Mistryl

I was wondering, has anyone experimented with removing the rev limiter? Or, at the very least, increasing the max rpm you can reach? Wouldn't this increase the max hp you can reach?

Also, wouldn't this work for both the automatic and the manual?

Sorry for the noobish question, but I don't know much about cars in general.

zyran

Can't be done for the automatic - Torque Converters can't handle high revs. Read the topic "A Stupid Idea?"

Manual? I don't know. Maybe the engine can't go that high. It would be awesome if it would go 10k rpm, just 500rpm shy. It can go higher without a doubt but there are lots of obstacles.

robertdot

I'm not a mechanic, but from what I gather, assuming the apex seals are good, it should be able to handle a fair amount more (at least 10K). I haven't done any research and I don't have the cash to lose an engine.

At any rate, the only "obsticals" I can thing of is telling the ECU to not cut the fuel at 9.5K. Further, I don't know what the fuel maps say about above 9.5. That may be the same problem.

Oh, and change when it beeps at you to shift...

It may just be a module to tell the engine how to run past 9.5 K RPM (or wherever the ACTUAL rev limiter is)

rjacobs

Well, I think this was on another post somewhere, but even if the engine could rev further, which it can, in its present state it would do nothing for it since the intake runners and port design and eveything is designed around the 9000 rpm redline, the engine makes peak power at 8500 so going anywhere higher than that is just risking damage that is not worth it.

Reeko

I can think of cases where it might be more efficient to be able to keep the car in a lower gear longer (such as the end of a straight before a turn, when you would only be going to the next higher gear for a brief period).
Another example would be in the 1/4 mile. Most of the RX8 1/4 trap speeds put the car right at the shift point to 4th at the 1/4 mile mark. Your options are to shift to 4th just as you trap, or hold 3rd and bounce off the rev limiter. a 10K rev would get you to 100 MPH in third which might be more efficient than shifting to 4th even with the power drop off.

Reeko

Just because it makes peak at 8500 does not mean that there is no advantage to running higher.
The question depends also on gearing. Take 3rd and 4th.

3rd at 90MPH is 9K RPM.
4th at 90MPH is about 7.5K RPM.

The question is are you still making more power above 9K (or 8.5 K from your statement) than you would be at 7.5K when you upshift.

Feras

iTrader: (1)

i believe i read somewhere that the hard red line is 13000rpm and the engine blows at 14000rpm...however to get any power out of this extra rpm band you'd have to completely overhaul the current ECU and possibly injectors and other things, because in the current format the car is built so that it peaks at 8500rpm period....lets just say itd be a different car completely with a 13000rpm redline although it is possible. I am not sure but the Mazda Star Formula (not formula one) cars (that incidently use the renesis) may be higher reving than our renesis's

robertdot

I did a very quick search for the revs on Mazda Star Forumla before I posted above... no luck. If anyone knows, I'm sure I wouldn't be the only one interested in hearing.

wakeech

nah, pretty much the same 9k redline i believe.

because of the current porting spec, you'd have absolutely no gain bumping the redline up with the engine as-is.

it's been for a long time with the 13B (whether it's series 3 or series 9 it doesn't matter) that going for a perhipheral inspiration port will give you a torque peak somewhere around 10k rpm, and will give you about 300 hp with a redline around 12k.

so yes, bumping the revs on a rotary will do you good, but only with extreme breathing.

epitrochoid

feras is right..the hard redline is 13k, and the engine will be torn apart by harmonic vibrations by 14k. mazda did a test to find that out i believe

NAVILESRX8

iTrader: (1)

The intake and ignition system start to peter out around 8500RPM...above that it starts losing efficiency...

Mistryl

hmm, just curious...are ALL torque converters incapable of handling high rpms, say...11-12k?

wakeech, can you explain the theory/numbers behind your statements? I don't quite understand.

zoom44

the engine can not breathe, in it's from factory condition, above 9.5k. the ports aren't big enough and the intake is not designed for it. also the maps in the pcm don't have any info on what to do. also the coils can't handle it. can it be done? sure. peripheral port the engine, change the ignition system, build and tune a completely different intake,remove the cut-off in the pcm and create completly new maps and a new cut-off in like an emanage or some piggyback. then spend alot of time and money on the dyno while tuning everything to work correctly. have fun.


edit: i didn't even mention cooling system and oil metering.

zoom44

all of the converters currently available to Mazda cannot handle above 8k. someone might be able to bulid a one off than can handle higher but at what cost?

Feras

iTrader: (1)

you can always pull that $10k automatic with a clutch out of a ferrari enzo, that can handle the revs lol

rotarygod

Actually, yes it does mean that. If your power is falling off, there is no point in staying there any longer. You hinted at the solution. It's gearing. If you are at the point at the end of the track where you need to shift, you really need a different gear ratio. If you are designing the car for single purpose track use, you should be near the top of the highest gear at this point and adjust the rest of the gearing accordingly. If you just want a dual purpose vehicle then change the gearing so you either have a higher ratio or lower ratio. The last option is to run a different tire size on the track. Problem solved. By merely staying in the same gear and raising the rpm limit past it's powerband, you are not going to get any gain. It'll make you slower compared to gear changes.

I don't know why some people are caught up on more, more, more when it comes to rpm's. More is not always better. The Renesis as it comes from the factory has a very well designed intake system that is designed around the current rpm range. It is a better manifold than anything Mazda has ever done before. Does it mean it can't be improved? No. It does mean that raising the rpm limit with the current manifold is pointless. No amount of tuning on the fuel or timing side can change that.

I'm going to elaborate on zoom44's post since he's figured it out. If you want to raise the rpm limit properly here's what needs to be done. Scatter shield on the transmission. You'll want this in the event that the clutch and flywheel explode and try to pierce the floorboard and your legs. It happens. Flywheels are not rated for more than 10000 rpm unless they are special race units designed around this purpose. The next thing you'll need is a new ecu. The stock one isn't capable of tuning this high. Larger fuel injectors will be in order as well as higher volume fuel pumps. You also need new coil packs since the stock ones aren't able to discharge fast enough at extreme rpm's. You'll also need an entirely new intake manifold designed to give you more power up high. The downside is that it will really hurt low end power and drivability on the street. People already complain about this now. New transmission is next. The stock gear ratios aren't set up around racing let alone a higher powerband. Since the stock tranny isn't geared this way, a higher redline really won't keep you in the transmission sweet spot for best performance.

Assuming you've done all of this, you should probably tear the engine apart and address some issues. You'll want to blueprint everything at this point. This includes bearing clearances, rotor to housing clearances, etc. Since the eccentric shaft can warp at high rpm's, it would be a good idea to get a Guru racing eccentric shaft. It has the provision to add a center bearing for better high rpm support so that shaft flex won't happen. I'd change the bearings also. Since the engine is open, it's a good time to do some port work. Since the stock ports aren't designed to flow at this rpm, not porting it will do practically nothing inspite of all of the other mods except make the powerband narrow and peaky. Don't just make the ports as big as possible. This is the single biggest error when porting rotaries and almost every amateur that tries to port their own engines does it this way the first time or so. Proper timing will give you the proper amount of flow to hit your target rpm range. You don't want more or less flow than you need. Yes, you can have too much flow. Raise the oil pressure in the system. Use a racing grade oil. Add a larger oil cooler. A rotary expells 1/3 or it's heat through the oil. This is completely unlike any other engine.

All of these mods assume you want to run over 10,000 rpm and do it quite often. If you don't intend to do it very often, there isn't much point in doing it. Don't just run this high because you can. The engine may or may not live through it. Is it worth it? The abive list is how to do it properly so that you can still get reliability. Can you get higher performance from higher rpm's? Probably if done correctly. By merely just raising the rev limit without any other changes, you are just wasting your time and your engine. The LeMans 4 rotor didn't go up to 10,000 rpm and it was a race engine. They just designed the rest of the system well.

Mistryl

Hmmm, thanks RG. Can't believe I got a response from you ^^

THat sounds good for my 8 right now, can't believe i thought that this might be a "cost-effective" way of increasing hp. -_-;;

how about for my friend's auto? Assuming you get a higher rev torque converter, are you still worried about the auto transmission? especially since they're stuck at 7.5k rpm?

Mistryl

I believe my friend was complaining about how everything with his car was fine, except he's missing about 2000 rpms.

Oh, and i tried convincing him that he could just go stick, except he doesn't like the gearing on the 6 port. Something about having to shift too often when we go on mountain runs, especially when he decides to finally up the horsepower or something. Anyone know what he's talking about?

rotarygod

The 4 port engine is seriously restricted on the intake side as even compared to the 6 port engine. There isn't much point taking it higher either. You wouldn't need to do any strength mods to take it to the 6 port engine's redline but the intake is seriously choked.

If you want an increase in accleration then you could change the torque converter. People don't just change them in order to raise the rpm limit. Most never do this. What you are doing is changing the stall rpm to get you moving faster. You are much faster if your engine is in the peak of it's power range. This is something the factory always gets wrong as far as sheer acceleration is concerned. You do understand of course that the odds of you keeping up with the 6 speed are pretty slim but you will go faster than stock never the less. There's nothing wrong with that. As with anything, street drivability is affected a little.

FWIW: The 4 port engine makes more power than the 6 port up to 7000 rpm. It is above this point though where the 6 port engine really starts to shine and is why it is faster. The auto transmission also robs more power away due to higher driveline losses.

Mistryl

btw, how easy is it to tune the 6 port? I was thinking about doing some timing improvements on it, but i heard rumors that it was harder than the 4 port engines, so i haven't started yet. any advice?

sferrett

There are other things to be concerned about other than the engine - at some point the flywheel/clutch will fly apart also as will the alternator, water pump etc. etc.

zoom44

it is not "harder" to tune than the low-power renesis. do a search for greedy e-manage. one forum member has managed to do quite a bit of tuning with his.

Mistryl

hmmm....i wonder which will be better suited for autocross and mountains in the long run.... FI auto or FI stick?

Only reason i ask is because in a real course, your speed and times are very rarely solely dependent on horsepower...gearing and other factors play a big role as well. Any ideas?

Also, my friend is now wondering what it would take to stuff a 20B into his auto. I told him that the transmission would probably need some sort of strengthening, but beyond that, I have no idea. Somebody help?