Sindregutt

Hi!

Im pretty new to the rotary (to engine bigger than 50ccm :P).
Ive never done any porting at all before but i thought it would be a good time to test now that im rebuilding my 13bRE engine.
The housings are s4 and are in okey shape (if i wreck em, i got spares ones though ).

It is not finnished yet! but i did some easy polishing to se all the scratches and bad edges

What do you think?
How do i smooth`n out the edges?
Is the shape TOTALY wrong?

Feel free to give me constructiv critics..

Thanks,
Sindre

WadeMCarter

I'm not positive, but I think aaron cake rounded off the edges on his ports so they didnt catch a seal or something. what did you port it with?

Sindregutt

I used a air drivn high RPM grinder to take the material. Then i used some sandpaper stuff on my dremel.

I only want feedback Negativ and positiv..

It actually looks worse on the pictures (doesnt mather acutally :P)

The shape is "exact" the same on both sides (the picture does the right side look more round..)

RX7Tuner.

If you look at an unmodified exhaust port there is a lip/champher on the bottom edge. You need to mimic the edge on your new port job. The reason behind this it to avoid the apex seal from sliding over the hole and then hitting a sharp edge. I have seen seals that are worn in the middle from this. Then can even chip and end up looking like a cheeto.

iceblue

Work on squaring the roof off more and add around a 20o bevel and I do not recommend porting the lower floor much if any at all. You really won’t see any flow gains and it cuts into the stroke. Defiantly polish your exhaust as best you can but do not polish the intake. It looks like a good port and that you spent a lot of time on it so far.

Sindregutt

On a stock port you got a tapered edge around the whole port. Should i just taper/bevel it on the lower side and just smooth out the ruff edge on the upper side?
Some people told me that i shouldnt port the upper floor at all but only the lower floor :P Im gonna read some about rotary ports so i understand the physics when going either ways.

Iceblue, you mean i should get the shape more like square in the top and round in the bottom?

EDIT: Actually, when i was figureing out how the port was going to look like i just removed most of the material that "blocked" for the sleeve. I dont know if thats the way to go, but it sounds logical to me.

Sindre

RotaryEvolution

iTrader: (30)

the bevel(or taper if you will) needs to be put on all trailing edges of the port, meaning the sides and top edge of the port need to be beveled.

RETed

Porting upward on the exhaust port induce more overlap.
Overlap is basically the same as in piston engines, so you can look up the effects of it for reference.

Porting downward causes the combustion / exhaust gases to exit the engine quicker.
This decreases torque (and power), especially on the low end.
This is the same effect as running a freer flowing exhaust system, as the combustion has less time to "work" on the "crankshaft" (or eccentric shaft for us rotary folk).
Porting significantly downward will decrease torque numbers, period.
But, here's the flip side...this also induces the combustion gases to exit and hit the turbo (if we're talking about a turbo'd rotary engine) quicker, so there exists a delicate balance on how much torque you would lose versus how much quicker the turbo will spool (and thus produce more boost, and thus more power earlier).

So, both don't sound like good options?
Your only other direction to go is outward...
The problem about going outward is that the apex seal now doesn't have a much support when passing over the exhaust port itself.
Some will argue that the apex seal will "bow", and if you don't have the important chamfer on the port edge, this will destroy the apex seal in short time.
Here's the counter-argument...with older 3-piece apex seal design, this might be a legitimate concern.
With the newer 2-piece (Mazda OEM) apex seal, it should be strong enough to handle lots of porting outward.
I've done exhaust ports that went outward to 10mm walls and even as far as 8mm walls with no problems with the apex seals munching itself.
I do chamfer all the exhaust port edges - very important!
Porting outward gives the exhaust gases a better chance of exiting the engine...which makes for a cleaner intake charge by lessening the "overlap effect".
Most exhaust gas exiting also means more power hitting the turbo...for turbo'd engines.

My criticism is that you need to chamfer the edges, and I would port more outward.
10mm walls is a good conservative number - I think you can go outward at least another 3mm?
Also, keep the profile more rounded, as this induces less wear on the apex seal as it passes over the exhaust port.


-Ted

Sindregutt

I was waiting for a reply from you Ted! Thanks for the info, it gave me an answer on many of my questions
Youre right, i measured up 13mm from the side of the housing to be on the "safe-side". So you say 10mm + chamfering? how many mm do you "use" on chamfering?(got a picture?)
I like the shape i got now so im gonna keep it that round and smooth.
The gain i hope to get from this port is faster spool/quick respons so it will be drivable/driftable with a GT35R turbo.

Sindre

Sindregutt

btw, I just looked at the other housing.. The chrome has flaked of at the edge (at most 1.5mm and 8mm long) Is this something to worry about?

And do any of you, more experienced, porters got any trick to transfer the porting from one housing to another? Since im not using a template i should maybe make one from the first housing. Good ide if the porting works great for future jobs.

Sindre

RETed

Yep, 10mm + chamfering.
Chamfering = same width as the thickness of the apex seal, so if you're using 2mm apex seals, the chamfer should be minimum 2mm.


I used to run a upside-down "D" port, as that was the shape for most power, but my ports are a lot more circular now - the rounder shape is just better for apex seal transition, and the apex seals should wear easier with a rounder port shape.
If you start to square up the exhaust port, it causes the apex seal to "see" a straight wear line (does that make sense?) when it rides over the exhaust port - not good for reliability...

Good luck!


-Ted

RETed

Yeah, that's normal using the stock Mazda OEM apex seals.
That triangle assist piece causes that chrome flaking, and it's fine.
Just make sure that when you're install the new apex seals that the triangle assist piece goes in the same side.


I use a piece of clear plastic (i.e. Plexiglas) to cut out the templates.
With the exhaust ports, using a thin (~1mm) thick acrylic sheet allows the template to flex with the rotor housing curve, so you get an accurate shape drawn.


-Ted

Sindregutt

Thanks again! Ill try to make a smooth chamfer tonight and ill post some new pictures. Still unsure if the "innerwall" (if you look from the turbo and in) is okey... Ill show you guys pictures later!

Sindre

RETed

I don't touch the exhaust sleeve.
It doesn't really do anything.
Having everything all shining doesn't do jack **** in my book.
All the surfaces tend to get coated with black soot almost immediately.


-Ted

RotaryEvolution

iTrader: (30)

yep, polishing the exhaust is a complete waste of time. anyone who has been working with any type of engine can tell you that.

Sindregutt

Im not gonna polish it very mutch. Just smoothn it and as a final i use the 600 grit paper..

Here are the latest pictures. Is the chamfering enaugh?







My cam sucks when it got low battery. Dont know why but i can get the focus right

Sindre

Sindregutt

i can still go more outwards but i dont know yet if ill do it or not since im pretty please with the result i got now..

iceblue

That is complete bull for exhaust and only holds true on intake. But then again more time I spend the more I see internet people really do not understand long time racing techniques.

RETed

Hard to tell in those pics...
I would go a little more "shallower" with the chamfer - I think your angle is a little too deep.
Look at the stock chamfer on the exhaust port and try and copy that...
You want to try and make the transition for the edges of the exhaust port as smooth as possible.
This also helps with exhaust gas flow, as you're trying to avoid a sharp edge.

Pretty good work so far!


-Ted

Sindregutt

Okey. I got the other housing at work. So im actually looking at it now
Ill try to copy the way its chamfered but making in smoother than the stock one..

Sindre

88rxn/a

iTrader: (6)

so how did this turn out?? some great info in here!!

micah

Lets see some intake porting!

RotaryEvolution

iTrader: (30)

uh, kid... if you want to try calling BS try growing up a bit more before you call anyone out here.

better yet, port and polish an exhaust port all you want, run it for 1000 miles and pull the manifold off and inspect the polish job, if it is still glass smooth i'll mail ya $100 because you're doing something no one else is able to accomplish. it only holds true if you are rebuilding the engine every weekend for drag racing purposes where the carbon has no time to stick with mileage.

apexFD

Porting lateraly on the exhaust ports seems very logical... I always like to hear and see rx7's with a good hp/torque ratio.

Sindregutt

Little update.
Polishing or not. If you do some mild polish its really easy to see where you have larger scratches and you`ll see the shape of the port better.
As mentioned thousand times here i dont see any point in polishing it like ppl do with theire intakes

My intake port is stock RE port.. I had a judgeito intake tamplate but the RE intakes are good enaugh for my power goal so i kept em stock for now.

The car is finnished and runs. It need some better mapping (only mapped at WOT with small injectors and boost)
I also had the 40mm hks wastegate mounted but thats waaaay to small so i have to be really carefull when driving it so i dont max my injectors
..

1680 injectors mounted last weekend but no new map...

The car ran really great befor new injectors and here are video proof :P

http://video.google.com/videoplay?do...g+wankel&hl=en

I got good respons and faast spool.. Since i didnt tested it befor exhaust port job i dont know if it helped (stupiiiid) but all over im really satisfied

Sindre