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MG MGB Technical - Dream Head - Revisited


About 5 years ago, there was a discussion of a Dream Head in the archives.

Steve S. suggested.

"Here's an idea: Why not just cast an mga twin cam head modified to accept the stud pattern of a five main bearing B Series block? Give it a duplex drive chain to the camshafts and you're ready for development. It should produce about 115 HP in undeveloped form right from the first prototype. Using what we now know about port contours and camshaft profiles progress should be quite rapid. Sounds a lot cheaper and easier than trying to come up with something totally original. It would respond well (not to mention sell well) to those who still think "could've been, should've been". As soon as it's ready for market, I'll buy the first one that's available. "

Though there might be conversion methods that are easier (Quad 4, T-16, Rover), I think some of us rather suffer the agony of keeping some parts stock.

I am living in Central America, where development costs are cheap. I have access to an aluminum foundary, that could product prototypes. I do not think the quality of the casting would be high enough for production. After everyone was satisfied with the design, we could turn over the molds to a foundary with higher quality melts.

In a few months we should have CNC machines here. With spare capacity time I am sure we can turn out nicely machined prototypes.

Anyone game? This will not happen overnight, but I am sure with enough time and effort, we could get there.


Shareef Hassan

Sounds like an interesting project but somehow I don't think it would be that easy. It may be simpler to keep the existing TC stud positions and move the stud holes in the block. And would it not be easier to go to a belt drive for the cams rather than a chain?
Myself I would love to have a twincam in my car (Blown MG-ZA) but as my workshop resources are limited it would be nice to keep things simple.

Rich McKIe

' Sounds interesting. Would you not have to have access to a Twinky head to copy it? Also, I'm waiting for Steve S. to weigh in on it again. Just when you thought it was impossible, he keeps learning new stuff, so I wouldn't hold him to a five-year-old opinion. 8^)

Steve, what's your opinion?

Allen Bachelder

Having just rebuilt a Twinky engine, I wouldn't copy it!!

You would need to retain the camshaft as an intermediate shaft to drive the oil pump and dizzy, unless you go to EDIS ignition and an electric oil pump.

The twinky has one chain off the crank to drive the intermediate shaft and a second chain from there to the cams.

The header tank and thermo housing are a nightmare of plumbing.

I would go for a true hemi head but drive the cams, the intermediate shaft and the water pump with a sepentine belt.

A new front crank oil seal will need to be designed and a new engine front plate to carry the pump and idler pulleys it also will help if we can use a standard timing belt from another application - possibly also the pump and pulleys from something like the M or T16 - in fact the front end of the M or T 16 would be a good starting point.

Perhaps the head from that engine would be a good basis for the new B head?
Chris at Octarine Services

Where there's a will, there's a way. If they can adapt a BMW K1 motorcycle head to the "A" Series, maybe there's a head from another car that could be adapted to the "B" Series.

Anyone got access to engine data that might give info like cylinder spacing, bore size, etc.

Derek Nicholson

I was doing some sketching this weekend. I think that no actual parts would be used from the actual twin cam head and drive.

I think it will be the inspiration. I am thinking along the lines of Chris above. The only problem my donor car would not be a M or T16.

I guess the first question is 8 or 16 valves?

Second cams driving the valves directly or a rocker type set up. I know that pushrods (apples to apples) make more low end torque. How does this get influenced.

I was thinking distributorless ignition, and oil pump driven by a belt, eleminating the intermediate shaft.

I was also thinking making two varients that allowed the shaft to be kept.

Shareef Hassan

I think it's a lot of added complexity for very little gain in performance.

With changes, the crossflow head (like an MSX or Derrington) would be very capable of producing so much power, there would be no point in using overhead cams.

All you gain with the overhead cams is higher-RPM reliability. The bottom ends of these engines were not built to run at higher RPM's, so this is a pointless "upgrade" in my opinion.

Sean Brown

Apparently Sports Car Spares in the UK is going to be producing repro Twin-Cam heads. Of course the head is just the starting point. I am sure that the finished head casting would cost a couple of grand then you have to add on all of the other expensive bits (I shudder to think what a timing cover would be worth), and of course the machining. The 5k mark would go by like you were standing still...and I don't mean 5000RPM!

Rich McKIe

Much more would be involved that just producing a head casting. Special intake and exhaust manifolds, pistons, exhaust downpipes, engine front plate, camshafts, alloy covers, gears, and endless camshaft drive chains, chain guides, chain tensioners, gaskets and seals, plus a bunch of miscellaneous hardware would all have to be specially produced. Maybe the valves as well. Such a kit would be terribly expensive on a limited production scale, possibly costing the price of a well-rebuilt engine. Because of this, I fear that it would be of interest only to the most fanatical buyers, further limiting production and skyrocketing the price. It is, however, a nice idea. If anybody ever does offer such a kit, I'll be first in line to buy one. Damn the cost, just the satisfaction of having such an engine would be worth it (to me).
Steve S.

I would lean toward Sean's idea of modifying the crossflow head. Maybe dual 1 3/4"SUs, hemi chambers, better routed exhaust ports? Hmm...
Jeff Schlemmer

While you are correct that a DOHC system has a decided advantage in terms of reliability at high engine speeds, I have to disagree with your premise that it is the sole advantage of such a system. With a Dual Over Head Camshaft system, it becomes possible to incline each valve at its own optimum angle for maximum airflow. It also becomes possible to use larger valves. Greater flexibility in choice of combustion chamber shape is yet another virtue of such a system (Hemispherical, Pent Roof, etc.). These options are not available in the case of a crossflow Heron head with its flat-roofed combustion chamber and parallel valves.
Steve S.

You can also run 4 valves per cylinder which improves flow even more....
Chris at Octarine Services


Steve, Chris, others:

I'll admit that a DOHC engine would be better in theory and possibly in practice as well. I guess what I was getting at more than anything is the added complexity and cost relative to the amount of returned performance. After a certain point it would be cheaper (and probably mechanically easier to put together) a supercharger conversion.

I've looked at this before and the fact remains that the bottom end limits what can be done on the top side. From a production standpoint, the basic crossflow head layout that is currently available makes the most sense. With this basic design, any cam can be used, the stock valves, valve hardware and rockers can be used, even the stock push rods and stock rocker cover. Additonally you don't have to take the engine out of the car to add one to it.

I deal with a lot of customers and believe me, you want to keep things simple for them. Nobody wants to have to re-invent the wheel to get better performance from their car. The average enthusiast would really like to have to do no more than bolt all the right parts up and have it work the first time out and I don't blame them. Whenever possible we like to provide packages that are a known quantity so that people will have all the right stuff, right off the bat (carbs, distributor, head, manifolds, etc.) While this can be a somewhat expensive initial cost, the satisfaction gained is worth the expense to most of our customers.

Ignoring what I just said, if you want to argue valve flow and layout, it's all really a bunch of conjecture. All the popular layouts have their advantages and disadvantages. Take a look at the head bolt pattern some time. It is the first thing that will get in the way of some of your more "ideal" layouts (I.E. Hemi and 4-valve). That realistically leaves you with either the same layout we have now, or a slightly canted valve or wedge design. The existing 1.625" valve size is the theoretical maximum for the bore. Canting it so that it would open from the cylinder wall towards the center of the cylinder would help, but there is really very little room for doing that while still maintaining a port that will feed it properly. Don't forget that the valve size also relates to RPM and efficiency.

Derrington had the right idea with the original crossflow head. Unfortunately nobody has made any significant improvements on that layout since it's inception. Right now, I'm up to just over 170cfm inlet flow (at 28")from the MSX heads I modify using a 1.625" valve, but that is becoming the limit of the casting. The chamber design leaves enough meat to get a fairly favorable shape/deshroud form, but the inlet and exhaust ports could benefit from some significant redesign. In short, I am a proponent that if the world needs another aftermarket upgrade cylinder head for the MGB, it should be a redesigned cross flow cylinder head because to me, it makes the most sense.

Sean Brown

Makes sense?

Isn't this mainly about the LCF?

Rich McKIe

If its cost efficiency that you're after, then I'd say go with one of Peter Burgess' cast iron Fast Road heads. A flowed Derrington Crossflow head will better it only in terms of a bit more power (maybe 10%) at mid-range engine speeds, but that's about all. To get that moderate advantage you need to purchase not just the head and have Peter rework it, but also intake and exhaust manifolds, Weber carburettors, aircleaners, air horns, plus convert to breakerless ignition and a remote oil filter (carburettors overhang the Original Equipment items). I've done this on my car, so I know what's involved. This adds thousands of dollars to the cost of the engine, so its simply not cost efficient in most people's eyes, but it is the ultimate classic set up for the guy who wants to go all the way. An 1800cc TwinCam, on the other hand, would have the greatest eye-popping "Wow factor" possible.
Steve S.


You're right! A reworked cast iron head is cheaper yet.

Did you ever dyno your engine? I'd be curious to see your results at each stage of tune.

A typical street engine running one of my cast iron heads usually dyno's to around 85hp at the wheels while I've seen 118hp at the wheels with my crossflow heads. Torque improvements are just as notable, 94ftlbs for the cast iron and 115ftlbs for the crossflow. Both engines quoted are very similar other than the heads and induction systems.

Yeah, a twin-cam would be a "wow factor" for sure. It's just not worth it to me personally though, I guess that's just my opinion.

Sean Brown


The stud layout should not pose any restriction.

The right hand side (inlet) has five studs between the cylinders - this is the normal layout for a twin cam 4 valve head.

The left hand side (exhaust) has four studs in line with the cylinders, but as the pushrod holes will be defunct, ports can run either side of the studs.

If the chamber design and valve angle is such that valve cutouts in standard pistons are not required then the installation would be a simple bolt on job - including replacement of the crank pulley with one which will drive the timing belt. The original cam and timing chain can be left in situ to drive the dizzy and oil pump.

Oil supply for the cams would have to be taken externally from the block as the intermittant rocker oil feed would be inadequate.

There would also be the opportunity to simplify the carb mounting by incorporating the inlet manifold into the head casting - allowing twin Weber/Dellorto/thottle bodies to be used.
Chris at Octarine Services


Yes, I saw that too, but now the exhaust header would have to have eight openings instead of four, or at least four "collectors" to match up to the head (additionally, this is another part that needs to be custom produced).

Not using custom pistons means the chamber is not going to be optimized (my opinion).

If you want to build it, go for it! I'm just saying I don't think it's going to be worth the effort. To me, it would be too easy to get power the crossflow way and I guess that's my bottom line...

Sean Brown

Just a different perspective on this matter: how feasible would it be to construct a DOHC system to replace the current cam-followers-...-rockers system?
This would then be installed 'on top' of the cylinder head (there is some spare room anyway) and could perhaps offer some gains (as pointed out above) while being cheaper to make at the same time.
Just an idea of course :-)

Alexander M

The Original Equipment head has a flat-topped combustion chamber and parallel valves that are aligned in a single row. This being the case, a Dual Overhead Camshaft option just isn't there.
Steve S.

My TDCi Mondeo has 155bhp and 400Nm of torque. As money is clearly no object to this 'dream head' conversion, why not go all the way and turn it into an MGB Diesel? Assuming that the bottom-end stayed together (but then this is a dream, right), then the torque will probably roll the car over and that really would cause a wow factor. Added benefit to motorsport competitors is that the capacity reduction factor would put you in the sub-1000cc class. Only real downside would be smelly hands after a fill up.

Neil Lock


You can always wear the rubber gloves....
Chris at Octarine Services

Pardon me while I go a bit off topic...

If you have an aluminum foundry and a brand-new
CNC machine that is itching for a workout, I'd like
to share a "Wish List" that I've had cooking in my
small pea-brain for some time.

The items I have in mind are, to some degree,
much less daunting to design, engineer and
produce than an all-new OHC cylinder head,
and there are few (if any) other companies that
are producing these items (= fewer market
competitors for you).

Here, in no particular order of preference:

1) Finned aluminum side tappet covers that have
dual raised lip edges for positively retaining the
cover gaskets (no more tappet cover gasket
slipping or leaks!!!); as well as have a thick,
unfinished boss for attaching a user-fabricated
breather (optional).

2) A slightly wider (not deeper), 5.5 qt - 6 qt, finned
aluminum oil pan. Something like the "T" pan on
early Shelby GT-350's. With baffles; and mounting
provisions for a windage tray; an unfinished boss
for an oil temp guage sender (user installed
option); and (very important) an extra-thick flange
in order to prevent warpage when torqued down
and eliminate oil pan gasket leaks.

3) A true high-volume oil pump with, say, a 0.20" -
0.30" taller rotor. Most "uprated" oil pumps on the
market are merely stock pumps with a slightly
modified stock end cover (with resultant oil
drain-back issues). An oil pump with a taller rotor
would be better capable of delivering oil volume at
idle and low-med speeds and maintain constant
oil pressure; and there would be no oil drain-back
problems to haunt you during each engine start.

4) A clutch slave cylinder that is somehow revised
to make air bubble trapping and retention, and the
resultant common fluid bleeding headaches,
a thing of the past (...once and for all!). Possibly
lined with stainless steel for extra durability.
Possibly incorporating a slightly smaller bore and
piston for a slightly longer throw-out travel and
more positive clutch release.

5) A transmission bellhousing for mounting a T5
or T6 tranny from a late model Camaro or Mustang,
or other high production American car that can be
more easily (and cheaply) found in a self-pick
wrecking yard than a Ford Sierra (very rare, and
long-ago extinct, here in the U.S.). Some T5 or T6
transmissions are capable of handling upwards
of 400 hp and would be virtually bullet-proof in a
4-cylinder MGB.

6) A Weber DCOE intake manifold (for the 5-port
heads) that has an integral balance tube with 2-3
unfinished bosses for vacuum take off(s), and an
expanded carb mount flange for mounting
a heat shield.

Thanks all, for tolerating my diversion from the
main subject of this thread, and for listening to
my whacky ideas.
Daniel Wong

Daniel; Great suggestions. I believe the bell housing is available in Australia or N.Z.

Clifton Gordon


1 Doug Jackson offers something similar. Hurry he is winding down his business. I have fitted one of his and it is great product.

2 Cambridge Motorsports offers these in aluminum and magnesium. The kick-out part of the pan, I am not sure they offer.

Having said that a pan is something that I am considering.

4 I think the gravity feed suggested by the BBS works quite well. After being frustrated with the active method, Mity-vac, just letting gravity do the work, was very effective. I was so pleasantly surprised.

5 The bellhousing was something for the future. Once the engine side was done, the difference for the various other gearboxes should not be too hard. Out of curiousity how do the 5 or 6 speeds feel with regard to shifting. Are the clunkly, or do they feel like a snick-snick gear box. I did a Ford type 9 conversion, and am pleased with it.

6 I am soon going to try a Minuki carb. I have seen some pictures of 2 90 degree bends with a tube, serving as a balance tube. I do not know if it works. You could e-mail me with a sketch of some sort. I have access to AutoCAD if that helps. I think Peter Burgess cautions about modifying the SU manifold balance tube. Maybe something of a hybrid design.

Hope it helps. Machines are not here yet. Should be set up in March. Remember MG stuff is on spare capacity time.

Shareef Hassan

Chris at Octarine Services


Your number 2 replicates the sump from a TF - they are a real pain to remove or fit in the car as there is absolutely no access from below with a socket wrench - it means using an open ended spanners and takes forever!
Chris at Octarine Services

Daniel has some good ideas, and I'd like to add a few of my own:
1) An aluminum engine front plate. Nobody seems to make them!
2) A finned aluminum cover for the Salisbury tube-type differentials. They were available back in the 1970's, but today are extinct!
3) An aluminum aircleaner box for the deep K&N airfilters.
Steve S.

Chris at Octarine Services, Essex, United Kingdom said

:"Having just rebuilt a Twinky engine, I wouldn't copy it!!

You would need to retain the camshaft as an intermediate shaft to drive the oil pump and dizzy, unless you go to EDIS ignition and an electric oil pump.

The twinky has one chain off the crank to drive the intermediate shaft and a second chain from there to the cams."

Chris, if you rebuilt a Twincam that had two chains, it was the only one in existence!

The Twincam engine uses a gear driven half speed shaft and a duplex chain from a sprocket on that shaft up to the cams. Count 'em - one chain, not two.

Not sure how you could believe it was otherwise if you really did rebuild one.

And guys - no one would pay the loot it would cost to convert an MGB to Twincam configuration when it would be considerably cheaper to simply use another engine - any number of DOHC Japanese engines would slot in nicely - the Miata fits especially well.

It is fun to toss ideas about but in reality, it ain't going to happen.
Bill Spohn

Bill has obviously overdosed on reality pills.

I wouldn't say that nobody would pay for such a crazy head. If it was proven to make good power then there may be a few who would buy such a beast, it would probably never be profitable though.

It is fun to dream. I dream daily and my dreams are pushing my budget and my horsepower to achieve 100rwhp.

Robert, you can do this right now - just go out and buy a core Twincam engine - usual cost 5-6K.

Then get a good MGB bottom end. Except that you need new pistons, and you may as well have some custom forged ones made up.

Then you can toss away the crankshaft and find yourself a crossdrilled, nitrided competition crank, or if you can't find one, buy a billet crank as used by the racing engine builders (insufficient oil flow with a stock one to run above 6500 and if you aren't planning on running higher than that you may as well not bother building the engine).

Now do all the machining necessary to mate the head with the block and builkd your engine.
Shazam - you now have an MGB engine capable of running to 7000 rpm and putting out 115 - 120 bhp.

It cost you around 12K to build. You have used up the engine parts that would have allowed a rare MGA Twincam to live again. And you have spent twice as much as it would have cost you to simply stick a Mazda MX-5 1800 in the car. Which would also run to 7000 rpm and produces 140 BHP.

Hmmmm. Yup, I think there would be a pretty limited market for such a conversion. Is it neat to old MG heads like us? Sure. Is it darned expensive - for sure. That's why very few people have ever done the conversion (you have to be some sort of idiot like me to want to do that - twice).

I really think that the crossflow solution is the far more attractive option, both from an economic and practical point of view.

No question that the engines are nice looking, mind you
Bill Spohn

I even knew of one lunatic who installed an MGA Twin-Cam engine in a TVR Grantura.

Oh My!

Rich :-)
Rich McKIe

The hole in number two piston that caused the twin cam rebuild - piston.jpg

And why I hate fitting & tuning xflow engines - 2.jpg - just try setting the timing, even with the filters off!
Chris at Octarine Services

Oh - I hate these old fashioned BBSs!!

Try and
Chris at Octarine Services

Thrid time lucky??
Chris at Octarine Services

Oh b******r - just goto my photo page at
Chris at Octarine Services

Rich - yes, I did have the Twincam in my Grantura for awhile - with no inner fenders and a flip front, it was a lot easier to access everything when I was developing the engine.

I put it back in its rightful place, however! ;-)

Chris - number 2 or 3 are classic pistons to hole - due to fuel starvation caused by engine vibration acting on the floats. It has long been known that flexibly mounting the carbs cures that - I trust that you did that when you put the Twincam engine back together.

And I'm still waiting to see the alleged Twincam lower timing chain....:-)~
Bill Spohn

This thread was discussed between 25/11/2006 and 21/12/2006

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