Go Back   Team-BHP > Under the Hood > Technical Stuff


Reply
 
Thread Tools Search this Thread
Old 27th August 2011, 03:22   #106
Senior - BHPian
 
humyum's Avatar
 
Join Date: Feb 2006
Location: Leicester/Mumbai
Posts: 2,306
Thanked: 2,188 Times
Default Re: Does Revving the Engine consistently damage the engine on a longer run ?

Quote:
Originally Posted by nukeblitz View Post
But what about the torque multiplying effect of the gears? AFAIK, both the Gearbox and the differential multiply the Torque going to the wheels. I've posted about the same on the first page.
I read about the torque multiplying effect, but What about the turbo ?It has not been taken into the equation at all and whatever the multiplying effect the engine characteristics are going to remain the same. The torque you start getting at 2000 rpm in case of the I20 is because of the smaller turbo so that you achieve a brilliant low and mid end, when you try to go over the torque band you are overspooling the turbo and it is not giving you any boost in the form of torque, hence the progress to the 4 k or 4.5 rpm is slower after the peak torque at 3200 or whenever in your I20 is reached. Hence you are slowing the acceleration down by revving it above the maximum torque band.

In case of the Swift Diesel which I drive everyday, If i rev it beyond 3400 around rpm's, it just rev's without any significant fast increase in rpm's and actually slows the car down if I drive it revving upto 4 k in each gear. On the other hand, if i start shifting at 3200 to 3400 rpm arounds, I get the max acceleration in each gear as after every upshift I still land in the meat of the torque band which because of the turbo propels the car to the end of the torque band at superman speeds.
humyum is offline   Reply With Quote
Old 27th August 2011, 03:55   #107
BHPian
 
Join Date: Jan 2009
Location: Hyderabad/Mysor
Posts: 155
Thanked: 58 Times
Default Re: Does Revving the Engine consistently damage the engine on a longer run ?

Quote:
Originally Posted by humyum View Post
I read about the torque multiplying effect, but What about the turbo ?It has not been taken into the equation at all and whatever the multiplying effect the engine characteristics are going to remain the same. The torque you start getting at 2000 rpm in case of the I20 is because of the smaller turbo so that you achieve a brilliant low and mid end, when you try to go over the torque band you are overspooling the turbo and it is not giving you any boost in the form of torque, hence the progress to the 4 k or 4.5 rpm is slower after the peak torque at 3200 or whenever in your I20 is reached. Hence you are slowing the acceleration down by revving it above the maximum torque band.

In case of the Swift Diesel which I drive everyday, If i rev it beyond 3400 around rpm's, it just rev's without any significant fast increase in rpm's and actually slows the car down if I drive it revving upto 4 k in each gear. On the other hand, if i start shifting at 3200 to 3400 rpm arounds, I get the max acceleration in each gear as after every upshift I still land in the meat of the torque band which because of the turbo propels the car to the end of the torque band at superman speeds.

Hmmm, the turbo works by using energy from the exhaust gases and using this energy to pump in more oxygen(air) into the engine, right? And AFAIK, this is independent of gearing as the whole process occurs before the torque reaches the transmission. I would think that the torque produced at the crankshaft would be independent of the gear you are in. And it's the torque produced at the crankshaft that's modified by the multiplier effect by the transmission. The transmission then delivers this torque to the wheels.

The swift with the Fiat multijet 75 has a pretty peaky torque band. That might explain things. Let me do some numbers with the swift DDiS and see what conclusion we come to
1st gear ratio - 3.545:1
2nd gear ratio - 1.904:1
Final Drive ratio - 3.944:1
Peak Torque - 190Nm @ 2000rpm
Peak Power - 75PS @ 4000rpm or 55.16240625kW @ 4000rpm
Torque at 4000rpm = (55.16240625/4000)*60000/(2*PI) = 131.690544412961Nm
2nd gear RPM if shift at 4000rpm in 1st gear = 4000*(1.904/3.545) = 2148rpm
At 2148 rpm, I'm going to assume that the engine is still making 190Nm at the crankshaft

Applying the torque multiplication
4000rpm in 1st gear - 131.690544412961*3.545*3.944 = 1841.22871289893Nm
2148rpm in 2nd gear - 190*1.904*3.944 = 1426.78144Nm

So, I still say that you are ending up in the torque band but are losing the torque multiplicaiton and hence have lower torque going to the wheels. Ideally, I would say that you actually have to go beyond your power peak for the optimal shift.

How far beyond the power peak? I don't know. For 2 reasons.
1. I can't accurately calculate what the torque drop off is beyond the power peak without dyno graphs. The info given by the manufacturer isn't enough.
2. Notice that I used 1st and 2nd gears in my example. Usually, the difference between 1st and 2nd is the greatest of all the gears. Other gears will be much closer together and would have different optimal shift points. 3rd to 4th and 4th to 5th will probably have you shifting closer to the power peak or even before as they are much closer.


EDIT:- Take a look at me previous post. It plots the torque curve modified by gear multiplier (but not by final drive - as it's constant for the car and I assumed it to be 1) against speed. Notice where the lines cross? That's the point at which the next gear will have more torque than the current gear. Notice how 4th and 5th cross right after 4th power peak whereas the 1st and 2nd don't cross at all? That a theoretical one for my Vista which makes 135Nm at 2500rpm and 75PS at 4500rpm. The swift makes 190Nm at 2000rpm. This means that the torque curve would have a massive peak. Which would mean that on your car, the lines would much sooner, especially the 3rd-4th shift and the 4th-5ht shift. So, what you experience when driving would be true...

Last edited by nukeblitz : 27th August 2011 at 04:11.
nukeblitz is offline   Reply With Quote
Old 27th August 2011, 04:28   #108
BHPian
 
Join Date: Jan 2009
Location: Hyderabad/Mysor
Posts: 155
Thanked: 58 Times
Default Re: Does Revving the Engine consistently damage the engine on a longer run ?

Uhoh, time to edit is over.

Anyway, I just wanted to say that we are going way OT and that I'll create one of those graphs for the swift DDiS and put it up on another thread today evening.
nukeblitz is offline   Reply With Quote
Old 31st August 2011, 23:26   #109
Senior - BHPian
 
IndigoXLGrandDi's Avatar
 
Join Date: Aug 2009
Location: Solapur (MH-13)
Posts: 1,029
Thanked: 160 Times
Default Re: Does Revving the Engine consistently damage the engine on a longer run ?

@nukeblitz...
Don't rev the Vista over 2-2.5K rpm for better life from your car's engine.

You have mistaken the Max Power with Max Torque.


Quote:
Originally Posted by JustCause
Consequences I've observed when frequently high revving are:
2.)Alternator belt squeaks & requires early replacement
But the Alternator Belt in our Indigo XL Grand Dicor gets wear out very soon (<10,000kms) even if the Gear Up-shifts are carried out @2000-2500rpm.
IndigoXLGrandDi is offline   Reply With Quote
Old 1st September 2011, 08:03   #110
Senior - BHPian
 
Join Date: Apr 2008
Location: Dombivli
Posts: 2,626
Thanked: 1,191 Times
Default Re: Does Revving the Engine consistently damage the engine on a longer run ?

But if the rpm range for the engine is specified to be from say 1000rpm (idling) to 5500 rpm, shouldn't the belt support these rpm? If the belt wears out early if the engine is revved high, it would mean the quality of the belt is not upto the mark.
honeybee is offline   Reply With Quote
Old 1st September 2011, 08:41   #111
Senior - BHPian
 
Gansan's Avatar
 
Join Date: May 2009
Location: Chennai
Posts: 3,427
Thanked: 875 Times
Default Re: Does Revving the Engine consistently damage the engine on a longer run ?

My two cents;
Any engine operated at mid rpms for a given number of years will last longer than one that has been run at high rpms for the same number of years, everything else remaining constant. Simply because the latter would have done more number of revolutions during the given period than the former.

Note: This logic can't hold good (or will do so only marginally due to the higher temperature generated) for the tyres, which will do the same number of revolutions for a given distance, irrespective of speed!
Gansan is offline   Reply With Quote
Old 1st September 2011, 10:46   #112
Senior - BHPian
 
Join Date: Aug 2010
Location: Delhi
Posts: 2,133
Thanked: 1,004 Times
Default

First to answer the question - No the engine will not be damaged by consistently revving it to the Red Line, provided it is warmed up and lubricants are flowing properly. But the engine will definitely wear out faster!

Now the Reason :

As far as I know, in non performance vehicles, the manufacturer puts the RED LINE, slightly before the designed red line (where the engine starts deteriorating faster?), so that a user does not harm the engine. The engine is capable of going quite a bit after the red line, but at the expense of higher wear and/or faster deterioration of components. The ultimate beyond the red line design is the F1 engine, which is designed to last one or two circuits only, so that it may deliver 2 or three times more performance than a normal vehicle.

So driving upto red line; once the engine is warmed up and the lubricants flowing freely; should not harm the engine. Driving at high RPM though, will wear out components faster than driving at lower RPM. Similarly driving at too low a gear, especially when it is at much lower portion of the torque curve, will result in higher fuel consumption - lower FE.

About FE and Acceleration

As noted a lot of times, HP = Torque x RPM x Constant

Hence the Peak HP will come after the Pear Torque. That said, Acceleration is proportionate to Torqe, hence best acceleration figures should be around the peak torqe. If the torque curve is flat, then the acceleration will be similar within a wide band of RPM. If the torque curve is peaked (as in highly tuned engines), the best acceleration will be in a narrow RPM band.

As the engine efficiency is maximum at peak torque, it follows that to get best FE, we should be driving around the peak torque.

Thus the best acceleration and FE will be within 10% of the peak torque, that means
. If the engine is designed with a flat torque curve, you get a wide RPM band for optimum driving. This design requires less gears as each gear can cover a wide speed band at optimum torque
. If the engine is designed for performance, the torque curve will be peaked, you get a narrower band for optimum driving. This design requires more gears as each gear covers a narrower speed band in optimum torque.

All said and done, components wear out faster at higher speed, so every thing - engine, belts, alternator, AC, Tyres, bearings etc will last longer at lower speeds than at higher speeds.

Quote:
Originally Posted by Gansan View Post
My two cents;
Note: This logic can't hold good (or will do so only marginally due to the higher temperature generated) for the tyres, which will do the same number of revolutions for a given distance, irrespective of speed!
The tyre wear is directly proportionate to the heat generated and the friction which is again proportionate to the speed, so tyres will wear out faster at higher speeds in hot climate. That is the reason Radial Tyres last longer, because they have thinner section and run cooler than the Bias Ply designs.

Last edited by .anshuman : 1st September 2011 at 19:59. Reason: Back to back posts merged. Please use edit option if posting again within 30 mins. Thanks
Aroy is offline   Reply With Quote
Old 3rd September 2011, 19:32   #113
BHPian
 
dhawcash's Avatar
 
Join Date: Dec 2008
Location: jaipur
Posts: 124
Thanked: 141 Times
Default Re: All you enthusiastic drivers : Do NOT OVER-REVV

Hi.

err..at the start of this thread there are reports of brand new engines failing after being revved hard and driven fast. Shouldn't new engines be driven calmly for a while for everything to settle (running in). I know modern car engines are made much more accurately due to advancements in machining technology...but still u cannot find two exact pistons ( if you can, your engine is partially blueprinted!). i mean a few microns difference will be enough to induce extra friction and any engine should be run in properly (not too slow, not too fast- there is a proper way to do it)

The first picture in the head shows a broken valve. belonging to a Honda s2000 (famous for its 9000 RPM redline) Might be due to valve float or the piston hitting the valve somehow? or just a faulty valve?

I'm not saying it is safe to rev an engine, but a healthy engine should not pose any problems. i regularly (on deserted roads) rev my esteem's lil 1.3 and shift at around 5800-6000 rpm. have hit the revlimiter (@6500rpm) manytimes as well, but no issues as yet. Wrong shifting will however be catastrophic for the engine as well as transmission.
revlimit is an engineered thing- taking into account the weakest link (generally the valvetrain) with a certain factor of safety used.

For example, it is adviced not to rev old bullets (which did not have a rev limiter) in neutral and in 1st gear. At high revs, valve springs cannot keep up with the engine speed and are unable to close the valve on time ( also the reason for valve float). it would result in the piston hitting the open valve and BANG.[ducati solved this issue using Desmodromic Valvetrain]

So i think its okay to rev it up occassionaly...and will continue to do so (its really hard to resist)..unless i learn the hard way!!

As they say, 'Akkal badam khane se nahi, Laat khane se aati hai'
dhawcash is offline   Reply With Quote
Old 3rd September 2011, 19:58   #114
Senior - BHPian
 
Join Date: Aug 2010
Location: Delhi
Posts: 2,133
Thanked: 1,004 Times
Default Re: All you enthusiastic drivers : Do NOT OVER-REVV

I also feel that simply over revving engines should not result in catastrophic failure. Most of the engine problems stem from insufficient lubrication, and at time due to parts failing.

The first is easily remedied by having proper oil and letting it attain proper operating temperature. That allows the lubricant to achieve optimum viscosity and coat all relevant surfaces. Of course if a wrong oil is used, which deteriorates rapidly at high temperatures (when you over rev for a long time), then your goose is cooked, as for all practical purpose you have no/insufficient lubricant.

The second is a tricky issue. Valve springs have been know to fail under extreme operating conditions, pistons and crankshafts have warped or cracked mysteriously, but these are rare instances of faulty material, and that is nearly impossible in modern factories producing performance machines, as all critical component are checked and tested at each stage starting from the OEM to the assembly line. You should see the testing of components at the Ferrari Factory on the Discovery Channel show to realise to what extent things are tested.

An engine has a lot of reserve potentiality for better performance. It is normally detuned for longer life for the average user. What normally happens, is that enthusiasts tune their engines for higher performance and use exotic fuels to achieve it. What they forget is that the components for normal engine are not designed for this duty and some thing can fail! Also some high octane concoctions use additives which are extremely corrosive for aluminum and can eat up the pistons and aluminum heads pretty fast, but they provide extreme performance till the engine lasts!
Aroy is offline   Reply With Quote
Old 3rd September 2011, 20:08   #115
Distinguished - BHPian
 
SS-Traveller's Avatar
 
Join Date: Jan 2009
Location: New Delhi
Posts: 6,618
Thanked: 10,787 Times
Default Re: All you enthusiastic drivers : Do NOT OVER-REVV

Quote:
Originally Posted by Aroy View Post
...the engine will not be damaged by consistently revving it to the Red Line...
Quote:
Originally Posted by Aroy View Post
I also feel that simply over revving engines should not result in catastrophic failure.
Ajoyda, I think readers may be a little confused between
  • revving hard,
  • revving to the red line and
  • over-revving.
An explanation ought to be in order from your side!
SS-Traveller is offline   (1) Thanks Reply With Quote
Old 3rd September 2011, 20:18   #116
Senior - BHPian
 
Join Date: Aug 2010
Location: Delhi
Posts: 2,133
Thanked: 1,004 Times
Default Re: All you enthusiastic drivers : Do NOT OVER-REVV

Quote:
Originally Posted by SS-Traveller View Post
Ajoyda, I think readers may be a little confused between
  • revving hard,
  • revving to the red line and
  • over-revving.
An explanation ought to be in order from your side!
OK
. Revving hard is going all the way slightly below the red line and staying there for some time
. Revving to red line is revving till you hit the red line. In most modern engines this is where the ECU intervenes and cuts the fuel, so you cannot go beyond it. I do it regularly when I want to carry out maneuvers at lower speeds - 1st and second gear most often.
. Over Revving is when you go beyond the red line. This is only possible if the engine allows it. Most ECU based cars do not, but you can reprogram the ECU to go beyond it.
Aroy is offline   Reply With Quote
Old 3rd September 2011, 20:21   #117
Senior - BHPian
 
oxyzen's Avatar
 
Join Date: Feb 2010
Location: Not fixed.
Posts: 1,026
Thanked: 265 Times
Default Re: Does Revving the Engine consistently damage the engine on a longer run ?

Quote:
Originally Posted by nukeblitz View Post
So, I still say that you are ending up in the torque band but are losing the torque multiplicaiton and hence have lower torque going to the wheels. Ideally, I would say that you actually have to go beyond your power peak for the optimal shift.

How far beyond the power peak?
You are absolutely 100% right. To do that calculation-
1) You need the (power vs RPM) graph.
2) You need V1000.

For a typically petrol engine Max power is at 6000 RPM and it tapers off after that. But it will reach 6500 RPM. It will somewhere be between (5500-6500). Infact power at 6500> power at 5500. Now depending on gear ratios RPM drops by around 30% on every upshift. So even at 6500, it will drop to 4500. So theoritically you should rev to the cut off limit in most cases.

Diesels can be a different scenario whatsoever.
oxyzen is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Is your kid as enthusiastic about cars as you!!! aryashiv1 Shifting gears 25 21st November 2013 15:24
Over revving MPFI Zen Engine( revv limiter doesnt cut at 6000 rpm!!) speedsatya Technical Stuff 4 30th October 2010 15:21
Ractive Tachometer 3.5'' does not cross 3000 RPM on Max Revv bugboy180 Modifications & Accessories 21 23rd January 2009 00:11
Are you an enthusiastic driver or a regular driver? mclaren1885 Shifting gears 51 27th November 2007 18:14
Over Enthusiastic Indica SLK Street Experiences 6 25th July 2004 14:25


All times are GMT +5.5. The time now is 10:22.

Copyright 2000 - 2017, Team-BHP.com
Proudly powered by E2E Networks