![]() ![]() Intake and exhaust centerlines are a measure of CRANK degrees away from TDC when the cam is installed in the engine. It is mearly a measure between the two lobe CENTERS. This measure has NOTHING to do with how the cam is installed in an engine. Lobe seperation angle (LSA) is a measure of cam degrees between the exhaust and intake lobe centers. There are a tremendous amount of variables that contribute to detonation, not merely cylinder pressure. Certainly the greater the cylinder pressure that's built, the greater the chance for detonation, but there is NO defined cutoff on the max pressure for a given octane rating.ĭetonation is caused by additional flame front(s) created by spontanious combustion of the air/fuel, AFTER the plug fires, creating to much pressure to early in the combustion cycle. Basically the compression ratio is recalculated using the position of the piston when the intake valve closes, instead of using Bottom Dead Center as the piston position for the static compression ratio. The difference is taking into account the intake valve closing point. GoOrdnance, I like your name (retired 63B4H speaking here) !ĭynamic compression is a RATIO, similar to the static compression ratio you mentioned of 9.2:1. ECL= 112 degrees (from where? bottom dead center?), and LSA = 112 degrees (from between the intake and exhaust lobe centerlines?). Last question, regarding cam specifications: How are "Exhaust Centerline" and Lobe Separation Angle" defined, in terms of degrees from what basepoint? Example: ICL=110 degrees ATDC (I got this part). Car weight is 3900 pounds with driver and full tank, 2.93 gears, TH400 trans, 25.5 inch diameter tires.Īlso, does anyone know of a reference for the maximum dynamic compression feasible without detonation on 91 octane fuel? My reference guide gives a figure of 160-170 psi for 93 octane, but 91 octane is as high as it gets where I live. I am after smooth idle more so than top-end power. My planning factor is 5 additional pounds of dynamic compression for every 4 degrees advance of intake closing. My intent is to determine how much sooner (in degrees) I can have an intake valve closing event, and thus decide what camshaft will give me the highest compression without detonating (minus a safety factor). 030 over 400 with #64 heads - estimate 9.2:1 static CR, with cranking compression an average of 138 psi using my neighbor's gauge). Is it just a matter of using a cylender compression guage while the engine is running? I understand that dynamic compression is tied to the intake closing event, and thus my measured dynamic compression is only valid for the cam currently in the car ('041 grind in a. It will calculate the DCR based on the modified stroke length, which in turn is derived from the rod length and the IVC.Does anyone know of a reliable way to measure dynamic compression? I can measure cranking compression at 30 RPM, but this is probably lower than dynamic (about 2000 RPM) compression. You can open the dynamic compression ratio calculator in our calculator's advanced mode. You can discover more in Omni's Carnot efficiency calculator. This is why the dynamic compression ratio (DCR) is dependent on the intake valve closing (IVC) point, which is expressed as an angle after the bottom dead center (ABDC). We can only speak about compression once the valve is completely closed. At that time, though, the intake valve is not yet closed, so no compression occurs – the air is "pushed out" through the valve. The piston reaches its lowest position (bottom dead centre) and starts moving up again. When it moves up, the volume inside the cylinder is compressed when it moves down, fresh fuel and air enter the chamber through the intake valve. In a combustion engine, the piston moves up and down. Why? It doesn't take into account the closing of the intake valve. However, this number does not perfectly describe reality. Using the compression ratio formulas above, you will be able to compute the static compression ratio. You may calculate it by multiplying the displacement volume by the number of cylinders. Our compression ratio calculator estimates the value of the CR and the total engine volume. V c h a m b e r V_ = \frac 14 \cdot b^2 \cdot c \cdot \pi V clearance = 4 1 ⋅ b 2 ⋅ c ⋅ π, where c c c is the deck clearance. ![]()
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