I have bounced around to several threads discussing how close the 25 is to the 35/36 as far as performance and speed. I for one believe that the 25 is able to keep up because these motors are strapped to beer car cans of a hull.

Simple formula:
F = M x A

F = horsepower (25, 35/36)
M = boat weight (big difference on smaller thinner hulls)
A = Acceleration (not exactly top end speed and performance, but close enough)

I believe that as soon as the so call "light hulls" get a few dents, the performance will fall off drastically. In the several threads, some have mentioned the speeds, others claim they could keep up in mud, marsh, sandy bottoms, etc. I was always told, "there is no replacement for displacement".

What will a 35 do on the .100 hull?

Isn't it similar to the comparison of stock v/s stage 1? I know that extra hp made a huge difference with my rig, especially with a load.

The 25's put out more than their rated power, the 35's put out less than their rated power.

Yes the 35 is probably better on bigger boats and/or carrying heavier loads and parts are readily available to make them even stronger, but stock for stock, 25 on a boat built for it, 35 on a boat built for it, the speed and load carrying seems to be very close.

The thread I was posting on was talking about the 27 kohler vs the 25 subaru. I don't think those two motors are comparable at all. I think the 25/35 comparison is worth looking at, but the 27's have never been known as runners or known for their outstanding ability to handle a load.

I had a 35hp mudbuddy surface drive and it beat the hell out the bottom of the .100 gauge boat I had it on. I ran a bunch of timber, most of the welds on the longitude bracing had hair line cracks in it. Hooks were a killer in performance for this setup.
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If you wanna compare the 25 to the 35 you should compare it to a 35 with efi bc the 25 with efi makes 28 hp. From what I heard the 36pd with efi has the same power as a 36 with a stage one with way better idle and exceleration. The 36pd with efi it suppose to pick up 3 to 4 extra mph also.

Wonder if pd is testing them and why they haven't made the switch yet? Subaru makes a vert shaft don't they?

Talking about the subaru's, not the briggs. They need to do something to compete for the smaller engine business. The kohlers are great engines. Well built and reliable, but they struggle, powerwise, in this application. On any frame you put them on...

I know they're working on efi for the big blocks...and no, voiding briggs warranty doesn't concern me that much.

35/36 has more torque. the 25 has a great torque curve with a more efficiant prop. In the thick ass mud, the 25 will bog down due to the lack of low end torque compared to the 35. That is not to say the 35 wont bog down either.....on the top end, its another story....these little 25's will scream at 4100 rpm. the efficiancy of the prop has the most to do with its speeds though.

the pd efi on a stock motor was running 30mph with 2 people in a 17x48 boat....

I know that, i'm an engineer. I was simply trying to show the difference that weight makes. If I would have written it the way its suppose to be (like yours), some on here wouldn't get it.

^^ exactly why I wrote it the way I did.