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Old 14th December 2005, 14:31   #1
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Smile Turbocharging of petrol engines?

I ve heard that it is not possible/ is difficult to turbocharge a petrol engine. why is it said?

the thermal efficiency of a petrol engine compared to its diesel counterpart is lower do\ue to its lower compression ratio, hence the exhausts should carry more heat, more heat implies more energy content, right?

but it is said that turbocharging in diesel engines are more feasible,why?
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Old 14th December 2005, 14:49   #2
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It is possible to turbocharge a petrol engine, infact VW is coming up with a 1.4 litre supercharged turbo which will put out 160hp.
Octavia RS is turbo petrol. But I guess its in the interest of fuel efficiency and complexity that this is sacrificed.
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Old 14th December 2005, 15:01   #3
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Quote:
Originally Posted by tsk1979
It is possible to turbocharge a petrol engine, infact VW is coming up with a 1.4 litre supercharged turbo which will put out 160hp.
Octavia RS is turbo petrol. But I guess its in the interest of fuel efficiency and complexity that this is sacrificed.
hey
VW is launching the Golf Super Turbo ..it has both a supercharger and a turbocharger ..and yes ofcourse they will also have the new 1.4l TCd golfs
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Old 15th December 2005, 23:24   #4
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Default Turbocharging

Dear Pratheesh,
Let me attempt to answer your question.
To understand why petrol engines cannot be turbocharged, you must understand the concept of a turbocharger.
A turbocharger utilizes energy of the exhaust energy, agreed!
However, it utilizes pressure energy and NOT heat energy. A turbocharger consists of two parts or compartments. One consists of a compresser connecting to the air inlet port, other consists of a turbine connecting to the exhaust port of the engine. The turbine and compressor are mounted on the same shaft (however both the parts are isolated from each other by means of seals).
The exhaust gases coming from the engine "dash" on the turbine side and the turbine rotates. The compressor also rotates (being on the same shaft) and compresses the inlet air. Now, the pressure of the inlet air is above atomospherric. Hence, you get a better pressure boost during the combustion stroke and hence more POWER !
So, prerequisite for turbocharging an engine is that the pressure of the exhaust gases should be adequate, which are ofcourse diesel engines (since, the compression ratio is more) or petrol engines with more no. of cylinders ( usually 6 or more).
If you attempt to turbocharge a usual petrol engine, its efficiency will reduce drastically. This is because the "back pressure effect' comes into picture i.e. during the exhaust stroke (considering a 4-s engine), the exhaust gases will suffer some resistance. So. more energy will have to be spent to remove the gases. Thus, lesser energy is avialable at the flywheel end, or precisely lesser torque.
This "back pressure effect" is to be considered always !

Supercharging is the umberella concept or supercharging is the "universal set" and turbocharging is its 'subset". There are several ways of supercharging the inlet air, turbocharging being one of them !

Please ask if there are any doubts !


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Old 16th December 2005, 03:01   #5
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Quote:
Originally Posted by samcore

To understand why petrol engines cannot be turbocharged



try telling that to our mad-scientist psycho ..anyone who has seen his conti would certainly disagree..
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Old 16th December 2005, 04:44   #6
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Quote:
Originally Posted by pratheesh
I ve heard that it is not possible/ is difficult to turbocharge a petrol engine. why is it said?
Have you heard of the Octy RS?
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Old 16th December 2005, 11:51   #7
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thanks samcore...
now let me ask.... you got a closed chamber (constant volume), and you are adding heat, naturally the pressure will rise....implies pressure energy is generated...
i think the same same happens in petrol engine too (constant volume heat addition)...
so only some part of energy is utilized and rest remains useless....

and about the turbochargers........well what if i design the turbine accordingly to develop max torque (at max efficiency) for the given inlet temperature and pressure...it is possible right.....or is it not???
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Old 16th December 2005, 13:16   #8
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Default Understanding Petrol Turbo charging

Firstly, let me clarify one thing.

A turbo Does use both pressure and heat energy. the hot exhaust gases expand over the turbine wheel, which causes both the pressure and the temperature of the exiting gases to reduce.

Secondly,

there are two major practical problems associated with turbo charging petrols.
1.) Knock
2.) Surge

If the CR of the engine is kept the same w.r.t the NA engine, turbocharging it will always cause it to knock at high speeds and high loads, i.e in case you are driving it hard and fast on open road.

there are many ways of avoiding this, but its a long list and involves a lot of trade offs b/w efficiency and power.

Another major issue is compressor surge, which is usually countered by using a blow off valve, control strategies for which are quite complicated.

The material for the turbine sg/wheel will also have to be high speed steel or some other expensive alloy.

So, usually OEMs prefer not to make turbo petrols as the trade offs b/w power, efficiency and cost vis-a-vis diesels are not feasible.

For any more clarification, leave a post....


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Old 16th December 2005, 17:00   #9
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Hi Pratheesh,

As Samcore said, heat from the exhaust gases is not the main propelling force for the turbo, its the pressure. You could even say that heat is infact bad for the turbo to some extent...

I think what you may have heard is the fact that you usually get a greater %advatage from turbocharging a deisel as opposed to a pertol.

Porsche_fan has some excellent points.

You MUST look at www.howstuffworks.com.
It is an awesome site and will help you get the basics right.

cya
R

Last edited by Rehaan : 16th December 2005 at 17:02.
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Old 16th December 2005, 18:16   #10
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Cool Alright!!!!

I am not an expert... But lemme talk what I know.
Turbo charging is possible in petrol Cars... I would say, any petrol engine can be turbo charged (theoratically)... the ones with Fuel injections makes it much easier.
I am not going to copy paste from any knowledge base or make my statements systematic. However, you will get a rough idea of what i am talking about.
U can even turbo charge your maruti 800 with EMS and Fuel injection.
Couple of things which you would require....
First of all U need to know the amount of air been pumped into ur engine and based on the math u need to choose a turbo charger. Small increase in power can be gained without much modifications but huge gains require lotsa home work to be done. I am gonna state a small increase in power with a boost of less that 7 PSI.
There is typically four main ports on a turbo. Two for turbo chargin (intake) and two for turning the turbine(Exhaust). Hope you can imagine how it looks.
Now Once u know the turbo, u need to setup the intake and exhaust ports on your engine since these require major modification. The intake filter should be connected to the intake of the turbo and (turbo charged air) from the out of the turbo to the intake manifold (**).
(**)Normally would would find a pipe connection to intercooler and from the intercooler to the intake manifold, coz the compressed air from the turbo which goes into the engine would get heated up due to the compression which is not desirable. Even Causes detonation coz the air burns with the fuel sometimes in the valve chamber.
Well the exhaust from the engine must be coupled through the turbo exhaust port so and from the out of the turbo port to the down pipe or the cat back exhaust.
Wastegate and BOV's are used to control turbo chargind to a certain extend. Wastegates lets the turbo charged air flow out when there is excess boost (located on the turbo charger itself) . BOV, a necessary evil, pumps out the air when there is excess turbo and the intake port on the engine closes, due to shifting of gears and the accelarator being cut off. These things make the whislting sound. However the BOV keeps the turbo spooling so that, there is no damage done and the turbo is still spooled up and has the charge ready to be delivered.
Now you might think , just implement this and everything is fine.... I dont think so... Most of the ECU understand and know that there is only a certain amount of air that need to be pumped in at a certain RPM and throttle. When it sense more Oxygen by the sensor, based on the programming of each ECU the engine might not work at all. So this all boils down to ECU Flashing and reprogramming. Alrite... is it done... not yet... who is going to provide the fuel for the additional air to burn... well seems like a bigger fuel injector. Wat about the addional fuel to the fuel injector, which means a different fuel pump and might require a piggy back module on the ECU to time that.


I don think i made any sense.. I can elaborate... but jst wanted to point out that it can be turbo charged.... Now everything is caliberated and tuned and tested on a Dyno... there is lotsa math and homework to be done... this cant be entirely relied on trail and error method coz u r gonna bust ur engine. High end turbo charging requires Electronic Boost control or manual boost control to make the car usable on a daily usage.

Sorry if i sounded like an idiot.. its ma style... heheheh
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Old 8th February 2008, 16:15   #11
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Turbocharging an NA engine is usually not that easy but not impossible either.
One needs to design a system where various existing parameters have to be redesigned/recalibrated to give the desired end result. These would include some or all of the below (there could be more depending on the way you approach the project)

Lowering the compression ratio - using after market pistons with new profiles or a thicker head gasket (this is done so that the engine does not detonate/pre ignite under boost pressure.

Considering the right turbo - depends on the targeted power output, engine capacity etc.

Engine/fuel management system - You could use a stand alone EMS or Piggyback EMS or use other tricks to make sure that the engine recieves the right amount of fuel at different load/boost conditions/ intake air temp (also making sure it does not run overly rich or lean). Besides fuel, the other factor to be calibrated would be the ignition timing. This has to be mapped against boost and intake air temp mainly.

You would need a turbo manifold and other plumbing to connect turbo (compressed air) to the engine intake through intercooler (if possible) and route exhaust through a relatively low back pressure exhaust system.

Add the other goodies like BOV and other misc needed - In theory your Turbo set up is now good to GO !!!!!
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Old 8th February 2008, 21:38   #12
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Quite an old thread that has been dug up here.

Somewhere in the interim, this article was written on TBHP >

http://www.team-bhp.com/forum/modify...-your-car.html (ARTICLE: Points to consider before TURBO-Charging your car)

cya
R
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Old 21st June 2012, 09:33   #13
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Default Re: Turbocharging of petrol engines?

Please let me know if anyone has tried turbo-charging their car using the Fiat Linea Petrol's Turbo Charger. Is it a good idea to try it on my Ikon 1.3 Rocam?

Thanks in anticipation
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