kennyboy

quick question:

I have a 993tt with rs-tuning phase 1 ecu and carpgraphic mufflers. I don't yet have 100 cel cats. The car seems to run great but recently on a UK forum I've been advised to dyno the car to make sure I'm not getting boost creep as my cats don't match the tuning package.

Should I be worried about boost creep?

I heard elsewhere that on k16's and with everything working ok I should be ok.

The car is in fantastic condition with relatively low mileage, I don't want to do anything to reduce the longevity of the engine.

TB993tt

This is the description of "boost creep" from the guy on PH:

...you get more boost than the ECU thinks you should have but is unable to trim it. The boost control is programmed for a specific flow rate (exhaust), so any change in fueling/exhaust/cats/headers/wastegates has a potential to effect the ECU's ability accurately control boost. Just worth checking, IMO.

He is probably right in as much as the ECU will be programmed for a specific set up of components however putting it on a chassis dyno and letting some "laptop wizard" fiddle with the (expensive) ECU program should be avoided IMO. I don't really know what he means by "boost creep" on a 993tt engine ? but suffice to say if the boost gets too high (like the chap describes above) the engine will protect itself -so don't worry about it, you won't blow it up
Getting the correct component set up for the ECU program which you have will yield the best results (obviously )

kennyboy

thanks for the assurances tb, I wonder if you could answer a couple of specific questions:

1. when you say I won't blow it up, can you confirm I won't damage the engine or affect it's longevity?

2. I will get the cargraphic 100 cels when I can afford it, I've already got the cargraphic sports mufflers. Do you know if the rs tuning package is designed to work with these? I've heard they are and also for techart.

3. The power delivery of the car feels as refined (it a tt 911 can be refined!) as it did when stock, perhaps even smoother. What I notice is the car feels lighter and it hangs on to power better in the upper part of the rev range. From this it feels like to me I'm not suffering any problems, do you think I would notice it if I was?

JamesE

I posted that responce on PH. I was just pointing out that I know (Alan?) had problems getting the ecu to control boost correctly. This, according to this forum, was a result of mismatched components. Having extensive personal experience of mapping complex boost systems, on my car, I can asure you that if components are not matched, wrt a fixed off the shelf ECU, then you may well have issues such as boost creep. There is no reason why a 993tt would not suffer boost creep (i.e. more boost than the ecu wants), just like any turbo. If you are generating more boost than can be bleed off by the wastegates you will get creep. There are a whole host of reasons for this. And what is the point spending time and effort moding your car to have the ecu pull all the timing because of a boost issue. Lastly, I was not suggesting any one remapped anything, just that he got his boost checked. At the end of the day it's not my car so feel free to ignore everything I say...

kennyboy

James I'm taking your comments seriously, you obviously have a lot of experience of this sort of thing.

What I'm trying to find out isn't whether you are right or not but rather whether in my specific case I'm actually suffering from boost creep.

At this stage I'm thinking that I'm not though I will be taking it to chassis dyno soon - not for a remap but to see if I'm getting boost creep, presumably this is the best way to find out?

This particular ecu is well known on PH and I'm the 3rd happy owner. Alan got spikes rather than boost creep though I'm assured this was due to some very hard-core and bespoke cats. Other owners of this ecu have run without sports cats and haven't had any problems. Do you think it's possible the mapping could be quite 'forgiving'? - I'm told these rs-tuning ecu's are very sophisticated.

JamesE

The ECU will have vast amounts of compensation tables that are designed to keep your car from expiring, even when the user does stupid things. The obvious ones are pulling boost/ignition timing to prevent detonation/pre-ignition given specific adverse conditions. But, personally, I would want my car to perform at its best, which if you had too much boost, you would not be (due to the compensation effects). As I have already said my post was a result of the issues that previous owner(s) have had. You can do a search of this forum yourself to find what they were. I'm no expert but have spent many hours mapping my ECU and good dynamic PD boost control is bloody difficult with a fixed setup. Change that setup, and you will most likely be remapping the boost...

kennyboy

would I be able to feel the pulling boost/ignition on the road?

at the moment all I feel is one smooth push to the red line after boost is set. it's all very elegant and like the stock car but just feels bigger though not by a huge amount.

TB993tt

I'm still a bit in the dark as to what you think "boost creep" relating to the 993tt engine ?
The ECU reads air mass and via an electronic signal adjusts the wastegates to allow enough air (boost) to hit predetermined targets (actual values of target #s determined by atmo/load) the only "creep" that I have seen on this set up is if (because of the speed of boost build up and/or the inefficiency of the wastegate actuatation) the boost overshoots the target then the ECU can trigger an ignition cut out, this (in my experience) usually happens in the mid range around peak torque when the boost has been allowed to climb to its maximum.
If this is what you mean by "boost creep" then it may well be accentuated by having less than ideal componentry for the program but it will not cause any problems (other than the cut out losing you power for a fraction of a second) and certainly won't damage the engine.

You will not "produce more boost than can be bled off by the wastegates" -if this is "boost creep" then don't worry that won't happen IMO -only the scenario above (it is the too slow activation of the wastegate mechanism which is the culprit) which I recall one of the previous owners of the ECU had.

JamesE

the butt dyno is never a good measure of anything. I'm sure you'll be fine, but i'd still put the car on a dyno. And do a search on this forum.

TB993tt

If you mean a chassis dyno - I'm intrigued by what testing you would do to detect the "boost creep" and then what steps you would take to recify it ?

JamesE

...If you have a proper boost gauge and your own 'road' that would be ideal. To fix it I would makesure I had the components that the ECU was designed for.

TB993tt

My point is, the Motronic boost control effectively varies the boost to a seemingly infinate degree according to atmo/load inputs so looking at the boost gauge tells you ziltch since there is no fixed point of maximum boost - this is one of the major benefits of the Motronic boost control, the full interaction of all the inputs to give the optimum bang

As you have pointed out, the less than ideal componentry may well give rise to less than ideal function of the Motronic but this "boost creep" you describe is a red herring IMO whereas the overboost cut out which a previous "guardian of the RS ECU" had is real and probably accentuated by the less than ideal componentry.

But it won't harm the engine, don't worry

JamesE

...ok, but if you have triggered the overboost cut out, by definition, you are overboosting. i.e. producing more boost than the ECU really wants. This is what I was trying to describe as boost creep.

TB993tt

I was just trying to save this (rightly) parnoid gentleman from a fruitless and ££ trip to a chassis dyno

MOD500

As TB says, the wastegates sometimes do not open quick enough when required so the boost ramps up abit for a short time.

I have seen 1.6 bar for a split second on my boost gauge as it rips through peak torque, before dropping back to 1.1 - 1.2 dependent on gear / ambient temp, etc.

Glad you are liking the new set up Kenny