SuzukiSavage.com /cgi-bin/YaBB.pl General Category >> Rubber Side Down! >> Exhaust Temps /cgi-bin/YaBB.pl?num=1583274734 Message started by SoC on 03/03/20 at 14:32:14

Title: Exhaust Temps Post by SoC on 03/03/20 at 14:32:14 I know it has been discussed/referenced in past, but just looking for an idea of the temperature of the exhaust as it leaves the head, and at the opposite end of the header pipe where it enters muffler. Ceramic packing for exhaust is rated to about 2500 degrees, which is the main reason for the question.

Title: Re: Exhaust Temps Post by verslagen1 on 03/03/20 at 15:14:44 If you're worried about melting that... you got problems. I had problems, I melted glass.

Title: Re: Exhaust Temps Post by Gary_in_NJ on 03/04/20 at 06:28:27 Depending on the mixture (air:fuel ratio) it will be between 1,600 (very lean) and 1,100 (very rich). A well jetted engine running at a stoichiometric AFR of 14.7:1 will run 1,250 to 1,300 EGT. An AFR of 12.5 to 14.7 is good for an air cooled engine.

Title: Re: Exhaust Temps Post by DragBikeMike on 03/06/20 at 11:39:55 Hey Gary, do you happen to have a source for those exhaust temps?  Maybe a reference book or a link.  I am very curious about this topic. Thanks, Mike

Title: Re: Exhaust Temps Post by Gary_in_NJ on 03/06/20 at 20:02:12 Dave, The data comes from 40 years and thousands of hours observing and setting EGT in air cooled aircraft engines. The data above is kind of “dumbed down”.  When setting EGT, peak EGT occurs at an AFR of 14.7:1. Whether that is at 1,300 degrees F or 1,500 F doesn’t matter. What is important is you observe the cylinder that reaches peek EGT first and then set the AFR mixture based off that cylinder. Once reaching peek EGT, any change in mixture will result in a reduction of temperature. A rich mixture causes the EGT to reduce due to the cooling effect of excess fuel, while a lean mixture causes an EGT reduction due to a power reduction. What is important to know is that a reduction of 100F due to a lean mixture is different than a 100F reduction due to a rich mixture. When setting a lean cruise power setting (lean of peek) one has to carefully observe CHT to ensure that the temperature stays in the normal zone (below 470F) and certainly below the 500F redline. I typically set power at 50-100F rich of peek. This results in a CHT in the 380-420 CHT. It’s also important to know that a high EGT (above 1600) combined with a high CHT (above 460F) can cause damage to the piston. Sorry for the long winded answer. Both Lycoming and Continental have Advisory Circulars that discuss setting power via EGT and CHT for normally aspirated, turbocharged and supercharged engines.

Title: Re: Exhaust Temps Post by DragBikeMike on 03/06/20 at 21:02:24 Gary, your reply is excellent, certainly not long-winded.  It is a subject that has mystified me for many years.  I know from personal experience just what a lean mixture can do.  I have managed to stick valves, burn valves, melt holes in pistons, seize pistons, and most recently pull the top off a piston.  All, I'm sure, due to lean A/F ratio. What baffles me is my former training in A&P school and also the USAF.  I was a recip engine mechanic in the AF.  I was always instructed, just as you described in detail, that peak EGT occurs at stoichiometric, and EGT falls off either side of 14.7:1. But all those melted parts I've accumulated over the years contradict that.  Your reply to SoC also seems to contradict the premise that EGT is lower either side (lean or rich) of 14.7: "Depending on the mixture (air:fuel ratio) it will be between 1,600 (very lean) and 1,100 (very rich)". I'm not denying your numbers because my personal experience supports very hot stuff goin on when mixtures are north of 12.5 at WOT.  But the aviation industry couldn't possibly be wrong. Your comment about CHT is excellent.  Are you saying that when a mixture goes lean, and as a result the EGT goes down, the CHT is going up?  Am I getting the two mixed up?  Is it the CHT that's killing the engine? This graphic from an aircraft engine manufacturer shows the CHT & EGT tracking.  Peak CHT & EGT are right around 14.7.  What the heck am I missing here.

Title: Re: Exhaust Temps Post by Gary_in_NJ on 03/07/20 at 05:01:43 I’m familiar with that chart. The thought is that as you move away from the ideal AFR (lean or rich), you are making less power and therefor CHT goes down. As you know, this is a subject where there is much debate. I have observed that CHT does in fact go up with a mixture that is LOP. However, with that said I typically don’t “wait to see what happens” and immediately enrich the mixture. In reality there may be a momentary increase in CHT...I don’t know. My experimental aircraft (RV6) with high compression pistons and a ram air induction tends to run on the high side of CHT. I also run an electronic ignition and if my memory is correct I have it set to provide as much as 38 degrees BTDC at cruise power settings, much further advanced than what a mag provides at 25 BTDC fixed. There are many factors that drive high CHT, and high cylinder pressure and ignition timing are some of those, so my “normal” reading of 380 degrees on cylinder number 3 is explainable.  This engine now has 1,500 hours on it, so I have confidence in its ability to survive. Here is a great article from GAMI (they make fuel injector nozzles) that discusses the disconnection between CHT and EGT. I have a 4 probe EGT and I have to agree, once power is set EGT isn’t a useful tool. There isn’t any data provided by EGT that CHT won’t tell you (other than mixture). https://gami.com/articles/egt_myths.pdf

Title: Re: Exhaust Temps Post by DragBikeMike on 03/07/20 at 13:53:48 WOW!  What a great article.  Thanks so much for posting it.  Very useful indeed. The article points out that EGT does not correlate with things typically associated with stress on the engine.  Examples: Ignition advance and higher compression increase stress but cause EGT to go down, while ignition retard and lower compression typically reduce stress but cause EGT to go up.  I can get into that.  A trick used on bikes with oversize turbos is to retard ignition timing for launch.  It raises the EGT dramatically and allows the turbo to spool up when the engine is unloaded, so the thing is really spinnin when you drop the hammer. I like that he stresses CHT over EGT.  It really does make more sense to monitor the CHT since it has a direct correlation to what's goin on in the cylinder. Why does he say "near or just rich of peak EGT is the worst place to operate the engine"? Gary, I would really appreciate your opinion on this.  Is it possible that Figure 4 has an error?  In Figure 4, cylinder 3 is labeled as the "richest" cylinder, while cylinder 1 is labeled as the "leanest" cylinder.  But the graph shows cylinder 3 at about 13.7 GPH (peak EGT), while cylinder 1 is about 14.1 GPH (peak EGT).  Shouldn't cylinder 3 be the leanest?  That would also seem to correlate with the EGT, where cylinder 3 is the hottest and cylinder 1 is the coolest. Excellent article.  Definitely a keeper.  Thanks again.

Title: Re: Exhaust Temps Post by Gary_in_NJ on 03/08/20 at 07:46:09 Dave, It isn't labeled "richest", it's labeled "richest cylinder peak EGT". What that graph is depicting is the lack of relationship between EGT and fuel flow (shown in GPH). Cylinder #3 has the highest EGT, yet the lowest FF at peak EGT. On a multi-cylinder carburated engine it is virtually impossible to get even fuel flows across all cylinders. FI is able to meter an even distribution of fuel, EFI is able to compensate for other variations within each cylinder. Even so, all cylinders may have a different EGT.

Title: Re: Exhaust Temps Post by DragBikeMike on 03/08/20 at 19:58:08 I agree, cylinder #3 does have the highest EGT and does have the lowest fuel flow.  Doesn't the fact that it has the lowest fuel flow make it the leanest cylinder peak EGT, not the "richest cylinder peak EGT"?  Figure 4 identifies cylinder 3 as the "richest cylinder peak EGT" but it has the lowest fuel flow, about 13.7 GPH.  In contrast, #1 fuel flow is about 14.1 GPH, which best as I can tell would be considered richer than #3. No disrespect intended Gary.  I'm asking the question because I don't understand and it seems to me you have much more experience on this topic than I do.  I think we have some sort of communication disconnect.  I want to understand that graph.  I think you can help me. Best regards, Mike

Title: Re: Exhaust Temps Post by Gary_in_NJ on 03/09/20 at 06:36:10 So there's no way to know which cylinder is leanest. We know the fuel flow....but we don't know the volume of air. Without both figures it's impossible to tell. If we knew the CHT that might give insite. Might. So we have been discussing engines that run a few clicks either side of  stoichiometric. But if you look at a lean-burn engine, engines that operate at an AFR up to 32:1 they achieve this with VVT that reduces compression and by retarding the timing. Even Homogeneous Charge Compression Ignition (HCCI), engines that rely on compression for ignition, they too run at a very lean AFR. These engines are able to run at lean AFR's without destruction of pistons and valves. The HCCI has a piston with a ridge that fits into an area on the cylinder head where all ignition occurs. Expansion happens in this ridge area first and by the time the piston moves down to reveal the rest of the piston, head and valves, the charge has cooled to the point that it isn't catastrophic, and expansion can continue. So getting back to our dumb air-cooled and carburated engines, they can only handle so much cylinder pressure and ignition advance. They rely on excess fuel for cooling, and running lean deprives them of the cooling, thusly causing damage at the hottest points of the combustion chamber. The lean mixture isn't too hot (it's cooler than stoichiometric)...it just doesn't provide adequate cooling.

Title: Re: Exhaust Temps Post by DragBikeMike on 03/10/20 at 17:10:18 Gary, I’m lovin your comment: “The lean mixture isn't too hot (it's cooler than stoichiometric)...it just doesn't provide adequate cooling.” That’s very clear.  Nice choice of words.  I agree. I guess I’m not gonna be able to nail you down on that Figure 4 issue.  I believe it’s erroneous.   I reached out to the author, and also to a friend of mine who was the service supervisor at Crown Air.  I’m very curious about it.  I think it should look like this.

Title: Re: Exhaust Temps Post by DragBikeMike on 03/10/20 at 17:15:53 I ordered a CHT gage.  It won’t fit the spark plug configuration on the LS.  I was thinking that the 8mm stud just below the exhaust port might be a good place to install the sensor.  I have lapped three LS heads and each one had a definite depression in the sealing surface located on the underside of the exhaust port.  One actually had a significant divot where the fire ring on the head gasket had sunk into the aluminum.  I suspect it got so hot that the aluminum started going plastic.  On my recent meltdown, I found the nut on the 8mm stud finger tight.  I had checked that fastener for tightness just shortly before I had the meltdown.  To me, this area seems to be one of the hottest locations on the upper regions of the engine.  I know its not exactly on the cylinder head, but its really close.  It must be very close to the same temp as the head in that area.   Any of you have any thoughts on that sensor placement? Here’s a look at the area of the sealing surface after quite a bit of lapping.

Title: Re: Exhaust Temps Post by Gary_in_NJ on 03/10/20 at 19:39:55 Ive seen CHT’s that are washers that go between the head and the spark plug. I’ve heard that they are fairly accurate too.

Title: Re: Exhaust Temps Post by DragBikeMike on 03/11/20 at 12:03:49 The one I ordered is a TrailTech.  It uses the washer under the spark plug sensor.  Unfortunately, the LS650 head has this tight counterbore in way of the spark plug.  It looks to me like it would be next to impossible to install the special sensing washer without doing some major surgery around the plug counterbore in the head.  The TrailTech guidance says it can also be installed under a fastener (nut or bolt). If I use that 8mm stud, I can get a feel for the temperature extremes and how it reacts to various tuning changes in that region of the cylinder/head, then move the sensor to the rear 8mm stud, or possibly under a head nut.  Seems like it would be pretty flexible.  Right now, I'm not too keen on disturbing any of the 9mm head nuts. I believe Dave has one of these installed under his right-rear head nut.  I think he said that the highest temp he has observed is around 300F.

Title: Re: Exhaust Temps Post by Gary_in_NJ on 03/11/20 at 12:54:59 Would it be possible to remove the washer from the spark plug, install the CHT device, and then reinstall the original washer back onto the spark plug?

Title: Re: Exhaust Temps Post by verslagen1 on 03/11/20 at 13:15:13 I just removed the washer. They are meant to be permanent but you can unscrew them if you try hard enough. The sparkplug hole is spotfaced, you may have to flatten a ridge.

Title: Re: Exhaust Temps Post by SoC on 03/11/20 at 18:10:28 Guys, all this discussion has been interesting and mindboggling to me, though I did learn some interesting things and gained some insite about running lean and rich. My original inquiry was about using some ceramic packing in an exhaust baffle that is inserted in a connector pipe btween the rear of the header and the muffler. I have a VooDoo slash cut on my '03', to quiet it and improve the sound I installed a 4" baffle just on the end of the connector pipe from the header. I am thinking of replacing the 4" baffle with a slight longer one that I could partially packed with some of the ceramic insulation. Currently the baffles in the VooDoo and the short baffle I added are just bent metal internal tabs. It's basically straight pass with deflectors. It is hoped to provide a bit more restriction and possible a little more back pressure. As it stands now when bike has an occasional backfire, which they do, I have some blue flame shooting from the back of muffler. This worries me as it would not be desirable when I shut the bike down if at a gas pump and it's a sure fire way to get pulled over if riding at night. Here's a picture of connector with current baffle. Replacemnet would be a perforarted baffle with the packing, replacing it on the connector.

Title: Re: Exhaust Temps Post by DragBikeMike on 03/12/20 at 13:25:25 SoC, please accept my apology for hijacking your post.  I lost sight of the original intent.  It wasn't cool.  Maybe I can shed a little light on your question. I must start by asking you some questions so I am sure that I understand.  Are you thinking of putting the ceramic packing inside of that baffle, like this?

Title: Re: Exhaust Temps Post by DragBikeMike on 03/12/20 at 13:29:23 If that's what you are thinking about doing, putting the packing material inside of the baffle, it's not gonna work too well.  Muffler packing materials are intended to be situated around a perforated tube, they go around the tube, not inside.  It would look like this.

Title: Re: Exhaust Temps Post by DragBikeMike on 03/12/20 at 13:40:27 Based on your picture, I must assume that it would be difficult, if not impossible, to assemble your muffler and "connector pipe" with packing material wrapped around the outside of the baffle. Muffler packing material (glass, ceramic, or stainless steel wool) reduces noise through absorption/attenuation, not restriction.  It is not intended for the hot gases to pass through the packing.  The packing material is usually wrapped around a perforated tube like this.  The hot gasses pass through the center of the tube unrestricted, while some of the acoustic energy transfers through the perforations and into the surrounding packing, where the enrgy is absorbed and attenuated.

Title: Re: Exhaust Temps Post by DragBikeMike on 03/12/20 at 13:51:48 I think your packing will handle the heat just fine, but I doubt that it will hold up to the force of the hot gasses trying to plow through the packing.  Even if it does stand up to the force of the hot gas, it will choke off the exhaust system. To give you an idea of what sort of material can handle the heat in that area, I seal all my muffler to header joints with Permatex Optimum Grey silicone sealant.  It is rated at a maximum of 700 degrees (F) intermittent.  That stuff holds up just fine and I am applying it in exactly the area you are concerned about. I doubt that you have any interest in running the stock muffler.  I have been able to make better than 40 horsepower with a modified stock muffler, and it is very quiet.  But this old post might give you some ideas for taming the roar in your VooDoo Slash Cut. http://suzukisavage.com/cgi-bin/YaBB.pl?num=1526453881

Title: Re: Exhaust Temps Post by SoC on 03/12/20 at 17:51:28 First off, not a hi-jack, more an education. You learn some interesting technical stuff and also how little you know and understand. But to my baffle, it would not be the one shown, it would be replaced with a 1 5/8" OD perferated baffled that is cimped down and welded at end. I was not thinking of trying some internal packing in the current one. As for the current baffle, there is a possibility of putting packing on outside, concern is keeping the packing in place and not blowing it through. It's not really a noise issue, the combo of the addtional baffle with the baffling in the VooDoo creates a nice low rumble at idle that is loudish, but not obnoxious when you are on throttle. In end it is a direct pass through, with just tabs blocking/redirecting flow. They are aligned, as I set it up, so you cannot see through them if you look into it from the end where it attaches to header. Like mentioned my bigger concern is back pressure and when you have an occasional backfire, like when you dump throatle after hard excelleration it shots some blue flame out the back. Occasionally when I shut bike down it backfires, it did it with the stock muffler also. I  have concern say if I go to get gas and shut bike down at a gas pump and it shots some flame out the rear, not a great spot for that sort of thing to happen. My thoght was with a littlemore back pressure and a bit of blockage it might help curtail that.

Title: Re: Exhaust Temps Post by DragBikeMike on 03/19/20 at 02:45:51 The fact that you had the backfire issue even with the stock muffler indicates that backpressure is not your issue.  Hard to get more backpressure than the stock muffler.  The afterfire is a known problem, and it certainly does occur even with the stock, restrictive muffler.  I think you should focus on carburetion.  Raise your idle speed and fatten up the low speed circuit. When you say that your 1-5/8" baffle will have the end "crimped down and welded", is your intent to direct the exhaust gas flow through the perforations and packing?  I don't think the packing is intended to have the gases flowing through, it's not intended to be part of the flow patch, it's intended to surround the flow path.  Howzabout doing a sketch of your baffle idea and posting it. Regarding all the hullabalou pertaining to EGT and LOP/ROP, my good buddy Atomic Tom from San Diego sent me this fabulous link on adjusting air fuel ratio on an airplane.  It's a great video and I think many of us can learn a lot from it.  It wont help with your muffler issue but it's so informative that I had to share. https://youtu.be/h3bATVXMHQg

Title: Re: Exhaust Temps Post by Gary_in_NJ on 03/19/20 at 06:02:31 That is a good video. I can't get my RV6 to run LOP. Whether it's the high compression pistons, the ignition advance, the ram air - it's probably all of it - the engine likes to run at best power. From my experience, fuel injected engines can be easily run LOP, but carb'ed engines not so much. The fuel metering is not evenly distributed...not even close.  My next plane will be FADEC.

Title: Re: Exhaust Temps Post by LANCER on 03/19/20 at 10:44:00 I’ve used the same type baffle you pictured near the top of the page many times over the years.  I had always installed mine with the punch points of the baffle downwind.  You have yours opposite.  If you want more back pressure in the exhaust you can just bend the punch points down a little, like 1/4” movement at the points, and it will make a difference.  Adjust as desired. Backfiring, as noted already, is a carb tuning issue with help from the exhaust.

Title: Re: Exhaust Temps Post by SoC on 03/19/20 at 12:46:11 Thanks for all the replies. I do know there is probably some issue with carb and jetting. In fact stop yesterday at one of the indenpdent local shops and discussion with the owner (who worked at the local Suzuki dealer for years) did confirm that. Basically he conveyed the same as DragBike Mike. There is room for me to install some packing around exterior of the current baffle, question is how to hold packing in place? I do have stainless cable ties, I was wondering about possibly a perferated baffle, like pictured with some packing in it. I have since found a couple of other interesting possibilities looking online. This muffler, baffle combo does not create a lot of resistence to exhaust flow. The combo surprisingly is not excessively loud. My wife pulled up unbeknownst to her next to me at a traffic light one evening and her comment later was she did not find it objectionally loud, but loud enough that she did take notice of a motorcycle when she stopped at light.

Title: Re: Exhaust Temps Post by DragBikeMike on 03/20/20 at 03:03:59 It's still unclear to me why you want to crimp and weld the end.  A sketch would be helpful, maybe with some arrows and notes that show how you intend the hot gas to flow through the baffle.

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