nova turbo diesel

Exception to the rule of no throttle means no dump valve required.

Sooner or later someone is going to fit a turbo to one of the latest bmw engines .... the petrol engine i'm thinking of has electrically operated valves, and has no throttle butterfly to restrict the air flow into the engine. (Essentially runs on full throttle all the while, with the valves providing the restriction).

Scary stuff ... gimme a camchain any day!!

yes it is intercooled, but after about 85bhp its inadequate. However the turbo is the restricting link in the chain- they wont allow the airflow to generate much more than 85brake anyways- the comnpressor housing is too small. Interestingly- like the 1.7 lump there is no wastegate- boost is controlled as a product of the max fuelling at the pump and the compressor being too small to flow any more air- so it naturally reaches a peak of about 1bar.

To get a reliable 100bhp out of the 1.5 you'd need to port the head, fit a larger intercooler and pipework and go to a T1.5 sized turbo with appropriate trims / housings.

Tim..

It won't make any sound, because if it's set up ptoperly it'll never open as there'll never be enough back pressure to make it blow off. Again because the diesel's intake is not throttled. All that happens when you lift off the throttle is the diesel injection duration is reduced, so less exhaust gas comes out, so the turbocharger gradually slows down and the boost pressure gradually drops. Hence dump valve not activated.

I know many others have explained this, but I'm not sure you quite understand yet so I'll try explain too; On a petrol engine running at high boost, when the throttle pedal is released this closes a butterfly valve which partially blocks the intake manifold. The turbocharger however takes a second or two to slow down. At this preceise moment, the turbocharger is blowing into a blocked manifold, so the pressure rises rapidly. Without a dump valve this condition would cause the turbocharger to stop spinning very suddenly, which may damage it. The excess pressure may also blow flexible hoses in the intake system. A dump valve releases this excess pressure safely, thus allowing the turbocharger to decellerate at it's natural rate.

As you can now see, this condition cannot occurr on a diesel engine as the intake tract does not contain a butterfly throttle valve.

James of Sunderland

Bugger ... i'll go read up some more.

I think Dan understands, but you can still get dump valves for TDs, as he says. I've read an article on one a few years ago that had one. No idea how this works - whether its a microswitch that actually releasses the pressure (unecessarily) or whether its a speaker (wouldnt be surprised). I would be intersted to get a look at one on the car! Any chance of getting that link Dan?

Or a wastegated T25 which would be cheaper and easier as almost any would do and you wouldn't end up having to get one built with just the right spec to give you 1.2bar

Matt

Havent done the calcs or looked at the compressor maps, but i'd be fairly certain a T25 would be massively too big on a 1.5 diesel. It might *just* have spooled up abit by 4000rpm! lol

Tim..

Ta daa -

And...

Havn't got any maps to hand for T25 but I'd imagine the gas flow would be sufficent to spool a small trim T25 sufficently to produce boost by a reasonable RPM. Depends if you've got the cash and want to spend it on a Nova diesel to get a turbo made up to exactly the correct spec, or spend a reasonable amount and slightly bodge it. I'd guestimate you'd have 1500rpm of decent power band. If someones got the VE of a 1.5 Isuzu derv lump I'll run the numbers.

Matt

i just keep noticing garett turbo's off transits and such just lying around at work.... :)

They aren't intercooled as standard, and they do use a wastegate to regulate the boost.... Getting it to around 100bhp isn't perticularly hard at all, adjust the fuelling screw, get yourself a bleed valve and a decent intercooler.

I know of one Nova TD that got 96bhp @ the Midlands Performace Centre and it was still on standard boost.

I think I see how it works now. The valve is controlled by an electric soleniod which is actuated when the control box senses the throttle pedal is released (it talks of fitting a modified throttle switch).

If so it's pointless but if sound is important then why not.... :-)

James of Sunderland

I beg to differ- the last 2 Corsa's I worked on were as I said. The Nova incarnation however may have been different as you say.

Tim..

Must admit, I have never checked much into Corsa's.... but Nova's are deffo how I said, and I was pretty sure early Corsa TD's have the same setup as well, cos people can stick a bleed valve on them. Newer types however, I have no idea lol