998cc turbo from a pile of bits
Turbo Mini Forums

Hi folks,

I’ve recently bought a GTM coupe that came with a pile of bits. My plan is to hopefully turn the pile of bits into a cheap 998 turbo to put into the GTM coupe. I’ve already got a gt1544 turbo that pulled off an old Vauxhall and I’ve got a nodiz ecu sitting on my shelf that I never ended up using on another project. I am planning on fitting the nodiz to the GTM now just so I can start getting the hang of it.

This will be my first time playing with forced induction, I’ve only ever played with na stuff.

Right so the pile of bits that came with it…

1. CAM4810 unleaded head

2. A-series 998cc bottom end (seams to be in good condition, standard size pistons and I can still see cross hatching on the bores)

3. 12G940 head. This has 37.2mm inlet valves and is ported.

4. A 1380cc 11 stud engine & gearbox. Unfortunately the block is scrap but it does have a decent standard 12G940 11 stud head and a decent crank and rods.

5. HIF44 carb (needs rebuilt)

6. HS4 carb (been rebuilt)

So my main question is has anyone built a 998 turbo using a small valve head like a CAM4810???

I know folk will say just get a 12g295 head or use one of my 12G940 heads and pocket the block but as this will be my first turbo build I don’t really want to put any decent/expensive parts on it just yet. Also if the 998 turbo engine works out I might get a 1275 block to build another turbo engine using my big valve 12G940 head so I don’t want to do any modifications to that just yet. If this 998 build works out and I’m happy with it I could even build another 998 turbo engine with the other engine that will come out of the GTM. In that case I’d be happy to use one of the 12G940 heads on it or even sell them both and get a decent 12G295 head for it.

I don’t mind doing a bit of work to the CAM4810 as they not worth much but it will still be a small valve head. I’m not looking for massive power from this engine but would 80bhp be achievable using this head?

Thanks,

Kev

I don’t think anyone would say get a 12g295 anymore, too rare, too expensive.

I’ve never liked the 12G940 on small bores because of the valve/block risk (and pocketing looks janky to my unprofessional eyes). Along with the valve sizes being too big in most cases but that will depend on the cam you use.

Many of the 998 builds on here start with a CAM4810 because it’s cheap and is a good enough starting point, my own build included.


When you’ve got all the bugs ironed out on a simple setup (because turbo conversions never go to plan) then start to look at what to change.