15 replies to this topic

[dotmatrix]

Hello.

apologies if this has been asked before, but here is my question:

 

which 12g940 is best for larger valves and flow modification for power?

which one should I send out to get modified?

old flat thermostat area or new metro 12g940 head?

 

thanks and merry christmas

Martin.

 

 

[Lplus]

Hello.

apologies if this has been asked before, but here is my question:

 

which 12g940 is best for larger valves and flow modification for power?

which one should I send out to get modified?

old flat thermostat area or new metro 12g940 head?

 

thanks and merry christmas

Martin.

Whichever you have that seems in the better condition.  I don't think there's any difference in chamber shape or ports between the two.  The older type might have a tapping for the bypass connection if that's how you want to set up the cooling system.  The MG metro head has bigger inlet valves and is maybe slightly skimmed for a fractionally higher compression ratio, but that seemss to be it.  Yes, I have examples of all three.

[nicklouse]

Either are fine. But on the older one just check for stamping on the flat surface (if 10 stud and 1 bolt fixing) as it may be worth a bit more as an original S head.

 

but in any case get them both crack tested first. No point send a cracked one out.

[dotmatrix]

Either are fine. But on the older one just check for stamping on the flat surface (if 10 stud and 1 bolt fixing) as it may be worth a bit more as an original S head.

but in any case get them both crack tested first. No point send a cracked one out.

so none of the castings are better for flow improvemens, 11 stud, flat thermostat or metro type, all equally good as a starting point?

[Lplus]

 

Either are fine. But on the older one just check for stamping on the flat surface (if 10 stud and 1 bolt fixing) as it may be worth a bit more as an original S head.

but in any case get them both crack tested first. No point send a cracked one out.

so none of the castings are better for flow improvemens, 11 stud, flat thermostat or metro type, all equally good as a starting point?

 

11 stud should already have the larger inlet valves. Some may also have larger exhaust valves, in which case they are likely a cooper S head and worth far more money in standard form.
 

[Ethel]

The casting with the raised profile on top was originally for the Metro Turbo. It's supposed to have a revised water jacket to improve cooling. Watch out for unleaded valve inserts, in later heads, if you want to  use valves near the limit of what'll fit.

[dotmatrix]

The casting with the raised profile on top was originally for the Metro Turbo. It's supposed to have a revised water jacket to improve cooling. Watch out for unleaded valve inserts, in later heads, if you want to use valves near the limit of what'll fit.

ok. thanks. those hardened inserts for leadfree fuel on original heads, does that exist? i have seen quite a few heads, versions up to 1990, but none with inserts from the factory

Edited by dotmatrix, 23 December 2022 - 02:16 PM.

[nicklouse]

 

The casting with the raised profile on top was originally for the Metro Turbo. It's supposed to have a revised water jacket to improve cooling. Watch out for unleaded valve inserts, in later heads, if you want to use valves near the limit of what'll fit.

ok. thanks. those hardened inserts for leadfree fuel on original heads, does that exist? i have seen quite a few heads, versions up to 1990, but none with inserts from the factory

 

Only after about 1988/9 did the inserts come as standard. And contacts to the above all A+ heads 998 and 1275 had the shaped top surface. It was all part of the reworking they did. 

[Ethel]

Interesting, don't think I've seen a small bore head with the raised profile. It was just on the turbo engines for a couple of years though. I presume they also had the more significant differences when it was adopted across  the rest.

[nicklouse]

Interesting, don't think I've seen a small bore head with the raised profile. It was just on the turbo engines for a couple of years though. I presume they also had the more significant differences when it was adopted across the rest.

Are we talking about the same raised/sculpted part?

A+ 998 head  7C3B56A1-7D8C-46A3-8825-E551847A4CC9.jpeg   48.93K   4 downloads

[ACDodd]

Use a small inlet valved 940 casting with unleaded seats already installed from the factory. Check they are not loose.
The smaller inlet valved head has more meat around the post throat to get a nice 4 angle seat on it.

Also use a casting with a thick deck.

The newer the casting the better.

Ac

Edited by ACDodd, 24 December 2022 - 01:45 PM.

[Ethel]

 

Interesting, don't think I've seen a small bore head with the raised profile. It was just on the turbo engines for a couple of years though. I presume they also had the more significant differences when it was adopted across the rest.

Are we talking about the same raised/sculpted part?

A+ 998 head 7C3B56A1-7D8C-46A3-8825-E551847A4CC9.jpeg

 

Don't think so, I mean the ones that match the gasket outlines.

[dotmatrix]

Use a small inlet valved 940 casting with unleaded seats already installed from the factory. Check they are not loose.
The smaller inlet valved head has more meat around the post throat to get a nice 4 angle seat on it.

Also use a casting with a thick deck.

The newer the casting the better.

Ac

but if i want oversized valves is it still preferable to start with this type of head?

[ACDodd]

Yes.

Ac

[Lplus]

Yes.

Ac

Presumably because the valve throat is a bit smaller than the big valve head but the shape of the seat is better?