I think you could get gain better power at lower revs using a larger turbo, so it pumps more air at lower speeds but yet keep the max boost down to nere normal figures.
would be allot cheaper and prob easyer tbh

I believe the larger turbo idea would mean the power would come in at higher revs as it would take longer to spool up...

Just crank up the boost on the std one and replace it when it blows!! A lot cheaper and easier than fookin about with superchargers or bigger turbos! These beasts aint built for speed anyways, I'm happy with my 200tdi as it is, and the turbo hasn't blown yet!!!

Supercharger still seems like the most fun idea and if the pulley was large enough or built with a double gear i.e at low speeds it stays on one cog and at higher revs it moves onto another it would be perfect. That would take a lot of work though but given that the charger would be providing a constant boost fuel economy should increase as theres more power throughout the RPM range so less thrashing to get up to speed would be required no ?

Dr_evil said:

That would take a lot of work though but given that the charger would be providing a constant boost fuel economy should increase as theres more power throughout the RPM range so less thrashing to get up to speed would be required no ?

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No, it doesn't work that way.

The advantage of a turbocharger on a diesel is that it boosts harder and stronger when under load. With a supercharger you lose this.

When a turbodiesel is just cruising at motorway speeds and not under heavy loads the exhaust gasses are not so dense and don't spool up the turbo to its maximum potential. Therefore the fuel pump isn't supplying 'max load' fuel and the fuel economy increases, more or less to that of an N/A diesel, since the turbo is being marginally used.

A supercharger isn't driven by the exhaust gases, so will always deliver high boost at higher revs, regardless to whether it's needed or not, to the detriment of fuel economy.

twin turbo might be a better idea then…….

Small turbo into big one?

TBH a variable geometry turbo is the best way to go. You can get the best of both worlds then, higher top end boost and boost pretty much right from the bottom of the rev range.

2.8TGV engines which are essentially updated 300TDis use these, and the benefits in driveability are fantastic.

EDIT: And you can get these for a TDi engine off the shelf since the ones off the 2.8 engines fit right on. You just need to re-jig the pipework slighly as IIRC the inlet and outlet are the opposite way around.

variable geometry turbo is basicly a twin turbo method but build into one turbo efectivly

Ooo I want one

discomark10 said:

variable geometry turbo is basicly a twin turbo method but build into one turbo efectivly

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That's not technically true, not if you want to be pedantic about it anyway.

It's more accurate to say it's akin to twin stage turbocharging, which involves two turbos but they operate differently.

Twin turbo engines have been around for quite some years, and in their basic form are 2 same size small turbochargers providing good overall boost but with less lag. Typically they're only used on 6 cylinder engines or above though, they don't really work on 4 pots due to the exhaust gas pulses off only 2 cylinders.

Twin stage turbos follow the same principle but only one turbo is doing the main job at any one time. The small turbo is used at low revs, the bigger one used at high revs. BMW were probably the major user of this type of turbocharging before the VGT turbos really started to come on stream.

Variable Geometry Turbos are single turbos that effectively change the internal gearing of the turbo, providing lower resistance to exhaust gasses at lower revs, and then reverting back to being a 'full size' turbo when the revs pick up. As it's still one turbo though they can be effectively fitted to 4 and 3 cylinder engines, both petrol and diesel.

As an example Ford's new 1.0 'Ecoboost' engine is a 3 cylinder engine with a VGT turbo housed in a unit about no larger in area than a sheet of printer paper. The engine output is about the same as you would have expected from a 1.6 or 1.8 petrol engine 10 or so years ago!

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