Dave Posted January 27, 2006 Report Share Posted January 27, 2006 i take it we all have a basic understanding of turbo's.. in that exhaust gases drive a turbine that forces more air into the combustion chamber.. the more air/fuel mix creates a larger explosion.. resulting in more power. One question i have.. do turbo's run all the time, or just when extra power is required? The way i understand it is that turbo's increase the pressure of air, but when the dump value opens then the pressure drops and it builds up again. But what happens when you are at 70mph crusing down the motorway.. is the turbo still pressurising the air, or is it efectivly off until the acclerator is pushed?.. and is this partly why you get lag? Link to comment Share on other sites More sharing options...
s4_sat Posted January 27, 2006 Report Share Posted January 27, 2006 the amount of air going through the turbo is reduced at cruise and is spinning at low rpm so it takes a bit of time for the turbo to build up pressure and speed to higher rpm to provide enough boost for acceleration. Link to comment Share on other sites More sharing options...
Dave Posted January 27, 2006 Author Report Share Posted January 27, 2006 So effectivly, at 70mph the turbo is still supplying air to the engine, albeit at a reduced pressure? Link to comment Share on other sites More sharing options...
Dave Posted January 27, 2006 Author Report Share Posted January 27, 2006 So what controls the wastegate?.. the amount of pressure built up, or is it part of the engine ECU? Link to comment Share on other sites More sharing options...
s4_sat Posted January 27, 2006 Report Share Posted January 27, 2006 yeah, the turbo is spinning at a low rpm but when you press the accelerator, the turbo takes time to spin up to provide enough pressure to force more air into the cylinders. Link to comment Share on other sites More sharing options...
s4_sat Posted January 27, 2006 Report Share Posted January 27, 2006 afaik the wastegate is controlled by the pressure build up, its closed when under load and opens when the load is reduced. Link to comment Share on other sites More sharing options...
Dave Posted January 27, 2006 Author Report Share Posted January 27, 2006 Ok mate.. makes sense! Link to comment Share on other sites More sharing options...
NeilB Posted January 27, 2006 Report Share Posted January 27, 2006 A good peice of info about turbo's Dave - http://auto.howstuffworks.com/turbo.htm Wastegates are on the 6th page. Link to comment Share on other sites More sharing options...
sitas3 Posted January 27, 2006 Report Share Posted January 27, 2006 partly - the wastegate on Audis at least is controlled by a wastegate control valve which itself is controlled by ECU input. Link to comment Share on other sites More sharing options...
Drillslinger Posted January 27, 2006 Report Share Posted January 27, 2006 Dave... http://auto.howstuffworks.com/turbo.htm The 1.8T uses a "Load-Based" system. IIRC the N75 valve plays a part in boost buildup as well. I'm not sure what you're trying to figure out though Dave?? How would you ask a 10 year old, THEN I'll probably be able to grasp what your looking for Link to comment Share on other sites More sharing options...
Dave Posted January 27, 2006 Author Report Share Posted January 27, 2006 Thanks guys, all i'm trying to figure out really is how hard a turbo is working (and hence how hot) when it's at a steady pace.. ie) crusing.. whether it is just spinning or whether it is still under pressure. Basically, if you have a turbo charged 2.0litre engine. We all know that the turbo increases the power of that engine above it's standard bore size. But after you have acclerated hard and used that extra power and you are crusing.. are you still utilizing the power from the turbo or are you just using the power from the cubic capacity of the engine? Link to comment Share on other sites More sharing options...
sitas3 Posted January 27, 2006 Report Share Posted January 27, 2006 mostly from the engine CC - AFAIK turbo's are used for acceleration only. Link to comment Share on other sites More sharing options...
Thorburn Posted January 27, 2006 Report Share Posted January 27, 2006 The rate at which the turbo spins will decrease under light load as there is less exhaust gas spinning the turbine. Link to comment Share on other sites More sharing options...
Soapsuds Posted January 27, 2006 Report Share Posted January 27, 2006 ah - i get where you are coming from! My Starion has a boost guague on it and before i fitted the boost controller, doing 30mpg in 3rd gear (it wont in 4th!!) the boost was -7 to -14psi.... with it fitted, it now holds steady at thie speed on approx 0psi - still spinning, but at 0psi most probably just using the engine. VERY sensitive to the smallest of throttle changes. I have mine upped to 14psi and you can get it to glow white hot - pretty cool at night After a lazy drive (rare in the Staz), the turbo is still very hot, probably because it's constantly spinning at very high RPM, even at low pressure.... Link to comment Share on other sites More sharing options...
sitas3 Posted January 27, 2006 Report Share Posted January 27, 2006 [ QUOTE ] The rate at which the turbo spins will decrease under light load as there is less exhaust gas spinning the turbine. [/ QUOTE ] and mainly because the ECU is telling the wastegate it doesn't need as much boost.. Link to comment Share on other sites More sharing options...
cruiser647 Posted January 27, 2006 Report Share Posted January 27, 2006 Also depends upon the engine characteristics. As Avant says, older engines had the boost push in something chronic, as it was a simple input/output formula. Newer ones like the VW 1.8T (electronic wizardry stuff) have variable vanes. These vanes adjust depending upon throttle input, exhaust gas volumes and more. At low revs, they spin so not much air is pushed in. At high throttle inputs, the vanes open and 'catch' more exhaust gas so spins faster - pushing in more air. But in effect, even at idle the turbo is still spinning (not doing much, but spinning all the same) Link to comment Share on other sites More sharing options...
Dave Posted January 27, 2006 Author Report Share Posted January 27, 2006 Wow.. so it's a technology that has come a long way! Link to comment Share on other sites More sharing options...
Drillslinger Posted January 27, 2006 Report Share Posted January 27, 2006 I thought the 1.8T had a fixed vane turbo, whereas the 1.9 TDI had variable vanes Link to comment Share on other sites More sharing options...
Tobes49 Posted January 27, 2006 Report Share Posted January 27, 2006 [ QUOTE ] I thought the 1.8T had a fixed vane turbo, whereas the 1.9 TDI had variable vanes [/ QUOTE ] Correct, The modern TDI diesel also use vaccum to control the wastegate, because a diesel has a vaccum pump for the brake the servo so they use this constance supply of vaccum to control the boost, this mean they can open the wastegate even before boost has started! In petrols they have a N75 valve in the feed to the wastegate that bleeds boost out the pipe, So where the turbo is making say 10PSI in the system the N75 bleeds boost and make the wastegate think the boost is lower keeping it shut longer! hence higher boost. Link to comment Share on other sites More sharing options...
BenjaminTDI Posted January 27, 2006 Report Share Posted January 27, 2006 I was under the impression the modern TDI units do not have a 'wastegate' - like the old Garrett GT15 turbos. The VNT15, 17 and 19/20 use the variable vanes to move and direct the gases at a different angle through the turbine, rather than bypassing it completely? achieveing the effect of a wastegate, without one Link to comment Share on other sites More sharing options...
Omi Posted January 27, 2006 Report Share Posted January 27, 2006 5 points, that man. I'm learning a lot about turbos presently, as I've decided to stick one on the E30 to liven it up a bit. I just now need to learn how to map fuelling and timing on a standalone ECU. Might also be fun if I can get the expandable ECU to perform software rev-limiting until the engine is up to temperature, shift lights replacing the service indication and, ermmmm, ignition cut anti-lag. Link to comment Share on other sites More sharing options...
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