Swapping 135 bubble manifold into '74 Johnson 115 w/ flat manifold

[Roj115]

Hi Everyone,<br /><br />This is my first post in this forum. This topic has probably been discussed before but I wasn't able to find the exact answers I need using the search engine so I'm posting my questions and sorry if I'm raising questions that have already been answered before. <br /><br />I have a '74 Johnson 115 which is on a 16' ski boat. It is propped with a 15 pitch SST and makes 5500 rpm at full throttle which is right at the top of the prescribed operating range. We use it mainly for skiing and it runs great. It has great low end power and comes out of the hole like there's no tomorrow. I guess I should also mention that it was bored out five or six years ago and has oversized pistons. I think it was a 0.020" overbore, but I'm not exactly sure. I don't have access to the invoice right now. The engine only gets used a few weeks every year so it doesn't have that many hours on it since the rebuild.<br /><br />In '74 the 115 had the same bore & stroke as the 135s but the 135s had the bubble back (tuned exhaust) manifold and the 115s had the same flat manifold as the 85s had. I'm not entirely sure what the other differences were between the 115s and 135s were.<br /><br />It just so happens that I have a seized up '72 or '73 Evinrude or Johnson 135 which I bought as a parts motor. It looks virtually identical on the inside as my 115 except for the bubble back manifold.<br /><br />I'm wondering if there's anything to gain by taking the bubbleback manifold from the 135 parts motor and putting it into my 115 ? <br /><br />I'm also wondering if the 135 had bigger carbs than the 115 in those years or if they were just jetted differently ? Would there be anything to gain by swapping the carbs or jets over too ?<br /><br />Would I gain any extra power or performance by doing any of these things ? If so, would I be sacrificing low end power to get more high end power ?<br /><br />If I would gain some power by swapping the manifold and/or carbs over, would I likely have to go to a larger pitch prop to keep the rpms down to 5500 at full throttle ?<br /><br />Thanks,<br /><br />Roj

 

[jimmbo]

Re: Swapping 135 bubble manifold into '74 Johnson 115 w/ flat manifold

The carbs are the same between the 115 and the 135, so is the porting of the block. The only differences are the bubbleback cover, the exhaust manifold inside the bubbleback, the fillers that bolt to the block in the exhaust chamber. Adding these might require some gringing and milling of the block. The cylinder heads are a litle tighter too. Last but not least is the exhaust tube is also different. You will gain a few hp in the upper rpm ranges but will lose some bottom end grunt.

 

[DJ]

Re: Swapping 135 bubble manifold into '74 Johnson 115 w/ flat manifold

Roj115.<br /><br />Leave your 115 a 115.<br /><br />The 135 had a few, I mean few, extra ponies at the expense of reliability and runability. They didn't always idle well.<br /><br />You have a nice running, stump pulling, 115 now. Leave it that way, in my opinion.

 

[Roj115]

Re: Swapping 135 bubble manifold into '74 Johnson 115 w/ flat manifold

Ok, that's good information. So I guess you kind of have to rob Peter to pay Paul if you try to convert to a 135. I don't want to lose any low end power to get more at the top end so I will leave the exhaust plate, etc., as is.<br /><br />When you say the cylinder heads were a little tighter do you mean they shaved a bit to raise the compression ratio a bit ?<br /><br />If so, would there be much to gain by simply switching the heads over from the 135 ? We always get Premium fuel delivered so I'm not too worried about causing any pinging if I raise the compression ratio a little.<br /><br />Is there anything that can be done fairly cheaply and easily to optimize the performance and perhaps squeeze a couple more ponies out of that motor ? <br /><br />This year that motor turned 30 years old. This spring, after sitting in the boathouse for 10 months it fired and started within 1 second of turning the ignition key for the first time. Gotta like that ! It was rebuilt several years ago but still that's pretty damn good performance out of an old engine.

 

[walleyehed]

Re: Swapping 135 bubble manifold into '74 Johnson 115 w/ flat manifold

1973 135 heads will do some good things to the 115. These had about the best swirl pattern of all the years.<br />The bubbleback can be added as well as long as the spacer block is used from the 135. The problem with the BB is you may need to change jetting...Not something you want to mess with unless you do it everyday.<br />If you use the 135 heads, run only 91-93 octane and back the max timing off about 2 degrees to start with.<br />The first of the 135's (I think) was 1973, in 1972 the V4's were 92 cube insted of 99, so '72-'73 are not interchangable.<br /><br />EDIT: another note here...If you want more low-end "grunt", add a set of Boyesen reeds..The best money you could spend on after-market punch.

 

[Roj115]

Re: Swapping 135 bubble manifold into '74 Johnson 115 w/ flat manifold

Kenny,<br /><br />Thanks for all the great info !<br /><br />> 1973 135 heads will do some good things to the<br />> 115. These had about the best swirl pattern of<br />> all the years.<br /><br />Ok. I'll check and make sure my parts motor is a '73 and if so, I'll pull the heads off it.<br /><br />> The bubbleback can be added as well as long as <br />> the spacer block is used from the 135. <br /><br />So just the bubble back and spacer block and nothing else ? Leave the original exhaust manifold in place ?<br /><br />> The<br />> problem with the BB is you may need to change <br />> jetting...Not something you want to mess with <br />> unless you do it everyday.<br /><br />I've never fiddled much with the Johnson carbs but I run some old Volvos with SU carbs. How different can it be ? <br /><br />> If you use the 135 heads, run only 91-93 octane<br />> and back the max timing off about 2 degrees to<br />> start with.<br /><br />Ok. I've never fiddled with the timing on that motor and my Clymer manual is at the cabin where the boat is. What's involved in changing the timing ?<br /><br />> The first of the 135's (I think) was 1973, in <br />> 1972 the V4's were 92 cube insted of 99, so '72-<br />> '73 are not interchangable.<br /><br />What were they in '72 ? 125 HP ?<br /><br />> EDIT: another note here...If you want more low-<br />> end "grunt", add a set of Boyesen reeds..The <br />> best money you could spend on after-market<br />> punch. <br /><br />I see they're not that expensive but I have some questions about them:<br /><br />a) what kind of performance boost can one expect from them ?<br /><br />b) what's involved in installing them ? (again, I don't have my Clymer manual here)<br /><br />c) how long will they last ? Are they as durable as the original reed valves ?<br /><br />d) Would they be worth putting in my 9.9 Evinrude as well ? I use that motor for pulling kids on waterskis so a little more power would be nice.<br /><br />Also, is there anything I can do on the intake side to help the motor breathe a little easier ?

 

[walleyehed]

Re: Swapping 135 bubble manifold into '74 Johnson 115 w/ flat manifold

I wouldn't use reeds on the 9.9, but the 115 you will see hole-shot improve and mid-range is incredible..on top, "maybe" 100-150RPM gain.<br />the 1972 was the 125 and 92 cubes..<br />Timing is simple as long as you have the manual handy so you understand which screw is which and the direction to move it.<br />The spacer block on the 135 is different than the 115. If you take the bb off the 135, take the spacer plate and use it too.<br />You can use the 135 carbs, but you will have to "sync" the whole system.<br />The jets in the 135 carbs should be OK, although I would pull one out and see if it's larger than the jets in the 115...it should have like 58C or what-ever number on the end...58 is .058, so the larger the number, the larger the jet.<br />If it were me, I'd leave the 115 carbs on, put 2 sizes larger jets in, back timing off 2 degrees and add heads and BB with the spacer (adaptor) plate. The 115 was a well-suited engine in the V4 class, and had alot of power over-all. The 135 gained it on the top-end...It won't be like bolting on a V6 though....It "might" allow the use of one size more pitch.

 

[ledgefinder]

Re: Swapping 135 bubble manifold into '74 Johnson 115 w/ flat manifold

You want the motor as high as it will go on the transom, without losing water pressure or cavitating too much on the turns. This will make more of a difference than swapping over the 135 parts. <br /><br />As a rough starting point, set the motor so that the cavitation plate is about 3/4" above the bottom of the hull. Tilt the motor so that the plate is parallel with the keel line, or slightly tilted up (back of plate higher than front). I use a 4' straightedge held up against the keel to give me a reference line. Note that the OMCs are typically 21", rather than 20", from the transom to the cavitation plate. <br /><br />On many boats, the rough starting point ends up being the third set of holes down. On take off, the front of the boat first comes way up, then settles down as it gets on plane. Once the bow comes down, I get a little cavitation and have to back off the throttle a bit. Once the boat builds speed, and the water gets hard, I can go back to full throttle. Note then for skiing I want to run the motor one set of holes lower (cav plate just above bottom of boat) for stronger take off. The difference is top speed is around 400-500 rpm, between the two positions.

 

[jimmbo]

Re: Swapping 135 bubble manifold into '74 Johnson 115 w/ flat manifold

The 125 and 135 were 99.6 in block, the early 85hp and 100hp were 92.6 in blocks. Early 115s used a 96.1 in block, after 73 115s were 99.6 and in 79 the 85hp and 100hp were also 99.6 in blocks

 

[Roj115]

Re: Swapping 135 bubble manifold into '74 Johnson 115 w/ flat manifold

Thanks again for everyone's answers.<br /><br />I know the parts motor is a 135 and it's older than my 115 so it must be a '73 which is what the guy said when I bought it for spare parts.<br /><br />Kenny, if I make all the changes you're recommending except for the reed valves, where in the power range will I see the most improvement and will that improvement cost me some sort of cost in terms of how smoothly the engine idles and runs, etc ?<br /><br />Will adding the Boyesen reeds help compensate for any "roughness" caused by these other changes ?<br /><br />What's involved in installing the reed valves ? Is it a difficult job ?<br /><br />And if I do all this, is there something I can or should do to help the engine breathe easier in order to take full advantage of these improvements or is the standard air intake setup more than sufficient to cope with the demands of the improved motor ?<br /><br />One other thing...I haven't had to buy many parts since I bought the parts motor a few years ago and things have changed with OMC since then. Is it going to be difficult obtaining the head and backing plate gaskets, etc I'll need to do this job ?

 

[reeldutch]

Re: Swapping 135 bubble manifold into '74 Johnson 115 w/ flat manifold

dont get angry at me but i think you are doing a lot of work to gain 20 hp more if lucky.<br />and i think you will get dissapointed in the differense. because i dont think you will clearly notice.<br />if you want more power switch over to a looper or a v6.<br />but of course its a lot of fun to make small inprovements.<br />i just think you have to be realistic in what the motor will be capable of.<br /><br />good luck reeldutch

 

[Dhadley]

Re: Swapping 135 bubble manifold into '74 Johnson 115 w/ flat manifold

At 5500 you arent getting full potiental from your 115. You can do all the work mentioned above but at 5500 I doubt youll see much. <br /><br />When we build a V4 crossflow for skiing heres what we look for;<br />No matter if we use a 90/115 or 135/140 style block (yes there is a porting difference) we install the bubble back exhaust without the inner exhaust stuffers. Better exhaust flow.<br /><br />We use the 115 carbs. The smaller venturis allow a quicker acceleration. <br /><br />We use the 115 heads. They idle smoother.<br /><br />We use Boyesen reeds. Obvious advantages.<br /><br />We set the motor up at 6000-6200 (No skier but normal load -- driver and observer, fuel etc). Allows for great pulling power -- much easier on a skier.<br /><br />We use at least a Raker or Stiletto prop but prefer a Turbo for max efficiency. <br /><br />A jackplate (usually a manual) for dialing in the height (X dimension) and balance. <br /><br />Good luck!

 

[walleyehed]

Re: Swapping 135 bubble manifold into '74 Johnson 115 w/ flat manifold

Good to have ya back, DH...

 

[DJ]

Re: Swapping 135 bubble manifold into '74 Johnson 115 w/ flat manifold

Roj,<br /><br />You just heard from the OMC performance guru-Dhadley. Heed his advice.

 

[Roj115]

Re: Swapping 135 bubble manifold into '74 Johnson 115 w/ flat manifold

Ok, thanks for all the great advice.<br /><br />Just to clarify a few things:<br /><br />So you're saying I shouldn't switch to the '73 135 heads and just stick with my '74 115 heads for a smoother idle ?<br /><br />What gaskets am I going to have to buy if I replace the reed valves ? (My Clymer manual's at the cabin where the boat is so I can't read up on what's involved in changing out the reed valves.) <br /><br />I'll stick with the 115 Carbs as advised but will I need to change the jetting if I improve the exhaust flow by putting the bubble back on or will the current jetting work just fine ?<br /><br />My current tach is broken. Hasn't worked for years actually. What would be a decent low - mid priced tach to get ?<br /><br />Thanks again,<br /><br />Roj<br /><br />'74 Johnson 115<br />'77 Evinrude 9.9

 

[Dhadley]

Re: Swapping 135 bubble manifold into '74 Johnson 115 w/ flat manifold

We like the 115 heads for a ski boat (defined useage) because of the idle quality. Many times we can actually set the idle lower which is nice when getting the rope tight just before lift off. <br /><br />Like Kenny said, its very true that the 135 heads will improve power slightly -- especially over 6000 rpm -- but on a typical ski boat there may be some longer periods of idling. Especially if you are trying to teach someone to ski. However, when pulling 1 or 2 skiiers (or a couple of tubes) that puts a tremendous load on the motor. So were not just getting the boat on plane anymore. There is a point where too much compression hurts acceleration in certian rpm ranges under certian conditions.<br /><br />Changing the reeds will require 4 reed box gaskets, an intake gasket and 2 carb base gaskets. You may need 2 air silencer base gaskets if yours tear when you take it off.<br /><br />Any carb you use should be fine with the factory jets at these rpm's. Because of the age of the carbs we may have to rejet the idle circuit. The carbs are always calibrated at the factory for the fuel available at the time. Todays fuel runs a bit leaner than the fuel of the 70's so rejetting the idle circuit is not that unusual. You may not have to mess with them at all.<br /><br />Installing the better exhaust manifold improves the "breathing" on the motor. If the motor pulls in more air thru the venturi (increased rpms) it will also pull in more fuel. At these rpm's we dont get too concerned -- as long as you use the right fresh fuel and Champion plugs. Its all a matter of combustion temps.<br /><br />The Evin/John tachs are very very accurate. I would go for that rather than price. While you may not need the accuracy of the digital tach a standard factory tach will serve you well.<br /><br />Good luck!

 

[walleyehed]

Re: Swapping 135 bubble manifold into '74 Johnson 115 w/ flat manifold

Correct me if I'm wrong, DH, but I would recommend enrichment of the Idle circut if using boyesen reeds. For the 115, 5 sizes richer is per instructions.<br />A lean "sneeze" can break the fiber reeds at Idle.<br />If there is another way around this, Dhadley will know it.

 

[Dhadley]

Re: Swapping 135 bubble manifold into '74 Johnson 115 w/ flat manifold

Kenny, your correct. If the motor "sneezes" at idle it must be richened up. We have found some that do need it, some dont. To be on the safe side its probably a good idea. The worst case scenario is that it runs rich at idle but it wont burn the reed tips.