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Old 8th February 2021, 12:29   #31
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Re: Why don't the new turbo-petrol engines rev as high as the NA petrols?

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Originally Posted by Dr.Naren View Post
I had driven Ciaz 1.5 DDIS

Oh Boy, That engine is so Petrol like in it's manners, almost too much at that.
Hope to see it soon in the BS6 avatar
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Old 8th February 2021, 13:17   #32
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Re: Why don't the new turbo-petrol engines rev as high as the NA petrols?

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Originally Posted by Raghu M View Post
Exactly my thoughts. What's the point of revving an engine beyond 5K +? You can't even run a car beyond 120 kmph on 99% of Indian roads.
I have read all the arguments and explanations with interest.

I think there is only one valid reason to have a high revving engine. The sound!

Given the right engine, and the right exhaust and right muffler, some cars on high revs, just sound glorious. You can make these sounds in any gear of course. You don’t need to be on the motorway, you can rev in second gear as well as in fifth gear.

My little Alfa Spider will happily rev close to 6000RPM. We used to live near the Hague in in the Netherlands. The motorway, A12, leading into the Hague runs in a concrete tunnel for the last couple of kilometers. Speed limit is 70 km/h and 50 km/h on the last kilometer. I used to get into my Spider, drive it for 15 minutes to properly warm up and then barrel down that tunnel at about 60 km/h in second gear, just to hear that sound, lift off and the engine would produce some even better sounds with lots of sputtering and banging! Echoing between the concrete walls!

I have not heard anybody on torque yet. Of course, high RPMs is a very effective way of dealing with high torque!

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Old 8th February 2021, 13:44   #33
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Re: Why don't the new turbo-petrol engines rev as high as the NA petrols?

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Originally Posted by Jeroen View Post
What is with the fascination of high revving?

We have countless threads suggesting trost Indian drivers never ever exceeds 1500RPM?

We are concerned about lugging not revving I thought?

Jeroen
I was just thinking this when I read the thread. I have driven a moderate amount overall (say 120k km), 90% of which is city driving. I am hard pressed to see where I can even push my car. Even now, on highway drives, I am not able to keep a consistent 80kmph speed. At 80-100kmph, my car barely touches 1700rpm (currently it is a turbo diesel). If I put it in sports mode and push the engine, it may touch 3000rpm briefly and that’s it before it settles down or I need to slow down or even brake.

I guess this could also be my driving style. In short, I don’t really understand the thought process behind high revving. Maybe some of you who understand more can educate me?
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Old 8th February 2021, 14:55   #34
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Re: Why don't the new turbo-petrol engines rev as high as the NA petrols?

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Originally Posted by PrasannaDhana View Post
Even the 1.3 DDIS is pretty rev happy and revs till 5000 rpm. That's in the top gear, still revving till 4300 rpm
Attachment 2119547
OT. I see someone ripping the road in some unmentionable speeds.
Please drive safe.
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Old 8th February 2021, 15:56   #35
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Re: Why don't the new turbo-petrol engines rev as high as the NA petrols?

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Originally Posted by Raghu M View Post
Exactly my thoughts. What's the point of revving an engine beyond 5K +? You can't even run a car beyond 120 kmph on 99% of Indian roads.
What's the point in having cars with more than 60 bhp? You can't drive a car beyond 120 kmph in 99% of the roads, and even if you can, it's illegal.

Now the answer to both the questions is the same.

It's not about reaching the 120 kmph mark or beyond, it's how you reach there.

You can't expect everyone to be gentle and do <2000 rpm always, some of us wanna have fun, and there is nothing wrong when you have fun within the legal limits. It's a nice feeling to feel rapid acceleration at times.

People with 250 bhp cars don't do 220 kmph all the time they are on road, same with 110 bhp hot hatch drivers, they don't do their top whack of 180-195 kmph always.

It's how the car accelerates in-gear, how much better and easier an overtaking manoeuvre gets, how aurally pleasing the exhaust note becomes and so on.
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Old 8th February 2021, 18:08   #36
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Re: Why don't the new turbo-petrol engines rev as high as the NA petrols?

Coming back to the OT, I believe the main reason for Turbos being limited in the rev range is the higher revs that the turbo has to endure than the engine. As per this link, a car cruising at 2000 RPM might have its turbo spooling at 280,000 RPM.

Guess, the speed of the turbo might not increase linearly with the engine speed, but still there has to be some increase in order to continue providing the additional boost the engine requires at higher RPM (Volume of air that needs to be compressed goes up). At those speeds, lubrication, heating and even centrifugal forces will dictate the integrity of the turbo.

Add to that, what many other members have pointed out, if you get what is needed from the engine before the RPM limit, where is the need to go beyond?
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Old 8th February 2021, 18:16   #37
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Re: Why don't the new turbo-petrol engines rev as high as the NA petrols?

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Originally Posted by Ravi Parwan View Post
Coming back to the OT, I believe the main reason for Turbos being limited in the rev range is the higher revs that the turbo has to endure than the engine. As per this
I have seen this point being made by several members, but of course that’s why we have a waste gaste fitted to our turbo. (when and where applicable)

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Old 8th February 2021, 18:55   #38
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Re: Why don't the new turbo-petrol engines rev as high as the NA petrols?

An engine usually produces peak power at twice the rpm of its peak torque. Turbo petrol engines are designed to produce peak torque at much lower rpms than their NA counterparts. Most turbo petrol engines mentioned here produce peak torque around 2000 - 2500 RPM, hence would produce peak power in around the 4500-5000 RPM range.

Allowing such an engine to hit 7000 rpm though feasible, would be pointless, as there'll not be power to match the higher revs. (Think about redlining a turbo diesel beyond 4000 RPM)

To allow it to hit peak power at 7000 RPM, the peak torque should be around 3500-4000 RPM (similar to NA petrols). This would negate the use of the turbo charger (in improving fuel efficiency, and low-end torque inside the city) and make it very similar to drive like a bigger NA petrol. In fact, it'll be worse because of the turbo-lag which will be highly pronounced at city speeds.

Slightly OT, most people don't redline the cars, as redlining our modern powerful cars will mean doing illegal and unsafe speeds easily. I don't redline our vento 1.6 tdi ever, but I find myself redlining my 800 5-Speed every-time the engine warms up. I can hit the rev-limiter safely in 1st and 2nd within the city speed limits. And it's waay more fun than what the vento offers.
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Old 8th February 2021, 19:26   #39
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Re: Why don't the new turbo-petrol engines rev as high as the NA petrols?

There is only one thing that I would like to add to this discussion that might be important.

The turbocharger runs at a very high rpm- if the engine is at 2,000 rpm the turbocharger might run as high as 150,000 to 200,000 rpm depending upon the design. One can only imagine the speeds at which it will run near the rev-limit.

Eventually there will also be a consideration of bearings that can withstand such high rpms. So, the rev-limit might also help in keeping the turbocharger in a safe operational speed range. Just my two cents. Cheers.
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Old 8th February 2021, 21:34   #40
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Re: Why don't the new turbo-petrol engines rev as high as the NA petrols?

A perspective from my side :- In general, engines producing higher torque figures (both turbo petrol/Diesel) will have taller gearing. For street purpose, this is a general thumb rule. With an high redline, the taller gear ratios will get into very high top speeds. Over and above the reasons mentioned by others in this thread, this gearing ratio aspect can be one of the reasons for having a lesser redline.

Last edited by shan_ned : 8th February 2021 at 21:39.
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Old 8th February 2021, 22:17   #41
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Re: Why don't the new turbo-petrol engines rev as high as the NA petrols?

It doesn't matter to me personally how much revs the engine has, if it has a nice punch, decent enough rpm range and a free-revving nature then it would do. Remember the Maruti 800 didn't have much revs but people loved to redline that sweet 3-cylinder engine. I remember many of the aftermarket tachometers for it used to show a max of 4.5-5k RPMs.


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Originally Posted by PrasannaDhana View Post
That's in the top gear, still revving till 4300 rpm
Attachment 2119547
Attached Thumbnails
Why don't the new turbo-petrol engines rev as high as the NA petrols?-img_20210208_221221.jpg  


Last edited by Lowflyer23 : 8th February 2021 at 22:24.
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Old 9th February 2021, 02:40   #42
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Re: Why don't the new turbo-petrol engines rev as high as the NA petrols?

Having owned and driven a Fiat Linea T Jet for 5 years, I can say that I did not miss going up to 7000 rpm or whatever. Heck the engine would not even do that. Post 6000 rpm, power would plateau and the engine did not sound good either. Besides; the car made swift progress without the need to wring it to levels you would on a NA engine. Yes; there is fun to red line engines and we probably do that for less than 1% of the time we spend with our cars. With these new direct injection new turbo petrol's, torque and power are developed so early that there is no point to redlining them.
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Old 9th February 2021, 08:29   #43
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Re: Why don't the new turbo-petrol engines rev as high as the NA petrols?

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Originally Posted by ashwinprakas View Post

Lighter Pistons/Shorter Strokes = Higher Revving

Heavier Pistons/Longer Strokes = Lower Revving

Car engine has the power to move a vehicle which is more than a ton. IMHO the weight of the piston/connecting rod/crankshaft has negligible effect on the performance.
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Old 9th February 2021, 11:16   #44
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Re: Why don't the new turbo-petrol engines rev as high as the NA petrols?

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Originally Posted by Guna View Post
Car engine has the power to move a vehicle which is more than a ton. IMHO the weight of the piston/connecting rod/crankshaft has negligible effect on the performance.
Hmmm... Unsure how you'd expect me to go about this.

But what I'd shared are facts rather than just opinions.
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Old 9th February 2021, 12:42   #45
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Re: Why don't the new turbo-petrol engines rev as high as the NA petrols?

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Originally Posted by Guna View Post
Car engine has the power to move a vehicle which is more than a ton. IMHO the weight of the piston/connecting rod/crankshaft has negligible effect on the performance.
Quote:
Originally Posted by ashwinprakas View Post
But what I'd shared are facts rather than just opinions.
Correct, weight of these component has a big impact on the engine performance. In particular, in context of this thread, how fast an engine could rev. Think moment of inertia and centripetal forces.

For similar reasons stroke has a big impact as it determines the maximum speed of a piston and thus impacts the same.


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