Results of boring

[bubbakat]

My brother has a 1993 70 h/p evenrude and he had it rebuilt. The wrench either bored it 10 or 20 over can some one tell me in close proximity what the h/p would be on both bore sizes.<br />Had all three bored due to heat damage.

 

[Solittle]

Re: Results of boring

70 h/p

 

[ZmOz]

Re: Results of boring

Boring doesn't increase HP...although the engine will probably seem stronger, because it's like new...

 

[walleyehed]

Re: Results of boring

Bubbakat, I don't think (as listed above) you will notice a HP gain, but should run more like a new engine.<br />Your Cubic inches go up ever so slightly but remember, you still have the same ports, carbs, exhaust and jets.<br />Remember as well, .010 or .020 is only taking .005 or .010 off the side, all the way around. 1/6 of the distance of a gapped spark plug....not much

 

[bubbakat]

Re: Results of boring

Guys thanks for opening my eyes. Man I must have had a brain fart when I posted this question <br /><br />Heck I wasn't even thinking . Thanks guys for posting. You are right it does seem larger but I was comparing to when it ran lousy.<br />Oh well another day in the life of information.

 

[walleyehed]

Re: Results of boring

My wife tells me these are "age related" issues..

 

[Terry H]

Re: Results of boring

I thought that was a trick question...

 

[LubeDude]

Re: Results of boring

Come on guys, you all know that his new HP figure will be about 70.0000185, why pop his bubble??? Sorry though, not enough for the seat of the pants Dyno to register, The SPD needs at least 1 HP gain to register.

 

[Forktail]

Re: Results of boring

Actually boring can increase the size of the ports on some cylinders. And it will give a seat-of-the-pants power increase in some cases, as there can be a corellation between displacement and HP.<br /><br />I recommend jetting up a size or two after over-sizing your cylinders. More displacement has the potential for a larger air intake charge. Without more fuel to go along with the greater air charge, you may get a lean condition.

 

[walleyehed]

Re: Results of boring

The intake ports on the tripples aren't ramped Through the sleeve for just that reason-they will stay the same size (for the most part) clear through max over-bore. Yea, I know, they "grow side to side".<br />OMC recommended a .001 jet change at .030, and above, only if plug color showed a lean condition.<br />I know you are the engineer, but I also understand the low pressure area thru the venturi, with the same carb, enlarging the displacement creates an even higher volume of air thru the venturi, pulling "some" extra fuel as well.