Nateb123

I've been looking at doing something different with my 88 6 port engine. I don't want to just swap it out, or turn it into a 4 port motor to turbo it. Basically, I want to keep it n/a and streetable, but really do some fun porting things. My best idea so far is to bridge only the auxiliary ports. The primaries would just get a bit of a slight port and polish, mostly to make things easier on the seals moving over them while retaining lower end torque. The auxiliary ports would get a bridge though and I'm wondering if anyone knows of anyone doing this, or has done it? Basically this port job will give me a compromise of low end torque and high RPM horsepower. Plus it will still idle like a normal car!



Thoughts? I don't imagine it's going to make tons of power, but it seems like the best bet for making due with the 6 port. Plus what's more fun than a rotary that at around 3800 feels like Vtec just kicked in, yo! :P

j9fd3s

bridging just the aux ports isnt a good idea for a couple of reasons.



1. the port timing is way way late, the stock 6 port closes at 70-75 degrees, a PP engine closes at 80. the real difference is that the PP opens way earlier, +80 btdc while the stock ports open at -25 btdc.



2. the aux port doesnt really flow much.



so when mazdas full race engine port timing closes about the same as the street engine, closing it even later than that isnt so hot, BUT and this is where the bridge might work, is there is 105 degrees of difference between the OPENING port timing on the race motor vs the street motor.



since the bridge can move around a lot, you can have the port open early, and still close at something sane.

Nateb123

That's the idea that I was coming to as well. Later closing by just putting the bridge on top of the aux port from end to end would clearly just be stupid. Moving the bridge closer to opening however could allow for a bolstering of the torque curve when it's needed. I imagine this would look like an bridge that's straddling the primaries and auxiliaries.



Positioning the bridge would be a bloody art form though. Too close to closing and I imagine some pretty high rpms will be required to make power out of it (plus torque could take a hit), too far and I end up slicing through into the bowl of the primary.

ColinRX7

Try this:



Get a 4 port TII block. Throw the turbo away. Streetport the primary ports (centre iron). Bridgeport the secondary ports (end plates). Get motorcycle throttles, keep the warmup plates in the secondary ports, control them with some kind of electromagnetic component. If it's linkage activated, use a door-popper electromagnetic deal to snap the warmup plates wide open. Default is closed. Know what I'm saying? Ditch the warmup plates for the primary port throttle plates entirely. Run it around town and figure out what RPM to set the warmup plates to open (and thereby activating bridgeport powas). It's probably going to be lower than 3800 RPM. So don't go with that. But start there, and move down. But, Bear in mind the primary ports have their own independent pulses now and aren't under a shared throttle plate. They both have their own which might be surprisingly sufficient. So I could be wrong, maybe it is not far from 3800.



Or if you really wanted to get tricky you could modulate the warmup plates (rather than on/off) to slowly allow more air volume as RPMs increase. That would require a dyno and some patience.

mazdaspeed7

Lets start with the basics, like which are the opening and closing edges, and where a bridge actually goes... As you are looking at the port, the top edge is the closing edge. The opening edge is the vertical side on the runner side of the block. Thats where the additional port goes. You have to leave a bridge for the corner and side seals to ride on as the rotor passes over the port, hence the name bridgeport.







Thats a bridgeport on a 12A end plate.







And that is my very large streetported 6 port motor. Still pulling like a freight train when I ran out of fuel at 9700 rpm.



Edit: those pics are on their side in regards to my description above. The opening edge is towards the top of the pic, and the closing towards the left.





Now onto the aux bridge. With the bridge being so small, and the shape of the runner, very little flow can be had. In addition, the stock port timing on the 6 port motors is already too long, and making it longer only makes the motor peakier. The long, restrictive intake manifold is the only reason hp peak is so low. Kahren dyno'd a stock port engine with a custom intake manifold, and peak power was at 8400 rpm if I remember correctly.



I did an aux bridge once. I scrapped the irons in favor of the streetport I posted above. And I picked up power. A very noticable amount even. The only thing the aux bridge did was make my power brake booster not work.