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It seems that people are confusing the rev limit and redline. The other thing I see is some people say we have a ignition cut revlimiter and others say we have a fuel cut revlimiter.
What is needed is the definition of the three (redline, ignition cut revlimiter, and fuel cut revlimiter).
1. Redline - The maximum recommended revolutions per minute (RPM) for an engine
2. Ignition Cut Rev Limiter- ignition and switching it back on at a predetermined rpm. Say rev limit 3000 once reached the ignition is cut until the rpms drop below say 2900 then igniton is turned back on on. One problem people have with this type especially the cattless is the back fires created because of the raw unburned fuel being dumped into the exhaust.
3. Fuel Cut Rev Limiter- This will limit your maximum RPM but cutting off fuel into the motor. There is a problem to this also the that it can cause a lean codition and detonation can occur. This type of rev limiter is extreamly more dangerous in FI (Forced Induction ie Turbo or Supercharged) engines.
Now on to the other problem It seems that People dont understand what type or revlimiter the rx8 has. This is another problem I would like to be cleared up. These are 2 different quotes from 2 differnt Threads. I'm not pointig fingers at who is wrong I just want everyone to be Informed correctly.
Originally Posted by NgoRX8
you'll hit fuel cutoff before you're in trouble.
Originally Posted by StealthTL
The rev limiter actually cuts ignition, if it cut gas it could create a lean/detonating mixture right at the rev limit - bad news!
S
I think we really need to clarify what is exactly in a RX8 rev limiting system and exactly how it works. Either it has a fuel cut, ignition cut, or both systems in place.
Now my 88 FC I know for a fact has no ignition cut revlimiter it uses fuel cut revlimiter. I do belive the same for the FD rx7 (IIRC).
As for the RX8 I have no idea what type it uses. My best educated guess would say its a Fuel Cut rev limiter do to previous experiance with RX vehicles.
So if some one could help enlighten the RX8 community about what type of Rev Limiting sytem the RX8 uses it would be very much apreciated not just by me but the existing forum members and new commers alike.
NEW INFO
Ok after searching and searching and some testing my self I have found that the RX8 does not have an ignition cut revlimiter. The RX8 uses a fuel cut revlimiter. After talking with Mazda and other rotary specialist I have learned the reason of why a Rotary engine from factory will have a fuel cut rev limiter. The reason for this because the Rotary engines combustion is never quite complete so unburned fuel will always go into the exhaust.
To much fuel in the exhaust causes high heat to build up in the catalytic cinverter and destroys it.
Mazda has realized that an ignition cut revlimiter would allow way to much fuel into the exhaust destroying the already high strained rotary specific cat.
This does pose a threat to the FI community as stated before but there are ways around this.
1. Use a aftermarket ecu with an ignition cut revlimiter.
2. Bee R 2 step rev limiter can be used but the problem is that you would need to raise the factory rev limit by at least 500 rpm and then have the ignition cut rev limit at the stock rpm and drop down 200rpm and would bounce between the 2 points. (this can only be done safely by using a ecu re-flasher)
3 Use some other form of ignition cotrol to set a rev limit.
(Mods feel free to edit title as I couldn't think of how to title this thread)
Last edited by RX-LR-8; 04-20-2008 at 08:39 PM.
Reason: New information found
I shift right at 9000 so I'm really shifting at 8500??!
Most of the time yes. I've watched the rpm needle hit 9k while my obdll data feeder says 8.Xk. But sometimes (not often) the tack will match the obdll.
<sigh> You said nothing to the newb about the 3 year old thread revival.
Not feeling well today?
I will add that the Series I tach's can be off by quite a bit.
When I'm doing a 4500 rpm cruise log, my Cobb AP reports 4500 rpm my Tach reads almost 5000 rpm ...
This gets even more noticable as the rpm's increase.
(Yes I have done 8500 rpm cruise logs)
My Tach reads almost 9500 rpms while the Cobb AP is reporting 8500
Just did some logs to try and determine how the factory rev. limiter works. I did this in my turbo 8 with 3psi spring in wastegate and used the warmup limiter set at 4300rpm to do the test.
Here's what I found :
1/ Air fuel ratio when you hit the limiter goes a little leaner but not as lean as it would if fuel was being cut.
2/ I was able to actually increase rpm after hitting the limiter ( at considerably reduced acceleration).
3/I saw nothing happening with the throttle (monitored every possible obd throttle and acc. pedal parameter)
4/Saw nothing crazy happening with ignition timing.
Blue line on the log is just before the rev cut is activated (4300rpm)
I was able to increase rpm/speed (albeit at a much reduced rate) after hitting the rev. cut which means whatever happens isn't either a total ignition or fuel cut.
The fact that AFR doesn't go super lean (and there is no indication of a fuel cut from the fuel pulse width parameter) means it can't be a fuel cut. At the afrs recorded the engine would still make plenty of power and accelerate the car normally if nothing else was happening.
possibilities :
Could there be an ignition cut on every 2nd or 3rd combustion event or even on 1 rotor ?
Could there be a fuel cut on every 2nd or 3rd combustion event ?
I'll have to data log my car, it seems to be able to power through the cold rev limiter but not the "real" rev limiter. I've ridden the "real" limiter a few times and it definitely just bounces +/- 50 RPM of the set rev limiter and goes really lean (I've seen as high as 1.4 or so lambda on logs). S2, so I wonder if it's different behavior than the S1.
I'll have to data log my car, it seems to be able to power through the cold rev limiter but not the "real" rev limiter. I've ridden the "real" limiter a few times and it definitely just bounces +/- 50 RPM of the set rev limiter and goes really lean (I've seen as high as 1.4 or so lambda on logs). S2, so I wonder if it's different behavior than the S1.
Or ....the behavior manifests itself differently at different rpms ?
If none of those move, perhaps it chokes the engine with the SSV/VDI/APV?
The ignition timing map might still be showing reasonable results for the load condition, but are the coils actually firing?
If none of those move, perhaps it chokes the engine with the SSV/VDI/APV?
The ignition timing map might still be showing reasonable results for the load condition, but are the coils actually firing?
VDI wouldn't do much and APV would be too slow acting ... but ssv would def have an effect .
Agreed re the coils.
I might have to do a log with the 'real' rev. cut at same rpm and see if there is any difference.
Ok ... so this is a log of my N/A with 'real' rev cut set at 4300. Note this show me holding throttle down well after cut was activated. See how rpms still increase after cut is hit (blue line) , then decrease at around 5000rpm back down to 4100ish then back up again.
* Afrs go very lean
*fuel pulse width on p1s follow normal path and seem unaffected by cut ...suggesting the cut is the other injectors .... not P1.
* Initial period after cut rpm feels/sounds like combustion is still taking place
*At 5000 it feels/sounds like ignition is cut as well ...
My feeling is that there is more going on than a simple fuel cut but.
This is probably off the subject.. But do you have to be a vendor on this site to post your RX8 for sale? I've been trying to figure it out for a few days now...
This is probably off the subject.. But do you have to be a vendor on this site to post your RX8 for sale? I've been trying to figure it out for a few days now...
possibilities :
Could there be an ignition cut on every 2nd or 3rd combustion event or even on 1 rotor ?
Could there be a fuel cut on every 2nd or 3rd combustion event ?
There is a " random fuel cut on vary faces of rotor/s".
There is " UNK" ( unknown) table on the ignition section in ecu which I believe it would randomly messes with timing in every case of pid.
Four stroke engine has 1 bang in two rev, where as rotary has 3 bangs in 1 rotor rev. ( 3 rotor rev = rev engine)
04-19-2008, 07:44 PM
rx8 redline and revlimit system
