Unleaded cylinder head - page 1

I have been thinking for some time now how to improve the performance of the Coupe and as you will know by now, I have been buying some carbs and an extractor exhaust to facilitate the improvements.  At the same time, old fashioned leaded petrol is well over 1.10 per litre (April 2005) and Lead Replacement Petrol being phased out locally, the time had come for an unleaded head conversion.  My plan was to whip the head off at the same time that I set about the carbs and exhaust.  Out of the blue, I had the opportunity to acquire a Morris 1800S head in a complicated deal involving a Wolesley 1500 and sourcing some rallying parts (I'll say no more).

Those of you with an anorak mind like mine, will remember that the Austin/Morris 1800 "Landcrab" ran essentially the same engine as the MGB and the Marina, but in a transverse position.  Well it turns out that to improve that cars' rather sluggish performance, BL improved the shape of the combustion chamber so that the engine was putting out about 5-10 bhp more than the equivalent MGB and this is what I have got hold of.  It is also the 'big inlet valve' version like my existing Marina head.

This is what it looked like when I picked it up.  It had been in store for a while but looked quite sound on a visual inspection, no obvious cracks or chips in the valves or seats.

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What to do to it?  Well being the sort of chap that I am, I thought that I should find out what was recommended for B series heads.  I came across this book on Amazon and had a good read.  "MGB 4-Cylinder Engines for road & track", by Peter Burgess and published by Veloce (ISBN 1-903706-77-7 or UPC 36847-00277-0).  It covers every aspect of tuning the engine, not just the head.

The options seem fairly straight forward; hardened steel valve seat inserts, open out the exhaust throats, 'bulletted' phosphor bronze valve guides, three angle cut narrow valve seats and gas flow the backs of the valves.

I realised that this work was beyond my abilities, so who to use?  I could send the head away to Peter Burgess, who wanted about 450 + vat, and I can't afford that, it's more than half the price of the car.  Several local friends recommended T&L Engineering, who are in my town (Bedford), as having done good work.

I telephoned them for a chat, to see if we were on the same wavelength.  We were,  I described what I was trying to achieve, agreed a price and they came and picked it up, together with some copies of the drawings in the book.  I dealt with Barry (one of the owners), good bloke.

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The 'bulleted' valve guides need some explanation.  To support the valve stem, the guide sticks out into the inlet and exhaust airflow, this acts as a block to the flow, so you have the end of the guide tapered, so that it presents less of a restriction.  The one on the right of the has already been done.

I wanted the restrictions in the exhaust port to be reduced further by grinding away some of the meat around the valve guide.  The sketch below gives you some idea of the effect in the exhaust port. 

I also asked for the valves and valve seats to be cut at three angles as shown below.  This creates a much narrower valve seat and hence allows the gases in and out more quickly.  In the sketch below, you can see that there is a slight lip on the back of the valves, this causes turbulence particularly on the inlet valve, so that had to go too.

 

This is what I got back from T&L, I was really impressed, really nice job, the pictures don't do the work justice.  Now all I have to do is build it up and fit it.  I shall run it initially with the single carb, as I have yet to clean up the inlet manifold and the heat shield.

 

click on picture to enlarge  click on picture to enlarge

Now read on:- Page Two