FS: Devek level 2 headers with Jet Hot coating
01-31-2020, 07:21 PM
#61
Nordschleife Master
To say something intelligent about a specific engine, one would need to know the peak power hp, peak power up rpm, ballpark volumetric efficiency, camshaft specifications most importantly the overlap, and either compression ratio or EGT.
For tuned “racy” systems that have high VE, high compression ratio, and a lot of camshaft overlap, keeping the exhaust port small in diameter and continuing that size pipe until say 12 inches from the exhaust valve and then going bigger helps not only mid range torque but peak power. If the system is production style emissions controlled and fuel consumption optimized engine with oversized intake and exhaust ports, relatively low VE, minimal camshaft overlap, and low compression ratio, then going “too big” doesn’t hurt the peak power because the header is doing approximately nothing other than separating cylinders. Might even reduce pumping losses a little bit.
So the question really is which kind of engine are we talking about?
For tuned “racy” systems that have high VE, high compression ratio, and a lot of camshaft overlap, keeping the exhaust port small in diameter and continuing that size pipe until say 12 inches from the exhaust valve and then going bigger helps not only mid range torque but peak power. If the system is production style emissions controlled and fuel consumption optimized engine with oversized intake and exhaust ports, relatively low VE, minimal camshaft overlap, and low compression ratio, then going “too big” doesn’t hurt the peak power because the header is doing approximately nothing other than separating cylinders. Might even reduce pumping losses a little bit.
So the question really is which kind of engine are we talking about?
01-31-2020, 07:31 PM
#62
Former Sponsor
To say something intelligent about a specific engine, one would need to know the peak power hp, peak power up rpm, ballpark volumetric efficiency, camshaft specifications most importantly the overlap, and either compression ratio or EGT.
For tuned “racy” systems that have high VE, high compression ratio, and a lot of camshaft overlap, keeping the exhaust port small in diameter and continuing that size pipe until say 12 inches from the exhaust valve and then going bigger helps not only mid range torque but peak power. If the system is production style emissions controlled and fuel consumption optimized engine with oversized intake and exhaust ports, relatively low VE, minimal camshaft overlap, and low compression ratio, then going “too big” doesn’t hurt the peak power because the header is doing approximately nothing other than separating cylinders. Might even reduce pumping losses a little bit.
So the question really is which kind of engine are we talking about?
For tuned “racy” systems that have high VE, high compression ratio, and a lot of camshaft overlap, keeping the exhaust port small in diameter and continuing that size pipe until say 12 inches from the exhaust valve and then going bigger helps not only mid range torque but peak power. If the system is production style emissions controlled and fuel consumption optimized engine with oversized intake and exhaust ports, relatively low VE, minimal camshaft overlap, and low compression ratio, then going “too big” doesn’t hurt the peak power because the header is doing approximately nothing other than separating cylinders. Might even reduce pumping losses a little bit.
So the question really is which kind of engine are we talking about?