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I have posted information about my efforts to tune Webers using a Zeitronix ZT-2 wideband AFR data logger at http://www.alfabb.com/bb/forums/carburetors-fuel-injection-air-intake/260689-weber-tuning-lambda-sensor.html
and http://www.alfabb.com/bb/forums/spider-1966-up/304825-79-spider-dyno-5.html

Correct AFR becomes increasing more important as specific engine power (HP/liter) increases. There is a good report on the nasty things that can happen and how they occur at Engine Basics: Detonation and Pre-Ignition by Allen W. Cline. My 2L motor made 169HP at 6200 rpm in April. Since then I have improved the exhaust system and the Weber intakes and the car is noticeably faster now so I may have 180 HP or thereabouts.

Al Mitchell suggested that I add an EGT sensor to establish a safety margin for detonation. The ZT-2 has a dedicated input for an EGT type K thermocouple and I bought one for about $40 - EGT Probe, Exposed Tip [TC-KEGT] - $36.50 : auberins.com, Temperature control solutions for home and industry
I bought the clamp-on style connection that uses a hose clamp. The blurb says that it will fit pipes up to 4" diameter but it does not specify a minimum. I had to make a shim in order to fit it. I selected a socket of similar diameter to the pipe and I found a piece of copper strip in my junk metal box. I softened the copper by heating it to glowing red in a propane torch then I quenched it in water. It was then easy to bend it to the required shape. The first picture shows that. I then mounted it to #1 header about 3" from the flange and drilled a 1/8" hole using the compression fitting as a guide. I then slid the clamp out of the way and opened up the hole to the required 3/16". The mounted probe is shown in the second picture.
I did some runs today. The EGT peaked at just over 1400F at 7200, WOT in 3rd gear. It rose steadily and there was no sudden dip that would be an indicator of detonation. The EGT reached 1350 when I was cruising at 65 mph in 5th up a gradient and the AFR was in the low 14's. That maybe a potentially dangerous situation and I will try richer idle jets to see if the temperature drops with a fatter AFR. I am also thinking about going to colder plugs. I have NGK BP7EIX now and I could buy BP8EIX or BP9EIX. I welcome comments from anyone who has experience with plugs as cold as these.

Many, many years ago I holed a piston in a 500cc Velocette motorcycle when I was cruising at 80 - 90 mph on the M1 in England. The most likely cause was detonation induced pre-ignition. I retarded the ignition a bit and it did not happen again. I don't want to do the same to my Spider motor.
 

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Hi Ed, interesting stuff. As you say, the correlation of EGT to AFR is important and relevant for tuning and avoiding pre-ignition or detonation. Absolute EGT is not that important, as it changes relative to altitude and distance of probe from cylinder (~100F per inch?). The change of EGT from peak EGT is the important thing. From memory, peak EGT corresponds to stoichometric, i.e. 14.7:1 AFR. Peak power occurs about 50F rich of peak, so should be about the 12.5:1 AFR as quoted for max power = peak cylinder pressure. Detonation is most likely near this EGT, anywhere 50-70F rich of peak. I guess the problem is when after max power we are naturally right near the detonation zone! In aircraft the rule of thumb is if below 65% of max power no destructive detonation can occur, so you can lean as far a smooth running will permit. If you go to https://www.flickr.com/photos/[email protected]/ you will find a graph showing the relationship between fuel flow, EGT, CHT (cylinder head temp), BSFC etc for an aircraft engine, but I don't think the physics changes for an Alfa! Temperatures etc will be relative, not absolute, just the relationship is of interest (I just added an air fuel hook graph also).
Note that lean of peak EGT the cylinder pressure and temperatures also drop, so the risk of detonation goes away.
The response time of the EGT may not be quick enough to avoid detonation or pre-ignition dmage. I think you will 'feel' it first.
I guess this is why knock sensors were created!
 

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ALF750 is correct, the latency of an EGT probe makes it pretty ineffective for instantaneous tuning purposes.

It will however help, if you have installed EGTs in each primary (close to the flange is better) tell you if you have a misbehaving cylinder if you are only using one AFR in the collector.

I had the good fortune of participating in an engine building program, over a three year period, wherein we used 10 AFR meters (one in each primary and one in each collector) and 8 egt probes (one in each primary). It was not unusual to do 200 dyno pulls over a weekend. Other than letting us know when we had an ailing cylinder, the EGTs we're not used for any tuning purposes. The AFRs provided timely and more valuable information. This was an engine development program for an engine competition wherein a couple of horsepower over the prescribed range could mean the difference between winning and not even placing.

Perhaps I can learn something from your experience, how are you able to determine that a detonation event has occurred using EGTs?

Thanks
 

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As to the question of sparkplug heat range designations. They have nothing to do with the heat of combustion. The designations have to do with the plugs ability to absorb and transmit heat to the cylinder head.
 

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Something to keep in the back of your mind is the effects of ignition timing on EGTs. As the timing is retarded, EGTs go up and that's regardless of AFRs.

Low 14's AFR when cruising. I'd be happy with that. But that temperature is worrying! If you had proper 3D ignition timing control, I'd suggest advancing that/those rev/load point(s).
 

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From memory, when detonation occurs the CHT will spike and the EGT will fall, as all fuel is burnt/detonated earlier in the compression cycle and the heat absorbed by the cylinder. Thus less energy/heat is left in the waste gas by the time it goes out the exhaust.
I'm not familiar with how ignition timing affects EGT, as most aircraft engines have fixed ignition timing (magnetos) optimised for the maximum power condition (20-25 BTDC, but I've heard reliably that ~28 is best for max power, so I assume the manufacturers back it off a bit to be conservative).
I fitted electronic ignition, which varied the timing dependant on load (via manifold pressure) to to my aircraft and did not notice a change in EGT at max power, but EGTs fell at low power settings. My reasoning for this result was at max power the EI default was ~26BTDC, the same as factory timing. At low power settings where the spark was advanced (max ~40BTDC), the slower burning lean mixture had more time to burn completely before going out the exhaust, thus lowering measured EGT (keeping peak cylinder pressure ~3degATDC or where optimum?). High EGTs are often caused partly by unburnt fuel going out the exhaust valve and continuing to burn in the exhaust - think diesel and smoke, which correlates to unburnt fuel and high EGTs.
Don't hold me to some of these numbers, memory sux sometimes. ciao
 

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Discussion Starter #7
My concern about spark plug heat range is I don't want a plug to be a source of pre-ignition. If NGK 8's or 9's will not be too cold for a road motor then they will give me some extra safety margin.

My ignition timing is 34 BTDC, all in at 4000 rpm. This was determined by dyno testing. Less advance made less power and more advance made the same power. I don't plan to change it. AFR was 13.2 at max power on the dyno. My tuning since then has attempted to maintain similar AFR's in the power region as I modified the exhaust and Weber intakes.

When I look at my EGT plots they follow rpm very closely, whether I am at part throttle or WOT. The thermocouple is 2.75" from the head.
 

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I use 8's in my Alfetta with standard engine and it seems OK. However the other Alfetta with 10548 cams and who knows what internal work has 5's as purchased!
Wonder what best power ignition timing is on the twin spark engines, I imagine it is less than 34 for single spark.
EGT probably correlates better with load, but in a car that is approximated by RPM at a constant MAP (WOT accelerations).
Great to read your findings.
 

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Discussion Starter #9
Interesting data

I had (wrongly) assumed that the highest EGT readings would be at WOT, full power, high rpm. Mine read a little over 1400F under those conditions. Yesterday I logged data when cruising at 80 mph in 4th and 5th gears. The temperatures in 5th were similar to those at WOT. 80 mph in 4th in my car with a 4.55 axle is 5200 rpm and the EGT's were about 1520 with AFR's about 14.5. I installed smaller air correctors; was 170, now 150 and did some more runs. They made a small difference . I then put the 170 AC's back in and replaced the 150 main jets with 155's. The EGT dropped 100 degrees and the AFR dropped from 14.5 to 13.5.

My next step is to do WOT runs with this configuration to see how it has affected the AFR at full power and the acceleration times.

I have also ordered a set of NGK BPR8EIX plugs which are one step colder than the ones that are in the motor.
 

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It would be interesting to see what timing changes would do.
 

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It would be interesting to see what timing changes would do.
I don't plan to do that. I optimized the timing on the dyno. It makes best torque and power at 34 BTDC. Less advance = less power. More advance = no more power.
 

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Didn't know that, good enough.

So you've removed any advance mechanism? Its a fixed amount?
 

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Discussion Starter #13
Here is the curve that I am using:
 

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Thank you, Ed.
 

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Many, many years ago I holed a piston in a 500cc Velocette motorcycle when I was cruising at 80 - 90 mph on the M1 in England. The most likely cause was detonation induced pre-ignition. I retarded the ignition a bit and it did not happen again.
I bought a Ducati 350 desmo when I couldn't find a Velocette anywhere in Texas. It was very good, but not the same. How could anything compare to a bike built in a cave, with a 30's fishtail exhaust and a generator belt intentionally intended to slip a high speed? But, I digress.

For reference: In one of David Vizard's books on building performance engines he mentioned that Otto cycle engines all have a detonation/preignition period at about 2400 rpm. I don't recall whether he was talking about just detonation (doubtful) or preignition (probable) or both? When I built my Alfetta engine back in the day I theorized that the 10.4 Borgos would find the 91 octane gas problematical. Sure enough I got some pinging at that 2400 rpm point under load. Vizard also talked about the (then) new MSD6A ignition as being better able to fire a charge in an open chamber, i.e., hemispherical, head like an Alfa's.

I extrapolated his two ideas and theorized that the MSD's powerful, long duration spart might better control the flame-front in my highish compression engine running on lowerish octane gas. Long story short, it worked! With the MSD on the same build, the pinging disappeared.

I never quite understood whether I was hearing preignition or detonation, however.

Re: spark plugs. A old-school Alfa Owner from the late 50's recommended Champion N-5 plugs (for town) and colder N-4's for highway driving. Now granted, Champion N-4C's lack the cachet of more exotic brands but they are commendably cold plugs. I've found that their heat-range works well with Alfas, showing nice color when doing plug-cuts.
 

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I bought a Ducati 350 desmo when I couldn't find a Velocette anywhere in Texas. It was very good, but not the same. How could anything compare to a bike built in a cave, with a 30's fishtail exhaust and a generator belt intentionally intended to slip a high speed? But, I digress.
A 500 Velocette Venom was the first bike ever to average over 100 mph for 24 hours. One of the riders was the managing director of the company. Legendary, not "built in a cave".
 

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Increasing the main jets from 150 to 155 lowered the EGT at 5200 in 4th gear by 100 degrees F but it also made the AFR too fat in the high power region so I replaced the 170 air correctors with 200's. The result is good. The high cruising speed temperatures and AFR's have changed very little and the high power AFR is right where it needs to be.
I did a rolling start 7 - 100 mph pull in 21.5 seconds up a gradient of about 2% which I think is very impressive for a 2L Nord motor running on pump gas. The EGT at the top of the pull - 6800 in 4th was 1420 F.
 

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EGT location

Hi All,
I read through and may have missed if anyone cited the "proper" cylinder to tap if you only have one probe.

Personally, at least back in my day, we probed the rearmost cylinder. This was typically for street cars. The thinking was that the last cylinder would likely run a little hotter overall, and indicate, "hopefully", a high baseline to judge the others.

?
KJM
 

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EGT's are much higher than engine temperatures and I think that the variation between cylinder temperatures will have little effect on EGT's. I installed mine in #1 cylinder because it was easiest to get to.
 

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Can I ask why you drilled another hole when you clearly have removable bungs in the exhaust headers, an adapter bung would have allowed you to move the probe around
 
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