How high can I safely rev this?
 

I'm in the process of building a new engine for my auto-x/track FC. I'd like it to rev as high as possible mainly so I never run out of second gear on an auto-x course.

S5 TII base (irons and anything else I don't mention)
9.7:1 S5 NA rotors letter matched and clearanced
Mazda comp rotor bearings
FD side and corner seal springs
ALS Apex seals
mazda comp oil control ring seal springs
RX-8 eccentric shaft and high power stationary gears
FD oil pressure regulator
FD front counter weight and thrust bearing stack

I'm thinking 9k maybe 9.5k?

anything else I can add to increase the revs that's fairly easy (I don't really want to modify the oil passages in the front cover...)

stock intake system?

It's turbo, it has an FD Upper intake and a v-mount IC

but I don't really care about making power up there.... I just don't want to have to shift or hit a rev limiter

i'd try to keep it @8500, but if it went to 9k, or a little more is probably ok

What's keeping me from going higher?

Rotors hitting the sides, mostly.

I took .005 off of each side, winged it over 9000 a few times, once the datalog showed 10.3k, took it apart and the edges were just a tiny bit shiny. So I took another .002-.003 off of each side and bumped oil pressure to 90psi.

That's the engine that is in the car now... it's fuel limited to about 9300 but it stops making power at about 8900.

It's kind of hidden up there, but I am clearancing the rotors.

Okay, then yeah, good to go.

One thing that I'm majorly a fan of is lead-in grooves in the main journals' oil holes and lead-out grooves at the rotors. I started doing this when I found out that at a certain high RPM, 100psi oil pressure in the engine was 7psi oil pressure inside the eccentric shaft. Centrifugal force is keeping the oil from feeding into the e-shaft, so the lead-in grooves act like a little pump to combat this. Likewise for the lead-out grooves.

I just make them about 3/4" long and about as deep at the end as it is wide, then radius the edge from the lead-in to the oil hole. Not sure if I'm at the point where it's critical, but on the flip side, I haven't had any bearing issues since I started doing it, either.

By "lead in" do you mean the groove is towards the rotation and by "lead out" it trails rotation?

What main bearings are you using? Sounds like the MFR 3 window race bearings would more than accomplish that.

I'll be running at 120 psi with RX-8 bearings (which go up to 9k stock) so they should be fine...

Stock bearings everywhere. I prefer to use used ones but I had to break down and install new rotor bearings this time around. Did an extra long break in because installing new bearings is a little sketchy, even Mazda thinks so, which is why the breakin time for an engine goes up by more than double if new bearings are used.

The MFR bearings have a little extra clearance, which is nice for when the eccentric shaft tries to turn into an S, and they have a deeper pocket in the middle, which is nice for keeping the eccentric shaft fed, but it still doesn't help that it's trying to feed a drilling that is moving at roughly 80 feet per second, perpendicular to the oil, against over 2000g of force trying to spit the oil back out at the main bearing.

Sure, the reciprocal outward force at the rotor journal's drilling compensates... but best hope that the oil in the shaft is SOLID and not aerated... which it will be unless you have a good deaerator stage in your dry sump.

Lead-in and -out grooves help a lot and are easy to do. I mean, it's easy while you've already got all the metal-removing tools out while you're porting the intake and exhaust ports and the oil passages to and from the oil pump and that nasty right-angle drilling junction where the oil feed goes out to the front cover...

(Hint maybe? :) )

I did all of that stuff, use a 12A oil pump, and still get 90psi by 4000rpm. And under 4000rpm there's no need for that much pressure, so why use a bigger pump that will just be more likely to cavitate at high RPM?

I also cut open my oil filters, cut out the filter media, and set it out to dry so I can inspect for bearing material and other nasties. Because I'm paranoid, that's why. I'm getting into the heart of third stage weird old-guy habits now.

It goes like this:

The first stage, you're green and don't know what you're doing so you do everything that the experienced guys tell you to do, without really understanding why other than just trusting their experience.

Second stage, you've got some time under your belt and projects completed successfully and you start to cut corners, because you know some people who did and they had no problems so why spend the extra time/money/effort?

Third stage, you do weird overkill crap because you had that one time when X happened and you don't want it to happen again. Then you tell green people why you do it and then second-stage people tell you that it's totally unnecessary... :)

Fourth stage is leaving everything completely stock and just driving it...

Sounds like you're talking about the rotor bearings

I was talking about the MFR rear stationary gear bearing:

http://www.mazdatrix.com/Pictures/b-...ing3Window.jpg

This is what the RX-8/FD bearings look like:

http://www.mazdatrix.com/pictures/b-...aring93onS.jpg

both much better than the stock FC one...

I know what you're talking about. I don't use them, because I prefer used bearings *everywhere*. Especially if they're out of an engine that was run hard and has a ring of copper showing at the ends. Pre-race-clearanced and no special break-in procedure required.

I also prefer to not remove the stat gear from the housing if at all possible. That one time where a tiny bit of "who knows" got between the gear and the iron during assembly and resulted in the bearing being crooked...

Copper showing is fine as long as the bearing isn't scored heavily. The overlay is only about as thick as the difference between MFR and standard bearings, anyway.

me too! good thing i test fit it before i even left the press, i'm headed to stage 4, but proper stage 4, worn out is still worn out. we were able to beat the living tar out of these cars when they were newer, without all the fancy engine parts

Please post pictures of what you speak. I am trying to understand this, but have no idea what you are refering to.

https://www.rx7club.com/attachments/...t-dsc00510-jpg
https://www.rx7club.com/attachments/...t-dsc00502-jpg

Exactly so.

It should be noted that in the top image the nose of the e-shaft is pointing to the right, not the left like the lower image. It'd suck to make them backwards.

It'd suck to make them backwards.

Yes, I wouldn't recommend doing these or any other mods until you have thought about it and understand what it is doing and what else it will affect.

For instance, this motor also has loop line mod, but just handling/looking at the e-shaft you would not know that and might drill the rear stat gear oil inlet on the e-shaft through copying this e-shaft.

If you do that without the loop line mod you have just increased the front stat gear and rotors oil pressure drop/differential by sending more oil through the rear of the e-shaft so making the motor less reliable instead of more.

That said, I am feeling pretty Stage 4 now. The benefits to most non bolt-ons aren't worth the time. Just spend the time driving and drive better/faster.

If you complete Stage 4 and max your driving I hear a rumor you go on to-

Stage 5- someone pays you to drive and listens to what you want the car to do and pays to make it do your bidding.

Yep. Most of the modifications on THIS car are purely in the interests of getting more seat time. Because seat time is more important than anything else.

Except for the modifications that make the car faster, those oddly enough are geared toward getting LESS seat time.

Unless you're driving for Subaru WRT in which case the engineers tell you that the car is perfect and the driver just can't keep up.

(Then the same drivers get into a Brand F or Brand C and go a ton faster...)

Hey Peejay, is there a way that you were able to measure the pressure in the eccentric shaft as opposed to the galleries?

Cheers.

I haven't heard about this. The Engineers really don't listen to the drivers? :scratch:

Could someone show a picture of what area of the rotor contacts the housing during high revs ?

The shiny area in this pic at the rotor tip.
http://xtremerotaries.com/images/ser...arancing_3.jpg

we race at the club level, and we have had this happen. we even have a joke about it, when the helmet goes on, 50 IQ points come off.

Does anything have to be adjusted when the rotortips are clearanced? I refer to the length of the apex seals or corner seals since the rotor will be more narrow that point.