Rev limit of a rotary? <searched>
08-30-06, 08:10 PM
#1
Nar
Thread Starter
Rev limit of a rotary? <searched>
What sort of limitations are there to raising the rev limit of a rotary? I did some searching and came up with some answers. So far I can see the limitations are:
- Oil Pressure & Fuel pressure
- Clearancing, balancing and matching
- Port sizing (intake and exhaust flow)
- water pump & alternator
- Stock ECU
- Ignition system
Which is basically the same as a piston engine. (I suppose that shouldn't be a big surprise) I also read somewhere I think it was in the old Rotary Rocket magazines that a big limitation for rotaries is the fact the bearings the e-shaft rides on cant handle temps above the normal operating temperature. Would you need race-bearings for the e-shaft as someone mentioned below?
Since I own one I'd like to know what modifications would be needed to raise the rev limit and fuel cut of an S5 NA 13B. Assuming there are any gains to be made above the stock powerband of course.
If you happen to know of any threads that have useful info on this topic please link them here thank you.
https://www.rx7club.com/showthread.p...ight=rev+limit
https://www.rx7club.com/showthread.php?t=319534&highlight=rev+limit
- Oil Pressure & Fuel pressure
- Clearancing, balancing and matching
- Port sizing (intake and exhaust flow)
- water pump & alternator
- Stock ECU
- Ignition system
Which is basically the same as a piston engine. (I suppose that shouldn't be a big surprise) I also read somewhere I think it was in the old Rotary Rocket magazines that a big limitation for rotaries is the fact the bearings the e-shaft rides on cant handle temps above the normal operating temperature. Would you need race-bearings for the e-shaft as someone mentioned below?
Since I own one I'd like to know what modifications would be needed to raise the rev limit and fuel cut of an S5 NA 13B. Assuming there are any gains to be made above the stock powerband of course.
If you happen to know of any threads that have useful info on this topic please link them here thank you.
https://www.rx7club.com/showthread.p...ight=rev+limit
Originally Posted by rx7tt95
It's been my belief that Mazda "race" bearings would be needed (possibly have deeper "channels" to hold more oil) and clearancing. I have the clearancing part done. Thanks in advance.
Michel.
I've heard that the oiling system has some sort of shortcoming but I don't know what that is nor how to fix it. Anyone?
Michel.
I've heard that the oiling system has some sort of shortcoming but I don't know what that is nor how to fix it. Anyone?
Originally Posted by EpitrochoidMan
: You should probably underdrive your water pump pulley. At that kind of rpm the impeller won't really pump it will just kind of swish the water around.
If it were mine I'd also go with a higher pressure oil pump.
If it were mine I'd also go with a higher pressure oil pump.
Originally Posted by vosko
judge ito told me as long as its a mazda matched unit you can goto 10k rpm safely. mine see's its 10.5K rev limit quite often
Originally Posted by DomFD3S
I do know that Mazda uses a alphabet coding system for their rotors (A - E). I'm assuming that it is based on the standard deviation of weight for each rotor, meaning, the perfect weight rotor would be a "C", but that is just a guess.
I wonder if this type of coding, pertains to the eccentric shafts as well?
The reason I know this is because it is in one of my Japanese magazines. Unfortunately, I don't remember much from my one of year Japanese class,...back in 1992!!!!
Hey Vosko, see if Judge Ito can confirm my assumptions...
I gotta bring my magazine over to the guys from Signal. See if they can translate it.
I wonder if this type of coding, pertains to the eccentric shafts as well?
The reason I know this is because it is in one of my Japanese magazines. Unfortunately, I don't remember much from my one of year Japanese class,...back in 1992!!!!
Hey Vosko, see if Judge Ito can confirm my assumptions...
I gotta bring my magazine over to the guys from Signal. See if they can translate it.
Originally Posted by DChan415
If you plan on running above 8K often, you need the clearanced rotors, MFR bearings which have .0005 more clearance and a .050 deeper oil groove, hardened stationary gears, a balanced rotating assembly, and if it were a perfect world, lighter apex seals would be nice too. If you only want to run it to 8500 once in a while. I think you're fine. I do it.
Originally Posted by diyman25
THE REV LIMIT. all depend on ur port. most street port make their power between 4000-7500. BP some time to 8000+ . and PP is much highter some time u can see 10000+. but the higher u got the short life u will get from ur engine . EVEN 4 rotors LE MAN RACE car's red line are 8000. if u want to know go get a RB catalog it explain pretty good.
Originally Posted by Wargasm
I'm no expert here as I shift at 8000... heheh ... but here are a few factors that come into play to determine your shift point (in no particular order)
1 - Mechanical limits of the parts. Once everything gets spinning, the eccentric shaft flexes. If it flexes enough you can get contact of the rotors against the side housings and the bearings and stationary gears can also fail. You can side-cut the rotors on the edges to reduce this problem, upgrade the bearings, put in harder stationary gears, pin the rotors and rotor gear together, run more oil pressure, etc etc etc to make things stronger if you want to get the maximum potential redline up. Did I mention that most flywheels are only officially rated to around 8000 RPM or so? They will do more, but do you want to see what happens to your legs when a flywheel or pressure plate comes apart at 10,500 rpm? Say hello to Stumpy.
I'm no expert with 8000+ operations, so don't quote me here...
I'll throw out some random numbers here for an FD engine... Again, I'm NO EXPERT here, just giving you some ideas...
8000 - stock redline ... pretty darn safe
8500 - a fair amount of people go to this on a stock block... probably pretty safe in the grand scheme of things. With the possibilities of bad AFR, bad fuel, blown coolant seals, cracked apex seals, overheating of water or oil.... 8500 rpm doesn't seem like the likely cause of engine death anyhow!
9000 - I know you can do it... requires some internal mods as I mentioned above to be safe about it.
9500 - If you're crazy enough and do enough mods to make it happen, you can probably do this too, but by this point, you probably have a pretty crazy FD.
2 - The next factor will be fuel injectors. Or lack of them. As your engine RPM rises, the amount of time to squirt the gas in during the intake cycle goes down. Just some food for thought... at different RPMs, here's how much time your injectors have to get the gas into the chamber:
4000 - 15 milliseconds
8000 - 7.5 ms
9000 - 6.7 ms
10000 - 6.0 ms
So you better have some seriously huge injectors or better yet, at lot of them so that they can open, fire, close that fast! Let's imagine a car that makes peak torque around say 6000 rpm. You may notice that you don't really start running out of fuel injection capacity until 8000? That's because even though you're using MORE gas at 6000, you also have more time to squirt it in. By 8000, you still need a fairly big amount of gas, but not as much as at 6000... but your time to get that gas in there is 25% LESS. So get some big *** injectors.
3 - Power band. OK so you've got this totally built motor that runs 9500 rpm all the live long day. You have a bad *** fuel injector setup so you can dump 2 gallons of fuel per minute into your engine... but you have stock porting and an Apex RX-6 turbo. Hmm. You go to the dyno and notice that your power is dropping FAST around 6000 rpm... By 9000 RPM it looks like your dyno curve is actually going straight down. Heheh. What's wrong? Well you made an engine/turbo combo that doesn't flow enough air at high rpm to necessitate a high redline.
A combo of items 1, 2, and 3 is why I shift my car at 8000.
My engine is built with stock FD parts. Nothing special for high rpm operation... I would not feel safe going over 8500 all the time. So right there I'm going to say to myself, 8000 or 8500 is my max.
My fuel injector setup is hitting around 90% injector duty cycle at 8000-8200 rpm. This is already pushing it a bit. 8000-8500 range is looking like the max here too... hmmm
With my dyno-proven power curve in hand, and MS Excel I can make a graph showing the power put the ground in each gear. I can estimate a little bit (not too far now!) past the end of my dyno graph and see what power I might make a few more hundred rpm later. So if my dyno runs up to 8200 before I lifted, I can probably guess pretty accurately what it might be at 8500... not that far away. So I can make a little spreadsheet... and you know what I found out? Holding out to 8250 or 8500 with MY CAR'S PERSONAL POWER CURVE is only going to get me a SMALL amount of power compared to just shifting at 8000. In other words, I'm not going to push the mechanical limits and the fuel injector limits for what is going to work out to be a VERY small change in the overall peformance of my car.
So anyhow, I know this doesn't answer your question, but I hope it gives you some ideas of what you might think about when picking your redline. I'm sure I probably forgot something too, but forgive me, it's late and I'm tired
Brian
1 - Mechanical limits of the parts. Once everything gets spinning, the eccentric shaft flexes. If it flexes enough you can get contact of the rotors against the side housings and the bearings and stationary gears can also fail. You can side-cut the rotors on the edges to reduce this problem, upgrade the bearings, put in harder stationary gears, pin the rotors and rotor gear together, run more oil pressure, etc etc etc to make things stronger if you want to get the maximum potential redline up. Did I mention that most flywheels are only officially rated to around 8000 RPM or so? They will do more, but do you want to see what happens to your legs when a flywheel or pressure plate comes apart at 10,500 rpm? Say hello to Stumpy.
I'm no expert with 8000+ operations, so don't quote me here...
I'll throw out some random numbers here for an FD engine... Again, I'm NO EXPERT here, just giving you some ideas...
8000 - stock redline ... pretty darn safe
8500 - a fair amount of people go to this on a stock block... probably pretty safe in the grand scheme of things. With the possibilities of bad AFR, bad fuel, blown coolant seals, cracked apex seals, overheating of water or oil.... 8500 rpm doesn't seem like the likely cause of engine death anyhow!
9000 - I know you can do it... requires some internal mods as I mentioned above to be safe about it.
9500 - If you're crazy enough and do enough mods to make it happen, you can probably do this too, but by this point, you probably have a pretty crazy FD.
2 - The next factor will be fuel injectors. Or lack of them. As your engine RPM rises, the amount of time to squirt the gas in during the intake cycle goes down. Just some food for thought... at different RPMs, here's how much time your injectors have to get the gas into the chamber:
4000 - 15 milliseconds
8000 - 7.5 ms
9000 - 6.7 ms
10000 - 6.0 ms
So you better have some seriously huge injectors or better yet, at lot of them so that they can open, fire, close that fast! Let's imagine a car that makes peak torque around say 6000 rpm. You may notice that you don't really start running out of fuel injection capacity until 8000? That's because even though you're using MORE gas at 6000, you also have more time to squirt it in. By 8000, you still need a fairly big amount of gas, but not as much as at 6000... but your time to get that gas in there is 25% LESS. So get some big *** injectors.
3 - Power band. OK so you've got this totally built motor that runs 9500 rpm all the live long day. You have a bad *** fuel injector setup so you can dump 2 gallons of fuel per minute into your engine... but you have stock porting and an Apex RX-6 turbo. Hmm. You go to the dyno and notice that your power is dropping FAST around 6000 rpm... By 9000 RPM it looks like your dyno curve is actually going straight down. Heheh. What's wrong? Well you made an engine/turbo combo that doesn't flow enough air at high rpm to necessitate a high redline.
A combo of items 1, 2, and 3 is why I shift my car at 8000.
My engine is built with stock FD parts. Nothing special for high rpm operation... I would not feel safe going over 8500 all the time. So right there I'm going to say to myself, 8000 or 8500 is my max.
My fuel injector setup is hitting around 90% injector duty cycle at 8000-8200 rpm. This is already pushing it a bit. 8000-8500 range is looking like the max here too... hmmm
With my dyno-proven power curve in hand, and MS Excel I can make a graph showing the power put the ground in each gear. I can estimate a little bit (not too far now!) past the end of my dyno graph and see what power I might make a few more hundred rpm later. So if my dyno runs up to 8200 before I lifted, I can probably guess pretty accurately what it might be at 8500... not that far away. So I can make a little spreadsheet... and you know what I found out? Holding out to 8250 or 8500 with MY CAR'S PERSONAL POWER CURVE is only going to get me a SMALL amount of power compared to just shifting at 8000. In other words, I'm not going to push the mechanical limits and the fuel injector limits for what is going to work out to be a VERY small change in the overall peformance of my car.
So anyhow, I know this doesn't answer your question, but I hope it gives you some ideas of what you might think about when picking your redline. I'm sure I probably forgot something too, but forgive me, it's late and I'm tired
Brian
Originally Posted by diyman25
SO the point is,Stock 13B REW in normal condion (this incl the good oil pressure) you can Rev to 8K Rpm (if any one dont believe it. I got this info from Racing beat)
but is point less with stock port of street port specialy with turbo to drag you engine to red line. I really think If you want to rev pass 8K you should aleast have B port and this will more sense to me
but is point less with stock port of street port specialy with turbo to drag you engine to red line. I really think If you want to rev pass 8K you should aleast have B port and this will more sense to me
08-30-06, 11:10 PM
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Shaft flex is the main factor, it causes all of the other problems with clearences etc. At high rpm the shaft starts to bend like an S due too the mass of the rotors and counterweights. This causes bad things to happen like the rotors touching the housings, the shaft touching the bearing and spining them, eathing stat gears etc.
Too counteract this you use lighter rotors, as even minor weight reductions reduce the load on the shaft at high rpm by a huge ammount. You also run large clearences on the rotors and bearings to give them room when the shaft flexes. Guru motorsports makes an E-shaft with a center bearing to greatly reduce this flex, they reporedly have a 14,000 rpm race car using this shaft.
The next problem is apex seals, at high rpm the heavy steel seals have a tendecy to skip, causing chatter mark wear. Using ceramic or carbon seals is required.
These are the mechanical problems associated with high RPM and the rotary, the other problems like the fuel cut, and producing power up that high are just a matter of a standalone ecu and the proper porting(P-Port, J bridge, etc).
Too counteract this you use lighter rotors, as even minor weight reductions reduce the load on the shaft at high rpm by a huge ammount. You also run large clearences on the rotors and bearings to give them room when the shaft flexes. Guru motorsports makes an E-shaft with a center bearing to greatly reduce this flex, they reporedly have a 14,000 rpm race car using this shaft.
The next problem is apex seals, at high rpm the heavy steel seals have a tendecy to skip, causing chatter mark wear. Using ceramic or carbon seals is required.
These are the mechanical problems associated with high RPM and the rotary, the other problems like the fuel cut, and producing power up that high are just a matter of a standalone ecu and the proper porting(P-Port, J bridge, etc).
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