Here we have some development work done to the Mk2 Spitfire head, which as we know is almost identical to the Herald 948 & Standard 10 head.

Some of this work was typically shown in the Triumph Tuning handbook of the late 1960s.
We didn't set out to replicate this kind of work but start with a clean sheet & take a look at what they recommended some time after.

Basically that involved being a bit more scientific than the crude stuff of 1964-66.
We took a brand new rusty NOS cylinder head, so no need to mess with the guides, but needed plenty of cleaning up.

Here is roughly how they look. To give you some clue, the really Early 850-950cc engines had even smaller bores that 69.5mm but the same stroke of 76mm so proportionately the chamber had to be shrunk a bit & all compacted.

As far as the rest is concerned, all the valves & rockers stayed in the same places, the head studs also, so the 1147cc engine was the ultimate version of the 1950s Standard, c/w with all of 60bhp DIN instead of about 25.

The works were claiming 100-115 from the 8 port Le Mans engines.

Being as I have BOTH original works camshafts in for analysis, I can assure you this was pure fantasy.
More like 95-100 would still be optimistic.
Here is one on a froude dyno back in 1964 for a bit of Nostalgia & co.
Maybe they were trying the famous 60-80 "hammer" cam on there, the one that gave almost no torque before 5500rpm and no power after 7400rpm!
We tried to set out to see if we could struggle it up way beyond anything they could imagine in 1955, or even 1964 or 2011, and of course that involves a certain amount of artistry on the hot end.

What immediately seemed obvious was the relatively conservative valve sizes of the original engine.

This involved much peering into ancient parts books and use of a vernier depth gauge and micrometer.
It appeared at first view, the engine had some weird stuff, whereby the exhaust valve had been stuck smack in the middle of the chamber while the inlet valve was confined to a corner of solitary confinement! The larger the inlet valve the less flow you will get, because it's so close to the chamber walls.

Here is a nice close up of the 8 port thing thanks to Leon.

What were they thinking?
From my photos of the 70X competition heads they didn't change this strange feature, which meant, the exhaust breathes disproportionately well compared with a thottled back undersize inlet valve.

What does this mean in plain English?
It means the average compression of a 9.5:1 engine is only about 7.5:1.
What we call the volumetric efficiency will be awful.

By my calculations it never exceeds 82% on any of the older conversions, and even with the assistance of a blower* didn't even make 96%!

Stick some awful tiny Solex & a cast manifold on it like they did on the Herald 1200 with 8.5:1 & you get very little power at all, much like they did on the USA Spitfire 1500.

Increasing the size of the exhaust port, we discovered a while back, makes not much difference to the flow of the seat & the final real flow rates.
The 8 port head has a larger exhaust port, but in reality I reckon it makes no difference, as the 6 port head exhaust port flows fine, and we were happy enough just to get it do some more.

If you go take a shot at the whole inlet & exhaust system, you have a thottled back inlet manifold, some tiny SU carbs (not known for great torque at high RPM) & a load of other strange stuff.

So much for the background, here's the sort of thing you can get today.

It's a fat lot of good telling people they used to make an 8 port head, or lots of other exotic stuff like alloy heads, when the people who have it are demanding astronomic prices for stuff which neither worked as well as they claim when new, or is now pretty much worn out old tat.

Hey, this article is mostly about how to get your REAL existing head to outperform any of that old rubbish at a fraction of the price.

Here is a photo of the "competition version" of the 1147cc the 6 port one...

Someone obligingly photographed one and tried to flog on EBAY some months back.
"scuse me chap, but when you decide to increase the valve size on a head, you don't intentionally set out to RUIN it by finding the largest possible valve you can squeeze in there.

IF you do that you will get a heap of rubbish that simply doesn't breathe...
Sigh! Some people you can't tell them anything!

Notice how similar this head is to the other "STANDARD" head, the one they put first on the Massey Ferguson then a generation of TR2-4 cars.

This is not about "design" as such, it's how to squeeze 2 overhead valves into a space.
The TR4 made basically a larger 8 port version of the Standard 10, pushed the inlet ports up into 2 giant casting bulges, then also made the inlet ports too big.
They struggle like crazy in the end, with exhaust ports that don't breathe & the valves being basically in the wrong place in the chamber.

Now we come back to some of the 8 port Spitfire stuff, which thanks to my Italian friend we could take a quick peek at...

This head has been messed about a bit in Italy. I guess they had a good excuse being as the car was designed by an Italian.

The result is clearly no better, but not having had the joy of sticking in on the flow bench I can only guess what happens.

A brief look and you can see the difficulties they had getting 2 head studs to go anywhere useful as they would have ended up in the middle of the 2 extra inlet ports.

With all this we could get some idea what NOT to do.
This meants being extremely careful NOT to increase the inlet valve size by very much, then to find the rest from clever porting.
Everyone else seems to believe completely the reverse, regardless of the fact, the Triumph ports are the bits that stop the thing in its tracks.
Thanks Mr Vizard for never having pointed this out, but there's masses to be gained from short side radius stuff.

As far as we can see, the ONLY possible advantage of the 8 port head over the 6 port is a little bit more top end, plus slightly less charge robbing. This can easily be arranged by keeping the cam duration short, & making the head run better at high valve lifts on the 6 port.
At least we don't have some silly shared centre exhaust port to worry about n'est pas?!
With that big shared inlet port behind it all, it's never going to run out of flow.

TBH I never even bothered to check what would happen if you put some fancy valves in & pushed the head across the top of the block to get the valves in the right places (a la TR4), but I'm sure it gives plenty more!

All things being equal we reckoned the 6 port head would probably give a much better result than the 8 port, because the inlet ports on the 8 port are far too big for such a small engine.

To make things worse, they invariably put really hot timed camshafts in the 8 port conversions, resulting in pretty much zilch torque low down, as you can see from the graphs.

If you also look carefully, you will see the 6 port head has has a much smaller port offset to the 8 port one.
Large port offsets very often result in poor flow at large lift increments because of the very high angle of attack from the port to the chamber.

I have no doubt at all, the 8 port head falls over exactly like the 1300 head does, at anything over 0.420" lift unless there's something very clever done to the ports.

In the case of our modified 1200 head, it carried on gaining flow to 0.500" lift and way beyond.
Roller rockers? Yes of course, the more lift the better on this one!
If you take a little look at a Hillman imp head, which easily makes 100bhp from 998cc, you can understand it all fairly easily. The excellent geometry makes it breathe like a storm at small lift.

Again "sigh!" a case of using some brains.

Golden rule, keep the ports as small as possible, keep the port velocity up, and make sure it doesn't stall at high valve lift,
In the case of the IMP, they reduced the port/chamber offset by inclining the head & the chamber. WIN-WIN.

Here is a direct comparison between the large back cut Mk4 1300 valves and the Mk3 Spitfire valve we opted to put in the Mk2 head.
We gained 1mm. It was all that could sensibly be done, then we modified it in the same way.

Looks tiny doesn't it? More suprising it's an old stock NOS Stanpart Mk3 Spitfire valve!
There's a reason for that photo. We managed to outflow the 1300 8 port large valve head by a nice margin, with those piddling little valves!

Small valves aren't neccessarily bad, so long as the rest works nicely together.

The exhaust ports are ALL much the same, no matter whether they are Herald 12/50, Spitfire4, le Mans or whatever. We opted to take that up just 1 mm also, no more.

The clever bit would always have to be the porting, and of course getting rid of that nasty mass produced manifold by making a really nice hand made one.

Here is an old one off the car.

We opted to reduce down our very successful 1300 design by a pipe size and use the same jig.
The difference is often hard to see, but we know the old factory exhausts had tiny outlet pipes, and mandrel bent primaries.
Do this the old fashioned way, with a highly skilled craftsmen with 40yrs experience in sand bending and you can kiss goodbye to modern stainless steel mass produced creations.
One of these we proved could make 10ftlb more on a 1300 compared with the maniflow one.
This one do doubt makes the same but on 1150cc.

It worked a treat!

Here is now a quick look down the inlet ports of what we did to this little 1200 head. It was quite a pain because there was SO little space in there.

The main mod consisted in substantially changing the divider between the 2 adjacent ports.

We don't need to follow the crap MGB kind of practices, keeping the divider long, because we don't have that yuck messed up Weslake piece of rubbish to worry about the other end.

The clever bit was all about making the right kind of compound angles from the merge thru the short side radii, to the back end of the seats.
I guess if you have to do this stuff in cast iron daily, it's not so bad, but it was an almighty squeeze to get in there!

In the end the options were obvious.
The finished port had to look incredibly similar to a modern 4V port, except it fed 2 cylinders.
In fact, you would be forgiven for thinking you weren't looking into some Renault Clio 16V port....

Some 16V heads like lots of lift, some don't.
We figured the port angle was so wide & open it would look more like a wide angle 4V port, so would need loads of lift, to clear the chamber,- and that hunch turned out to be spot on the money.

Hey look! You can see into the chamber now, just like on the Imp head!
So what did we get from all this?

In short, loads of flow... 36% more.
It's hard to imagine a head where you can get such a huge jump in flow, - using almost the same size valves but there it is.

It's enough to take our humble little 1200 engine up to over 90bhp from around 60, with most of the gain coming from masses more torque, with some extra compression.
In the end we skimmed off about 2.5mm from the head (quite a bit, as that's 0.100"!, so we end up with a VE that's respectably over 90% from 4500rpm up.

Here finally is a Spitfire head on the flow bench.

As you can see it's far from ridiculous. In fact being as most 1300cc "full race" large valve heads don't get beyond 72-73cfm, we thought 68cfm from a tiny valve little 1200 road head was pretty good, in fact every bit as good as an IMP head as you can see!

It's certainly enough for 100bhp, if you felt like going for it. Which do you want? The little 1200?
Or the 1300 version?

Now it's not so clear cut after all?

As you can see from the graph, the original inlet valve scarcely flows better than the exhaust valve, despite the 3mm difference in size.

The little exhaust valve on the 1147, in fact flows as well as the 1300, never mind the tiny exhaust port.

Increasing the exhaust valve size by 1mm & making a decent job on the seat & port, ups the flow yet again to better than most modified 1300s.
That's guaranteed to get the engine to rev!

What is nice is to see is, the huge increase in flow of the inlet valve.
It actually outflows the factory large valve head fitted to the early Spitfire Mk4 and 1500TC by a good margin, but as you expect of small valves wants loads of lift to do it.

Small valves = light valves, so it's no bother really whacking another 3mm of lift on there to get it to work properly.

From here, the next thing was to slice off a big chunk of metal from our Herald 8.5:1 head to get it up to 10:1.
The casting was just about OK to allow us such a big skim, and this contributed to some of the extra flow.

Now it's time to start looking at what the 60s tuning companies were at.

Here are excerpts from the most important pages of Leyland ST manual for parts supplied by SAH.

As you can see, SAH marketed a conversion called "Interim" where they claimed to reach 70bhp with a downdraft weber and a slight increase in compression.

Nothing could be further from the truth.
The conversion could only gain about 2bhp in reality & that only above 4000rpm, so would just about scrape to the 61bhp the engine was claimed to make from the factory.
We integrated our REAL flow figures we got from the flow bench plus the various cam duration and lift figures to get these power figures.
We are rarely wrong.

They did lots of this sort of stuff years ago, making believe you could get loads more torque just increasing the CR without improving the flow. It DOESN'T work.

Here's the curves you get from what they did.
We also included the 513964 head, 8 port conversion with the whole Weber/cam shebang.

Here it was on Leon's car some light years ago, which sensibly used a much milder high lift camshaft.
In this case we were extremely charitable in using flow figures from OUR modified head as a basis to calculate the 85bhp of the graph but using the cam duration & lift from the SAH cam Pt No. 211030, they actually used.

In reality they probably never got even close to those flow figures in 1966, so it was probably not much better than 80-83bhp at best not the 90 claimed.....!

The funny part is, it's what everyone is searching for, for their "works racing cars" today.
As you can see the "8 port works" stuff actually has worse torque below 4000rpm than the little lethargic factory Mk2 spitfire engine.
It's hard, but they managed all that!

There would be a fat lot of anything before hitting that noisy cammy 4000rpm, with a 290 degree cam & only 0.365" lift.
The early webers of 1965 which didn't have adjustable idle flow with mixture, probably gave a pretty iffy idle as well.

They claimed 10.6s to 60mph which would easily be bettered by our car with the torque curve shown in our 2nd graph.
In fact looking at it carefully it's strongly probable it would lop nearly 1s off that figure.... Here are the various mods they suggested from the same booklet:-

As I suggested from the very beginning, we started with a clean sheet of paper, and you can see why.
Here is the result of modifying the 6 port head properly to the spec we managed above doing nothing else to the engine apart from the mods we described then adding a single weber 40DCOE.

Ideally today we would go for a single 40DCOM or a Dellorto DHLA40.
That would bring in all that superb progressive bottom end, without the well known gremlins people get from that rubbish they make in Spain.

The result is fairly shocking because it literally blows the 8 port SAH conversion out of the water at all RPM, using nothing more than a bit of brains, some nicely made bits and retaining the original 6 port head & the original Mk2 Stanpart 212164 camshaft!

We knew we could easily do better than this, because the one thing our nice little new head expects is masses more inlet valve lift.

We might need one of these after all?

As our hybrid cams have turned out to be wildly successful, we set about re-engineering the camshaft timing and a few more tweaks.

Here is the result of doing a cam change to our 25H profile on the same engine.

As expected with this kind of mild duration, you just get MUCH more of the same thing as before.
Again what is shocking is the 90ftlb of torque which it's making now.
It's much better than most modified 1300 engines are making, & actually exceeds the torque over 4000rpm of a properly built/blueprinted long stroke 1500 motor we tested 2-3 years ago.

In view of the very low weight of the Mk1 spitfire, compared with the 1500, we're pretty sure this engine would push the car to be doing a 0-60 time not far short of the original TR5Pi,- which is no slouch.

Here is another thing they used to do in the 60s with that engine. Addition of a single SU and a *Shorrock supercharger.

This is roughly the curves you would expect to get from that rather voluminous bit of kit.
It does what you expect, the initial torque is nice, but then all falls over as the combination of losses & poor valve flow mounts up as revs rise.

Some people no doubt will get wild and angry with my criticism but I've seen the results of increasing boost on modern turbo diesel engines.

You get exactly the same results. If the valve behind it doesn't flow, all you end up doing is stacking up boost in the inlet manifold and heating up the air. On a diesel you get black smoke, and no more power.
On a force induction petrol engine, you just get less power, because the air temperature has risen and the engine is also using more power to drive the compressor.

Using a few brain cells is what it's all about. Sticking a compressor or a turbo on an engine with very poor inlet valve flow is a brain dead solution.
Some people were claiming 100bhp from the Shorrock conversion. As you can see, you gotta be KIDDING, you would be lucky to hit 70!

If you were lucky it would hit 85ftlb of torque at 3500rpm, that would give you a small impression of power, and after that, all downhill!
That very much confirms the impressions I had driving one or two of these, some 20yrs ago.

We still thought we could go one better than our 25H and restore a bit of extra top end.
Inevitably you lose a tad low down, & we can't skim any more off the head to compensate. It's what's called the "school of having your cake and eat it".

With the "41" cam the thing is still going at 7500rpm, but personally I would prefer the version with more low down grunt.
It's already making more power & torque than any of these expensive unreliable historic "Le Mans" 8 port engines claiming silly horsepower.
In reality they haven't enough torque to pull the skin off custard!

Those who claim you can't somehow win at every RPM, had better take some lessons in engineering.

I like engines like this.
On top of it, they are amazingly fuel efficient, don't have high stresses & don't wear out quick.

Refreshing the inlet & exhaust seats 1mm bigger, putting new guides & valves in & giving it a whopping skim is going to make an 50yr old head as good as new anyhow.

Most people call this WIN-WIN, and so do I.