maybe someone could help me out.
why is it that when you calculate the cylinder pressure from the compression ratio, that you have to multiply the compression ratio to the power of 1.1?
example-
10:1 compression, standard pressure.
(10^1.1)x14.5=182.5 psi.
why does the compression ratio need to be multiplied to the power of 1.1?
compression pressure
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Q45tech
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- Car: 1990 Q45 342,400 miles 22 years ownership with original engine
1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl
Because the gauge reads zero at 14.7 psi [normal air pressure]14.7 x 10.2=149.94 + 14.7= 165.64 real pressure. You are forgeting the air volume from removing the sparkplug and the volume in the test hose and gauge.......this lowers the effective compression ratio. Why various correction factors. Also as the air compresses it raise the air temp and the pressure.
They just provided a number in FSM that works for their gauges in a brand new engine sample.........Accurate not really!
Cranking compression is not a real test of engine status other than cranking.
What you want is idle and cruising running pressure:
Measure the idle vacuum say 18" subtract it from 29.92=11.92 so the real filling air pressure is 11.92 x 10.2= 121 psi.http://www.misterfixit.com/dyncompr.htm ... af....html
They just provided a number in FSM that works for their gauges in a brand new engine sample.........Accurate not really!
Cranking compression is not a real test of engine status other than cranking.
What you want is idle and cruising running pressure:
Measure the idle vacuum say 18" subtract it from 29.92=11.92 so the real filling air pressure is 11.92 x 10.2= 121 psi.http://www.misterfixit.com/dyncompr.htm ... af....html
i was messing around trying to figure out the static compression ratio of the vh45 motor with 14 psi of boost.
165.64 is what i came up with for actual compression for the vh45, but the service manual states 185 psi standard.
the equations i found like to use 14.5 psia for atmo., but im at sea level, and i like to use 14.7
so, what your saying is that the equation above [ratio^1.1 x atmo.] is really just to compensate for adiabatic expansion from compression.
what i was getting at is theorectically [100% VE], a vh45 at 14 psi of boost, WOT, and an efficient intercooler, the static compression would be 28.7psia x 10.2 = 292.74 + 14.7 = 307.44 psig
since the motor doesnt run at 100% VE constantly, that would be close to the cylinder pressure at 4000 rpm.
did i figure that correctly?
also, what is the cam overlap with the VTC engaged and disengaged? is there an easy way to disable the VTC actuator?
165.64 is what i came up with for actual compression for the vh45, but the service manual states 185 psi standard.
the equations i found like to use 14.5 psia for atmo., but im at sea level, and i like to use 14.7
so, what your saying is that the equation above [ratio^1.1 x atmo.] is really just to compensate for adiabatic expansion from compression.
what i was getting at is theorectically [100% VE], a vh45 at 14 psi of boost, WOT, and an efficient intercooler, the static compression would be 28.7psia x 10.2 = 292.74 + 14.7 = 307.44 psig
since the motor doesnt run at 100% VE constantly, that would be close to the cylinder pressure at 4000 rpm.
did i figure that correctly?
also, what is the cam overlap with the VTC engaged and disengaged? is there an easy way to disable the VTC actuator?
DAEDALUS wrote:I've seen another formula for calculating the pressure. Either way, it's only a good estimate. There has to be an "upper" in the estimate to account for the fact that the air is heated by the rapid compression. Hotter air = higher pressure.
thats what i was thinking. the 1.1 was to account for adiabatic expansion/heat. no other reasonable explanation i could find.
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Q45tech
- Moderator
- Posts: 14296
- Joined: Tue Apr 30, 2002 3:19 am
- Car: 1990 Q45 342,400 miles 22 years ownership with original engine
1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl
370 cc/min [35 lbs/hr] at 43.4 psi BUT the coils are not designed to be reliable at over an 80% duty cycle over heat and melt insulation at continuous duty.35/0.5= 70 x 0.8= 55-56 HP per ibjector at 43.4 psi ~~ 440 HP gross without considering supercharger parasitic driving HP.
Just to be safe use a 0.55 BSFC instead of normal 0.50.........408 HP less 25 for supercharger] = ~~385 HP.
Static pressure means nothing what you must use is VE corrected compression ratio due to filling rate of cams valves.........running pressure.
Just to be safe use a 0.55 BSFC instead of normal 0.50.........408 HP less 25 for supercharger] = ~~385 HP.
Static pressure means nothing what you must use is VE corrected compression ratio due to filling rate of cams valves.........running pressure.
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Q45tech
- Moderator
- Posts: 14296
- Joined: Tue Apr 30, 2002 3:19 am
- Car: 1990 Q45 342,400 miles 22 years ownership with original engine
1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl
Measure the area of sparkplug tip and the internal volume of adapter, hose and compression gauge:4494/8=561.75/10.2=55cc head volume with spark plug with compression gauge attached maybe 62 cc............9.0 CR actually measured .
The FSM forgot to explain this.........that things might read 162 psi or less.
The FSM forgot to explain this.........that things might read 162 psi or less.
i dont like superchargers. motor would be turbo.
ive been pricing parts for the motor, just a basic rundown.high silicon forged pistons [.002 clearance] [ross, arias]4340 steel rods [pauter]550 cc inj.aeromotive FP, FPR [1 liter swirl tank]sheetmetal/aluminum intake, velocity stacksswaintech ceramic coating- pistons, heads. light portingmoly coat on piston skirts, bearing shells.ect ect. i also want to adapt the Z32 manual trans and flywheel.
just an example. i figure the ceramic coating on the heads and pistons would do a good job protecting the motor for short bursts of power. considering it would be a street car, the motor wouldnt be subjected to much stress regularly.
ive been pricing parts for the motor, just a basic rundown.high silicon forged pistons [.002 clearance] [ross, arias]4340 steel rods [pauter]550 cc inj.aeromotive FP, FPR [1 liter swirl tank]sheetmetal/aluminum intake, velocity stacksswaintech ceramic coating- pistons, heads. light portingmoly coat on piston skirts, bearing shells.ect ect. i also want to adapt the Z32 manual trans and flywheel.
just an example. i figure the ceramic coating on the heads and pistons would do a good job protecting the motor for short bursts of power. considering it would be a street car, the motor wouldnt be subjected to much stress regularly.