everyones boost numbers
#27
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Join Date: 03-15-05
Location: tennessee - bartlett
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Was 12.5/13 before stage 2
Installed stage 2 today and now it hits 17 psi every time
And very LOUD!!
Jeff
2005 SS/SC
gm stage 2
k & N typhoon
1 of only 2 ss in memphis area
Installed stage 2 today and now it hits 17 psi every time
And very LOUD!!
Jeff
2005 SS/SC
gm stage 2
k & N typhoon
1 of only 2 ss in memphis area
#38
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Join Date: 04-03-06
Location: Mesa, AZ
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Originally Posted by Waylin22
I think 06black would take the win on most boost on the entire forum....over 20lbs of boost.
#44
I don't know anyone
Originally Posted by 06blackg85ss
20 with my mods.... hopefully @22 tomorrow after some blower work...
I have seen many folks reference 12.5 # boost with the stock 85 MM 3.346" pulley. This is incorrect. According to the Cobalt SS S/C factory shop manual, under engine controls, 2.0L, 6-1395, "Max engine boost is 83 kpa/12 psi."
I stumbled on this chart on another forum and thought I'd share it for anyone interested. I did the math with my car-2006 SS S/C-Stage II, K&N factory filter in opened up filter box-Borla cat-back, extrude honed exhaust manifold-2.8" pulley, and the reference numbers for loss at altitude are very close to what I calculated using the complicated (for me at least) formula given, for each altitude with my car. Remember I am not a mathametician. The numbers to the far right are subtracted from the boost you should have. For example, I should have about 17 psi with my mods at sea level, but at my altitude of 4000' my boost gauge shows 15 psi (-2 on the graph for 4000').
Altitude/ Air press(in. Hg)/ Air press(psi)/ Loss as referenced to sea level (psi)
Sea level/ 29.92/ 14.7/ 0
1000 ft/ 28.86/ 14.18/ -0.52 psi
2000 ft/ 27.82/ 13.67/ -1.03 psi
3000 ft/ 26.81/ 13.17/ -1.53 psi
4000 ft/ 25.84/ 12.7 / -2 psi
5000 ft/ 24.9 / 12.23/ -2.47 psi
6000 ft/ 23.98/ 11.78/ -2.92 psi
7000 ft/ 23.09/ 11.34/ -3.36 psi
8000 ft/ 22.23/ 10.92/ -3.78 psi
9000 ft/ 21.39/ 10.51/ -4.19 psi
10000 ft/ 20.58 / 10.11/ -4.59 psi
I had to do this piecemeal to fit this screen-hope it shows correctly. I can't get them to line up, use the dividers and read corresponding with dividers at the top.
This chart is "ideal" ie., it assumes 100% efficiency and doe not factor losses due to backpressure or heat. S/C boost is somewhat of a black science, with many variables to consider. However in my case, at 15 psi at least, it is right on, considering my mods and altitude. Everyone's situation is different, so just use the table as a ballpark guide, don't consider it to be 100% exact. Remember, noone so far has been able to tell me how to read the factory gauge in between the major numbers. Not even Autometer tech's can tell me how to read their gauge. I E-mailed Chevrolet and they said they would refer me to someone in engineering who could tell me how to read the gauge. Never heard back, so I guess they can't read it either. I have raced cars for many years, and I have never seen a gauge that is any harder to read than the factory (U.S. version) Autometer boost gauge in our S/C cars. It moves up very quickly, and it is hard to watch the road and check the gauge, trying not to run up on the rev limiter-trying to look at the tachometer at the same time. I have noticed that since I installed the Stage II, my boost does not start to drop back at 5600 to 6000 rpm. With the boost bypass mod, I don't know if that has any affect on the boost gauge's calibration/accuracy or not. But I would suggest being careful with that mod. The factory shop manual states that damage to the engine can occur if the boost bypass valve is stuck in the position to allow full boost, unchecked.
Maybe the factory Aurometer gauge isn't off that far after all.
Doc
Last edited by mrdoc442; 07-26-2006 at 06:50 PM.
#50
Senior Member
Originally Posted by shiftingloco310
i really dont understand either why some people with 2.8" are getting 15psi..i was getting that with my gm stg 2 3". I thought 17-18psi was accurate for a 2.8" pulley.