Jimmy325i

I know in the time I've been around here there have been numerous threads talking about rev limiters and why they don't need to be raised and what not... I don't care what you all think about the reasoning. (being honest here) I am in a situation where my engine will breath and make power beyond stock so I NEED to get rid of the limiter in the ECU.

I just got off the phone with Kevin Landers and he says the S4 ECU from what he's heard is reprogrammable to eliminate the rev limit. How is this done using conventional aftermarket diagnostic scanners and code modifying software? My buddy is in a tech program learning the ins and outs of ECU's, but the instructors are not familiar with the rotary engine management to be able to point these things out to him. Finding the information has been less than obvious as well, so now I'm asking for help.

Is this done through an E-prom and needs to be removed from the board then re-burned, or can this be done while the car is in a diagnostics loop? Any assistance would be greatly appreciated.

Icemark

this a T2???

S4 NAs don't have rev limiters, your more limited on what the stock flywheel can do before it shatters.

or do you mean the over rev buzzer???

Jimmy325i

lol Over rev buzzer was unsoldered from my dash months ago. Stock flywheel will stay in one piece long after the rotors collide with the side housings at 10.5K

Well, something is causing me to top out at between 8200 -8400rpms based on ambient temps. I was sure it wasn't spark cut before, but now I'm questioning it.

The other possibility is that the max duty cycle is being reached on the injectors and I'm simply flatlining their flow at the stock rail pressure. Changing the max duty cycle allowable by the ECU would also be very good information if that is also modifiable.

This is a heavily ported n/a.

It feels like a lean misfire when you run out of revs. She pulls hard all the way till she craps out. The car is in my buddies hands at the moment. We'll see what he comes up with tomorrow on the scope. I'd mess around with the fuel pressure but it runs so good other than having the top end lower than I built it for. (I wanna try to see 10K)

inboost

Just to be clear, the duty cycle is the time the injector is on divided by the available time between cycles. For example:

10,000RPM / 60 = 166.67 Rev per second

1/166.67 = 0.006 seconds per rev = 6 miliseconds

If your injector is on for 5 miliseconds at 10,000RPM then you divide this by the 6 miliseconds available ( if this was a piston engine we'd have twice as long because they inject once in 720 degrees while we inject once every 360).

100 * (5/6) = 83.3% Duty Cycle

The industry standard for duty cycle is no more than 85% for reliability and 'overhead' seen on colder days, lower alititudes, and other 'richer' trims appplied to the base tuning. Most injection systems will also prevent you from doing much more than this.

The bad news is that you can't change duty cycle...

The good news is that if you put twice the injector on the engine you only need half the time to deliver the same amount of fuel. That's why we have four injectors on our rotary engines!

So what you will really need to do here is get something that can tweak your injector's milisecond on-time at these higher RPM's. You might just run out of duty-cycle which means you'll then need bigger injectors.

On my bone stock S5 T2 I see about 7.7mSec on all four injectors at 6000RPM and 6 psi boost. This is about 77% duty cycle.

The big joke here is that my motec PLM shows that Mazda is delivering 10.8 to 1 A/F (0.73 lambda) at this moment in time. This is insanely rich! Probably to make sure that some idiot towing jet ski's up the Cajon pass in the dead of summer with his foot planted doesn't tank the engine.

Jimmy325i

A site I was looking at the other day said that most stock ecu's limit the duty cycle to <65% which would indeed necessitate larger injectors to flow the needed fuel. (if this cannot be overwritten) I'm more interrested in tweaking what I have if I can, being that I have access to the equipment (and people) to do it. If we do discover that the fuel injectors are maxing their flow rates at the stock psi. I will be investing in larger secondaries and tuning them with the s-afc.

I want to get this engine runing to the 10K mark before I dyno it. I don't need to be spending extra cash on consecutive dyno sessions to "see if this did the trick."

Tuners in my area are worthless when it comes to the rotary and all they're really good for is finding the best a/f ratio's and what ignition advance is best for the fuel you're running. Diagnostics better be left to someone more capable.

I just hope to learn something useful tomorrow from the cars visit to school.

NZConvertible

If those instructors can play with piston engine ECU's, they shouldn't have any trouble with rotary ones. EFI is EFI no matter what engine it's on. The basic operation is identical; injectors, ignitors, sensors, etc. It's just the timing of certain events that's different. I don't know who told you that, but I've seen stock cast iron flywheels let go at a lot less that 10,000rpm, and it's not a pretty picture. A steel flywheel is a lot cheaper than a new motor, gearbox, clutch, flywheel, bonnet, wiring loom, brake lines, etc, etc... ECU's don't have work on duty cycles, they calculate pulsewidths. It's quite possible (but highly inadvisable) to run up to 100% duty cycle if the ECU calculates a pulsewidth equal or greater than the time for a single engine revolution. 80-85% is the sensible limit, because after that the opening and closing time of the injector becomes a factor and the pintle can actually float instead of completely closing, sending accuracy out the window.
If you really think this is a duty cycle issue, buy/beg/borrow a DMM that can measure duty cycle and hook it up to an injector wire the ECU. Above 3800rpm all four injectors fire together with the same pulsewidth, so it doesn't matter which one you connect to. Let us know what you find.

Icemark

Actually the stock manual S4 NA wheel is only good for about 8500... Much past that and it becomes a grenade.

Now an lighter manual S5 wheel should be able to go to 9.5-10K

Jimmy325i

Like I said, right now its out of my hands. The instructors are pretty **** about keeping outsiders out of the classroom at my buddys school. Fortunately he's also a rotary guy, so I'm not so worried about them playing with my car.

Sorry if my terminology is off in trying to explain my thoughts on this stuff. This is my first time messing with the engine management of a car. I've had it easy in the past being able to simply upgrade ECU's, get a chip, swap weights in a distributor, or change jets in a carb.

When I say duty cycle being an issue, I guess I mean that the pulswidth is limited in the ECU to prevent exceeding the preset max duty cycle. Everyone disses mazda engineers all the time around here for a reason. If they'd explain more of what they did and exactly how it works in the FSM (or at least somewhere on the damn net) I wouldn't have this problem right now.

Anyone that has a spare haltech or motech taking up valuble storage space, or needs a last minute tax deduction, can give it to me whenever they want. I'll get that thing out of your way.

annuerysm

all this talk of flywheel grenades makes me want a scatter shield, you guys know any good places to get one?

Rotorific

iTrader: (1)

Thats bullshit whoever says there isnt a revlimiter or fuel cut on an NA cause i bounce off that junk every day at 8100 rpms. (APEXi tachometer) -Gabe

Jimmy325i

I'll actually be making them here shortly out of Ti. (if they'll be approved by santioning bodies at the thickness I want to use)

A friends parents have a metal stamping business that can get the materials cheap, and then we can simply punch them out and bend them up and away they go.

For the problem at hand....

Just got off the phone with my buddy.

I'm really not impressed with his school right now. They have a perfect learning opportunity and refuse to utilize it because it doesn't follow their curriculum. He's learing engine management (courses he's taking now) and they won't let him put the car on the scope! He hooked it up to the Snap-on engine scanner and discovered that my alternator is a bit weak, (no ****!) and that was the only thing he could find out that my guages didn't already tell him.

They have the scope but don't want to put the car on it yet. ARGGGGGGGGHHHHHHHHH ******* public education!!! (state tech college) He's already told them he wants to become rotary certified or whatever and work for mazda... I want to beat their heads in with an e-shaft!

On a funnier note. The rotary produces so much exhaust pressure that the 4" vent tube wouldn't stay on the tip. He had to stuff it inside my 4.5" tip as it was and it kept blowing out.

I also learned that they have an old analogue dyno, nothing to write home about. He won't have access to it untill fall either.

Whats the factory pulswidth for the 460's @8200? I'm going to start reverse engineering the damn thing and find my solution through better understanding of the current setup.

Jimmy325i

The car is back home and nothing has changed.

Roger, (renns) Got any input here as to the factory top end fuel mapping?

rotary>piston

why do you want to rev so high? Do you like rebuilding your engine all the time?

Jimmy325i

I like wining races, and if I can get another 15mph out of first and 20 out of second it'll be pretty hard to beat me out of the hole.

High revs in rotaries are less traumatic on the innards than you might think. The rotors are spining at 1/3 the speed of the e-shaft. So when I hit 10K the rotors are still only moving at 3,333rpm. (although thats moving pretty good considering the power they'll be making up there)

I still have no idea when my powerband will stop. Maybe the flow will choke at 9.2K. I'd like to be able to find that out before I make any more engines with the same porting. This is a great motor and I love it to death, but the ECU is really pissing me off right now.

dr0x

You can ignore it using a hks fcon.

Icemark

You have something wrong with your car... I have taken plenty of S4 NAs up to 8500 without any issues (other than the torque and HP curve drops pretty noticeably at above 8000).

But that drop off is more related to the intake design and stock porting not holding up, like the S5 one with the VDI does, instead of a rev-limiter in the ECU.

Jimmy325i

Icemark, Mine use to hit 7900 and crap out. (stock) and Pauls never did. Mines an early 86 and his is a later 86 production version. I'll be ganking his ecu when it warms up (his motor is fried) and trying that. I stole a little add on circuit from his car before when I was hitting the rev limit and that seemed to work.

I've always doubted the rev limiter being the problem, but was thinking about it from what kevin had spoken to me about on the phone when I started this thread.

I have major reservations that it is the problem because of the 200+ rpm variation in my highest rpm based on ambient temperature. When its warm out and the air is less dense I can hit 8400 and change. Now that it's -5 outside it wont break into 8300rpm. This is precisely why I think its fuel delivery. I was simply wrong in thinking the fuel pump was the culpret.

Jimmy325i

Two 550's will be here next week. I'll keep you guys posted.