25 replies to this topic

[timmy850]

Although the photos are rotated in opposite directions you can see the difference in the "beak" that blocks flow between the valves on the stock 202 head

Modified head

[Rorf]

Nice head work there - did you do it yourself timmy?

[Pauljb]

Ok cool. Any engine machinist will be able to sort it out.
Thanks guys

[timmy850]

I had it done at an engine shop that mainly does mini gear. Id recommend finding a machine shop thats familiar with A Series engines

[Turbo Phil]

Your generic machine shop is unlikely to be able to port a head for you. Porting a head is completely different to the kind of work your general engineering place will do. Most of these places will do bread and butter work like rebores and block/head skimming but are unlikely to know what to do or be interested in porting a head.
One of the many Mini specialist companies will sort you out.

Phil.

[Avtovaz]

The ruff grinding on the ports help the air and fuel to mix better.

 

The 295  or 206 heads are the ones to have modified, the 202 or the cam 4810 have smaller valves so not much gain.

You will prob need the head skimming to raise the c/r depending on the pistons you have.

 

In all honesty a 1275cc lump will be the best power for the £££  The 1100cc isnt the best lump to modify. But some did come with the 295 head. A better cam will see more power output.

 

jsut had a little read of the thread,

 

i was told by the guy who built my engine that if you use a rough port, when fuel lands on it, there is less surface tension to get it off again that with a smooth polished surface. i dont know how droplets work, but i think i can see what he says. They kidna land on the rough bits and lift easy as not getting the full surface land if you get what i mean?

 

There is also on youtube a 2 hour lecture from Mr Vizard himself back in the day, and he had just built a 1100 engine that he bored to 1200, and he was getting suprisingly good results with it. Mr Vizard also says that mini like larger droplets of fuel, whcih maybe why minis like Su;s and escorts like webbers more?

[Turbo Phil]

What a slightly rough surface will do is cause a small amount of turbulence, keeping the fuel atomised in the airstream and helping avoid the fuel pooling or trickling down the port walls.

Phil.

[Pauljb]

This is mind blowingly complex for my little brain. So no porting but a good heads skim

[timmy850]

It's not too tricky really!

 

For more power from the head you want:

Bigger valves 

Better port flow (reshaped and/or ported)

Correct compression ratio (measure combustion chamber and skim if necessary)

De-shrouding combustion chamber

 

BUT don't get the ports "polished" shiny smooth. This will reduce performance

[Pauljb]

Thanks alot. That clears it all up. What am I looking for when I measure the chamber?

[Cooperman]

The volume of the chamber in cc's.