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Re: MGA head vs. MGB head - have I lost my head???

Subject: Re: MGA head vs. MGB head - have I lost my head???
From: Barney Gaylord <>
Date: Wed, 13 Jul 2005 03:55:25 -0500
At 01:43 PM 7/12/05 -0400, Albert Escalante wrote:
>.... What  ever happened to Barney Gaylord, .... lately, I haven't seen 
>too much (or any!) of his concise and informative entries and answers to 
>this list's constant Q&A. Anyone know if he's still amongst us. You out 
>there, Barney?? ....

Yeah, I'm still here, mostly lurking.  As long as you're all getting decent 
answers I can lurk.  If you get a bad answer, sometimes I hop in with a 
comment.  If I may have some special answer I may respond.  I've been 
spending a lot of time posting more tech pages on my web site, now up to 
about 750 pages of MG tech info.  If y'all look there first you might not 
have to ask so many questions.  And if you can ask an MGA question that's 
not answered there, maybe I post another web page.

Lemmesee if I can summarize this.

1.)  The 15 head used on 1500/1600 engines has 38cc chamber volume.
2.)  The 16 head used on 1622 engines has 43cc chamber volume and larger 
valves, used with flat top pistons.
3.)  The 18 head used on 1800 engines 1962-1967 has 43cc chamber volume and 
is very similar to #2.
4.)  The 18 head used on 1800 engines 1968-1971 has 43cc chamber volume, 
and add air injection ports.
5.)  The  L  head used on 1800 engines 1972-1974 has (about) 38cc chamber 
volume and larger intake valves.
6.)  The 18 head used on 1800 engines 1975-1980 North America is similar to 
#4, add water take off at the back.

Any of the heads will bolt on to any of the blocks.
1-4 have dual valve springs.
5-6 have single valve springs (unless converted to dual springs).

If you install a 38cc head in place of a 43cc head you have higher than 
stock compression.

If you install a 43cc head in place of a 38cc head you have lower than 
stock compression (but you can shave the head to reduce chamber volume).

If you install a "15" head in place of any other you have smaller than 
stock valves.

If you install the "L" head in place of any other you have a larger intake 
valves (and high compression).

As to the specific example under discussion, having a 1800 block under a 15 
head (must have premium fuel) will give more torque than a 1500 or 1600 
engine, but will not be up to stock 1800 performance.  Depending on your 
point of view, the 1800 block is an upgrade for an MGA, or the 15 head is a 
downgrade for an MGB.  Aside from the differences in net torque, the only 
problem I see with the 15 head on the 1800 block would be side effects of 
the high compression ratio.  A high performance camshaft may like higher 
compresion ratio, but does not like not small valves.

One of the easiest performance upgrades you can do for a B-series engine is 
to switch the 15 head to any one of the other heads, which all have larger 
valves and better porting.  The larger valve 18 head will run better on the 
1500/1600 engines, even with lower compression ratio.  Any of the 18 heads 
can be shaved to reduce chamber volume for use with 1500/1600 engines, but 
you may need to add clearance eyebrows in the top of the block (as was done 
for all 1800's from 1971 on).

Barney Gaylord
1958 MGA with an attitude

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