Turbos! Diesel to petrol

The exhaust flow from a diesel engine, is at far lower temperatures than a petrol engine. As the only reason that the exhaust gas has increased in volume, is because it's been massively heated, deisel engines won't "flow" as much exhaust gas compared to a diesel.

what does that actually mean in real-world use though?

To accommodate the higher exhaust flow, the turbo for a petrol engine, will be much larger than a turbo meant for a diesel engine, of the exact same size.



A petrol will usually only operate usually upto around 10psi of boost without spending lots of money (some even less!) whilst a deisel will regularly operate at around 20psi, straight from the factory. The boost pressure is essentially known as the "pressure ratio" (compressed pressure, vs atmospheric) and if you try to make a turbo deliver boost at less than half it's reccomended pressure ratio, it will do one (or more) of three things:

1) stall. The compressor isn't spinning fast enough, to deliver and contain the required boost pressure. The air ends up reversing, and goes through the compressor wheel the wrong way - stalling the compressor, and introducing LARGE loads through the turbo shaft, snapping the shaft is a large possibility.

2) Choke. You're trying to pass too much air through the turbo - it literally "chokes", as it can't pass enough air (ie: you're using too small a turbo for your flow levels)

3) Massive air heating. Being above "stall", but below "choke", but not at the required pressure ratio, will just mean the turbo is out of its efficiency range by quite a large amount - what this means for a turbo, is more energy just goes into heating the compressed air, rather than moving it.



Also, the turbos have physically different cores too - as diesel turbos won' run anywhere near as hot as the equivalent petrol turbo, they won't have additional cooling capability that some large petrol turbos need to keep from overheating. One example of this, is a water jacket around the turbo core.




so the main question is - are you trying to turbo a diesel, or a petrol?

yups! Lol, you can go the other way - and put a petrol turbo on a diesel..... but by the time it's on an engine big enough to make it spin up, the extra airflow it'll give is practically pointless!


Tbh, shove the diesel engine in - much more fun than petrol

I had considered it but the diesel has 20hp less and a much lower top speed than the N/A petrol so whats the point?
Thanks.

Autobahns, track days etc! I don't know what the engine code is, I will check that out. Its from one of these;
www.carfolio.com/specifications/models/car/?car=29590

160bhp?? Keep talking?!

for 160Bhp+, if yours already comes with a Bosch pump, just fit a decent FMIC, decent exhaust, up the boost a little, and up the fuelling

That's it.... seriously


to get about 180bhp, with just shy of 200lb/ft torque, you'll need a bigger turbo. Beyond that figure really isn't reccomended, they tend to fall apart in a rather vigorous[/b] manner

That'll be the JTD engine won't it? Think thats whats also in the newer Saabs and if you get the Saab version you can get 230ish bhp and 500nm of torque (385lb.ft) just by plugging it into a computer (the TTid engine)

Its a JTD engine it turns out. I think I will stick with the N/A petrol for now!

Appartently, the Volvo B18FT with a Garrett T2 (440 Turbo) can be upgraded with a turbo (T3) from a Volvo 940 Turbodiesel.

Ok, ignoring diesel's then - what Modern(ish) petrol cars could I rob a Turbo that would spool nicely on my Mini? Some take the Gt1725 but they are like a T3 - a bit big and laggy.