Evinrude 6HP To 8HP

[Dizz]

I have a 99 6 Hp Evinrude that had my local dealer order the stuff to make it 8HP.He ordered carb that came with a new ing plate under flywheel.It started&ran fine,but really could tell little diff in power.I asked&he looked in his book and the rest was the same.Have any of you made this change on this motor?I know on the 9.9 to 15 up grade you also have to change something in the exhalst.
Regards,Dizz

 

[Barnacle_Bill]

Re: Evinrude 6HP To 8HP

I wouldn't think you would notice much difference in 2HP.

 

[WillyBWright]

Re: Evinrude 6HP To 8HP

I'll bet you spent a few hundred for two Hp and little to no noticable improvement. Hardly seems worth it to me.

Did you also get the 8Hp stickers for the hood to make the convesion legit?

 

[Dizz]

Re: Evinrude 6HP To 8HP

2HP would be quite a hike I thought.That`s over 30% increase.Should be likegoing from 100 to over 130HP in your Fatboy,Hey??
No change in decal`s,yet.
Regards,Dizz

 

[CATransplant]

Re: Evinrude 6HP To 8HP

Could be, too, that the 8hp uses a prop with a higher pitch, since it now has a couple more horsepower to spin it. Did you check that?

At the same RPM, the same prop would produce the same speed. Unless the 8 hp runs at a higher RPM, you accomplish nothing. Check the props.

 

[steelespike]

Re: Evinrude 6HP To 8HP

My 89 aftermarket ser manual indicate 500 more max rpm. 6 is 4,500 to 5,500 8 is 5,000 to 6,000.In this older book the 8s reeds have 3 retaining screws instead of 2. The 6,7.5 and 8 are all 10 cu.in in my book.
With a 30% increase I have to wonder if a little porting may have been done.

 

[Dizz]

Re: Evinrude 6HP To 8HP

The book showed the same prob.It`s geared high enough,just takes time to build up RPM.You can hear the larger carb,just very little HP increase.you may be on to something with the porting.Thanks,Dizz

 

[F_R]

Re: Evinrude 6HP To 8HP

If the part number for the cylinder & crankcase assy is the same between the two motors the part is the same, porting and all. I haven't taken the time to look it up. An 8 horsepower will run at a higher RPM with the same prop and load because it has more power to develop the higher RPM, and therefor goes faster.

 

[Chinewalker]

Re: Evinrude 6HP To 8HP

The 1980s 6s and 8s had different crankcases and intakes. The 6 had two reeds per cylinder - the 8 had three, and there was no converting without swapping motor blocks. Not sure if the change held true into the 1990s models...
- Scott

 

[Dizz]

Re: Evinrude 6HP To 8HP

Next time I`m at the dealer,I`ll look it up.Thanks,Dizz

 

[R.Johnson]

Re: Evinrude 6HP To 8HP

If you are the builder of these little engine's, the biggest horse power gain is with a typewriter.