Turbo Lag?

[GandalfS6]

Thanks Paul! I'll quickly try to borrow a DV to see what that does. Any ideas on what is the best DV to get? Are the Forge, Hyperboost, GFB etc better than a stock DV?

[audiman]

I think that the stock DV is more than good enough, i have never had any problems with using one, still on the original one and its working fine!

[GandalfS6]

I will try to pick up a S3 Bosch DV 710N today. I saw that the guys here thought it worked better than the S2 DV and it is cheap. Down here in South Africa it is also easier to get as the Forge Hyperboost etc normally has to be imported and takes a while to get!

[andre]

I hope the pipe work for the DV on your motor is still intact. Let me know if you need to chat regarding a comparision of what you have and what it should be.

Andre

[GandalfS6]

Geez Andre, now you have me worried that it might not be a Dump to Air DV but a stock DV without the pipe to recirculate :eek2: I'll have a look tonight!

[andre]

Ah, yes. Never thought about that option. However, either way, if it is dumping to air then there is (should be) a pipe that would have been blocked off on the inlet pipe, should be quite easy to see, but you may need to remove the headlight for better viewing.

[GandalfS6]

Oh Dear! I just had a look and the DV is the standard Bosch plastic thingie! Now what would then sound like it is a dump to air valve?

[GandalfS6]

Update

I was quite lucky, a friend had ordered Forge DVR's for his RS6 but they did not work on his car. I was very disappointed with the prices Audi South Africa charges for parts - they want GBP33 for the S3 710N DV whereas vagparts.com charges GBP15.60

I got the Forge for a good price (less than 2 DV's from Audi SA) and fitted it. The old DV was a 710A which was probably on the car since 1995! The diaphram was cracked and the spring extremely weak - there was no way it could have held boost. At the same time I cleaned the MAF using carb cleaner. The car is much smoother but the lag is still there. Cleaning the MAF took away the fault 00553 - Mass Air Flow Sensor (G70) but I still have:

00515 - Camshaft Position (Hall) Sensor (G40)
30-10 - Open or Short to B+ - Intermittent
00515 - Camshaft Position (Hall) Sensor (G40)
01-10 - Signal Shorted to B+ - Intermittent
00513 - Engine Speed Sensor (G28)
03-00 - No Signal

Surely the car shouldn't even start with these faults? I'll see what I can sort out with these :confused:

We had a Audi Club meeting on Sunday where a Racelogic VBox was used to establish 0 to whatever speeds and times. Even with a great launch I only mananged 0-100km/h in 7.1 sec and a 1/4 mile of 15.1 sec. This is as a result of the lag I think. The lag is less of an issue at higher speeds (gear changes all above 4500 rpm) so I managed a terminal speed of 189km/h at 800m - only 6 km/h less than a RS6!

One of the technical boffins at the meeting thinks the lag problem is as a result of the 2.25" exhaust - it "sounds as if the turbo produces too much air for the exhaust to handle"! I'll put in a 3" custom exhaust hopefully this week. He thinks it could also be the wastegate that might not be holding pressure but one thing at a time.

[GandalfS6]

I forgot - the dump to air sound is as a result of the BMC cone filter - the Forge also sounds like a dump to air (nicer noise though) as the air that normally would go back to the air box blows out the filter. I think I need to find a standard airbox!

[dan_b]

You said earlier that one of the sounds you hear is the turbo sucking air. Are you sure this isn't actually an air leak in the intake system?
If you have a leak that could well be contributing to your problems?

[GandalfS6]

Yep dan, it could well be. If there is a leaking pipe lag would be bigger! I just have to figure out how to check for leaks! I guess that it would be a good practice to replace all the 10 year old hoses with new silicon hoses.

[GandalfS6]

Leaking Hoses!

I finally got round to doing a pressure test - actually quite easy to do!

Started pumping in air and it holds no pressure! The hose from the MAF to the Turbo has a large hole in it where it connects to the turbo. I have no clue as yet if any of the other hoses leak as well but I guess this is one step at a time. Now if I could just lay my hand on a set of Samco hoses!

I did also see that the boost guage istallation wasn't the best - the pipe to the ECU was splitting and nearly falling off! So I guess the ECU didn't have any idea what the boost was?

Quick question - If there is a leak in the MAF to Turbo hose, it is sucking in air that the MAF does not know about - what effect would that have on the car?

[Pisobiker]

Lean fuel mixtures !

This shouldn't be a big problem at part throttle, since ECU can adjust fuelling by monitoring exhaust through the Lambda. But problems might occur at WOT (which is also the worst place where running lean mixtures), where ECU does no more read the Lambda but fuelling is determined by its internal maps.


Marco

[GandalfS6]

Turbo lag continued

I have tried all I could to solve the lag problem - checked the hoses, tested the WG, replaced the WGFV and DV - all of which helped to reduce the lag a bit. The max torque is still coming in at 4500 rpm.

I recently had an incident where the little notch in the camshaft pulley broke off and the valve timing went out. With the turbo out, I had a good look at it.

On the cold side the KKK number is 5326-101-5160 and not 5324 970 7200 as a RS2 (thanks to SJM) should have. I therefore have a K26 cold side and I have to assume it is the reason for the lag! I know the RS2 has a K26 cold side but the numbers aren't the same - or am I confused?

See picture:

[GandalfS6]

Here is a picture of the top of the turbo. I didn't get a pic of the exhaust side but does it look like a RS2 exhaust side? I'll check the numbers on it tomorrow.

I can't live with this much lag so I guess I need a new turbo - any suggestions what to do?