115 head swap will it interchange??

[dpg5]

I have a 98 evinrude 115 spl and was wondering if anyone knew if a set of 1970 115 evinrude heads would interchange. The next question are these older heads a smaller cc ? Would they add compression? Thanks for any info.

 

[Dhadley]

Re: 115 head swap will it interchange??

What are you wanting to accomplish?

 

[dpg5]

Re: 115 head swap will it interchange??

My current compression range is 110 to 115 psi on all cylinders. WOT rpm is 5600 with a 13 3/4 by 15 prop. Looking to add rpm and top speed. While your here, I saw a old reply of yours about milling out the wall on the intake passages would this help me also.

 

[Dhadley]

Re: 115 head swap will it interchange??

What kind of boat are we talking about?

 

[dpg5]

Re: 115 head swap will it interchange??

Somehow I knew you were going to ask that, now comes the cross-roads if you will ever reply. It is a 1998 20' tri-log pontoon. I know it isn't a speed boat and wasn't meant to be but it is a great fishing platform. Currently runs 28mph on gps. Would be happy with 6000-6200 rpm from same prop, I think this would put me over 30mph.

 

[Dhadley]

Re: 115 head swap will it interchange??

A tri-toon. OK. What brand/style prop are you running now?

 

[dpg5]

Re: 115 head swap will it interchange??

a aluminum hustler, by far not the best or may<br />not even be good but they are cheap to replace. Here on the Mississippi we hit alot of logs and stuff. Messed up two stainless and said the heck with high dollar props. Do I need to go back to stainless. This experince was with a smaller motor haven't tried stainless with this setup.

 

[Dhadley]

Re: 115 head swap will it interchange??

Oh yeah. I remember the OMC guys telling me about the logs and debris when they ran Mike Reagans boat there. They sheared lower units completely off. <br /><br />You're right about both points. The aluminum prop isnt the best for speed but its certianly less expensive to replace. A stainless will carry the boat better and will have more bite. Especially something like a Stiletto. The Turbo has a bit more technology but it may not make a whole lot of difference here.<br /><br />Have you tried playing with your X dimension? If not try raising it amd see what happens. Your rpm is OK but you could really use some more. If you raise the motor and the prop cavatates, you can add some cup and/or extend the cup. Raising the motor should increase your rpms and give you more speed (less drag). <br /><br />Keep us posted!

 

[dpg5]

Re: 115 head swap will it interchange??

I have moved this motor all over and it is in the best postion I could find. A compromise between blowing out the prop on a turn and straight line rpm.

 

[Dhadley]

Re: 115 head swap will it interchange??

When it was on the verge of blowing out, what was the top rpm?

 

[dpg5]

Re: 115 head swap will it interchange??

Not sure I can answer that with a exact number. I did several "test runs" this summer and didn't pay alot of attention to that, just new when it blew out eaisly I had to go down with the motor. I do know that when turning hard at the current motor height it does bog down the motor to around 5100 to 5300 rpm. I put a hydrofoil (stingray)on the lower unit and this helped some with blow out and alot with torque steer.

 

[Dhadley]

Re: 115 head swap will it interchange??

When its on the verge of blowing out you can, as you did, lower the motor slightly or add more bite to the prop and retain the higher X dimension. The Stingray acted as expected to help the prop get slightly more water.

 

[dpg5]

Re: 115 head swap will it interchange??

Any opinion on the different heads or on the open plenum intake????

 

[WoodsJ]

Re: 115 head swap will it interchange??

DPG5,<br />I know this is not much help, I think a jack plate would get the speed you want out of the boat. Just a curious question. It seems you are willing to spend a bit of money to gain 2-3 mph, why not sell that motor and buy a used 130-150 in good shape?

 

[ledgefinder]

Re: 115 head swap will it interchange??

Have you tried a 13" pitch prop? No-slip speed would be 37mph @6000 rpm. <br /><br />A 13" would probably help a bit, but in general sounds like you're near the limit of what you can get out of it as is. Try mounting that bubbleback on a 15 footer (with "85hp" cowling) if you need to move faster...

 

[dpg5]

Re: 115 head swap will it interchange??

I understand what everybody is saying about a bigger motor or smaller boat. Its not always the kill but the thrill of the chase. I had not thought about going any lower in pitch. I figured I would just loose top end, wouldn't hurt to try.

 

[G DANE]

Re: 115 head swap will it interchange??

I understand your question isnt about changing motor or boat,but about improving your speed with what you got. 5600 rpm with your 15" and 15% slip should normally give you 34 MPH. I calculated your slip to 36 %. If I did it correct, maybe it would be a good idea to borrow a 13" prop to try.<br />If you are able to reduce your slip to - let say 20%, it should give you 30 MHP at 6000. But depending on less slip. I think 36 % slip is much, but not sure if I calculate it right.

 

[dpg5]

Re: 115 head swap will it interchange??

Never did hear from anyone it these older heads would fit and if they have a smaller combustion chamber??