Intake and exhaust timing table

[Grant Monkhouse]

I have began re-reading my street rotary book again to pick up on stuff I never noticed before.

This table I found really interesting as working out the timings always confused me a little

So here is the table
now I\'m not saying this is 100% correct but it must be if it\'s from a published book right???

Now I have taken the timings from the Mazda factory peripheral port and worked out how long the intake is actually open for 360* rotation of a rotor which I think should be 3 turns of the eshaft??? I may have that Wrong though.

Anyway here is how I calculated it

360* - 86* BTDC (Pport intake open) + 75* ABDC (Pport intake closes) = 349* of intake port duration!!! That is insane.

Now I have seen a Mazda pp housing and I can say that I have also seen other pp housing where the inlets were much much bigger than mazdas.

Now thinking of an engine being an air pump the pp is superior to any of the ports in the table, even moreso than the racing beat j port which actually opens 29* earlier than the pp.

What I also find interesting is that the overlap in the j port is greater than that of a pp?!?!?! Now from what I understood PPs were the worst for overlap, obviously not so.

[m1tch]

You can see from the heavier ported engines how much overlap there is which creates the brap brap brap sound you can see that the street port only has slightly more overlap than the turbo 13B but the intake port is open for much longer

[Grant Monkhouse]

You can see from the heavier ported engines how much overlap there is which creates the brap brap brap sound you can see that the street port only has slightly more overlap than the turbo 13B but the intake port is open for much longer

Overlap is good for spooling large turbos too so if you can take your porting and port in terms of degrees you can increase overlap to benefit spooling a bigger turbo.

It would be nice if other peoples take on their street port could be put on a list instead of the usual, go a bit this way and take a bit out that way etc, that way people\'s ports wouldn\'t be on show but people that understand the terms would be able to take the info given and try some porting.

I would like to know the sizes a street port could go to on a turbo application and the same with a bridge port in terms of degrees.