What should the boost gauge show?
10-10-2016, 04:27 AM
#1
What should the boost gauge show?
I suspect I have a boost leak on my 2008 957 Turbo and am curious to hear what I should be seeing on the boost gauge and when
So if I drop the speed/RPM and select a low ish gear (so 2nd or 3rd) then accelerate hard the gauge climbs steadily to almost 0.8 but not quite, it lingers just shy for a second then hits the full 0.8 but only stays there for a second before tapering off to 0.6/0.5 again. This happens in any gear but its more pronounced in the lower gears plus doing this in the upper gears is a good way to lose your license cos the numbers are getting up there by the time it runs right through the cycle
Is this normal? Should the boost be all over the place like this? I figured it would consistently build to 0.8 and then stay there for as long as I`m accelerating - is this not the case?
Also the car feels lumpy while accelerating hard and the flat spots/spikes coincide with the boost gauge dropping/rising
If something isn't right here is there anything else I should be looking out for apart from leaks (sensors) etc?
I have Durametric and am picking up a compact tablet/laptop tomorrow to use while on the move to see live data - is there anything specifically I should check with this?
So if I drop the speed/RPM and select a low ish gear (so 2nd or 3rd) then accelerate hard the gauge climbs steadily to almost 0.8 but not quite, it lingers just shy for a second then hits the full 0.8 but only stays there for a second before tapering off to 0.6/0.5 again. This happens in any gear but its more pronounced in the lower gears plus doing this in the upper gears is a good way to lose your license cos the numbers are getting up there by the time it runs right through the cycle
Is this normal? Should the boost be all over the place like this? I figured it would consistently build to 0.8 and then stay there for as long as I`m accelerating - is this not the case?
Also the car feels lumpy while accelerating hard and the flat spots/spikes coincide with the boost gauge dropping/rising
If something isn't right here is there anything else I should be looking out for apart from leaks (sensors) etc?
I have Durametric and am picking up a compact tablet/laptop tomorrow to use while on the move to see live data - is there anything specifically I should check with this?
10-11-2016, 09:18 AM
#4
Race Director
Not sure if the 957 is different or if my Cayenne is stock, but my gauge pegs at .8 and starts to drop to .6 after 5K rpm which it holds to nearly 7K rpms
10-11-2016, 05:03 PM
#5
10-11-2016, 05:04 PM
#6
10-11-2016, 05:32 PM
#7
Race Director
probably around 3600 rpm in every gear but first. I do feel its a bit laggier than it should be. I was expecting full boost no later than 3K rpms - Porsche advertised full boost by 2500 rpm IRRC.
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10-19-2016, 09:35 PM
#8
Race Car
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Can't speak for 957s, but on 955s that's totally normal. I think about 3600 or 4k rpm or whatever the boost tapers off to 0.6.
If you want to really peg some boost, hook up a trailer and do some 3rd gear pulls. You can keep the gauge pegged between 2k-3.5k rpms with all that load on the car. Exhaust sounds like a jet from all the extra boost pressure getting dumped into it.
If you're having lumpy acceleration, try cleaning the MAFs and inspecting all the vacuum lines, especially the ones around the fuel rail. Also inspect the y-pipe thing that goes onto the throttle body, the seals on the throttle body, and the seals on the outlet side of the intercoolers.
Also apparently the MAF bodies themselves can develop leaks, but can be sealed back up with RTV.
If you want to really peg some boost, hook up a trailer and do some 3rd gear pulls. You can keep the gauge pegged between 2k-3.5k rpms with all that load on the car. Exhaust sounds like a jet from all the extra boost pressure getting dumped into it.
If you're having lumpy acceleration, try cleaning the MAFs and inspecting all the vacuum lines, especially the ones around the fuel rail. Also inspect the y-pipe thing that goes onto the throttle body, the seals on the throttle body, and the seals on the outlet side of the intercoolers.
Also apparently the MAF bodies themselves can develop leaks, but can be sealed back up with RTV.
10-22-2016, 01:21 AM
#9
Can't speak for 957s, but on 955s that's totally normal. I think about 3600 or 4k rpm or whatever the boost tapers off to 0.6.
If you want to really peg some boost, hook up a trailer and do some 3rd gear pulls. You can keep the gauge pegged between 2k-3.5k rpms with all that load on the car. Exhaust sounds like a jet from all the extra boost pressure getting dumped into it.
If you're having lumpy acceleration, try cleaning the MAFs and inspecting all the vacuum lines, especially the ones around the fuel rail. Also inspect the y-pipe thing that goes onto the throttle body, the seals on the throttle body, and the seals on the outlet side of the intercoolers.
Also apparently the MAF bodies themselves can develop leaks, but can be sealed back up with RTV.
If you want to really peg some boost, hook up a trailer and do some 3rd gear pulls. You can keep the gauge pegged between 2k-3.5k rpms with all that load on the car. Exhaust sounds like a jet from all the extra boost pressure getting dumped into it.
If you're having lumpy acceleration, try cleaning the MAFs and inspecting all the vacuum lines, especially the ones around the fuel rail. Also inspect the y-pipe thing that goes onto the throttle body, the seals on the throttle body, and the seals on the outlet side of the intercoolers.
Also apparently the MAF bodies themselves can develop leaks, but can be sealed back up with RTV.
Anyone know how to see boost levels on the fly with Durametric? That would prove or disprove my theory
10-22-2016, 01:24 AM
#10
Can't speak for 957s, but on 955s that's totally normal. I think about 3600 or 4k rpm or whatever the boost tapers off to 0.6.
If you want to really peg some boost, hook up a trailer and do some 3rd gear pulls. You can keep the gauge pegged between 2k-3.5k rpms with all that load on the car. Exhaust sounds like a jet from all the extra boost pressure getting dumped into it.
If you're having lumpy acceleration, try cleaning the MAFs and inspecting all the vacuum lines, especially the ones around the fuel rail. Also inspect the y-pipe thing that goes onto the throttle body, the seals on the throttle body, and the seals on the outlet side of the intercoolers.
Also apparently the MAF bodies themselves can develop leaks, but can be sealed back up with RTV.
If you want to really peg some boost, hook up a trailer and do some 3rd gear pulls. You can keep the gauge pegged between 2k-3.5k rpms with all that load on the car. Exhaust sounds like a jet from all the extra boost pressure getting dumped into it.
If you're having lumpy acceleration, try cleaning the MAFs and inspecting all the vacuum lines, especially the ones around the fuel rail. Also inspect the y-pipe thing that goes onto the throttle body, the seals on the throttle body, and the seals on the outlet side of the intercoolers.
Also apparently the MAF bodies themselves can develop leaks, but can be sealed back up with RTV.
So roughly 1000RPM of full boost (0.8)?
10-22-2016, 10:44 AM
#12
Because of tolerance differences even new engines wont all behave exactly the same. There are so many variables that affect boost, what you are seeing on the gauge, etc. Engines that have free'r flowing intakes,exhaust, internals, or engines with different states of the internals will be able to develop equal power at varying boost pressures. The me7 ecu is really expansive with so many tables and hard to understand. wiki has some really good info on how it works. With it being a torque request sytsem I don't think it is aiming to make a specific amount of boost, just to hit the desired torque request @ whatever boost level that works out to with a limiting cap. Its going to be really hard to take different Cayennes and expect them all to behave the same. I think a better indication of the overall health or state of tune would be to vbox or the like and develop a general performance baseline for the specific model Cayenne to gauge against.
10-23-2016, 12:22 AM
#13