Originally Posted By: Srt20
Originally Posted By: DriveHard
Originally Posted By: Srt20
Originally Posted By: DriveHard
Any concern about free revving a properly warmed up engine within the safe operating zone (below redline) is COMPLETE GARBAGE!!!
When I drive down a mountain pass with my engine sitting between 4000 and 5000 with ZERO load for minutes on end...
When I blip my throttle every time I downshift to rev-match...
When I downshift to let my engine do the braking...
When I coast down the highway in a lower than normal gear...
Every time I go down a hill when towing in a lower gear...
Your engine is revved with no or little load all the time when operating your vehicle. Simply revving it up there in neutral is no different.
Actually your engine IS loaded in every one of your scenarios. Well except the blip to match rpm to down shift. But thats only for a second.
When you decelerate, your crankshaft, rods, and pistons are loaded. Though a diesel is less loaded, unless you have a engine brake.
No...no it is not. There is no combustion events taking place (in modern FI engine). The only "load" is friction that is resisting the force that is spinning the engine.
If you are talking about forces inside the engine, the diesel engine has MORE force pushing the piston into the con rod under free spin than a spark ignited engine. The diesel takes a full "breath" of air every single time, whether you add fuel or not...so there is always the same compression force, and you get that energy right back out (which is why it seems that a diesel has less drag than a SI engine). On an SI engine you are drawing a near vacuum when the engine is in free spin...so you don't even get the force of compression. You get a pumping loss...which is why it feels like an SI engine has more drag.
If you throw de-compression braking into the mix you get an even "worse" type of loading. You get the compression forces on the piston as it approaches top dead center, then quickly and violently that force disappears as that compressed air is allowed to be released into the exhaust system. The con-rod and piston is then dragged back down to bottom dead center with no help of the compression force to push it down...by the logic being thrown around here, that means every time you use your "Jake brake" you are destroying your engine!
https://www.youtube.com/watch?v=o8Cta2cC2Co
Pistons trying to pull air, creating vacuum, IS a load on the rotating assembly.
Yes, I understand that quite well...and that loading is on the assembly when spinning all the time no matter what (making power, coasting, free revving, idling, etc.).
Originally Posted By: DriveHard
Originally Posted By: Srt20
Originally Posted By: DriveHard
Any concern about free revving a properly warmed up engine within the safe operating zone (below redline) is COMPLETE GARBAGE!!!
When I drive down a mountain pass with my engine sitting between 4000 and 5000 with ZERO load for minutes on end...
When I blip my throttle every time I downshift to rev-match...
When I downshift to let my engine do the braking...
When I coast down the highway in a lower than normal gear...
Every time I go down a hill when towing in a lower gear...
Your engine is revved with no or little load all the time when operating your vehicle. Simply revving it up there in neutral is no different.
Actually your engine IS loaded in every one of your scenarios. Well except the blip to match rpm to down shift. But thats only for a second.
When you decelerate, your crankshaft, rods, and pistons are loaded. Though a diesel is less loaded, unless you have a engine brake.
No...no it is not. There is no combustion events taking place (in modern FI engine). The only "load" is friction that is resisting the force that is spinning the engine.
If you are talking about forces inside the engine, the diesel engine has MORE force pushing the piston into the con rod under free spin than a spark ignited engine. The diesel takes a full "breath" of air every single time, whether you add fuel or not...so there is always the same compression force, and you get that energy right back out (which is why it seems that a diesel has less drag than a SI engine). On an SI engine you are drawing a near vacuum when the engine is in free spin...so you don't even get the force of compression. You get a pumping loss...which is why it feels like an SI engine has more drag.
If you throw de-compression braking into the mix you get an even "worse" type of loading. You get the compression forces on the piston as it approaches top dead center, then quickly and violently that force disappears as that compressed air is allowed to be released into the exhaust system. The con-rod and piston is then dragged back down to bottom dead center with no help of the compression force to push it down...by the logic being thrown around here, that means every time you use your "Jake brake" you are destroying your engine!
https://www.youtube.com/watch?v=o8Cta2cC2Co
Pistons trying to pull air, creating vacuum, IS a load on the rotating assembly.
Yes, I understand that quite well...and that loading is on the assembly when spinning all the time no matter what (making power, coasting, free revving, idling, etc.).
