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MG MGA - 1622 motor - 15,16,or 18 head>?

I'm rebuilding a 1622 motor that came to me with a 15 head on it. Of course, there are no 16 heads available, at least that I can discover. Does the 18 head work with this motor or would I be better off using the 15 head? Your comments would be very welcome.

By the way, I tried emailing Barney G using the link on his web site but it csme back undeliverable. Is he just tired of being bothered or did I have the wrong link?

Thanks for any advise you can give me.

Jerry Hudrlik
J. Hudrlik

An 18 head will be fine - same volume on the early heads. Later MGB heads do vary a bit.
Bill Spohn

Jerry, Have a look at the site below -"Casting numbers" - this is related and very comprehensive.
Barry
BM Gannon

Hey, J.H. - my web site e-mail link works fine, as I get lots of messages that way every day. A link at the bottom of every web page goes to the same FormMail page for sending me a message If you ever find one that doesn't link properly, let me know, but it should be a very rare bird as they are all clones (about 1700 of them).

I did get your message on Jan.9, but my reply bounced the first time because you typed a comma in the middle of your e-mail address. I think I got it right on a second try on Jan.11.

The short answer is, a 15 head on a 1622 motor with flat top pistons makes for abnormally high compression. 18 heads work fine, except the "L" head which has smaller chamber volume similar to the 15 head.
Barney Gaylord

Barry,
You mention "the site below" but I don't see a link.

Barney, sorry about the bad address.I'm forever making mistakes in typing. Would you please give me a little more information about the "L" head.

Thanks to all for your responses
J. Hudrlik

http://www.flowspeed.com/cylinder-ident.htm
dominic clancy

Jerry, There are alot of different opinions regarding the large valve vs small valve 18 head. After some research I went with a ported small valve 18 head. I run it on a vintage race car with a 1622 block, high compression at about 10.5:1, and it works very well. Also, it is a good idea to refer to the casting number reference mentioned above because some of the castings had a shift btwn the two halves and can cause airflow issues. The best thing to do is to look at the head yourself once cleaned.

Here are a couple of links to more info on compression ratios, combustion chamber volumes, etc.
http://mgbmga.com/tech/mga6.htm
http://mgbmga.com/tech/mgb25.htm

Have fun with it!
John
J Bries

Jerry - depending on how early a given engine came in the production cycle it could have the MkII head but have a "15" casting. That was the case with my engine, original with a MkII built in April 1961 chassis #GHNL2-100870 and engine #16-UH-554. There's also a thread about this from 2000 on the archives.

Have you pulled the head to check the size & shape of the combustion chamber and valves so you are sure it is a 1500 and not an early "16" head?

- Ken
Ken Doris

Not all 1800 heads are the same -a good option to a 1800 head on a 1622 block is to use the Austin 1800 head 12H2709. This has a combustion chamber of 38cc (compared with MGB head of 43cc)and following the method given in the British Automotive web site would give a compression ratio of 8.73 to 1 assuming slightly dished low compression pistons. I think that this level of CR is OK for normal use. The inlet valve is 1.565". I believe but cannot be certain that this does not require eyebrows in the block.
J H Cole

Jerry, Look for the Thread Heading below this one:
"Casting numbers" H Speer 5 12 January 2008
It is listed under THREAD HEADINGS and is all about the different heads, pictures and all. Good luck, Barry
BM Gannon

A 1500 head is no good with this engine, compression is much too high and you will have severe detonation problems and / or piston and gasket problems.

You need either a 906 or 1326 casting head, all the others have the smaller chambers. I use the 12h1326 head on a flat top piston 1622 engine. Works great, even with a Supercharger. Don't need any mods to the block either, so the best head to use on the 1622 block. They have large valves as standard, as well as the larger chamber that you need. Will also make the car run cooler as they breathe better than a 1500 head.

Neither of these should be hard to find. I found one on my second phone call.

Now if anyone wants my redundant Oselli Stage 2 1500 head (just a few hundred km on it) , just make me an offer



dominic clancy

Dominic. the Flowspeed site with pictures is great. Ken, unhappily, my motor is "16 GC-U-H3694" so not likely that the 15 head is one of the early production with same specs as the "16" but will check.
Thanks to you all for great information.

Jerry Hudrlik
J. Hudrlik

"A 1500 head is no good with this engine, compression is much too high and you will have severe detonation problems and / or piston and gasket problems."

Not even close.

The small chamber head used on the 1489 and 1588 engine is perfectly compatible with the 1622, using flat top pistons. The compression will indeed be higher, but quite suitable for a semi-competition build, and will not result in any detonation problem. It comes in at just under 9.5:1, hardly a cause for detonation.

That notwithstanding, the larger chamber 18 head is more suitable as it uses the larger valves of the 1622.
Bill Spohn

Bill's experience is different to mine - so I can only put it down to both block and head having been skimmed. In any case, with the 1500 head on my 1622 block, the compression readings were *extremely* high even before the SC was fitted. I guess this comes under the category of your mileage may vary.,,,

In any case I can reaffirm the suitability of the 1326 head with a flat top piston 1622 application, even when adding a SC.

dominic clancy

Yes, Dominic, if the head and or block had been skimmed all bets are off - but that doesn't represent stock parts.

The flat top pistons available from the factory for the 1588 cc engine gave 9.25 compression with the small chamber head.

The 1622 is precisely 0.030" larger bore than the 1588 and also has flat top pistons. Boring a 1588 to .030" over will not make a 9.25 compression engine into a high compression monster. It raises the compression to 9.45.

BTW, anyone doing the calculation should not just use the cylinder swept volume and the combustion chamber volume. There are also several cc of additional volume including the volume in the plug tip, and the slice of cylinder below the deck, as the pistons do not have a zero deck height (jard on heads and gaskets if they did) - they normally site .020" - .030" down the bores.

I am sure that if you took a shaved block and head with compression closer to 10:1, it would definitely counter-indicate use with a supercharger. For normal use, however, the small chamber head on the 1622 can be quite useful, particularly as you don't need to screw up the rocker geometry by whacking great chunks off the head to get more compression. The larger Mk 2 valves can be fitted to the small chamber, and with a little attention to the valve throats will flow quite well.
Bill Spohn

I'd be very surprised to find a block or head these days that have never been skimmed (though one of our club found a new MGA TC block and 2 TC heads in the last two years, so they do exist).
dominic clancy

This thread was discussed between 13/01/2008 and 19/01/2008

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