omc v-4 motorstein

[SHO-OFF]

I've got a 1987 90hp johnrude, the powerhead took a ****. I've found a new 87 power head and I was wondering if anyone could help with improvements I sould do while the powerhead is off? I've got an old 135hp, for the bubble, heads, etc... also I've heard of cutting the exhuast tuner. Any input would be greatly appreciated!

The motor is on a small lightweight 14 foot boat, if that helps.

[Greg Moss]

What 87 do you have? There are several things that you can do to increase the performance of the cross-v OMC. First to use the bubble you need to make sure the block you have has the bosses cast in to it for the filler blocks. If not you will not be able to use the bubble. If it has the bosses you will has to drill and tap them for the blocks. Then you have to machine the block for the exhuast at the bottom of the block. Square the ports and scallop the pistons and the bottom of the cylinders helps alot. Install boyesen reeds and if you can find a set of 1 3/8" carbs. If the carbs come of a v-6 you will have to change the throttle shafts. Order an ehuast snout from Bob's Machine and install it, the lower unit is small and restricts the exhuast to much to run it all throught the prop. This should give you a substancial increase in power and performance. Greg

I did all those to an 85hp (except the snout). Save yourself the hassle, its sitting on a stand in my shop waiting for a good home; http://briefcase.yahoo.com/bllkmlmarine

It took a while to get the low speed jetting/timing set just right with the reeds. But its perfect now, idles better than most kickers. It has the 140 heads, 1 3/8 carbs, bigger 140 ports with all the machine work done to the back that Greg described. All OMC new coils, power packs and timing base as well. Yours for 2k. Awesome power for the weight!

-bll

[Rickracer]

That sounds like a pretty good deal to me. Between man-hours and parts, you can tie up a whole lot more doing up a strong V-4. I have an old 135 X-flow that can turn over 8000, but it took me about 5 years of good advise, spare time tinkering and lots of and trial and error to get it there.

[Greg Moss]

We have one that was on the back of a 14 foot Laser. Let me tell you it would fly. I would imagine that it would run 90 or a little better. best running boat witha v-4 I had ever seen. Steering cable broke and the boat flipped have to do some fiberglass work on it now but the motor is still awsome. The snout not only lets the motor breath better but the sound of that little motor cranking on is bad ass.

No doubt! With the paint and graphics I have about 4k in it. 50% loss/depreciation, that sounds about right.

Nice thing about this motor is that if you decide to take the power head down to try bigger/higher ports or tighter heads, all the bolts were replaced with stainless and anti- seize used where the stock bolts usually get stuck.

-bll

14 ft laser huh!?! I'm searching the web as we speak ;)

I thought about doing just that! But this would make my 3rd boat and that means that neither of them would actually see water! hahahahahaha :)

-bll

[tunnel dorc]

Do all v4's have power trim, if not whats the weight difference. What is the best motor to start with to modify, how much hp (prop shaft) can be attained safely, at what rpm? Thanks !!

[BarryStrawn]

According to the '78 Johnson service manual, a manual trim 20" 85 & 115 weigh 292lb and the 140 is 296lb. Power trim and tilt 20" 85 & 115 weigh 312lb and the 140 is 318lb. Don't know why the 85 & 115 gained 20lb and the 140 gained 22lb.