AF175 Cast Kit Timings

[Captain Chaos]

Just been measuring up an AF175 kit that has had a very light seize.

The combination of piston skirt length and inlet position seem to point to the inlet timing being very conservative indeed.

Exhaust and transfer come out at around 157 and 123, but the inlet seems to be around 130!

Anyone had a measure of one of these and found similar? Or have I had a senior moment with the vernier? I was rushing a bit, but measured all heights twice.

Skirt on the piston was 69mm on inlet side and bottom of inlet port was 89mm from head gasket face.

Am I cracking up?

[Darrell Taylor]

i think the inlet is fine but the mild ex duration means the transfers are too high ,need to raise ex port to balance it out ,approx 173

what pipe you got

[Captain Chaos]

Hello Darrell

Thanks for the reply

The engine is having an old AF clubman fitted along with a 22mm Jetex.

The chap will only be "pootling" rather than trying to squeeze every last drop of go from this lump and isn't expecting the earth performance wise. I'd suggested a sensible expected cruise of 50 and maybe topping out 58-60 if lucky. Li150 15/46

The inlet seemed really timid to me. I was expecting to see around 140-145 ish from the kit "as supplied".

Could you give me some pointers as to why the inlet would be ok at that duration? I'd like to learn more....

We'd talked about his requirements last night and i'd suggested bring the exhaust up to around 165/170 to start with.

Would there be little gain from increasing the inlet timing a bit (either by skirt removal or lowering the port?)

Cheers Darrell

[Darrell Taylor]

the inlet and other ports are a combination of duration and port area so a port with wide area and limited timing can perform better than a narrow port with higher timing ,but obviously higher timing and maximised width will give the highest output but on a clubman and 22 carb with those moderate timings the inlet at 130 wont hinder performance too much but will maintain really good manners from the carburation approaching reed valve type delivery
from experienceon a 225-240 on 150 - 155 inlet on a developed port width,bigger carb and expansion etc can cover 30 bhp with nice delivery hence i suspect the 130 inlet on the 175 motor that will probably have 8 - 10 hp will be more than adequate especially if the kit has a wider inlet port (on the cylinder wall)

[Captain Chaos]

thanks for that darrell - appreciate your time