Tips for max HP from L6 engines

Im wondering if there is any modifications that can be used to get max horsepower from Merc L6 engines...Porting, polishing, reed block tricks etc...Car engine builders are always finding hidden horsepower, granted these are 4 stroke engines, but it just seems to me there must be some tricks for getting more HP out of these 2 stroke motors...Any ideas ?

Re: Tips for max HP from L6 engines

What year?? Inlines are hard to hop up due to intake design and limited CFM of reed block and reeds. Boat weight determines what you can do and get away with. On a 400-600 lbs hull I would modify it to 1500XS spec's. This requires intake/exhaust work(ports and tuner),replacing with "banjo" style reeds and blocks(more flow) or 10/10 block is not equipped,thinning reed block,high dome pistons(compression),correct carbs,timing increase,reedstop setting,a XR4 or XR6 lower unit(gear ratio XR4=1.78 XR6=1.87 stock =2.1) Below are pics of stock reeds (1st pic) banjo's(2nd pic) and 10/10 reed block and 10/8 reed block.(10/8 has 10 on one side and 8 on other)

Re: Tips for max HP from L6 engines

Very interesting...Im working on two different motors, a '75 1150 and a '78 1400 (primarily the 1400) First, should i be using high dome or low dome pistons...this 1400 came with low domes...will the high domes contribute more HP....this 1400 also has the 10-10 reed blocks w/ the 2 piece reed valves as pictured in your 2nd pic (are these the Banjo's ?)...and how can you safely increase the timing on these motors without damaging the pistons due to cylinder temps..? Good start...Thanks !

Re: Tips for max HP from L6 engines

Your 140 should be a power port block/piston and is basically a 150 rerated to 140 and in 1982 rated to 115. It could have the ADI ignition as in middle of 1978 was electronics change. If you build it like a 1500XS it will put out about 155 hp at the crank and 125-130 at prop, get to radical on a heavy hull and it wont plane out as torque builds about 3000 rpm.I build all my personal and customer inlines with high domes as inlines love the compression, run 87 octane(cooler) up main jets .002 and WOT timing 1 degree. 80% of the piston failures to #1 are cooling related followed by trigger failure(belt driven) due to incorrect set-up,damage by rotten wiring, damage by removing battery cables while running or bad connections. You rarely see a piston failure on a ADI motor from a trigger,its usually a switch box or bia's failure in one or both boxes. If i get a motor in with damaged piston and cannot find a A HA cause it gets boxes tested and replaced if needed. I have had too many DIY customers and dealers rebuild a engine and not find out the cause of failure and have it fail again within a few months, usually on a EFI it the ECU and all other it the electronics. A OMC can double fire due to coil design as it uses a powdered core and thats why the large washers that no one reinstalls are there. Overtightening cracks the core and can cause a double fire at plug or overspike back into pack at the time of discharge..

Re: Tips for max HP from L6 engines

Check out a thread from a few months ago titled Frankenmerc. Very detailed thread on a complete rebuild of an older Merc including a lot of performance upgrades.

Re: Tips for max HP from L6 engines

That threads for a V-6 and this is for a inline, still a pretty good link for trying to hop up a stock engine, will get ya about 15 hp extra..

Re: Tips for max HP from L6 engines

Thanks...my 140 is NOT the ADI ignition...and it IS the power ported block...When you speak of Trigger failure causing problems with the #1 pistons, with mine being the distributor type ignition could there still be trigger problems...i thought with this ignition set up either the trigger works on all cylinders or it doesn't work at all...isn't that a correct statement..

Re: Tips for max HP from L6 engines

Usually piston erosion (eyebrow melted) on cylinder #1 & #3 is due to igniton problem mainly the trigger. Overheating/low flow will scuff and gall the pistons with aluminum transfering to liner. Just because it fires dont mean its good... what failed on yours???

Re: Tips for max HP from L6 engines

Well, faztbullet...Im not 100% sure what happen to it...I inherited this motor, it had been sitting outside for years and years (10 +) without having been fogged or anything...I had it at the lake doing the link an sync and it started running rough...i shut it down and was hand spinning it and i could here the pistons scuffing against the cylinder walls...brought it home tore it down and observed that almost all the pistons had started scuffing the cylinder sleeve...boy i shut it down just in time too as the scuffing is very light and can be cleaned up...I do believe the seals in the lower end cap failed because at one point i seen a lot of black/aluminum looking fluid run out the LU...like the block was emptying a bunch of crap that had built up over the years...there is a light coat of rust on all the internal components so i also believe the rust got to the needles in the pistonpin end...thing just sat too long...i should have tore it down before i ever tried to start it...i would still have six good pistons, now i have none...LOL...!

Re: Tips for max HP from L6 engines

Improper storage and dirt daubers make a mess in a engine. Had a 200 EFI this summer that dirt dabbers built nest on throttle plate, it dumped into intake taking out #4,5 & 6Mike the cylinders as they just may need a good hone to clean up and you can glass bead the crank to clean up. When I polish a crank I inspect all the journals and if they are good,I glass bead it and polish journals.

Re: Tips for max HP from L6 engines

Yeah, i think there was just a bunch of trash in the motor...rust, bug stuff, who knows what...im sure the cylinder walls are ok, i gently sanded the aluminum deposits from the sleeve and inserted a NEW piston ring into each cylinder, then i put a flashlight behind it and looked for light between the ring and cylinder wall and seen no light. Im going to hone it with a 320 grit ball hone...Would that be the correct grit to use or do you recommend something different ? The crank has one spot i do not like...it is a "pit" mark on the lower main and it's PARALLEL with the needles...im not sure if it will clean up at .001...but i sure dont want that little "ditch" in there...I have a good 1975 1150 crank i willl use if the original doesn't clean up...What do you think..?

Re: Tips for max HP from L6 engines

monk-monk said:

Yeah, i think there was just a bunch of trash in the motor...rust, bug stuff, who knows what...im sure the cylinder walls are ok, i gently sanded the aluminum deposits from the sleeve and inserted a NEW piston ring into each cylinder, then i put a flashlight behind it and looked for light between the ring and cylinder wall and seen no light. Im going to hone it with a 320 grit ball hone...Would that be the correct grit to use or do you recommend something different ? The crank has one spot i do not like...it is a "pit" mark on the lower main and it's PARALLEL with the needles...im not sure if it will clean up at .001...but i sure dont want that little "ditch" in there...I have a good 1975 1150 crank i willl use if the original doesn't clean up...What do you think..?

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Monk Monk, the pit will not "clean up" the journal surface is hardened and if you were to remove .001 from the journal you may or may not have the correct hardness. Remember, its only surface hardened. If you have another crank that is not pitted you will be further ahead to go with it.

Re: Tips for max HP from L6 engines

I doubt that i use the original crank...i know it is a hardened surface and only .001 can be removed...but i still don't think it will clean up, plus like i said, it is a little ditch parrallel with the needles so thats really bad...it took a 10X lighted magnifier to see this mark! NOW, let me ask this: what about just wee-tiny circular pits on a crank journal (only visible with a magnifier)...nothing longitudinal with the needles, but just wee tiny pits...what is acceptable...

Re: Tips for max HP from L6 engines

Tiny pits are acceptable and get a rigid hone as a ball will follow all uneven contours in cylinder. A rigid hone like a Sunnen will show the low spots in liners in just a few seconds, a ball hone is used to break the glaze and removes minimal material..

Re: Tips for max HP from L6 engines

Well, thats all i really want to do is "break the glaze" on these cylinders to establish a new surface for the rings to seat to...as i stated previously, i put a new ring down in these cylinders and see no out of roundness at all...I wish i could afford a new sunnen hone, but if i had to go that route i would probably be better off just shipping the block to a marine machine shop and let them do it...Im still taking all this "in"....weighing my options...i really appreciate the advice...

Re: Tips for max HP from L6 engines

At least measure around the ports as this is where most of the wear takes place and inspect reed block labryth seals ...