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More Tdi fuelling/EGT stuff


GBMUD

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I drove a friends 200Tdi 90 a couple of weekends ago. It is similar in weight to mine but has a much larger intercooler which accounts for the much improved power over mine - it also smokes like billio when accelerating hard! The thing that impressed me, apart from the available power at speed was the fact that the turbo seems to come on boost much sooner then mine making it much more driveable off-road or in traffic.

Now I know that adjusting the star wheel down will have an impact on how quickly the fuel delivery rate rises when the boost comes in and that adjusting the diaphram affects the overall amout of fuel delivered but how do I get it on boost sooner? Would that be with the smoke screw? I guess that screwing the smoke screw in allows more fuel delivery without the turbo on boost? Presumably, one stops screwing it in when the engine becomes smokey at tickover?

So to EGT. As I understand it, EGT is a measure of the combustion temperature and that if the EGT gets too high then the piston crowns melt? I had an RD125 whose party piece was melting pistons. :( Is there anything one can do to allow higher EGTs in a Tdi? For example, if i were to re-build mine with new pistons, is there something on the market which will allow the running of highter EGTs? Different material, shape, some sort of oil cooling system perhaps?

Thanks

Chris

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Guest diesel_jim

I've heard of some engines (not sure what though) that pump in more fuel on the power stroke to keep the piston cool (it's then expelled on the exhaust stroke i assume).

don't think this will do much for your economy though! :rolleyes:

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Yea, Jase is right. Extra fuel is good power but excess fuel will cause bore wash and less power in a few thousand mile's. Its a case of getting it just right.

I think Diesel Jim is talking about dual stage injection which is the norm on common rail injection diesels. It tends to put in lots of small amounts of fuel to along with the main injection. Its to try and make them run quieter and stop some of the harsh diesel knock that you get with direct injection diesels.

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Yes the smoke screw adjusts the off boost fuelling. Though a tweak on the full power screw increases everything too :)

In theory you should stop screwing when it starts smoking (ooer!) but in practice - and I don't understand why - you still get more power (and smoke) even after the onset of smoke. If you adjust it to the "full Jap spec Mitsubishi" levels of smoke then it goes like stink but it's a bit indecent and in your part of the world probably highly illegal? :huh:

EGT's, fit water injection ;)

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Yup, I was wondering about that, any top tips for measuring it without spending cash on a boost guage?

Chris

I made one out of a £10 halfords tyre pressure gauge, six feet of window washer tubing and a plastic T piece I nicked from somewhere.... all bound together with insulating tape. Works a treat and for one off use you can keep the tyre pressure gauge for its original role afterwards, they are very good gauges seem accurate and graduated in 1psi increments on a nice clear analogue dial :)

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Yep,, not wrong there, shame for the poor sod, following :ph34r::(

:rolleyes: Sorry Tim. ;)

I will go see what Halfrauds have on the shelf by way of a proper boost guage I think. I would like to develop a greater understanding of what the turbo is doing and when.

Chris

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any easy way of checking EGT without buying a guage? I suppose the answer is no as you need to check it under heavy load to get the max figure.

I would love to know what my 200TDi is producing powerwise, I have tweaked the pump and it really flies, a mate followed me up a local 1in4 a few weeks ago in a 300TDi truck cab 90 and I left him for dead, he was amazed to see the back of the 110 completely full of tools and junk.

I am sure its going to die soon.

Will )

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Yeah, an EGT is a must. Here's the gauge I use and I've been very happy with it. Its not expensive (about £150), comes in a vaiety of differant colours (one does not want to clash :P ) and is superb quality.

As far as making the engine survive high EGT it is possible but its hard to do. The thing the internals mostly suffer from is heat, not temperature; a couple of seconds of 1000 degrees is OK, 5 minutes of 900 is not! This is why I chose not to run a particularly large I/C as I'll use the power in short bursts (step away from the keyboard Bish :P ), not for long periods like a road car. Appart from the cast manifolds which tend to crack under highish temperatures. The best way to solve this is with a custom made, SS, manifold (not cheap, though). As I understand it, to help with short burts of high EGT pistons and bores can be ceramically lined (££££££££££) as this'll stop the initial conduction of heat into the metal. However, once the ceramic's heated up you're back to square one. Turbos will also be an issue at high EGT. They don't like high temperatures either! AFAIK race pistons won't help that much, the main reason for them is to give better ballance making the engine smoother and pickup faster.

Basically, you just need to try and get the coolest possible air in and the exhaust gases out as fast as possible. The later will also mean faster turbo spool up but will reduce turbo life.

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What I am really after, at least in the shorter term, is to get the turbo to wake up a little sooner. I had the head gas flowed in the hopes of imropvement but there was little forthcoming. I went into Halfrauds earlier to look at boost guages. The only one they had hits the red line at 0.6 bar and tops out at 1 bar so it may not be that much use to me.

Higher power, mega fuelling and larger intercoolers can come later - probably in the engines next life - as with 176k on her I do not want to over do it. I am not after ultimate power, just improving/gaining useful power.

Thanks all

Chris

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Tim ones are worth having calibrated

as they can be tad off.

a forum member did mine for me unsure if he would do others.

He probably would ;)

Though it's not that easy to calibrate some of them, but can accurately tell you the error. Is a pain to strip some of them and reset the needle.

Ian

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does the boost pressure change as an engine wears? im assuming my gauge isnt to far out as it was displaying the correct pressure for a stock engine till i fiddled with the wastegate.

yes, as the actuator will get slightly softer, so will open at a lower pressure.

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Will, wot are you on?! :lol::lol:

M, temperature is an indication of how much kinetic energy the gas/solid/liquid has on a molecular level, heat is a measure of how much actual energy the system has ie a grinder spark has high temperature but low heat. Yeah, I know its a bit strange but I don't make the rules :ph34r:

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