EGT Gage readings

[Bobalouie]

If you are going to mess with your fuel curve, then they are a must. By looking at your EGT readings you can determine if you are running too lean in any given RPM band (leaner = hotter EGTs). As a result, if you are getting too hot you can (theoretically) shut down before you burn a piston, or make a change at that particular RPM to your fuel curve. The reason I say theoretically is that while they are better than a wild guess as to how you are running, they are really no substitute for reading the plugs and pistons. I am pretty sure that mine are reading the flame front and not the exhaust gas temps, so while they are telling me something, it is all relative. With mine reading 1335 deg F (which is pretty hot) I still have nice color on my plugs and my pistons are not ashy or anything. So really you have to know at what temp your egt reads when you are running good according to the plugs and pistons, then you have a baseline. Right now I just use it as another gage (my boat had them when I bought it) and I know about where it should be depending on my RPMs. So if it strays from there, I know there is something going on I should look into. But I only know I am a bit on the rich side due to my plug readings and the way my pistons look. Its like my water temp gage. Once up and running It says that I am at 175 deg F, but it is not correct. I am not really that hot, it is just the merc sensor reading on a nordskog gage, because I can put my hand on the heads and they are not too hot to touch. So, I dont really know what temp I am running at, but I know if the needle goes over 175 something is amiss. Thats kindof how I use my EGTs right now.

Mine are installed in the exhaust divider plate down at the bottom. The plate was drilled and tapped for the egt probes.

 

[Allyfishing]

Thanks Bobalouie, I don't know if I want to mess with installing an EGT. I guess I should just first do a compression on my engine now to see where it is and then determine whether or not I want to install different heads.

Btw, what is the stock compression on a 1996 225PM anyway?? And is there a given compression number associated with specific cut heads?? Meaning does a set of 34cc heads = xxx pounds of compression??

To install an EGT probe etc. must the powerhead be pulled from the mid?

 

[Bobalouie]

I dont know what the stock compression is on that engine. But yes, there is a given compression number associated with a certain cc head.

I wouldnt think that you would have to pull the powerhead (although that is a pretty easy thing to do). I would imagine that it would be easier just to pull the exhaust divider plate and drill / tap it on your bench.

Give Jay Smith a call, he will be able to answer all your questions (281) 576-5088, and is a good guy to shoot the bull with. I had never done any business with him (but will in the future) when I called him with questions and he was more than happy to help out.

 

[F2008]

Btw, what is the stock compression on a 1996 225PM anyway??

My book has it at 110 - 135# and the variance between any should not exceed 15#.

 

[suicidealli]

stock mercury specs suck!!!!!!!!!!!!! you wouldnt believe the tollerance they say is ok on a nic sleeve!!!lol if you have 15 lbs different comp there is a problem on a stock motor.... cc heads, new gaskets, check the cylinders for scratches, and to see if they are straight. leakdown if the problem isnt found. the variance is from different elevation. the higher elevation the lower compression.

roy

 

[chad202]

On my motor cold the numbers would vary a good bit but warm the motor up and recheck, they were all the same.

 

[Allyfishing]

What then would 34cc heads do for compression on a stock 1996 225 PM...and I do apologize if I am hijacking this post...don't mean to.

 

[Bobalouie]

No prob, my questions were answered already, so the more the merrier!

 

[suicidealli]

depends on a few thing, but average should be around 140

 

[Allyfishing]

Thanks!

 

[JaySmithRacing]

I cut HUNDREDS of heads and on most healthy 2.5 with stock porting most at 34 CC's with a 1 MM head gasket at sea level will yield 140 -145 lbs cranking, I find that to be a safe compression using pump gas premium. Pryo's as a tuning tool are fine but can sometimes steer you wrong. AS the other posts varify at 10,000 RPM's a Mercury piston speed is at 120 times a second and IF the user feels they can "catch" a lean condition before the failure occurs is living a pipe dream. Even the quickest digital EGT's when they resgiture a spike your motor blew up 10,000 cycles ago if it hasn't already locked up , I find an "attentive and tuned ear" can sometimes reduce some of the carnage by listening to the engine carefully. EGT probes's also coke up and become insulated and give a false reading. Also I get a kick out of those that tell me their "seeing" 1400 + degrees on a EGT gauge, well folks most forged pistons would be a melted pile of GOO at 1400 so that is proof that gauge reading is a bunch of HOOIE..

This is a suggestion I have shared on ALL forums, I've passed this info along for 15 years and its NEVER failed me yet about the "jetting" subject:

When tuning I start with a known RICH condition, I make a hard pass with a set of new plugs installed and if safety allows kill the motor clean at top rpm. Remove the #5 plug and roll to BDC ( bottom dead center ) with a dark towel over the power head and my head to block all sun light I inset a bendo lite in the plug hole, look of the intake wash side of the piston and observe the intake wash wetness, if the piston crown is wet half way across the piston its very rich, if its the size of a quarter ( coin ) its very safe, if its the size of a nickel is just about correct if any less than that your running a bit lean you need more fuel and if its dry your lucky that pass didn't get a piston , remember ALWAYS start rich and work down never the other way you might not get a chance to richen BEFORE the piston burns..

Always makes me feel good when I read in print one of MY suggestions I've reported on for years to be successful and folks are passing the info on year after year ....

Good luck,
Jay

 

[Bobalouie]

Jay, what do you do to clean kill an Allison? At 9000+ rpms mine is running awfully fast to kill the ignition, and it wont get into the upper reaches of its RPM band unless it is trimmed, so keeping the hull in the water to look at the pistions at 9500 rpms wouldnt be possible.

Just curious how you guys do it?

 

[JaySmithRacing]

As I said "if it can be done safely".. An A boat will need to be brought down off pad ASAP safely and then killed. The trick is not to allow the engine to run at a lower RPM than WOT as least as possible as any long term lower rpm will taint the readings..

Jay

 

[Allyfishing]

Great information and explanation Jay! Thanks. I checked with Tony first on what to do with his ACU as far as adjustment to fuel if I up my compression by swapping out heads. He advised checking plugs too but mentioned about the EGT if done properly. An EGT is something I'm not comfortable with and would not know what I'm doing anyway. Time for a compression check now with stock heads!

 

[wj225]

O.K. Since Jay, and others, are on board, I guess I will throw my EGT question in here. I have a 2000 225 ProMax. Brucato SVS and PCU. Jay Smith cut heads, 16 amp. flywheel and G-force tuner. I have a Pyro 2000 digital EGT gauge with the rifle probes in the reccommended bolt holes. Up until last January, at WOT the temps between each cylinder bank never varied by more that 10-15 degrees. Often times, they would read identical. Last January on a trip to the late as I left the ramp, I noticed huge variances in the temps. Even running part throttle the temps would vary by 400-500 degrees. At one point, I have seen one bank read in the 700 degree range and the other over 1300. After cruising for 20-30 minutes around 4000 rpm, the temps will equalize and vary by no more than 10-15 degrees. I have checked wiring, grounds, timing, injectors cleaned, etc. with no problems noted. I swapped banks with the pyros and the temp on the gauge changed sides which, to me, indicated I had an engine problem. Also, all engine modifications were completed two years prior to this problem developing.

Any help?


Bill

 

[zatchmo]

O.K. Since Jay, and others, are on board, I guess I will throw my EGT question in here. I have a 2000 225 ProMax. Brucato SVS and PCU. Jay Smith cut heads, 16 amp. flywheel and G-force tuner. I have a Pyro 2000 digital EGT gauge with the rifle probes in the reccommended bolt holes. Up until last January, at WOT the temps between each cylinder bank never varied by more that 10-15 degrees. Often times, they would read identical. Last January on a trip to the late as I left the ramp, I noticed huge variances in the temps. Even running part throttle the temps would vary by 400-500 degrees. At one point, I have seen one bank read in the 700 degree range and the other over 1300. After cruising for 20-30 minutes around 4000 rpm, the temps will equalize and vary by no more than 10-15 degrees. I have checked wiring, grounds, timing, injectors cleaned, etc. with no problems noted. I swapped banks with the pyros and the temp on the gauge changed sides which, to me, indicated I had an engine problem. Also, all engine modifications were completed two years prior to this problem developing.

Any help?


Bill

Sounds like a spark problem to me. Check plugs, wires, coils, coil wiring, and switch boxes. Swap switch boxes from one bank to the other to see if the problem moves. My money is on a weak coil though. You can swap those from side to side too and isolate which one is bad.

 

[wj225]

Sounds like a spark problem to me. Check plugs, wires, coils, coil wiring, and switch boxes. Swap switch boxes from one bank to the other to see if the problem moves. My money is on a weak coil though. You can swap those from side to side too and isolate which one is bad.

By the way, I have checked the timing on each cylinder with full advance when the problem exists and with the exhaust temps were equalized and observed no change. Wouldn't this expose a bad coil?

Bill

 

[zatchmo]

By the way, I have checked the timing on each cylinder with full advance when the problem exists and with the exhaust temps were equalized and observed no change. Wouldn't this expose a bad coil?

Bill

That's a good question, I guess you could still have intermittent spark on a hole and probably not see it with a timing light. I would think the EGT wouldn't fall off so much then either though. Have you checked the wires and changed plugs? A timing light will still trigger if either is bad.

 

[wj225]

That's a good question, I guess you could still have intermittent spark on a hole and probably not see it with a timing light. I would think the EGT wouldn't fall off so much then either though. Have you checked the wires and changed plugs? A timing light will still trigger if either is bad.

New plugs all around & wires look good.