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I think my Corvette hates me...

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  • I think my Corvette hates me...

    Not sure if it does or not, but it seems it sometimes.

    Been doing some tuning on the fuel and getting things to really start feelin' good. You know the drill. You THINK it's running good, then you put a few degrees timing into it and THEN it FEELS good!

    Well, finally had a chance to have someone else drive it for a bit while I tuned the timing and it really did start to feel pretty good. Not really going for super-boost stuff, just part-throttle drivability stuff. On the way home, I goosed it a little bit and heard something weird. It was running okay, so when I got home, I popped the hood. Turned out that the belt tensioner on the supercharger belt broke! The housing cracked. And of course, the belt snapped and wound up coiled in the corner by the frame. Thankfully, it didn't get tangled up into the other belt.

    Now, I'll be pulling the supercharger to replace the tensioner (it's under the supercharger and otherwise inaccessible). It just always seems to be something. Like I said, if my car DOES like me, it's got a weird way of showing it! LOL!

  • #2
    Ha, we have all been thru this, Why is it that the exact same tensioner and belt set up will run 100k miles with no issue on a Cadillac, but as soon as it goes on a hot rod, it becomes crap? No one knows it is just that way sometimes, and it is so aggravating, what ever it is, is the exact reason you see non-car guys get into the hobby, and then bail out, after huge losses, Only real car guys can understand this phenomenon and persevere,

    Honestly it drove you home, you should of done the church lady dance!!!

    On the tuning note, you always want more, But you have to be very very careful, More Timing feels Way Better!!! But equals much closer to hole punched in piston!!!
    Also running lean Feels stronger!!!! But equals much closer to melted piston tops and crushed ring lands, its not a race car that you have to have the very last nth out of for the next record run,

    IMO, Get a good safe spot on timing and fuel, let that be your performance Base line and call it good, You can always default to well it runs X, but I can bump timing and lean it out and get some more!!!

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    • #3
      That is true. When I was chassis dynoing mine, seemed like every time we added a little timing or boost, it loved it. I was trying to be conservative...but it's easy to want more. The guy running the dyno (good guy...tunes lots of high end cars under boost)....was real happy with the tune, the inlet temps and just generally everything. He's like Dude....you're over 1100 RWHP on 91 octane pump gas and it's happy. You can keep adding more until eventually we lift a head and blow a gasket..no telling where that point is...or start trying to figure out how to use what you have. It was a good calming moment and I decided things were good! And it's been in "safe" mode ever since and it runs fine and hasn't hurt itself yet.

      You've got enough power to run low 11's /high 10's easily.....just keep playing with the driveability part.

      JIM

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      • #4
        Yeah, that is my plan. As a matter of fact, I had thought about pulling the belt at one time so I knew that it wouldn't go into boost no matter what. All I'm really dealing with right now is non-boosted driving, so not having to worry about it is slightly appealing. I decided not to remove it but the car had other plans. LOL!

        So, now I'll continue to tune it conservatively and then worry about tuning for boost later. Not really setting it on "Kill", just looking for a nice, responsive engine. Will keep you all informed on how it all plays out.



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        • #5
          Keep an eye on the Holley learn tables. That will give you a good feel for things. It will self learn a lot the more you drive it. You can data log things too as you cruise around to be able to sit back and view what's happening and when.


          JIM

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          • #6
            Yeah, it's a pretty incredible little box. The idle learn table may get up into double digits, but everything else is pretty close, maybe -/+ 3 %.

            Holley basically works on the fuel side when making adjustments whereas some other folks adjust the VE tables. The two are interlinked obviously, and I'm trying to figure out if the Holley system uses the suggested A/F ratio + the learn factor to figure out the engine's VE at that point. If you go to the fuel table and hit conversion, it will show the engine's VE table. You CAN make changes to that table, but then it will adjust as the system learns. Many tuners use VE as the foundation for the tune, while I think Holley basically wants to you "tell it what you want" and it'll adjust to it, noting how efficient the engine is at any particular parameter along the way.

            I can see the benefit of doing it this way, since I can TELL the ECU my engine's efficiency, but that doesn't necessarily mean it IS that efficient at that point. Therefore, my foundation would be off, and the rest of the tune would be built on an incorrect foundation. If what we are looking for, is a specific A/F ratio, and we can learn how much fuel to add/subtract, then we can extrapolate how efficient the engine actually is, thereby getting the correct VE amount for that particular rpm, load, etc.

            While the fuel does adjust +/-, the system only removes timing from the base spark. I did a little adjusting on the core timing at the balancer to make sure that what the ECU says, is what the crankshaft SEES. It was a little off, so now I'm looking at the entire table to see how it now flows. That's another reason that I'm not too disappointed that the tensioner gave up the ghost. I adjusted the Inductive Delay and Reference Angle from what they were during the base tune. (yes, I changed them only after checking with a timing light as per instructions.)

            That changed the entire table, so now I'm slowly bringing in the entire spark table to the "new normal", non-boost first. On another note, the supercharger had some gear noise that was quite evident at idle. I think the knock sensors were picking this up as well as there was a LOT of activity at idle but when the rpm got up around 2500-3000, it would drop significantly. I can tell the ECU to ignore the noise down low, but with the belt off, I can now tune that area's spark without having to fight the noise. Will also let me use that lower area to tune the sensitivity of the knock sensors so I get a true reading without severe consequences.

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            Thinking it through, there are several good reasons for not having boost right now!

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            • #7
              I just use the A/F ratio I'm looking for and let it do what it needs to get there. If it's having to add or subtract a lot to maintain it...you can see it. That can point you to other issues.

              Then I plug in the numbers for the spark table and let it go.

              JIM

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              • #8
                Well, I got into my supercharger belt issue. As suspected, the tensioner gave way, but I didn't know the extent of it all until I got the entire assembly out of the car. Things got REAL unhappy for a short period of time!

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                • #9
                  Wow...that's a lot of ugly right there!!


                  JIM

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                  • #10
                    I got everything put back together and took it for a ride. Seems to hold water. I'll do some more driving to make sure it's reliable again and then start enjoying it.

                    Going back into this reminded me how little space there is in these C4s. If you can see it, you can't touch it. If you can touch it, you CAN'T see it! You get used to removing things just to do other things. In that way, I envy the C5 guys. They're a LOT nicer to work on.

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