Port Timing Advice

[servetakid]

I've just had my Rapido Race Barrel bored to 71mm with 4thou clearance, I've double checked this. The set up is, 71mm piston, 60mm stroke and 110 rod on Spanish jet 200 casings.

I've just measured my ports and stuck them in the calculator.

With a .4mm base gasket fitted the piston crown is inline with the top of the barrel and I get the timings of;

Inlet - 153.24
Trans - 125.59
Exh - 177.78

Without it;

Inlet - 154.71
Trans - 123.61
Exh - 176.24

Even with the gasket fitted, there is a slight lip between the piston crown and the exhaust port, I was wanting to reduce that by fitting another base gasket to pack the barrel up. But think the transfer and exhaust port timings will be too harsh?

Inlet - 179.31
Trans - 127.55
Exh - 151.77

I'm thinking the first set up will give the best medium? Unless someone can advice otherwise?

Jordan

[paul213]

I would build it with no base gasket the port timings without are almost identical to my 1980's stg 4 from taffspeed (175,125,155) . the real problem is when the piston is lower than the exhaust port this causes turbulence in the gasses leaving the barrel a small part of the crown showing in the port is common.