rxspeed87

I've tried to find information on what all this is how it works what good/bad it can do but I can't find much information on it. the only reason I heard of it was due to rx8club.com

but can someone give some information as to why you woudl want to or even how you would setup a negative split?

J-Rat

iTrader: (2)

I cant imagine why anyone would want (what I assume to be) a negative split (trailing firing prior to leading?)

That would make no sense that I can come up with.

Icemark

maybe they wanted to blow the motor, since the trailings firing before the leadings pretty much distroys the apex seals

rxspeed87

when I was doing some searching it seems on the rx8 club (if I read that right) at idle they are running negative split. I also swear I have seen some even with boost running close to even split or negative split.


all I see though are people saying they are doing it but no real information as to why they are, what they are doing or what else is going on.

icemark how does it destroy the apex seals?

J-Rat

iTrader: (2)

Running a negative split would cause the trailings to fire before the leadings. This would cause pre-ignition. Pre-ignition = knock = poofed apex seals.

The only thing I have ever read on negative split is the rumor that people running the E6K have damaged thier motors by running 0 deg split. The rumor goes on to say that because the Haltech timing control is a bit "sloppy", the ECU actually induced negative split which damaged the engine.

*disclaimer* I have ABSOLUTELY NO firsthand experience on this its ALL RUMORS!

If you even could get negative split, I dont know the ECU that would allow you to do it.

CrackHeadMel

iTrader: (2)

i have a thread bookmarked on another computer with some reputable member running HUGE negative split under highvacume (IIRC upwarards of 30*) I printed out all 3 of the ignition maps that were posted (PFC maps iirc, has leading, trailing, and a 'split' map)

EDIT

im holding the maps right now, if i could get my damn scanner to work id post em

there is a thread around the single turbo or rotary performance sections with a thread on it


when i had my car running i started playing with neg split in vacume situations, my car still runs fine, however its apart now for a new turbo setup

J-Rat

iTrader: (2)

On what ECU? I find it hard to believe the car would idle correctly with the trailings firing 30 degrees PRIOR to the leadings.

Unless we have our terminology wrong.. I run about 20 or so degrees of split at idle, but thats normal split..

rxspeed87

I will see if I can find the threads I was referencing also either here or on rx8club

how would the negative split cause detonation. sorry I'm not trying to be an *** but I honestly have no idea as I just have my stock ecu doing stock timing on a mostly stock motor. it was just something that more or less caught my attention. thank you guys for the help so far though :d

RETed

There is a thread somewhere in the Single Turbo or Rotary Performance section.
I don't believe in it.

For some reason the FD guys go ga-ga over it.

The trailing was never designed to be the primary ignition trigger.
Look at the really tiny trailing spark plug hole, and you'll understand.
Most of that stuff is in the vacuum ranges anyways, which translate to very or little gains in power.


-Ted

rxspeed87

think I saw one in the archives and you where involved. as far as my car goes that is all I will ever see is vacuum anyway. my main reason to doing so would be more along the lines of fuel mileage if it would do anything. but then again I don't think I can change it on the stock ECU

kind of off topic though how much should I be able to grab a TII TMIC for? it would be around the right size for a small turbo for my accord.

RETed

Check it out...
https://www.rx7club.com/forum/showthread.php?t=443709


-Ted

coldfire

iTrader: (1)

yup, read through that thread i started before coming to any conclusions about negative split...
there are maps in that thread also.

to sum it up (for a turbo car):
- running in vacuum ONLY
- brings the combustion temperature up, advantages being faster spool once you get back into boost and apparently better fuel mileage. so it's not a power tuning mechanism (won't gain any power from it)


on non-turbos there has been some negative split usage, but this might be more relating to combustion efficiency (maybe due to the higher temperature). the stock RX-8 will run negative split around no-load/idle, presumably for emissions reasons.
someone in that thread had claimed better mileage from negative split on an FB...

there is more to it when tuning negative split then just having the trailing firing first. a lot of attention has to be paid to the actual advance i think...in any case, i don't think it should be messed around with to any large extent unless you have some serious tuning knowledge...

drago86

Negative split in vacume= good, leaner mixtures ignited, better gas mileage

Negative split at WOT/boost = bye bye motor