12 replies to this topic

[turboman]

I was chatting with a technician the other day about wastegates, who advised me that by opening it slightly could increase power quite a bit, as long as you dont over do it. Wont go into the story, but lets just say, I know about a VXT that arrived and the wastgate was closed, so by fixing it, the dealership not being Turbocharger experts, set it up by touch and feel, and theres a VXT out there which goes like SOAS, better not say which one, because he thinks they all go like that. Does anyone know anything about wastegates?

[Jim_Cross]

Wayne, I think you want to stop the wastegate from opening up quite as much as it does if you want to increase power. The wastegate is used to control the boost pressure by letting exhaust gas out of the turbo and into the exhaust. When the wastegate is open, gas can flow out of the turbo and into the exhaust. When it is closed, the gas is kept in the turbo, allowing pressure to build. So, stopping the wastegate from opening quite so much will allow boost pressure to rise quicker (giving more boost at lower revs), and/or increasing peak boost pressure (depending I guess on how it's set up). More boost means more power, so yeah, this could be used as an easy way to up the power. However, obviously it'll put more stress on the internals of the engine, and the turbo itself if the boost pressure is higher, so before playing with it, it's probably a good idea to fit a boost gauge, and work out how much boost/power the engine can handle. *** I think this is right, but feel free to correct me if I've got it arse-about-tit! *** By the way Wayne, what's the chance of my car being ready on Friday morning? My Dad's offered to give me a lift over if it's ready. Are you in tomorrow? If so, I'll give you a call...

Edited by Jim_Cross, 25 May 2003 - 12:54 PM.

[R1 nur]

Interesting. So do you know anything about 'Dump valves?' Keep getting told to do fit one on the VXT.

[Jim_Cross]

A dump valve basically dumps out unused boost pressure. When you're accelerating, the pressure builds up in the turbo, and this air is forced into the engine. However, when you lift off, the throttle is closed, so the air can't go into the engine, so you've got lots of compressed air and nowhere for it to go...so it ends up going back through the intercooler towards the turbo the wrong way (potentially making the turbo stall). If this pressure is high enough, it can damage the turbo. A dump valve opens when you lift off the throttle to allow this built up pressure to escape, and can keep the turbo spinning, so reducing turbo lag further. There are two types - recirculating, and atmoshperic. Recirculating dump valves release the air back into the inlet tract to be used again, while atmoshperic ones release the excess pressure into the air. These are the ones that make the rally-car (Max Power-esque?) stylee whooshing noises. I would have thought the VXT has some form of DV fitted, unless it runs at very low boost. What people are probably saying is that you need to get a noisy (atmospheric) one fitted

[R1 nur]

Is there a "DV" fitted to the VXT anyone? I don't think there is but what do I know! Regal do one. Anyone had that fitted. I wish Minime had a turbo to test out all the bits!

[Dave T-S]

You are getting into a quite complicated area when you start playing with wastegates, which is a quite dangerous area too for people that don't know what they are doing - my wife's old Impreza STi Type UK had a full decat exhaust fitted, and because the turbo was spinning up earlier and before the boost control solenoid/ECU could open the wastegate, it was spiking at 1.7 bar boost (25psi). That isn't good for the long term health of the engine! Re dump valves, I would only fit a recirculating one, not an atmo. What has the VXT got ? - i'll have a look tomorrow and let you know

[Emmy]

Hey all, Jim - you're quite right Wastegates release exhaust gases (i.e. "gates" the "wasted" exhaust) so that the turbo doesnt spin itself to oblivion (remember, turbos can spin up to over 150,000 RPM!)... Also, it controls the boost pressure (pressure of air in the inlet system). If the pressure continues to build, you get huge amounts of air in the engine cylinders, which (assuming there is enough fuel) you get a continous power build up until the piston rings rupture (or the pistons melt!), and the engine becomes very sick However, something else usually happens before that. Basically, you end up with an excess amount of air versus fuel (the "perfect" ratio is usually 14.7:1, and this is known as the stoichroic ratio), because the injectors reach their maximum capacity and cant flow anymore (or the ECU doesnt supply any more fuel because it doesnt know about the excess air). This is called running 'lean', and most engines do this a little in the midrange RPM for maximum power, and usually a little rich (less air than the stoichroic ratio) at the extremes (idle and redline) for safety. If an engine runs excessively lean, this is where the most damage occurs. Pistons, cylinders, crowns, and spark plugs can all crack, temperatures can rise dramatically causing warped engines, etc, etc. Personally, I think playing with wastegates should only be left to people that know what they are doing (cuz of the above scenarios if you get it wrong), but you can adjust it yourself if you really wanted to. For safety, I'm not gonna explain exactly how this is done here, in case of problems! The best way to increase your boost pressure safely (and reliably) is to allow someone to re-map your ECU. I havent really investigated yet, but I know Superchips does a re-map for it, and produces a claimed 24BHP additional horsepower - but ultimately you can probably expect a little more. Probably quite a few other companies can offer this as its basically the same engine as the Astra Coupe Turbo. As for DV's, the VX definately has one - and it's probably a recirculation type (known as a Diverter Valve), as the car uses a Mass AirFlow meter (MAF sensor). Atmospheric types (known as a Dump Valve) dump all their air, so it's not closed loop, and the ECU loses track of whats going on. Hope this helps! Thanks! Shash. PS - Hi Thorney!

Edited by Emmy, 25 May 2003 - 11:34 PM.

[Thorney]

Just to intro Emmy....he's one of the heavily modified TT gang and can be quite scary when he catches you in the corner of the pub and starts talking gear ratios with you you gonna bring your TTR on the Nomties run mate?

[Emmy]

Heya Thorney! Just taken a look, and might very well be up for that If you guys dont mind, that is! Thanks! Shash.

[Thorney]

If you guys dont mind, that is!

Very friendly bunch mate........drives can be a bit quick mind

We all know inside every normal car driver is a VX driver waiting to come out

[R1 nur]

Well thanks for that. You seem like you know your stuff! I might as well "come out" and let you know I am only slightly more technical than Martinh (difference is I want to know more - I know MH won't care about that!). So am I right in concluding DO NOT FIT ONE?

[Emmy]

Thorney - the quick drives are the best R1 NUR - If I'm correct in that the Z20LET engine (2.0 Turbo VX220) has a recirc valve, then no, dont fit an atmospheric-type "dump valve"... You can replace it with a faster moving piston-type recirc valve, and that should improve throttle response a little tho... Thanks! Shash.

[Chuck]

Emm, if that's what your techinican said then I think getting a service at your garage might be very dangerous. Does he have any training !!