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Thread: Help with LQ4 swap in 91 Z71 RCSB

  1. #1

    Help with LQ4 swap in 91 Z71 RCSB

    this is my second engine swap from the original 5.7 TBI it came with in 91 - currently being pulled out 358ci SBC

    I just picked up a LQ4 6.0 with 70k miles on it - I have a built 700R4 with 3500 stall and I'm stuck deciding to just cam it or change/upgrade the heads/intake?? If I stay with the 317 heads I know I'll need to upgrade the pushrods and springs (suggestions???) been talking to comp cams about a 228/234 .627/.602 112 - I'm interested in a choppy idle with strong power thru 6000+rpm

    should I mill my heads and get a thin gasket to up compression or spend the money to swap out to a 799/243? If I swap do I need a new intake?

    I'm also having trouble finding headers - there are a lot of LS swap headers for 2WD OBS but I'm not finding any for 4WD - mechanic doing the swap said to get a shorty or mid length and he can make the bends the rest of the way..

    lastly should I keep my stock injectors or go to the 8.1L injectors?
    1991 Chevrolet Z71 - build in progress - LQ4 6.0

  2. #2
    Join Date
    Sep 2005
    Location
    Austin Tx.
    Posts
    13,396
    I would do Patriot Dual Springs rated up to .650 lift. I would upgrade injectors as well.
    1951 3100
    1984 C10

  3. #3
    cool, same springs I was thinking!

    regular 8.1 injectors or the marine injectors?

    anyone know which headers will be the easiest to install on a 4WD??
    1991 Chevrolet Z71 - build in progress - LQ4 6.0

  4. #4
    Looking at $964.59 for the cam,pushrods,and spring kit - sound about right?
    1991 Chevrolet Z71 - build in progress - LQ4 6.0

  5. #5
    Sounds like a good price on the cam kit, wouldn't hurt to do new lifters at the same time.

    As far as injectors I would say whatever set you can get a better deal on. The marine injectors flow about 10# more than the truck injectors.

    Check out Schoenfeld they should have something for your swap.

    If you decide to, the 243 heads on stock gasket thickness should bring your compression up to about 10.5:1 and you can use the stock intake with them.
    2000 RCSB
    LQ9
    Torquer V2
    T56 Magnum
    305 drag radials
    3/4 lowering kit

  6. #6
    I didn't know I could use stock intake with those heads - 10.5:1 sounds great! would I have to worry about a .627 lift cam with those heads?

    I'll look at Schoenfeld now and see what I can find, maybe call them on Monday

    I'm a marine dealer so I can probably pick them up cheaper than the truck injectors..
    1991 Chevrolet Z71 - build in progress - LQ4 6.0

  7. #7
    Yeah the truck intake will work with any cathedral port heads.

    I did some math to figure out exactly what your compression would be.

    Bore:4.000

    Stroke:3.622

    Head Gasket Bore Diameter:4.03

    Compressed Head Gasket Thickness:0.051

    Combustion Chamber:64cc (243 heads)

    Piston Dome Volume:-6.7cc

    Piston Deck Clearance:-0.010

    Compression: 10.4:1

    I couldn't fine a concrete answer on deck clearance for the LQ4. Some people said -0.007 and some said -0.013. So I went with -0.010 just to get an idea.

    Your Compression may vary a little depending on which gaskets you use and your deck clearance. But worst case you will still be above 10:1.

    I'm not sure as far as your piston to valve clearance on the cam I would assume it's safe but that's a complete guess. Your max lift isn't as much of a concern as the lift at and before 5-15 degrees TDC. I would give a reputable cam manufacturer or a performance shop a call and ask for some advice there.
    Last edited by Gemini; 07-18-2015 at 08:33 PM.
    2000 RCSB
    LQ9
    Torquer V2
    T56 Magnum
    305 drag radials
    3/4 lowering kit

  8. #8
    Great info!! thank you!!

    I'm shopping a few 243/799 heads I'm going to go that way - any advantage to swap intakes while I have it apart or my stock one flow good enough?

    I'm going to call comp cams back before they make my cam and let them know what I'm going with incase we need to make adjustments..

    I see you did a similar swap in your truck - how did you have yours tuned? did they dyno it or just go off of your mods?
    1991 Chevrolet Z71 - build in progress - LQ4 6.0

  9. #9
    I've read that the truck intakes actually flow pretty well but they fall off compared to the car and aftermarket intakes on the top end around 5500RPM. If you've got the budget for it then an aftermarket intake would be worth it plus it'll dress up your engine a little.

    For my tune I just did a mail order and they went off of my mods.
    2000 RCSB
    LQ9
    Torquer V2
    T56 Magnum
    305 drag radials
    3/4 lowering kit

  10. #10
    well considering how much I've already dumped into this project so far I think I'll keep my truck intake for now - I do like the cosmetics of the car intake but if the flow isn't much better I'll hold off and get a fast later..

    I'm going to do mail order for now too..
    1991 Chevrolet Z71 - build in progress - LQ4 6.0

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