Comments on: Engine Performance Parts for the Mazda Millennia http://horsepowercalculators.net/tuner_report/engine-performance-parts-for-the-mazda-millennia Reach your power goals Thu, 17 Nov 2011 11:37:49 +0000 hourly 1 http://wordpress.org/?v=3.3.1 By: D. Juarez http://horsepowercalculators.net/tuner_report/engine-performance-parts-for-the-mazda-millennia/comment-page-1#comment-105 D. Juarez Tue, 11 May 2010 21:56:42 +0000 http://www.superchargerperformance.com/?p=188#comment-105 The comment that there is a power loss from exhaust backpressure during overlap is clearly wrong. The engine isn't making any power from the overlap portion of the stroke. The power loss is from pumping the exhaust gas out and the gains (during non-combustion portions of the cycle) are from pressurized intake stroke. The overlap period and exhaust backpressure are related, too little exhaust backpressure will result in charge loss into the exhaust, which results in more volume of air pumped with no increase in power, thus the resultant is a loss. If you have a lower backpressure exhaust a slight reduction in overlap timing would correspond. But it isn't something we change often. The real reason low exhaust backpressure robs power from the supercharger is that while the supercharger pushes one piston down on intake stroke another piston has to force gasses out against the backpressure. So the backpressure robs the power through the crank, not overlap. And all of this discussion is assuming constant pressures and steady flow, which are clearly not the operating conditions. While this explination is simplified yet correct the overlap is more about flow than about pressure differential in this engine. Supercharged cars are not signifigantly different than N/A cars in relation to exhaust modifications, whereas turbocharged cars are signifigantly different reguarding pressure differential and overlap. Supercharged cars do have a high specific output and do require high flowing exhaust components near the engine, but once you are downstream of the primary collector the supercharged car is much like the N/A car. Larger exhaust piping will result in lower flows at low speeds and higher flows at high speeds. You will not gain low end from oversizing your exhaust as you would in a turbocharged application. Also, there have been aftermarket headers, pre-cats, collectors, and main cat components for over a decade, though they are not a signifigant improvement due to space constraints and design restrictions. The O2s are finicky. One more thing. The reflection wave comes from the tailpipe exit, but its not just a high pressure wave or low pressure wave, it's entirely length, pressure, and RPM dependant resonation. Very well researched and has nothing to do with smooth transitions. The pipes could both dump into a box at horrible angles and they would still have pressure wave resonance. Look into helmholz manifold design, and realize that it is much less effective on exhaust. Smooth transition and equal length transitions are more about flow and velocity. You want to maintain velocity by having smooth transitions, and you want to balance size of pipe versus volume of gas so that the pulses dont compete with eachother at the junction. Boost won't drop from 14 to 10 and increase power without head porting (and adding aftermarket bypass control valve, obviously over the heads here). 50 HP from intercooling improvements isn't far fetched, but exhaust will never get you farther than 10 HP, and it won't be broad banded, same with the increased throttle size. Both will cause low end loss and driveability issues. The car is well designed and I make almost the same amount of power increase with CO2 injection on my intercoolers. And my mod doesn't cost me gas mileage or rob my low end. This write up is full of technical inaccuracies, but I'd like to see it developed properly. The comment that there is a power loss from exhaust backpressure during overlap is clearly wrong. The engine isn’t making any power from the overlap portion of the stroke. The power loss is from pumping the exhaust gas out and the gains (during non-combustion portions of the cycle) are from pressurized intake stroke. The overlap period and exhaust backpressure are related, too little exhaust backpressure will result in charge loss into the exhaust, which results in more volume of air pumped with no increase in power, thus the resultant is a loss. If you have a lower backpressure exhaust a slight reduction in overlap timing would correspond. But it isn’t something we change often.

The real reason low exhaust backpressure robs power from the supercharger is that while the supercharger pushes one piston down on intake stroke another piston has to force gasses out against the backpressure. So the backpressure robs the power through the crank, not overlap. And all of this discussion is assuming constant pressures and steady flow, which are clearly not the operating conditions. While this explination is simplified yet correct the overlap is more about flow than about pressure differential in this engine.

Supercharged cars are not signifigantly different than N/A cars in relation to exhaust modifications, whereas turbocharged cars are signifigantly different reguarding pressure differential and overlap. Supercharged cars do have a high specific output and do require high flowing exhaust components near the engine, but once you are downstream of the primary collector the supercharged car is much like the N/A car. Larger exhaust piping will result in lower flows at low speeds and higher flows at high speeds. You will not gain low end from oversizing your exhaust as you would in a turbocharged application.

Also, there have been aftermarket headers, pre-cats, collectors, and main cat components for over a decade, though they are not a signifigant improvement due to space constraints and design restrictions. The O2s are finicky.

One more thing. The reflection wave comes from the tailpipe exit, but its not just a high pressure wave or low pressure wave, it’s entirely length, pressure, and RPM dependant resonation. Very well researched and has nothing to do with smooth transitions. The pipes could both dump into a box at horrible angles and they would still have pressure wave resonance. Look into helmholz manifold design, and realize that it is much less effective on exhaust. Smooth transition and equal length transitions are more about flow and velocity. You want to maintain velocity by having smooth transitions, and you want to balance size of pipe versus volume of gas so that the pulses dont compete with eachother at the junction.

Boost won’t drop from 14 to 10 and increase power without head porting (and adding aftermarket bypass control valve, obviously over the heads here). 50 HP from intercooling improvements isn’t far fetched, but exhaust will never get you farther than 10 HP, and it won’t be broad banded, same with the increased throttle size. Both will cause low end loss and driveability issues. The car is well designed and I make almost the same amount of power increase with CO2 injection on my intercoolers. And my mod doesn’t cost me gas mileage or rob my low end.

This write up is full of technical inaccuracies, but I’d like to see it developed properly.

]]>