yeah what I have been saying applies to ALL 4 stroke engines.
Stroke is the piston starting at top of cylinder, down the cylinder, and back up to top.
The Four Strokes of a Engine: 1.)Intake stroke- piston starts at top dead center moves down with Intake valves open, exhaust closed, pulling in air/fuel mixture from the intake manifold. 2.)Compression Stroke- Piston moves back up compressing air/fuel mixture Intake and Exhaust valves both closed. 3.)Power Stroke- Both valves still closed, air/fuel mixture compressed to greatest point, ignition fires the mixture and the piston moves back down the cylinder producing the power as a result.(i.e. hp/tq) 4.)Exhaust Stroke- Piston moves back up the cylinder with intake valves closed and exhaust valves open pushing out the used exhaust gases through the head port out the manifold or header.
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quote:
ORIGINAL: Wickerbill
yeah what I have been saying applies to ALL 4 stroke engines.
Stroke is the piston starting at top of cylinder, down the cylinder, and back up to top.
The Four Strokes of a Engine: 1.)Intake stroke- piston starts at top dead center moves down with Intake valves open, exhaust closed, pulling in air/fuel mixture from the intake manifold. 2.)Compression Stroke- Piston moves back up compressing air/fuel mixture Intake and Exhaust valves both closed. 3.)Power Stroke- Both valves still closed, air/fuel mixture compressed to greatest point, ignition fires the mixture and the piston moves back down the cylinder producing the power as a result.(i.e. hp/tq) 4.)Exhaust Stroke- Piston moves back up the cylinder with intake valves closed and exhaust valves open pushing out the used exhaust gases through the head port out the manifold or header.
yes, i'm very aware and understanding of the engine cycle. thanks for the review anyways. my recent questions related to step 4 to 1. i was just wondering if there was any overlap between the exhaust stroke and intake stroke.......now, one more question, during the exhaust stroke, where would backpressure be needed? wouldn't backpressure make the exhaust stroke a "harder push" and therefore decrease hp/tq?
< Message edited by Sancho805 -- 10/15/2007 12:35:46 AM >
yes, i'm very aware and understanding of the engine cycle. thanks for the review anyways. my recent questions related to step 4 to 1. i was just wondering if there was any overlap between the exhaust stroke and intake stroke
NO, if there was any overlap between the strokes as you call it there would be a major malfunction. This all has to do with the engine timing. Any overlap would result in a dropped valve which is when the piston comes up with a valve open and it will break the valve off. You can advance or retard the timing to leave the valves open a little longer to either pull in more air/fuel mixture or to expell more exhaust. Either way you just adjust the timing a few degrees either way, to get overlap like you are thinking the timing would have to be WAY off and the enigine wouldnt run.
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quote:
ORIGINAL: Wickerbill
quote:
yes, i'm very aware and understanding of the engine cycle. thanks for the review anyways. my recent questions related to step 4 to 1. i was just wondering if there was any overlap between the exhaust stroke and intake stroke
NO, if there was any overlap between the strokes as you call it there would be a major malfunction. This all has to do with the engine timing. Any overlap would result in a dropped valve which is when the piston comes up with a valve open and it will break the valve off. You can advance or retard the timing to leave the valves open a little longer to either pull in more air/fuel mixture or to expell more exhaust. Either way you just adjust the timing a few degrees either way, to get overlap like you are thinking the timing would have to be WAY off and the enigine wouldnt run.
yeah, understood. what about my backpressure question?
A certain amount of backpressure is needed for a enigne to perform. Whether it be single exhaust or dual exhuast, x, y, or h pipe. The mufflers will provide the small amount of backpressure through the pipes thats needed to dispel the exhaust gases and help intake air more effeciently. Straight outs is not good on a factory engine. It will decrease the life of a engine by raising temperatures in the cylinder. The only engines that benefit from absolutely zero backpressure, i.e. open headers or straight outs, are race engines and 2 stroke small engines.
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quote:
ORIGINAL: Wickerbill
The mufflers will provide the small amount of backpressure through the pipes thats needed to dispel the exhaust gases and help intake air more effeciently.
this is where i'm baffled with your explanation. i dont doubt your knowledge but i'm confused with your descriptions. how does backpressure "dispel" when it's pressure thats returning or bouncing back to the exhaust port, hence the term "backpressure". From what i'm reading, what you are describing here is scavenging which i understand as an effect caused by high velocity pulses of exiting gases that create a low pressure tail which "pulls" (or scavenges) remaining gases out of our vehicles. maybe i'm misunderstanding your detailed explanation but correct me if i'm wrong on this one.
there is valve overlap but not as much as to let a minimal amount of backpressure re-enter the cylinder, it all depends on the grind of the camshaft and its lift and duration. You can beleive me or not it doesnt matter, I really could care less. Im just trying to explain the dynamics behind the inner workings of a engine but it appears to me that your mechanical knowledge is so limited you will never fully understand what I am explaining.
< Message edited by Wickerbill -- 10/16/2007 4:20:36 AM >
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there is valve overlap but not as much as to let a minimal amount of backpressure re-enter the cylinder, it all depends on the grind of the camshaft and its lift and duration. You can beleive me or not it doesnt matter, I really could care less. Im just trying to explain the dynamics behind the inner workings of a engine but it appears to me that your mechanical knowledge is so limited you will never fully understand what I am explaining.
yeah it shouldn't let back pressure in I just wanted to reassure what you were saying.
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Yeah but sancho doestn understand what Im saying about backpressure. The exhaust gases leaving the head acutally forms a vaccum on the cylinder that when the valves are on split overlap for that milli second, the vaccum helps clear the cylinder of exhaust gases while at the same time helps pull in the fresh air fuel mixture. I wish there was someone else on the forum that knew engine design that could help me explain it maybe in a better way, I dunno I might be making it hard to understand or something. This is where restrictive exhuast will hurt performance because too much backpressure will hinder the vaccum affect while just the right amount of backpressure will help.
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quote:
ORIGINAL: Wickerbill
Yeah but sancho doestn understand what Im saying about backpressure. The exhaust gases leaving the head acutally forms a vaccum on the cylinder that when the valves are on split overlap for that milli second, the vaccum helps clear the cylinder of exhaust gases while at the same time helps pull in the fresh air fuel mixture. I wish there was someone else on the forum that knew engine design that could help me explain it maybe in a better way, I dunno I might be making it hard to understand or something. This is where restrictive exhuast will hurt performance because too much backpressure will hinder the vaccum affect while just the right amount of backpressure will help.
haha......no need for anyone else to explain it. i completely understand what you are saying now and i agree except that you are calling the scavenging effect "backpressure". i understand the term "backpressure" as being pressure that is returning or bouncing back to the source ("BACK" pressure) which would actually hinder the scavenging effect. you have been calling backpressure that low pressure tail behind each exhaust pulse that "pulls along" or "vacuums" any leftover gases. i think thats whats been throwing me off the whole time. and you also threw me off when you said there was ZERO valve overlap and now you are stating that it does happen even if its for a millisecond. i know that the overlap is very small but overlap is overlap and it does occur which is what i stated much earlier in this thread but i guess i should have stated that it was for a millisecond only. i just thought an engine technician would already know that. i think whats happening is that the definition of backpressure is varied from person to person which is what confuses a lot of people in this forum and starts these misunderstanding debates. this is all nothing personal or do i doubt your knowledge but this whole thing has been a misunderstanding form the beginning and clear explanations is something that is critical in forums since all we can do is type and not "show" what we mean.
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quote:
ORIGINAL: basketballord
so did we reach an agreement here yet? Certain amount of "backpressure" is necessary/not?
whats your definition of "backpressure"?.......haha, jk . i dont think backpressure is ever necessary but it happens nonetheless. the balance between lowest possible backpressure and optimal velocity of exhaust gases is the ideal setup. "scavenging" or the low pressure tail behind exhaust pulses IS necessary which is what i think wickerbill was actually explaining.
< Message edited by Sancho805 -- 10/16/2007 10:00:43 AM >
yeah sancho were talking about the same thing. You call it scavenging and it is, its referred to as a vaccum effect in all the literature from training. But thats just because the exhaust leaving, or scavenging the cylinder, will also pull in the air/fuel charge, vaccum, but thats just on split overlap until the piston starts its intake stroke. But yeah you got it, its all about finding that right balance between too much or too little, and thats how you build performance out of a engine is balance everything out and make it as an effeciant as possible. So i guess that from all this we can come to the conclusion that removing the cats will not make for a gain in performance. The best thing to do would find some hi-flows and install those for the optimal exhaust setup.
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RE: CATS or NO CATS? - 
. i dont think backpressure is ever necessary but it happens nonetheless. the balance between lowest possible backpressure and optimal velocity of exhaust gases is the ideal setup. "scavenging" or the low pressure tail behind exhaust pulses IS necessary which is what i think wickerbill was actually explaining.
...oh well. 