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Choosing a cylinder head for the 998 engine
https://www.ausmini.com/forums/viewtopic.php?f=5&t=69039		 Page 1 of 2
Author:  mini7boy [ Thu Feb 24, 2011 5:09 pm ]
Post subject:  Choosing a cylinder head for the 998 engine
for those who have not seen it yet, Keith Calver wrote an article for the March 2011 issue of Mini Magazine that covers some of the cylinder head options for use on a 998. He specifically covers the 12G295, 12G202 and 12G940 heads and also provides flowbench data that can be used to compare the heads.

Calver wrote a related, but different, pair of articles for the Mini Magazine special edition Mini Expert publication that is now only available on CD at:

http://www.calverst.com/

These articles also had flowbench data for a selection of heads that could be used on a 998, including the 12G295 and a standard 1275 A+ head.

Either of these sources should provide useful information for the aspiring 998 owner looking for better performance.
Author:  mattsmadmini [ Thu Feb 24, 2011 9:35 pm ]
Post subject: 
Small bore engine, the 295 is the best stock head you'll get for it (or a 206)

the 202 is a great standard head, and can be worked to flow as good as a 295(hell even better with more $)

i have a worked 202, i love it.

940 is cool, but it is a large bore head, some pocketing is needed so valves dont hit the deck, alot of work that wouldnt be reversible.

my 2cents.
Author:  mini7boy [ Sat Feb 26, 2011 11:15 am ]
Post subject: 
A 12G940 head does not necessarily require that a 998 block be pocketed. As Calver relates in his articles(mentioned above), it is possible to run a 940 head on a 998 block without pocketing the block. It all depends upon: bore size, valve size, valve lift(lobe and rocker), how much the block and/or head have been skimmed, deck height(how far the piston runs below the block's deck).

Depending on all of these factors, it is quite possible to run a 940 head on a 998 block without pocketing. Calver even goes through a project build and provides measurements to support the installation. This is documented in one of the several 998 tuning articles Calver wrote for the Mini Expert CD mentioned in my previous posting on this thread.

There may be reasons why a 940 head is not a good choice of head for a given 998 engine, but the need to pocket the block isn't one of those reasons.
Author:  Lillee [ Sat Feb 26, 2011 11:21 am ]
Post subject: 
It's a lot of trouble still for little gain over a well ported 202 like Matt says. If you have to run low lift cam, low compression (so that the pistons don't reach the top of the block) then you're looking at less than optimal tune for a 998.

Get a 202, port it properly, high compression ratio, good cam: I doubt a 12G940 head will beat this combination

While you're at it, throw in a 1098 crank...
Author:  CARTER_GT [ Sat Feb 26, 2011 11:46 am ]
Post subject: 
so a noob question because i have forgotten. Is a 12G295 a cooper head
Author:  drmini in aust [ Sat Feb 26, 2011 12:01 pm ]
Post subject: 
Yes a 12G295 was the head on a 998 Cooper (but most 997 Coopers got the 12G202 head, never the 295).
Good 295 heads are getting rarer, but 202 heads port out as well or even better (according to Graham Russell), and there are heaps more about.
Author:  CARTER_GT [ Sat Feb 26, 2011 12:04 pm ]
Post subject: 
ok thats good, ive got a 295 on my 1100 so it looks as if ive got the good one, from a stock perspective atleast
Author:  Super-mini [ Sat Feb 26, 2011 2:09 pm ]
Post subject: 
what head did the A+ engines have?
Author:  poeee [ Sat Feb 26, 2011 4:13 pm ]
Post subject: 
Super-mini wrote:
what head did the A+ engines have?


The 998 auto A+ I have hear looks like a 998 clubby head, whatever the number is on them??
Author:  mattsmadmini [ Sat Feb 26, 2011 4:15 pm ]
Post subject: 
mini7boy wrote:
A 12G940 head does not necessarily require that a 998 block be pocketed. As Calver relates in his articles(mentioned above), it is possible to run a 940 head on a 998 block without pocketing the block. It all depends upon: bore size, valve size, valve lift(lobe and rocker), how much the block and/or head have been skimmed, deck height(how far the piston runs below the block's deck).

Depending on all of these factors, it is quite possible to run a 940 head on a 998 block without pocketing. Calver even goes through a project build and provides measurements to support the installation. This is documented in one of the several 998 tuning articles Calver wrote for the Mini Expert CD mentioned in my previous posting on this thread.

There may be reasons why a 940 head is not a good choice of head for a given 998 engine, but the need to pocket the block isn't one of those reasons.


Ok.

So you go get a bog stock 998 and a bog stock 12g940, then make it work ok?

:wink:

-Matt
Author:  mini_mad_matt [ Sat Feb 26, 2011 4:20 pm ]
Post subject: 
No offense mattsmadmini, but i think you totally missed the point of his original post
Author:  GT mowog [ Sat Feb 26, 2011 5:24 pm ]
Post subject: 
Super-mini wrote:
what head did the A+ engines have?


Very similar to a 202 head, nothing that would make any real difference between them.
Author:  mini7boy [ Sun Feb 27, 2011 10:12 am ]
Post subject: 
I'm not happy with the way I worded this last sentence in my second posting(above) on this thread.

I said: "There may be reasons why a 940 head is not a good choice of head for a given 998 engine, but the need to pocket the block isn't one of those reasons."

I could have better conveyed the thought I intended by instead saying:

"There may be reasons why a 940 head is not a good choice of head for a given 998 engine. It may be that a given 12G940 head has ports and/or valves that are too large to support good port velocity on a 998 engine that is of a fairly mild build spec. The head may also have been skimmed too much to allow a suitable compression ratio or room for an adequate amount of cam lift. But, a 12G940 can be used successfully on some 998 engines without the need to pocket the block."
Author:  david rosenthal [ Sun Feb 27, 2011 1:44 pm ]
Post subject: 
mini7boy wrote:
I'm not happy with the way I worded this last sentence in my second posting(above) on this thread.

I said: "There may be reasons why a 940 head is not a good choice of head for a given 998 engine, but the need to pocket the block isn't one of those reasons."

I could have better conveyed the thought I intended by instead saying:

"There may be reasons why a 940 head is not a good choice of head for a given 998 engine. It may be that a given 12G940 head has ports and/or valves that are too large to support good port velocity on a 998 engine that is of a fairly mild build spec. The head may also have been skimmed too much to allow a suitable compression ratio or room for an adequate amount of cam lift. But, a 12G940 can be used successfully on some 998 engines without the need to pocket the block."


I found a 940 head bolted to a stock 850 engine . it worked but a waste of a good head.

As for port velocity you can have low velocity and high volume flow, or high velocity and low volume flow. So what is better. What ever the head is "flowed at" does not mean much if you have a variable flow restrictor in the system.

On the subject of valves consider the shape of the combustion chamber and the amount of valve shrouding it has. This also has a BIG influence on air directional flow into the cylinder.

I have used cylinder heads on my performance 351 V8's that were "U beaut" flow tested and they would not pull the skin of a rice pudding, yet other heads had less "maximum flow' and left them for dead.
With any performance engine it's a balancing act to get everything to work.
Author:  mattsmadmini [ Sun Feb 27, 2011 8:11 pm ]
Post subject: 
Apologies mini7boy.
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