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


Reply
 
Thread Tools Search this Thread
Old 21st September 2012, 09:15   #1
BHPian
 
groom's Avatar
 
Join Date: Dec 2007
Location: Yokohama
Posts: 143
Thanked: 187 Times
Post Why the Twin-Stage Turbo & not a VGT?

I was discussing the launch of Quanto with one of my ex-colleague and also a friend (who is extensively working on Turbo Tech) but we could never understand why Mahindra went for twin turbo instead of VGT.

Lets compare the specs of similar engines which have same or similar displacement, but achieve a similar power and torque using Variable nozzle/geometry turbine type Turbo charger instead of a Twin turbo,

Name:  Engine_Spec_Comparo.png
Views: 6407
Size:  12.2 KB

As you can see, most engines have reached to 100 or over 100BHP easily by just changing the turbo technology from normal turbo to VGT.

My Friend: Normally a two stage turbo will have a turbine size of 42mm (Low Pressure) and 35mm (High Pressure), but VGT covers both the flow ranges and still able to deliver the power density.

Me: More over, look at the loss of mileage Quanto has over Duster. (could be weight issues)

The change from normal turbo to VGT is simple, not much modifications, cost less, and frugal engineering. On the other hand, twin turbo is a major modifications, even bigger for Mahindra, especially hearing how things proceed in Mahindra on the THAR threads,

So what made Mahindra not choose the simpler path. Why did mahindra use twin turbo. Especially the twin turbo has risks - lubrication and oil leakage.

is it just to differentiate ?
What challenge was mahindra trying to overcome by this path? and is it future proofing ?

Can any experts throw light on this, Please
groom is offline   (3) Thanks Reply With Quote
Old 21st September 2012, 09:39   #2
Distinguished - BHPian
 
sgiitk's Avatar
 
Join Date: Dec 2007
Location: Kanpur
Posts: 7,162
Thanked: 3,757 Times
Default re: Why the Twin-Stage Turbo & not a VGT?

A twin turbo is likely to have a lower turbo lag.
sgiitk is offline   (6) Thanks Reply With Quote
Old 21st September 2012, 09:40   #3
Awaiting Email Confirmation
 
Join Date: Aug 2006
Location: Hyderabad
Posts: 531
Thanked: 350 Times
Thumbs down re: Why the Twin-Stage Turbo & not a VGT?

Not sure why Mahindra went by a twin Turbo.

Twin turbos have their own issues, however i believe, they are more reliable in the long run if maintained properly. A VGT will have to take too much of load on it. and Mahindra's have an image like "Rough gaadi hai" and they might not want to take chances (Not sure of this. Just an opinion.)

The other reason could be. Mahindra's have invested around 900 Cr in the R&D process for Xylo platform. so they might be trying out different alternatives possible and their reliability. This might be an outcome of that. I am pretty sure that they have tested this engine with VGT and with Twin turbo till its death. The results of this testing might be one of the reason for opting a Twin turbo.

Another dumb reason could be. Mahindra's dont want to go out of work. so they intentionally introduced a probable bug in their product in the name of Twin turbo. Because of this, they have more sales of some spares, mechs have more work. Remember, the cost of the base model is 5.9 and this is a 7 seater so the margins would be low. so they need to earn somewhere. May be they are inspired by google.
gemi_kk is offline   (1) Thanks Reply With Quote
Old 21st September 2012, 09:44   #4
BHPian
 
groom's Avatar
 
Join Date: Dec 2007
Location: Yokohama
Posts: 143
Thanked: 187 Times
Default re: Why the Twin-Stage Turbo & not a VGT?

Quote:
Originally Posted by sgiitk View Post
A twin turbo is likely to have a lower turbo lag.

lower turbo lag can be easily solved with VGT, you already have such engines in Indian market, where the turbo lag is not felt at all.

Like i said, the risk weighs more than the benefits.
groom is offline   Reply With Quote
Old 21st September 2012, 10:31   #5
BHPian
 
Join Date: Jan 2009
Location: Chennai
Posts: 41
Thanked: 15 Times
Default re: Why the Twin-Stage Turbo & not a VGT?

VGT doesn't completely eliminate the turbolag.Twin turbo reduces the turbo lag further than VGT. Also, with the twin turbo the low end torque improves. The torque delivery is flatter. Quanto delivers 240 Nm from 1600-2800 rpm. Twin turbo helps in this regard.
VeeTee is offline   (6) Thanks Reply With Quote
Old 21st September 2012, 10:38   #6
BHPian
 
Frankenstein's Avatar
 
Join Date: Jan 2011
Location: Bangalore/hyderabad
Posts: 334
Thanked: 274 Times
Default re: Why the Twin-Stage Turbo & not a VGT?

Quote:
Originally Posted by groom View Post
I was discussing the launch of Quanto with one of my ex-colleague and also a friend (who is extensively working on Turbo Tech) but we could never understand why Mahindra went for twin turbo instead of VGT.
Groom check out the torque the mahindra produces at 1600rpm.

If vgt can be tuned to reduce turbo lag, so does a twin turbo setup .
Even with a vgt setup to kick in at 1000rpm , there is not much boost , vgt does a twin turbo job , but a twin turbo performs better .

Last edited by Rehaan : 21st September 2012 at 14:03. Reason: Hi, please avoid quoting an entire large post. It inconveniences our small screen & mobile readers. Thanks.
Frankenstein is offline   (1) Thanks Reply With Quote
Old 21st September 2012, 10:48   #7
Senior - BHPian
 
AutoIndian's Avatar
 
Join Date: Aug 2010
Location: PCMC, Pune-MH14
Posts: 3,120
Thanked: 3,818 Times
Default re: Why the Twin-Stage Turbo & not a VGT?

Quote:
Originally Posted by sgiitk View Post
A twin turbo is likely to have a lower turbo lag.
Quote:
Originally Posted by VeeTee View Post
VGT doesn't completely eliminate the turbolag.Twin turbo reduces the turbo lag further than VGT. Also, with the twin turbo the low end torque improves. The torque delivery is flatter. Quanto delivers 240 Nm from 1600-2800 rpm. Twin turbo helps in this regard.
with sgiitk & VeeTee. Look at the peak torque figures which the other engines produce & @ what rpm. The mCR100 of the Quanto produces the peak torque from as low as 1600 rpm & goes all the way to 2800 rpm (very wide rpm band). Other engines produce the peak torque at higher band & taper out quickly on either sides of the peak torque rpm.

Attaching below the Torque curve for the Quanto engine (source: the pdf shared earlier on TBHP).

Name:  Torque Curve.jpg
Views: 8974
Size:  45.4 KB

Would be interesting to compare it with the torque curves of other engines. If someone can post them over here, it would be really helpful.
AutoIndian is online now   (3) Thanks Reply With Quote
Old 21st September 2012, 11:07   #8
BHPian
 
hemen's Avatar
 
Join Date: Feb 2008
Location: Bombay
Posts: 83
Thanked: 24 Times
Default re: Why the Twin-Stage Turbo & not a VGT?

IMHO Mahindra had to go twin turbo due to huge weight of Quanto in comparison to others and using a 3-POT engine. Just see how early the torque is created and the spread of the FLAT torque curve. Using a VGT for Better lower end would have resulted in blunted top end.
hemen is offline   (5) Thanks Reply With Quote
Old 21st September 2012, 11:19   #9
Team-BHP Support
 
tsk1979's Avatar
 
Join Date: Feb 2005
Location: New Delhi
Posts: 22,955
Thanked: 15,648 Times
Default re: Why the Twin-Stage Turbo & not a VGT?

Also do not forget, when cars with VGT have a turbo failure, its a 90000 bill. Two smaller turbos will be cheaper than the VGT, and less prone to failure too. VGT is a very complex piece of kit as compared to a simple turbocharger(which costs 20,000 odd)
However, tuning an engine with VGT is a lot simpler. The Quanto can manage a puny 99 horses, while similarly engined VGT vehicles can touch 130bhp without breaking a sweat
tsk1979 is offline   (1) Thanks Reply With Quote
Old 21st September 2012, 11:29   #10
BHPian
 
brraj's Avatar
 
Join Date: Feb 2006
Location: bangalore
Posts: 794
Thanked: 351 Times
Default re: Why the Twin-Stage Turbo & not a VGT?

Before we get into conclusions
Is there any difference between a

- Twin-Scroll Turbo (cardekho)
http://www.cardekho.com/india-car-ne...usive-8786.htm
- Twin-Turbo
- Twin-Stage Turbo (source: Mahindra web site)
http://www.mahindraquanto.com/images...o-brochure.pdf

Explanation of staged turbo charging
http://en.wikipedia.org/wiki/Twin-turbo

Looks like its having a single turbo which is staged
brraj is offline   (4) Thanks Reply With Quote
Old 21st September 2012, 13:30   #11
BHPian
 
groom's Avatar
 
Join Date: Dec 2007
Location: Yokohama
Posts: 143
Thanked: 187 Times
Default re: Why the Twin-Stage Turbo & not a VGT?

Quote:
Originally Posted by VeeTee View Post
VGT doesn't completely eliminate the turbolag.Twin turbo reduces the turbo lag further than VGT. Also, with the twin turbo the low end torque improves. The torque delivery is flatter. .
Quote:
Originally Posted by Frankenstein View Post
Groom check out the torque the mahindra produces at 1600rpm.
.
VGT can eliminate the turbo lag, One may not feel at all. Flatter torque can be achieved by many means, surely this is an advantage. But see my post at the end.


Quote:
Originally Posted by AutoIndian View Post

Attaching below the Torque curve for the Quanto engine (source: the pdf shared earlier on TBHP).

Attachment 989600
Thanks Autoindian for this curve, this perfectly compares how much improvement that engine has made. But disappointing that percentage wise, it is very small (9%). For such improvements why do so much modifications ? and the peak torque is coming later than MDICRDE engine. And important point - the torque point is moved later than before. It is not coming earlier. I have penned down my version of thoughts below.



Quote:
Originally Posted by hemen View Post
IMHO Mahindra had to go twin turbo due to huge weight of Quanto in comparison to others and using a 3-POT engine. Just see how early the torque is created and the spread of the FLAT torque curve. Using a VGT for Better lower end would have resulted in blunted top end.
This is exactly my point, if the weight was the issue and we needed lots of torque, then why the improvement in torque is only 10% over the previous engine. Even with twin turbo. When VGT can delivery even more than this torque.

Integrating one turbo in the engine is lot easier than twin?

Quote:
Originally Posted by tsk1979 View Post
Two smaller turbos will be cheaper than the VGT, and less prone to failure too.
Consider the reliability of turbo is 0.99, then twin turbo reliability will be .98, hence twin will be more prone to failure.
More over, the smaller of the two turbo can have serious lubrication issues.


When i kept thinking today and went through all the material, here is what i came up with.

1) Strategically, the twin turbo technology can extend the engine viability on many platforms. Means if the turbo is uprated further the improvement can be significant. also means this engine will reach 120HP, which is being used in Scorpio. --> the current mill running in Scorpio will be axed soon?

2) Emissions - I read in the presentations and in Wiki, this engine can easily meet the BS5 norms and further on. That means this has long term capability.

3) Underrating this engine means, this engine will be used in Verito!! --> No dependency on Renault --> Lots of savings and Lots of mileage from such an engine. Also this engine can be used in Verito Hatch Back. The mileage of 17 is quite impressive for mHawk variant ?

4)The flat torque / early torque is just a consequence of a particular technology but not the reason to choose the technology. Looking at what goes on in THAR threads Mahindra would not take so much pain in engineering, invest so much and develop this new platform.

And more over, excess lower torque in such a small diesel engine means - possibility of higher Free Acceleration Smoke, additionally this is derivative of mHawk engine, the guys driving THAR surely experience uncontrollable torque.

But in the end my conclusion is, this engine may be available in entire power spectrum, such variations in power (64bhp to 120bhp) can be possible with twin turbo?
groom is offline   Reply With Quote
Old 21st September 2012, 13:42   #12
Team-BHP Support
 
tsk1979's Avatar
 
Join Date: Feb 2005
Location: New Delhi
Posts: 22,955
Thanked: 15,648 Times
Default re: Why the Twin-Stage Turbo & not a VGT?

Quote:
Originally Posted by groom View Post
Consider the reliability of turbo is 0.99, then twin turbo reliability will be .98, hence twin will be more prone to failure.
More over, the smaller of the two turbo can have serious lubrication issues.
Normal Turbos are less prone to failure than VGTs, and can take more abuse. Most users do not follow start stop regimen for proper turbo maintenance.
tsk1979 is offline   Reply With Quote
Old 21st September 2012, 15:09   #13
BHPian
 
hemen's Avatar
 
Join Date: Feb 2008
Location: Bombay
Posts: 83
Thanked: 24 Times
Default Re: Why the Twin-Stage Turbo & not a VGT?

Quote:
Originally Posted by groom View Post
the twin turbo technology can extend the engine viability on many platforms.
Different Variations of the engine could be used to replace the Verito engine and another in CS/hatch version i.e to be launched. This could also provide a lesser royalty payout to Renault.
hemen is offline   (1) Thanks Reply With Quote
Old 21st September 2012, 16:43   #14
Team-BHP Support
 
suhaas307's Avatar
 
Join Date: Aug 2009
Location: Bangalore
Posts: 8,055
Thanked: 6,602 Times
Default Re: Why the Twin-Stage Turbo & not a VGT?

Quote:
Originally Posted by sgiitk View Post
A twin turbo is likely to have a lower turbo lag.
True.

But the Duster 85's engine's torque peaks at 1900 RPM, not much higher than the Quanto's, which peaks @ 1600-2800 RPMs. The Duster is also feather light, at 1180 kgs (kerb weight) and that's nearly 500 kgs lighter than the Quanto. This despite the Duster's considerably larger foot-print on the road.

The Duster 85's peak-torque is 200 Nm @ 1900 RPM but being 500 kgs lighter, there shouldn't be too much difference between the two. The 110 makes more torque but only marginally (248 @ a higher 2200 RPM) while the Quanto's twin-turbo unit is still spooling-up, eventually peaking 240 @ 2600 RPM. The Duster's 1.5 is a single VGT turbo application. All this is what's on paper. What happens in the real world is anybody's guess.

But the Renault is a bit of a stretch for anyone with a tight budget and in the market for a car priced between 7-10 lakhs. The Quanto shouldn't be more than 10 lakhs OTR Bangalore and a similar spec'ed Duster 85 would be 10 lakhs too but that's before road tax, registration, insurance, accessories..

The 110 should be a few lakhs more, still!

I've driven the Duster and it feels more car-like to drive than most Mahindras I've driven, XUV included. The Xylo will tend to feel awkward for someone used to driving sedans / hatchbacks. If you're used to the weird ergonomics and regularly drive a Scorpio or Xylo, the Quanto shouldn't be different, I presume? The Duster feels like a sedan. The clutch is heavier, as is the steering. The gearbox slots in well but the shift feel isn't positive. It still is much better than the Scorpio's and the Xylo's. And the Quanto's too, seems like.

If it's absolutely necessary for someone to buy a sub-4 meter car and you just can't wait for the EcoSport and the Rio doesn't cut it (and why would it?) the Quanto is your only option. If you don't mind a larger (but still relatively compact) SUV, the Duster 85 with the option-pack is the way to go. It's brilliant VFM.

Why the twin-turbo and not VGT? Well, I'm not sure. Perhaps it was cheaper to build and assemble? It probably lasts longer? Either way, you're going to make compromises.

Last edited by suhaas307 : 21st September 2012 at 16:52. Reason: typo
suhaas307 is offline   (1) Thanks Reply With Quote
Old 21st September 2012, 16:55   #15
BHPian
 
Join Date: May 2008
Location: Mumbai
Posts: 43
Thanked: 10 Times
Default Re: Why the Twin-Stage Turbo & not a VGT?

While a VGT in theory is supposed to eliminate lag, in my experience some of the engines with a VGT have the worst lag. Case in point being the Fiat 90bhp 1.3 MJD. The Linea is plagued with turbolag and so is the SX4 diesel to some extent. Same story for K9K Renault in the 110bhp form
santosh911 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
80K run Verna VGT. Turbo working or not? dicor99 Technical Stuff 26 5th September 2015 08:22
Twin Turbo GTO or Turbo MR2 spiff Luxury, Imports & Niche 32 29th September 2014 01:52
Tata Safari Turbo Swap : Can I fit a VGT? Raider Technical Stuff 5 26th November 2011 21:10
Tata Indica Turbo & Indigo TDI twin test tsk1979 Test-Drives & Initial Ownership Reports 43 4th November 2009 11:28
Variable Geometry Turbo - VGT NFS_Carbon Technical Stuff 7 1st December 2006 23:12


All times are GMT +5.5. The time now is 21:09.

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