Merlin Heads

kiwicar · Post by **kiwicar** » Wed Jul 07, 2010 9:19 am

Hi
Spacers can be used to tune single and duel plane manifolds, and not just by adding gas. As a general rule on a single plane manifold adding more spacer will add to peak power and torque but on the down side make the carb more sensative to setting up (to a point where they no longer can match the requirments of the engine) and make it difficult to get it ro run at idle and low revs, it can also compleetly bog the engine when you open the throttle fully. Most single plane manifolds are designed to use one or two inches of spacers as it is easier to add them than machine off the top of the manifold. On a duel plane manifold they start to make the manifold behave like an single plane manifold, this can be good in that you can end up with a halfway house that flows like an single plane jobbie at high revs whilst still giving good low rev performance, however it is difficult to see the effects without time on a rolling road and as they tend to make the power curve more "lumpy" it can be difficult to get the aparent improvment in BHP numbers to translate into better performance on the road.
Best regards
Mike

mgbloke · Post by **mgbloke** » Fri Jul 09, 2010 7:27 am

One thing I have noticed with the merlins is that the idle is much improved and its happy to tick over at 750rpm with the mechanical 238 cam. With the rover heads it preferred about 1100rpm

Perry
Think Ill steer clear of the laughing gas, its probably better suited to the drag strip.
Mike
I have found a 1" spacer that came with my Huffaker so ill try that.
Ive also noticed that the opening in the inlet manifold is slightly smaller than the carb size causing a slight restriction. Is this a good thing, speeding up airflow or would I be better matching the two?

Mark

Will Reeve · Post by **Will Reeve** » Fri Jul 09, 2010 7:59 am

I saw these heads at RPi last weekend, they look superb, and actually very cheap. I paid £1200 just for porting on a straight six head back in 2000! It was by Bill Blydenstein but puts the price of the Merlin's into context!

kiwicar · Post by **kiwicar** » Fri Jul 09, 2010 9:08 am

Hi
There should not be any step in the inlet path, if necessary open out the top of the manifold to match the spacer. you should also try and ensure there are no sharp changes in area anywhere through the inlet tract, ie the outlet side of the venturies should be radiused, or fitted with a flairing spacer.
Best regards
Mike

mgbloke · Post by **mgbloke** » Tue Jul 13, 2010 7:07 am

Mike
Thanks, your post has promped me to check the alignment of the carb. Looking down through open secondaries with the flap open I could see a step of about 3 to 4mm where the manifold flange protrudes. Now taken it back and shaped spacer to suit,

With the carb off I noticed how the unusual inlet port shape blocks off some of the huffaker runner. Looking through the ports they seem very smal. The shape of the runner must be very important.

kiwicar · Post by **kiwicar** » Tue Jul 13, 2010 9:23 am

Hi
I suspect the very rounded profile to the devider at the centre two runners is as much as anything to ballance the flow twhen comparing the middle two and the end two runners being so short it would be very easy to get very high flow rates on the middle two runners whilst struggling to get good numbers on the end two, realistically the biggest influance on overall flow will still be the area immediatly behing the valve but you want to be carefull in any modifications you make to the profile of anything, just match things up and smothe out any steps. Looks nice by the way.
Best regards
Mike

mgbloke · Post by **mgbloke** » Wed Aug 11, 2010 4:09 pm

Done a few more trackdays and the only issue that I have now is the fact that oil is blown out of the breathers at High rpm >5500rpm ( problem originates with Yella Terra roller rockers ).
Im using a 1.5mm reducer to restrict oil flow and with the rover heads this was OK as long as the rocker cover baffles were fitted.
Its chucking out about half a litre every 15mins when on track.
The Merlin rocker covers dont have any baffles and I was wondering if I could use a smaller reducer and what effect this might have at lower rpm.
Was thinking of a 1mm hole or is this too small.

Found a clip of the car from trackside at a Vauxhall trackday (managed to blag 2 sessions)
MG appears at 5mins in http://www.youtube.com/watch?v=dUkATXMHUiM

Mark

mgbloke · Post by **mgbloke** » Mon Sep 06, 2010 12:17 pm

Had my first long trip in the car yesterday, up to Silverstone (100miles). The merlin heads have definateley changed the cruising characteristics of the engine. Doesnt feel so rough.
Changed engine oil from 15w40 to 20w 50 which seems to have cured the oil out the breather problem.

Still not much out there regarding the Merlin heads.
Anyone else getting similar results?

Did a few laps on the New GP track yesterday
http://www.youtube.com/watch?v=n5wGQC0zM14

Mark

kiwicar · Post by **kiwicar** » Mon Sep 06, 2010 1:27 pm

Hi
Very nice bit of driving, very smooooothe looking, just one comment, get some bigger brakes, you could have had that scooby (even though he could out accelerate you) if only you could have slowed quickly enough to take advantace of his sloppy driving and huge turbo lag.
great stuff
Mike
Edit, by the way I just love the things you are passing in an MGB, that guy in the lotus must be so pissed off, you got passed him by turning in tighter and having more grip!!!

CastleMGBV8 · Post by **CastleMGBV8** » Mon Sep 06, 2010 2:10 pm

Mark,

Great stuff, just love to see an MGB with it's design origins 50 years ago being able to beat modern machinery, albeit with a few simple suspension upgrades and some decent driving.

The engine sounds great, very smooth with good solid torque and doesn't sound stressed at all.

Regards,

Kevin.

mgbloke · Post by **mgbloke** » Tue Sep 07, 2010 6:33 am

Thanks guys,
Mike
Brakes are well up to the job, its me that needed to guage the braking points. Unusually overtaking was permitted on both sides but was not allowed in the braking zones. Did 3 sessions on track without spinning or going off.
What a buzz.
Kevin
Will I be seeing you at some trackdays next year?

Mark

CastleMGBV8 · Post by **CastleMGBV8** » Tue Sep 07, 2010 4:02 pm

Mark,

If you mean driving. that's a little unlikely, old age and poor health is catching up with me and I'd probably just get in the way.

If you intend going to Brands anytime do let me know, as I'd definitely come down and watch.

Kevin.

mgbloke · Post by **mgbloke** » Tue Sep 07, 2010 4:15 pm

Actually I Fancy having another go at Brands but that will probably be next year now.

I know im getting a bit off topic but here is the view from the Evo

http://www.youtube.com/watch?v=lWNtItfW6qU

At least people can see what the rover V8 is capable of with the Merlin heads.

Mark

mgbloke · Post by **mgbloke** » Wed Feb 01, 2012 12:49 pm

I am amazed how many people have been looking at this thread.
Anyway thought I would add some feedback.
Just to recap im running a 4.6 top hat linered RV8 with the Merlin Heads (un modified) MK 238 cam. In an MGB GT

I did have a problem with a small flaw on each head in exactly the same place. The result was water escaping into the oil. These flaws developed after 18months of use. Real Steel were excellent and had the flaws laser welded which has totally cured the problem. Aparently it is only a problem on the very early heads and they have only had one other experience of this.

Last summer I had big end failure on Nos 5 and 6 which damaged the crank and put a score in one of the cylinder walls. ( I think caused by oil surge).
Decided to keep the 4.6 stroke and fit 96mm Forgrd pistons making a capacity of approx 4800 Also fitted the intermediate cover with crank driven oil pump and to overcome the counter rotating mechanical waterpump I fitted a Davies Craig electric one (EWP115)
Rolling road showed an extra 10bhp @ 336 but it actually feels like more to drive.
The Merlin heads have been out of production for some time but I have been told that another batch is due in the Spring.

Cheers

Mark

JP. · Post by **JP.** » Sat Feb 04, 2012 3:21 pm

mgbloke wrote: I did have a problem with a small flaw on each head in exactly the same place. The result was water escaping into the oil. These flaws developed after 18months of use. Real Steel were excellent and had the flaws laser welded which has totally cured the problem. Aparently it is only a problem on the very early heads and they have only had one other experience of this.

Can you be more specific at this flaw...
Running Merlin heads from the first batch ( bought june 2007) for years now and I am loosing a slight amount of water( for a few years ). Not enough to worry about for me and always thought it might had something to do with that one head bolt running through a water jacket.
Engine is still running fine ( 10psi SC 3.5V8 ) so I never bothered to investigate further. Still no water traces in my oil.