hi guys what port timing would be good for a 12a pp used for track be any sugestions would be good just ler me know what opening and closing you guys have tried for inlet and exuast



thanks tony

Mazda Factory timing spec:

Inlet opens 86° BTDC

Inlet closes 80° ABDC

Exhaust opens 73° BBDC

Exhaust closes 55° ATDC



Inlet opening is pretty straight-forward decision, highest VE% is attained at 80-90° BTDC. Inlet closing will affect peak power RPMs, 80° ABDC is good starting point for peak around 9000 RPMs. Exhaust opening again alters powerband, but not to such degree like inlet closing. Racing Beat opens exhaust ports very early, why is beyond me... around 75° BBDC is probably enough for any aplication. Exhaust closing is determined rather as side effect of sufficient port area. Later closing pushes powerband higher with certain loss in low-end.



Hope this helps...

is that mazda factory race spec if so yes helps heaps

thanks tony

ive got one running about these size ports, and with a carb+locked dizzy, drivability is not that bad. making the ports a little smaller will help, and give you a little fudge room to have things like mufflers that make it quieter, but not much

cool i will make a manifold and run it on a nicky lol cause it will be a experimental engine what power and torqe figuers is your engine and is the port timing the same for 13b? if you ddo a 13 b pp

i dont know the power yet, im still getting all the parts to work harmoniously together. right now the fuel pump isn't big enough. since its setup like the mazda competition manual says, i'm expecting about 260flywheel hp @9000rpms



13B, i think is just a wider port, same timings. although since its wider, you could probably run slightly less timing, and get a power band that is lower RPM

once this motor is done i will start on the housings for the 12a pp [attachment=46921:6.jpg][attachment=46922:3.jpg]bridge port primarys extended secondories and a turbo yea ha