: Is this OK (boost question)



longbow0404
08-01-11, 10:28 AM
First off all; Hi everybody, Im new to the posting but not new to the forum.

My question is that recently a have notice that the car is boosting a little shy of the last line on the gauge on first and second gear and on the rest of gears (3-4-5) it goes between the last line and 15psi

Im thinking that each line is 3PSI so that would be 1&2 gear just shy of 12 psi and 3, 4, and 5 maybe 13.5 to 14 psi.

Is this normal? Thank you guys in advance

Miami weather 90 F
Mods: 2.55 upper / air intake mod / cat backs / 160 thermostat / tune (W4M)

All pulls where done with the TC on (street pull) Could this be the reason?

cbloveday
08-01-11, 10:50 AM
I cannot comment on whether it is ok or not but I can say that my boost gauge appears to reflect 10 psi.

However, when I log it over several seconds, and then look at the chart (which is very high resolution), it spend the majority of the time around 9.5 and goes to a peak of 10.15. I guess I am saying the gauge may not have a high resolution and it could be ok.

Perhaps someone more knowledgable can comment.

longbow0404
08-01-11, 11:21 AM
thanks for the imput cbloveday, I was thinking that it could be a combination of Not a acurate gauge, Hot weather and the TC on.
since all of this will affect the boost reading.

thebigjimsho
08-01-11, 12:27 PM
I don't know if the TC or torque management would affect boost. But I don't like our tiny gauge...

KevinR70
08-01-11, 01:24 PM
Gauge in my car is off. I was reading about 11.5 with just a 2.55 upper (which actually seems like what you should be getting with 2.55). I had Jesse put on an 8.5 lower to go with 2.55 upper this past weekend and my gauge is maxing out over 15psi, but the dyno showed me at 13.5. I imagine you are around 11.5 or so with just the upper. I also had Jesse port the blower, snout, and tb and add a CAI, but I lost a couple of psi with the Kooks headers he put on. Bottom line, don't trust the gauge.

haterinc
08-01-11, 01:41 PM
factory boost gauges are always notoriously inactive

tedcmiller
08-01-11, 01:57 PM
According to the service manual, 12 psi is the most the stock supercharger can produce.

longbow0404
08-01-11, 02:33 PM
I think TC on its own will not reduce boost but will reduce throttle, and less throttle = less boost. Its more complex that this but we i think we get the point.

deckofficer
08-01-11, 04:17 PM
Just a thought, since our positive displacement blowers offer up boost just off of idle and everthing is controlled by a computer, and add traction issues in lower gears, I would think our Caddy design engineers would just have the computer limit boost in the lower gears. Look at what this buys, first and most important, the torque multiplacation of the lowers gears is not taxing all down stream drive components = less warranty issues. That is the reason why on turbocharged cars, the peak power feeding the same drivetrain can be set much higher than on the same drivetrain using a positive displacement blower. Don't tell me you never wondered how the aftermarket tweakers have no problems with parts longevity when they pull our blowers and set up for 1,200 hp worth of twin turbos. I am aware of all the forums I hang my hat on, this one leans the most towards "turn key performance" and aftermarket tuners, than doing your own wrenching and using the G-Tech to confirm results of said wrenching. Not meant to be a negative, as under the skin we are all hot rodders at heart and I truly enjoy this forum and the people here, but it isn't like my "roll your own" hot rod forums.