26 replies to this topic

[70K1100]

I've been looking everywhere I can think of but can't find the answer I'm after. Is there any difference between the intake port sizes of a small valve 940 head and a MG Metro 940 head?

As a side question, can I use the 33mm 940 inlet valves in a small bore head with standard exhaust valves from a 295 head?

[Dusky]

I think the valves are a different lenght, but not 100% Sure.

[Spider]

There were at least 7 different castings (that I've seen so far) of the infamous 12G940 heads, basically the Inlet Ports between them were similar in size and shape, but the exhaust ports vary considerably. On the factory heads that used the bigger Inlets (Late Cooper S and MG Metro) they had more machined from them, above the seats.

[70K1100]

My reason for asking is that I have a 295 head where the inlets have been bored out to suit 33mm valves. The other option is to build a 1275 that I found. The 295 head would go onto an 1100. My aim to get close to the 70-75hp and same in torque for a road Mini.

[Cooperman]

With very large (relatively) inlet valves in a small-bore engine to get power means a cam with more overlap & lift. this, in turn, requires higher mixture inlet flow velocity which moves the torque band higher up the rev range, so useable torque low down is reduced.

A good compromise would be to use an MG Metro cam with twin HS2 carbs which will improve throttle response lower down and hopefully give slightly better torque. A different distributor curve will be vital.

70 bhp will be possible, but it will be a bit 'cammy' and with a 1098 engine, with its low rev limit, those size inlet valves may well not be ideal, although they will work OK.

[ACDodd]

I only use 1275 valves in modified small bore heads now. The 33mm inlet is a perfect item to use in a 295 head. The 1275 based valves are longer. You will need to run shims under the rocker gear to correct the rocker geometry. The 1275 exhaust valve will need machining down to 26.4mm to enable it to fit in the original bore size.
 
In my view a bigger capacity small bore makes the best use of the 295 head as the intake ports are very large. I only use the 295 on 1100 or bigger engines. For the 998 I use a thick deck 998 based head fitted with 1275 valves, usually machined to 1.27" inlet and 1.040" exhausts.
 
What you are planning is what I advise my customers. Go for it.
 
For your info the ports are different on the 940 heads. Original factory 35.7 intake valve heads have a slightly larger intake port than those heads fitted with the 33.3mm inlet valved heads.
 
AC

Edited by ACDodd, 27 December 2015 - 03:46 PM.

[70K1100]

I'm looking at a 266 camshaft from Russell Engineering because of the torque they produce in a suitable rev range of the 1100. Compression ratio will be around 9.5:1 to 10:1.

[70K1100]

I only use 1275 valves in modified small bore heads now. The 33mm inlet is a perfect item to use in a 295 head. The 1275 based valves are longer. You will need to run shims under the rocker gear to correct the rocker geometry. The 1275 exhaust valve will need machining down to 26.4mm to enable it to fit in the original bore size.
 
In my view a bigger capacity small bore makes the best use of the 295 head as the intake ports are very large. I only use the 295 on 1100 or bigger engines. For the 998 I use a thick deck 998 based head fitted with 1275 valves, usually machined to 1.27" inlet and 1.040" exhausts.
 
What you are planning is what I advise my customers. Go for it.
 
For your info the ports are different on the 940 heads. Original factory 35.7 intake valve heads have a slightly larger intake port than those heads fitted with the 33.3mm inlet valved heads.
 
AC

AC what are some of the figures that your 1100 engines producing? I've seen your camshaft range but don't know how they compare to the RE266 camshaft.

[ACDodd]

I would expect a good runnin 1139cc engine to push 73 to 75hp with a good head and my ACD - RS cam.

Ac

[70K1100]

That's the figures I would like. What are the specs for your ACD RS cam?

[70K1100]

Do you think that a 12G295 head with the 33mm inlet valves and the 26.4mm exhaust valves and 10:1 compression achieve those type of figures?

[ACDodd]

Absolutely. Have you got an email address, I'll send you some info.

Ac

[Vipernoir]

What is an 1139 ?

 

+.040" on a 1098 is 1133cc.
+.060" on a SA is 1129cc.

[ACDodd]

Sorry typo, that should have been 1149cc.

Ac

[Vipernoir]

My 1150 (+.060 1098) with unknown origin 12G295 and horrendously badly timed-in MG cam (long story, but it's about 7° retarded !!) was around 63-66 nanas & torques from what I remember, so mid 70s should be easily achievable.

 

Did I send you my capacity and compression ratio calculator AC ?
I know I sent it to Keith and a couple of others - allows for tweaking numbers to work out static compressions on all sizes of A-series and run comparisons across standard overbores.