Some Heads are about to Explode!

[MALAK]

We always see threads about overheating, radiators, 2 vs 4 blade fans, effects of engine pans, GAV adjustment, what thermostat temp to run (if any), etc.

And then there's the #4 cylinder running hot thread. What does that even mean? I've seen the effects but never quantitative data saying how much hotter it runs.

With all this there are many opinions, some with corroborating data, most without.

I set out some time ago to quantify some of this data. So with a couple current threads going on about overheating/radiators I thought I'd post this to titillate those who might find it interesting.

I've added a data logging system to one of my A's. Currently logging Lambda, IAT, MAP, Ambient Temp, Engine Inlet (coolant) Temp, Engine Outlet (coolant) Temp, and Throttle Position. Ultimately I will be adding individual cylinder EGT, and a coolant temp sensor in the block behind cylinder #4.

My ultimate plan is to test the various things noted above on a triple digit SoCal summer day, then also during less severe conditions.

I've already found some interesting things: for instance my A experiences a mild stumble, right off idle, when accelerating from a stop. Initially I thought this was a lean stumble since the Zenith doesn't have an accelerator pump. Looking at the data its clear this is actually a rich stumble condition. The carburetor is rebuilt and I've checked the float level several times. I hypothesize the stumble is caused by the cap and main jets filling up during idle and the sudden rush of air when the throttle blade is opened draws the fuel out of these 2 jets down to their running level causing a short, but noticeable rich condition. So I may play with float and jet settings as well. The car runs fantastic and the stumble doesn't cause any drivability problems but I do notice it.

A couple other interesting things noted are: there is a sharp increase in IAT after idling. I suspect this is due to heat soak and lack of air flow from the fan and currently the car doesn't have pans. I'm thinking pans may help this but I'm gonna find out.

In the near future I'll be adding the EGT's using a plate between the manifold and block and a coolant temp senor located on cylinder #4.

Finally, with the Lambda probe (wideband O2) I've installed a mixture gauge on the steering column. I find this gauge very useful for adjusting the GAV.

[BN]

Very interesting Makak. Looking forward to seeing more results and interpretations.

[Jacksonlll]

Don't forget the wind speed and direction when at idle.

[MALAK]

Some pic of the install so far.

[MALAK]

Originally Posted by Jacksonlll

Don't forget the wind speed and direction when at idle.

And accelerometers!

[GPierce]

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I don’t have pans either. Looking forward to the data for IAT and cooling after you put the pans on.

[California Travieso]

Malak,

Pardon my ignorance, but what are Lambda, IAT, and MAP?

David Serrano

[MALAK]

Originally Posted by California Travieso

Malak,

Pardon my ignorance, but what are Lambda, IAT, and MAP?

David Serrano

Lambad is a way of expressing the air/fuel ratio relative to stoichiometric.
value = 1.0 = stoichiometric
value < 1.0 = rich
value > 1.0 = lean

IAT = Intake Air Temp = The air temp entering the carburetor.

MAP = Manifold Absolute Pressure. Can be expressed in Bar or PSI. This is relative to atmospheric pressure so at idle the pressure is low (what we'd call a vacuum) and the more open the throttle is the closer to atmospheric pressure it is (low vacuum).

[Kurt in NJ]

The position and size of your iat can cause change in airflow over the jets ----- just as movement of finger around airmass on modern car can change mixture---

I ran my car on the inspection dyne to see how different gav settings worked--- and I used "Honda civic "as test car entry--- they didn't have model a in the database, kept upping the year till it failed, got to 2005 then nox got too high, ran it in 2nd gear up to 3200 rpm

When you are done with the sensors you will be close to setting up for efi--- but I still haven't found a system that works with 6V+ grounding

[MALAK]

Originally Posted by Kurt in NJ

The position and size of your iat can cause change in airflow over the jets ----- just as movement of finger around airmass on modern car can change mixture---

I ran my car on the inspection dyne to see how different gav settings worked--- and I used "Honda civic "as test car entry--- they didn't have model a in the database, kept upping the year till it failed, got to 2005 then nox got too high, ran it in 2nd gear up to 3200 rpm

When you are done with the sensors you will be close to setting up for efi--- but I still haven't found a system that works with 6V+ grounding

I initially hesitated (questioned myself) about installing the sensor in this position, for that very reason. I considered installing a short tube upstream of the choke with the sensor in it but that too can affect carb's operation. So I opted to just try it and see how it worked.

I agree with what you're saying but the hesitation I detect occured before and after I installed the IAT sensor. I didn't notice any difference in performance after installing the sensor.

[MALAK]

Some more install pics.

Sent from my Nexus 9 using Tapatalk

[SAJ]

That is pretty neat MALAK. I put an exhaust gas thermocouple in the manifold between 3 and 4 because I had almost-burnt exhaust valves when running plugs a light grey colour. I did not see any difference in temps when adjusting the GAV at top speed up very long hills. I am overseas in UK at present, away from my data, but I think I saw peak exhaust temps of over 800 deg C. and nothing to suggest altering mixture or ignition timing from where it ran best actually lowered valve temps. Running retarded did increase manifold temp though, as expected.
I will follow your results with great interest. In particular I notice jerky motion in first and second gears at low speeds in both my cars running B carbs and Stipe IB330 cams. GAV and ignition settings do not cure this and most, if not all, borrowed cars do the same thing on A carbs too. I flow tested and adjusted all jets and run with light grey plugs (full speed plug chops-I have not checked plugs at low running speeds). I would love to fix this jerky running phenomenon. Maybe your results will lend a clue?
I think you may dispel many myths and settle once for all questions like stalling on quick stops where most say lower the float to cure a rich stall but many still say raise the foat or richen the idle screw. With a B carb pivoting the float "across" the car, I do not have this stalling problem.
I run a large KandN filter with no inlet pressure balancing and return 22 to 24 imperial mpg too, so here is another question about air filters you may answer very definitively.
Thanks again for doing this most interesting investigation.
SAJ in deepest Cornwall at present