Idle Speed. What makes it right?

Big Block A body Tech

  1. Kent mosby

    Kent mosby FABO Gold Member FABO Gold Member

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    This is my setup.
    1973 Plymouth Scamp
    RB 512ci, 440 source stroker kit with lightweight crankshaft, forged pistons, 10.83 CR. Trick Flow 240 heads, 440 source aluminum rockers 1.5RR, Trick flow single plane intake. Holley super sniper EFI, hyperspark ignition, coil and distributor. TTI 2 inch headers. Hughes 3000 stall converter. 727 transmission with transgo tf2 valve body mods. B&M Quicksilver shifter. Gear vendors overdrive to 8 3/4 rear end with 3.91 gears, braced in back. SS leaf springs. Competition engineering race shocks. Pypes exhaust 3" into 2.5 inch. RacePro mufflers. Mickey Thompson ET street SS Drag radials 255/60-15 27.3 inch) but going to 275/60-15 28.2 inch diameter. Current cam specs 244/252 @ .050”, 282/290 adv, .516”/.537” lift(1.5:1 rocker), 112 sep, .016”/.018” lash, Solid lifter from Oregon Cams.


    I finally have the EFI working correctly. Bad O2 sensor. I know that there are many variables as to what is the correct idle speed. My question is, How do you set it? What order do you do it? For example, with EFI, do you set base timing, AFR and then Idle. What do you look for to know that you are correct? Is there a tuning book/recipe? Something like, adjust timing as such until you reach maximum vacuum (just making that up). Then adjust AFR, Then Idle speed. There has to be some verified, validated sequencing to tuning an engine. Not just something that says Mopar RB should be 850 rpms at idle... With each motor being different and unique, What steps and procedures would you do to setup and tune an EFI motor? How do you know that it is right without a DYNO at every step??
     
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    • Dana67Dart

      Dana67Dart The parts you don't add don't cause you no trouble FABO Gold Member

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    • my68barracuda

      my68barracuda Well-Known Member

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      What you mention, timing-AFR-idle speed is about right. But the process can be iterative, meaning that you may need to go back and slightly re adjust the timing and - or AFR to get the idle quality that you desire.
       
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      • TT5.9mag

        TT5.9mag Two atmospheres are better than one

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        In the Holley super sniper tuning software, isn’t there a “target” idle rpm? I’m not familiar. But typically you have an afr target and an idle rpm target and you would adjust idle ve and ignition timing (and any idle modifiers) until the target is met. You can typically run a log and watch the trace. But again I am not familiar with the super sniper software. The actual rpm is subjective. Whatever makes your engine (and driver) happy. Typically a larger duration, big overlap cam likes a higher idle speed. Flat tappets splash oil so idle speed is a concern there. Manual or automatic trans is a concern. Idle vacuum for power brakes etc etc etc. when is it “right”? When you’re happy with it.
         
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        • Kent mosby

          Kent mosby FABO Gold Member FABO Gold Member

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          The variables are all easily set in the sniper software. The question is where to set them.

          Maybe I should have broken it down to -
          When setting the idle timing, what parameters do you look at? Vacuum, idle, surging, lugging off idle???
          When setting AFR, What parameters do you evaluate first, second and so on? Idle quality, stumbling, Plugs etc.
          When setting Idle speed, What is your primary consideration? Smoothness, vacuum, stumbling off idle, etc...

          I understand that all parts must come together and that you will go back and forth to get it right. How do you approach the initial setup?
           
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          • Dartnut

            Dartnut Don't hate me because i'm beautiful

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            I would be getting ahold of Holley to determine what procedure to use for your specific combination.
             
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            • TT5.9mag

              TT5.9mag Two atmospheres are better than one

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              I’m sure some tuners follow some kind of self imposed process but really it is a process that is learned and experience makes a big difference. On the few Ive done for myself I plug in some numbers that I know will get it to run. At 13:0 afr 16deg initial timing almost anything will run. Once the idle afr is stable, safe, and kinda rich I’ll bump timing small amounts and watch rpm and vacuum while pulling idle air to keep the rpm the same, usually targeting 1000 on new tunes. Then start trimming fuel to get the o2 correction in line. Once the ve table is close at idle and o2 correction is minimal your idle afr will closely match your target. When your targets match with little correction from o2s then you can mess with target Afr. It’s not just a “set it and forget it” process. You have to move around the tune for a while to find out what the engine likes.
               
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              • 67Dart273

                67Dart273 FABO Gold Member FABO Gold Member

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                Just remember that whatever the manufacturer's did was after months or years and lots of money R&D.

                You, that is we, have created a completely new and unique engineering prototype with any custom engine build

                "What might be easier" would be to revert to carb and dist to optimize it, then measure AFR and look at timing so you know where you ended up

                The way I see it the big stumbling block is there is no "knobs" in the software like screwdrivering the carb idle mixtur, or grabbing the distributor "bodily"
                 
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                • TT5.9mag

                  TT5.9mag Two atmospheres are better than one

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                  “Knobs” or idle mixture screws and jets have been replaced by strokes of a key board. While some people are less apt to embrace that kind of change, I will say once you learn it, it’s much easier to hit a couple keys and make changes than it ever was getting out a screwdriver and turning a “knob”. With the correct sensors every single change you make happens in real time and you can watch what each one does. Maybe not so much on the sniper/fitech type of efi systems where your just plugging in some engine parameters and letting the ecu self tune, but real multi port efi.
                   
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                  • TT5.9mag

                    TT5.9mag Two atmospheres are better than one

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                    @Kent mosby are you tuning with the Holley hp software on a lap top or are you tuning with the handheld that comes with the sniper?
                     
                  • Kent mosby

                    Kent mosby FABO Gold Member FABO Gold Member

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                    I have a laptop where I can see the changes live when adjusting things. For example when I change the idle timing I can see the changes in the vacuum and RPM. What I am trying to get at is what order to do things and then redo things and then redo them again until all is stable. It seems to me that arbitrarily picking 850 rpms for example and making all things revolve around that is not sensible. Starting at 850 and then adjusting timing and AFR to reach optimum levels and then going back to adjust the rpms up or down a bit and fine tuning the AFR and timing again , you should be able to reach an optimum level.
                     
                  • 413

                    413 Well-Known Member

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                    Let’s make it easy. Idle high enough it runs smooth and doesn’t die in gear with foot on the brake. Idles low enough it won’t bang when putting in gear or drive away and have to ride the brakes, or brakes not hold it still.

                    So now we are back to thinking somewhere between 700 and 950. Depends on cam and converter.
                     
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                    • TT5.9mag

                      TT5.9mag Two atmospheres are better than one

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                      I know what you’re getting at. But it’s not that simple. Because everything effects everything else, and I’ve never tuned a super sniper. There is no list to follow really. You just have to keep moving around adjusting all of the variables until you’re happy with it. Maybe this will help.
                      Solving Holley Sniper High Idle Issues
                       
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                      • Dartswinger70

                        Dartswinger70 Only thing I ever bought new was a Fender Strat

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                        Eh...I dunno...
                         
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                        • famous bob

                          famous bob mopar misfit

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                          ur exhaust is way too small for a 500'' engine . mine idles at 1150 , adjust everything from there , timing is controlled by my f.inj. system. 20-23 initial , 3-4clicks leaner than self learn everywhere else. ngk-5 plugs. '' ur results may vary'' ---lol
                           
                        • Rmoore

                          Rmoore Well-Known Member

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                          I'm not sure if you have a problem, or just as you state just keeping running in circles ! You may make sure you don't have some unmetered air somewhere ! That can cause a lot of problems with the idle ! Like some others have said , I've never tuned a holley efi either !! I do know that no matter what you have the motor wants air, fuel, compression and it all happening at the right time !! I would say if it will idle , i would get my timing where i wanted it ! The timing will generally change your idle and a/f ratio.. Then i would get my air fuel ratio where i wanted it , cause that can change your idle !! Then I would set my idle speed ! I would do a carburetor engine the same way.. Rich or lean or idle speed both will be affected by timing ! I would sure make sure you do not have some unmetered air somewhere though ! This is the typical order of operation though !! Then if you have to keep going back and chage things , i would say you have a problem somewhere ! I hoped i didn't make things more confusion !!
                           
                        • MOPARMAGA

                          MOPARMAGA FABO Gold Member FABO Gold Member

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                          I think you have to take your rpm below 1200 rpm off of closed loop so the sensor doesn't talk to the computer, then manually on laptop reset your idle
                           
                        • Bewy

                          Bewy Well-Known Member

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                          Selecting the idle speed for EFI is no different than it is for a carbed engine. Look/feel/touch/listen/common sense.
                          You would pick the lowest idle speed that the engine can comfortably support the load of the tq converter in gear. If you go too in idle rpm, the engine will shake excessively & demonstrate it's 'F....you' attitude to you for going too low with idle rpm.
                           
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                          • RustyRatRod

                            RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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                            That's kinda what I was gonna say. I call it "where then engine is happy". In other words, high enough so it doesn't ever try to stall, yet low enough so you don't get any harshness shifting into reverse or drive from park. It boils down to personal preference, really. Although not really comparable, my carbureted slant 6 isn't really "happy" unless it;s pretty close to 1000 RPM. I've got it a tic over 900 now and so far it's not stalled. But it will every once in a while if I idle it down much lower.
                             
                          • famous bob

                            famous bob mopar misfit

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                            agree^, looser convertor has a part in this too.
                             
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                            • Kent mosby

                              Kent mosby FABO Gold Member FABO Gold Member

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                              From An expert.. Andy Finkbeiner . 2 posts. First is more seat of the pants and experience. Second is more procedural and what I am looking for. They do go hand in hand though for setting idle timing, rpm and AFR.
                              First post.
                              """First thing to do is to get the car running and warm up the engine so you can work on the hot idle. Once you have the engine warm you adjust the idle settings just like you would a carb. Slowly drop the idle speed and see how it does. Play with the ignition timing to see what it likes. Adjust the AFR to see what it likes. Adjust the throttle position to get the IAC into the correct location. It is exactly how you tune a carb engine except you don't have to change jets and mess with the distributor springs. You can do it all on the laptop by changing the values in the tables.

                              There are a bunch of Holley tuning videos on youtube so I'd suggest starting there if this is all new to you. It is like anything else. Once you know how to do it it is very simple but when you don't know how to do it it is intimidating. Watching a few videos will get you comfortable with the process of paging thru the menu and opening up the tables and stuff like that."""


                              Second post

                              """You aim for minimum kPa when tuning. kPa is pressure. You want to aim for maximum vacuum which is the opposite of pressure. Your idle pressure should be around 50 kPa on a well tuned engine with a modest performance cam in it. That is 15 inches of vacuum. A race car might idle at 70 kPa while a car with a stock cam will idle at 40 kPa. When you adjust the timing and/or the idle AFR you shoot for lower kPa. The other way to do it is to watch the IAC position. The IAC controls the idle air flow so what you want to do observe what is happening to the IAC position as you adjust the timing and the AFR."""
                               
                            • TT5.9mag

                              TT5.9mag Two atmospheres are better than one

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                              Isn’t this what I’ve been telling you for 3 days?
                              :lol:
                               
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                              • Kent mosby

                                Kent mosby FABO Gold Member FABO Gold Member

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                                I reread the thread and everyone with lot of experience are saying to use what makes the engine happy etc.. That is a learned process and it takes some experience to get it right. @TT5.9mag you did say to "watch" the vacuum and RPMs while making adjustments. What I did not know was what to "watch" for, More or less vacuum, more rpms, what vacuum should be in the ball park. I am a rookie here and trying to learn from others. Unfortunately, I have no one to show me the ropes and a recipe to follow would help. Everyone is so well intended, knowledgeable and helpful but they were speaking as though I knew what a happy motor was. My experience is inline 6 chevy only. Not a big block mopar. It runs ok but I wanted to go through the process of refining the idle speed, the AFR at idle and the timing at idle. Just for my own benefit and knowledge. The base parameters work but are they the best? I will adjust all for maximum vacuum and try to find where it is happy.
                                 
                              • TT5.9mag

                                TT5.9mag Two atmospheres are better than one

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                                Ok gotcha. We all learn regardless of how much experience we have. The quest never stops. Idle vacuum is a good indicator of efficiency. As you increase timing at idle vacuum will go up until the engine looses efficiency. The idle timing should be kept around that number. Whatever it ends up being. Lots of things effect what that number is. So each engine is different. Fuel will do the same thing. Lean it out and watch the vacuum and rpm. Fatten it up and do the same. You’ll find the sweet spot. The idle quality will degrade going too far both ways too rich or too lean. After you’re happy with the afr and timing at idle you can set the desired rpm. Once that is set go back and do the timing and fuel adjustments again to see if anything changes. Sometimes it can be monotonous but it’s how it’s done. Good luck.
                                 
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