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Thread: LQ4 with Summit 8707 cam with stock 8.1 injectors

  1. #21
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    People sure can be sensitive to what random people on the internet think about them.

  2. #22
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    That and it is a stock OEM part which while not foolproof, makes it easier to tech and also reduces the chance that old guys turn their nose up at it. They don't know what an (x) lb/hr injector is. I just have to tell them it's from a stock 8.1L. To cheat it they'll have to find a bigger Multec injector. Not saying it can't be done....but it reduces the chance someone tries. Not everyone knows about marine injectors.

    The fuel system is a Corvette fuel filter system that doesn't require permanent modification of the truck or fuel cell if they sell the truck and someone wants to run a carb engine again.

    Monitoring competitors' fuel pressure is already going to be hard enough with a Corvette filter. I thought about seeing if the stock injectors can get there with just more pressure, but it gives competitors something to tinker with and then complain that it doesn't run right because they think "more pressure equals more HP".

    I have to speak a language they understand, and one less modification to a harness they are already going to say "look at all those wires" at. Sales is part of the deal. The only reason I built a truck is because none of them will consider it unless I put one in front of them....and it makes enough power for them to be afraid of it.

    That's the other thing I did with the 8.1 file was swap the injector data into the 6.0 tune. I'll get them installed and see what it does. I kept the MAF harness when I weeded the harness. I also used two 36 pin lever lock connectors from a Trailblazer to allow easy engine changes. Actually the LS should be easier and faster to pull than the Gen 1 small block.

    The cam was chosen because it pretty much exactly matched what COMP recommended when I told them what I was doing. At the end of the day, I don't have much control over how someone builds their engine. I don't know if it's a junkyard engine or if it's a built bottom end with bigger valves I DO have to know what exactly is in the tune. One of the best giveaways something smells funny for me as the tech guy is if it doesn't run right. If I put a small cam in it... someone's going to put THIS cam in it. What they don't have access to is the tune.
    We will have several PCMs so if I think something is up, I probably won't even check the CVN....we'll just swap the box. I just take the box and compare the files if they don't match.... you're DQ'd.

    After this one goes across the Dyno, we'll build a 5.3 the same way, and put it across the Dyno. We'll probably have build a couple fresh engines as well. Just have to see how it goes.

  3. #23
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    Well the 8.1 injectors are in and it starts and runs. Not bad, almost all I need to do. It will idle sometimes and sometimes it idles at 2k. I can make it idle with my "finger iac" and can even stall it, but none of my scan tools nor the VCM scanner will drive down the idle. I have taken the TB off and watched the IAC go through the park sequence and the tap test with a screwdriver does seem to change....something. I for sure don't have the ve refined enough to do any final tweaking to get the counts within the sweet spot. It would idle and then once I came off idle once warmed up it hangs. TPS is at .6 and this is a completely unmolested stock TB. I played with some of the throttle cracker setting but no dice. Counts don't seem to be consistent at all.60 CRS Truck 8.1 injectors high idle.hplCRS Truck Stock 6L big injector starter tune.hpt

  4. #24
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    You turned off adaptive idle?

  5. #25
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    I tried a couple things to see if it would help in the current tune I set the min and max adaptive idle ect to 283. Made no difference. Trying to see if that RPM is being commanded by a strategy or whether I am literally having an IAC issue. It seems too erratic to be the tune but I'm not positive. Seemed to me it was good cold and then when I got to what would be around a normal closed loop temp of about 160deg then it started to hang the idle. Since it will never have VSS or anything MPH and is manual, I wonder if maybe I missed something on the trans side? When it was idling at the desired RPM the iac was working pretty hard anywhere from single digit to 50 but I also saw counts over 100 at different times as well. No surging...just high...and when it is at 850 it will sit there and idle for 10 minutes... until you transition out of idle TPS and then it never returns to desired idle. TPS makes it back to idle, but the RPM doesn't. Did I maybe miss something in throttle cracker? I'm trying to run through all the different airflow adders in my head. As a tech I usually deal with one at a time...not all at once.

    This is a boneyard engine with no history and high miles, a custom built harness for the application with extra connectors added, and very little run time because it makes your ears bleed (especially above idle in a garage).....so the possibility for "wild cards" is decent. Thanks to header paint burning off in my face I found that the original #7 injector was dead. Once I checked the harness and put the bigger injectors in, it resolved. I'm sure the lack of contribution didn't help things.

    I also am not set up for wide bands and probably won't be. I do have bungs in the collectors and the van O2's in them and supported in the harness. I'm not sure whether I should plug them in or not or whether I'll just create false leans due to the cam and exhaust. Right now it actually runs better than I thought it would. Starts decent when the IAC is under control. No load of course but snap throttle is pretty crisp and other than the idle it runs good enough to start doing some street tuning just to see where I can get before it hits the dyno. I haven't even touched the VE table at this point. Today is the first day that I tried to mess with it. If I can get a predictable idle anywhere under 1,000 RPM I'll take it.
    Last edited by Evracer; 4 Weeks Ago at 12:07 AM. Reason: grammar

  6. #26
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    You're wasting time with idle until VE is correct. For that you need to use the narrowband fuel trims.

  7. #27
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    I don't disagree with that. I was happy that it would start and run after the injector swap especially after not touching the ve table. This is where I have a "me" problem as far as whether I just want to load it on the trailer and hand it off versus how much I want to play.

    Honestly at this point I will admit to being a little bit wishy-washy as far as how far I personally will go, but knowing me and my creeping death of curiosity mixed with my background will probably lead to me spending more time on it than I should to figure it out. I was kind hoping that since I did have a kinda somewhat idle....that if I could just keep it, I would be good with loading it on a trailer.....but if I hook up the O2's and actually start doing idle tuning....I know where this goes.... 😂

  8. #28
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    Yeah but if you want to make adjustments between runs you need to know how to do it. Might as well learn.

  9. #29
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    I was afraid someone was going to say that...lol. I've learned from doing in cylinder pressure transducer graphs on street engines and experimenting with it on race engines, that race cams can absolutely make something that works stellar on a production vehicle be absolutely worthless in a different application. What are the limits of the narrow bands in this type of application?
    Obviously wide band is better for staying on stoich especially at high loads/rpms. And I can totally see how you can get false leans from narrows....but how far can I trust them? I wouldn't trust them for a final answer for sure especially when the application is essentially 2 dyno pulls per lap.

    On a side note: throttle hangs are absolutely TERRIFYING to a circle track driver. On the other side, some drivers will crack the throttle on entry to remove compression braking at some tracks so the transitions are going to need to be silky in the end product. I actually have to think about nightmare fuel like an IAC failing full open from a safety standpoint. May be the only application that gets a minimum air test and a MAXIMUM air test. That's also why not only drive by cable, but drive by solid cable. Standard is that the driver must have a toe loop on the accelerator and be able to (or at least attempt) to pull the throttle shut. I also have to think about a TPS failing to get back to idle voltage for the same reason....stuff that normally isn't an issue because normal people don't hurl themselves at walls at 120 mph and hope they can turn at the last possible moment...lol

  10. #30
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    No big deal tuning the entire VE table with widebands on this application. Either way, getting correct VE is your next step.