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?