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MG TD TF 1500 - Porting the head

The engine is in the shop. The guy I use is very, very good and specializes in race-tuning.
I'm not looking to turn my MG into a demon, but I do think that porting the head to improve gas flow would be a good idea. So I'm going to talk to him about porting the head and maybe microfinishing it.
What should I make sure NOT to do?
Geoffrey M Baker

Do you have inserts installed for your exhaust valves? That would be the primary focus at this point.

Since you're replacing your valves, now would be the time to make the jump to the larger valves. One reason I went larger, is they then grind virgin metal for the intake seats, rather than have to excavate deeper down into the old, pitted seats. They've been ground a couple times before and the valves don't all sit at the same height. Also, I needed to go to larger exhaust inserts to clean up one ugly one. You basically aren't going to notice any vast improvement in power, but you can brag a little.

If your seats are fine and you already have the inserts, I wouldn't bother with the upgrade.

Other than larger valves and enlarged ports at the seats, porting would be a lot of work for very little benefit. I saw a lot of ugly casting surfaces in the ports but didn't bother cleaning them up.

The best investment for performance and longevity would be to consider a roller lifter cam package. Putting your pennies in those parts would be the most bang for your buck and eliminate worn lifter syndrome in the future. Oversized valves, porting & polishing might gain your 1 or 2 horsepower. The Mark ll had the larger valves AND larger carbs and only got about a half dozen horsepower.
JRN JIM

Attached is a photo of the head I did.

The seats have a 3 angle grind and it was fitted with larger valves. The wall of the combustion chamber was ground to make space the airflow near the edge (I hope I'm clear with this explanation).

I have read that the XPAG ports shouldn't be enlarged too much and that the XPAG benefits from the whirl effect caused by the rough casting. So don't go overboard.

Willem van der Veer

Here's the 3 angle seat and you can see I removed the sharp ridges left by the machine work in the combustion chamber.

Willem van der Veer

And of course I couldn't leave the inlet separator untouched, slimming it down a bit and streamlining it. It is a bit hard to see in this photo but I haven't got a better one...

Willem van der Veer

When you talk about larger valves, I assume you are referring to the ones Moss sells that are intended for a TD MKII and are 34/36mm in size? That does seem like it might help the head run cooler and smoother...
Geoffrey M Baker

Not sure porting will help much with a stock engine. Do check the intake manifold to head joint- just loosely assemble and check for a ledge or overhang from one to the other. I had to replace my head a few years ago, and there was a significant ledge in several places at the junction. I have also run across manifold gaskets that really intruded into the air flow.
George Butz

Geoff, this is the head for my TC special, almost exactly the same as on my TF.
It will be cleaned up and surfaced, new valves and guides, 36/34 mm.
The TF runs 9.3 cr with 1 1/2 SU's and a mild cam.
Regards, Don

D J Walker

Geoffrey, The modification that Don's head shows (tapering or the block between the intake), is an easy one. Smooking the intake at the same time is another one you can do.
Bruce TD4139 Cunha

I do not recommend polishing the intake ports as this will cause fuel to puddle at lower rpms, The casting acts to vortex the air fuel mixture on the rough surface and aids in keeping the fuel atomized past the carburetors. Only on a high revving engine should you worry about porting. On a street engine that will rarely see rpms over 4500 you will suffer low and mid range response jmho

Regards

Bill Chasser Jr
TD4834
W. A. Chasser Jr

This thread was discussed between 28/03/2015 and 29/03/2015

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