Me in actual 'post about modifying' shocker!

Put a 2nd smaller turbo in series with the current one.

Reply to
Carl Gibbs
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Right. Turbo diesels, well specifically mine, which I'll say for those who don't (and those finding this on google in the future) - is a 5-cylinder 2.5 TDI Audi engine (140bhp).- to increase the power the straightforward way is a basic chip upgrade, from which mine is capable of something like 173bhp. All well and good, but all that really does is increases the peaks that occur on the torque and power curves. Nice, and still quicker, but it's still gutless off-boost (cue cries of "why the f*ck did you buy one then?").

Now I keep on hearing about the latest Merc CDIs, which pull really strongly from about 1500rpm, and that BMW on ebay the other week

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where theysaid the turbo kicks in at 1700rpm instead of the usual 2200rpm, and wonder"what could I do to mine to make it more like them". I've heard something vaguely about some sort of device that reduces turbo lag, but all I heard is that things like that are generally avoided as they're basically a bit s**te, and are bollock all good for engine longevity - so that's not an option.

But what is? How do they get the turbo to kick in at, say, 1700 instead of

2200 on that BMW for example? Is it to do with commonrail technology, or something more to do with the turbo itself?

If I did get mine boosting much earlier on, what sort of engine mods would I need to do so my engine could withstand the extra torque at lower revs? Uprated head gasket? Forged crankshaft? I'm guessing doing it properly won't be cheap?

Any insight would be fan-bloody-tastic.

Cheers,

Peter

Reply to
AstraVanMan

what about a smaller turbo or one with lighter blades? i know on the MR2 that the CT20 spools faster than the later CT26

Reply to
Vamp

Well it would spin up quicker, but it wont produce as much top end power, but of course by this point the larger turbo will have spun up making the smaller one insignificant. No idea about having it at full boost by 1000rpm, you'd have to ask someone in the know. But a turbo off something small would probably do the trick. Something like an astra TD (the 1995ish model), a mates got one and the turbo looks weeny.

Reply to
Carl Gibbs

Would that be to kick in at lower rpm then? Would having it on full boost at something like, say, 1000 rpm be pushing it? :-)

Sounds mad, but I reckon it would actually save fuel as I wouldn't need to use the revs nearly as much.

Peter

Reply to
AstraVanMan

How would you do it then? COuld you put them in parallel? Would make things a bit complicated i'd imagine. Perhaps some sort of 'wastegate' type device blocking off the weeny turbo at say 2000rpm and letting the bigger one take over. Or am i just talking crap. Enlighten me Mr Burgerman sir.

Reply to
Carl Gibbs

Turbos boost due to enough exhaust gas getting produced to get int a self sustaining state.

Earlier boost can be from, exhaust valve opening earlier, retarding the injection pumps timing (more pressure left later to spin the turbo), smaller turbo exhaust housing, higher compression, insulated manifold, smaller exhaust turbine, less exhaust restriction, more efficient intake system/turbo compresser/difuser, (so less heat made by compressing the air) etc.

All (well most!) which make it worse or less efficient at peak power...

A bigger capacity does this too, as well as making more torque anyway!

Reply to
Burgerman

The real problem is simple. IF the turbo exhaust housing "nozzle" that spins the turbo up is small enough to start at low revs, it becomes increadibly restrictive at full power and sort of gets in its own way...

And if its big enough to flow full power on boost exhaust properly it would never actually come onto boost at all! Thats why my Bike had a HUGE T4 turbo, on 1.1 litre engine. It would not boost below 7 or 8 thousand rpm, but on a bike that has go anyway its not important. But then from say 7 to

10,000 it can really m,ake some power because it isnt restrictive in itself.

On the strip of course full 30lb boost from as soon as you hit the nitrous button at ANY rpm. Because the nitrous makes enough instant exhaust gas (and power) to spin it so hard that its on full boost and the wastegate open! Now the clever bit... The gas turns OFF at 15psi boost. So it only actually operates for a second, during a run just to make it boost instantly off the line.

Reply to
Burgerman

There isn't any point putting a small one in series! It will spin up early ok, and then block the exhaust from here on!

Reply to
Burgerman

Exactly what a mate of mine said earlier on when I mentioned that idea. Would there be a way to have them in parallel, and have some sort of shut-off valve to stop the little turbo from spinning its bollocks off when it's doing bugger all to help things?

Peter

Reply to
AstraVanMan

that the CT20 spools faster

Maybe an idea. I've just had another mad idea of some sort of turbo that would be spun by an electric motor up until 2k, when the zorst gases would take over. Mind you, that would put extra load on the alternator, and if you're going to uprate that then you may as well have a supercharger.

Talking of which, I wonder if it'd be possible to have a supercharger on some sort of viscous clutch whereby the supercharger would work early on, then the turbo would take over - ISTR someone vaguely talking about stuff like this before - would this work or is it just bollocks? :)

Peter

Reply to
AstraVanMan

I think its already done in parallel with a type of boost/rpm controlled swap over valve on industrial/boats and stuff. So we know that can work but its a bit complicated to sort out under the bonnet of a car I think?

Rally guys use an extra injector on overun into exhaust to KEEP it spinning, but that would just cause smoke off boost... Supercharge it!

Reply to
Burgerman

People have done such things with dual super/turbochargers. I seem to remember a MK1 Fester with a super and turbo charger in an issue of C&CC, the bloke used a windscreen wiper motor to operate the valve, and it apparently worked seamlessly.

Reply to
Doki

It would also put one hell of a strain on the chassis, towing the trailer with the coldfusion reactor based powerstation to provide the electricity.

Reply to
MeatballTurbo

I see. I'd imagine the space would be the main concern under the bonnet. You could get over complicated (if you're clever enough), but if theres no where to put you're fudged!

I dont think they use an extra injector (well not the big boys anyway), the timing is retarded so the fuel ignites whilst the exhuasts valves are still open. Very cool but i'd imagine it puts the turbo and exhuast under a fair emount of pressure. Sounds like a supercharger may be the way forward!!

Reply to
Carl Gibbs

Ed with the Micra! IIRC his micra has a supercharger with an electromagnetic clutch that disengages it when the turbo spools up. And it can also be disengaged by driver intervention (i think Ed added this feature in himself though). So yes it would work.

Reply to
Carl Gibbs

I think its the shape before that one. I think it is a 1 litre SOHC, but i could be wrong. I also think he has a website (search on google groups, it was in his sig), so might get his email addy from there.

Reply to
Carl Gibbs

Oooh, cool!!!

Is Ed's Micra the K10 shape one (I think - the type I mean is the bubble shape that started around K reg) with the 1 litre DOHC engine? Any idea how many miles it's done since it's had that arrangment fitted?? (PING - Ed).

Peter

Reply to
AstraVanMan

Ah, that all sounds pretty expensive, and if it significantly decreases the economy, then maybe I'd be better off with a V8 or something :-)

My 2.5's got plenty of torque, but virtually nothing off boost. 'tis the nature of the beast I suppose.

I was reading on Dervman's site about modern TD's, like variable vane turbocharges etc., and it sounds like what I really want if I'm not happy with mine is already is a more modern engine!

Must look into the Ed-style supercharger though!

Peter

Reply to
AstraVanMan

So when you say the gas turns off at 15psi boost, does that mean when it gets to 15psi boost the gas powering the turbo is purely from the nitrous kit, or what?

Clever stuff anyway, and thanks to all for the advice - keep it coming.

Peter

Reply to
AstraVanMan

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