get closer together the further up the box you go. Give me a power graph of a stock 130 PD engine & the gearbox ratios (mph per 1000rpm is fine) & I'll plot you a power v's speed or thrust v's speed with change point rpm per gear.

 

[thePHILosipher]

Sounds great but to increase torque by 25% (a noticeable torque drop) you increase the ratio by 30% (a not uncommon ratio increase) you'll find that the lower gears are typically the ones that holding onto the revs beyond peek power becomes more advantageous, as typically gears get closer together the further up the box you go. Give me a power graph of a stock 130 PD engine & the gearbox ratios (mph per 1000rpm is fine) & I'll plot you a power v's speed or thrust v's speed with change point rpm per gear.

is that an open offer?? im sticking mine onto the rollers tommorow so i'll be able to post up the print outs?? i have the same querie as stated so many times in this post, but my car is fairly irractic in its performance. I tend to get the shove at 2500rpm upto about 3500rpm (the majority of the time), but other times its as low as 2000rpm to 3000rpm, i personally dont understand why it changes

 

[gulzar]

all fair and well wanting to do plots and stuff mate, but i have to add, have you ever driven a vag tdi and what one if so? most people who have will agree ,that whats said by me and others is what happens with them. vag tdi's and fiat tdi's are different in character and how they create there power and at which point. trust me when i say that in the low gears when you cross 4000 rpm the cars loose thrust and stop giving you punch. boost tails off here. the top gears are the ones that allow you to go further into the revs to the limiter creating thrust.

gulzar.

 

[techathy]

Yeah that's an open offer, I need a power or torque graph plotted against rpm (preferably from the wheels but est fly is fine) & the gear ratios raw ratios (1st 3.535, 2nd 2.048... final drive 4.078) & tyre profile or mph/1000rpm.

Driven 3 stock VAG 1.9 TDIs; 1 PD 130, 2 PD160, also drove a remapped PD 150. Thing is though seat of the pants stuff doesn't work, in my Seicento from around 5000rpm the torque just died & felt like you wanted to change gear. A run on the rollers showed that in 1st you wanted to take it to the limiter & 2nd was well passed the red line.

 

[gulzar]

thats fair enough but to add. in the vag tdi's that you've experienced, non mapped you must have realised and felt that as soon as u pass 4000 rpm inthe first three gears your goin no wheren speedo stops rises the lot.if you keep yourself in the torque band then you can actually feel and see on speedo the forward motion happening.;-)

 

[thePHILosipher]

Here you go mate, this is a pretty much stock FR TDi with a Cupra intake run on V-Power diesel, the results are at the flywheel. Looking at these it definately seems that beyond 4000rpm the powers gone.

On another note, does anybody know the rough conversion to the wheels?? i know its dependant on the transmisson, but on average what sort loss should i expect??

 

[CJRamze]

156BHP on an FR at the Flywheel?
:S

My PD 100 hit 150bhp at the flywheel!

 

[thePHILosipher]

156BHP on an FR at the Flywheel?
:S

My PD 100 hit 150bhp at the flywheel!

was yours mapped at 150 or was that before map?? Its been feeling down on power for a while, but then again it does need a service as its now just told me!

 

[techathy]

Here you go mate, this is a pretty much stock FR TDi with a Cupra intake run on V-Power diesel, the results are at the flywheel. Looking at these it definately seems that beyond 4000rpm the powers gone.

On another note, does anybody know the rough conversion to the wheels?? i know its dependant on the transmisson, but on average what sort loss should i expect??

It looks like he's hit around 4000 to 4025 then shut the throttle totally, it certainly isn't a red-line run, iirc the red line is 4750. I also need ratios for the gears to plot anything.

A rule of thumb for aprox peek power is (whp+10)/0.9=bhb, reversing that you get to (bhp*0.9)-10=whp

 

[thePHILosipher]

It looks like he's hit around 4000 to 4025 then shut the throttle totally, it certainly isn't a red-line run, iirc the red line is 4750. I also need ratios for the gears to plot anything.

A rule of thumb for aprox peek power is (whp+10)/0.9=bhb, reversing that you get to (bhp*0.9)-10=whp

ok so using that conversion mines coming at about 130.4bhp at the wheels (156*0.9)-10??

 

[CJRamze]

Wo wait...
I assumed it was remapped because I'm a gigantic pleb.
Mine was 120bhp prior to a map
150bhp after map.

 

[thePHILosipher]

Wo wait...
I assumed it was remapped because I'm a gigantic pleb.
Mine was 120bhp prior to a map
150bhp after map.

lol,

so in actual fact the results aint to bad then?? i havent mapped her yet but will be in the new year.

 

[CJRamze]

Their fantastic, After a remap that should hold higher up the rev range.

 

[gulzar]

that graph shows clearly that the power peaks at about 4000rpm then tails of so therefore no more power rise available beyond , time to shift gears as said earlier.;-)

 

[techathy]

But peek power isn't when you change up, it's some time AFTER that... could be 10rpm after it but typically is at least a few 100rpm where is dependent on the shape of the power/torque curve after peek power & the gearing. As you don't know the exact shape of that torque curve you can't work out where the change point is, you also need the ratios so you can work out where the overlap point is but not having a clue about the beyond peek-power curve is a show stopper. If you look at Adam R's power graph you can see you're still holding good power to 4600, assuming a 1200rpm drop on gear change it looks like you want to change up at 4500rpm, holding onto the gear almost 500rpm beyond peek power. Looking at his torque curve, this will probably feel slower but will measure faster.

This is what really annoys me about most RR operators, they see peek power & let off the throttle. The thing is you also want to know what the power curve looks like after peek power. Does it fall off quickly or is it held high, e.g. how does the power compare at 65mph in 3rd to 65mph in 4th? You have no clue cause 65 in 3rd is 500rpm beyond peek power so not plotted , in my panda's case anyway.

 

[thePHILosipher]

CJ do you still have your rolling road results which you could post up to compare the 2??

Bare in mind mine was confirmed to need a new fuel filter today so may have made a slight differance to the results