Building an engine can be fun and for me its even better when you race it cause you really give it the business on the racetrack. The stock mini engine is pretty peppy and fun for the mini but its no race engine. it runs hot on the track and it overheats even in street trim.
I used a computer engine design program and found out pretty quickly that the five port head would make at least ten percent more power if it just had a regular eight port layout. Its a pretty poor performer right from the start. That doesn’t mean that it is useless it can be massaged to make some impressive power but its a lot of work! and i have spent a lot of time doing various kinds of mods. and i have changed countless head gaskets, usually at the track and once in a rainstorm. Something i have done enough and I was hoping the twin cam would cure the head issue with the race cars. yes the mini and now the 1100.
Measuring the bore centers it came out to 76mm (2.992) for the head and 3′ for the center two cylinders and 3.030 for the outer cylinders. I have found on the mini that the smallest piston to do the job is the most reliable way to go and the 73.5 is the biggest piston i will use. The 74mm just is a bit too big for the head gasket in my opinion. i really prefer the 73mm. The pistons i use in everything is the Hypatec 73mm available from minisport Australia. Now before you see the price and exclaim they can’t be good enough let me just say the team and i have put these pistons through the wringer and in the racing mini they have gone through many thousands of miles of full throttle use with a dozen different drivers and we have never had a piston failure. One key item to note is my machinist (who used to race mini’s himself) sets the bore clearance at .003 no more and no less. This is more than the recommendation on the piston box but after break in the engine will not use oil and the pistons will not be scuffed between rebuilds. I have used the chrome and the cast rings neither seem to have an advantage to me. Just to be clear the race mini also has a five port (used to be the main engine but is now the spare) with these pistons and with the main bearings replaced evey three races and the syncros at the same time. There are a few other things i now do at this time. Primary gear bushes and a inspection of the transmission and idler gear bearings under a magnifying glass. But i digress and here is one main point. OIL is the lifeblood of your engine and after trying seemingly every oil. I now break in the engine with castrol 20/50 with zddp additive and from then on MOBIL ONE 15/50 You will get three times the life out of your bearings. don’t bother with anything else. Thats it for now next post will be how to move the bores and get the engine block ready.