Landracing Forum
Tech Information => EFI Questions => Topic started by: MattS on July 12, 2007, 10:40:15 PM
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So I got a Mychron 3 XG log for my 1948 BSA 500 single. I figure I can get some good tuning info from the A/F & EGT readings. But I have no idea where the EGT's should be. It has 9.5:1 comp and I'll be using the ERC 110K.
It has an 85mm bore & an 88mm stroke & redlines around 6500 rpm or so.
Anyone have any info on where it should run? Max not to exceed?
I've heard 1300 to 1500 degrees.... does that sound right?
Thanks in advance,
Matt
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I guess the ones that would know would be the ones that have holes in the pistons...
Ask JoeA...
Jon
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With our NA motors we like to keep them under 1300, but have seen 1800 without a hole in a piston :-D
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Hey Matt,
Kinda depends (but not as much as some would say) where the probe is in the exhaust. Most of the time it is 2-5 inches away from the exhaust valve. If your running a "K" type thermocouple and a non-supercharged engine on gasoline 1350 degrees is a safe number to use (I start to look at things after that). Keep in mind that a closed end thermocouple takes longer to react than the open tip type.
Good Luck and have a good time.
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Hey Matt,
Kinda depends (but not as much as some would say) where the probe is in the exhaust. Most of the time it is 2-5 inches away from the exhaust valve. If your running a "K" type thermocouple and a non-supercharged engine on gasoline 1350 degrees is a safe number to use (I start to look at things after that). Keep in mind that a closed end thermocouple takes longer to react than the open tip type.
Good Luck and have a good time.
I guess I should have said NA, even though for B'ville I should be turboed. I mounted the sensor per the instructions, which said 5.9" from the edge of the exhaust port in the head. It is a "K" type thermocouple.
I have a hard time finding pistons for this engine, so I'm trying to make this one last till I have to use the 12.5:1 one I have.
Thanks,
Matt
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Gentlemen, :-D
The specific use of EGTs is a very shaky business as a singular tune-up tool. UNLESS one knows where the A/F ratio peaks the temps (typically at stoichiometric or chemically correct for the fuel used), any target numbers are pretty spooky. :roll:
As an example, if the temperature where you are reading this comment is 70-750F - Is that rich or lean? It is an indication of temperature. :lol: When isolating EGTs and evaluating the bell shaped curve of A/F ratios vs Temperature, one can be referencing the same temperature at two (or more) different exhaust gas temps. :evil: :?
Also as the thermocouples are fairly slow to react, you are looking at history more often than not. :wink: :-o
Lots more could be said here, but sufficient to state that it is spooky business without the correct supporting inputs of other sensors.
Yours for less detonation and more fun, :lol:
Regards to All, :-)
HB2
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In the movie World's Fastest Indian old Bert gives step by step instructions on how to obtain hard to get pistons.
DW
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i'm pretty sure you'll only hit 1500 once! :-D best thing is to put her on the dyno with a sniffer up the tail. when ya get af around 13 or your best hp check your egt, remember it, then try to tune around your number. like others have said egt's are history and not a great tuning tool.
kent
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Nahh Good for finding the dead hole fast with data acq...
Jon
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One advantage to running a single - no doubt which one and never have to replace more than one at a time. Been there, even tried welding a plug in the hole for a second go round. Didn't work.
Hope you get in some good rides and have fun, partial to the Beeza bangers myself.
Ed Purinton
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Yep, I know there's no number to just tune to, but I just want to know what to avoid. Since E.M. is so short, I might be able to get away with a higher EGT & not do any damage. Also, since my bike has a manual spark advance, I can retard the spark if the EGT starts going too high... if the sensor reacts fast enough, if I react fast enough. But that's probably a pipe dream.
It gives me something to play with.
Thanks for all the info,
Matt
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EGT is ok if you start out on the rich end and watch not to go above a temp. Not all of us can go to the dyno when we want to, so we use the large white dyno to tune :-D
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Your egt`s are more affected by your ignition timing than by your fuel mix.
Pay more attention to your a/f and where you mount your sencers.
If your engine is blown, and your egt`s are over 1500, put some more timing
in it and you will be amazed. Use all of your information to tune, not just one
thing. Plenty of people will argue with this, so take it for what its worth.
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One point not mentioned is that if you have egt's on all cylinders, they will give you a pretty good idea of which, if any, need re-jetting which helps a lot especially if you are running alcohol and trying to read the plugs...........
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jon your killing me.........
holes is my pistons were a function of cylinder
combustion characteristics..........you can hole em
at 1100 or 1800.......if your real good.........
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If your egt is high and you retard the timing it will probably go higher.. retarded timing and way rich two very easy ways to hurt an engine..the more the rpm goes up the worse it gets..think about the burn time per unit of fuel and where you are in the cycle vs how many milliseconds left to finish you can end up with combustion in the pipes..way rich has issues with end gases and all that jazz just remeber an engine has both a rich and lean knock limit.. high combustion pressure and lots of unburned fuel is a grenade.
egt is a tool to be used along with other ones in the end. I put the probes about an inch from the port and see 1500 all the time on a sustained run. In a drag race or typical dyno pull they are too slow to get up to temp before the run is over.
Dave
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What if your pipe is only say, 4 inches long? (turbo)
What thermocouple should I use?
Begging knowledge,
Sam
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The whole issue of EGT references is somewhat cloudy and mostly neurotic from folks carrying tales of magic solutions. The reading on an EGT is dependent upon many variables. Open or closed types, size of the wire of the thermocouple, location in the exhaust pipe, and many others. Using the EGT to tune with is a sure recipe for disaster! Unless you have a reference temperature for the chemically correct ratio, you can "see" the same temperature at two points on a bell shaped curve, with each one referencing a different A/F ratio. When you are looking at an EGT reference you are always looking at history because they are fairly slow to react to changes.
As an example: What is the air temperature where you are? Is that rich or lean? There ya have it. It is an indication and must be related to other issues to really mean anything important.
BTW, exposed chromel-alumel wire (type K thermocouple) will only react to a temp change in about 800ms or so. Pretty slow.
Regards,
HB2
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Wise statement, Mr. Bettes, EGT understanding varies like the opinions of the blind men and the elephant.
I especially liked the neurotic reference.
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Horsepower is a product of heat. The EGT gives you an indication of where you are in the heat curve. As Harold mentioned it is a bell curve. As you lean out the engine the temperature will increase, peak, and start down the other side. If you are on the wrong side of the curve you are in trouble.
Like all tools, you need a full tool box to do the job. EGT is only one of the tools that you need. I think they are worthwhile for long pulls like Bonneville. Even at El Mirage they provide decent information. On a short run like El Mirage you can manage 1500 and get away with it.
The aluminum piston is going to melt in the 1200 range depending on alloy. But the piston actually sees much higher than the EGT indicates on the power stroke, like 4800 degrees. Then it gets cooled by the incoming charge. You get the average at the EGT.
The distance, type of thermocouple, open or closed tip, and other things keeps it from being an absolute tool. As a relative tool, being able to compare run-to-run helps.
At 1200 you are giving away HP. At 1300-1400 you are close. Over 1500 it better be short!
An oxygen sensor coupled with the EGT gives you a really good tool. The amount of oxygen exiting the engine should be zero. In a perfect world that would be the case. In the dynamic environment of the cylinder, you can't get a perfect mix of fuel and oxygen because of the short time for that to happen. Excess fuel is required to make sure that you get peak HP.
And that doesn't even begin to cover fun subjects like detonation, the effect of compression ratios on flame temperature, incoming charge temperature, humidity . . .
On the other hand, with a single thumper, run it till the valves float, then SHIFT.
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Related question: How far from the exhaust port (or back of valve) should the EGT probe(s) be placed? Engine is a supercharged Triumph Rocket 3.
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At very high EGT's nitrous will actually ignite aluminum pistons, at least in a diesel. Nitrous is kinda like a catalyst, and aluminum is flammable.
Your turbocharger has a limit to how much heat it can run. 1500 deg sustained will damage most turbines. But the key is sustained. For 10 seconds you can go past 2000. Drive pressure comes into play as well. I've melted inconel turbines, cracked turbo hsg's, and turned 400 stainless thick wall tubing into plastic. Yeah, and ignited pistons.
I mount pyrometers near the turbine hsg, away from the exhaust port, but that is only because I do just one or two pyros. If you mount it too close to the valve, seems they don't last as long as if you go several inches downstream, if you are doing one-per-header-pipe.
GM has a new design pyro that I'm playing with. It reads in ohms instead of microvolts. Not a thermocouple, a "thermistor" that appears to read very accurate from 0 deg out past 1850 deg.
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Jack Connelly and Al Holoway ran a partial streamlined BSA triple with a small roots blower at Bonneville about 35 years ago. It was thought to be some sort of cabin compresser. Jack still has a Triumph triple in a Rickman frame. Very pretty. PM me if you would like Jacks email.
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MCR... thanks for your response, but I run a Rotrex blower, not a turbo.
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DOH!!! Sorry! :-D
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I would only consider the dyno numbers if you are willing to hang with them until they stabilize on a value. Doing a 5 second pull and calling it the target is mindless when you have to run for 2 minutes.. I woory more about and egt that will not settle down and keeps going up that is a failure waiting to happen.
Dave
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I always ask our engine builder before each run, 'what temp should I click off at?" He always says "if it noses over then you went too high".