[nick the tubman]

does the torque peak earlier than the horse power?
i had the car mapped again and boy does it give some shove from 4000rpm upto about 6000rpm. i reckon in this rev range it is almost at its most powerful - so i think revving it beyond, say 6.5k rpm is pretty pointless?

its running 1bar in low boost and 1.2 bar in high with twin HKS 25-30 turbos, HKS cams and apexi intakes, race exhaust, intercooler etc etc...

i have set my rev limiter to 7,250rpm but im not sure you need to go this far.
i had an E46 M3 and you had to rag it all the way to the red line to get the best.

where do you guys rev too when giving it a bit?
and just out of curiosity, whos car revs beyond the manufacturers redline? and why?

 

[m6beg]

Well i found when watching the master at Mapping Dan0.
There is a peak figure were your car reaches if it is 6800 or 8800.
Why push the car anymore beyond that point.
In the Lemon the revs were set to 8500 if i can remember.
the peak power was at 8200 again if i can remember.
So why rev any higher.
I think mine was set i bit higher because the car hardly looses any boost or revs because or the box.;
Good god its SAVAGE.

****

 

[Snowfiend]

1 bar boost, standard turbos (that's a sad story!), HKS cams, Blitz intakes, Mines exhaust, HKS intercooler

I rev mine to about 6500-6700...

My dyno printouts showed that was were my power and torque started tipping off steeply.

Optimum torque range looks about 3250 - 6000

 

[turboslippers]

Nick, there are a load of threads here about torque, bhp and rpm. You can't give a definitive answer as it totally depends on the exact engine and it's characteristics. Remember though, BHP is only a calculation based on torque at a particular rpm. I can't remember the exact constant but for BHP and lb/ft the BHP the equation is roughly bhp=torque x RPM/5150.
As the torque curve tails off at higher rpm you'll reach a point where you'll actually be generating less accelerative force with the gearing advantage of the lower gear but reduced torque versus the next gear but with more torque lower down the rev range. In a theoretical world you'd want to produce the torque as high up the rev range as possible and then have a CVT to hold it at this point (ignoring the losses you get with these systems)
In reality, leave a safety factor and if you change at a point so that in the next gear you are still on the crest of the torque curve you won't go far wrong. I think you'll actually feel this rather than worry about precise numbers. If you change up and feel that it's still 'climbing' the torque curve then maybe you need to change up a little later. Then it just comes down to a trade off for a 1/10 here or there versus engine wear

 

[Snowfiend]

damn dude, pass that reefa

 

[turboslippers]

Lol...take it logically and this is why race (or road?) bikes are geared/tuned the way they are. Long first gear and then a series of very tightly stacked ratios that keep the engine a couple of thousand rpm (or less) either side of the peak torque (which is usually very peaky). If you've heard these sorts of bikes go through the gears at the top end there isn't a huge transition in revs. Take that further and imagine it had 15 gears and then infinite you'd just want to hold the engine at it's peak torque.
On a road car the only time you'd want to hugely exceed the peak power RPM was if you had such long gearing that by changing gear, you'd drop out of the torque band. This isn't usually the case though
Take another example, e.g griff 500. The torque curve was so flat between 2 and 5k that if you revved much beyond 5k the torque would drop off so dramatically that it was pointless staying in that gear. Even if it was a much longer ratio and you dropped back 2k rpm the torque was still within 80% of peak that it meant you would actually be accelerating quicker in the next gear as opposed to wringing it's neck to 6.5k.
As I said, I'm sure you will feel it. If you change at 5k and then it feels 'sluggish' in the next gear then you need to change higher. If you find a change point though and hit the 'sweet spot' in the next gear then you really don't need to rev it any higher. You might gain a few tenths but at the detriment to your engine longevity

 

[nick the tubman]

thanks for the input chaps. really helpful.
i have a volvo s60 D5 as a daily commuter and if you want to pull away fast (at any speed) then i need to keep the revs below 3,500rpm, slowly down on the accelerator, and it pulls like a train. however, if i boot it too quickly, and the kickdown puts the engine into the 4000+rpm range it doesnt really do anything. - now that, i assume is ALL down to torque, and nothing to do with bhp?

i suppose its exactly what you are saying - as soon as you "feel" there is no more urgency in acceleration, then its time to change up, therefore, hopefully staying in the "real power band".

 

[turboslippers]

Nick, I'm surprised that a diesel would kick down to over 4000rpm? Similar to a big old lazy torquey V8 lump these diesels work best between 2 and 4 (rough rule of thumb). But, yes, you are totally correct
These diesels are actually artificially governed so they govern the fuel/boost over peak power. Even if they weren't there would be no point revving them past 4500 as the peak torque (and bulk of the torque curve) is happening way before this point. Torque curve on this engine, I'm guessing, is all between the 2-4k mark so to make progress changing above 4 is futile. In fact, with the flat torque curve these types of engines make you probably wouldn't notice a huge difference if you changed up at 3k or 4k.
The torque spread on modern diesels is a lot wider and lower down though than a tuned petrol engine such as a skyline so gearing/change up point is more relevant on the skyline. The same rules apply though... try and keep the engine within the peak torque band. If it's an eiffel tower tower peak like on a tuned bike then you need the gearing tight to keep it around the peak torque and if its flatter 'like aers rock (sic)' then you can get away with more 'lazy' gearing like on modern diesels. The skyline fits somewhere between these two extremes i guess

 

[shade]

Nick, there are a load of threads here about torque, bhp and rpm. You can't give a definitive answer as it totally depends on the exact engine and it's characteristics. Remember though, BHP is only a calculation based on torque at a particular rpm. I can't remember the exact constant but for BHP and lb/ft the BHP the equation is roughly bhp=torque x RPM/5150.
As the torque curve tails off at higher rpm you'll reach a point where you'll actually be generating less accelerative force with the gearing advantage of the lower gear but reduced torque versus the next gear but with more torque lower down the rev range. In a theoretical world you'd want to produce the torque as high up the rev range as possible and then have a CVT to hold it at this point (ignoring the losses you get with these systems)
In reality, leave a safety factor and if you change at a point so that in the next gear you are still on the crest of the torque curve you won't go far wrong. I think you'll actually feel this rather than worry about precise numbers. If you change up and feel that it's still 'climbing' the torque curve then maybe you need to change up a little later. Then it just comes down to a trade off for a 1/10 here or there versus engine wear

That is the best explanation of this issue that I have ever read, and I've read a few in my time. Totally agree!

 

[nick the tubman]

Nick, I'm surprised that a diesel would kick down to over 4000rpm? Similar to a big old lazy torquey V8 lump these diesels work best between 2 and 4 (rough rule of thumb). But, yes, you are totally correct
These diesels are actually artificially governed so they govern the fuel/boost over peak power. Even if they weren't there would be no point revving them past 4500 as the peak torque (and bulk of the torque curve) is happening way before this point. Torque curve on this engine, I'm guessing, is all between the 2-4k mark so to make progress changing above 4 is futile. In fact, with the flat torque curve these types of engines make you probably wouldn't notice a huge difference if you changed up at 3k or 4k.
The torque spread on modern diesels is a lot wider and lower down though than a tuned petrol engine such as a skyline so gearing/change up point is more relevant on the skyline. The same rules apply though... try and keep the engine within the peak torque band. If it's an eiffel tower tower peak like on a tuned bike then you need the gearing tight to keep it around the peak torque and if its flatter 'like aers rock (sic)' then you can get away with more 'lazy' gearing like on modern diesels. The skyline fits somewhere between these two extremes i guess

your explanations are great..... love reading them.

i will check tommoz with regards to the exact revs the car kicks down to...sorry if i got it wrong, but all i know, it seems to be pointless - i.e, no power there.
so why program a cars gearbox to do it, if its useless? ahhh, but that suggests the ECU can not determine when high revs are needed. although why would high revs be needed with an automatic, torquey diesel?

confused? i am!

 

[turboslippers]

I'm waffling now but two points that are important

'as soon as you "feel" there is no more urgency in acceleration, then its time to change up, therefore, hopefully staying in the "real power band".'

In a diesel that loss of urge is not the engine running out of puff...thats artificially done to aid longevity and also because running it to 5.5k would be useless...you'd drop back to, maybe, 3.5k at the next gear change and waste the useful torque between 2k-3.5k

Secondandly, when you say it down to torque and not power...as i said..power is only a calculation based on torque. If you can make torque (i.e twisting force) high up the rev range then you can gear it down for maximum wheel torque (which is what accelerates you). This will give you a peak power but this is only based on your torque and at what speed you can create it.
I.e you have 2 cars, same weight etc (ok..this ignores a fair bit of relevant physics and transient conditions...)

Car 1 develops 200lb ft torque at 4000rpm and in, say 2rd gear, is travelling at 30mph
Car 2 develops 400lb ft torque at 2000rpm and is in a gear that is twice as long between crank and wheel is also travelling at 30mph

The instantantaneously acceleration is the same betwen the these two..i.e shove in the back

Diesel's score because they have a wide flat torque band which means you don't need to be so precise with the gearing and they'll generate near peak torque throughout most of their limited rev range. If you have a petrol engine though, say a civic tpye R that might generate 1/2 the torque but can develop it at twice the rpm i.e 8k rpm and you gear it down then you have similar acceleration. The difference is, the civic is much more peaky so needs to be kept in that peak torque bracket high up with the lower gearing to achieve the same wheel torque as the more 'lazy' diesel

Ok ,so the above is very generalistic but...

 

[moosedoog]

from memory............torque x rpm/5252=bhp........i think

 

[turboslippers]

Yup...ta..it is 5252. i,e if you look at at torque & power curve done in lbft and bhp the lines always cross at 5252 rpm as bhp=torque X rpm/5250 will be bhp=torque at this point

 

[Snowfiend]

can tell your an enginner eh