morrowcarl72

^^^^^^ this is more than likely what i am going to do... run the 415 until i cant stand it and need more speed

morrowcarl72

also whats the difference between a 502 mag and a older 502 hp500

and does anyone know anything about merc tbi 502's?

Boat1

The 502 Mag carbureted had flat tappet cam, Webber carb (quadrajet style), dual plane manifold, non adjustable rockers. The carb HP500 had hydraulic roller cam (significantly larger), single plane manifold, 800 Holley, roller rockers. I would check your specs for the 502 MPI roller cam, I think they are 224/224 duration at .050 at about .318 lobe lift, could be wrong though. Good luck.

morrowcarl72

last thing.... i knnow guys and buddies of mine that race cars and do high performance stuff that run different ratio lifters on intake vs exhaust

any theories on that

morrowcarl72

im sorry boat1 but i dont think your numbers are anywhere near correct a lot of people have been throwing the number around but it doesnt make sense.... 115 separation would suck the water right in

here is where i get my specs from!

http://www.perfprotech.com/store/art...fications.aspx

im going to call merc and see what they say personally

morrowcarl72

im sorry boat1 i personally appologize i called merc and there specs are 224 224 with .300 lift but he had no seperation number fo me

jeffswav

Your wrong, higher numbers are less prone to reversion. Lower LSA numbers will suck in water.

jeffswav

All of this information about cams has been covered many times. You can do a search of this site and find all of this out. If specs are posted by RMbuilder or YoungPerformance you can take that as fact.

Gimme Fuel

The MEFI ECU's on these motor do not have the "learning" or "self tuning" ability like automobiles do. The fuel and spark curves are set. If you do any major mods, you will see little to no benefit unless you recalibrate your computer for those mods. Plus, you run the risk of damaging your engine if it gets thrown too far off. You can get the adjustable regulator to tune in fuel, but without an AFR meter (O2 sensor) in your exhaust, you are tuning blind or have to make high speed runs, shut down immediately, and try to read plugs.

The previous owner of my boat upgraded the exhaust to EMI with long runners and a Keith Eckert breather without a recal on the ECM......gained hardly anything (so he claims).

With changing the rocker ratios, the biggest increase you will see is just from going from stamped to roller rockers. That is usually around 14 (+/-) hp on dyno just from reducing friction. That little bit of added lift won't do much.

There is a rule of thumb to be considered when you are gonna build an engine. What ever you think you are going to spend......double it and that will be a more realistic final cost. There is nothing cheap about upgrading a BBC and especially a MAG EFI version.

There is not a single part on my 540 that I have not modified or am in the process of modifying. You are almost better to find a second block and piece together a whole separate motor and take your time on it if you want big power. That way you have your stock one as a back up to keep you on the water.

morrowcarl72

technically now that you mention it i could run a fuel pressure regulator like my buddy does on his turbo charged 318ci dart.... super simple it runs off of vacuum vs boost and they make them for na applications and a afr gauge isnt alot of work.... im going to do some more looking into this... i was also hit up by a guy on here from cmd marine (the power commander company) and they are dropping a piggy back system for factory merc efi this march at the la boat show and he sent me a bunch of info.... seems pretty easy and itsnt too costly