So, I thought it would be a good idea to start this topic; in order to get a bit of advice, but also to share the information with anyone who is thinking of doing something like this in the near future.
I recently decided I wanted a bit more power from my 998 Mini City. Obviously a 1275 is the way to go, but I wanted to keep the charm and originality of a 998 (plus 1275s are expensive) so that's the direction I took. After finding three 12G940 heads kicking about at my dads' lock-up, I saw this as a subtle sign that the A-series Gods wanted me to use one...
Now, I have read that that to be on the safe side I would either need to recess the valves or pocket the block in order to get the necessary clearance on the exhaust valves, especially if I wanted to use a higher lift cam. Somewhere or other I read that recessing the valves could help to improve efficiency or power/torque, by essentially making it more difficult for intake gases to escape into the exhaust port during valve overlap, as it would have to travel further. Is there any truth to this? Not important really as I purchased a pocketed engine with gearbox for £50.
A few weeks ago I picked up my newly machined A+ block from Roland Alsop just down the road in Chobham.
Here's what he's done:
- Re-bored to +20thou
- Refaced block
- Camshaft bearings
- Freshly re-profiled the original camshaft to early MG Metro spec.
- Opened up pockets as they were done on the piss (Must have been done either under the influence of alcohol or upside down - who knows.
- Ground crankshaft.
Also got a few bits from him including flat top pistons, bearings and cam followers etc.
Additional things that I have accumulated include a custom made exhaust manifold with twin box rc40 system, inlet manifold, oil pump etc.
Now my thoughts have turned to which head I should use, and what (if any) modifications I should do to them. Two of the heads have 33mm ish inlet valves. The other has 36mm ish inlets. Possibly a turbo head, but I will have to check. My first thought is that on a road going engine are these larger valves just going to lower the torque output of the engine? Would I be better off with the smaller valve head?
Secondly, what kind of compression ratio should I be aiming for? Somewhere around 10:1?
Would you recommend porting it? I will be reconditioning whichever head I use.
At a later date I will also need to consider what carb to use. Would an Hs4 be too small for this application. I think I have an Hif 44 laying about.
Here are a few pics of the engine. Needs a lick of paint, best colour suggestion gets a free thumbs up!
DSCF1486.JPG 32.17K 26 downloads
DSCF1481.JPG 24.04K 16 downloads
Attached Files
Edited by Stiggytoo, 12 September 2013 - 07:02 PM.