998cc rebore project
Turbo Mini Forums

Hi all,

I am a newbie in the Mini world, starting a new project!

i would like to rebore my 998cc (A+ Series Engine, Metro) up to the most suitable size (maybe +0.60), to give it some more power. Some questions:

- What extra considerations should I be making when reboring an engine?
- What suitable Fast Road cam would fit this engine configuration?
- I have an HIF38 and HS4 carbs available - which one fits the engine better? Which needle should I use (ideally matching the camshaft recommended above)?

Appreciated!

Firstly, what mods have you already done to your engine?

You will get more benefit (power wise) from a stage 1 kit and a better cylinder head than you will from a rebore.

My favorite cam for a 998 is a Kent 276.

As for needle, search on here fore how to polish your needle.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

Hi, the engine is stock so far (no mods yet) and so starting from scratch..

any further suggestions would be really appreciated :) thanks!

AH, ok.

In which case a rebore is very low on the list

As above, start with a stage 1 kit and a decent cylinder head. The problem with the 998 is that the standard head is useless and it doesn't modify well.

In the past you were better to use a 12G295 head, but these are rare now, but still a few on ebay. The other option is a 12G940, but then you need to modify the block.

There's no easy ride here.

With the above modes I'd expect 50hp, a nice cam would get you to 55.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

Many years ago (before turning to forced induction) I ran a modified 998.
It was +020" bore with a 12g940 metro turbo head (10.5:1 CR) which was ported and polished and std size valves, SW5 Cam and twin HS2's, 3 into 1 manifold and a RC40 exhaust.
It made a healthy 65HP on Minipeed's rollers. It was an absolute hoot to drive and I wouldn't hesitate to replicate it again if I was building another.
Prior to that I used to use a 12G295 head with similar results.

Shane

Edited by shane on 22nd Dec, 2019.

The 998 castings can be made to flow, but there’s a serious amount of work required.
The key to using the 940 casting on a 998 is to keep the porting standard size and retain the standard 33/29mm valves. The ports are already a little on the large side for any road going 998 & going larger on either will kill off bottom end/midrange torque.

Phil.

WWW.TURBO-MINI.COM