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


Reply
 
Thread Tools Search this Thread
Old 1st April 2011, 16:06   #61
Senior - BHPian
 
oxyzen's Avatar
 
Join Date: Feb 2010
Location: Not fixed.
Posts: 1,026
Thanked: 265 Times
Default Re: All you enthusiastic drivers - DONT OVER-REVV

Quote:
Originally Posted by ph03n!x View Post
That would be dangerous, may result in accidents or losing control.
Why? The only thing you will loose is the engine braking. Yes you are right to some extent. It may be a bit dangerous. But once you brake and get the RPM below 7000 it will be back on.

Downshifting to 2nd at 120 is already an accident. And that can very well be saved by disconnecting the transmission.

I beieve it is very easy for AMT (Automated manual transmission) to avoid over revv. Wont just allow to get into a gear too low.
oxyzen is offline   Reply With Quote
Old 1st April 2011, 16:14   #62
Senior - BHPian
 
vnabhi's Avatar
 
Join Date: May 2007
Location: DC -> DC
Posts: 5,272
Thanked: 1,236 Times
Default Re: All you enthusiastic drivers - DONT OVER-REVV

Good thread! On my first long trip on my Fiesta, my son mistakenly down-shifted to 2nd instead of 4th. But fortunately, the speed was only about 50 kmph, and I am not sure what the tacho read at that point of time. In a jiffy, he pressed the clutch and brought the revvs down.

The reason for his error of judgement was because he was used to the rubbery shifts of the WagonR and not the smoother ones in the Fiesta.

Touch wood, nothing happened to the car!!
vnabhi is offline   Reply With Quote
Old 1st April 2011, 22:13   #63
Distinguished - BHPian
 
Join Date: Jul 2009
Location: Kolkata
Posts: 3,506
Thanked: 2,072 Times
Default Re: All you enthusiastic drivers - DONT OVER-REVV

Quote:
Originally Posted by jaysmokesleaves View Post

OT > If anyone can please answer this.
What is the effect(on the engine) of idling the engine with ac on for over 48 hours in the middle eastern desert summer above 50'c ?
Hi,
Interesting question.

Sticking my neck out.

Assuming NA Petrol. Also assuming you are not alluding to things like battery running down, and only referring to engine.

If the car does not start overheating in say 3 to 4 hrs in daytime heat, then the suspect point would be inadequate camshaft lubrication, or its corollary excess oil in combustion. Which along with low exhaust temperatures might cause problems with the catcon. Other than that in a modern car, don't think it should have any effect.

In an older car with iffy carburettion, and non bulletproof lubrication, you would also have problems of scoring of pistons and cylinder walls, and maybe even bigends.

Would like to know the definitive answer.

Regards
Sutripta
Sutripta is offline   Reply With Quote
Old 1st April 2011, 22:29   #64
dot
Senior - BHPian
 
dot's Avatar
 
Join Date: Dec 2007
Location: Ban Chang
Posts: 1,681
Thanked: 714 Times
Default Re: All you enthusiastic drivers - DONT OVER-REVV

Quote:
Originally Posted by Mustang.101 View Post
Yes the RPM will go above 6K in that case and will cause over revving.
Thanks for the reply. However I don't understand this. If gear is downshifted from 4th to 1st and RPM shoots from 1500 to 6000, shouldn't a modern engine be robust enough to withstand that sudden change. I can understand if the RPM goes suddenly beyond the redline limit then it might cause damage. Consider this, one starts a well warmed car and floors the accelerator. RPM zooms from idle (700-800) to 6000-7000. How is it different from the previous scenario.

Looking forward to learn on this topic.
dot is offline   Reply With Quote
Old 1st April 2011, 22:57   #65
Senior - BHPian
 
ph03n!x's Avatar
 
Join Date: Jun 2008
Location: Madras
Posts: 1,705
Thanked: 118 Times
Default Re: All you enthusiastic drivers - DONT OVER-REVV

Quote:
Originally Posted by oxyzen View Post
Why? The only thing you will loose is the engine braking. Yes you are right to some extent. It may be a bit dangerous. But once you brake and get the RPM below 7000 it will be back on.

Downshifting to 2nd at 120 is already an accident. And that can very well be saved by disconnecting the transmission.

I beieve it is very easy for AMT (Automated manual transmission) to avoid over revv. Wont just allow to get into a gear too low.
Someone would shift down from 120 to 4th (or any gear by mistake) only for engine braking, without which most cars on our roads wont stop effectively from 100+ purely on brakes, no matter how good the stock brakes are.

Now imagine what would happen if the transmission disengages the engine - You have a lorry in front, you cut down gears while on 120, slot it into 2nd instead of 4th or 3rd by mistake. And hey, instead of engine braking (which will blow up the engine), the car rolls along with only the red hot discs and useless drums to stop it - this accident will mostly end up in loss of life, than just a blown up engine, no?!
ph03n!x is offline   Reply With Quote
Old 2nd April 2011, 02:59   #66
Distinguished - BHPian
 
dhanushs's Avatar
 
Join Date: Oct 2009
Location: Bathery/BLR
Posts: 3,446
Thanked: 4,057 Times
Default Re: All you enthusiastic drivers - DONT OVER-REVV

Quote:
Originally Posted by dot View Post
... I don't understand this. If gear is downshifted from 4th to 1st and RPM shoots from 1500 to 6000, shouldn't a modern engine be robust enough to withstand that sudden change.
If the RPM increase is within the revv limit range, its fine. 6k is well within the rev limit of the IKON.

but.. If the RPM, on downshifting, increases well above the revv limit, the engine might bear the stresses generated.

Oh, and by the way, I too own a Ford IKON Flair, 07. The sound on revving is way too addictive, and I redline it almost every other day. but yes, the engine isnt as much as fun as the v-tec above 5k.
dhanushs is offline   Reply With Quote
Old 2nd April 2011, 09:19   #67
dot
Senior - BHPian
 
dot's Avatar
 
Join Date: Dec 2007
Location: Ban Chang
Posts: 1,681
Thanked: 714 Times
Default Re: All you enthusiastic drivers - DONT OVER-REVV

Quote:
Originally Posted by dhanushs View Post
If the RPM increase is within the revv limit range, its fine. 6k is well within the rev limit of the IKON.
but.. If the RPM, on downshifting, increases well above the revv limit, the engine might bear the stresses generated.
@dhanushs, that what I would think too. IMHO, find it very strange if a movement, regardless of its source, from 1500 to 6000 RPM can be called "over revving" in any modern petrol engine. By source I meant whether it is flooring from idle to redline or downshifting.

Quote:
Originally Posted by dhanushs View Post
Oh, and by the way, I too own a Ford IKON Flair, 07. The sound on revving is way too addictive, and I redline it almost every other day. but yes, the engine isnt as much as fun as the v-tec above 5k.
Yes, I know, my friend. I have followed your posts on Ikon. Wish we had exchanged posts before. Unfortunately I have sold the Ikon last december. I miss it very much and a thought comes once in while whether to call up the buyer and buy the Ikon back!!

Also, agree that the R18 i-Vtec revvs much more smoothly than the 1.3 ROCAM.
dot is offline   Reply With Quote
Old 2nd April 2011, 10:27   #68
BANNED
 
Join Date: Feb 2010
Location: New Delhi
Posts: 1,316
Thanked: 233 Times
Default Re: All you enthusiastic drivers - DONT OVER-REVV

Quote:
Originally Posted by dot View Post
Thanks for the reply. However I don't understand this. If gear is downshifted from 4th to 1st and RPM shoots from 1500 to 6000, shouldn't a modern engine be robust enough to withstand that sudden change. I can understand if the RPM goes suddenly beyond the redline limit then it might cause damage. Consider this, one starts a well warmed car and floors the accelerator. RPM zooms from idle (700-800) to 6000-7000. How is it different from the previous scenario.

Looking forward to learn on this topic.
You see you're not getting the point.

Damage scenario : For eg: when your car is at 4000 RPM in 4th gear and you downshift by mistake to 1st gear. Thus your RPM goes well above the limited range of 6500 rpm and thus your rpm might be at the 8000 or so level. This will cause damage.

No Damage : For eg: your are in second gear and you do not change gears and just floor the pedal. What happens is that at 6500 rpm the limiter kicks in and it does not allow you to cross above 6500 rpm and thus prevents any immediate damage.
Mustang.101 is offline   Reply With Quote
Old 2nd April 2011, 10:34   #69
dot
Senior - BHPian
 
dot's Avatar
 
Join Date: Dec 2007
Location: Ban Chang
Posts: 1,681
Thanked: 714 Times
Default Re: All you enthusiastic drivers - DONT OVER-REVV

Quote:
Originally Posted by Mustang.101 View Post

when your car is at 4000 RPM in 4th gear and you downshift by mistake to 1st gear. Thus your RPM goes well above the limited range of 6500 rpm and thus your rpm might be at the 8000 or so level. This will cause damage.
True I agree that going beyond rev limit will cause damage. However with the rev limiter in place and active all the time, how come the RPM will shoot to 8000+. Does it mean that rev limiter will not work during this scenario?
dot is offline   Reply With Quote
Old 2nd April 2011, 10:37   #70
BANNED
 
Join Date: Feb 2010
Location: New Delhi
Posts: 1,316
Thanked: 233 Times
Default Re: All you enthusiastic drivers - DONT OVER-REVV

Quote:
Originally Posted by dot View Post
True I agree that going beyond rev limit will cause damage. However with the rev limiter in place and active all the time, how come the RPM will shoot to 8000+. Does it mean that rev limiter will not work during this scenario?
It does work but it takes time to adjust to this sudden change of rpm. Its after all the ECU which is doing it and is a computer which does take a few split seconds to calculate.
Mustang.101 is offline   Reply With Quote
Old 2nd April 2011, 10:42   #71
dot
Senior - BHPian
 
dot's Avatar
 
Join Date: Dec 2007
Location: Ban Chang
Posts: 1,681
Thanked: 714 Times
Default Re: All you enthusiastic drivers - DONT OVER-REVV

Quote:
Originally Posted by Mustang.101 View Post
It does work but it takes time to adjust to this sudden change of rpm. Its after all the ECU which is doing it and is a computer which does take a few split seconds to calculate.
Thanks for the explanation.

So this is it. In a split second the damage can occur.
dot is offline   Reply With Quote
Old 2nd April 2011, 11:25   #72
Senior - BHPian
 
Shan2nu's Avatar
 
Join Date: Feb 2004
Location: Hubli - Karnata
Posts: 5,525
Thanked: 87 Times
Default Re: All you enthusiastic drivers - DONT OVER-REVV

Quote:
True I agree that going beyond rev limit will cause damage. However with the rev limiter in place and active all the time, how come the RPM will shoot to 8000+. Does it mean that rev limiter will not work during this scenario?
The ECU can only limit the revs when you are using fuel to accelerate past the redline. But in a deceleration scenario where you shift into a low gear at high speeds, the vehicles momentum causes a mechanical over rev, which the ECU cannot control.

Shan2nu
Shan2nu is offline   Reply With Quote
Old 2nd April 2011, 16:23   #73
Senior - BHPian
 
Join Date: Nov 2007
Location: Bangalore
Posts: 2,376
Thanked: 528 Times
Default Re: All you enthusiastic drivers - DONT OVER-REVV

General consensus seems to be that it is alright to rev the engine to redline occasionally, but causing the engine to over-rev by slotting to a wrong gear is harmful to the engine.
But here is my thought:
In case of intentional redlining with acceleration input, the engine is working harder, as it is pushing the car to higher speeds overcoming the retarding forces.
In case of a scenario of slotting to a lower gear at high speed, the engine shoots to the higher revs, but there is no load on it and it is simply free-reving. The engine will be probably burning lean or in some advanced engines, even the fuel will be cut off.
This is similar to a what happens to the engine when it is going uphill (working harder) against going downhill (almost no load) at similar engine speeds.
By this logic, intentional redlining looks more harmful then the engine shooting to higher revs due to slotting lower gear.
Guna is offline   Reply With Quote
Old 2nd April 2011, 17:00   #74
Distinguished - BHPian
 
Join Date: Jul 2009
Location: Kolkata
Posts: 3,506
Thanked: 2,072 Times
Default Re: All you enthusiastic drivers - DONT OVER-REVV

^^^
No. Overrevving without load is quite bad. In fact one of the stress points is the sudden closure of the throttle at full revs.

To fully explain this would take half a semester. So beyond my abilities. Will leave it to the engineers on this forum.


@Mustang and Shan2nu: Agree with Shan2nus PoV.

Regards
Sutripta

Last edited by Sutripta : 2nd April 2011 at 17:02.
Sutripta is offline   Reply With Quote
Old 26th August 2011, 10:41   #75
BHPian
 
Kimified's Avatar
 
Join Date: Mar 2011
Location: Bangalore
Posts: 242
Thanked: 80 Times
Default Cons of over Revving the Engine consistently

I have a i20 Diesel which i have been using from the past 9 months. I absolutely love the engine. Being a diesel, Its still quite Rev happy.

Now, Here is my Problem.

I come from a school of thought where i don't mind spending a bit more on the fuel if i can have some fun while driving. I would rather give up on a dinner at a restaurant and use that 500 bucks to have fun for one full month. .Considering that there is a difference of .5 rs/km (A 2kmpl dip in mileage) and i drive 1000 km a month.

I have been advised that the normal gear shift for a diesel i20 is around 2 or 2.5 rpm. And i have noticed while sitting in the passenger seat that most of my friends shift well before what i do it at. But, I have never really given too much thought into it except for the first 1k kms.
I had gone on a longish drive last weekend and i noticed that i shift well beyond 2.5rpm and sometimes do it at 3.5k or even 4k rpm
I get really bad mileage figures both for the city and the highways (12 and 15 respectively). But then, I don't really care about it cause i know its because of me and not the car. (I ones forcefully drove it very sanely and got a highway mileage of 17!).

So, Will this high revv usage of the engine reduce the lifetime or cause any unwanted problems at a later stage ? I have never red lined it (The red line is at 4.8k rpm) but just wanted to get this thing clarified.

PS : Mods. I searched for this kind of thread, did not find one. Please merge it with the right thread if needed. Thanks.
Kimified 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 18:39.

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