MSD distrubitor cap part number for 99-00 Si = Part # 8292
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How to select a compressor size to your application.
first you need to know how much air it will need to flow to reach your target horsepower. to figure that, you would use the following formula:
(CID x RPM) / 3456 = CFM
here's an example of a B16:
(97Ci x 8000) / 3456 = 225CFM
of course, if your engine is bored or stroked, you will have to compensate the CID.
the engine will flow 225CFM at 100% volumetric effeciency (VE). great, in a perfect world. actually VE is about 80-90%. so you'll need to adjust to the VE. 85% is a good number to work with. so addjust your CFM to 191CFM
next up is the pressure ratio. the pressure ratio is basically the pressure of the air going into the turbo in comparison to the pressure coming out. unless you are running sequential turbos, the inlet pressure will be the atmospheric pressure, which is an average of 14.7. so if you want 12psi, here's the formula:
(12 + 14.7) / 14.7 = 1.82:1
now you need the temperature rise. as the compressor compresses the air, it will raise the temperature. there is a formula to figure that rise! there is an ideal temperature rise to where the rise is equivelant to the amount of work it takes to compress the air. here's the formula!
T2 = T1 (P2 ÷ P1)0.283
confused yet? of course not! but lets break it down with some back spins and stuff.
T2 = Outlet Temperature in °R
T1 = Inlet Temperature in °R
°R = °F + 460
P1 = Inlet Pressure Absolute
P2 = Outlet Pressure Absolute
easier now huh?
assuming it's 80º outside and we're shooting for 12psi, your inlet temperature (T1) = 80º + 460 = 540ºR
the P1 inlet pressure will be atmospheric in our case and the P2 outlet pressure will be 12psi. atmospheric pressure is about 14.7 psi (as mentioned earlier), so the inlet pressure will be 14.7 psi, to figure the outlet pressure add the boost pressure to the inlet pressure.
P2 = 14.7 + 12 = 26.7 psi
we now have everything we need to figure out the ideal outlet temperature. now take this info into our original formula ( T2 = T1 (P2 ÷ P1)0.283 ) to figure out T2:
T2 = 540ºR(26.7 ÷ 14.7)0.283 = 676ºR
676ºR = 216ºF = ideal oulet temperature. that's a 136º temperature rise.
once again, in a perfect world, these formulas work grear. unfortunately, there's our old friend adiabetic effeciency (AE). a 136ºF temperature rise is at 100% AE. AE of the compressor is usually 65-75%. so you would use 70% for average. so to figure out the actual temperature rise from the ideal temperature rise, you can use this:
Ideal Outlet Temperature Rise ÷ AE = Actual Outlet Temperature Rise
so, 136º ÷ .7 = 194º
then you add the actual temperature rise to the intake temperature (80º) = 274º
now you can figure out your density ratio! as the air is heated, it expands and increases the volume and flow. to compare the inlet and outlet flow, you must know the density ratio. the formula for that is:
(Inlet °R ÷ Outlet °R) × (Outlet Pressure ÷ Inlet Pressure) = Density Ratio
ok, so our example formula would be:
(540ºR ÷ 676ºR) × (26.7 ÷ 14.7) = 1.46 Density Ratio
with all this crap, you can figure out what the actual inlet flow is in CFM. to do this, use this:
Outlet CFM × Density Ratio = Actual Inlet CFM
so!
225CFM × 1.46 = 328.5CFM
that's a 31% increase in CFM, which is a potential for 31% increase in power. ei, 160hp = 209.6hp. of course, that number is directly effected by intercooler, downpipe, exhaust, fuel flow, etc.
so now you know you need about 328.5CFM to reach your target of 12psi, you now can find compressor maps for different turbos to select the compressor that would best suit your needs. some maps are in CFM, and some maps are in lbs/min. to convert CFM to lbs/min, you would multiply CFM x .069.
when looking at a compressor map, you match the corrected air flow (22.7lbs/min in our case) to the pressure ratio (1.82:1 in our case). what you are looking to do is plot your graph where it would be most efficient for the turbo. anywhere below 60%, your turbo will spin entirely too fast of a shaft speed rpm and burn itself up.
here is an example of a compressor map (garrett T03 60 trim):
when you plot our numbers, they end up in the 75% range, that is good. the turbo will be a perfect match for what we want to do.
voila! you now can boggle your dates with your infinite mathmetician knowledge...
