Disco92 Posted September 18, 2015 Share Posted September 18, 2015 Hi i have just fitted a vnt turbo gt2256v from a ml270 benz and it worked well. But when i went up for a run it is not boosting early after 1700rpm and then it hit lot of boost.. How can i limit that boost and open early like 1200rpm.. Thanks .. I used the oe 300tdi acuator for the vnt.. As it works with vacuum. Quote Link to comment Share on other sites More sharing options...
Boydie Posted September 18, 2015 Share Posted September 18, 2015 My guess is that your - possibly standard 300tdi - exhaust manifold is ill suited to the required exhaust gas flow for your cobbled vnt turbo. The actuator for the 300tdi is designed to operate on pressure, not vacuum, so unless you can supply photos of your set-up I'd say that the exhaust release gate is open. Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted September 19, 2015 Share Posted September 19, 2015 1200rpm is really low for generating more boost... means great big thumps down through the main bearings with little oil pressure. For VNT's you need a control box normally, or a coupe of cleverly rigged diaphragms, one to pull at low revs and one at higher. Quote Link to comment Share on other sites More sharing options...
Carloz Posted September 22, 2015 Share Posted September 22, 2015 No boost @ low revs has nothing to do with the standard exhaust manifold: low revs means low exhaust volume so no (big) disadvantages because of a standard manifold. I think the vanes are not set for maximum effect at the desired low rpm hence the sudden boost @ 1700rpm. I don't think the turbo is to big hence 270Cdi = 2,7L vs 300tdi = 2,5L, but still there are other parameters than engine capacity alone off course... As a test you can set the vanes fixed (without the actuator) in maximum effect ("closed") and see if it pics up boost earlier. Watch out for overreving the turbo, so not going full throtlle all the way to the higher rev range! Only full throtlle from stand still to maybe 1800rpm or so. If it pics up boost earlier maybe the 300TDI actuator steers the vanes open to early (maybe in this case a bleedvalve kan help) or your start adjustent of the vanes is wrong (too open). Normally when coming on boost the vanes has to open in a way that boost will be sort of constant thru the rev range and finaly it going down in the and of the rev range (depending on the flow capacity of the turbo of course). I think it is doable to control the VNT with a normal actuator but maybe not the 300TDi actuator, I don't know. There are many actuators avalable with all their own carracteristics. Difficult or almost imossible to find the perfect one. But maybe there is an acceptable one... Best would be to use a programable boostcontroller (and that is not a bleedvalve!!) which can be programmed according to boost, rpm and throtlle position. When using this the choise for a actuator is much easier because the caracteristcs of it will be integrated in how the boost controller is programed. That was me thinking up loud. Quote Link to comment Share on other sites More sharing options...
Carloz Posted September 22, 2015 Share Posted September 22, 2015 Still thinking loud: be sure your actuator acts in the right way. So opening the vanes bij increasing pressure. It's quite obvious but still... Quote Link to comment Share on other sites More sharing options...
vulcan bomber Posted September 24, 2015 Share Posted September 24, 2015 The 2256 is what the 2.8 tgv used, it's what the likes of bell and what not would sell you but with a different badge on it. As said, you can't use a pressure actuator on vac, it's all wrong. Quote Link to comment Share on other sites More sharing options...
Carloz Posted October 3, 2015 Share Posted October 3, 2015 Problem solved? Quote Link to comment Share on other sites More sharing options...
Landy-Novice Posted October 3, 2015 Share Posted October 3, 2015 surly its just a case of playing around with pressure actuators? im sure i read that the vnt kits use a td5 acutator but dont hold me to that! actuator needs to be taking off turbo intake like std turbo as apposed to from manifold as it causes boost spikes and general poor performance from turbo, Quote Link to comment Share on other sites More sharing options...
Carloz Posted October 3, 2015 Share Posted October 3, 2015 Hmmm... TS lost his way to this site already after one post... Quote Link to comment Share on other sites More sharing options...
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