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Diesel vehicle often use turbo chargers. Petrol vehicles frequently do not. What are the advantages and disadvantages of using a turbo charger on a petrol engine?

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    I've got a great answer for this and no time to write it ... hopefully I can come back to it. – Pᴀᴜʟsᴛᴇʀ2 Apr 22 '15 at 16:06
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    This question is likely better for the chat. It's definitely open ended and the answers are likely to be opinion based. – Bob Cross Apr 22 '15 at 16:22
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    @Paulster2 please make time! =) if you guys havent discussed it already. – chilljeet Apr 25 '15 at 2:34
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    I think the basic question has a flaw - until very recently here in the UK petrol turbo cars were much more common than diesel turbo. Turbos on diesel engines were only on trucks and buses. Even now, turbos are really only common on diesels made by the big German manufacturers. – Rory Alsop May 14 '15 at 6:54
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    @BobCross I think we could make the argument that this question will have factual answers, the question is about why people might not put a turbo on a petrol engine not whether people should do so. Writing a list of pros or cons helps one to form an opinion, but isn't necessarily an expression of opinion. – Nathan L May 15 '15 at 2:46
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Several reasons:

  • First: Diesels have a very simple operation which is basically more air, more fuel = more power. On gasoline engines you have to worry more about running too lean, too hot, having incorrect timing. And, you generally already have enough air. You run at higher RPMs and suck in more air. Gasoline is much more volatile than Diesel. It burns very hot! Even most modern diesels now have inter-coolers to deal with the heat. But, with gasoline engines that's a bigger need as the higher exhaust temps are more easily reached. On a diesel it does help with exhaust temps as well, but it's also there just for added power as cooler air = more air. It likely adds less cost, in most cases, to a diesel than it does a gasoline engine because of the lack of additional complications to consider. And you are already paying a premium to get a diesel.

  • Second: Diesels typically have a more narrow effective power curves over RPMs. The main reason the domestic version of Diesel engines all seem to have a turbo is to help with that shorter power curve. You get 1/4 mile times a lot closer to the gasoline counterpart with no real extra complications other than the engine just has more power.

  • In Addition: Diesels ignite their fuel from pressure, as opposed to spark. Thus,it makes more sense to add a turbo to increase the volumetric efficiency in order for compression based ignition to occur. When adding additional air to a Diesel you are helping with the ignition process. When you do that on a gasoline engine you are also helping, but that's only a good thing to a point and then you can create knocking (pre-ignition or pinging), timing issues, etc. You are increasing pressure on a platform that isn't designed to run at higher compression like a diesel is. Diesels are designed to run on much higher compression because that is how they ignite their fuel (pressure/not spark). So, adding a little more compressed air won't hurt it. In fact, it helps your fuel burn cleaner and may even increase the life of your engine as less carbon buildup from un-burnt fuel occurs.

  • Beauty answer. Well said. – DucatiKiller May 14 '15 at 7:21
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In addition to the other reasons mentioned by maplemale, I would add the following:

Cost - Depending on the car, price may be a more important factor for the manufacturer and the buyer than the marginal power gains from a turbo charger. It's not just the parts price that increases, it's also an increase in design cost.

Space - Turbos require plenty of space in the engine bay for all of the additional plumbing.

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