There seems to be some confusion so this may help. I've studied them closely before even considering their use in a non renisis engine and heres what I found. NOTE I said non renesis so no side exhaust ports.



1. The rotors are much cheaper than earlier versions, I'm paying 280NZD per rotor (195USD) from Mazda. Compression according to Mazda is 10:1. S5 n/a is 9.7:1.

2. The rotors weigh roughly 4225g each. Thats a whole kg less per rotor than the Rx4/5 rotors but only about 100g less than a S5 n/a rotor. Weights include bearing but no springs/seals.

3. In my opinion the gas sealing ring that sits in the groove outside the oil seals is not needed. a) it costs more and b) I believe the added friction would outweigh any benifits (although I would like to test this on an engine dyno). I believe Mazda use this sealing ring in the renisis engine because the sideseal crosses over the exhaust port puting combustion pressure directly on the oil control rings plus larger sideseal clearance would increase blowby.

4. The biggest problem I could see with the RX8 rotors was the side seal clearance. Because the sideseal is directly exposed to exhaust gases it expands more in length than in earlier engines. When purchased from Mazda they come cut to length. There are several different lengths (4 I believe) that correspond to the sideseal grove length (denoted with a letter stamped beside each grove). Even with the longest seal in the shortest groove sideseal to corner seal clearance is still around 12 thou! Earlier sideseals cannot be used as the RX8 items have a wedge like cross section (one side is tapered) and the groove matches. When I last enquired a few months ago Mazda still don't supply overlength side seals and apparently the don't plan to. I should note here that the corner seals come in 2 sizes also, denoted by a L (large) or S (small) stamped by each hole.

As any good engine builder would know this is to much sideseal clearance to consider. The simplest answer I have found to date is to buy oversize solid type corner seals from Mazda which are .2mm larger diam (and cheaper) and mill each cornerseal hole slightly larger to suit. Any competent machinist can do this and the cost is minimal (about 100NZD or 70USD per pair of rotors). My cornerseal to hole clearance is about the same as factory and sideseal clearance is now well within spec using the longest seals available. Some fit right in and others need only a fraction off them. I set my clearance at 3thou to be on the safe side (NOTE side seals must be compressed on their springs to their running height or the clearance will appear larger than it is because of the tapered seal and groove). The oversize cornerseals suit the 3mm apex seals so ofcourse the existing apex slots must be widened and deepend by whatever method is preferred. I prefer cnc endmilling.

5. The standard RX8 oil control rings and springs are used.



The biggest advantage for me is the cost, even with the modifications needed the RX8 rotors are still much cheaper than S5 n/a rotors, have slightly higher compression and are a tad lighter.



The rear counterweight to suit is about 40NZD but I don't use the front counterweight as it interferres with the oil pump chain. I use an earlier counterweight and get the rotating assm balanced.



I have not used an RX8 crank as I have a big stack of earlier ones. I admit I have not yet compared the 2 but there is nothing in the rotor and stat gear design/measurements to suggest any difference except maybe bearing clearance.



The stationary gears are also dirt cheap, less than 100NZD (70USD) each.

1. They are nitrided and have 8 window bearings front and rear (like 13BREW & 20B).

2. The rear main oil seal is pressed in further but this is no problem.

3. There is no O ring groove in the rear gear but RTV or master gasket seals it up fine.

4. The oil feed hole in the rear gear is 1/4 of a hole out. If you look down the gallery from the oil filter you'll see what I mean. A die grinder soon fixes this, the hole must be ovaled 2mm towards the rear of the gear. The oil passage in the front gear lines up.

5. Mazda say they changed the tooth profile for the RX8. I cannot detect any difference just by looking and I have not yet tried the RX8 stat gears with earlier rotors. I hear others have but do not know the results.



I hope this helps a little. Feel free to add to or correct, the more info the better, the reciprocation engine has a 70 year head start on us!

 

Good stuff. I was about to start a thread with a few questions on the ren stats. The new gear profile is a little concerning, but its cool to have a quality, mass produced gear at a good price.



Price list from Mazdatrix.



Front stationary:



Stock 13b $ 95.97



Racing Beat $166.00



"Mazdaspeed" $111.00



REW $312.00



Renesis $102.00





Rear Stationary:



Stock 13b $102.28



Racing Beat $194.00



"Hardened rear" $158.19



HRD 3 window $186.20



REW $353.90



Renesis $134.49

 

Mazdacomp price for rx8 front is 74 USD and rear is 93 USD + shipping

 

Dam, thats quite a difference.

 

For the side seals, you can get the custom long from mazdacomp and then file it down to the clearance needed.

 

you have a part number?

 

Mazdatrix has them, not cheap though at 16.90 a piece.



http://www.mazdatrix.com/getprice.as...m=11-C11C-N3H1

 

its a comp part.....

 

I rememeber the argument of wether-or-not the renesis apex seals were strong enough to be run with peripheral exhausts. In a turbo aplication I don't think I'd trust them(10:1 rotors + boost. Woohoo!...*pop* ), but what about N/A? Has a conclusion been reached?

 

From what I hear, even in a n/a application the seals are too shallow and the heat from a PP exhaust warps them in a short amount of time.