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2-Step Rev Limiters

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Gench Quote  Post ReplyReply Direct Link To This Post Posted: Apr/27/2022 at 1:58pm
Originally posted by WesternRed WesternRed wrote:

I've actually had the 2 step setup with my Sniper system for a little while, but haven't got a lot of runs on it yet.

I'm interested to know what others do in regards to using it and how you tune the system with EFI. I'm running it with the foot brake activation and seems like it takes a little while for the engine to recover after I release the brake. I feel using the 2 step is hurting 60' times a little bit.

I have been pressing the throttle until the 2 step starts to kick in and then going WOT when I launch it, haven't tried going WOT on the 2 step yet, maybe that will give better results.

Also wondering how to tune it as the AFR goes a little bit crazy while the car is misfiring on the 2 step, the system should be in open loop mode at this time, so not sure how to set this up.

Data log below for posterity, notice there is a little bit of a delay between hitting the throttle and the revs starting to pick up, this is almost instantaneous without the 2 step.
 

WesternRed

Foot to the floor, might fix your lean during 2 step?

I believe smoothing your timing map to flat within your limiter RPM will help. AFR looks fat at idle, not sure what fuel your running but with EFI I’d stay leaner at idle and lower RPM… fatten after RPM of limiter blip. 

Summary: no timing or fuel changes within the 300 rpm the limiter fluctuates within. Also, does the car run good in open loop? How much fuel compensation is happening?

Not an expert but a few ideas…
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Post Options Post Options   Thanks (0) Thanks(0)   Quote WesternRed Quote  Post ReplyReply Direct Link To This Post Posted: Apr/27/2022 at 8:02pm
Thanks for the input, you have raised some good points, it has highlighted that I need to spend a lot more time understanding this fuel injection stuff.

One of the problems with the 2 step is that if it's cutting spark, then you suddenly have unburnt fuel and more importantly the unused oxygen going down the exhaust, which will give you a lean spike on the o2 sensor, but you don't really know what is going on the cylinders when they are firing.   

This is a good launch without the 2 step in play, it's actually a PB for the car with a 60' time of 1.64 seconds. The run above with the 2 step was maybe 1.75, have to look up the actual run to confirm that. on this run below, it seems it's going lean just before launch and then rich immediately afterwards. it's also switching from closed loop to open loop and then back to closed loop again. I think I need to look at some of the other data and also see what the acceleration enrichment is doing. You have given me a lot more to think about, I need to find some bad runs now for comparison.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Gench Quote  Post ReplyReply Direct Link To This Post Posted: Apr/27/2022 at 9:23pm
WesternRed - tuning until closed loop map runs perfect sounds like the solution? Still recommend no timing changes during two step and cold/hot idle rpm range… removes surging IMO.

Good luck


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Post Options Post Options   Thanks (0) Thanks(0)   Quote WesternRed Quote  Post ReplyReply Direct Link To This Post Posted: Apr/28/2022 at 5:09am
Timing is pretty steady on the two step, basically RPM dependant, looks like it is all at 38 deg somewhere between 3500 and 4000, will have to look at what I have programmed in. Any thoughts on what it should be on the 2 step if I was to lock it down? Do I just set it up to go to max timing (38 deg) at a RPM lower than where the 2 step is set of put a heap of retard in to kill power there? Seem like some 2 steps work by retarding timing, while others drop spark, the Sniper seems to do the latter based on the charts, you can see the green spikes in the first chart that indicate 2 step activation, the timing doesn't change. 

The system uses timing to help maintain idle in addition to the idle air control, you can turn this off and just rely on the IAC circuit, but I find it idles smoother with the timing control on. There is really no idle showing in the first chart above, bottom chart is pretty steady at 900 RPM.

I think I do need to do some work on the base fuel map so there is less closed loop compensation required, then it should theoretically run perfectly in open loop control all the time. What you can do then is lock down the closed loop compensation limits. This is all stuff I know a little bit about but need to spend more time understanding properly. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Gench Quote  Post ReplyReply Direct Link To This Post Posted: Apr/28/2022 at 8:39am
Timing is the place to start IMO. Set start timing to 6 degrees or whatever the engine likes warm. Then jump straight to base timing that offers highest, most stable vacuum at idle RPM, mine was in the low 20’s I believe. Then I scale hard to 32 by 3k, 36 by 5k, then dribble the last two in out to redline. That’s what my motor liked but they are all unique. Mine has the old speed pro forged pistons that remove most quench, it’s also fairly low compression for the cam it has and the elevation I moved it to. I have a new motor ready to assemble and fix those issues.

Once you have timing based, let it tune the fuel for some decent miles. Then tweak the timing in areas to see if it adds fuel, if it does… just like the eye doctor, 1 or 2, selecting the option that draws more fuel. IAC is good for sure but make sure you do the lockout process to set the distributor and ensure timing doesn’t drift at higher RPM’s, and correct it if it does.

Not sure how the two step works, didn’t know it forced loop mode myself; that said, if they cut spark you’d go rich from the raw fuel flowed, no? I would do full throttle during two step, the ecu probably locks during two step saving your tps, introducing the delay because you really want full throttle but it releases to saved tps position first. Just a guess…
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Post Options Post Options   Thanks (0) Thanks(0)   Quote WesternRed Quote  Post ReplyReply Direct Link To This Post Posted: Apr/28/2022 at 5:03pm
Just looking at the last saved calibration, I have it cranking at 10 deg then idle at 15 deg up to 800 RPM, from there it ramps in (linear) to 38 degrees max at 3750 RPM. In addition to this there is up to 6 degrees vacuum advance available depending on the MAP pressure, obviously none at WOT.

Being a dedicated drag car, I'm at a bit of a disadvantage when it comes to driving around to let the system learn, it's basically full throttle up the strip and a gentle cruise back down the return road, that said, general road manners are not the least bit of a priority for me.

I'll definitely try some WOT launches on the 2 step nest time I'm at the track, hopefully that will be next week. I really need to get into the habit of looking at the data logs after each run at the track and making adjustments as I go. At the moment I tend to review them when I get home. I think the car runs pretty well for what it is, upper 11 second range and most changes I make don't seem to make a measurable difference to performance. 

The whole idea for the 2 step was to improve 60' consistency, which it sort of does, but I think it is costing me maybe a tenth off the line. If I stick the incrementals into the Wallace calculator, they all seem to line up, so it's not likely to see a big improvement without some engine upgrades of maybe a different convertor.

Regards the effect of misfiring on AFR, remember you are measuring the presence of oxygen in the exhaust gas, not the presence of unburnt fuel, so if you have a misfire, you don't use up all of the available oxygen burning the fuel, which the system interprets as a lean condition. The system is smart enough to know this will happen when the 2 step activates, so it will go into open loop control and just use the base fuel settings without applying any closed loop correction. 

What I probably need to do now is to use the data logs to better tune the base table for those points where it is funning in open loop mode.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Gench Quote  Post ReplyReply Direct Link To This Post Posted: Apr/28/2022 at 7:46pm
Understood now on lean during two step… didn’t read up on the O2 sensor… but the O should have been my sign.

Didn’t realize it’s not a street car. Sounds like some power braking in the driveway in the two step RPM range should help you tune that area to low/no fuel compensation, then smooth it out both ways and maybe fix other areas? Sounds like you only need those few hundred RPM. Don’t recall which direction, believe lean, but read it’s slower to calculate compensation of tune is real lean and relies on compensation… always a hair fat vs lean was my take away… accurate?? No idea

Good luck. Feel free to message me logs if you want another view point as you adjust, think you’ll get it quick.


Edited by Gench - Apr/28/2022 at 7:48pm
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