ACEparts_com

I've got the RS tuning installed and i'm about to whip the engine out next week to do the clutch and install new IC pipes, DV's, 100 cell cats and plugs etc.

What i've noticed is that when hitting the gas from 3K in fourth and fifth, i can feel the boost come in really strong, then backs off a little and then go again, it feels like it's surging.
I'm wondering if the installation of the 100cell cats will make this more or less noticable or if i need to wind the wastegates in a bit (tighter) to help hold the boost as has been discussed before?

Thanks!

Camber

Sounds an awful lot like the symptoms I had with failed diverter valves. You may want to check the vacuum lines to the diverter valves as well to see if they're well seated.

Jim

ACEparts_com

Thanks. This is why I'm doing a clutch a little earlier than required. It will give me a chance to do all these things easily rather than struggle with the engine in and then have to do a clutch in 3 months!

ACEparts_com

Great further reading!

http://dv.mistertam.com/4.htm

There I was thinking it was all in my mind!

fc-racer

The kind of surging you would get from a severely failed diverter valve is of a higher frequency than what you describe. You would feel it oscillate 2-3 times per 1,000rpm. The frequency you describe above sounds like over a span of 2-3,000 rpm. If the latter is the case, then it's more likely the Motronic system giving you full boost, hitting peak torque and detecting some knock, dialling it back and then rebuilding the boost again towards redline as you move away from the torque peak.

An easy way to test this theory is to run some race gas, 100 octane unleaded. On 91 octane, the dip in my stock 993 Turbo's powerband is very noticeable, it's almost gone with 94 octane and is just a rocketship on 100 octane. There are quite a few dyno graphs on rennlist from stock 993 Turbos on street octane and you can clearly see the point where the boost gets dialled back and then comes on again hard at around 5,500rpm.

Hope this helps,
Farzaan

ACEparts_com

Hi, I've got an RS tuning stage 1 ecu fitted. The DV's were making some weird parppp noises, now they don't.
I was wondering if it could be the wastegates opening prematurely as I've read elsewhere. It could also be an effect of the higher back pressure caused by the current standard cats.
When Verysideways had the kit (with sport cats) fitted to his car he said it revved freely to 7K, my car runs out of puff a little over 5.5K.

Of course, I could simply be feeling the motronic controlling the boost as it's around peak torque. I know one thing, goes like stink with the new ECU. My grin is 50% excitement 50% fear!

Acropora

Had a similar problem here. Stock plugs instead of Iridiums were the solution.

Rob 97 993c2

brad,
why where stock plugs the solution? i though the upgraded plugs are much better.

TB993tt

ACE
My take on it FWIW is that there is probably nothing specifically wrong. I don't know your configuration or the exact configuration which the RS program is set up to deal with, but I would guess that they are not exactly the same (you mention the cats which is the obvious difference) whether it be your turbos - weren't they supposed to be some sort of subtle K16 RS hybrid for this ECU ?

What I am getting at is that whilst the ECU WILL work with your set up, it will not be 100% optimised so you will probably get dips in the delivery. What you can feel is the ECU allowing the turbos to ramp up the boost at peak torque ~4000-4500rpm then activating the wastegates and possibly pulling the timing quite aggressively as knock is detected - this is your dip (which may feel particularly accentuated since you have just experienced a nice slug of RS style torque, and when it shuts off there is a big difference) then the ECU will increase boost and timing and follow the knock curve up to the limiter, which typically on this type of configuration will mean 1.1 bar at 4/4.5K then 0.8/9 bar at peak power ~5.7/6K then rising 1 bar to 7K.
If you don't have the sports cats this may well be limiting your top end >5.5K

ACEparts_com

The stage 1 ECU is deisgned to work with standard turbos according to RS. The car has already been transformed with just this. I'll update my results once the cats and DV's are are installed.