Differences

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--- techtalk:evo:carb04 [2021/03/31 23:19]
ixl2relax [Gaskets]
+++ techtalk:evo:carb04 [2024/01/02 22:24] (current)
hippysmack
@@ Line 9: / Line 9: @@
 "Use the factory studs - They're the only ones out there\\
-with interference fit threads on the head side. ((aswracing at http://xlforum.net/forums/showthread.php?t=2070093))
+with interference fit threads on the head side. ((aswracing at https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-motor-engine/sportster-motorcycle-motor-top-end/193941-installing-exhaust-head-studs?t=2070093))
 {{:techtalk:evo:carb:exhaust-stud-16715-83.jpg|}}
@@ Line 20: / Line 20: @@
 There are a number of XLForum threads regarding installing the Exhaust Port Gaskets.\\
-http://xlforum.net/forums/showthread.php?t=44022\\
+https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-intake-and-exhaust/sportster-motorcycle-air-intake-carburetor-efi-fuel-and-exhaust/26591-exhaust-gaskets-are-new-ones-needed-everytime?t=44022\\
-http://xlforum.net/forums/showthread.php?t=143646\\
+https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-intake-and-exhaust/sportster-motorcycle-air-intake-carburetor-efi-fuel-and-exhaust/44394-exhaust-port-gasket-help?t=143646\\
-http://xlforum.net/forums/showthread.php?t=204486\\
+https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-motor-engine/sportster-motorcycle-motor-top-end/49878-cometic-gaskets?t=204486\\
-http://xlforum.net/forums/showthread.php?t=856566\\
+https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-intake-and-exhaust/sportster-motorcycle-air-intake-carburetor-efi-fuel-and-exhaust/99840-exhaust-gaskets?t=856566\\
-http://xlforum.net/forums/showthread.php?t=1597528\\
+https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-intake-and-exhaust/sportster-motorcycle-air-intake-carburetor-efi-fuel-and-exhaust/146979-se-exhaust-gaskets?t=1597528\\
-http://xlforum.net/forums/showthread.php?t=1779860\\
+https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-intake-and-exhaust/sportster-motorcycle-air-intake-carburetor-efi-fuel-and-exhaust/165416-se-exhaust-gaskets-are-junk?t=1779860\\
 \\
-Here are some comments from this thread: (http://xlforum.net/forums/showthread.php?t=558421)
+Here are some comments from this thread: (https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-intake-and-exhaust/sportster-motorcycle-air-intake-carburetor-efi-fuel-and-exhaust/77767-exhaust-gasket-se-or-oem?t=558421)
 "The SE ones are preferred by almost every engine builder I've ever spoken to.. More so then any of the aftermarket versions.. They are generally much better at sealing and last longer then the stock ones."
@@ Line 40: / Line 40: @@
 "I don't get it, I have swapped back and forth from SE to stock depending on pipes for years and never had an issue intalling the stock gaskets. Yes they are more difficult than the SE but you just work them in one edge slightly in then in a circle pattern until just the edge is in all the way around then keep pushing them in in the same manner until they are seated. Then I take and run my thumb all the way around the inside to make sure they are completely smooth. When installing the exhaust you do so CAREFULLY. Leave the clamp out of the way and pull the heat shields if you can't see up there perfectly. Center the pipe in the gasket and hold tight, slide up the clamp, install the nuts and tighten them evenly. Then again the SE ones work good too and are easier to install. I think if the stock head pipes are on it and you can get the stock seals installed and done correctly that they will last longer, but hey to each is his own."
 There is a Jims (#788) Exhaust Seal Installation Tool: ([[techtalk:ref:tools167#jims_788_exhaust_seal_installation_tool|Sportsterpedia Tool Section for Jims #788]])
@@ Line 48: / Line 47: @@
 | Scremin Eagle Exhaust Port Gasket (17048-98)\\ \\ Notice that the gasket is squared off. | {{:techtalk:evo:carb:exhaust-gasket-se-17048-98.jpg?direct&300|}} |
 | Aftermarket Copper Ring Exhaust Port Gasket\\ \\ Essentially an o-ring shape. | {{:techtalk:evo:carb:exhaust-gasket-alt-copper.jpg?direct&300|}} |
 \\
 ====== Exhaust Pipes & Cams - Power or Reversion ======
@@ Line 60: / Line 56: @@
 This complex combination of frequencies causes each exhaust system design to have it's own characteristics of helping the combustion cycle at certain rpms (making more power) and hindering that cycle operation at other rpms (creating reversion and less power). The trick is to match the right exhaust system and cams so they are working together to efficienctly create the most power.
-In the following quotations, of an XLForum discussion about stock 'D' cams versus Andrews 'N4' cams, Aaron Wilson provides a very good explanation:
+Back Pressure is NOT a good thing. But it may come along with other efforts to make a good exhaust.
+**Quoting Aaron Wilson from the XLForum (aswracing):**((https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-motor-engine/sportster-motorcycle-motor-top-end/110036-s1-lightning-heads?t=1028905 - Post#81))
+Reversion is caused by positive pressure from the exhaust during overlap. How is it exactly that "back-pressure" cuts down or prevents reversion? (Note: It doesn't.)
+Nobody attempting to find some virtue in "back-pressure" has yet to explain how it would be advantageous to a four-cycle motor to have the exhaust pushing back at any point in the exhaust cycle, other than the comment about preventing draw-through. My question still stands.
+The fact is, you want negative pressure in the exhaust system while the exhaust valve is open, especially during that critical window in time called overlap, where both valves are open.
+Exhaust systems, by their nature, generate both positive and negative pressure waves that move up and down the pipe, reflecting and changing polarity at both ends. What the pipe designer tries to do is make the negative waves arrive at the chamber during the time the exhaust valve is open, and expecially at overlap, and positive waves arrive while the exhaust valve is closed, where they do no harm. That's done with diffusion devices (baffles, megaphones) to broaden the negative wave such that it arrives over a wider rpm range, and with the length of the system to vary the timing.
+Devices that provide diffusion or alter timing while introducing "back-pressure" will incur some pumping losses. But the wave timing is the dominant effect. So even though the back-pressure is a bad thing, it's more than made up for by the corrected wave timing. Back pressure is not what helps, it's a bad side effect of what helps. But if you can provide the proper wave timing without introducing back pressure, it runs even better. That's very difficult to do on a motorcycle, running at low rpm, where the system needs to be long and space is at a premium.
+And ((https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-motor-engine/sportster-motorcycle-motor-top-end/110036-s1-lightning-heads?t=1028905 - Post#23))
+I think we can all agree that, while the exhaust valve is closed, it's pretty irrelevant what the exhaust system is doing.
+What I'd like to know is when, during the period of time that it's open, it would be a good thing to have the exhaust system pushing back?
+The exhaust valve opens roughly two thirds of the way down on the power stroke. It opens early like this because there's still some pressure in the cylinder, and this pressure will help get the spent exhaust gases moving. The rod angle is such that the pressure isn't really helping turn the crank anymore anyway.
+The valve remains open as the the piston goes through bottom dead center. All you're trying to do here is empty the cylinder. You don't want anything pushing back.
+By the time the piston starts coming up, the pressure has been relieved, and now the piston starts shoving the remaining spent exhaust out. Again, you don't want anything pushing back. You're pushing the gases out.
+As the piston nears top dead center, the exhaust valve starts closing. But you really don't want it closed until all the exhaust is out.
+Then the intake valve starts opening. You REALLY don't want the exhaust pushing back now. It'll push back right into the intake tract, shoving the charge back out the carb.
+Now you've got both valves open, and the piston passes through top dead center. The piston starts down and starts pulling. But both valves are still open! Which port will it pull from?
+You've got a cold, dense charge sitting still in the intake tract at near atmospheric pressure. You've got hot, high pressure sitting in the exhaust. Why doesn't it pull from the exhaust? Especially if the exhaust has "back pressure"?
+Now the exhaust valve closes and the exhaust system becomes irrelevant again.
+I didn't see anywhere in that whole exhaust cycle where it would've been helpful to have the exhaust system pushing back.
+An XLForum discussion about stock 'D' cams versus Andrews 'N4' cams:
-**Quoting Aaron Wilson from the XLForum (aswracing):**((http://xlforum.net/vbportal/forums/showthread.php?t=1028905 - Post#12))
+**Quoting Aaron Wilson from the XLForum (aswracing):**((https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-motor-engine/sportster-motorcycle-motor-top-end/110036-s1-lightning-heads?t=1028905 - Post#12))
 Well, contrary to what you might hear, the N4's are quite capable of delivering more bottom end than the stock D cams. The reason is that they have overlap, where the "D" cams have very little.
@@ Line 89: / Line 124: @@
 (end quote)
-**Quoting Aaron Wilson from the XLForum (aswracing):** ((http://xlforum.net/vbportal/forums/showthread.php?t=1637390 - Post#8))
+**Quoting Aaron Wilson from the XLForum (aswracing):** ((https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-motor-engine/sportster-motorcycle-bottom-end/151669-n4-cams?t=1637390 - Post#8))
 With respect to your question on the powerband, it has an __enormous__ amount to do with the pipe.\\

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