Over boost in cold weather, Why ?
10-07-2019, 04:38 PM
#1
Rennlist Member
Thread Starter
Over boost in cold weather, Why ?
Hey Turbo friends
I own a (2 964 C2 Turbo (965), Completely stock, with fabspeed cat deletes. And GReedy manual boost controller. I have it set 0.95 bar boost. I also replaced the over boost sensor with a Porsche part,
As we all know, We all enjoy the extra power when it's cold out but I noticed when the weather changes and the temperature drops the boost goes over 0,95 bar and the over sensor cuts out the power. It only happens when it gets cold out. The sensor should cut off around 1,1 to 1.2 Bar. I don't have a manual boost gauge in my car just the stock one and it only goes 0.7 bar.
It's an easy fix for me, I just dial my manual boost controller down a touch about 0.9 bar and all good. Then when it warms up I just dial it back up.
The question, Why the produce more boost when it's cold out even though it's set, set at 0.95 bar. ?
Thank you for your insight
Helio
I own a (2 964 C2 Turbo (965), Completely stock, with fabspeed cat deletes. And GReedy manual boost controller. I have it set 0.95 bar boost. I also replaced the over boost sensor with a Porsche part,
As we all know, We all enjoy the extra power when it's cold out but I noticed when the weather changes and the temperature drops the boost goes over 0,95 bar and the over sensor cuts out the power. It only happens when it gets cold out. The sensor should cut off around 1,1 to 1.2 Bar. I don't have a manual boost gauge in my car just the stock one and it only goes 0.7 bar.
It's an easy fix for me, I just dial my manual boost controller down a touch about 0.9 bar and all good. Then when it warms up I just dial it back up.
The question, Why the produce more boost when it's cold out even though it's set, set at 0.95 bar. ?
Thank you for your insight
Helio
10-07-2019, 11:09 PM
#2
Rennlist Member
Hey Turbo friends
I own a (2 964 C2 Turbo (965), Completely stock, with fabspeed cat deletes. And GReedy manual boost controller. I have it set 0.95 bar boost. I also replaced the over boost sensor with a Porsche part,
As we all know, We all enjoy the extra power when it's cold out but I noticed when the weather changes and the temperature drops the boost goes over 0,95 bar and the over sensor cuts out the power. It only happens when it gets cold out. The sensor should cut off around 1,1 to 1.2 Bar. I don't have a manual boost gauge in my car just the stock one and it only goes 0.7 bar.
It's an easy fix for me, I just dial my manual boost controller down a touch about 0.9 bar and all good. Then when it warms up I just dial it back up.
The question, Why the produce more boost when it's cold out even though it's set, set at 0.95 bar. ?
Thank you for your insight
Helio
I own a (2 964 C2 Turbo (965), Completely stock, with fabspeed cat deletes. And GReedy manual boost controller. I have it set 0.95 bar boost. I also replaced the over boost sensor with a Porsche part,
As we all know, We all enjoy the extra power when it's cold out but I noticed when the weather changes and the temperature drops the boost goes over 0,95 bar and the over sensor cuts out the power. It only happens when it gets cold out. The sensor should cut off around 1,1 to 1.2 Bar. I don't have a manual boost gauge in my car just the stock one and it only goes 0.7 bar.
It's an easy fix for me, I just dial my manual boost controller down a touch about 0.9 bar and all good. Then when it warms up I just dial it back up.
The question, Why the produce more boost when it's cold out even though it's set, set at 0.95 bar. ?
Thank you for your insight
Helio
10-09-2019, 12:44 AM
#3
Rennlist Member
Thread Starter
Quote:
Originally Posted by RarlyL8
There's likely nothing wrong with your boost system it's just that because you are close to the edge you see the change. Boost level drops in the summer (hot/humid) and increases in the winter (cold/dry). Cooler engine bays and larger intercoolers can temper the change, lack of intercooler or hot packed engine bays exaggerate the issue. You'll also notice that your turbo spools up faster in the winter and is more laggy in the summer. It's all about air density and pressure.
That's what I was thinking. I was hoping to have technical information on air density and pressure and how it works cold vs hot. How much variation on a completely stock 930 boost, for example on a hot day you may see 0.8 bar and on a very cold day you may see 0.89 bar is that normal to have that big of swing depending on air temps ?
Originally Posted by RarlyL8
There's likely nothing wrong with your boost system it's just that because you are close to the edge you see the change. Boost level drops in the summer (hot/humid) and increases in the winter (cold/dry). Cooler engine bays and larger intercoolers can temper the change, lack of intercooler or hot packed engine bays exaggerate the issue. You'll also notice that your turbo spools up faster in the winter and is more laggy in the summer. It's all about air density and pressure.
10-09-2019, 12:46 AM
#4
Rennlist Member
Thread Starter
Quote:
Originally Posted by Alan L
But Brian, why does it overboost? Surely the boost control system is designed to cope with these variations? It should be consistent. The turbo performance may vary with variable conditions, but the ultimate result should still be the same? Unless you are maxed out on the turbo.
Regards
Alan
Hey AlanOriginally Posted by Alan L
But Brian, why does it overboost? Surely the boost control system is designed to cope with these variations? It should be consistent. The turbo performance may vary with variable conditions, but the ultimate result should still be the same? Unless you are maxed out on the turbo.
Regards
Alan
I have noticed when I had my manual boost gauge hooked up for testing the boost controller, it wasn't consistent from one day to another. But that may be because of air density and pressure as Brian said, It may have varied from one day to another while testing.
For example, I had the controller dialed to 0.094ish bar tested on a cool morning, all good I thought but on a hot day I would see 0.74 to 0.79ish bar and the next day on a cool morning when the engine bay was cool, I would see 0.89 to 0.94ish it's not really consistent. Does that make sense?
I know the 965 has an intercooler temperature sensor that gives input to the EZ69 ignition unit and adjusts the timing. Not sure how that would affect the boost.
Helio
__________________
10-09-2019, 12:47 AM
#5
Rennlist Member
Thread Starter
Quote:
Originally Posted by Alan L
I can understand lack of boost on a marginal system struggling to supply enough air to the engines requirements on a hot day. But your query was about o/boost on a cold day. Air density and boost gauge should not play in to it in as much as this should be controlled externally. And the gauge should be measuring whatever whenever - irrespective. So I still don't think we have the answer to the o/boost Q.
Regards
Alan
LoLOriginally Posted by Alan L
I can understand lack of boost on a marginal system struggling to supply enough air to the engines requirements on a hot day. But your query was about o/boost on a cold day. Air density and boost gauge should not play in to it in as much as this should be controlled externally. And the gauge should be measuring whatever whenever - irrespective. So I still don't think we have the answer to the o/boost Q.
Regards
Alan
I get it , and I was thinking the same thing, I don't what to think because Brian's quote also makes sense to me. I know the workshop manual says the boost test should be 0.75 to 0.81, there's got to be a reason why it varies. I'm not an engineer. I hope Chris from TurboKraft would chime in he would be able to shed some light on this.
Helio
10-09-2019, 12:49 AM
#6
Rennlist Member
Thread Starter
Quote from RarlyL8
There is no automatic compensation of the boost pressure system. The 964T is the most complicated 930 engine and it does not do this. The EZ69 pulls timing when air temps get too hot which while helping to protect the engine from detonation exacerbates the boost situation (advanced timing quicker boost response). At stock boost level there is enough headroom that over boost on a cold day will not happen on a stock engine. Change the exhaust and/or the boost level and things become exaggerated. You are on the higher edge with a more free-flowing and arguably cooler running exhaust system which exposes this phenomenon. Having an adjustable boost controller changes the baseline making it a bit harder to clearly see what is going on.
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RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds
There is no automatic compensation of the boost pressure system. The 964T is the most complicated 930 engine and it does not do this. The EZ69 pulls timing when air temps get too hot which while helping to protect the engine from detonation exacerbates the boost situation (advanced timing quicker boost response). At stock boost level there is enough headroom that over boost on a cold day will not happen on a stock engine. Change the exhaust and/or the boost level and things become exaggerated. You are on the higher edge with a more free-flowing and arguably cooler running exhaust system which exposes this phenomenon. Having an adjustable boost controller changes the baseline making it a bit harder to clearly see what is going on.
__________________
RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds