MGB Stage 2 cylinder head

[Michael Dunn]

Hi I am considering upgrading to a stage 2 head on my 1974(chrome bumper) MGB Roadster.
Can anyone who has had this upgrade advise what improvement can be expected with regard to acceleration & cruising speed.
Oselli are my area offer this upgrade.
Any experience/conclusions would be greatly be appreciated.
Mike Dunn
















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[Vic Butler]

Evening Michael.
Your MG is fitted with the coveted "big valve" head and there will be no guarantee if you get a stock Stage 2 you will get the equivalent and Oselli take your old head.
Why not have your existing head modified to Stage 2 spec. Have a word with Peter Burgess who is well respected in that field.
Now to the benefits. In 1981 I was given a cylinder head from an Austin 1800. This was subsequently identified as a Downton head. It was fitted in conjunction with a pair of genuine British Leyland Special Tuning SU HS6 carburettors and manifold, a freeflow manifold and exhaust and a different distributor as the rubber bumper ones are unsuitable. This improved the performance of my 1977 BGT which previously was gutless.
Over the years the exhaust system was replaced with a large bore stainless steel exhaust with a stainless 3 branch manifold and the ram pipes on the carburettors with K&N filters and stub stacks for an MGC.
4 years ago the head developed a crack so I was lucky to find a big valve head. I had it modified by the man who was ace cylinder head guru at Downton and because one of the inlet valve seats was damaged he fitted MGC inlet valves. The performance far exceeds the previous modified head yet it's very easy to drive in urban traffic which was a characteristic of Downton heads. The camshaft is standard. Timing is a guess as is what carburettor needles to use but a rolling road will sort that out but even now it will teach the red line very quickly and the same with illegal speeds so I don't know how fast it will go.
The distributor was rebuilt by the Distributor Doctor to suit the state of tune and Burlen rebuilt the carburettors.
I hope this is not too long winded but I have found a huge improvement and there is no running on. The head is bespoke and superior to one off the shelf. You will notice an improvement even with the HIF4 carburettors.
. Vic Butler

[Peter Cresswell]

Hi Michael
Good advice from Vic, and I too think that if you just swap your existing head for an off the shelf Stage 2 head you will get a nicely modified head with standard size 1.56in inlet valves. The 12H2709 casting is very good and flows very well even as a raw casting. that is why it is so sought after by people racing in the standard classes. The larger inlet valves are usually found in a Stage 3 head which they charge quite a bit more for, and if you want to ensure you get a big valve casting back, check the casting number on the head and it should read 12H2709. This will be found on the top of the casting between the mountings for the 3rd and 4th rocker shaft pillars.

Personally I'm not a fan of stainless steel exhausts, as they can have a 'hollow ring' note to them. On my roadster I have used the Maniflow Rally system which is 1 3/4 in bore, which is quieter than a standard MGB system and very strong.

Peter Burgess can also recommend a cam if you really want to exploit a modified head. All he needs to know what sort of driving do you do and is the car to be used for any competition work - including Touring Assemblies.

[Peter Cresswell]

Another thought!
It is always worth remembering that Torque gives you acceleration and BHP gives you top speed, so for road driving there is more performance to be gained by increasing the Torque as top speed is largely academic. Extra torque comes from a bigger bore size, as that exerts greater leverage on the crank, so my MGB Roadster which until recently had a standard engine, but had a 20% more torque than a standard MGB (129lb ft against the stock 105lb ft) by having a 60 thou overbore. You can also get more torque by filling the cylinders better and this is where a good cylinder head comes in, as the bigger the bang the more leverage on the crank hence more torque.
By increasing the BHP you get the same top speed unless you change the rear axle ratio (not easy on the later tube axle) as you reach the rev limit of the engine before maximum speed is reached. My first MGB, a 1966 roadster, had had some engine work done on it and the speedo reading topped out when the needle got to the main beam warning light! It was dynamo smooth as well. Unfortunately I never found out what had been done to is it was stolen before I got to find out.
I have made reference elsewhere on the forum about a drive I had in Gerry Brown's FIA race/rally car, so is a pure no compromises competition car, and that had stunning acceleration, but top speed was still 105 mph as the rear axle ratio was 4.875:1 (from a Z - Magnette I think) but achieved at something like 7,000 rpm. Difficult to live with that day in day out! The Le Mans MGBs could reach over 130mph on the Mulsanne straight, but needed a 3.04:1 axle ratio (and a more streamlined nose) to do it.
Horses for courses I guess!

[Paul Hollingworth]

Sorry to disagree with you Peter, but a 060" overbore only results in an increase in piston area and hence capacity of of 3.8%, so cannot be responsible for your increase in torque alone. I know Roger Parker also believes in increasing capacity as the route to better performance. I think you would agree that its necessary to get the air in and out of the engine better and the key to that is the cylinder head. I have a Burgess Econotune on my B and although I've not measured the increase in torque, it feels substantial. I haven't noticed an improvement in economy though, but as Peter (Burgess) suggests, I'm probably giving it more wellie now it performs better. I'm just about to have a re-bore myself (+0.040") as my compression on all cylinders is down, but it doesn't use any oil (strange).

[Peter Cresswell]

I wouldn't disagree that getting more mixture into the cylinders results in more torque, but when my engine was run on Aldon's Rolling Road it produced 129 lb ft of torque, with the standard 'saucepan' air cleaners in place and a standard exhaust. When I recently stripped the engine down the only non-standard feature was the 60 thou over bore giving 1868 cc - so a total of 70cc over the standard bore size. The increase in bore would 'pull in' more mixture as well. In Peter Burgess' book, one of the engines in his 'Power Recipes' chapter has a 60 thou over bore and he attributes the engines increased mid range torque to the increase in bore size.

[Vic Butler]

Of course there is a downside of increasing the volume of airflow into a naturally aspirated engine and that is the larger the inlet tract the slower the airflow is at lower rpm, but allowing higher rpm.
My cylinder head had to be fitted with 1.75" MGC inlet valves because one of the seats was damaged and that was what was done at Downton Engineering thus saving the head from being scrapped.
With the 1.75" SU's combined with the much larger inlet valves I was expecting there would be no go at lower rpm. How wrong I was. Downton heads were renowned for their tractability and mine being built to that spec is no exception. Drop down a gear or 2 and the red line is reached very quickly.
Michael a stage 2 head is ideal for a road MGB and the standard camshaft is more than adequate.
I would still advise you to have your current cylinder head modified to Stage 2.
. Vic Butler

[Vic Butler]

Morning Michael.
One important thing to do if you go ahead with the Stage 2 conversion and that is to inform your insurance company. I'm with Peter Best and when I informed them of my Stage 2 conversion the premium did not increase. I've told them everything that has been done to my MG not just the conversion but even down to fitting LE alloy wheels.
. Vic Butler

[Michael Dunn]

Thank you everyone who responded to my question regarding Stage 2 cylinder head modification for my MGB.
It has been very helpful in understanding this process. I will now make a decision as to what route to go.

Mike Dunn

[Michael Barclay]

Hello Michael
I had my 1974 roadster head ported and polished to Stage 2 at the same time as converting to run on unleaded fuel. (18V582 engine)
When installed back on the car with standard exhaust and carbs set up I did not notice any real improvement in performance apart from the engine ran a little smoother.However after saving up the pennies, I fitted a maniflow 3 branch manifold,changed the needles to AAA and K&N air filters (In original housings) there was a huge improvement in performance. The lumpiness at tickover normally associated with B series engine was gone , the engine pulled so much better and it is just generally better to drive. It will easily cruise at 70 -80 with no problem. Overall I would say it was a worth while exercise. Hope this helps.
Regards
Mike Barclay