16 replies to this topic

[fuse]

hello guys am new to the mini scence and want to keep my standered 998 block so am getting it all rebuilt but i have heard about u can pocket a 1275cc head so the 998 has more power? how does this work? and how much?can use a race cam and like a stage 4 head 1275 head on a 998 bottom end. just really confused sameas the rockers what are they reeally for and do u need them. am goin to build a fast road/ race 998 engine but dont want to spend loads so dont know were to start

[Retro_10s]

hello guys am new to the mini scence and want to keep my standered 998 block so am getting it all rebuilt but i have heard about u can pocket a 1275cc head so the 998 has more power? how does this work? and how much?can use a race cam and like a stage 4 head 1275 head on a 998 bottom end. just really confused sameas the rockers what are they reeally for and do u need them. am goin to build a fast road/ race 998 engine but dont want to spend loads so dont know were to start

hello mate, bit of confusion here....

Yes you can fit a 1275 head to a 998, However i'm not sure you understand pocketing:

You don't pocket the head, Pocketing is done to the engine block. When you fit a 1275 head to a 998 block you have to remember that because the bores on 988 block are smaller than the 1275's, it means that when the valves open they will hit the top of the block, this can cause lots and lots of damage to the engine.

In order to overcome this, small pockets can be ground into the edge of the bores of the block to allow the valves to open, the valves will travel down and into the pockets safely. This can be done with a dremel. the best way to do this is to put some blue tack around the engine bores. Then lower the head onto the block. Then turning the engine over slightly will open the valves. The valves open and make a mark in the blue tack, this is your template to cut the pockets.

You must also remember that by fitting a 1275 head to a 998 block, you are already fitting the equivalent of a stage 3 988 head onto it! there are loads of cams around, The Swiftune SW5 is a very good upgrade giving bags of torque and nice on emmissions too.

Rockers.... if i'm correct, High lift rockers enable the Valves in the head to open more (hence letting through more fuel/air mixture), so fairly significant gains can be had... if set up correctly, often hig lift rockers also have a feature called 'roller rockers' these claim to dramtically reduce side loading on the valve stems, especially good at High RPM, which is what you'll be looking at in a revvy short stroke 998.

[Dan]

The block needs pocketing, not the head. This is because the 1275 head is designed for larger cylinders so the valves in it are on wider centres meaning they overhang the sides of smaller cylinders. They will strike the block in operation if you just whack the 1275 head straight on a 998 so you need to cut pockets in the top of the block for the valves to move into when they open. The larger head can allow the engine to breath better but is by no means a guarantee to greater power. In any case you would not be able to state a certain amount of power increase, it all depends on the quality of the build and the design of the whole engine. You can use a hot race cam in any 998 if you like but it won't be much fun as a daily driver, race engines are for race tracks. A stage 4 1275 head might be too much for a 998 but that would depend on who made it, stages of tune don't mean anything really and there are no hard and fast rules as to what a stage 4 is. It's just a rule of thumb. Rockers open the valves, you need them!

I would suggest you need to learn more about the engine before you try to build it and also learn more about what you want from it and how Minis perform and drive. Asking questions like this is a good start but also feel free to search our archives for threads you may find useful or read the FAQs. There's an awful lot of knowledge on this site and there are also many good books available such as David Vizard's 'Tuning Bls A Series Engine'.

Welcome.

[Retro_10s]

hahah quickdraw mcgraw, i beat dan to it

[Dan]

I was distracted by considering whether or not I should mention in a certain thread about wheels that Hillman and Triumph weren't BMC companies......

Edited by Dan, 30 April 2007 - 02:29 PM.

[fuse]

thanks alot folks am not so confused now lol. so basically is i got my 998 block pocketed to fit the 1275 head then that acts as a stage 3 head so to speak and i dont really need like a stage 5 1275 head but i would get more power from it. cams is bascially personal prefrence then. what about roller rockers like the 1.5 ratio ones what are they for then? basically i want to build a fast 998 or is it 1040? but not spen loads and loads. also what makes a race cam not very usable on the road?

[Guess-Works.com]

if using high lift rockers, you have got to be aware that you pockets in the block are needing to be deeper.... depending how deep they need to be they may interfere with the bore and the top ring of the piston...

Not sure as I've never seen the need to do it... may aswell save the money and buy a 1275...

[Retro_10s]

I was distracted by considering whether or not I should mention in a certain thread about wheels that Hillman and Triumph weren't BMC companies......

bah

[fuse]

been lookin so if i got a 998 bottom end fully rebuit a pocketed the got a 1275 head some sort of cam and some roller rockers. it would give me a good power gain? also what about a stage 3 1275 head. so if u say a normal 1275 head is like a stage 3 on a 998 what would a stage 3 1275 head be like on a 998?

[Guess-Works.com]

overkill....

[fuse]

ok kool but a 1275 stage one head would be good with a nice sporty cam and some roller rockers. and a good gear box. what about carbs and what sort of power should i expect

[Guess-Works.com]

probably about the same as a fairly mundain 1275....

and if you think it would be cheaper on the insurance, think again !

[fuse]

was thinking would be better to keep the 998cc and keeping is small bored really doing something diffrent. as it nice and cheep etc a 1275 with stage 3 or 4 kit would be nice though

[Guess-Works.com]

Honest guv' I'm not trying to put you off....

there are some very nice high powered small bores out there, but IMO, it's a pounds per HP issue.... you get more for you heard earned when starting with a large bore..

[fuse]

no it is ok just any help is welcome just want to build a good powered engine to shut chavs up round my area in there 1.4's etc but dont really know were to start to be honest