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Thread: LM7 w/Truck Norris Low RPM Surge

  1. #21
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    Sirius Tune R1.hpl

    See log attached, low speed much more stable, did a little bit of driving around to fill in the tables.

    Dropping out of gear will stumble a touch to catch idle, but did not die.

    So far good improvement to drivability.

  2. #22
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    Second one. Load it then use VCM Scanner>Vehicle Controls & Special Functions to clear LTFT's. Log again.

    Tell me about the fuel system. Pump, reg, injectors, layout.
    Attached Files Attached Files

  3. #23
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    Sirius Tune R2.hpl

    Stock 1998 Jeep Wranger Fuel pump with pump regulator bypass to boost pressure to rail. Stock LS fuel rail and integral regulator + fuel return line. stock injectors.

  4. #24
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    Quote Originally Posted by jCaspary View Post
    Sirius Tune R2.hpl

    Stock 1998 Jeep Wranger Fuel pump with pump regulator bypass to boost pressure to rail. Stock LS fuel rail and integral regulator + fuel return line. stock injectors.
    Not able to follow this. Do you have two regulators?

  5. #25
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    Sorry, no not two regulators. The regulator that used to be in the jeep fuel pump has been pulled and bypassed. So just the one regulator on the rail itself.

  6. #26
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    Ok reg on the rail and vacuum line attached? Factory truck rails, basically.

    Injector P/N?

  7. #27
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    Quote Originally Posted by grubinski View Post
    That's interesting ... never heard that.

    Summit has a truck cam, their 8727R1, with specs of 200/205 113+4, so IVC @ .050" is 29 ABDC. Do you think that'd be too early for a 5.3 in a half ton truck used for towing?
    With the throttle plate mostly closed and intake manifold vacuum in the manifold, the exhaust valve is a lot better source of airflow during the overlap period as the piston descends on the intake stroke. With the IVC earlier for a given duration that means the IVO is also earlier meaning more overlap and more exhaust contamination especially when the throttle plate is mostly closed.
    Last edited by Fast4.7; 3 Weeks Ago at 03:33 AM.

  8. #28
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    From idle through ~2,000 rpm a truck norris will have some overlap induced roughness especially at very light throttle. Actually cruised around in a friends 1967 Chevelle this evening that he thought had a fueling issue. Turns out the wideband just died. But this is an iron block "5.3L". It is an iron LS1 in reality with milled and ported 241s, LS6 intake, Howards 228/234 @ 0.050, .604 lift, 112 LSA and 108 ICL cam. Long tubes. Converter stalls 4K. Shift it at 6,700 on a 7,000 rpm limiter. Has 4.10 gears in it. Cammed LS wants to spin even at lighter throttle, not lug along at 1,500 rpm. The engine likes the tune on the richer side with a good chunk of timing in the low-mid load areas from all the exhaust dilution in the cylinders from the overlap. You can dial setups with overlap in until the fuel trims look perfect and the engine will hate life. Leave it rich, let the 02 sensor pull a little fuel if they want and it will run and cruise smoothly with sharp throttle response. I just give it what it wants until it runs smoothly, sometimes that is adding 100-200 mv above idle to the 02 sensor target voltage to keep it richer in closed loop as well. This was just cruising around, briefly went into PE at 40% throttle on the 1st clip but otherwise all closed loop and never even hit half throttle. When PE richens the air/fuel ratio even more you can just hear how that engine comes alive too. It loves fuel lol.

    https://youtu.be/o1QMT8ZmT4I?si=o4QqVS4pb6MVBu78

    https://youtu.be/cDZxUPnOyMA?si=EZiFdHBvG2LQYQdc
    Last edited by Fast4.7; 3 Weeks Ago at 03:21 AM.

  9. #29
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    Quote Originally Posted by Fast4.7 View Post
    With the IVC earlier for a given duration
    With that clarification, it's not so surprising ... it's really the overlap, not the IVC. A Truck Norris has a minimum overlap (depends on the stupid BTR 'X' in their spec) of 2 degrees. The summit cam I asked about has overlap of -23.5 degrees. Should run just fine.

    Thanks!

  10. #30
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    Quote Originally Posted by Fast4.7 View Post
    Cammed LS wants to spin even at lighter throttle, not lug along at 1,500 rpm. The engine likes the tune on the richer side with a good chunk of timing in the low-mid load areas from all the exhaust dilution in the cylinders from the overlap. You can dial setups with overlap in until the fuel trims look perfect and the engine will hate life. Leave it rich, let the 02 sensor pull a little fuel if they want and it will run and cruise smoothly with sharp throttle response. I just give it what it wants until it runs smoothly, sometimes that is adding 100-200 mv above idle to the 02 sensor target voltage to keep it richer in closed loop as well.
    Currently mine is running as well as it ever has with a bunch of timing taken out of the coastdown areas below .20 cyl. air and 2000 rpm. I'll have to try your approach above, and see if it runs better or worse.

    Thanks again!

  11. #31
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    Let me check the injector I have laying in the shop that I changed a while back when I get off work tonight.

    Yes factory truck rails with regulator and vacuum hooked to it.

    Stock offering for a 2004 Chevy Tahoe 5.3L from auto parts store. Pretty sure its Delphi PN FJ10062 for the injector.

  12. #32
    Senior Tuner TheMechanic's Avatar
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    Done a few TN's on rock crawlers but the guys I tune for are a bit on the wild side. There idea of rock crawling is how high in the air they get going over the rock. Hahahaha. Biggest single help is a high stall converter.

  13. #33
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    Quote Originally Posted by SiriusC1024 View Post
    Ok reg on the rail and vacuum line attached? Factory truck rails, basically.

    Injector P/N?
    Injector P/N 25317628

  14. #34
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    Quote Originally Posted by TheMechanic View Post
    Done a few TN's on rock crawlers but the guys I tune for are a bit on the wild side. There idea of rock crawling is how high in the air they get going over the rock. Hahahaha. Biggest single help is a high stall converter.
    Yep except OP has a manual. The fluid coupling of a converter especially a looser one that is unlocked helps eliminate that shudder from the light load, lower rpm misfiring.

  15. #35
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    Quote Originally Posted by Fast4.7 View Post
    Yep except OP has a manual. The fluid coupling of a converter especially a looser one that is unlocked helps eliminate that shudder from the light load, lower rpm misfiring.
    Totally agree with you on that. Nearly every one that I have done is a TH400 and a NP205. GREAT combo.

  16. #36
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    Quote Originally Posted by TheMechanic View Post
    Totally agree with you on that. Nearly every one that I have done is a TH400 and a NP205. GREAT combo.
    I have a similar cam to a TN in an 11:1 383 SBC in my Express van. Even in the bigger engine I cannot stand the converter being locked under ~1,700 rpm. I will let it stay in lockup down to ~1,500 rpm but I do not let it apply until it will hold ~1,700+ rpm. SBC cam is 271/284 @ 0.006, 218/228 @ 0.050, 0.536 lift with a 1.6 rocker, 108 LSA and 106 ICL. The 4L85E converter is fairly tight, it will move the van forward at its ~780 rpm idle speed in gear but flash stalls ~2,900 behind the torque. Even in that 3.75" stroke high compression 6.3L SBC that cam is happiest above 2,500 rpm. 85 mph is 2,500 rpm with the 4L85E and 3.73 gear. When it idles in gear it actually surges noticeably especially in reverse where the 4L85Es pump is heavily loaded to the point it feels it is skipping/jumping. As I said previously that cam is coming out too. Getting a 265/265 @ 0.006, 219/219 @ 0.050, 0.544 lift with 1.6 rocker, 112 LSA and 108 ICL Erson ground cam that Lloyd Elliot and I came up with in its place. I had a very similar cam in my 5.7L Ram close to 15 years ago. It was a Comp XFI lobe 265/265 @ 0.006, 214/214 @ 0.050, 0.540 lift with the stock shaft rockers, 114 LSA and 110 ICL. It drove like the stock cam just more power everywhere.
    Last edited by Fast4.7; 3 Weeks Ago at 12:48 AM.