More information on EGT's
Mounting instructions (Digatron DT-2E) say to mount the sensor on the exhaust header,
1-3/4" from the face of the exhaust port. This is from the inside of the cylinder (not where the
pipe mounts up), correct? Haven't measured yet but I think that may be a problem on the TRX.
Also, the instructions talk about tuning for full throttle and full load, as that is when the EGT
reading will stabilize. Do you tune for all engine ranges at full throttle and full load? (i.e. wot
and see what the reading is at low, mid, and high as the engine revs through these?)
In this position the instructions mention exhaust gas temp range of 1100F - 1350F as likely
normal, which is probably a lot higher than what you would get than when mounting 6" from
the piston face, so I'll tune for the low end of that scale and post what I find.
rustyATV
Those instructions are for a Kart engine and are the same as they were when I cought my
first Digatron back in the early 80's. If you run your probe that close you'll get very cold
readings. If not careful you'll try and rejet your engine to bring the temps up but doing so will
cause you to melt down. Move the probe to 6 3/4" from the face of the piston for accurate
readings.
Rick
I think what is more important than exact distance of probe placement is dialing in the exhaust temp
readings with piston wash and plug checks. If you find 1100 degrees your piston wash looks good along
with your plug color than I wouldn't worry about the slightly low reading. What I am trying to say is
don't use exhaust temp numbers to jet the motor, piston wash and plug color are a better indication of
what your motor is doing. I have seen snowmobiles run all day long at 1350 degrees on the gauge and
I have seen some run 1150 and both were jetted right on. There are many variables to the exhaust
temps, timing can play a huge factor in exhaust temps, the more advanced the timing the lower you
temps(piston and cylinder are absorbing all the heat) retarding the timing will raise the temps (piston
and cylinder have less time to absorb the heat) Exhaust port height will also affect slightly the temps,
the higher the exhaust port height the hotter the gasses exiting because of less time for the heat to be
absorbed. I have mounted my exhaust temp probe 6 3/4" like rick suggested but my buddy has his at
the 1 3/4 from the flange, and his will run consistanly around the 1200 degree mark.
Dave
That's funny because I noticed about a solid 100 degree temperature change for every inch I
moved the probe away from the piston face - it gets hotter and hotter as you move the probe
away from the piston until it starts to stay the same. The sweet spot is just before where the
pipe turns blue (as witnessed on many pipes). Reading plugs is the most important thing to
do in either case, that is, establish your peak temperatures from how well your plugs look.
Rick
Here is from another discussion on EGT's
I thought there was a post in one of the forums but I couldnt find it when I did a search. I just
got an EGT (avengerII) for my banshee and I need to set the probes up.... I thought Rick had
mentioned that they go 12" from the face of the piston. I was told by 2 other people that they
go approx 8" from the piston face. While I have my new pipes off the motor I would like to set
this up, but I want to make sure I put them in the right spot. I also thought Rick had a link on
his main page reguarding the EGT, but I couldnt find that either.
thanx again for the help
walter
Darn that Rick! Where'd he put that stuff!
I know there's some talk about EGT's in some of the Thread Spread articles but I don't
remember which ones - I suppose I'll have to go back and read those bits again one of these
days.
I set up my TRX with the probe 6 3/4" from the face of the piston and dialed in the jetting from
there. Since the time I set mine up I've had many TRX owners put their probe in the same
location with comparable results. The Banshee seems to read a little cooler at that distance so
it may be best to move the probes a little further away from the piston to get a more accurate
reading - I like 7 1/2" to 8" on that engine. These silly-semi-supercharged two strokes spit so
much fresh, cool mixture out the exhaust during the pipes suction phase it cools the probes -
to the tune of about fifty to seventy five degrees for every inch it is placed closer to the
piston. There seems to be a kind of "sweet spot" that can be noticed if attention is paid to the
color of the exhaust pipe(s). Sometimes there's an area on the head pipe where it shows
some discoloration from the engines exhaust heat - where that starts would be a bit too far
down the pipe to locate the probe.
An EGT gauge is a tool. By itself it adds no power. In fact the obstruction in the pipe (the
probe) probably robs some. The up side is that when used properly the gain is much more
than the loss. The peak operating temperatures can be dialed in from almost any probe
location. The trick is to perform a lot of plug chops to verify the reading from the gauge, then
make adjustments to the jets accordingly. When someone starts to notice the changes in
exhaust gas temperature due to the air temperature and/or quality and the changes in
exhaust gas temperature which result from the changes made to the jetting they are
becoming well-tuned to the real moment to moment requirements of the engine. It is often
then, for the first time a rider will confidently jet the right direction and cure the "not quite
perfect" running condition, without guessing.
Rick
what exactly is an EGT?
and what is it used for?
I am sure Rick can answer this alot better than I can..... but here goes.
An EGT measures your Exhaust gas temperature. Useing the reading from the EGT you can tell
if your bike is running too lean (high temps) or too rich (low temps) But you need to set a
baseline but making sure that your jetted right and useing that as a guide. By using an EGT
you can save yourself from melting down and dial in your jetting if your too rich.
http://www.exhaustgas.com/ has a lil more info on it.
Like I said... I am sure that Rick can explain it better, since I am new to it.
walter
I have a problem that I hope some of you can help me with. I have a pro X 310R. I recently
bought a egt for it and I don't know if I should trust it or not.
On a recent trail ride, my bike was running what it sounded like, very rich from 1/4 to 3/4
throttle and the egt never got past 925. Carb is 38mm, rad valve, eej needle on bottom
groove, with a 185 main. Elevation was about 600 feet.The sensor is exactly 6 inches from the
piston. When I stop to inspect the plug there is hardly any color on it at all, even after an
hours worth of riding, just has a light brown hue. I run 76 110 race fuel with amsoil mixed at
40:1. The plug is a br8es. Should I try a br9es? Does running race gas with a synthetic oil
make plug reading more difficult? Should I lean it more as the egt and performance would
indicate, or leave it alone as the plug color would suggest?
I want to get maximum performance from my bike, but I don't want to seize it again either.
Rick, could use your advise, i know you have lots of experience with egt's
Thanks alot
schmuc71
You still have to read your plug chops to establish a base-line. There are MANY variables that
can affect EGT's. Ignition timing is one of the most prominent.
While this doesn't necessarily apply to you, timing advance will create higher combustion
temps than the gauge will indicate. With ign advance the heat is held within the cylinder for a
fraction longer, allowing more heat to be absorbed by the piston and cylinder walls. This heat
absorbtion will create higher combustion temps(and associated components) than the gauge
will indicate.
Retarding the timing will do the opposite, the heat will "move" more to the pipe, showing
higher EGT's in realtion to the true combustion process.
Too rich of jetting can cause high EGT's as well. Excess fuel will burn down the head pipe and
indicate a false high EGT.
EGT's aren't the perfect answer to tuning. You still have to do plug reading to establish your
baseline to work from. It allows for super-fine tuning, especially the low and mid range circuits
more than ride tests and plug reading are able to do.
EGT's allow you to keep an eye on what's going on in your engine. You are able to instantly
see any changes from the norm and take action if needed. Colder air like down on the beach
at the dunes, seen more than a few top-end get toasted from that. Also air leaks, I had a
base gasket going on me, and was able to see the rise in EGT and shut it down before total
failure. Long, long, runs like down the flats at Florence, you're able to watch your EGT and if it
rises too high, roll-out(completely) and let her cool off.
Changes in ambient air temps are probably the best use to tune with your EGT gauge.
Morning cool air or hot afternoon air, if you choose to jet for both you're able to see the
changes indicated.
Backcountry
With EGT locations there is a "wet line" that has to be taken into consideration. The fresh
mixture dumped into the pipe leaves a damp line inside the header pipe where it is sucked
back. Before you mount your probe you can run the bike at full throttle, remove the header
pipe when it cools and look inside to see the line.
If the probe is placed inside this wet area it will be cooled by the fuel charge and subjected
to a lesser temp reading then is actually present.
The probe wants to be just outside the "wet line". Ours turn out to be about 7" off the
face of the piston...but that distance may very well be from the characteristics of the pipe.
Rick AKA MacDizzy is well rounded in 2 cycle engines make sure to check out his web page
http://www.macdizzy.com and this thread about EGT's