Mazdanowski

I have bought a number of porting template through the years and none of them under cut any of the corner seal. Looking at some professional build motors I noticed some are not undercut, ie stock openning. Others are opening a lot sooner by cutting away a lot of the side housing under the corner seal. The motor that made the most power had very little support under the corner seal (early openning), had the outer oil seal removed and ported partially into the oil seal area. So I can't tell which factor helped increase the power.

One question is, for a race only motor, how much of the housing under the corner seal can I port out to get the intake flowing sooner? Do I need to leave around 60% of the corner seal supported?

I realize this will add a little overlap between the closing exhaust port and opening intake port and that can be good. Without infinite access to a dyno and housing I'm not sure how much overlap is ideal with an open exhaust. For a race motor would anyone suggest using a different exhaust closing in this case?

For a street motor that you want to last can the side housing be ported to partially undercut the corner seal?

I have heard that Renesis rotors don't make make power when dropped in an S4 or S5 iron. I have not had a chance to look at them but heard that the seals are closer to the face allowing the earlier opening in the side housings. Would using the Renesis rotors in a NA motor allow you to port the side housing for earlier openings?

Thanks

rotarygod

iTrader: (1)

Renesis rotors shouldn't make any more peak power but they should make better low to midrange power. If you were to use the seals that were intended for each rotor by matching letters on each seal up with the letters on the rotor sides, you'll have very large tolerances and lowered compression. This was done to allow for heat expansion of the side seals since the exhaust goes out the sides. If you buy the longer seals that you need to clearance yourself to fit, you can get clearances equal to those of the 13B.

peejay

You will have problems with the side seal well before you have problems with the corner seal.

A rule of thumb is, don't let the leading edge of the side seal fall into the port, and shape the closing edge so that the trailing end of the side seal doesn't slam into it. It's common sense if you think about it but apparently a lot of people don't think about it. The ports aren't just holes, the seals have to slide over them, and an engine with crapped out seals doesn't care how pretty the ports are since it won't be running.

Some people DO let the leading edges fall in... but I wouldn't do it on an engine destined for longevity.

Mazdanowski

Peejay I had heard that the Renesis side seals had to be cut like normal like in non Renesis motors but no one said why. Thanks for the explanation.

Rotarygod since I don't have a Rensis rotor to hold up next to my S4and 5 rotors so I can't verify the position of the corner and side seals. I think the stats I see says you can take the normal 32 degree's after TDC opening for the intake and cut it back to 25 degrees in my second gen. Looking at the Renesis intake opening stat I think it said it opens at 3 degrees ATDC. If I run the Renesis rotors and open the intake ports 22 degrees sooner in that S4 won't the intake breathe a lot better?


If I am really missing something let me know. Thanks guys.

rotarygod

iTrader: (1)

The side seals on the Renesis are moved farther out by 2 mm. The corner seals are in the same place. The apex seals are much shorter on the Renesis though so my recommendation would be to have the grooves machined deeper to accomodate the 13B apex seals. Then use the Mazda 2 piece 2 mm seals.

If you are using Renesis rotors, you can also use Renesis port open timing. I actually wouldn't go quite that far though as I believe they pushed it a bit too much on that engine.

peejay

And I think they didn't go too far enough!

(sorry, had to go there)

That IMO is something in favor of the rotors. One could reeeeally push a street port.

ultimatejay

iTrader: (1)

If you're going with Renesis rotors and have the cash. Ianetti makes ceramic seals for the Renesis rotors. No need to groove out the rotor slots for the 13b seals and the Renesis seals are lighter which is better for a N/A motor.

rotarygod

iTrader: (1)

I've seen a couple of bone stock motors where the side seal crashed into the closing edge of the intake port. There really isn't much support there. They went too far. The intake ports are MORE than adequate for upwards of 300 hp in naturally aspirated form anyways. The problem is that the exhaust ports can only flow enough for about 260 hp. Since the intake ports aren't hurting performance due to their size, they could easily be slightly smaller with no effect on power but only positive benefits on seal life.

Mazdanowski

Ok so if the Renesis side seals are 2mm farther out and they are too far out then I am guessing you are saying that if I use the Renesis rotors instead of the S4/5 rotors I can maybe go one more MM out splitting the difference?

If the S4/5 rotors opened around 32 degrees ATDC and the Renesis opens 3 degrees ATDC then then would splitting the difference open the intakes around 18 degree ATDC?

Every thing else being equal how helpful would the extra 18 degrees of early intake timing be in either a street car or EP car? Is your educated guess 5hp? 10hp?

So if I use the Renesis template should I leave an extra MM metal than the template suggests?

Rotarygod I think you are saying the Renesis intake irons may flow enough air for 300 plus hp but what about our 6 port irons, what Hp are they good for?

Are you saying our 13B peripheral exhaust housing top out at 260?

If the exhaust housing are the limiting factor is it worth the effort to try to get more intake airflow by using the Renesis rotors just get the extra intake timing?

Thanks

BLUE TII

iTrader: (9)

I haven't had the Renisis side housings in my hands, but it looks like Mazda cut the intake ports to "drop" the leading edge of the lower side seal for just the first part of the intake opening while the majority of the seal is supported (so it won't sag too much) and then it goes back to being fully supported.

I base this on how you can see the lower section of the port has a strange rounded profile that opens first.

So the excessive sideseal wear RX-8s are having is probably from people letting the engines operate at too low rpm and too high load barely dropping that side seal tip in wearing its corner off.

If one were to use RX-8 rotors for the bevel and outboard placement of sideseals and port so that just the trailing edge of the upper sideseal drops in the port with a scissor and bevel to the closing line while the leading edge of the lower sideseal is fully supported you would make great power and no problems with sideseal wear.

Having the beveled rotor does make the engine a little more sensitive to pinched sideseals if you ingest any large foreign material, but this is rarely a concern.

BLUE TII

iTrader: (9)

You would have to make a template like this to see how much you can port whether you use RX-7 or RX-8 rotors.

You assemble a rotor on side housing with e-shaft and rotor housing to support your plexiglass template positioned exactly with the engine dowel pins.

Then you put in a corner seal and a side seal spring in place of top or bottom side seal with an end bent up to just scratch the plexiglass surface.

Rotate the rotor in the direction that forces the spring against the corner seal while scribing the path of the outermost edge of the side seal.

Repeat the procedure for the other sideseal and you have your the outer most edge of your porting template as well as seeing where the other side seal will come back on the plate so that you do not put in too rounded of a corner and thus bad scissor.

rotarygod

iTrader: (1)

The peripheral exhaust ports aren't limited to about 260 hp. The side exhaust ports of the Renesis are.

quattro4now

It'd be interesting to see what the Renesis could do if it had peripheral exhaust with the side ports blocked.

rotarygod

iTrader: (1)

Just as a bit of information for those who are curious. If you want to install a Renesis into an RX-7, you will need to address the front housing and oil pan issues as the Renesis is longer. The front housing thickness of the 13B is 40mm. The Renesis front housing is 55mm thick. If you install a 12A or 13B front housing on a Renesis front plate, and it does fit, the eccentric shaft will not stick out of it. It will basically be flush. For anyone who thinks a 12A front plate will work so it will fit in a 1st gen, think again. The same is also true for those wanting to use non-Renesis front plates for crank angle sensor or distributor use. Have fun getting pullies on!

gawdodirt

I imagine it would be like using TII side housings with early 13B N/A center plate. Prolly work fine . Largest cast N/A possible engine. Similar to The LOORRS Super Lite rotaries.

gd

TonyD89

iTrader: (10)

By front housing do you mean front cover? I suppose the front plate (iron) only change doesn't work because the Renisis center plate is also thicker ? I'm not getting this. If the shaft is basically the same, rotor housings thickness the same, iron thicknesses the same (if the front is changed to 13B), ......

rotarygod

iTrader: (1)

The Renesis front end plate is thicker. The front cover, while it has the same bolt pattern with the exception of one added bolt hole, is thinner than the 12A/13B front cover by 15mm due to the thicker end plate.