Comments on: Stairway to heaven http://www.ret-monitor.com/articles/705/stairway-to-heaven/ Specific mission-critical info for professionals Fri, 18 May 2012 10:52:48 +0000 http://wordpress.org/?v=2.7.1 hourly 1 By: FMG_V6_btb http://www.ret-monitor.com/articles/705/stairway-to-heaven/comment-page-1/#comment-4374 FMG_V6_btb Sun, 03 Oct 2010 22:13:30 +0000 http://www.ret-monitor.com/articles/705/stairway-to-heaven/#comment-4374 I'm not agree also, first max piston speed is around 70-80 degree ATDC depending on rod stroke ratio, as stated before. Design parameter to dimension a performance intake or exhaust ducts is not overpass a flow velocity around Mach 0.5 at max power speed. to me, valve lift beyond the needed to obtain the necessary effective area (at least equal to the throat area) have to be based on the particular design of the engine, angle between intake duct and valve, curvature radius of the duct in the valve seat area, masking of the valves with the head or cylinder walls, etc. Sure it has to be higher but it is a case study. Paco. I’m not agree also, first max piston speed is around 70-80 degree ATDC depending on rod stroke ratio, as stated before.

Design parameter to dimension a performance intake or exhaust ducts is not overpass a flow velocity around Mach 0.5 at max power speed.

to me, valve lift beyond the needed to obtain the necessary effective area (at least equal to the throat area) have to be based on the particular design of the engine, angle between intake duct and valve, curvature radius of the duct in the valve seat area, masking of the valves with the head or cylinder walls, etc. Sure it has to be higher but it is a case study.

Paco.

]]> By: Erland Cox http://www.ret-monitor.com/articles/705/stairway-to-heaven/comment-page-1/#comment-2093 Erland Cox Thu, 07 Jan 2010 19:57:41 +0000 http://www.ret-monitor.com/articles/705/stairway-to-heaven/#comment-2093 I do not agree with the article. First, for a given duration you can only have so much lift or the acceleration will be excessive. Less duration means less possible lift. I think it is a good idea to lift as much as possible and higher than the cylinder head flow rises because this gives a higher lift at maximum piston velocity. Peak lift usually occurs after 100 degrees after TDC and maximum piston velocity is around 77 degrees after TDC. A cylinder head never approaches the speed of sound at high lift and the velocity is only highest in the throat in a 2 valve engine. Usually an engine starts choking past Mach 0.62-0.64 and that is what you will have in the smallest part of the intake port at peak power rpm. There is no way the engine can rev so high as to obtain close to Mach1. Because the flow is piston driven it will become less and less dense in the intake tract with higher rpm. At a certain rpm the charge mass in motion goes down more than the gain from ramming gives and VE drops. Best Regards, Erland. I do not agree with the article. First, for a given duration you can only have so much lift or the acceleration will be excessive. Less duration means less possible lift. I think it is a good idea to lift as much as possible and higher than the cylinder head flow rises because this gives a higher lift at maximum piston velocity. Peak lift usually occurs after 100 degrees after TDC and maximum piston velocity is around 77 degrees after TDC. A cylinder head never approaches the speed of sound at high lift and the velocity is only highest in the throat in a 2 valve engine. Usually an engine starts choking past Mach 0.62-0.64 and that is what you will have in the smallest part of the intake port at peak power rpm. There is no way the engine can rev so high as to obtain close to Mach1. Because the flow is piston driven it will become less and less dense in the intake tract with higher rpm. At a certain rpm the charge mass in motion goes down more than the gain from ramming gives and VE drops. Best Regards, Erland.

]]> By: an Performance http://www.ret-monitor.com/articles/705/stairway-to-heaven/comment-page-1/#comment-2091 an Performance Thu, 07 Jan 2010 17:19:17 +0000 http://www.ret-monitor.com/articles/705/stairway-to-heaven/#comment-2091 Maximun piston velocity is not at 90 ATDC, never! It is depending on rod-stroke ratio at 70 - 78 degree ATDC. Maximun piston velocity is not at 90 ATDC, never! It is depending on rod-stroke ratio at 70 - 78 degree ATDC.

]]> By: Scott Tucker http://www.ret-monitor.com/articles/705/stairway-to-heaven/comment-page-1/#comment-1935 Scott Tucker Sun, 03 Jan 2010 02:26:11 +0000 http://www.ret-monitor.com/articles/705/stairway-to-heaven/#comment-1935 Excellent article and a great point. This is exactly what my mentor and esteemed camshaft engineer, Dema Elgin, always taught me. In order determine ideal cam lift you need to have the heads flow tested to determine where flow 'levels off'. The intake valves need to be open to this point by the time the piston reaches maximum velocity. Any more is just wasted motion in a system where, by design, mechanical needs must be satisfied before flow needs can. Excellent article and a great point. This is exactly what my mentor and esteemed camshaft engineer, Dema Elgin, always taught me. In order determine ideal cam lift you need to have the heads flow tested to determine where flow ‘levels off’. The intake valves need to be open to this point by the time the piston reaches maximum velocity. Any more is just wasted motion in a system where, by design, mechanical needs must be satisfied before flow needs can.

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