Max safe EGT

[red57]

Hello all,

Does anyone have any idea what the maximum safe EGT is for a Healey 3000? I have an aircraft egt with 6 probes that scans all 6 and can show the hottest, or can be manually switched from cyl to cyl. It's really neat but the problem I have is not knowing the safe max.

One fellow told me 1230f is max. for a Healey 6.

In order to stay below 1300f I have been running around 10:1 a/f mix which is on the verge of stumbling - not a way to make max power.... If I lean to say 11-11.5:1 temps will climb to 1500-1600 very quickly.

But I go on line and find forums for newer cars saying 1400-1500f is safe, eg: Supra safe to 1450-1550f, Subaru WRX safe to 1500f, Suzuki DR2400 bike safe to 1600f. I know these are generations newer w/different materials/design but they all seem to handle 14-1500 fine.

I know all motors will be a bit different, but I am looking for the max safe temps (and any other info that helps)


Thanks in advance.
Dave

 

[Hap Waldrop]

I always monitor EGT on the straights at WOT in 4th gear, and I'm looking for about 1300 degrees. I don't see that the Healey six cylinder would being any different than any other multi carb LBC as far fuel requirments for mixture. I have to admit I almost chuckled on the guy telling you 1230 degrees, most folks use analog EGT gauge/s and nailing it down to exactly 1230 on glance would be kinda difficult. I use Westach analog EGT gauges, I'm guessing he is using LED gauges, but still narrowing it down to to exactly 1230, is kinda funny.

 

[red57]

Hap,

Thanks for the input. The problem I'm having is that to keep it under 1400 degrees WOT at 6k (red line for me) I have to have about 9.75:1. At that a/f it is just starting to stumble, plugs are black and sooty. If I run it at say 11:1 WOT at 6k it gets up to 1700 and climbing.

BTW I'm running stock cast flat top pistons, headers, twin 2" SU and I have 2 wide band a/f gages, one in each collector. It seems like I am compromising max power to keep it cool, and have been having no luck at keeping it below 1300 WOT at 6k.

By your comments above, it sounds like you are comfortable w/1300 WOT, but you might be getting nervous at 1400? In other words, if I can stay below 1300 most of the time and only have a few seconds at the end of a straight getting up to 1400 or so would the motor live a while?

Thanks,
Dave

 

[Spridget64SC]

One thing to consider is the fuel type used. Race fuel and street fuel perform significantly different in an engine. Ran into this many years ago when running 93 street fuel in a 1275 Spridget engine on the track. The street fuel burned so much slower (in relative terms) that the fuel was still burning as it exited the exhaust valve. The paint on the head at the exhaust ports would blacken due to the heat. Especially at the rear port. EGTs were way past 1500. The header would glow red quite quickly.

When we switched to running the lowest octane race fuel available at the track (108 at the time), the paint on the head maintained color and the EGT's calmed down.

If you are using race fuel, then I would consider changing needles to something fatter (leaner) for part throttle, but quickly richens (thinner) at the top end when you are at WOT.

1450 is usually my panic point for Spridget engines. 1350 is comfy all day. Occassional 1400's is something the pistons can usually endure for a number of laps when this condition is something short and followed by deacceleration/cooling into a corner.

The material of the piston, cam design (lobe separation) and the design of the combustion chamber is what really makes the difference in an acceptable number.

HTH,
Mike Miller

 

[red57]

Thanks to both of you. This really helps.

Mike, I think you hit on a big factor - gasoline. Because I drive it to the track (and camping trips, etc.) I have always run pump gas and I was wondering if that is contributing to my high temps. I'm thinking of bumping the spark from 34 all in to 36 all in just to see if that helps. I've got a race next week and I may have to break down and buy some high dollar gas....

Anyway it really helps to hear some real-world experiences, thank you again.

Dave Phillips

 

[Michael Oritt]

Dave--

I have the Westech dual analog guage on my Courier (MGA engine) and as Hap commented I glance quickly at it rather than read it precisely, but temps run about 1250-1300 at WOT.

I'd be concerned about washing the oil off cylinder walls at the mixtures you mention. I don't know whether the effect would be significant but perhaps a colder plug might help reduce combustion chamber temperature a bit. Also you might consider sending the head and probes to Westech to check for accuracy.

 

[Hap Waldrop]

Another to keep in mind with EGTs, not speaking wide band AFR, just EGT, is if you are oeverly rich, you will have raw fuel igniting in the header tubes askewing your readings. I've seen the very thing with a SCCA limited prep 1275 engine, the guy was running way richer needles than I was using on my exact same engine, and he was getting 1500+ readings. We took the car to the chassis dyno, and sure enough it was 1500+ but the AFR ratio showed way rich, the car owner just could not digest that he was too rich, plus the car was missing up in the upper rpm range. I put my carbs on his car and all was good, so I set his carbs with the same needle and jet setting as my carbs I was running, and got almost the same exact readings, and he was good to go.

AS for 1400 degrees, I got a vintage MGB I do the engines on running twin HS6s, the front carb no matter how darn rich I get it seems to almsot always read 1400, but the plugs look good and the tailpipe is a nice grey, we'll have a wide band AFR gauge for the next race , so we have two readings to look at, but thus far the car is running great and he's the fastest MGB everywhere we gone so far, so I've not lost alot of sleep over the front carb being 1400 FWIW.

As for fuel, it's funny thing, I'm guess if you drive the car on the road the compression ratio is 10.0 to 1 or lower, so unleaded premium would be your best fuel to use, higher octane leaded fuels at street CRs would actually lower your HP, race gas actaully burns slower and produces less energy in street going cars with steetable compressio ratios, but the higher oactane lower engergy fuels actually does wonder as CR rises, but a waste in lower CR engines. Lower octane unleaded fuels, burn quicker, and hotter (thus the need for hardened exhaust seats in our old engines) but prodcue the most HP with streetable compression ratios. With that being said I've not seen alot of difference in tuning a streetable performacne engine on unleaded premium vs a race engine on leaded race on the chasss dyno, of course they are needled and jetted differently and are different animals, but they seem to tune the same on the dyno, in other words I've not seen extremely high AFR numbers that could not adjsusted down on the street engines on unleaded gas.

 

[red57]

Michael, I agree, I worry about washing all the oil away - OTOH I am getting fed up with melting things....And I have been trying some cool race plugs, but they don't seem to have a big impact on my egts and they foul easily.

My EGT system isn't from Westech - Mine is made by Aerospace Logic, Inc. in Ontario Canada. It is aircraft certified and their literature says the gage "has been software calibrated and never needs recalibration". It also says "Every reading you will see displayed on your instrument has been validated at least 256 times before you see it. This all happens in less than a second. When you see the result you know the instrument is functioning correctly as it is monitored by an independant microprocessor just to ensure that it is functioning correctly. In turn the main processor validates the independent monitoring processor. Any failure detected in either processor and your instrument display will be shut down or an error message displayed - depending on the failure status"

Sounds good on paper, but I am beginning to wonder if the probes themselves can get carboned-up and somehow send incorrect info to the gage?

Hap, Thanks again for the info. It is helpful. You are correct, because it is a street motor I run about 9.5:1 and I agree it will make more power with pump gas. The biggest problem is me, I am sure. Part of my problem is that there are no rolling roads near me and since I cannot afford to pay someone do any of this for me, I bought the egt and the 2 wide band a/f gages so I could do the old fashioned 'back roads' dyno. I live in a rural area and can get away with some careful test & tune sessions. Right now I don't really care that much about peak power/torque - I just want to have a fun weekend without the constant worry of melting something.

I am about to go back to using the wide band a/f and plug cuts and ignore the egt - you all are right, it could be too rich, it could be the fuel, it could be the cam design, could be the porting work a fellow did for me a couple of years ago where he opened up the exhaust ports a bunch, could be ignition timing, could be that the car is red for all I know. I do tend to think it has to do with fuel still buring in the header and the chambers may well be lots cooler - I say that because the plugs are black with a soft sooty look even though the egts are high.

My head hurts with all the what-if/could be scenarios I have whirling around in there. So, it's quitting time and I think I'll have a cold one and go make another set of needles to try.....after all, I have a whole week till I leave for my first race this year.

If I ever get a handle on this I will surely share it, again thanks all.

Dave

 

[Hap Waldrop]

Dave, if you seeing rich, sooty plugs after a clean cut at rpm, than I tend to think your problem is the same as the fellow I helped on the chassis dyno.

 

[Spridget64SC]

Sounds to me like "Marketing-speak" for Cold Junction compensation. They use a second sensor to sense where the Type K thermocouple leads terminate and create a "junction" that offsets the temperature reading for the gauge itself. Probably the same microprocessor your dishwasher or coffee maker is using. Most racers don't realize their Westachs are calibrated at 70 degrees F (no compensation) and they need to "adjust" whatever the ambient delta is between the gage location and 70 degrees. In the greater scheme of things, doesn't make that much of a deal as long as you shoot for the 1300-1350 range.

FWIW, the rear EGT read 1400 for two races this weekend. Never could get it to drop to 1350 with jet adjustment. Should have changed needles. Didn't see 1450, so kept racing. Front wouldn't get much better than 1250-1300.

A new set of plugs should look kind of greenish/yellowish where the plating burns off and then a nice light khaki color on the center insulator. Sometimes when using street fuel, the additives will cause a funny color on the metal. But the insulator is the real key. Burned oil looks like little black balls on the insulator.

I'm sure the sparkplug companies have something on their websites that show various spark plug conditions in nice color presentations.

Mike