BroadSpeed vs Downton Cylinder Head

[albino_hedgehog]

So then,
I have been doing some reading and run into a bit of a rut...

Does anyone know the technical machining differences between the Broadspeed and Downton Cylinder Heads?

[mk1]

That is an "almost" impossible question to answer.

The technical specs, valve sizes, port dimensions etc. were in actual fact very, very similar. Both used standard sizes S valves in all their road going conversions & usually used these in most of their race heads too. Although various tricks to fit bigger valves were tried successfully at one time or another by both companies.

The truth is that as far as head design goes, they are ALL trying to do the same thing, get air & fuel in & out as fast as possible. So it stands to reason that both makes of head would look very similar if they have been well developed.

Without seeing the stampings on a head I doubt that anyone could definitively identify one head from another.

[albino_hedgehog]

I figured this would be along the lines of the answer I would receive...


So if someone wanted to recreate one of those heads, what work would they be looking to do?

[mk1]

I cannot see the point in "recreating" a Broadspeed or Downton head unless I was planning on passing them off as original.

Modern heads done by the likes of Brett Simms (still uses Downton / Longman profiles), Keith Calver, SMMC or Bryan Slark are just as good if not better than the heads produced 50 odd years ago.

Remember that Broadspeed had no more than a passing interest in Minis after the end of the 1965 season.

The hardest thing nowadays is finding a 163 head that is in good enough condition to modify.

[66S]

Hi guys,
I have what I am told is the original AEG 163 Broadspeed head from my Broadspeed GT. It passed it's used-by date in the hands of the previous owner and was replaced with a 12G940 that was modified to replicate the Broadspeed build. I cannot locate Broadspeed identification markings, only the standard BMC ones as Mark suggests. I could supply pics if that was any help.

Regards
Al

[mk1]

Hi Al,

It would be very nice & illustrate my point if you could publish some pics of your 163.

[albino_hedgehog]

Very much appreciated!

[66S]

Hi everyone,
Here are pics of the head from my Broadspeed GT. Inlet port diameters are 1.3/8". The outer exhaust ports are 1.1/8" high and 1" wide. The centre port is 1.3/16" high and 1.1/16" wide. The only markings visible are the highlighted "U" at the front and an incomplete "O" at the rear, both on the top face. The seats have been Stellite welded and the rocker pedestal mounts have had cracks welded. Although I don't have the valves, it would appear that the inlets were around 36 mm and exhausts were 31 mm.



I hope this is found useful and look forward to answering any questions.

Regards
Al

[App K]

Valve profile as well as valve size has a lot to do with flow characteristics
This is the inlet valve off my original Taurus 12g940 casting head that's on my 970.

Think I might need a manicure as well looking at the photo.

[rich@minispares.com]

Hi everyone,
Here are pics of the head from my Broadspeed GT. Inlet port diameters are 1.3/8". The outer exhaust ports are 1.1/8" high and 1" wide. The centre port is 1.3/16" high and 1.1/16" wide. The only markings visible are the highlighted "U" at the front and an incomplete "O" at the rear, both on the top face. The seats have been Stellite welded and the rocker pedestal mounts have had cracks welded. Although I don't have the valves, it would appear that the inlets were around 36 mm and exhausts were 31 mm.



I hope this is found useful and look forward to answering any questions.

Regards
Al

good lord - look at that crack!

its definitely scrap.........


(the drive, that is.... )

[66S]

Hi Rich,
If you like looking at cracks, Christchurch (NZ) is the place for you. Bloody earthquakes !!

Al

[mk1]

Thanks for posting those great pics Al! As your head came with your Broadspeed GT & is "a little souight into" I think it is fairly safe to assume that it is an original head.

In comparison, please see these pics of an original stage 1 Downton head that is also definately correct. There are a series of good quality pics in this thread.

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