MGB MGB head info.

[bob67bgt]

Here is what i have for my thoughts and info. Add what you have to the mix so we all learn something!The top head is a 68 to 71 and the bottom is 72 and newer combustion chamber design the next pic is the combustion chamber on a 67 head. next pic is the water temp gauge area. What i found is generally the flat top at the sender is a big valve head from a 18 V engine. Round is up to when the V started and has smaller valves and combustion chamber as pictured in the other shots. We'll get to exceptions in the next post. Bob

 

[bob67bgt]

Well that worked so far. Next shot is the cross flow head and here are shots of the X cast head. The combustion chamber looks like the 71 and earlier head but the head is a non polution head and has the flat top at the water temp area. I have not checked to see if its a big valve or small valve yet. When i was at Tony's place last year he had 2 X cast non pollution heads and one was round and one was flat at the temp area. The latest heads (sorry i do not have one available) has a tear drop shape at the water temp area. I would guess this is when the factory went to the smaller valves but can not confirm. What observations have y'all made?

 

[bob67bgt]

One more thought regarding heads and interchange. All the heads up to the 18 V used the long lifters. If you have a pre 18V head and try to use the short lifters you will run out of adjustment (or be close to running out)when setting the valves.(with stock or mild cut head). So if you see a flat top on the water temp area you can use short lifters. Now that X cast head may be a exception!

 

[Hap Waldrop]

Bob you can custom pushrod a tick longer, or any length you want for that matter, for that and they don't really cost much more than new long stock pushrods.

How about some casting numbers, I don't think they are any hidden "magic" heading casting out there as for performance, maybe the factopry used different foundries, I seen this on 1275 heads, but at the end of the day they are pretty much all thae same, of course with a die grinder any of them can be made magic As for the X-flow, I built tow engine with those heads, I wanted to port both of them and the customer didn't want to spend the money, I guess the engine gods were looking out for me, the later xflow heads, anyhthing not Derrington, has bad casting flows and can be trusted to be ported, ask Sean Brown anbout that one, and as stock the ports don't flow alot better than the siamese head, x folw heads are not really worth it my opinion, more bling than anyhting else, kinda a shame though, if the casting was done to a higher standard it could have been a real performer.

Another thing folks always get excited about the big vavle factory heads, you can make any of them big valve heads easy enough, even go bigger than 1.625, I used alot of the 1.7 intakes.

One thing you got to watch for is putting later 18V heads on early model blocks, if you do that, and try to run a performance cam you need to nothch the block for the exhaust valve.

I've seen people do alot of crazy, stuff, recently I had a early model head that had been already repaired when I got a hold of it, the ealry head you got me was to repalce that head, I had a shop owner buy that thing form me pressure check, well atleast he said he did, and then put it on a MGA 1500, while it will work, you beeter never run any cam more than stock, shave the head, and at best it probalby 7.5 to 1, needless to say, not the hot set up

Ok, with all that said, I heard Tony drool over the "X" head for years, so maybe it is time to put this mytstery to bed, bring one down Bob, we can clean it up, CC it and flow if you like, that way we can see if they are anyhting special about them or not.
Oh and now that you've had a chili cheese, I'll take you out for some soul food

 

[tony barnhill]

Ok, with all that said, I heard Tony drool over the "X" head for years, so maybe it is time to put this mystery to bed, bring one down Bob, we can clean it up, CC it and flow if you like, that way we can see if they are anything special about them or not.

That might be an interesting thing to do....

There were 4 types of cylinder heads fitted to USA market MGB's, casting #'s 12H906, 12H2389, 12H2923, CAM1106....some have smaller intakes & some have larger....some had smaller combustion chambers, other larger; some has dished pistons, some flat pistons...combined with their correct piston, some had 8:1 compression ration while others had 8.8:1.

The "X" head is casting number 12H1326 AFIH (never offered in North America)....as I understand it, the "X" has both larger intake & exhaust valves along with larger throats for both intake & exhaust valves....plus, the shape of the compression chamber is different and it has more capacity than heads offered here.

Plus, as I understand it, the pistons originally combined with the "X" head were shaped to help increase the compression from 8.8:1 (largest offered in US).

 

[bob67bgt]

The cross flow on the engine i just purchased has pretty smooth intake and exhaust ports and the intake also looks slick. I do not have any history on the engine build up but it sounded good running on the garage floor! With around 5000 miles on it i will plunk in into my next project and see if $2000+ in add on parts does any good or is just bling. I need to take the X cast head apart to get it crack tested and can measure the valves. The combustion chambers sure do look like 65-71 heads. It would be interesting to see how it cc's and flows. Sharing good information always holds my attention! Thanks Hap and Tony for adding to the information. Hap i have not forgot about bringing that block your way. Its just been busy around here buying junk and swapping stories. Soul food sounds interesting....Burp.... Bob

 

[tony barnhill]

Interesting, Bob, check the "clock" in your "X" head....bet it was built somewhere between '65 & '71...all mine are '71's.

 

[bob67bgt]

Tony, the clock has 01,k and 3. Bob

 

[Hap Waldrop]

There were 4 types of cylinder heads fitted to USA market MGB's, casting #'s 12H906, 12H2389, 12H2923, CAM1106....some have smaller intakes & some have larger....some had smaller combustion chambers, other larger; some has dished pistons, some flat pistons...combined with their correct piston, some had 8:1 compression ration while others had 8.8:1.

The "X" head is casting number 12H1326 AFIH (never offered in North America)....as I understand it, the "X" has both larger intake & exhaust valves along with larger throats for both intake & exhaust valves....plus, the shape of the compression chamber is different and it has more capacity than heads offered here.

Plus, as I understand it, the pistons originally combined with the "X" head were shaped to help increase the compression from 8.8:1 (largest offered in US).

Caution, this is a really long winded "gearhead" post

The 12H1326 is the stock head for any MGB 1965-1968, it's that last of the 42cc closed chamber pre smog heads to come to America. More than likely rather than your "X" being some magic special performance head, it's just the home market head. Begining in 1968 in the US we saw the introduction of the smog punp with the 12H2389 cylinder heads and it's smog pump air rail injection ports, keep im mind the US was the only place the smog pump was required, so more than likely, the X head was for everyone else, it should be easy enough to find about form a Brit who knows his home market MGB engines. Aslo it imortatant to mention, US was the primary market for these cars, about 70% of all them ended up here, so we have way more of them than the Brits do, heck the reason MG wnet out of business was because the US market, the dermise of the convertible, ever growing emission laws, the growing popularity of Japanese cars. Therie car never got the dreaded single ZS and single intake/exhaust manifolds, they had twin HIF4s, just like their Midget 1500 all got twin HS4s carbs set up, they all got rubber bumpers, becuse since the US was the primary market, it was cheaper just to give everyone the RB cars, than have different chassis, but the rest of the world didn't get any of the smog crap. At this poit they were spending alot of money trying to make their cars faster, factory racing was dried up by 1978, and for the most part the company was on life support. My bet is all the X heads are, are UK and world market (other than US) cylinder heads,the and the reason a few of these head ended up hear is more than likely these heads got gobbled up the aftermarket, and offered as new replacement heads for MGB in the US with cracked heads.

Here's run down of US MGB heads

12H906 1964-1965 42cc closed chamber heads, .400" deep combustion chambers, pre smog,1.5625" intake and 1.343" (1.343" exhaust valve were used in the entire MGB production run, no other size exhaust valve was ever used by the factory)Thes heads used the wide collets, and cotters on the valve hardware. These heads were fitted on engine using the shallower 8.8 to 1 dish pistons.

12H1326 1965-1968
These heads were pretty much the same head as the 12H906, just casting improvements were made, valve sizes, collet style, hardware all remained the same. 8.8 dish piston were used

12H2389 1969-1971.
This was the begining of the smog heads, so this is the first head you see with the smog pump injection holes. These heads are also 42cc .400" deep closed combustion chambers. These heads also used the 1.5625" intake valve. This head is also the first MGB head to use the new narrow collet valves and hardware. All MGB heads for the US market from this point on had smog pump injection ports. 8.8 dish piston were used

12H2923 1972-1974.5
This the first of the open chamber 38cc .375 deep combustion chambers heads. This is also the head that folks referred to as the
"big valve heads" as the intake valve size was increased to 1.625". Because of the shallower combustion chamber this is first MGB head to require exhaust valve cut outs in the block, these engines were fitted with the deeper dish 8.0 to 1 dished pistons.

CAM1106 1974-on
This head was also a 38cc .375" deep open combustion chamber head, they went back to the 1.5625" intake valve, they also move the oil feed in the rear rocker arm predestal form center to offset and this head require a new offset rear rocker arm pedestal.

Other heads that made it to the US either as factory or cast iron aftermarket replacments.12H4743, exact copy of the CAM1106.
12H4736, I recntly rebuilt one of these, they are mechanically exact to the CAM1106, but the other casting was much smoother, and thes heads wwere over all better casting, much less likely to find one of these uncracked than a CAM1106

OK, on to the piston, there were really only tow piston, compression ratio wise ever used from the factory the the 8.8 top 1 shallow dish pistons used up to 1971, and the 8.0 to 1 depper dish pistons used form 1972 on, now it reasonable to think that a 8.8 tom 1 piston may have been used for the home market form 1972 on, due to lack of emission laws to deal with outside the US. And it alos noteworthy to menation most 18V replacment piston used these day, County, AE are offered in 8.8 to 1 dish. I know of no factory flat top piston ever offered. There are no real records showing any uprated MGB engine within the years of production, in otherwords no engine options within a given year, we pretty much all got the same stuff, after the smog stuff, the hoime market engines were still kept to the pre US smog standards, but thats about it.

It would be interesting to flow a X head on my flowbench to see if it flows better than any of the other stock heads, mainly because I build a few SCCA limited prep 1800 race engine, in SCCA limited prep engine rule, head porting is not allowed, so the hot ticket is flow as many stock heads as you can get your hands on and find the best flowing heads, at this point no one has done alot of this, because in G p[roduction the LP MGB was a dog, but now moved to H production, this dog has new life, and we may see some more interest, but we're still talking a small market. What we found about A-series stock heads flowing them, that they was more than one foundry, and some foundry's heads flowed beter than other, most it has to do with the size of the valve guide humps, and even within the "good" we see better and wrose examples. For the performance street I don't see the X head beiong a big deal, because any head can be made great with a die grinder and decking, and I see no great market for unported head for the street for any other reason than repalcing cracked heads.

So Bob, Tony if one of you want to loan me a cleaned X head for flow testing, I should be ready to do this by late june early July, then maybe we can all learn something.


Oh last but surely not least, most of the head casting number information needs to be credited to Sean Brown at Flowspeed, www.flowspeed.com Sean has compiled some great info about MGB heads on his site.

 

[Hap Waldrop]

Bob my guess it that equates to 10/73 and that is a home market non smog pump head. It was probably bought here from a vendor as a replacment head.

 

[bob67bgt]

I am not sure the clock would be for a late 73 head. Unless the eruo spec engine still used the early combustion chambers into 73. I have a bunch of things to do in the next few weeks but i will submit my head for a flow test. It just may take a while to get to that point. The rest of this week will be getting ready for british car days south, picking up the new 67 BGT in Spartanburg and ....Yep i found another MGB while on vacation at the beach! Next week will be a bit slower pace for me. Hap, Great info that can be printed for reference. Bob

 

[tony barnhill]

My "X" heads are all stripped & cleaned & magnafluxed.....Hap, you may be correct that they were UK-only offerings (like I said in my earlier post, they were not offerred in North america)...but, I think we'll find differences in the flow characteristics, not necessarily in the combustion chamber capacity.

 

[Hap Waldrop]

Well not to fret, I'm in the middle of making a new MGB flow plate for my Superlfow 110, I found the piece of pipe I was looking for, now I got to go source some plate, and fab and weld it all up.