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MG MGB Technical - Aluminum heads good?

I was thinking about purchasing an aluminum (non-crossflow) head for my '73 B GT. Is the gain in power and engine cooling worth the money?

thank you! Don Scott
donald scott

Donald-
Aluminum has less thermal efficiency than cast iron, thus forcing the use of a higher compression ratio to produce the same amount of power, which in turn creates a problem with preignition. The head is actually made by Pierce Manifolds. It uses the larger capacity combustion chambers of the G-GK series engines, so you'll have to install a new set of pistons to raise the compression. Don't expect an increase in power unless you have the ports reworked by a professional as the castings are essentially a "mirror image" of a stock casting. In short, unless you're a racer or a gadget freak, don't bother.
Steve S.

How come that so many people think by simply changing the material of a cylinder head they will get a power gain?

wonders

Jörn
Jörn

Joern-
I presume that because these aluminum heads are popular with the racing set, some owners of street cars believe that all they need to do is bolt them onto their engines and the performance of the engine will be transformed. They don't realize that the aluminum head is just "raw material" that will need professional portwork. Kind of like the high school kids of my day who believed that if they put a pair of 4 barrel carburetors with high rise manifolds on their otherwise stock V8s they would have a streetable race engine. Ignorance is blissful, in a way. Of course, when they put those ideas to the test in the real world, they couldn't understand why the engines actually ran worse! They were ignorant of the one great Engineering Truth: If you change one thing significantly, you've got to change it all.
Steve S.

Don;

Even Peter Burgess (MG head tuning guru in England) states that a properly tuned iron head will put out as much power as an aluminum head for anything but a full race mod head. Save the money that you would spend on the aluminum head and ship your iron head to Peter for a Class II or Class III build-up. Proper porting, polishing, valve grinds, etc. will generate much more power than just slapping on a stock aluminum head.

Now, that said, if you do it right with all the proper engine modifications, a crossflow aluminum head can generate more power. It may only cost you $5,000 or $6,000 to get it right though.
Ron Kluwe

Don:

As the well-advised observations above note, other than the increased thermal efficiency of the aluminum head, there is no real difference between those currently available and the stock cast-iron head in terms of increased power.

The reason for this is simple. The main problem with the stock MGB cylinder head is the terrible design of it's exhaust ports. If you were to cut a cross section of the exhaust ports, you would see the boss which holds the exhaust guide protrudes so far into the port itself, it prevents gas flow to a remarkable extent. Whether the casting is aluminum or iron, this blockage is the main problem with gas flow in these heads, not the material of the casting itself.

This is why so many people have been disappointed with modifications to the OUTSIDE of the head itself. No matter what set of carburetors you bolt to the intake side of the head, or what kind of header/exhaust system you bolt to the exhaust side, all gases burned in the combustion chamber must somehow squeeze past this obstruction in the exhaust ports.

With this restriction in place, exhaust can never properly exit the cylinder during the exhaust event and thus "backs up" in the cylinder rather than effecting a complete blowdown. This in turn, prevents a full charge from entering the cylinder during the intake cycle which thus limits the amount of fresh charge available for combustion during the next cycle, and so it goes.

Certain camshaft manufacturers have attempted to "correct" this defect by producing camshafts with longer durations during the exhaust event. This does nothing to address the problem itself, however, but attempts merely a "band-aid" approach which is never very satisfactory.

The correction for this inherently bad design is a complete modification of the cylinder head. In our shop, we begin by removing a great deal of cast iron in the exhaust ports using special air die-grinders and carbide bits. This takes a lot of power (read EXPENSE) and cannot be done with some sandpaper wrapped about an old bolt chucked in a Sears hand drill. Once the cast is removed, both intake and exhaust ports need to be re-contoured in special places and left completely intact in others. If cast is removed in the wrong places, port velocity will be disrupted and the results will not be satisfactory. The heads we modify are all given correct 3-angle valve and seat facing and when all this is completed (about 16 hours highly specialized labor, by the way) one is then left with a head which will flow approximately 35% better than a factory-original head and is more reliable in the bargain. Performance is unbelieveable to most owners who've never felt such power in their engines, and most would never believe the improvement possible without more extensive modifications.

As a BBS testimony to the effectiveness of this head modification process, I might recommend the experience of Barry Kindig. Barry's late model rubber bumper car sports one of our modified heads, a stock engine we prepared for him (he assembled it very nicely himself), .020 HC pistons, a Crane camshaft which is Moss's OE replacement camshaft, a Peco exhaust header, and a newer type 45D distributor. From what we can determine, Barry now has an nice 115 BHP, up from the original 65 BHP of his factory smog engine...while still using his original single 175 CD Stromberg carb! The carb has been modified only by the addition of a different needle, a manual choke system, and an air intake which incorporates a K&N filter. As Barry has so kindly noted, the performance of his car is breathtaking to say the least...mostly because of the tremendous gain in performance from the now free-flowing cylinder head. One enjoyable feature of Barry's installation is the ease of tuning with the Stromberg plus it's genteel idle, excellent fuel economy and low-speed tractability. But when he needs power, down on the pedal and the torque hits hard. He enjoys all the power throughout the RPM range one could ever want in a street MGB.

Hope the above gives a bit of helpful information about these matters.

Best regards,

Mike Brown,
Seven Shop British.
Mike Brown

Mike,

Very interesting points. How much does a modification to the engine head like this cost? Its sounds just like the thing i need!

Ralph
Ralph

115 hp? Uhhh, BS.
Ted

Gentleman;
I got the feeling reading above that no one has used the alum head. Well I have the second one that I have installed sitting on a engine on my tool box right now. First let me say it is a quality product and works very well. They come stock with 37cc combustion chambers and .045 cut will get you down to 35cc. or about 10.7 to one with .060 pistons. Thus they come stock with the comp raised to make up for the alum. I have had no spark knock problems with this setup. With out mods I won't say they are superior to a cast head but they do have a better flow/design from the get go.
I would not dump a cast head in favor of one but if you need a head I would go for one in lew of a pig in a poke head from a unknown source. If you need a head go for it. Bob
Bob Thompson

Ralph:

The cost for this modification is $595.00. Customer pays shipping both ways. This includes head inspection to be certain it's a sound core, surfacing to clean up irregularities and ensure the head is perfectly flat, chrome-nickel exhaust seats, intake seats if needed (not usually), all new manganese-bronze guides, all new intake and exhaust valves, a new spring set, new studs, Heli-coiling of any stud holes needing this, prime and paint. Of course, the port modifications and 3 angle cut on valves and seats are included as well. Turnaround time is 6 working days from the day we receive the head. When the head is received by the customer, it is immaculately clean and ready to bolt onto the engine. We also include a competition intake/exhaust manifold gasket and new brass manifold nuts. It's a very complete service.

Ted:

You may wish to reflect on the fact the STOCK MGB engine, circa 1964-1967, developed 95 BHP from the factory. This was without a 3-angle cut on the valves and seats, with stock paper air filters, NO port modifications, and a stock restricted exhaust system. Given these facts, it's not really a stretch to claim a mere 20% power increase at red line with the newer, improved, cast and shaped heads, modified as described above, together with the other simple bolt-ons I've mentioned. I might suggest a consultation with Peter Burgess or a referral to his excellent book, "How to Power Tune MGB Four Cylinder Engines" to set aright any confusion on the matter.

For your additional reflection, you may wish to recall the Group 44 Team MGB (Bob Tullius/Brian Fuerstenau) which took and held the West Coast SCCA championships several years in a row, produced 116 BHP at 5000 RPM! This was a simply but well-prepared Doane Spencer engine using a very mild cam and "only" 1 1/2 in. SU carbs. The engine produced 140 BHP at 7000 RPM and was bulletproof. It idled very smoothly, had excellent torque, and could have just as easily been driven on the street. It often beat prodified Jaguars and other more expensive marques, a testimony to qualified and logical workmanship throughout it's preparation and track work. These BHP figures, incidentally, are actual dyno figures.

Best regards,

Mike Brown,
Seven Shop British

Mike Brown

Mike,

I'm working on my first MGB, a 1973 street restoration. I've decided to have an engine rebuilt and swap out the sound engine presently in my car. Main reason for a swap is to keep the the car rolling while the engine work is being done. Smog etc. not an issue, car is exempt w/PA Antique plate. What should I look for in an engine, year etc?
Ken Knize

I have read this thread with interest, alot of things have been thrown about on this thread and others. I have a Pierce aluminum head purchased almost three years ago. It came with 37cc chambers (I cc'ed them) My problem was to high of a compression ratio 18GB engine bored .060 over. (YOU WELL NEED THE EXHAUST CUTOUTS IN THE BLOCK) I had to open them up to 42 cc's to get the ratio down to about 10 to 1. They had the large valves as in the 2709 head. Ports were a bit rough, but better than the stock cast iron head. It was much easier to port and polish than a cast iron head. My main concern was the unleaded problem. I had a good core that needed to be rebuilt, I looked at the cost etc and bought the aluminum head at a swap meet from a know supplier for $550.00 with valves. I have not been to a dyno, I ported and polished the head to the specs in Peter Burgess's book (fast road) and have been happy with the results. I would not recommend doing this as your first try, better to let a pro port your head, a bad attempt makes the head junk and less effective than a stock head. It really comes down to how deep your pockets are and what you want to acheive. A cast iron head will work fine, as well as the aluminum one. I would not choose one over the other, depends on what one has to start with and where one wants to go. As to tuning read Peter's book, look at Doug Jackson's web site as well as Apt's. Alot of good info.

SFTYFST

Ron
Ron Smith

Ken:

I personally like the 1975 and up engines found on rubber bumper cars.

They were so smogged down, they developed only 65 BHP and thus, as a general rule, are not worn to any great extent. The smog equipment also caused these engines to not run much of the time, thus the cars just sat while owners tried to figure out how to get them running...or find some shop who could! Again, this tends towards these engines not being worn very much and not having high mileages. This has changed to some extent with the passage of time and the fact many states no longer require smog equipment on cars over 20 years or so of age, of course.

So if I were to select an engine for building into a "dream" engine, I would select one of these...after careful inspection, to be sure.

It also appears these blocks and heads are cast of a better grade of iron, although this is just subjective observation. The Leyland blocks found in the TR's and midget 1500 appear to be alloyed with chrome and possibly manganese. Again, this is speculation based on outward appearances and I would be interested in comments from a person who knows more about this. When one hot tanks a Jaguar block, for example, one can see the high chrome content in the casting by it's color and overall appearance after removal from the tank. This is the similar appearance of the later MG blocks and heads (post Leyland) although not to the same extent as Jaguar. I've noticed the same appearance in Midget 1500 heads and blocks.

One can also note the bore wear in later blocks is almost negligible if oil is changed properly. It's widely known a later MG block will need reconditioning only after about the third reconditioning of it's cylinder head. Ditto the crankshaft. These cranks are very substantial and hard-wearing. Perhaps this is due to a change in alloy as well, but a more knowledgeable person than I would have to confirm this.

For a street engine build itself, I would go for the later block and head as described above, overbore .020 with 9:1 Hepolite pistons, Moss's OE replacement Crane Cam, double row timing chain in the block. The head would be modified per our specs. For induction I'd use the later HIF carbs with their original manifold but substitute pistons with 005 needles from HS 4 carbs. These pistons are interchangeable with the HIF's by the way. I'd be certain the throttle plates were of the earlier type without smog overrun valves, yet with the small slot at the very bottom of each valve. I'd use 3 in. K&N filters. For exhaust, I'd use a Peco header and straight pipe all the way to the rear, then a 26 in. glasspack beside the fuel tank. For ignition, I'd choose an earlier 25D or later 45D distributor and pull vacuum from the carburetors which need to be modified slightly for this source. (Archives explain this modification.)

This package provides just about all the torque and top end power any reasonable person would want in a street machine, yet is tractable, bulletproof, gets good fuel economy, and is simple to build and work on. It's performance compared with the "average" MGB engine on the road today is just plain thrilling and for most, has to be felt to be believed.

Best regards,

Mike Brown

Mike Brown

This thread was discussed between 08/10/2001 and 13/10/2001

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