Turbo Overboosting

[Guest]

My turbo gauge is hitting the stop when pushed, not sure if it has been chipped or whether the gauge is over reading. The boost does kick in earlier than I would have expected. I am unsure as to when or if the car was chipped as I have only recently bought it. I did try and open the DME box and have a look but the mass of wiring put me off. What damage can this have caused??

 

[Fen]

Absolutely none. If there is a fault and car overboosts it will cut fuelling and yu'll know all about it. It's probably just the cold weather as chipping alone can't make the boost come in any earlier. The dash mounted gauge is a rough indication at best so don't pay too much attention to that.

 

[Guest]

Cheers Fen, everyone you talk to tells you different things. Someone told me that it pushes the engine too hard and it could overstress it, guess I am just a bit panicky, paid £10K for the car and don't wanna do it any damage.

 

[Diver944]

Here's a good guide to removing the DME and taking a look at the chip. If it's an aftermarket one it's 'probably' got a sticker on it with where it came from.

http://members.rennlist.org/951_racerx/ChipsInstall.html

In standard form the car should boost no more than 0.8 bar (that will be 1.8 bar on the dash gauge) and if it overboosts for more than a few seconds the safety will cut in and DRASTICALLY limit the power. If the chip is modified it will have removed the safety cutout and if its a good one will have increased the fuelling to match the extra boost and you will have no problems.

Best to double check the boost with an auxilliary gauge, check the chip and perhaps ask the previous owner if he knows.

These cars can make awesome power if modified sensibly and with good products, and I have to say you are the first person to say the boost cuts in early, most new owners complain about the lag [] I know I did [8|]

 

[Diver944]

Just had another thought []

If you come to our dyno day on 7th May at Silverstone then for £30 you will get a plot of the power and torque your car is making as well as graphs to show the amount of boost throughout the rev range and very importantly a graph showing your air-fuel ratio as well. This will show you if its chipped properly and not running lean.

Much cheaper than buying an auxilliary gauge and you get to sniff high octane petrol all day [8D]

 

[drummerboytom]

ORIGINAL: Diver944

Just had another thought []

If you come to our dyno day on 7th May at Silverstone

Do you need to book up for this , or just turn up on the day ?

 

[Guest]

Hi Chaps,

Firstly Andrew, it does have a bailey dump valve, the kind that goes whoosh which I would like to replace, would this stop the wastegate opening and cause it to overboost, sorry I am a Turbo virgin, all new to me. I haven't experienced any detonation although it is hard to hear over the roar of the engine, it does seem to keep accelerating without tailing off, maybe I am just not pushing it hard enough for this. I will send a picture of the engine bay when I get home this evening.

Paul, There is still a definate lag in the turbo but seems to build up before the standard 3-3500 that most people seem to record??? I haven't experienced a fuel cut out, so maybe I am just being overcautious. I like the sound of the Silverstone day, can you let me know the details. Cheers for the info on removing the DME, I will give it a go this weekend.

 

[Diver944]

Just add your names into this thread and I'll book you in:

http://www.porscheclubgbforum.com/tm.asp?m=98772

I think we are at 31 cars now [] I'd better do a recount

 

[Fen]

ORIGINAL: Bigglesdan
it does have a bailey dump valve, the kind that goes whoosh which I would like to replace, would this stop the wastegate opening and cause it to overboost

Ahh, it has been messed with then. Those dump valves are generally not a great idea unless you are running MAP in place of the standard air flow meter so it's worth getting rid of for that reason alone, even if you like the car sounding like a bus (which I don't think you do).

The overboost protection is all to do with the KLR chip as stated above. If that has been modified then I retract my original statement; I didn't realise at the time that there was any likelihood the car was modified. If it hasn't been modified then the dump valve alone will not prevent it from working.

 

[Guest]

You are right I do want to remove the dump valve if only to stop it sounding like a chavmobile. Is this an easy job??? I will post a photo of the engine bay this evening. I think this is the only mod, can't see any additions like a boost enhancer etc apart from the suspected chipping

 

[944turboS]

Hi Dan,
I also am having problems with my Turbo, if you look at the other threads in this forum there is one about the dump valves & replacing the std Porsche one with a Saab unit. Replacment is easy just a couple of jubilee clips & the vacuum hose.

 

[Guest]

Cheers Graeme, I might get one of the silent ones from Promax. Am I right in thinking that they prolong the life of the turbo as they let it continue to spin???? Or do they cause more problems than they are worth. Ideally I would like to get the car back to standard maybe with a boost enhancer to stop the lag. Any suggestions chaps???

 

[Diver944]

A dump valve (or recirculating valve as Porsche call it) is there to relieve excess pressure in the pipe after the turbocharger as you change gear and help keep the turbo spinning. As you lift the accelerator to change gear the throttle closes and you have in effect a closed pipe from the turbocharger to the throttle. The turbo is still spinning wildly and tries to pump lots of air into this pipe, at this point the dump valve opens and diverts excess air back into the intake after the air filter.

Without the dump valve, pressure would build and cause the turbo to slow down or stall. I'm not sure it would actually cause damage but it means you will then have more lag to overcome as the turbo has to spool up again once you get on the power. Do a search on here and you will find the standard Porsche one for around £35 and an identical Saab one for about £25 (they are both the same Bosch valve IIRC)

Personally I think you should replace the dump valve back to standard, get a boost enhancer which will reduce lag even more (Andrew has a S/H one advertised in Porsche Post), and double check what chip you have.

 

[Guest]

Cheers Paul, I will contact Andrew. Is there a link missing from your post says "Do a search here" with no link??

 

[944turboS]

The link you want is HERE

 

[Guest]

Cheers graeme, just booked in with Andrew to get a few jobs done, the DV is one of them

 

[Guest]

Remind us (that haven't been here that long!), what's the problem?

Are you hitting the boost limiter in the chip so it stumbles and stutters when your foot is on the floor?

What's the gauge say?

 

[Diver944]

Have you fitted the Accuboost back to front? I helped Turboboy with his and we couldn't turn it down below 21psi!!!!!

Turns out it was fitted back to front. Doh!

You're not getting overboost if the car carries on running. The overboost protection is like hitting a brick wall when it triggers

The only true way to check your dash gauge hasn't been replaced incorrectly is with an aftermarket gauge, or take it to a Rolling Road that can plot boost. Now you mention the white dials I suppose the previous owner 'could' have knocked the needle off so it's no longer pointing in the right place?

 

[Guest]

Hi Chaps,

Mike, (just to recap) my gauge hits the stop, ie passed 2 bar, but I don't get the boost limiter kicking in, I must admit I usually ease off when this happens and maybe I would get cut off if I kept my foot down hard.

I followed the instructions that came with the accuboost from Andrew and am pretty sure it is on the right way round. (I will post a pic) It is not in the usual place as it directly replaced the brass valve that was previsouly on there (on the downpipe to the waste gate, next to the oil filler.) Andrew tells me that this should be fine?

I don't get the fuel cut out (hitting the wall feeling) but was told that this might be to do with the original chips being replaced.

I was hoping to sort this problem out for myself, 1 - to learn more about my car and 2 - to save a few pennies, but I think it is time for the experts to take over.

Thanks for your help

 

[hartge bob]

ORIGINAL: Bigglesdan

How easy is it to fit an external boost gauge??

Well I managed it so it must be incredibly easy as I am usually a liability when I have a spanner in my hand (not that you need a spanner to fit a boost gauge) []

I followed the instructions here;

http://www.davidsims.ukgateway.net/944t/boostgauge.htm