Different boost pressures in hot weather
15 May 2001, 11:12 PM
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This could be a question for Nito or anyone else that knows. I have a MY00 UK Turbo Impreza, Mods include exhaust (mid and backbox)without centre 'meow' 
cat that is, cold air duct with K&N filter, fuel cut defender and Blitz DSBC. On 98 Ron SUL, standard ECU.
1. Is it safe to run 1.2 bar in Summer? we are talking days over 35 and 40 deg Celsius.
2. Why do I get a little over 1.2 bar on cold days and 1.15 bar and lower on warmer days without touching the boost controller? I am talking peak boost.
3. Would I be able to turn up the boost via the boost controller to 1.2bar on warmer days to compensate or would I be doing damage?
Your answers would be greatly appreciated, as I thought electronic boost controllers always gave the same amount of boost regardless of anything.
WREXY.
[This message has been edited by WREXY (edited 15 May 2001).]
[This message has been edited by WREXY (edited 15 May 2001).]
cat that is, cold air duct with K&N filter, fuel cut defender and Blitz DSBC. On 98 Ron SUL, standard ECU. 1. Is it safe to run 1.2 bar in Summer? we are talking days over 35 and 40 deg Celsius.
2. Why do I get a little over 1.2 bar on cold days and 1.15 bar and lower on warmer days without touching the boost controller? I am talking peak boost.
3. Would I be able to turn up the boost via the boost controller to 1.2bar on warmer days to compensate or would I be doing damage?
Your answers would be greatly appreciated, as I thought electronic boost controllers always gave the same amount of boost regardless of anything.
WREXY.
[This message has been edited by WREXY (edited 15 May 2001).]
[This message has been edited by WREXY (edited 15 May 2001).]
16 May 2001, 07:48 AM
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Because of charge temperature. There is a set volume of air that can flow through your turbine. On a cold day the air is for some reason cooler 
which means that your intercooler is removing heat from already cooler air. The cooler the intake charge the denser the air the more power you're gonna get.
On a warm day, your intercooler is working on removing heat from . . . well . . . warmer air and all things being equal, will not drop the charge temp down to that of the colder day.
You could compensate with the boost controller, but I don't know how safe this would be as I don't own one. A more efficient intercooler would assist.
which means that your intercooler is removing heat from already cooler air. The cooler the intake charge the denser the air the more power you're gonna get.On a warm day, your intercooler is working on removing heat from . . . well . . . warmer air and all things being equal, will not drop the charge temp down to that of the colder day.
You could compensate with the boost controller, but I don't know how safe this would be as I don't own one. A more efficient intercooler would assist.
16 May 2001, 10:27 AM
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I dont profess to be an expert but something sounded fishy here.
The evc and also the standard ecu controll the boost according to the info they get from the map sensor.
Should the temperature rise they will still see 1.2 only the density of air will be lower at higher temperatures.
this means that the turbo will be flowing less air but it will still be 1.2 bar.
If you were running the jecs, it is possible the ecu would compensate for the temperature ambient temperature and reduce the maximum boost to avoid det. But since this is not the case it must be another issue.
I think it is more likely the turbo is struggling, this is because it has to work harder to produce the same boost pressure when the air is thinner. This will have a compound effect of reducing the efficiency of the turbo, and hence it will be even hotter.
If I am correct, then asking the turbo to produce even more boost is not going to be a good idea. Regardless of det potential, the turbo life could be seriously affected.
If this is a big concern, then fit a vf series turbo or a modified TD05 like pat had done.
This will be far more efficient when running 1.2 and will flow a lot more air, meaning more power. At that point you can worry about in cylinder pressures.
The evc and also the standard ecu controll the boost according to the info they get from the map sensor.
Should the temperature rise they will still see 1.2 only the density of air will be lower at higher temperatures.
this means that the turbo will be flowing less air but it will still be 1.2 bar.
If you were running the jecs, it is possible the ecu would compensate for the temperature ambient temperature and reduce the maximum boost to avoid det. But since this is not the case it must be another issue.
I think it is more likely the turbo is struggling, this is because it has to work harder to produce the same boost pressure when the air is thinner. This will have a compound effect of reducing the efficiency of the turbo, and hence it will be even hotter.
If I am correct, then asking the turbo to produce even more boost is not going to be a good idea. Regardless of det potential, the turbo life could be seriously affected.
If this is a big concern, then fit a vf series turbo or a modified TD05 like pat had done.
This will be far more efficient when running 1.2 and will flow a lot more air, meaning more power. At that point you can worry about in cylinder pressures.
16 May 2001, 01:45 PM
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Hi,
The JECS ECU uses a mass airflow sensor to calculate the air density and adjust the fuelling to suit, so the ECU should adjust within limits.
Link uses a speed / density system to adjust fuelling according to MAP reading (and optionally a temp sensor) to adjust it's fuelling. This also works but apparently isn't quite as reactive to transient changes.
As the external temperature rises air density drops so your fuelling will be relatively richer which will help cool the charge a little (with a fixed map).
As Adam says, your turbo will be working harder to deliver the same level of boost, and consequently will heat up the charge even further so the density drops again, turbo works harder and so on.
A bigger more efficient turbo will help reduce intake temps quite a bit, and should be considered for the temp range you are running in.
Also your boost gauge shows boost relative to barometric pressure, so It may read higher or lower depending on weather conditions...
Cheers,
Alex
The JECS ECU uses a mass airflow sensor to calculate the air density and adjust the fuelling to suit, so the ECU should adjust within limits.
Link uses a speed / density system to adjust fuelling according to MAP reading (and optionally a temp sensor) to adjust it's fuelling. This also works but apparently isn't quite as reactive to transient changes.
As the external temperature rises air density drops so your fuelling will be relatively richer which will help cool the charge a little (with a fixed map).
As Adam says, your turbo will be working harder to deliver the same level of boost, and consequently will heat up the charge even further so the density drops again, turbo works harder and so on.
A bigger more efficient turbo will help reduce intake temps quite a bit, and should be considered for the temp range you are running in.
Also your boost gauge shows boost relative to barometric pressure, so It may read higher or lower depending on weather conditions...
Cheers,
Alex
16 May 2001, 02:59 PM
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Stick, Adam, Tizard99, and Alex,
I thank you for your comments. They all make sense to me. I will go for a bigger turbo later on and also a larger intercooler. In the meantime I have concluded that I need to and will lower my boost settings probably to around 1.1 BAR to 1.15 BAR just to be on the safe side for summer. I am also waiting for a Knocklink to arrive so I may be able to experiment with boost, only by a bit though, till I go to the UK for correct fuel and ignition mapping, as there are no 4wd RR's here.
Cheers,
Wrexy.
I thank you for your comments. They all make sense to me. I will go for a bigger turbo later on and also a larger intercooler. In the meantime I have concluded that I need to and will lower my boost settings probably to around 1.1 BAR to 1.15 BAR just to be on the safe side for summer. I am also waiting for a Knocklink to arrive so I may be able to experiment with boost, only by a bit though, till I go to the UK for correct fuel and ignition mapping, as there are no 4wd RR's here.
Cheers,
Wrexy.
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