my friend has just mapped a vrs with only a pd160 intake to 189bhp and 312lbft at 1.55 bar.

How does this compare with other tested methods of remap? I am considering my post warranty options.

Results will vary considerably from rolling road to rolling road so it is difficult to compare figures unless all cars are run on the same dyno on the same day. Also bear in mind that if you go for ultimate power you will considerably reduce the life of several components (notably clutches and turbos). I have read that the accepted max for a standard turbo is 1.55 bar. I think that the revs to which this boost is maintained is important as well . A turbo will be working twice as hard at 4000rpm as it will at 2000 rpm for the same boost pressure.

agree re rolling roads, don't agree re turbo working twice as hard.

The work done by the turbo will be entirely dependent on its compressor map and you may find at a pressure ratio of say 2.55 at 4k rpm and and 100% load, it is far happier and more efficient than it would be at 2k rpm with a 2.0 pressure ratio and 80% throttle/load.

It is purely dependent on the physical characteristicsof the turbo.

Ok I'm willing to learn . Right or wrong here are my thoughts on the subject:-

Are we taking about turbos in general, a modified turbo, or the turbo in the fabia VRS? Compare 1.55 bar at 2000 rpm with 1.55 bar at 4000 rpm. Double the revs uses double the air so the turbo will be flowing twice the air and therefore working twice as hard. Ok, the variable geometry will cloud the issue but it's a reasonable assumption. Given that the quoted maximum torque is at 1900 rpm I am taking an educated guess that the turbo is very efficient at that rpm.On all standard dyno plots that I have seen, the torque curve slopes down gradually after this point. I think this is partly to reduce power to sensible levels and partly to give a reasonable service life for the turbo. I have serious doubts that higher than standard boost at double the rpm can be anywhere near the centre of the efficiency island. The turbo cannot possibly last as long under these conditions.

Feel free to put me right (explanation appreciated:thumbup: )

I don't think we are in disagreement.

All I am saying is that the compressor map will show a drop in effieciency towards its edges as the pressure ratio and flow of the turbo increases.

Your guess that it is probably most efficient closer to the torque peak may be right, but thanks to vgt at higher outputs its efficiency will be more cosnsitent than a fixed geometry turbo. Thats why they use them

Don't think you need to learn anything, just thought that double the air at double the rpm was a bit of a sweeping assumption.

In all of this, the turbo would really be the least of my concerns. I would be more concerned about the drivetrain.

If anything that is what is putting me off the idea.

I have given some turbos some stick in my time, vgts included, and as long as you use keep using a decent dumpvalve, don't cross the surge line and allow them to cool down before removing water and oil flow, I would not be overly concerned.

It seems we are broadly in agreement Adam. I've done a bit of research and it seems that the turbo in the fabia is the KP39. This turbo is rated to 100kW (134 bhp). I couldn't find an efficiency map for it anywhere though.

134bhp?

seems a little low for a car running 130ps as standard

That said, as has been discussed, perhaps since compression ignition engines operate at wide open throttle anyway, it means the turbo will flow 100kw more air beyond the power output the engine would have normally aspirated.

Only a guess.

I think these turbos were developed for diesels only so the power rating should be accurate. There is only one current petrol production car that uses VNT (911 turbo). Petrol exhaust gas temps are too high for the VNT mechanisms unless high temp materials are used. The 134bhp power rating means the turbo is ideally matched to the application. Thats why the 150/160 bhp engines with the bigger turbos do not respond as well at low revs. It is probably safe to go 20 percent above the rating to say 160 bhp with comparible fuelling. Upping the fuelling should sneak the engine into the 170-175 bhp range.

I thought the PD150/160 turbo GT1749VB is less responsive due to the fmic that is used in these engines. Bigger pipe work plus increased intercooler = more lag :confused:

Also thought the difference betweeen the gt1749va (pd130 golf platform) and the vb was the shaft in the vb was stronger to take more boost. Both turbine and compressor are the same size? :confused:

With standard boost pressure and tweeked fueling the KP turbo in the fabia vrs can make 163bhp/300ftlbs

I do tend to get a bit lost here.

diesels work at far leaner afrs than petrols. They always operate in excess air at WOT.

That means you can't really rate the turbo in terms of bhp but should surely do it in terms of lbs of air at given boost pressures. I say this because the volumetric efficiency of the engine can be altered drastically by tinkering with injecion timing.

I have filed many patents on injection timing in diesel engines, so am well aware of the potential gains. Also in relation to split pulse timing for catalyst light off and reduction of cumulative emissions during the drive cycle! But I can't really go into that in any detail as I would lose my job!

Anyway, by retarding the igntion to later point in the cycle, I am told there are substantial gains to be had, the effect being an increase in egt. I could understand why this would be a problem for the vgt though.

Incidentally I know of several other car companies who have vgts on petrols in development already.

I can only assume that the 189bhp and 312lbft I have witnessed must be either on the edge egt wise, or lucky.

Either way, I think I am more convinced that I don't want to be risking it on my new car, and perhaps even after the warranty has expired I may not bother. No one can say that the car is slow at the moment!