veryhumid
Veteran Member
It seems almost all diesel engines have turbos. why?
The 1.9 SDI makes about 75 HP I think.Gothmolly said:I'd guess that since a diesel makes less HP per displacement than a gas motor, the diesel needs a little help. The 2.0 is about 110 hp, and the turbo 1.9 is only 90. Imagine what it would be w/o the turbo.
so why doesn't every honda 4 cylinder come with one? i'm certain the main reason is something else. air is free, but turbos aren't. there is something more essential about running them on a diesel than getting more power.cp said:Air is free?
It's just a way to get more power out of a smaller engine package. A displacement replacement, if you will.
It's not a homogeneous mixture like you (should) find in a gasser. When the diesel fuel is sprayed in the droplets need oxgen to burn. It only used what it needs however to complete the combustion. The reason for the copeous amount of extra air is to improve the chances that all the fuel will be burnt.veryhumid said:so the turbo makes the cumbustion leaner?
That would decrease the rated MPG of the motor and wouldn't really be needed for most folks. You can get 0-60 in less than 10 seconds with most (any?) I-4 NA 2.0 gasser (say around 120 HP), and still get high 30 MPG with that same motor. Throw a turbo on there and I bet the MPG drops to mid 20's (WRX for example) but you get 50% or more power.veryhumid said:so why doesn't every honda 4 cylinder come with one? i'm certain the main reason is something else. air is free, but turbos aren't. there is something more essential about running them on a diesel than getting more power.
Bob_Fout said:That would decrease the rated MPG of the motor and wouldn't really be needed for most folks. You can get 0-60 in less than 10 seconds with most (any?) I-4 NA 2.0 gasser (say around 120 HP), and still get high 30 MPG with that same motor. Throw a turbo on there and I bet the MPG drops to mid 20's (WRX for example) but you get 50% or more power.
the compression ratio is just a ratio of the distance between the extreme points traveled by the piston. turbo doesn't change that. It does compress the air fuel mixture, which gives you a more dense air/fuel mixture in the cumbustion chamber, but it doesn't change the compression of the engine. I get the part you said about diesels liking to run lean, that agrees with the fact that when you turbo a gas engine, it needs more fuel and MPG goes down.bhtooefr said:Now, another factor. A turbo ups the compression ratio. Upping the compression ratio in a diesel helps the combustion, even on D2. Upping it in a gasser, however... you've gotta get higher octane fuel to prevent detonation.
sorry i'm a little confused. a turbo changes the effective compression ratio, NOT the actual ratio, correct?cp said:It changes the actual compression pressure or effective compression ratio. Turbo diesels generally have actual compression ratios in the 16:1 to 18:1 range whereas non-turbo'd ones are typically 22:1 or more. Actual compression pressures end up about the same.
Another way of saying this is that it changes the effective engine displacement?TurbineWhine said:Turbocharging effectively increases the compression ratio of the engine. Do very much turbocharging to a gasoline engine and you are going to need higher octane, more expensive fuel to prevent pre-ignition. Additionally, the engine would have to be built stronger and heavier to handle the increased cylinder pressures. More weight to carry around.
Diesel engines with the direct injection do not have this pre-ignition issue, as long as the injection timing is correct.
TW
Yep, sure did. http://forum.mazda6tech.com/about3527.htmlDPM said:Ah, the Comprex. Didn't Mazda use that in the 626 diesel in the early '90s or so?