Irish Mini Owners Club

I remember doing a bit of research for small tweaks for the Swift GTi a few months ago and I came across alot of English boys getting a 1600 Baleno (Swifts big brother) bottom end and putting a 1300 Swift GTi top end for added compression...... The power increases are supposidly decent but didn't see any pictures of the pieces of paper to back it up. I had never heard of this being done but again, done some research and turns out its fairly popular with the Toyotas and Hondas.

So, story short, is it possible to put a 1275cc bottom end under a 998cc top end? And if so would it keep going?

Edited by Moderator to remove inappropriate language that doesn't meet IMOC Forum guidelines.

It will decently stays going probably indefently as you will reduce the power of the motor by more than Half. 998 heads have tiny inlet and exhaust valves and ports.. Now a 1275 head on an 998 and you have a wining combo

Merlin wrote:Now a 1275 head on an 998 and you have a wining combo

Has it been done before? If so, what sort of performance you talking here Paul?

I knew of at least 3 engines with a 998 block and 1275 head. All worked ok, one Mini was sold so no idea what happened to it, can't remember what happened the second and the third ran up a decent mileage over about 3 years and made two IMM trips.

No idea of the performance upgrade in bhp or % increase, but the 1275 head made a difference.

Paul will have more info on this

I put a 1275 head on a 998 when I was a young poor student..about 12 years ago now , it was on one of my first minis that was done on a budget.
it did make a nice power difference... the head I used had a big enough head face to exhaust valve face clearance so I didnt need to do any cut-outs into the block and I was staying with standard cam etc...no money at the time
although we did have to adapt the front water gallery if I remember correctly, not a bad mod for the 998,

Mark

Dose the 1275 head just bolt on or do you have to modify anything and do you have to leave the standard 998 cam or would the standard 1275 cam work ?

molly the mini wrote:Dose the 1275 head just bolt on or do you have to modify anything and do you have to leave the standard 998 cam or would the standard 1275 cam work ?

I would also like to know the answer to that!

Any that I knew of kept the standard 998 cam.
You also need to use a deep enough head to make sure the valves don't hit the top of the block.
I didn't build them though so can't give you any more info than that.

If it was me I would just stick a Stage 1 kit on the 998

So are there different types of heads ?

If the 1275 head has been modified it may be skimed so distance from the face of the valve to the top of the block may be less.This distance needs to be more than the valve lift which is determined by the rockers used and cam lift. You also need to determine the cc of the head chamber to work out the CR of the engine.

Would a standard 1275 spi head that was never modified or skimmed do the job

How long is a piece of string? If you don't understand the concept of tuning an engine may I recomend a book , David Vizards Tuning BL's A-series Engine. Anybody who wants to work on mini engines should read this book first as it will point you in the best direction for the result you want for the least cash. Changing one part of an engine inevitable means it will have a different effect on other paramiters of the engine.Other than that stick with the commercially proven stage 1/2 kits designed to fit "standard " engines.

you can normally get away with an unskimmed 1275 head running the standard cam. always beat to trial fit and make sure nothing hits. I.e valves and pistons
if your planning on changing the cam then you will have to pocket the block to allow clearebce for tue exhaust valves.
if you have a copy of mini expert he has covered this conversion in detail. worth a read

Stage one kit and a cam (SW5) or such like make for a nice 998 You need to know what you are doing to put a 1275 head on a 998 but as was said it can be done

I fited a 1275 head on a 998 engine that's in the shed and it works using the 998 rocker and 998 cam and ill stick a hif38 on as well just for good measure

Miss a gear and it game over, word on the street is that u d want to take out the vernier, from the book of John F