Back Pressure

[RIDER11X]

Another rider and me got on this subject. Is backpressure required to keep a motor from tearing it self up, to get best performance, or any other reason? I think it is required to a degree but he says it's not. :confused:

Yuuup it's required...:cool:

[UglyMotha™]

Rico knows all about back pressure http://ricoracing.netfirms.com/Smilies/humpin%20smilies.gif


:eek: :blah:

Originally posted by UglyMotha™
Rico knows all about back pressure http://ricoracing.netfirms.com/Smilies/humpin%20smilies.gif


:eek: :blah:


:mad:

Consider your arse kikked ugly boy...:grr:

[remlapr]

Originally posted by UglyMotha™
Rico knows all about back pressure http://ricoracing.netfirms.com/Smilies/humpin%20smilies.gif


:eek: :blah:


Dayumm that was funny - wrong, but funny.

Ugly 1
Rico 0

[UglyMotha™]

Originally posted by Rico
:mad:

Consider your arse kikked ugly boy...:grr:



http://ricoracing.netfirms.com/Smilies/nanny_nanny.gif neiner neiner neiner..............



muwhahahah :devil:

[Crazy Honda]

Here is my point we all know how a engin works so why would we need spent gas trying to get back to the combustion chamber? there is not enough presure to realy help open the valves. so why would it be needed?:confused:

[Crazy Honda]

ok found this on a diff site interesting aint it:eek:
No, you absolutely cannot have too little backpressure. That is one of the biggest and dumbest fallacies that exist in relation to 4 stroke IC engines. Why? I'll tell you.

Pumping Losses The concept of backpressure means that there will be a high pressure area at the exhaust port. When the valve opens, the escaping exhaust gases have to push against that high pressure area. How can a parasitic loss be good for your engine? The only engines that NEED backpressure are various small engine designs, mostly 2 stroke. The problem with them is they have the tendency to be too effective at driving the exhaust out, loosing compression. I assure you that on a big 4 stroke engine such as an SBC you want the exhaust to have the free-est path possible. In fact, it would be ideal to have a low pressure zone at teh exhaust port. A low pressure area would help to pull the exhaust gases out. Freeing up more power that your engine would have wasted pushing the gases out...which brings up the next topic beautifully.

Scavenging We've heard this before, but what does it mean in relation to our discussion of exhaust. Easier for me to use an example. So your engine fires and now it's on the way up on the exhaust stroke. Exhaust doesn't come out at a consistent rate, it comes out in pulses. Each pulse is a high pressure area, and as it moves, it leaves alow pressure area behind it. Aha, there's our scavenging. You want that low pressure area to be at it's peak when the exhaust port opens on the next exhaust stroke. Thats another reason why headers make better power than manifolds. besides just flowing better, instead of all the pulses being dumped in a log fighting with each other, the tubular runners allow the exhaust pulses to stay seperate and create a nice low pressure area behind it. This is also where tuned and equal length headers come into play. Tuned headers are sized such that the length of the tube corresponds the speed of the exhaust pulses so that the low pressure area is maximized at certain rpms. No surprise that short headers are better for high rpms than longtubes.
Problems can surface if you use too large of a primary diameter, loss of torque. The morons are quick to spout 'you lost backpressure and thus torque.' Next time you hear that you will smile and know that that person failed physics in high school. The problem with using too large of a primary is this. The exhaust pulse only has so much gas and energy in it. If the tube is too large, the pulse expands to much, losing energy and thus velocity. When it loses velocity, it can potentially stall and stop moving in the tube, or at least slow down. aha! Too large of a header actually CAUSES backpressure, and thus lost power. We feel this power loss as a loss of torque because usually this effect is much more pronounced at low rpms as much less gas is moving.

[Crazy Honda]

Originally posted by UglyMotha™
Rico knows all about back pressure http://ricoracing.netfirms.com/Smilies/humpin%20smilies.gif


:eek: :blah:

Or does he lol





(crazy honda) 1


lol :devil:

[MOFO]

Where was that article copy and pasted from?

[sickmojave]

Originally posted by Crazy Honda
ok found this on a diff site interesting aint it:eek:
No, you absolutely cannot have too little backpressure. That is one of the biggest and dumbest fallacies that exist in relation to 4 stroke IC engines. Why? I'll tell you.

Pumping Losses The concept of backpressure means that there will be a high pressure area at the exhaust port. When the valve opens, the escaping exhaust gases have to push against that high pressure area. How can a parasitic loss be good for your engine? The only engines that NEED backpressure are various small engine designs, mostly 2 stroke. The problem with them is they have the tendency to be too effective at driving the exhaust out, loosing compression. I assure you that on a big 4 stroke engine such as an SBC you want the exhaust to have the free-est path possible. In fact, it would be ideal to have a low pressure zone at teh exhaust port. A low pressure area would help to pull the exhaust gases out. Freeing up more power that your engine would have wasted pushing the gases out...which brings up the next topic beautifully.

Scavenging We've heard this before, but what does it mean in relation to our discussion of exhaust. Easier for me to use an example. So your engine fires and now it's on the way up on the exhaust stroke. Exhaust doesn't come out at a consistent rate, it comes out in pulses. Each pulse is a high pressure area, and as it moves, it leaves alow pressure area behind it. Aha, there's our scavenging. You want that low pressure area to be at it's peak when the exhaust port opens on the next exhaust stroke. Thats another reason why headers make better power than manifolds. besides just flowing better, instead of all the pulses being dumped in a log fighting with each other, the tubular runners allow the exhaust pulses to stay seperate and create a nice low pressure area behind it. This is also where tuned and equal length headers come into play. Tuned headers are sized such that the length of the tube corresponds the speed of the exhaust pulses so that the low pressure area is maximized at certain rpms. No surprise that short headers are better for high rpms than longtubes.
Problems can surface if you use too large of a primary diameter, loss of torque. The morons are quick to spout 'you lost backpressure and thus torque.' Next time you hear that you will smile and know that that person failed physics in high school. The problem with using too large of a primary is this. The exhaust pulse only has so much gas and energy in it. If the tube is too large, the pulse expands to much, losing energy and thus velocity. When it loses velocity, it can potentially stall and stop moving in the tube, or at least slow down. aha! Too large of a header actually CAUSES backpressure, and thus lost power. We feel this power loss as a loss of torque because usually this effect is much more pronounced at low rpms as much less gas is moving.



seems that part of this story is missing. like the part about all the burnt valves you will have with no backpressure :confused:

[swamprider7]

Originally posted by sickmojave
seems that part of this story is missing. like the part about all the burnt valves you will have with no backpressure :confused:

That's because it doesn't burn your valves!

[sickmojave]

Originally posted by swamprider7
That's because it doesn't burn your valves!

I disagree.

[UglyMotha™]

Originally posted by sickmojave
I disagree.


I don't that's all hearsay you could run open headers on an ex from now until it's death and never burn a valve i still have yet to figure out why everybody believes that :o

[sickmojave]

Originally posted by UglyMotha™
I don't that's all hearsay you could run open headers on an ex from now until it's death and never burn a valve i still have yet to figure out why everybody believes that :o


I have allways heard that it would.never seen it happen first hand so I very well could be wrong. but I'm not going to run mine without a pipe just because of the noise. ;)

[300exOH]

Originally posted by UglyMotha™
I don't that's all hearsay you could run open headers on an ex from now until it's death and never burn a valve i still have yet to figure out why everybody believes that :o

The only possible issue I know of is that when you shut down the quad the cold air can rush in and cool the valve too quickly causing a bent valve. I have seen many atv's with open headers with no problems so who knows??? I don't see a need to run an open header on a quad. Just gives the rider a headache and really irritates people that don't like atv's.

[UglyMotha™]

running a open header is fine but is pointless makes no low-end torque and makes for a real noise annoyance now running no header is where you goin to do motor damage

[RIDER11X]

Originally posted by UglyMotha™
I don't that's all hearsay you could run open headers on an ex from now until it's death and never burn a valve i still have yet to figure out why everybody believes that :o

Probably because a few people tried it and never rejetted for that, and caused an extremely lean condition to occur which would burn a piston or valves in short order. Anytime flow is increased you mixture will be leaner, and if your desire is to run with no silencer at all, then you probably don't know much about motors or proper jetting.:o

[Crazy Honda]

Originally posted by MOFO
Where was that article copy and pasted from?




Exhaust/Another vote of NO for duals..........Unless the output is 250 or more:www.s10forum.com