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Discussion Starter #1
HI, I have just added three EGT probes to a Mach Z motor. What is the correct EGT's
and at what EGT's will it give the most power?. So far they are up to 1350F ?

Thanks for the help

Glenn
 

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1350 seems like you have already burned down your engine. I thought that 1250F was the danger zone. Are you sure you have the probes in the right spot? How is your wash? plugs?
 

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Discussion Starter #3
Hi thanks for the comment,   No I haven't burned down the piston ... yet when I saw the high temp I backed off quick ( I did a compression test and all still 127 PSI.  The probes are about  6 inches from the piston.  The plugs lookm OK to me But then that is why I put in EGT's because I have no experience in reading plugs !!. I am using synthetic oil and the "pump gas" here is 96 Octane so they burn pretty cleanly which doesn't help reading ?.

Thanks  Glenn
 

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GlennM, those temps. are a little high, with your compression, and if your motor is stock. You should also put your probes about 8"-9" from piston face or 6" from cyl. flange for most accurate temp. reading (hottest). I've also had difficulties reading plugs unless they are at the extremes (black/rich&oily or white/lean). I do however like reading piston wash with a cyl. light (see attached pic. of my piston wash which is safe and I had egt. temps. of 1250-1270 F for that wash, with probes at 8" from piston). The more clean piston you see and the less carbon you see, means you are running richer, the more carbon (black) and less clean piston (shiny metal), the leaner it is running. Also, wash has to be measured with a long wide open stretch (at least 1200'- 2000&#39
then shut down and stop quickly to measure wash.
Hope this helps!
 

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Use the piston wash methond to get your baseline jetting. This will give you a baseline for correct jetting. Then you can calculate the approx. jet for the day. You can use the EGTs as a SECONDARY indication of engine condition/ performance.

I have always said. I have only burned up one motor since I have been sledding, and it had gages on it. Since then, I have gone by wash. EGTs are needed on a engine that is very picky or finecky.
 

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This is right out of the race manual:place probe 100mm from piston:                                                                           Detonation=720 celcius(1330 farenheit)                                                                       (E.G.T's are not absolute.Engines have siezed with EGT's in the allowable range) I would use piston wash to verify my jetting and use the EGT's as a safety measure.
 

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Discussion Starter #8
Thanks for all the comments Guy's really helpful, I printed the photo and pinned it to the Wall.

Thanks again Glenn
 

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Isnt 127psi low for compression for a mach z.  Mine are 152psi in all three and i though 149 -154 was the normal.  

Ive measured the was many times and everytime i put the head back on its always around 152 unless i am dreaming and just cant remember what it really was.  
 

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if your running above 1300 and still not burning down, then your probes must be too close to the pistons.      i would do like everyone else says and find a baseline for your sled using traditional techniques and then go from there.       also, i find the bigger triples(800 and up) like fuel. Also, i have not noticed any gain from running these engines at 1250 rather than 1170 or 1150. a lot of the times I have found the sled sort of falls off at the end of a drag race when you run higher temps.      try a few different things with your sled and see what happens.
also what sort of gauges are you running, analog or digital?
 

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Discussion Starter #11
The engine is quite new and still less than 5 hours on it, so mI guess that may be the compression hasn't come up yet ?. I looked in the service Manual and it explained when to do a compression test but didn't give a reccomended PSI ?. So what is correct compression ??

As to the gauges they are digital so quick response

Cheers Glenn
 

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Glenn how did you do the compression test.

The correct procedure is to.

Make sure engine is cold.

1. Screw in the gauge.  

2. Make sure kill switch is off.

3. Hold throttle wide open and pull 3 times hard.

Im and %99.9 certin that the proper compression for a stock Z is 150.  But you made me unsure and im guessing my self.  

Also compression may come up or down by a few psi but it wont go from 127 to 150.  Whats strange is how you say all of them are 127.  

Maybe its the gauge your using or your technique.  Try it my way and type back.

Im just hoping that your EGT's werent right and you just shut the engine down before a piston failure. Because loss of compression is the first thing that will happen.

Take care..
 

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Discussion Starter #13
Machzzzz1  
               Thanks for the tips. My technique was wrong, firstly I was leaveng the throttle closed
and secondly I was using a gauge with a 15" hose on it.  

Have now retested and all are about 145 PSI.

I am thinking of shaving the head a little to up the compression (the pump gas here is 96 octane and I can buy Aviation gas easily too) what are the limits to compression ?.

Yes I backed off very quickly when I saw the high EGT's,  I am jetting richer and will keep an eye on them.

Thanks Glenn
 

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I thought compression tests give you a truer operating compression if you use a warm engine.
 
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