Upgraded Cylinder Head

[tony105]

I wonder if anyone has experience of replacing the standard spec cylinder head with a stage 1, 2 or 3 to either a 998 or 1275 automatic Mini? Also how this may affect the gearbox? Secondly, the limitations of tuning a 1.3 single point injection unit?

[mra-minis]

Unless you keep it fairly simple you will need to change a lot of parts, mainly the convertor to enable you to actually drive the thing.....

Unless you go down the bigger bore or turbo route, which will add a lot of power with not too serious mods, except heavy duty automatic clutch plates etc.....

[tony105]

Hi Martin, Good to hear from you and thanks for this. Have you any experience of the replacement and mapable injection system to replace the standard Rover system? The mild modifications I have made so far to my Mini have been very effective but I'd like to maybe change the cylinder head too. Kind regards, Roger.

[sartine]

A head change, without any other modification, would probably add a very little gain in power.
According to "the yellow bible" aka DV tuning A series, the major breathing capability of a 12g295 vs a standard 998 head is sensible from 4000 rpm and up, where the curve of the std head start to drop and the cooper head continue to rise.
My idea is that an automatic engine will hardly turns so high, simply because the automatic gearbox will not allow so, it was not designed to give a race behaviour to the car but a comfort and touristic instead. Gear shifts will probably happen at a lower rpm, so you cannot appreciate the power gain.
For the same reasons, if you change the camshaft for a sporty one, you will end in an engine which is probably weak until 2000 rpm or so, ad if you think that the standard stall speed of the Tc is around 1300 - 1500 rpm, you get a very low driveable engine, almost dead in urban traffic and at standing start.
If you're searching for bolts-on and reversible modifications, i think that the automatic engine should be upgraded in the direction of a gain in general brilliance and responsiveness.
My personal formula is a stage one kit, tuned on the rolling road in order to gain every single bhp from the std engine, followed with an upgrade in compression ratio, say to around 10:1, and a good ignition system, like the 123 dizzy or the Megajolt.
Assuming that the rest of the engine is in good shape, these mods could add around a good 7 - 8 bhp, enough to perceive a sort of "rejuvenation" of the car and, more important, to save the auto gearbox reliability, expecially if it's totally std ie wthout the fwd clutch mod.

Having said that, my 998 engine has been rebuilt with a new set of Powermax "D shaped" pistons and a 12g295 head, just because i had them NOS and they were laying on a shelf getting dirt and dust. I will change the dizzy for the 123 and i will add for sure a stage one kit, the rest, from the carb to the camshaft, is original.
I haven't still started the engine, my time is low and i'm proceeding very slow, but i will report here as soon as i will be ready to get the car on the road again...

[mra-minis]

Sartine, I like your answers above very true, I prefer the Megajolt over a dizzy anyday, even the fabled 123. the difference is truly amazing, better driveability is worth a lot of power on an auto :-)

You can however rev the engine if you are "stick" driving the car. just dont lose the bottom end performance or you will regret it, unless you install a convertor with a higher stall speed (and yes they are available and yes the change points can be modified to suit a higher revving engine

[supasamurai]

I put a stage two kit from Mini Sport on my 998cc Mayfair. A new head, roller rockers, cone type air filter, intake and exhaust manifolds, and exhaust came in the kit. The car definitely went from golf cart performance to regular car performance. The kit was made for standards, so there is a lower exhaust manifold strap that I haven't figured out how to install yet, but everything went in nicely besides.

[mra-minis]

Supersamurai, make that bracket otherwise it will start to leak and exentually something will break :-(

[simonw]

Jan 6, 2013 13:50:25 GMT sartine said:

A head change, without any other modification, would probably add a very little gain in power.
According to "the yellow bible" aka DV tuning A series, the major breathing capability of a 12g295 vs a standard 998 head is sensible from 4000 rpm and up, where the curve of the std head start to drop and the cooper head continue to rise.
My idea is that an automatic engine will hardly turns so high, simply because the automatic gearbox will not allow so, it was not designed to give a race behaviour to the car but a comfort and touristic instead. Gear shifts will probably happen at a lower rpm, so you cannot appreciate the power gain.
For the same reasons, if you change the camshaft for a sporty one, you will end in an engine which is probably weak until 2000 rpm or so, ad if you think that the standard stall speed of the Tc is around 1300 - 1500 rpm, you get a very low driveable engine, almost dead in urban traffic and at standing start.
If you're searching for bolts-on and reversible modifications, i think that the automatic engine should be upgraded in the direction of a gain in general brilliance and responsiveness.
My personal formula is a stage one kit, tuned on the rolling road in order to gain every single bhp from the std engine, followed with an upgrade in compression ratio, say to around 10:1, and a good ignition system, like the 123 dizzy or the Megajolt.
Assuming that the rest of the engine is in good shape, these mods could add around a good 7 - 8 bhp, enough to perceive a sort of "rejuvenation" of the car and, more important, to save the auto gearbox reliability, expecially if it's totally std ie wthout the fwd clutch mod.

Having said that, my 998 engine has been rebuilt with a new set of Powermax "D shaped" pistons and a 12g295 head, just because i had them NOS and they were laying on a shelf getting dirt and dust. I will change the dizzy for the 123 and i will add for sure a stage one kit, the rest, from the carb to the camshaft, is original.
I haven't still started the engine, my time is low and i'm proceeding very slow, but i will report here as soon as i will be ready to get the car on the road again...

Any update?