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TR4/4A Spark plugs, what do you use?

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Simon TR4a

Simon TR4a

Jedi Knight
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I had noticed the car running on a bit after turning off the ignition, so felt it was time for a tune up, carb adjustment, plugs, air cleaners etc.

I took out the plugs, which looked a little rich on the two front cylinders, but about right on the back, and found they were NGK BPR6HS. Why I would use resistor plugs when I have no radio in the car I cannot imagine, but anyway, I changed them for a set of B7HS, on the theory that the cooler heat range and shorter centre electrode and insulator would solve the problem. (I had filled up recently with 91 octane instead of the 94 octane I usually use, and this may also have contributed to the problem.)

The plastic container I use to store feeler gauges, used distributor rotors and such also had a variety of used spark plugs- Champion L87Y and L82YC, and various NGK, including some weird long reach plugs which may have been for the Spitfire when we had that. For a while I had been using an electric fuel pump and Holley pressure regulator, and had not been able to get consistent mixture, so had done a lot of plug readings and since they were almost new, I kept the plugs.

So I am interested in what plugs you have found work well, particularly with some performance upgrades?
 
Hi,

I have a TR3a with a TR4a engine. I have run the NGK BPR6HIX Iridium plugs for 3 seasons without issue. The rest of the ignition is a recurved Mallory distributer, MSD-5A and MSD Blaster coil. I gave up on reading the plugs, I have an air fuel meter. My air/fuel ratio is 12-14 and it runs well. Prior to this I had Champs and they did not like a rich mixture. How the plugs work with a stock ignition I do not know.

As far as other performance changes, the head been cut .030, I have a 4 tube header and a mismatched re-ground cam. The flywheel is aluminum and it likes to rev. Mine would run on until I put the Aluminum flywheel on. It shuts off now!

Roy
 
Roy
.030 cut on the head. What is your compression readings?
 
Hi,

The cylinder compression is 190 -195 psi. That's with a K-D gauge that I believe is correct, but it sounds high to me. I know the cam is strange in the car. It measures 300 degrees, with .350" lift at the valve. That's less lift than stock. All the valves read the same lift. The cam centerline is 119. Cams will change the cylinder compression. Anyways, a cam change will likely happen over the winter.

Roy
 
My car has nearly 100 thou off the head, I had to get shorter pushrods from Ken Gillanders to restore the correct geometry in the valve gear. Also though, I removed a huge amount of material from inside the combustion chamber to unshroud the valves and radius the curved edges. My static compression ratio is 9.7:1, and the Kent cam has 290 degrees duration, 310 lift at the lobe with the stock rockers which I think have a 1.43 ratio.
I have not used expensive platinum or iridium tipped plugs as I feel the longer plug life is not important for the mileage I drive the Triumph.
 
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