falcongsr

i can control a relay from the AEM ems and cut off the spark or cut off the fuel (ground signal that goes to each one) and set up overboost cut.

what would be best? the stock ecu does fuel cut for rev limiter. i am thinking of just doing fuel cut.

any opinions? just spark cut would make a big boom when spark returns and all that fuel is ignited in the exhaust.

ImAcracker

Could you send it to both?

falcongsr

yes, i could. what would it hurt to leave the spark active though?

dmotoguy

would it make it run really lean for a second?

ekb18c

What I like to to generally, to protect from overboost, is to create a "wall of fuel".

speedworks

if you fuel cut it will run lean and detonate, i would recomend spark cut.

ekb18c

You can add a ton of fuel to the overboost area on the map("wall of fuel").

So lets say at 14psi is the max you want to run. At 15psi and up you dump mad fuel @ let's say 6-9000rpm. You should never reach that area of the map unless you overboost.

Get what I'm saying?


[Modified by ekb18c, 8:02 PM 1/29/2003]

MikeMAN

i third that

Sonny

Good idea.

Sonny

BoM

very cool. when im ready, we can do that too.

turbotypeR@SPEC

here is something i got from racelogic.they make the traction control for formula one as well as a very good system for our cars.it explains very well how fuel cut works.after reading this you should see that fuel cut is actually fine.after all, almost all manufacturers use fuel cut.if it were so bad don't you think they would use spark cut.

"The idea of cutting fuel to an engine sets alarm bells ringing in engine builders, as they all know of the potential disaster of a high revving race engine running lean. Running in a lean combustion mode will elevate in-cylinder temperatures very rapidly, the denser the air/fuel charge, the more heat the lean burn can generate. Therefore it is vital that a fuel cut system will not cause a lean burn.

The simplest way of preventing a lean burn is to remove more than 50% of the fuel from the pulsed delivery. A mixture will only ignite if the air/fuel ratio is within a tightly defined window, look at the efforts being put into making lean burn engines fire on very low air/fuel ratios (1:20 or more). Removing more than 50% of the fuel will cause an air fuel ratio of over 1:25 and will result in a complete miss-fire, with the unburned fuel passing out through the exhaust valve. Even if a high air/fuel ratio did manage to ignite, the energy available from the amount of petrol injected wouldn't be enough to elevate temperatures significantly. Of course the ideal system will remove 100% of the pulsed fuel delivery, allowing the cylinder to take a gulp of fresh air, and the in-cylinder temperature would remain virtually unaffected.

Prolonged fuel cut on one particular cylinder would cause scavenging of the petrol lining the inlet tracts, and when the next full fuel pulse arrived, it would be partially reduced in quantity by the re-wetting of these tracts. Therefore it is often important to manage a rotation of the cylinder cutting to prevent this situation from occurring.

Spark cut
Cutting the spark to an engine will stop any chances of a weak mixture occurring, but it carries it's own potential problems due to a large quantity of unburned fuel travelling through the cylinder and out of the exhaust. This petrol can remove some of the oil lining the inside of the cylinder, and pass it thorough the exhaust, again this only becomes a problem if the fuel to one particular cylinder is cut for an extended time. The best way to overcome this is to rotate the order in which the cylinders are cut.

The unburned fuel in the exhaust will have a catastrophic affect if there is a catalytic converter in the exhaust, as it will try to convert the unburned fuel to harmless elements, effectively burning the mixture. This causes the catalytic converter to heat up very rapidly, reaching temperatures in excess of 1000°C, and possibly melting down completely."

Ltech

The above post make sense. I don't see why we would have to cut sparks. If you don;t have fuel it won't fire simple is that.


[Modified by Ltech, 7:42 PM 1/29/2003]

falcongsr

with all the discussion in the thread here, do you think i have a chance of running lean where i'd detonate if the injector never opens?

i guess the real issue is that when the fuel cut engages, the injector will likely be open (high duty cycle in boost), so i will have one combustion cycle with less then enough fuel, since i cut the injector closed while it was injecting fuel, which will cause a bad lean condition at high boost.

ideally if you could get the injector to NOT fire at all, then you'd have almost 100% air, and then the spark would fire and nothing would happen, right??? or is there trace amounts of fuel left in the chamber from the last go-around and it will ping anyway? i want to know if the "ideal" solution is for the ECU to not open the injector, or if it will still go lean and ping. or if you made the injector not open at all it would be ok to fire the spark plug with 100% air and no fuel injected?

Thanks,
Joe

aka falc0n

edit - the wall of fuel sounds good as long as its not something like a complete WG failure - i think the boost would still rocket up on my 18g turbo - briefly at least. how rich are you guys talking? 10, 9, 8:1?

falcongsr

ttt

dmotoguy

im also interseted in the wall of fuel, on exactly how rich you would aim for.. i dont have any tuning experience yet, but will be learning how to tune a basically stock rx-7 in the next few weeks with the Apex-i power FC, so i am trying to learn as much as possible.. if anyone is knowledgable with the power fc, feel free to im me with tips!!

VaporTrail

I can see where you are going with this, but that would work if you had injectors that are larger than needed. Most of us don't have this when racing, we're usually running in the range of 90% duty so there isn't much room for error. I prefer fuel cut for over boost, spark cut for rev limit.