Mercury 115hp inline six port map/ power port dimensions

**janihei** · 07-03-2016, 02:50 PM

Hello, Want to squeeze some power from 1984 90hp block, is the power ports only difference what comes to the port timing between 90hp and 115hp engines.

**baldad45** · 07-03-2016, 06:45 PM

No, the intake and exhaust ports are both larger and higher . If you ported your late 90 to 1972 140 specs you could expect to see 105- 110 propshaft horsepower but this would be a major undertaking and a little too high on the exhaust porting would kill your low end power .Easier to find a old 150 or newer 115 powerported block and rebuild that . Glen

**janihei** · 07-04-2016, 02:39 AM

Ok, where can i find older 140hp specs? Low end power loss is not problem the engine is coming to light weight tunnel hull..

**milkdud** · 07-04-2016, 09:03 PM

Id start with a 140 ADI or 115 ADI to begin with and save the work.

Several options on eBay right now. None of these are mine.

115 http://www.ebay.com/itm/Mercury-Mari...JXazWW&vxp=mtr

140 http://www.ebay.com/itm/1980-Mercury...FWIWuA&vxp=mtr

The 115 needs to have the power port cut out in the block. The one I posted should have it. I believe 1984ish-1988 115's all had the power port slot.

The late 115 and the ADI 140 are basically the same motor and they are basically the same as an old 1500 with newer electronics and derated sticker hp.

**milkdud** · 07-09-2016, 08:33 AM

So what did you decide to do?

**baldad45** · 07-09-2016, 08:35 PM

For your application , if you do the porting you can open up the intake ports to the top of the opening and widen the ports towwords the center leaving good rounded radius in the center . On the exhaust you can open it up to the cast ports size again leaving rounded corners . This should really let your 90 catch soom revs , of course you;ll have to richen up your main jets for higher revs . the top end will be the easiest to tune however the bottom end will test your patiece .If you have trouble getting on plane the engine will load up with too much fuel and refuse too rev up . small adjustments in the idle needles until you can accelerate cleanly. I have a older 150 ported this way and if the timing and carbs are set right it responds good on the bottom , but it has to be just right or you'll end up pushing a lot of water at 2500 rpm , once over the top it will have great power . I'm running the moded 150 on a 14' cobra and 7000 comes real quick . If you need any help you can PM me on here, Glen

**janihei** · 07-10-2016, 02:20 AM

Dont know yet, i just dismantled my 90hp powerhead for inspection, cyl-3 piston is ruined by detonation and crank shaft splines are gone.. I am afraid to buy those powerheads without seeing and tax/shipping to Finland triple the price.. I have been wondering how fingerports would work in this block with 140hp port timing?

**janihei** · 07-10-2016, 02:21 AM

Thanks Glen, How about the tuner?

**baldad45** · 07-10-2016, 08:04 AM

I don't think there's much to gain at the tuner, the old 150 supercedes to the one you have , if you can find an old tuner from a pre 80's 115 or 150 to compare, it may be better suited to higher RPM . i think some of the later tuners may have been aimed at better low end power . Finger ports were used in the later T2X and the 650X-700X ,But that is a much more involed task , stiick to finding a good crankshaft , porting your present block , hone and rering , plus find a new piston. You could put older high dome pistons in it, but you need to fix the detonation problem 1st. Were you trying to turn a prop with too much pitch and lugged it , what octane fuel can you get . These engines will not tollerate a lot of lugging or too much timing advance ,better to overrev a little . Glen

**janihei** · 07-10-2016, 09:23 AM

OK, i have decided to port my current block and use it. i have been told that later 90hp motors have high compression pistons and 115hp has the low copression power port piston..how about machining finger ports to same line with the c-shape combustion chamber ends, from the level of transfer port top to all the way down..

**janihei** · 07-10-2016, 10:21 AM

Looking for piston with casting number: 776-8895

**baldad45** · 07-10-2016, 10:44 AM

I found the part #776- 8899A3 , if you private message me your email I can tell you where you can order a new piston for $ 33US also i'll send you the factory finger porting details for the T2X .

**janihei** · 07-11-2016, 09:27 AM

I was holding the front half of the block in my hands today and had crazy idea to machine 6 injector seat to it. I am just wondering how reeds will work if there is only air flowing thru them

**Mark75H** · 07-11-2016, 09:46 PM

The reeds would tolerate it, but flow may be reduced ... evaporating fuel behind the carb venturi cools the air potentially creating greater pressure differential between the reed cage and crankcase vs ambient.

You would not be the first to attempt injection on an inline, but if you could get it to work without ruining several blocks in the attempt, you would be the first.

To do a clean porting job with a milling machine may require making a special tool for the cutting; its a long reach into the bores. Keeping a hand file job straight on all 12 ports is extremely tedious and virtually impossible.

**janihei** · 07-11-2016, 11:12 PM

One choice is to use motorbike throttle bodies with injector seats, and do it with 3 injectors.. dont know if the semi sequential ECU be enough for this kind of combo..