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.
Turbo overboosting
- Thread starter Fen
- Start date
Diver944
Active member
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|]
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
Active member
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]
]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]
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
New member
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.
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.
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
New member
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
Guest
New member
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
Active member
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.
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
New member
Hi Chaps,
I know you are all probably bored of my overboosting problem by now [] but please stick with me, I am trying to get it sorted.
I bought an accuboost from Andrew to replace the brass restricting valve that was attached to the wastegate pipe, I have also fitted a standard shut off valve in place of the non recirculating dump valve.
I have released the accuboost pretty much all the way out which has reduced the boost a lot, despite this I am still hitting the stop on the gauge when I put my foot down all the way.
I tried to check the chips (KLR and DME) but the mass of wires put me off ( alarm/immobilser box installed in footwell with yet more wires all cable tied together ) Could this problem be down to the chips alone???
I am beginning to think it might be the dials (the originals have been replaced with white dials) and the temp gauge is faulty as the fan cuts in when the needle is just above the first white line. How easy is it to fit an external boost gauge??
Cheers for your patience []
I know you are all probably bored of my overboosting problem by now [
] but please stick with me, I am trying to get it sorted. I bought an accuboost from Andrew to replace the brass restricting valve that was attached to the wastegate pipe, I have also fitted a standard shut off valve in place of the non recirculating dump valve.
I have released the accuboost pretty much all the way out which has reduced the boost a lot, despite this I am still hitting the stop on the gauge when I put my foot down all the way.
I tried to check the chips (KLR and DME) but the mass of wires put me off ( alarm/immobilser box installed in footwell with yet more wires all cable tied together ) Could this problem be down to the chips alone???
I am beginning to think it might be the dials (the originals have been replaced with white dials) and the temp gauge is faulty as the fan cuts in when the needle is just above the first white line. How easy is it to fit an external boost gauge??
Cheers for your patience [
]
Diver944
Active member
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?
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
New member
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
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
New member
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
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