21 replies to this topic

[chris211083]

Ok my wife wants to make her mini faster and more reliable, so as the Mechanic husband I started by fitting Specialist Components 5 port injection kit.Which Upped power out put and reliability of our 998 1988 austin mini to 50.9bhp over the carb output by 5bhp with more torque. Here is the link.......

http://www.theminifo...omponents +port

However this was never the end, the final though is a supercharger which we will fit next year. However being more into Triumphs I didn't know the most cost effective way to go with heads etc. So after a bit of searching it turns out that the early 12G295 heads are suppose to be the mutts nuts. So for the wifes Christmas Present I bought her a Standard 12G295 head. This was a bit of a gamble as I can't find any evidence as to why this would be better, no pic's anyway. So before I fit the head here are some photo's and measures of the 12g and the standard late 998 heads. The Difference is MASSIVE!!!!



Obviously the one in green is the 12g295 and the one above is a cam4810 head.

So inlet ports:
Standard 998 Starts at 31mm but has a harsh taper closing the hole quite a bit.


The 12G295 starts with a 35mm recess with a 32mm hole which doesnt taper but instead goes into the port and gets wider at the valves. Massive difference over the late head.


Here on the 12G295 head you can see into the port and the is alot of space in there. Not how mucch of the valve you can see!!




And the late standard head, here is the taper and below the inner port. Note how much the chanber is reduced and how little valve you can see. It really is that different.




Then there are the combustion chamber shapes. the 12g shown below with a short chamber with rounded edges and unobstructed valves.


The Standard Head combustion chamber is totally different in that the chamber has a large ridge on the point of the heart shape and also the heart shape is much more pronounced than on the 12g head. Also note the steep and deep walls that are close to the valves and will reduce flow into the cylinder.


Next the spark plug holes, the standard:


and the 12G295



What a difference.

Finally the tops and valves. The 12G uses double valve springs with securing clip, the springs and caps are much smaller.



Then the standard heavy single valve springs.



Next is valve sizes, my measures are not accurate but you get the idea.
12G
Inlet

Exhaust


Standard late head:
Inlet

Exhaust


The Difference is very clear to see, so next job is to fit it and then Dyno test it. Changes will be just the head and see what difference it makes. This will happen in warmer drier weather so give it a few weeks but it will come.

Merry Christmas all 2012.

Chris.

[jonny95]

the 12g295 has large combustion chambers so the compression ratio is lower. You may want to skim it and then you should see excellent gains in power. About 10:1 should be good

Also, the 12g295 doesn't have hardened valve seats so if it hasn't already had them fitted then you may want to or you will need to use additive

[chris211083]

Hi I will be sending this head away to be flowed and prep-ed for the super charger later next year. Just wanted to know what you can get out of it in standard form for those who want to know. So don't want to raise the comp ratio or fit hardened seats as it's going to be removed again. However it will have the seats done etc when it's flowed for the Super charger next year. I have the original head for this car that is currently in use, this was recon-ed 6 months ago so will use this while the 12G is away for modifications later next year. Looking forward to Supercharging the car, Should be fun.

Chris.

[jonny95]

Ah right ok. You should stiull get a significant improvement over the standard head

[Ethel]

It does look to be in need of a skim to get rid of that pitting. Measure the chambers first, the chances it's already had a shave are pretty high. On a 998 Cooper the head was good for 55hp (against 39) with some other extras (twin carbs, better exhaust...)

[chris211083]

If I take it for a Skim then I should probably get hardened seats fitted but in that case I might as well just send it away for all the work to be done in one swoop and save the cash. The Guy only wants £480 to do the head with all the above aswell as new larger valves etc. Maybe I should just send it away instead of trying it first??? Will have a think.

Chris.

[Camshaft1982]

I'm only asking because I'm new to mini's, but do you have to pocket the block of the 998 to clear the valves on the 12G295?

[Alex_B]

No, only the 1275 12g940 heads which have a larger combustion crown need you to pocket the block so the valves dont contact the block :)


incidentally the 12g295 was a evolution of the 12g202 head fitted to 998s hence not needing to pocket anything with this head :)

[Camshaft1982]

Perfect Thankyou for clearing that up for me.

[chris211083]

The 12G295 is suppose to give you 10bhp over the standard head but apparently thats not the impressive bit. Apparently the way the engine responds at all speeds and the way it accelerates is what makes the biggest difference. I'm still working off what people say at the mo as I've not fitted it yet but I will and i'll get some evidence to prove what it gives you.

Chris.

[Ethel]

The 12g295 is very similar to a 12g940 in design, but it's intended for a small bore block, matching the spacing of the cylinders. The porting isn't as "all out" for the engine size either, so more responsive on part throttle.

£480 for head work seems a lot to me, but that depends on what you get done I suppose. I'd be tempted to run it first (after a minimal skim) before committing to spend that much more on it.

[chris211083]

I'm now leaning towards just getting the work done to the head. MiniSpeed will fully work the head with new valves, hardened seats and when you use their supercharger kits they use a large thickness head gasket so if you decide to change back to N/A engine then all you need do is fit a standard head gasket and the comp ratio is increased. This would mean I could fit the new head and get the most out of it till the new engine is ready and the supercharger kit is bought. Still I can add more photo's once its done and then add the dyno run with the modded head. This makes sense to me and it will save me the price of another head gasket set.

Chris.

[chris211083]

Hi Guy's,
just to update the thread, the head is being sent away to be worked by Minispeed and will be modified and then run on a dyno. Dyno power sheet will be added to this thread in a month or so. Sorry if anyone wanted to see what gains you get from the standard head.

Chris.

[surfblue63]

Just fitting a 12G295 onto a standard 998 engine will not give the promised 10 bhp without the head being skimmed. The combustion chamber on the 295 head is around 4cc larger, thus you need to skimmed quite a few thou off the face to get the compression ratio up. I replaced the head on my Mk2 Traveller with a 295 head and removed 60 thou to get the compression ratio up. The Cooper engines were fitted with what is known as D-Top pistons, unlike the standard 998 which are either flat or dished depending on original spec.

Read the bit below which I have taken from Kieth Calvers web site.

http://www.calverst.com/

http://www.calverst....her_options.htm

The much coveted 12G295/12G206 heads are all-but non-existent realistically now. There are some about - most have been well used and abused, many cracked or modified into uselessness, with just a few, rare, un-molested examples of the species. But even a good example is likely to need complete refurbishment, particularly for the modern world where unleaded fuel is to be used. Suitable exhaust valve seat inserts will need fitting, new guides, seats re-cut, probably new valves, valve stem seals, and in all probability new valve springs. And then there's the machine-work needed to get it to work on your 998 - hefty re-facing to get CR to a sensible level since the standard head has a capacity of 24.2cc, the Cooper heads 28.4cc. That's a chunk to remove; charged by the cut it'll cost plenty. And having gone through all that - reliability is a problem - they're prone to cracking.

Edited by surfblue63, 04 January 2013 - 10:13 PM.

[twistedtorment]

mini speed did my 12g295 head and i have to say i was very happy with the results it just loves being revved! mines standard 3.1 diff stage 1 and i kept up with my friends 1275 metro engine til 3rd gear anyway lol