fcdrifter13

SO I figured I would ask here. I was cleaning out my basement because we are moving in the next couple of months and what do I find but the box with my old GTU motor bits I had stashed away. The irons are junk, but the rotor housings are in decent shape along with everything else, and there are some S5 NA rotors in that box also.

So this gets me thinking, I have some 4 port irons I could seal off and access to a machine shop so I though why the hell not I'll use this as a learning experience and try to build a P port motor. I have seen a couple of thread were people have done this to 12as but they did not go into much depth in there threads, it was mainly just pictures saying look what I can do.

So a few questions.

Would I be right in assuming that if I made the measurements and lined the place where the P port should go to the stock side ports o these irons that this would give me a rough estimate exactly where to drill and how much port timing there should be for it to atleast run, or is the port timing completely different on a p port.

I am unsure on how big to make the opening. I have seen some that choose to use a large rectangular port and some that use smaller circular ports. I am assuming that the smaller ports would be better for longer engine life, but just how big can you go without putting the seal into to much danger.

What do you fill the 4 port opening with to make them air tight or are they welded shut with some type of plug. I have also seen some debates on whether or not to have your plug flush with the irons face or leave a small indention to help improve side seal life.

What kind of mods do I need to do to the rotating assembly to get the most out of this setup. I understand that A pport pushes the power band higher up in the RPMs, would it push it so far up in the RPM range that I would have to worry about shaft flexing and chipping corner seals.


Thanks in advanced.

DelSlow

iTrader: (2)

The port timing will be completely different because the port is opened/closed with the apex seal instead of the sides of the rotor. There doesn't seem to be a whole lot of information about how different port sizes and timing will affect the powerband, but there are bits and pieces here and there so you have to do quite a bit of searching to get an idea of what you need. To locate the port timing, you will have to locate TDC and go from there with a degree wheel, there are several threads around that show in detail how to do this. There are also several good threads about this process on nopistons. The side ports can be epoxied in, but you should definitely leave a 1/32-1/16" or more recession below the iron face. A high quality epoxy such as Devcon Aluminum is recommended to fill the ports and coolant jackets.

peejay

A P-port isn't necessarily a top-end-only beast. The one I built was definitely not.

Exhaust is absolutely critical, though. So is spark.

Also, make sure the tubes are a close fit, and support the rotor housing... the one I did was not, and the rotor housings collapsed slightly under tension bolt load. Still ran fine, and was sealed to water, but it worried me that the housings had cracked.

fcdrifter13

This brings up another question. If I machine the hole slightly smaller than my port and have it pressed in, would I have to worry about adverse effects on the housing its self, such as pushing the coolant passages around and ruining a housing.

DelSlow

iTrader: (2)

That depends on how much oversize you make the insert. A general rule of thumb for aluminum press fits is 0.001" per inch of diameter. So for a 2.5" round port, you will want to make the insert with a 2.5020-2.5025" OD.

j9fd3s

iTrader: (3)

mazda has an sae paper 90032 or 90036 i cant remember, and its the one i dont have! but they did a power vs size vs timing comparison in the PP engines.

you really need to look at the intended use for the car, for max NA power, its pretty clear what to run, but for a turbo, or a more streetable car, less is more

fcdrifter13

Well thats just the thing it isnt going in anything at the moment. I just have all the bits laying around to do it and I think it would be a cool project. Although there is a Chevette down the road for sale for a couple hundred................