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TR4/4A Exhaust Manifold Temperatures

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RJS

RJS

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Hi,

I may be looking for trouble but, just for fun I pointed the infra red thermometer at my exhaust manifold at idle after a drive. I was quite surprised at the variation. Cylinders 1 and 4 were cooler, in the low 500*F. Cylinder 3 was probably 550*F but, cylinder 2 seemed hottest at 575-610*F.

Any thoughts? Good, bad, nothing to worry about?

Bob
 
RJS said:
Hi,

I may be looking for trouble but, just for fun I pointed the infra red thermometer at my exhaust manifold at idle after a drive. I was quite surprised at the variation. Cylinders 1 and 4 were cooler, in the low 500*F. Cylinder 3 was probably 550*F but, cylinder 2 seemed hottest at 575-610*F.

Any thoughts? Good, bad, nothing to worry about?

Bob
Click to expand...
1 and 4 on the outside?
 
if you have looked at the block and how the water moves from the pump into the block, you will see there is no internal control of the flow direction. The head water passages control where and how the water goes. A single hot cylinder may indicate a vaccum leak (lean condition).
R
 
Thank all. I'm going to let the differences in temp b/t cylinders go. The car runs top notch in every other way with no other signs of a vacuum leak or other issue. TBH, I am trying to track down high under hood temps when idling stationary or in traffic. Water temp rises a bit but, within acceptable levels. But, what happens is the fuel in the float bowls percolates which leads to rough running and (eventually) dying.

I suspect the exhaust manifold is throwing off a lot heat due to ignition timing issues (not advanced enough) combined with running E10 gas. I've never adjusted my timing from when she was originally set at 4* BTDC static. On top of that, I recently tested my vacuum advance unit and it is not advancing as it should (it comes in eventually, just later than it should - I've read that the rubber diaphragm inside the vac advance unit can become hard and brittle over time and reduce sensitivity - mine is original from 1966). At idle, the vacuum unit should add another 6* of advance - so I am 6* "under-advanced" at idle.

On top of that, I understand the 4* BTDC was super conservative by Standard Triumph in order to accommodate all the poor quality gas available around the world in 1966. Many say the Triumph TR4A can handle 10* BTDC static based on top quality "super" gas available today.

This is a very long way of saying that if I set static advance at 10* BTDC and have my vacuum advance unit rebuilt, I will be adding 12* of advance at idle with will/ should reduce exhaust manifold temps and under hood temps. The theory goes that late timing at idle starts the combustion process late enough that unburned fuel exits on the exhaust stroke and continues to burn in the exhuast manifold - drivng up manifold/ under hood temps.

My plan later this summer is to have my distributor & vac advance unit rebuilt so they work properly, and then reset my ignition timing to 10* BTDC. I'll let you know if this helps and exhaust manifold temps come down at idle

Bob
 
Hi Steve

Right now, at 4* BTDC static, she idles at 650RPM. Not planning playing with this until later this summer. As you may have seen from my other post, the oil pan is off right now for repainting and re-sealing. I suspect once I advance the timing, the idle speed will rise and I'll have to adjust it back at the carbs.

Bob
 
EGT is an indicator of the cylinder mixtures. Higher temp would be a leaner mixture. What you are seeing is why all cars now use direct injection. With carburetors you cannot get even mixtures for various reasons. What's more, you are limited in power by the leanest cylinder, meaning one is working optimally,while the other cylinders are various amounts below optimum power.
 
Thanks Mad Dog
Great advice. Thanks also CJD. Plugs look slightly light white. May need to richen mixture a flat or two.
These are completely minor issues as car runs great. My problem is I cannot stop tinkering. I need to simply drive more and stop fiddling!
Bob
 
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