? for Don

[esdbass]

Don: I assume if one was running EGT temps of 1350 with 100 Octane fuel all things being equal if that same motor was to run 93 Octane fuel it would run even hotter?

Does higher Octane fuel ( Ie 100+) give one the ability to run a 3 L EFI motor at higher EGT temps than on lower Octane fuel? I would assume metal is metal and temperature is what it is?

By the way what's a maximum safe EGT temp on a 3L ?and does anything in the set up, fuel pressure, type of fuel itself,or richness effect what the maximum EGT temp would be? I would think not based on the characteristics and thermal properties of the metal does not change?

[Nikon Man]

Interesting question..........

[esdbass]

Gary: I actually thought you might have some very helpful and informative thoughts on this yourself

[Nikon Man]

<table width="90%" cellspacing=0 cellpadding=0 align=center><tr><td>Quote, originally posted by esdbass &raquo;</td></tr><tr><td class="quote">Gary: I actually thought you might have some very helpful and informative thoughts on this yourself </td></tr></table>

Eli,
You know I never really gave that subject any thought....... , but when I read the post I thought, damm that's something of interest. I'm totally limited to 93 octane with 10% Ethanol here so it's a mute point for me due to no availability of better fuel....but still very interesting. I could speculate but that's worth nothing. Richard probably knows the effects but I really don't, but I'd like to be educated on it...........

[EuropeanAM]

Boy, you come up with some "doozies"!

Opinions on this topic will vary as widely as those on lubricants. The hard part is that you have to judge what's best for YOUR engine and setup (not someone else's)... and you have to live with the success (or failure) of that decision.

EGT temps are usually expected in the 900-1100 degree range (this can vary based on "where" the EGT sensor is located, as well as obvious other factors).

Higher octane fuels burn SLOWER and COOLER (resulting in LOWER EGT's).

As the octane lowers, the EGT will usually rise.

A leaner mixture results in a higher EGT. So fuel delivery, injector pulsewidth, timing, fuel pressure can all play a role in actual EGT's.

Richening the mixture will usually result in a LOWER EGT.

[Nikon Man]

Don,

Thanks for the detailed info, that is really some good info to know since I run dual "Pyro's" on my motor. I've never had an issue with high EGT's but I now have a better understanding if something were to change. I do know about the temp changes from either rich or lean conditions, but the fuel info is great.

Knowledge is priceless and this is a good piece of knowledge to know.

[esdbass]

Don: "doozies" Well I wouldn't want to ask you a "no brainer"

Thank you for the info, what's Merc say the maximum safe continual running EGT temp should be on a steel sleeved 3 L motor?

Very interesting about EGT temps can vary based on where EGT sensor is located, Where does Merc take their specs from ?

Can I surmise that Octane, fuel pressure, timing, injector pulsewidth and richness all effect EGT temps and varying any of those has an effect on EGT temps. I'd also assume additives like ethanol in the gas can effect EGT temps as well even if the octane is the same as a non ethanol fuel?

One last one, how does Sea Foam, Merc Quickclean, and Marine Stabil ethanol formula affect burn/EGT temps?

[canadabullet]

Be careful ... Once detonation starts , egt can be misleading in that it drops .. Higher octane fuel prevents detonation better and can show substantially higher egts than the exact same engine with lower octane that is showing low egts because of detonation...This misleading sense of security with low egts has caused many burndowns...


Modified by canadablazer at 1:23 PM 7/29/2010

[JAZII]

One reply for the ETHANOL. I would say ethanol will raise the temps, that is why Merc says no more than 10% ethanol.

JAZII

[esdbass]

Joe: That's what I'm assuming as well But it's interesting that while 2 gasoline's with the same 93 octane can produce different burn temps based on the content of ethanol.

I wonder if Merc says only 10% more due to EGT burn temp concerns or due to that ethanol higher than 10% will melt all the fuel lines and internal plastic components etc in the motor? Look what's happening now with all the fuel line probs at or around 10% ethanol.

[esdbass]

Trust me I don't want to go anywhere near detonation point with any fuel

[canadabullet]

Thats why egt misinterpretation can be a false sense of security....

[esdbass]

OK thank you for modifying your post to explain this aspect better. But it confuses or adds another question in that higher Octane fuels burn cooler so you would think it would produce lower EGT temps?

I was given the example of a motor that was running 1250 EGT temps with 93 octane fuel the fuel was changed to 100 and the EGT temps dropped to 850 ish IE higher Octane burns cooler. I'd also assume that a motor that while running 100 octane fuel showed EGT temps of 1350 would melt down and run much higher EGT temps on 93 fuel?

Lets assume the compression of the motor is low enough to support running 93 Octane fuel with out detonation occurring and not require the running of 100 octane fuel but I guess the variables of fuel pressure, pulsewidth, and the fuel itself again plays into what the detonation point and EGT temps would be??? OK now I don't have a clue

I'd assume though you got two thresholds 1) The motor can't be running in a state of detonation, that's mostly affected by Octane and head compression as well as fuel pressure and pulse width and 2) regardless of lack of detonation there is an EGT temp that can't be exceeded? What temp is that given suitable Octane/no detonation? Is this even close to being right???

[canadabullet]

The EGT guage should only be used as a baseline ;once the fuel grade , compression ratio, ignition timing and jetting have been established by testing to get a favourable plug reading. This can be anywhere from 950 to 1400 degrees on the egt because of the variables that come into play such as distance of probe from bore , state of tune and ignition timing.. Most 2 cycle race engines are around 1000-1200 egt deg. but that is not a no problem guarantee... Every tuning change can then be monitored after the baseline has been determined , but ,remember that a cool EGT does not always mean safe... When detonation begins the boundary layer on the piston gets scrubbed off and the heat goes into the unprotected piston, causing seizure and a rise in coolant temp...

[canadabullet]

Your example of 93 octane running hotter egts that the same engine with 100 octane is because the engine did not require 100 octane . It is not beneficial to run higher octane rated fuel than the state of tune of the engine requires...

[esdbass]

I fully agree with that you should not run higher than necessary octane and it is of no benefit to performance but was using that example to illustrate how in the same motor higher Octane fuel burns cooler and thus a cooler EGT temp.

[EuropeanAM]

<table width="90%" cellspacing=0 cellpadding=0 align=center><tr><td>Quote, originally posted by canadablazer &raquo;</td></tr><tr><td class="quote">Your example of 93 octane running hotter egts that the same engine with 100 octane is because the engine did not require 100 octane . It is not beneficial to run higher octane rated fuel than the state of tune of the engine requires... </td></tr></table>

+1

This has been discussed previously at great length.

To go back to a couple of Eli's questions- Mercury doesn't equip any of their current engines with an EGT (Pyrometer). Yes they offer one as an accessory.... but it is not standard (or required) equipment.

As for the affect of individual items on EGT's.... there are a few requirements to even CONSIDER the effects:

-Engine must remain within the stochiometric "window" (near 14.7:1 fuel to air ratio). Anything substantially outside of this "window" will have heavily altered EGT's, could be detonating, or may not run "at all".

-ALL parameters MUST remain constant (with only ONE item being a variable). If more than one item varies... it's nearly impossible to determine WHAT item caused a variance in EGT.

As for the question of the affect of "cocktail ingredients" on EGT.... I've never tracked that on any particular engine. However, I'd be surprised if the difference was even "distinguishable" on the instrument (everything else remaining constant).

There's not much more I can say to give a hypothetical answer to your hypothetical question.

[esdbass]

So the first step in the process should be to get a good plug reading correct? One question any other method of doing that than a WOT pull the kill switch

[EuropeanAM]

I've never been to keen on the "WOT kill switch" scenario. However, if you're trying to get a "true" reading of the plugs from a WOT throttle setting.... there aren't a whole lot of other options (aside from some very expensive monitoring equipment).

[canadabullet]

Start overly rich and lean down in small increments.... Without a dyno that can measure bsfc ; the only way is WOT then kill the engine with the tether. This will give you only the full throttle jetting. The off idle up to WOT jetting will have to be more of a listen to how it runs and adjust to suit deal. Unless you have access to a dyno. It helps to have a pile of jets and can be confusing and expensive... good luck...