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is there a different
goodall - 23/6/07 at 10:37 PM

between a turbo for a petrol engine and one for a diesel engine?

would the wastegate be set up differently to allow more boost or anything?

been reading maximum boost and its really got me interested but i cant find much on the things im looking at on google to say different between the two

[Edited on 23/6/07 by goodall]

blakep82 - 23/6/07 at 11:19 PM

diesels can't have a wastegate/dump valve, but i really don't know why... something to do with the way they're piped in


edit: forget that, it seems you can get them now. not sure why diesels were any different before though

[Edited on 23/6/07 by blakep82]

UncleFista - 23/6/07 at 11:48 PM

The dump valve is to dump excess boost when the throttle butterflys snap shut.
Diesels don't have throttle butterflys

Goodall, I was under the impression that diesel turbos aren't built to take the same high temps as a petrol turbo, probably wrong though...

[Edited on 24/6/07 by UncleFista]

worX - 24/6/07 at 02:19 AM

yes
no
good book isn't it?

Steve

robertst - 24/6/07 at 03:56 AM

i thought diesel turbos were set up for lower revs so they are designed to spool up at aroung 2000 rpm... thats why they're incompatible with gasoline engines because diesel turbos are designed to give max boost at around 3500 rpm, way too low for a gasoline engine...

Ivan - 24/6/07 at 07:02 AM

quote:
Originally posted by robertst
i thought diesel turbos were set up for lower revs so they are designed to spool up at aroung 2000 rpm... thats why they're incompatible with gasoline engines because diesel turbos are designed to give max boost at around 3500 rpm, way too low for a gasoline engine...


I think the engine revs that a turbo boosts at has little to do with the engine type but more to do with the exhaust gas volume and turbo configuration - so you have to look at the engine you want to fit it to and the boost profile you want - then select the right turbo combination to give the boost profile you want for that particular engine using flow charts for the turbos.

Almost certainly a turbo for a 2000cc diesel engine won't suit a 2000cc petrol engine. Although it might well work it is unlikely to be efficient and give the boostlevels desired and might well be working outside it's design envelope giving surge problems and overheating the inlet air.

Overall the turbo is the relatively cheap part of the turbo conversion and to get a turbo that gives even torque spread with minimal lag takes carefull and knowledgeable selection and is one of those things that should not be done on guess work.

A well selected turbo gives an engine that is a joy to drive with minimal lag and an even and awsome torque growth that is easily controled out of corners. A wrongly selected turbo is a pig to drive and will just continue give turbos a bad name with everybody who drives the car.

[Edited on 24/6/07 by Ivan]

oliwb - 24/6/07 at 08:27 AM

quote:
Originally posted by UncleFista
Diesels don't have throttle butterflys
[Edited on 24/6/07 by UncleFista]


How do you control how much air goes in the engine then? Oli.

iank - 24/6/07 at 08:55 AM

AFAIK you don't control the air, just the amount of fuel you inject.

Another difference (mentioned in a PPC article I don't have to hand) is diesel turbos melt if put on a petrol engine.

matt_claydon - 24/6/07 at 09:11 AM

On a diesel you get a full cylinder of air for every stroke, you just vary the amount of fuel you put in.

Unlike petrol, diesel will burn with a very wide range of air/fuel ratios so this strategy works. With petrol you need the mixture to stay around 14.7:1 and so you restrict the amount of air going in when you want to put less fuel in.

This is one of the main reasons diesels are so efficient at part-power compared to petrol.

Edit: Petrol will burn at leaner mixtures, but it won't ignite by spark. Clever people are working on 'stratifed charge' engines where the mixture around the spark plug is 14.7:1 and then gets progressively leaner towards the outside of the cylinder.

[Edited on 24/6/07 by matt_claydon]