Fuel cutoff settings- Softer rev limiter?

[dreksnot]

disable ETC and try the fuel cut only...

I'm a little nervous about a fuel cut at WOT and a load on the car....

[10_SS]

i was too... play with it down low... i never get any knock when all this is going on.... who knows if its really knocking but none ever shows up on the scanner.

Now i just hang at 6000rpm while the car picks up speed, fuel cut almost sounds like msd limiter but not quite.

im slowly upping it to 6400, just dont want to overrev

[dreksnot]

Ok, played with it a bit. Not as smooth as the ETC cut, but RPMs hang nice and tight with the Fuel Cut, and boost remains high.

So, here's the $25,000 question - is this safe to do? Anyone heard of someone blowing a motor because of this? I've just seen many opinions on this, but nothing to back up the blown motor happening.

[10_SS]

The internet says it's fine, in theory it is fine, OEM's do it. But I just feel like it's wrong because I've never done it before. I passed a mustang on the limiter (wheelspin) the other day. I wonder what he thought of the racket.

[gmtech16450yz]

Yay! I'm so happy you guys are getting something out of this idea and expanding the knowledge of this further.

10_SS, yeah that's exactly what I did a couple times, it hit the limiter in 2nd gear and I just let it stay there for a little bit until the vehicle speed got up a little higher and the wheel speed lowered. Not sure if that's the most efficient or fastest approach, but it's good to have that ability if you can't grab the next gear right away for some reason.

As far as the safety of fuel cut only, like Chris mentioned, it's simply pumping air through the engine because there's no combustion happening. So it being "lean" isn't really a problem. But just pumping air through a few cylinders doesn't do much for cooling since there's no fuel going through. I guess it's still far "cooler" than actual combustion though.

What I don't like is the boost tends to climb quite a bit above normal when it's on the limiter and you only have fuel cut. Again, if you were in a race or track situation, that would be ideal to keep the boost high or even higher. I'm not so sure that's a good idea for a daily driver though. I still think having throttle cut in there lowering boost and overall load is probably a good thing. But like has been mentioned, the OEM's do fuel cut only on a lot of applications. Which is why I really wanted to see a log from an LS9 with the stock limiter settings. I want to see what it looks like during PTM or rev limiter situations. Anyone reading this have access to an LS9?

[dreksnot]

Thanks to both you guys!

Because turbos.... no boost climb with Fuel Cut.

Still need to mess with the Torque numbers in the delta table to smooth things out.

[NJ_Phil]

I use launch control and real close to fully automated launches with tunable rear tire slip but getting tripped up by RPM/torque bounce sitting at launch RPM waiting for the light. Hopefully this stuff can tighten that up. Goal is automation controlling tire slip regardless of boost/track/tire conditions. Thanks

[10_SS]

Im not really getting any boost increase when fuel cut happens either... Whipple 2.9L.

Where are the launch control settings? Are you referring to the built in Traction Control launch control? I thought that also used the brakes? No?

[07GTS]

ill be trying some limiter settings over the next few weeks, after my new exhaust i must of gained some hp and my limiter now using ETC only cant hang onto it, usually sits about 6800 but now peaked just over 7000 and i dont want that, ill try fuel cut also and the changed torque settings see what it likes for control, is it worth changing the "acceleration based" "accel thresh" table..? ive seen that used quite differently in some tunes

[10_SS]

ill be trying some limiter settings over the next few weeks, after my new exhaust i must of gained some hp and my limiter now using ETC only cant hang onto it, usually sits about 6800 but now peaked just over 7000 and i dont want that, ill try fuel cut also and the changed torque settings see what it likes for control, is it worth changing the "acceleration based" "accel thresh" table..? ive seen that used quite differently in some tunes

sometimes I do notice the cut kicks in earlier to anticipate the RPM limit... other times not. Hard to say. I to get 200-300rpm over limit,, so if I set 6200rpm and I have bad wheelspin then I hit 6400-6500 and I dont like that. If I come up on the limiter slower, then it's fine.

[NJ_Phil]

Im not really getting any boost increase when fuel cut happens either... Whipple 2.9L.

Where are the launch control settings? Are you referring to the built in Traction Control launch control? I thought that also used the brakes? No?

There are no launch setting in HPT, I wish... Using competitive mode where RPM is limited to 4,000, ECM limits tire slip, but how much slip can be hacked with VSS settings. This way I can vary boost @ launch and other parameters and let the ECM pedal the car if it breaks loose....That all works good but I'm having the same problem staging at 4,000 RPM these guys are having with the limiter and hope it's the same fix.

[s57_s2k]

for me I have tried lingenfelter 2 step and I like it. it is set at 6900 rpm sounds Little different than stock limiter somehow smother and faster the car is 2004 gto.

[Iam Broke]

Worked with John's (GMT's) settings today on my pig of an LS3, hit the limiter by chance at the top of second and had 3 oscillations in the half second it took my old foot to get out of it. Throttle is just starting to close at the marker. Oscillations just after the index line in the screencap below.



Took a little milder approach around limiter threshold to see if it helps the ringing some. At any rate, it's loads better than the fall on the face limit I used to have. I think it took so long for me to get out of it because at first I didn't realize I was there.

Thanks John for all the posts and help over the years. I got the DSteck flexfuel sensor kit installed (pin 40 was a bugger) and seeing if I can get to 60% before the fuel pressure suffers. If not, E47 it'll be for this year. P.S. Still working on the fuel trims.

[10_SS]

Is there any way to disable Stability Control but leave the Traction Control active? Mine seems to work really good at limiting most or all RPM's but if I get sideways a bit then Stability kicks in and messes crap up pretty bad.

[LeForce]

I'm reviving this great thread as I'm still trying to figure how to set my cutoff (LS9/manual) to be best suited for drifting. The key as per this thread as I understood it, is adjusting both tables 12070 & 12073, & particularly limiting torque upon RPM drops. But what is the best cut off method or combination of methods to accompany this adjustment, spark, fuel, ETC?
I'm posting a screen shot of my settings & I'd appreciate any advice.