Tuning with IR Gun

[Steve Proctor]

In a discussion of carburetors, David Jones mentioned that he uses a heat gun to tune his carburetors. I use one as well, basically shooting for about 400* where I can measure on the exhausts. I think the 356 offers some challenges for this method because it is hard to find a place where the distance from the exhaust port is the same with heater boxes in place and am curious what others using this process have found.

* What is an acceptable temperature range from cylinder to cylinder?
* If too far off, how long do you have to wait for the temps to equalize after an adjustment?
* Where do you measure?
* What is a good temperature for that measuring location?

In my case, there is a wild card, as my exhaust is ceramic coated, so believe my temperature measurements will be lower. That said, with target temperature known and assuming a methodical and systematic idling adjustment, it would seem that temperature measurement would be an ideal way to set and verify idling mixture volume.

STP

[David Jones]

You are correct Steve, there are challenges unless the engine is out of the car and you can measure the temp on all four at the same distance from the manifold flange. With engine in the car I compare side to side and combined with the synchrometer it works well for me.

[Wes Bender]

Tuning to balance temperatures is something I've been intending to try on my 356. Keep us posted, Steve. When I had M-B diesels, I used to adjust the injection pump (much to M-B's horror) to obtain mostly equal temperatures inside the combustion chambers. I used the glow plugs as thermocouples. Because they contained two dissimilar metals, they produced a minute voltage that increased with cylinder temp. Had to calibrate them by rotating a new glow plug through the system to obtain a correction factor for each glow plug, but I got the results I wanted. Interesting concept and it worked rather well. Of course, M-B didn't like the idea much........

With the 356 I would like to try cylinder head temperatures, using aircraft technology.

[David Jones]

Wes, I tried using TC's under the spark plugs on the F Vee but found egt's worked better. Of course all I was interested in was wide open throttle readings so I did not run too lean and fry the engine. Either way you have to run a thermocouple wire back to the cockpit and if you want to monitor all the cylinders you obviously need 4 pair of TC wires and the a gauge and the a switch. Too much trouble for me I'm afraid.

[Dave Wildrick]

That all seems too complicated.
I like Jack Staggs method of adjusting each mixture screw separately until you achieve the same rpm drop at each cylinder when you lift the distributor terminal wire for each cylinder one at a time. (motor warmed up and carb down rods disengaged of course).
When the rpm drop is equal for each cylinder, balance should be reached.

[Chuck Allard]

I ran thermocouples under the spark plugs and two EGTs back in the '80s. Now I use wideband CO readings as a race car tuning method. For customer engines, I use an IR gun on a test running stand to help dial in the carbs where I can shoot right at the exhaust ports. On an engine in the car, I get two different readings since I can't "see" the exhaust pipes at the same distance from the ports. 911s are much easier since you can "see" each pipe at about the same length from the port.

[Steve Proctor]

I like that RPM drop method as well, Dave, but who doesn't like to mess around with technology? 8)

[Wes Bender]

I have one EGT TC and an accompanying gauge left over from my B-47 Crew Chief days (don't ask how long ago) but I think it would take too much fiddling to get an EGT TC installed in each cylinder's exhaust, although I'm sure they're available surplus. When I get back down from my 8000 ft summer digs, I think I'll give Jack Stagg's method a try. The gain that I think I'll get is probably going to be pretty small. Balancing with a Synchrometer and with well-adjusted linkages has my car running pretty well. Steve, retirement allows a lot of time for messing around with technology.

[Martin Benade]

The old Hungarian guy that got me hooked on 356s in the early 70s used the rpm drop method. He did very well with it.