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Boost control

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I changed my turbo at the weekend (300 tdi) for a known good one. I also had to swap the pipe between the turbo and wastegate as it had perished and split (this caused an overboost situation , 1.5 bar at the manifold!!). All I did was swap the pipe from old to new. Now I am pretty sure that the pipe I have fitted has got an internal blockage, as it is boosting to 1.4 bar, which is nice enough, apart from last time it did this I blew the head gasket.

This had got me thinking....at the moment it's very driveable, I get boost from 1500 rpm of about 0.5 bar, which I am sure is more than normal. I haven't been booting it hard either.

If I extend the wastegate hose and fit an adjustable valve in it, is it safe to say that I can control the boost pressure? Essentially doing the same as adjusting the rod,but more controllable

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The 300Tdi engines run at 1Bar of boost as standard, have you checked to see if the wastegate is free and not seized up? I ran my 300Tdi at 1.5Bar for a while with no ill effects.

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Will check that first. I was getting 1.1 bar at the manifold. Was just toying with upping it in a controlled and easy to reverse way.

Did you do any specific mods to allow the use of 1.5 bar?

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mine was box standard, ran it for over 15,000 before undertaking an engine conversion. I used a boost bleed valve to control the amount of boost and had a larger intercooler fitted.

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Already got full width cooler and tweaked pump. Would love to run it like this all the time, just worried about reliability as it's a daily driver.

General driveability is much better than standard. May just try the valve in the wastegate pipe to increase the pressure to 1.2 or 1.3 bar see what happens. Can do the hg in 3 hours these days :)

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As a bit of a noob, am I right in thinking the boost pressure blows the wastegate actuator open, which reduces boost, actuator closes, boost increases and so on, thus maintaining max boost at a given level as decided by the length of the rod?

Does a bleed valve bleed off boost pressure, thus easy in car way to alter wastegate actuation?

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Yes, and no. It's not as much an opening and closing, more of a how far it is open, it's constantly variable.

The bleed valve is basically an adjustable sprung valve which is normally closed, when the boost pressure exceeds the force of the spring the valve opens and the waste gate is allowed to operate as normal

Bleed valves are about £25, they're a bit carp really, and you'll need a boost guage so you can see what adjustments you are making. A better but more costly option would be an electronic boost controller, such as a Gizmo. I've used a second hand Blitz twin sbc before. Most of these allow on the fly, in cab adjustment and a number of saved settings, these functions are a bit of a gimmick really as once you have it setup right you'll probably never touch it again

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I've had a bleed valve on my 300 for about 3 years running at 23psi still runs fine probably done 25k or more.

Will.

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Perhaps they are more acceptable/reliable on a diesel, but petrol tuners don't rate them

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The 'bleed valve' I was going to use is essentially a brass tap. Open to increase the amount that can reach the wastegate, so stock turbo tune, close it to restrict the flow, increasing boost (in theory)

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All they actually do is stop waste gate creep so you'r turbo spools a little bit faster, I've got one on my 110 but I probably wouldnt bother again.

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