27-04-2012, 12:02 PM
4WayDiablo Wrote:ginge191 Wrote:Think ruan speaks a lot of sense - i wouldn't bother going near a derv related turbo, they're derv related for a reason.
What about everyone who went for td04? Were they all wrong because they're perv related turbo's?
T2 or T25 describes NOTHING to do with the actual turbocharger... It's just it's frame... You can get "T25" turbos thathave a smaller compressor than a "T2".
The A/R is totally wrong on TD04s, don't get me wrong, they're not ideal by any stretch of the imagination... They're just pretty good and cheap - to get something CORRECT... That's when you go to Turbo Dynamics or whoever.
Diesel turbos are NOT the same as Petrol ones, they're designed with two different power deliveries in mind... One provides it's power at 7000rpm, the other at around 4000rpm... The airflow demands are vastly different there... That's where A/R comes in - it essentially compensates for the airflow out of the exhaust so it doesn't restrict the engine at higher RPMs... A Diesel will have a fairly small A/R (i.e. the gasses are heavilly restricted, however the velocity that it hits the turbine blades is much higher) whereas a Petrol will have a larger A/R (i.e. the gasses are less restricted, it's more laggy, but it means you can pump more air at a lower pressure through the exhaust housing)
As always it's a compromise...
This is the exact principle VNT turbos work on, they essentially change the A/R of the exhaust housing, so when the vanes are closed up, it accelerates the gasses through a small nozzle (Hence variable nozzle...) which hits the blades quickly, when the vanes open, it reduces backpressure and allowsmore gas to move... Hence why if you keep the vanes closed, you'll see 60psi of boost, but you won't go anywhere and you'll successfully melt the cylinder head in the process..
Remember - air in has got to equal air out.
Using petrol turbos on a Diesel isn't a bad thing - it just means you'll end up having to rev it harder to get the airflow out the exhaust to spin the turbine... Whereas using a Diesel turbo on a petrol means you'll just end up restricting the engine, it'll have shit all power off boost, then as it comes on boost, it can't pump enough air through the exhaust housing, quickly getting things very hot and running out of power very quickly...
