took my flat bottom boat out with the stock tune and only 13-16 degrees of timing it turned only 4000rpm then bumped it up to 21-25 in WOT area and picked up some rpm to 4500 rpm whats a safe rule of thumb on the L29 heads?? I know regular bbc heads like 36 degrees or so the engine only runs at 160 degrees
On local pump gas 32* is as far as I get gains with. You upgrade the cam/springs? Truck engines dont rev much past 4500 usually, weak springs.
Its an actual mercruiser motor so its a mercruiser marine hyd roller with springs already it is larger than a truck cam. Its abt the same size as a 70's 454 LS5 cam. It does still have a heavy marine cast iron L29 truck intake manifold im sure thats alomost past its limits. Eventually ill swap to a single plane with an elbowOriginally Posted by mecanicman
Marine tunes are notoriously rich. Not sure why... maybe to keep exhaust or cyl head temps low??? More timing possible when mixture doesn't burn as well. I like to lean 'em out some to improve performance.
all that is changing now.
if you had a car that ran nice and cold, but its main operating spec was climbing a hill while towing a trailer for 4 hours at full throttle and emissions were not a concern... that's how you'd tune it too. like a big RV. a bit rich, and conservative timing.
the new marine inboards being sold are mandated to have cats, even with wet exhaust, and they are (afaik) mandated to have NB o2 sensors aiming for stoich during cruise conditions.
NB o2 in a wet exhaust system is a nightmare, no matter which part of the pipe you put it in, you really need to build a trap system for it so it doesnt get soaked. honda did that with their outboards, and so did some of the yamaha 2-stroke stuff, and they were always the first thing to die, even with elaborate systems to avoid just pouring salt water over them. scary stuff, but good for a skiboat, once its on plane, it's pretty efficient, so stoich would be a good thing.
im not even sure what they've done to mefi controllers to deal with it. we aren't getting stuck with them in canada until next year, but im curious to see how they figured 'er out. increases the price of a new boat by a couple grand apparently, since the cat plumbing is expensive stuff.
I have over the transom headers and just shut the water off when I use my innovate wb O2 sensor clamp I have fuel dialed in pretty good so far
MEFI was designed to use NB O2 input since MEFI 1. Big money "upgrade" to have AS&M do a reprogram and add one wire to harness...
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