Tutorial for mounting a big valve cylinder head on a type E.

[BAHADORI]

Hello everyone,

If you want to mount a big valves cylinder head on your E-type, the next thing to do is find an XJ6 4.2 S3 cylinder head. This is the option I chose on my E-type 66, and which offers 2 advantages:
* The engine runs on unleaded fuel.
* The power gain (probably around 20 hp).

But, we have to do a modification before installation: Recap off 2 water passages that do not exist on the older XK block of E-Type.

For this, I suggest you:

1- Tapping holes (it must be of 12 mm).
2- Install a screw cap with thread lock (red Loctite) and clean.
3- Put some cold welding (resistant to high temperature) on the screw cap and wait 24 hours of drying.
4- Planer everything. If you are careful, you can do it by hand with a ruler (to check the flatness during the operation) without rectification, by filing and after with sandpaper.
5 - You will also need to drill and tap four holes (it must be n?10 UNC) to mount the tachometre sensor and the cap at the end of the exhaust cam shaft, because there is no holes (see first picture).

If you have a serie 1, you will get your cam shafts, especially the right for the tachometer sensor, and the last cam shaft cap near this sensor.

Good luck.

Jacques

[christopher storey]

which offers 2 advantages:
* The engine runs on unleaded fuel.

I hate to tell you this , but ALL XK engines, from 1948 onwards , will run perfectly well on unleaded fuel, for the simple reason that all XK engines have hardened valve seats

[PeterCrespin]

It's a good swap but has no effect on unleaded use. All XK heads used chilled iron valve seats and can use unleaded - the S3 is no different

The head does not give a 20 bhp gain IMO, probably nearer half that, which is still worth having. The larger 1.875" valves give a small benefit at low rpm and the valves plus larger ports give some benefit together at high rpm.

The cam caps should stay with the head as they are line-bored as a unit. If you use the extended E-type inlet cam cap on number 1 cylinder of the S3 head (not number 6 as in your photos), you may easily have a cam bearing problem. But if you line bore it to the head as you should, your original head loses value with one cam cap missing.

It is possible to fit a rev counter generator to an S3 head but not trivial. Easiest is probably using an electronic tach from a laterJag, which is what I did.

[BAHADORI]

hello

Yes, I had heard too that all engines with steel valve seats mounted could run on unleaded fuel. But, to my knowledge, Jaguar has never been clear about that. In many official documents, only the jaguar 80s appear to be compatible with unleaded fuel.
Now, maybe the cars of the 80's have a little harder valve seats ? Do you have any informations about this ?

About the gain of 20HP, this number comes from WinSU simulation software.

Finally, for the "inlet cam cap on cylinder 1" (actually it's not the number 6), I understand your explanation, but when I mounted the E-type cap on the XJ S3 cylinder head (see the picture below), it did not seem to be any alignment problem. But maybe I will have problems later ...


Jacques

[PeterCrespin]

They aren't steel - the valves are steel, the seats are medium hard cast-iron. This is better than seats cut direct into a cast-iron block or head but not quite as good as modern materials such as Stellite which are almost glass hard but strong too. Jaguar would have no reason to spell things out for cars they were making before unleaded fuel became the norm.

I think the XK history article on the website of AJ6 Engineering is a good summary.

If you checked the cam cap bore was concentric with the head bord you may be OK. They are double dowelled and should not move in service, plus there is a soft bearing shell anyway to protect the alloy.

However, the whole reason the caps and head are numbered is to keep them matched in both location and orientation as they were the day they were first machined. Switching caps around on the same head, let alone between engines, is definitely risky. Rather like relying on simulation software for power outputs on old-tech engines I suspect, although I have not used that software.

[jag68]

I've adapted a number of Ser III heads to E Type blocks over the years. While I've never dyno tested a stock head against a big valve head with everything otherwise stock, I have had stock heads on a dyno, and my impression, strongly held, is that the bigger valves add about 20 hp. I've also adopted the tach drive to the later heads without issues - using the drive as a guide to where to drill holes. Lately I've simply modified a couple of stock E Type heads to use the bigger valves, which entails new intake seats being installed and some porting.

I don't know what the seats are made of - but I've also never heard of anybody suffering excessive valve seat recession on these engines in the 30 so years since no lead fuel was introduced.

When I first did this conversion I used the stock Ser III cams that came with the head instead of the E Type cams. I found that these cams were dead above 4500 rpm. Swapping back to E Type cams resolved the problem. I never bothered to try and find out why - as I thought it was only the ramps that were changed. Perhaps I'd installed them with a bit of timing error or perhaps they were never meant for high rpm being used in a sedate sedan engine?

[PeterCrespin]

Functionally, the parabolic and non-parabolic cams are identical. Indeed there are plenty of parabolic E-type cams so there isn't even a semantic distinction.

Consequently, your impression of there being a performance difference is like my feeling that deep down Jeremy Clarkson is a tree-hugging introvert - forgivable but not supported by the available evidence.

Likewise, in the absence of comparable before/after dyno numbers controlled for all variables but head swap, we are both merely trading impressions on power increases. Ignoring the optimistic gross bhp numbers of old, the most powerful production XK engine ever offered was the Series 3 4.2 at about 220 bhp, but I'm not sure that 1/8" on the inlets yields circa 10% more power. I've been wrong many times before so you may be right, but numbers are needed to be convincing.

[jonr]

Is there any disadvantages?
And will the fuel economi suffer much?

[PeterCrespin]

Is there any disadvantages?
And will the fuel economi suffer much?

Jaguar purposely left even the larger S3 ports slightly smaller than they could have made them, to keep fuel economy bearable if not great.

If you flow more air through bigger valves and ports and keep the mixture in range then you burn more fuel, other things being equal. In practice, other things like gearing and driving style affect economy more. I got up to 25 mpg with a light throttle at 70-75 mph in my 5-speed big valve car.

In general though, you shouldn't go tuning for power if economy is a key priority, or vice versa.

[christopher storey]

Is there any disadvantages?
And will the fuel economi suffer much?

Well, yes, there are disadvantages to bigger ports and valves . Generally speaking, the higher the gas speeds at moderate rpm , the higher the torque. Consequently, if you increase port and valve size, you lower the gas speed and therefore lower the torque . The best combination is a larger valve and no change in port size, but the ultimate power will be lower

[jag68]

It takes - say 25hp to drive your car down the road, at say 65 mph. That requires a certain amount of BTU's from the fuel. Somebody with a real brain could probably calculate how much gas efficiently burned would generate those BTU's, but lacking such a brain it isn't me. The theoretical BTU's required doesn't change because the engine changes, but only because it becomes more or less efficient. At part throttle increasing potential flow though larger valves decreases the amount of throttle opening you need to maintain 25 hp so in theory fuel economy should remain the same. But as Chis says larger ports and valves with smaller throttle openings decrease the velocity of the incoming air, and this causes the fuel to drop out of the air and coat the walls of the manifold more readily - all causing less efficiency. Peter' excellent fuel economy suggests that it has no such effect. So where are we - who knows. One constant remains - if you want more power when you press the load pedal use bigger valves. If you want better economy use a leaner needle for cruising, or buy a Prius! (Who said that!!!!)

By the by I know that the head with the parabolic cams had less performance than it had with E Type cams, as it was in a car I competed with on the track. I just don't know why. I re checked the timing - it was ok. Is it possible that these cams with their greater valve clearance give less actual lift?

Terry

[PeterCrespin]

At part throttle increasing potential flow though larger valves decreases the amount of throttle opening you need to maintain 25 hp so in theory fuel economy should remain the same.

It's more complicated as you know, but actually easing off the throttle increases pumping losses, which is why warm intake air (less dense) is better for fuel economy than cold air (which is better for outright power). This is also why raising the gearing tends to improve economy, because at higher gearing for a given speed you have to open the throttle more to make the same power at lower revs. The reduced pumping losses from a wider throttle improve matters more than reduced friction from lower revs.

BTW, I wasn't suggesting the big valve fitment with parabolic cams didn't reduce power for you, since you seemed pretty certain that fitting E-type cams made the engine noticeably stronger and I take your word for that.

What I was saying was that since the cams are effectively identical in lift and duration (the ramps just serve to refine the opening closing with larger clearances) any reduction in power had nothing to do with actual cam spec. There are a few ways that stripping/rebuilding engines can alter power output and you identied a likely reason.

Pete

[christopher storey]

Effects of higher gearing : I don't think it is anything to do with pumping losses. With a throttled engine ( i.e petrol engines of the era we are discussing ) , the smaller the throttle opening, the lower the effective Compression ratio because of reduced filling . Hence if the gearing is raised, thus requiring increased throttle opening , the effective CR is increased with a corresponding increase in efficiency . This is why the specific consumption of diesels is superior, because , being unthrottled, they are always operating at full CR

[PeterCrespin]

Several issues being mixed I think. Talk to Roger Bywater.

[lee-type]

I got up to 25 mpg with a light throttle at 70-75 mph in my 5-speed big valve car.

Good evening

What camshafts do you have in that engine?

[PeterCrespin]

It had standard parabolics in a big valve S3 XJ engine fitted to replace a 289 Mustang lump. The Getrag overdrive 5th gave an overall top gear ratio a fraction taller than 2.88, from memory. That and a trailing throttle driving style at cruise, probably account for mpg I haven’t matched in other Es

[mgcjag]

Hi All....just picking up on this old thread....a friend is wanting to use a XJ6 S3 big valve head.....the head has water channel holes between the combustion chambers that line up with slits between the bores on the XJ6 S3 block.....what to do with the holes in the head......do they need welding/pluging up or will the head gasket on the E type seal/block them off and be adaquate...or am i missing something....thanks...Steve
Edit....just had an answer....tap the holes and fit machine screws (sealed)

[E600]

And don’t forget the tacho generator fixings and some juggling with the no1 cyl inlet camshaft cap.