LS Intake port length

Discussion in 'Cams, Heads and Valve Trains' started by BILL JULIANI, Aug 12, 2018.


    BILL JULIANI New Member

    Currently deciding on an intake for my 383 boat engine, AFR heads, 224/228 @ .050 roller, performance exhaust, came across an LS Intake dyno test with variable length runner test, but it appears the runner length is shorter on the LS head, so using the listed intake runners for comparison when looking at the dyno graphs is not relevant. Does anyone know the port length difference between the SBC Vortec and the LS?
    I am considering either porting the stock Mercruiser which has an approx. 9" runner and appears to based off of the stock truck vortec intake, or using a performance Mercruiser tunnel ram style EFI with 6.25" runners. Tunnel ram runners seem too short for the max ~5600 RPM, but then again if Mercruiser used it...
    Yes, I know they are different animals, but the torque curve shape based on the different runner lengths should be able to provide some relevant additional info in helping decide. Seems a stock style intake with larger ports would work best, but if so, why would Mercruiser go to the trouble of coming up with a different intake for their higher HP offerings?
  2. Grumpy

    Grumpy The Grumpy Grease Monkey mechanical engineer. Staff Member

    just so others can look over the test results, on those ls intakes


    both cross sectional area, and length effect flow but remember, displacement compression and cam timing also are major factors.
    what most people fail to take into account is that the cam timing and exhaust scavenging being properly matched is critical.
    changing the cam timing or header configuration would change some of the resulting intake flow rankings .
    tests like that are helpful, as a basic parts selection guide and starting point,
    but you can,t assume the results will remain consistent on different engines.
    I'd also point out that component cost and easy packaging,
    and parts availability all are significant choices and factors,
    that were used in the components used.


    Last edited: Aug 12, 2018
  3. Maniacmechanic1

    Maniacmechanic1 solid fixture here in the forum

    If you Purchase Pipe Max it will help.
    Maybe John here has it.

    I know the Truck LS2 Intake has been preferred over most offerings.
  4. Strictly Attitude

    Strictly Attitude solid fixture here in the forum

    So is this a vortec style block or LS?
  5. Strictly Attitude

    Strictly Attitude solid fixture here in the forum

    Standard or reverse rotation curious?

    BILL JULIANI New Member

    AFR 195 Vortec heads
    The Mercruiser tunnel ram has 6.25" runners with an area of 2.25"
    The runners that seemed to work best in the rpm range I'm looking at in the LS test used an 8.25" runner.
    My question was
    How long is the intake port on the LS head?
    Looks shorter,
    Trying to make some comparisons to see if the Mercruiser intake I'm considering will make power where I want it to.

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