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Old 9th May 2013, 21:56   #16
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Default Re: Small displacement, turbo engines

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Originally Posted by nim_peter View Post
I always wanted to ask this question to experts here, didn't find the right thread. Can the same turbo setup in diesel car be used in a petrol one? If no, what are the differences? Also need to understand why petrol turbo cars are expensive than diesel turbos, shouldn't it be less? Eg. Polo and Linea.
The basic job of the turbocharger will be the same in both engines but since diesel and petrol engines work differently I am sure there will be subtle differences in the way the end result is achieved. Temperatures, boost pressures, rpms will vary.

Turbochargers in petrol engines have to deal with higher rpms and higher temperaturers and they have lesser exhaust gases to force into the combustion chamber compared to diesel engines. THis could be one reason why they're more expensive. Second and more important reason is that petrol engines can do fine without turbocharging. A Turbocharged petrol engine is seen as a luxury or sport variant and hence is not common. Smaller numbers always mean higher costs. And most turbocharged petrol engines in the country are imported, which translates to higher duties.

In contrast turbo diesel engines have completely replaced NA diesels. Higher numbers + Local manufacturing + Mass production = Lower costs.
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Old 9th May 2013, 22:08   #17
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Default Re: Small displacement, turbo engines

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Originally Posted by ACM View Post
In the Safari TCIC being in the Turbo zone most of the time got me a FE of 8-9kmpl over 175,000 kms. Due to the 90 bhp on offer it did need to be driven that way for one to feel alive. The same engine on the Sumo got people in the transport business 14 kmpl in a Non Turbo Lower BHP form - it was a 25% lighter vehicle though.
Long back, when i went to TD the Sumo Victa, the salesman there told me not to go for the turbo version(saar, black smoke, turbo will reduce FE). I did not believe him then!
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Old 10th May 2013, 02:51   #18
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Default Re: Small displacement, turbo engines

Hey guys just wanted to know how is a FGT different from a VGT? As I understand the work of a turbo is to force more air in for combustion then what is with variable and fixed geometry?
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Old 10th May 2013, 05:40   #19
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Default Re: Small displacement, turbo engines

The future for almost all cars is a small petrol engine which has forced induction. As well as the emission regulations making it impossible for anything else, this is also possibly the highest-profit route for manufacturers. Diesel cars have a finite lifespan, I reckon.

I already miss engines which have been culled by profit or exhaust emission - we will cope with what is round the corner. The up-side will be lightweight and agility and less tyre wear and the opportunity to realise 35 or even 50 kmpl if performance takes a back seat. The air will be infinitely cleaner without so mcuh diesel being burnt, it's never pleasant to die of lung disease. (So says someone who loves good diesel engines!)
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Old 10th May 2013, 15:31   #20
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Default Re: Small displacement, turbo engines

Petrol turbos have to deal with higher temperature thresholds than diesels because of the exhaust gas temperatures. The reason being the fuel itself. Therefore, the petrol turbos have better materials which are of high tensile strength and have better seals for the same boost pressure as in a diesel engine. I do believe a diesel turbo can be fitted to a petrol engine with the exception being that the boost pressure will have to be reduced and the engine must be made to run slightly rich to reduce the EGT if my understanding is right.

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Originally Posted by rockporiom View Post
Hey guys just wanted to know how is a FGT different from a VGT? As I understand the work of a turbo is to force more air in for combustion then what is with variable and fixed geometry?
Fixed geometry turbos have a fixed vane structure which actually begins to spool only once sufficient exhaust gas has begun pressurizing the vanes. This results in the turbo spooling a little late and leading to the turbo lag many cars face. Small turbos spool up fast but do not deliver sufficient boost at higher speeds leading to the engine choking. Bigger turbos will make the lower rpms hell for the driver since it isn't being driven near the rated speed since the exhaust pressure is low.

In order to curb this, variable geometry turbos have a variable vane structure which are adjusted using an actuator. What this actually does is that it ensures sufficient boost is available throughtout the operating range of the engine and this ensures minimal to no lag. Also, VGT applications do not usually require a wastegate. In simpler words, it is a one-size fits all application.

Last edited by Arch-Angel : 10th May 2013 at 15:42.
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Old 10th May 2013, 15:39   #21
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Default Re: Small displacement, turbo engines

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Originally Posted by rockporiom View Post
Hey guys just wanted to know how is a FGT different from a VGT? As I understand the work of a turbo is to force more air in for combustion then what is with variable and fixed geometry?
http://en.wikipedia.org/wiki/Variabl...y_turbocharger
The above link and the references will answer all your questions.
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