MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Aftermarket Heads?

I finally got around to tuning my reasonably acquired B. It's a 75 smog engine, but I must say I was pleasingly surprised by how much of a difference a tune-up could make. I've came from the V8 racing background and am used to doing a tune up for a tenth of a second, but this was like a new car (probably a function of marginal ignition and a much lower scale of horsepower). I'm not here to flame these little engines at all, but actually have been rethinking the engine conversion idea. Do any of you have experience with the aftermarket crossflow heads that Moss sales? I've read the UK publication and it refers to the British made head. Stating that it makes more mid range torque, but gives up on the big end due to small ports. How relative is this to the Moss head? Is this a good idea with the cost being a lessor issue? My engine is running fine, but more power would be great. Thanks in advance to all responses.

Luke
Luke Staley

Luke-
The British-made head that you're refering to is the famous Derrington Cross Flow head. It is indeed reputed for increasing mid-range torque. However, it doesn't sacrifice top end power to do it as it uses standard MG (or should I say BMC) valves. The American-made cross flow head is made by Pierce Manifolds. There's been some complaints about quality with them. Both of these heads are made of Aluminum, which has lower thermal efficiency than cast iron, thus forcing the use of higher compression ratios to produce the same amount of power. This creates a problem with preignition if you don't have ready access to racing gasoline. The Pierce head uses the deeper combustion chambers of the early G-GK Series engines, meaning that you'll have even less compression than before, so you'll have to install a new set of higher compression pistons to get any advantage out of them. If you do decide to install one of these heads, remember that they will overhang the distributor and oil filter, so you'll need to convert the distributor to pointless ignition and be prepared to do a lot of cursing when you try to replace the oil filter. In short, unless you're just a gadget freak or a track racer, don't bother.
Steve S.

If you live in a place where you can get away with a cross-flow head, you can probably do a lot just be returning the engine to standard MG specs before the smog equipment was required.

1. Remove the air pump.
2. Replace the single car with dual SU's.
3. Replace the restrictive exhaust with a less restrictive one. Even the stock cast iron exhuast manifold for the SU equipped cars is much better than the one for the single carb.
4. Change the distributor to the Euro-spec 45D from Brit-Tek. It has gotten a lot of positive comments on this list.
5. Replace the single row timing chain with the earlier double chain. There has been some talk that this also changes the valve timing back to the pre-smog specs.

There are probably a lot of other things you can do, but just the purchase price of the cross-flow head will exceed the costs of the above changes. The cross-flow head does not come ready to bolt on. It must be machined and you need new carburetors and exhaust anyway.

The late-model MGB's were rated at around 65 horsepower. The earlier ones, with the same block and displacement, but with dual SU's, etc. were rated at around 95. That's quite a difference and you can probably get close to it for a few hundred dollars, rather than the $1,300 starting price for the cross-flow head.
Paul Noble

I have also read (in David Vizard's book) that the cross flow head only performs marginally better than a standard flow aluminum head with all the smae modifications. The 5 horsepower differance never seemed like it was worth the extra $800. With some mild port work, the Pierce head (from Northwest Imports) was a huge improvement from stock, and only about $700.
Jeff.

Jeff Schlemmer

Wasn't the 95 hp rating at the flywheel, while the later 65 hp rating at the wheels?

I know my car was dramatically improved with the conversion from the ZS to dual SU's, but with a baseline of 65 hp, even 5 hp is "dramatic"!
Aaron Whiteman

Thanks for all the replies, and I was familiar with the reduced thermal efficiency of Al heads, though I wasn't aware of an increase in combustion chamber size for the Moss Head. I obviously would check these details out before making concrete plans, but decided I would source this boards vast knowledge before hearing their biased opinion. So, it doesn't sound as if the cross flow head is ideal for me. My short block has just been freshened up before I bought the little car and changing out pistons to new forgings makes the V8 option sound more appealing than a few grand in the 4 cyl.

How about you guys opinion on Peirce Head that Jeff S. mentioned above as an improved Al replacement for unleaded fuels? Can anyone give me the heads up on when MG started hardened exhaust valve seats?

I was also under the notion that the 65 hp was at the rear wheels. I know this is about the time (circa 72 in the States)that we switched from gross rating to net, but if only all autos were rated at drive wheels!

Luke
Luke Staley

The alum head from moss, (not cross flow) weighs 20ls less than stock head. Every 100lbs removed equals 2.5 hp at rear wheels.
Fred Horstmeyer

Luke-
It's the Pierce heads that have the deep combustion chambers (43cc), both cross flow and five port variants. With your stock pistons, the compression ratio would be about 7.7:1. Look on the bright side, you could run the engine on the worst batch of Regular that you could find and go out and drag race buses and garbage trucks! I can't say what the combustion chamber volume is on the UK-made Derrington heads is as they're now quite rare.
The MGB went over to lead free tolerant heads with the CAM 1106 head casting in December of 1974, but this was accomplished by tempering the heads, not by heat treating or installing lead free valve seats. Once the seats are machined, they're no longer lead free tolerant.

Fred-
The Chrome Bumper MkII had a curb weight of 2,303 lbs. Even with a desmogged motor of power output equal to that a of a MkI (93 HP), that would be a power:weight ratio of about 1 HP:25 lbs. Thus saving 20 lbs. would be equal to less than 1 HP. The Rubber Bumper models were even heavier, so the gain would be even less.
Steve S.

Not sure about the Pierce cross flow heads, but am confused about the commints on the standard aluminum head. Perhaps there are two different types, one for later emmission cars and one for early non-emmission cars. By that I mean the chamber cc volume. I have a Pierce head for the 62-67 non emmission engine (18GB) and my chambers cc'ed at 37.5cc as received. I had to open them up to 42 cc's to get the compression ratio to a point that I could run with pump gas. Engine was bored .060 over with standard (18GB) HC pistons. Perhaps things have changed with the specs, but looking at the head it seems no different other than the bosses for the air rails are not drilled, it even has the rear water outlet marked and a drilled template. I have had this head for three years, perhaps Pierce has changed the chamber shape and volume.

Ron
Ron Smith

Luke: Before you decide anything get Peter Burgess' book and go to his website. Forget the aluminium head and send your stock head to Peter in the UK or Mike Brown in the USA for porting and combustion chamber contouring. Much less expensive and better flowing than crossflow. Change to dual SU's and install a Piper 270 or equiv Crane or Elgin cam along with uprated head and you'll just about double the HP of a stock '75 at less than the cost of the crossflow.
The V8 conversion is "the stuff dreams are made of" but know that you will spend several thousand to do it properly. Check the V8 board for advice from people who have actually done it.
The MGB was rated at 95 HP SAE net up to '68. Air pump dropped this to 92 till the 18V engine came out for the 72 model year. HP dropped to 78.5. In 1975 hp went to 65 with the single carb setup. All figures are SAE net at the flywheel for USA cars. At some point in the UK hp figures were quoted in DIN figures which are less than SAE but USA was always SAE. Confusing, ain't it?
Terry d

Luke-
I have to agree with Terry. Being on the East Coast I shipped my head over to Peter Burgess in the UK and the improvement over a stock head was very impressive. Dual SUs and a Piper 270, coupled with a Brit Tek Eurospec or Stage II distributor, K&N airfilters and a Peco exhaust will make it hard to believe that it's the same engine! Use your CAM1106 head casting as it has better cooling for the rear combustion chamber (You'll need it!).
Steve S.

A burgess cast iron and a Burgess Alum should perform the same if the compression is adjusted for the heat loss of the alum.

20lbs is 20 lbs. Weight = hp so aluminum should be a better choice, unless the high compression makes you a higher octane rating than premium which I think is 92.

I got on the weight kick after I realized that a passenger in my MGA 1500 had a big effect on the performance. Without the top, top frame, spare, jack, sidecurtains, alum head, tubular headers, floor mats, bumpers, etc. etc., I can easily drop about 200lbs from the car for a kerb wt of about 1704lbs or 1900lbs with me. This is = to 5hp at the rear wheels-or more than 10% of the max hp of 45 per Burgess Power Tune.

I realize that an MGB would be much harder to trim down.
Fred Horstmeyer

Steve: what is the best way to ship a head to Peter and what are the shipping charges? Thanks
Terry D

Mike Brown in the USA was mentioned above for cylinder head work. Does someone have the contact details for Mike? Any experiences with his head porting work?

Kelvin Palmer

sevenshop@terragon.com e-mail

I've contacted him about a head and he emailed specs, pictures, and price. Still plan to do it when I get my GT back on the road, my modified roadster is the daily driver for now. Other contributors here have heads done by Mike and they have been very satisfied with the quality of work and the power gains.
Terry D

Kelvin. Mike Brown does excellent work and I am pleased with the head he did for me. He does, however, only offer one basic rework (or did when I had mine done). Peter Burgess offers several and the one person I know who had his "economy" head rework job was very pleased. His fast road head seems to be very similar to Mike's work at about the same price. In either event, you need to box the head up in either a heavy cardboard box or a wood frame with cardboard cover and ship it off via FedEx, UPS or USPS to whomever you wish to do the work. Les
Les Bengtson

Thanks so much for the input. Could anyone supply us with the contact information for Mike Brown and any applicable websites? You guys have given me a lot to think about, but I guess I'll be passing on the crossflow head, since I have no immediate plans on a new short block and 7.7:1 doesn't sound like much fun!

Luke
Luke Staley

Luke-
Mike Brown's Email address is sevenshop@terragon.com

Terry-
Box the head up as Les described and check with local carriers to find out the best rate. Be sure to insure your shipment both ways.
Steve S.

Kelvin and others,
Less than a month ago I had mike do my head, and all I can say is wow. I have a 69 B-GT with stock high compression motor, and he did big valves, hardened seats, bulleted bronze guides, the whole deal for a very reasonable price. When he found out I was running a side draft weber and a high flow exhaust he put in extra hours porting the head (more of a race port) to take advantage of my weber and exhaust. When it came back it was beautiful, painted, clean, had manifold studs, and a race manifold gasket to fit the bigger ports for no extra charge. Basically he went beyond the call of duty to make me, the customer, happy. And he answered all my questions, some probably dumb, both email and on the phone in a very informative and pleasant manner. I slapped the head on, broke it in, and the damn thing flys now. I had a great run with a '70s vintage 911 and was actually pulling on him in the twisties. Mike guessed between 105 - 115 hp for my motor assuming the compression is still good, and it is tuned properly, and I believe it. It feels great.
Bill
69 B-GT
Bill Mertz

Bill. Glad you got the problem solved and decided to go the route you did. Les
Les Bengtson

Yes Les, I forgot to thank you for your recommendation. After I talked to Mike and he gave me his price I was sold, and he lived up to his promises and your acclaim. I'm still tuning my carb, and want a eurospec dizzy, but things will only get better from here, and there already pretty good.
Bill
Bill Mertz

You grow wiser, grasshopper. But, several of us recommended that you go with a proper head job, not only myself. That is what old men are for. To tell you how we screwed up at your age and you will be smarter than we were. You were. Les
Les Bengtson

I can only add that the new aluminum head would need the same port work as a factory casting. If you're going to shop around, I hear Advanced Performance Technology does good head work also. They have lots of dyno proven info and recommendations.
jeff.

Jeff Schlemmer

Steve said:
<<I can't say what the combustion chamber volume is on the UK-made Derrington heads is as they're now quite rare.>>

They are around 38cc or so. hard to tell as most of them have been milled. I just picked up a HRG head and we're looking for 9.8:1 cr. Using a cam with .394 lift and 1.625 roller rockers. The cam has 280 degrees and 103 degrees at full lift.
Have a pair of 40 DCOE's to go with the set up.
Should run fine on 92 pump fuel.

Ron
Ron

This thread was discussed between 21/09/2001 and 27/09/2001

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.