Strategy for tuning idle for large engines

Tuning concepts, methods, tips etc.

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JAM
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Strategy for tuning idle for large engines

Post by JAM »

Looking for some general feedback on tuning large engines for idle

For those who have done this you know how a big cam and CID this can be be a bit tricky- I do not have much experience in this so i would like to learn about others experiences, this seems more challenging than the other cars i have tuned

Engines over 11 Liters, long duration and overlap cams etc- The engine will target idle at 1400 rpm - speed density

getting it started and running is no problem bringing up rpm 2k rpm and runs ok, the hard part is that with the short header and the o2 in collector i really don't get much of an AFR reading until higher in the rpm. So when bringing the idle down i get a bit lost as to if it is rich or lean. Even at 1400 rpm this will never have an super stable idle, it just wont- we have run this on mechanical injection before. it will always hunt just a little and being that it has large throttle body it has large tip in so keeping it stable enough to get a handle on the fueling has proven to be tricky.

I am sure many of you have dealt with similar things, wondering your strategy to get a handle on the idle without an o2 sensor and with the engine swinging all over the fuel map.

i was considering things like my cell grouping around idle, maybe that should have a little larger cell space after my target idle cell etc. It seems like there are some tricks i am missing
Matt Cramer
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Re: Strategy for tuning idle for large engines

Post by Matt Cramer »

Large engines are a bit easier to tune than small engines in one way - the friction load (which is pretty much constant) is much bigger than accessory loads (which are highly variable). The biggest challenge here is the large cam. I've found in that case the best option is to ignore the O2 readings completely and tune the fuel table to pull the most vacuum possible.
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JAM
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Re: Strategy for tuning idle for large engines

Post by JAM »

Matt Cramer wrote:Large engines are a bit easier to tune than small engines in one way - the friction load (which is pretty much constant) is much bigger than accessory loads (which are highly variable). The biggest challenge here is the large cam. I've found in that case the best option is to ignore the O2 readings completely and tune the fuel table to pull the most vacuum possible.
thanks Matt,
that was my plan to tune fuel to pull most vac, but i am struggling getting things stable enough down low to get the portion of the map that it is supposed to idle in tuned in. Do you take a different approach to the cell spacing?

being this is a race only application with about 28 deg of timing max, how would you deal with the timing at idle?
Rick Finsta
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Re: Strategy for tuning idle for large engines

Post by Rick Finsta »

IMHO, adjust fuel for max vacuum, then repeat with timing. Then go back and check the fuel again. Repeat until you don't see better vacuum at idle.
subwoofer
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Re: Strategy for tuning idle for large engines

Post by subwoofer »

That way, just set fuel for 13:1, because that is where it will need the least air.
If you need to pass emissions, set for 14.7:1 and work injector timing and spark for a stable result.
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Yves
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Re: Strategy for tuning idle for large engines

Post by Yves »

subwoofer wrote:That way, just set fuel for 13:1, because that is where it will need the least air.
If you need to pass emissions, set for 14.7:1 and work injector timing and spark for a stable result.
Just curious how do you work injector timing for a stable result ? I suppose you're talking about MS3 ?
JAM
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Re: Strategy for tuning idle for large engines

Post by JAM »

subwoofer wrote:That way, just set fuel for 13:1, because that is where it will need the least air.
If you need to pass emissions, set for 14.7:1 and work injector timing and spark for a stable result.
there will be no need to pass emissions -
this will probably idle at around 12:1 but i will likely never know what it is really at....
JAM wrote:the hard part is that with the short header and the o2 in collector i really don't get much of an AFR reading until higher in the rpm
kaeman
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Re: Strategy for tuning idle for large engines

Post by kaeman »

why is the short header a problem for o2 readings, manufacturers are putting sensors in the cast manifolds right at the head. also if you want the o2 corrections to help at idle, then make sure you are allowing it to read the sensor at the idle rpm. If you do the tune for what the engine wants not some specific ideal afr... you should be able to get a good idle on the large engines with large camshafts.
tune it like you would a carb in the idle sector of the ve table... if the engine wants more fuel give it more, if it wants less give it less. make sure your timing isn't to advanced for easy start and idle. I have seen engines that like to idle at 8bdc timing and others that liked 20 bdc. sometimes the old school tuning even applies to efi.....
Good luck.
64 el camino, 383 SBC, 11.7 to1 CR, accufab tb/rhs intake, 44lb injectors, trick flow heads, xr292r solid roller cam, belt drive camshaft, dry sump oil system, 2400 stall, turbo 350, spooled 9 inch, strange axles, 3.89 gears, dual wideband, full sequential fuel/cop, MS3x using 1.4.1 code.
JAM
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Re: Strategy for tuning idle for large engines

Post by JAM »

kaeman wrote:why is the short header a problem for o2 readings, manufacturers are putting sensors in the cast manifolds right at the head.
What manufacturers are putting o2 sensors into a 11-12L engine with tube headers [2 3/8" (60mm) primary and 4"(100mm) collector] with the o2 sensors a few inches from atm/ open header? Please post info i would like to check it out. in my experience the o2 sensors near the edge of collectors can be problematic short or long at low rpm with big cams

Sounds like you have some knowledge in this, it would be great if you could outline your strategy in detail for the following scenario:

engine target idle is 14-1500 rpm
first start up - have to keep it at 2-2500 rpm to have stable running
when you try and back it down and it wants to hunt real bad
you really dont know what the afr was at 2000 rpm and not sure if it really wants more fuel or not
adding fuel doesn't seem to help and taking any away seems to want to kill the engine
dll67
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Re: Strategy for tuning idle for large engines

Post by dll67 »

Was some of this topic lost?
671 to 732 Cubic Inches ... yeah .. Go big or go home ...
Sounds like a very interesting tuning scenario.
MS3PU/IOx/CAN-EGT/DBWx2 540ci BBC 325cc int runners (2)innovate LC2 wbo2's, Hilborn ITB injector cnvrtd to EFI, 55LB Inj, d585 coil near plg, 60-2 trg whl & cam ph snsr, Muncie 4spd w/10T VSS, Tilton 7.25" cerametalic cltch 8.5LB flywhl
JAM
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Re: Strategy for tuning idle for large engines

Post by JAM »

Learned a bit about this and got it sorted out on the engine I was tuning. Short pulse widths can be a challenge on some injectors, specifically some certain low Z injectors.
dll67
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Re: Strategy for tuning idle for large engines

Post by dll67 »

Did you have to get into ego delay and injector timing? Mine is sensitive to both with a over sized throttle body and a lot of valve overlap running 8 72lb injectors full sequential injection.
MS3PU/IOx/CAN-EGT/DBWx2 540ci BBC 325cc int runners (2)innovate LC2 wbo2's, Hilborn ITB injector cnvrtd to EFI, 55LB Inj, d585 coil near plg, 60-2 trg whl & cam ph snsr, Muncie 4spd w/10T VSS, Tilton 7.25" cerametalic cltch 8.5LB flywhl
JAM
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Re: Strategy for tuning idle for large engines

Post by JAM »

This particular engine is running 160# injectors, never did get an o2 sensor to read at the collector so put 1 in each primary - 8 total with 8 egts. Pretty much threw out the idea of any closed loop control until about 4000 rpm. The collector is short and large diameter. On the dyno it never did pick up reading at the collector even at 8000 rpm.
dll67
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Re: Strategy for tuning idle for large engines

Post by dll67 »

From your previous posts it sounded like open collectors .. Wouldn't take much fresh reversion air to screw up readings .. Even raw fuel from valve overlap causes o2 sensors to read lean.
8 - 160# injectors? What were idle pulse widths?
Edit ...
Do you have a data log showing egt's through the range of map/rpm?
I'm having trouble deciding what egt temp to tune to. My egt sensors are mounted externally to headers, ceramic coated inside and out, exactly 2"from the ports. I'm sure the coating causes then to read low .. Adding more difficulty too picking a temp to tune to.
MS3PU/IOx/CAN-EGT/DBWx2 540ci BBC 325cc int runners (2)innovate LC2 wbo2's, Hilborn ITB injector cnvrtd to EFI, 55LB Inj, d585 coil near plg, 60-2 trg whl & cam ph snsr, Muncie 4spd w/10T VSS, Tilton 7.25" cerametalic cltch 8.5LB flywhl
kaeman
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Re: Strategy for tuning idle for large engines

Post by kaeman »

Sorry about the late response, I was thinking that you had a short piece of exhaust behind the header, so that you would have some chance of getting a reading from your o2 sensor. My egt runs between 650 and 750 degrees F. when idle is about 750 rpm, when fully warmed up my temps can get to 800 on a hot day at idle speeds. but my temp probes are in the collector. I have been running about 8 degrees timing at idle, and have now moved that up to about 16 degrees advanced, I changed over to wasted cop and semi sequi. from batch and fixed mechanical advance distributor. I have noticed that I am pulling fuel out of the ve table and my idle is now around 850 rpm. with the big cubes and large cam, what does your map signal look like and what is you idle injector pulsewidth in ms. I am assuming that you have very large intake runners and therefore have a low velocity air flow in the runners at idle speeds. Have you tried to change the injector timing at the idle speeds to see if that made any improvement to the stability.
64 el camino, 383 SBC, 11.7 to1 CR, accufab tb/rhs intake, 44lb injectors, trick flow heads, xr292r solid roller cam, belt drive camshaft, dry sump oil system, 2400 stall, turbo 350, spooled 9 inch, strange axles, 3.89 gears, dual wideband, full sequential fuel/cop, MS3x using 1.4.1 code.
dll67
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Re: Strategy for tuning idle for large engines

Post by dll67 »

kaeman wrote:Sorry about the late response, I was thinking that you had a short piece of exhaust behind the header, so that you would have some chance of getting a reading from your o2 sensor. My egt runs between 650 and 750 degrees F. when idle is about 750 rpm, when fully warmed up my temps can get to 800 on a hot day at idle speeds. but my temp probes are in the collector. I have been running about 8 degrees timing at idle, and have now moved that up to about 16 degrees advanced, I changed over to wasted cop and semi sequi. from batch and fixed mechanical advance distributor. I have noticed that I am pulling fuel out of the ve table and my idle is now around 850 rpm. with the big cubes and large cam, what does your map signal look like and what is you idle injector pulsewidth in ms. I am assuming that you have very large intake runners and therefore have a low velocity air flow in the runners at idle speeds. Have you tried to change the injector timing at the idle speeds to see if that made any improvement to the stability.
Heres a screen shot idling from last data log
2015-07-20_16.05.53msl.jpg
kaeman wrote:"I was thinking that you had a short piece of exhaust behind the header, so that you would have some chance of getting a reading from your o2 sensor"
Your thinking of "JAM", he had the open headers with the o2 sensor near the collector. I had commented a few posts back
dll67 wrote:From your previous posts it sounded like open collectors .. Wouldn't take much fresh reversion air to screw up readings .. Even raw fuel from valve overlap causes o2 sensors to read lean.
kaeman wrote:My egt runs between 650 and 750 degrees F. when idle is about 750 rpm, when fully warmed up my temps can get to 800 on a hot day at idle speeds. but my temp probes are in the collector.
My EGT sensors arent data logged, I have 2 handheld, 4 channel EGT meters that I use to monitor the 8 EGT sensors in the cylinders and the 2 in the collectors. So I am working from memory here .. Half of the cylinders run close to 400 degrees, a couple more close to 300 degrees and 2 more under 300 degrees. This is measured on the outside of the ceramic coated primary tubes 2" from the head. The 2 in the collectors, I remember the temps corresponded with the lean and rich AFR's, cylinder bank to cylinder bank in tunerstudio. It seems like one was low 800 degrees the other was close enough to 900 degrees to call it that.
kaeman wrote: I have been running about 8 degrees timing at idle, and have now moved that up to about 16 degrees advanced, I changed over to wasted cop and semi sequi. from batch and fixed mechanical advance distributor.

Here's a screen shot of my ignition table
ignition table.jpg
I have been running 19 degrees idling, if the rpm drops to far while letting the clutch out while starting out it pulls a couple more degrees. For engine starting is fixed at 5 degrees till it fires.
kaeman wrote:I have noticed that I am pulling fuel out of the ve table and my idle is now around 850 rpm.
I use the "idle ve settings" it enables a seperate idle ve map, in my case, below 1200 rpm, which is a little high when its decides to idle at 800-900 rpm.
My MAP signal without an orifice and small fuel filter in the MAP line, would swing from about 70-85. With orifice and filter its 80-81, the only problem is orifice/filter sslow response time. If i cant tune around that ill have to work on a happy medium.
kaeman wrote:with the big cubes and large cam, what does your map signal look like and what is you idle injector pulsewidth in ms.
My idle pulse width's are currently anywhere from 2.4ms to 3.4ms. I have never really hammered down my injector dead time which I think is the root to several of the motors ill mannered traits. On my to-do list is trying the 1 simultaneous/2 alternating trick to narrow in on dead time. It's a long list these days.
kaeman wrote: I am assuming that you have very large intake runners and therefore have a low velocity air flow in the runners at idle speeds.

My intake runners, i dont think are overly large (325 cc intake runners and a modified carb single plane intake). But I agree a velocity problem. Ive modified the throttle linkage to give progressive operation and that gave the throttle noticeably more modulation but hasnt helped throttle tip in surging.
kaeman wrote:Have you tried to change the injector timing at the idle speeds to see if that made any improvement to the stability.
Injector timing, ego delay, PID ego settings, TPS WOT curve and injector trims are all settings ive tried almost every way imaginable to smooth off idle and tip in throttle when at cruise.
MS3PU/IOx/CAN-EGT/DBWx2 540ci BBC 325cc int runners (2)innovate LC2 wbo2's, Hilborn ITB injector cnvrtd to EFI, 55LB Inj, d585 coil near plg, 60-2 trg whl & cam ph snsr, Muncie 4spd w/10T VSS, Tilton 7.25" cerametalic cltch 8.5LB flywhl
kaeman
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Re: Strategy for tuning idle for large engines

Post by kaeman »

Hm.... I wonder if your engine is a good candidate from alpha-n.... to get rid of the idle problems and the slow map response during throttle tip in.

The problem with your throttle tip in, is it a stumble with a lean spike, that even if you give more fuel is still there? I was having that problem for a while and found that if I stabbed the throttle the engine stumbled and when doing auto tuning it kept adding fuel, but looking at the data logs I was finding lean readings when the engine had the largest pulse width...... rich misfire.. I started taking bunches of fuel out of the ve table and the stumble got smaller and smaller, I turned the settings for accel enrich up so high that it doesn't even trigger when I do a hard throttle stab and the engine runs better without it. I found the autotune kept adding fuel because of the false lean reading until the engine would stumble and die if I made a hard throttle change and kept my foot in it, I no longer have that issue.

I am thinking that because of the 80 kpa idle map, you would be better off using the alpha-n rather than speed density, not much range left in the table if your idle is 80. Do you have a good way of testing the dead time of your injectors, because that setting can be a real make or break point on most of the engine parameters. If I were in your shoes, I would get the dead time ironed out, then change to alpha-n and attack the idle problem. after you get that sorted out and smoothed down then I would do some steady state tuning. get the fuel table close enough to allow auto tune or datalogging to help tune the rest of the table. Good Luck.
64 el camino, 383 SBC, 11.7 to1 CR, accufab tb/rhs intake, 44lb injectors, trick flow heads, xr292r solid roller cam, belt drive camshaft, dry sump oil system, 2400 stall, turbo 350, spooled 9 inch, strange axles, 3.89 gears, dual wideband, full sequential fuel/cop, MS3x using 1.4.1 code.
dll67
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Re: Strategy for tuning idle for large engines

Post by dll67 »

kaeman wrote:Hm.... I wonder if your engine is a good candidate from alpha-n.... to get rid of the idle problems and the slow map response during throttle tip in.

The problem with your throttle tip in, is it a stumble with a lean spike, that even if you give more fuel is still there? I was having that problem for a while and found that if I stabbed the throttle the engine stumbled and when doing auto tuning it kept adding fuel, but looking at the data logs I was finding lean readings when the engine had the largest pulse width...... rich misfire.. I started taking bunches of fuel out of the ve table and the stumble got smaller and smaller, I turned the settings for accel enrich up so high that it doesn't even trigger when I do a hard throttle stab and the engine runs better without it. I found the autotune kept adding fuel because of the false lean reading until the engine would stumble and die if I made a hard throttle change and kept my foot in it, I no longer have that issue.

I am thinking that because of the 80 kpa idle map, you would be better off using the alpha-n rather than speed density, not much range left in the table if your idle is 80. Do you have a good way of testing the dead time of your injectors, because that setting can be a real make or break point on most of the engine parameters. If I were in your shoes, I would get the dead time ironed out, then change to alpha-n and attack the idle problem. after you get that sorted out and smoothed down then I would do some steady state tuning. get the fuel table close enough to allow auto tune or datalogging to help tune the rest of the table. Good Luck.
I guess its not really a stumble at all its really a surging at steady low throttle angles which is always at cruise where it just wont run smooth, not even really so much as miss just not smooth like when accelerating. As soon as I accelerate or get to a larger throttle angle cruise it goes away. During the surging events Ive noticed that AFR's hunt and adjusting the O2 sensor delay and injector timing will make it better but never completely eliminates the AFR hunting. I'm also toying with the idea of locking out half the throttle plates and just tuning with half the CFM's available.
I too have the same symptoms with autotune, always tunes VE tables rich at anywhere I;m at steady low throttle angles. Megalogviewer's autotune feature does the same thing. The best way ive found to adjust my VE table so far is by studying datalogs for RPM/MAP points that best reflect my VE table cells and adjust up or down the VE cells depending on the AFR numbers in the datalog.
Early on I experimented with Alpha N but with such a large Throttle Body I fought tuning at such small throttle angles. But now that I think about it no more than I'm fighting tuning Speed Density .. It might be time to revisit Alpha N once I get my AFR's steady somewhere close to idle RPM's so I can adjust Injector dead times.
Right now i'm testing my redneck rolling road and once I see if its going to be able to give me a steady load to tune with I'll tackle dead times first andgo from there.
Thanks for brainstorming this with me I tend to get so involved with what im working on I miss whats smacking me up side the head (injector dead times, alpha N)
MS3PU/IOx/CAN-EGT/DBWx2 540ci BBC 325cc int runners (2)innovate LC2 wbo2's, Hilborn ITB injector cnvrtd to EFI, 55LB Inj, d585 coil near plg, 60-2 trg whl & cam ph snsr, Muncie 4spd w/10T VSS, Tilton 7.25" cerametalic cltch 8.5LB flywhl
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