Joe100S

I've replaced the old DV on my UrS4 with the Forge Motorsports billet DV-R and am using the middle weight spring (the lightweight one is approx stock).

The improvement is good, once started the car is idling smoothly at ~8500rpm, but just after start there is a brief fall in rpm to about 4k before the car spins up to normal idle rpm. Had anyone else noticed this? Any thought on how to deal with this or should I just live with it?

Joe100S

As an aside from the above posting, I will say that the turbo spins up MUCH better (or I'm not getting turbo lag like I was between shifts) with this new DV-R. It's a nice improvement over stock. I should mention though the old one may have been quite worn out so there's no saying how good the spring was in the stock one, let alone the diaphragm itself, which from inspection was complete sh*te in the OEM model.

Whatever the case, the car is much peppier now (not that it wasn't already a hell of a sleeper car).

scarman

That's your imagination working overtime to justify your spending the money on a fancy valve you didn't need. A correctly working bypass valve will correct any problem with leaking boost there but that's about it.

The idle problem can probably be traced to vacuum leaks or the idle stabilization valve sticking.

I don't understand this 3 Bar wastegate and map in your signature? Do you mean you have a 3 bar map sensor installed in the ECU ? And the wastegate, are you running a manual boost controller set for 3 bar ? Is all this on an otherwise stock motor and turbo?

Joe100S

The DV-R came with the car and has been sitting in a box since. After cracking the stock unit being somewhat stupid earlier today I figured what the hell and tossed the Forged Motorsport one in. A free performance part is always cheaper than than a new OEM one from the dealer.

It has the IA Stage III+ - ECU, 300 kPa Transducer and the N75 wastegate has been modified as the racing version and has been drilled out and has a 3 bar spring in it (also IA).

The new valve has a much stiffer spring than the old one.

Stock EM has been cleaned up to help #5 run cooler although an aftermarket RS2 EM is on the near horizon along with the 3" downpipe.

Turbo has been replaced with a new one, in addition to ceramic coating to help it cool more consistently, the new one has been slightly modified (custom machined compressor wheel) and has aerospace grade Abec 9 rated bearings instead of the bushings in the stock turbo (as you would find in a jet turbine to reduce friction and improve spin up).

Having spent a few years racing GP motorcycles with a professional engine builder and crew working the bike I can say that I can generally tell the difference when an improvements been made to throttle response and acceleration. This is not a big change, but it is a real one. It may be that the stock valve was just not capable of keeping up with a more efficient turbo.

So no, there's been some work done here and there.

I'll look at the idle stabilization valve, that could be the issue.

scarman

That was a good price for a Forge DV, and certainly worth changing out a worn out stock valve since any leaking robs the engine of boost, so I am sure you noticed the change even with your senses dulled from years of motorcycle racing. : ) I would expect a new valve to correct the idle dip rather than create it, so cleaning the ISV would be my next step.

IA's stage 3+ chips run about 21 psi maximum boost IIRC, so I wouldn't expect there is much danger of burning valves unless the wastegate spring is not allowing the ECU to control boost as might be the case if there actually is a 3 BAR spring in the wastegate. I would be inclined to think it is a 1.9 BAR spring for those chips. I got confused in there because the N75 is the WGFV that the ECU uses to control the wastegate operation. The RS2 manifold is certainly good insurance and Wagners clone is an improvement over that.

Yours is the first report I have heard of making improvements to the stock turbo. Most are always looking bigger for any turbo changes, at least to RS2. That custom machined compressor wheel must have been an expensive little project, unless you meant machined compressor housing for a different wheel. Off the shelf offerings are expensive enough.

My little dig at the Forge valve was to see if anyone was reading this forum, since there is little traffic here. Any need for help or advice will be found elsewhere in most cases.

Joe100S

The compressor wheel was off the shelf and then modified. It was about $80 for the wheel before the machining. The shop that did it does this a lot. Because all they do is turbos (from cruise ships to race cars) they start from scratch in most cases. Their thought is that for the money we would have spent on an RS2 turbo we have a much better unit that will be far more reliable and make more boost. It fit the stock mounting as well which was a bonus.

So the new turbo is not stock, but custom assembled from standard bits from other turbos. The cool side is pretty close to original save for the bearing section, and the hot side is custom (but ordered from another vendor who has them in stock I'm told). It spins up MUCH faster, mostly because of the bearings and the new compressor wheel.

The expensive part was the bearings, we used aerospace grade ceramics.

The Wagner EM is, as mentioned, the next toy. But this is a commuter car and often has a baby seat in it so I'm not going to get too crazy.

Joe100S

For anyone looking to upgrade to the Forge units I came across this article from someone who's actually done a bunch of testing with the Forge valves and his testing reinforces my initial conclusions.

For those interested: https://www.audiworld.com/tech/eng16.shtml

Happy S4'ing