200hp carbs on 1989 150

[99yam40]

they list a range of WOT RPM
so a motor that lists 4500 to 5500 could reach max HP at 4500

[BQUICK]

I talked to Hydro Tech and they said for some reason only the PROV 150 and later PROV 200 had the choked down exhaust. He said it limits their potential but said they did get 200 out of the same 2.6 block despite the choke. He said the tiny venturis (24 vs 32) are more of a factor though.

Unless freshwater probably 4 outta 5 manifold bolts are going to snap....and that's if you can get the powerhead off. No thanks.....

[99yam40]

How much of the 50hp difference do you think will be gained by putting 200hp carbs on? The 150 is slightly lower compression 5.6 vs 5.9 and possible exhaust tuner difference but going from 24mm carbs to 32mm would have to make a top end hp gain, I would think....

Reeds and intake manifold are same part numbers.

Exhaust manifold is main difference....any way to derestrict it without removing powerhead?

Maybe this is wrong forum....

so is this motor you have a PROV?

and how did they up the compression ratio

[Masonmobilemarine]

Sorry, yes I was talking about a 4 stroke.

I don't remember the exact RPM number, it may have been 5k. But I do distinctly remember it was a bit before WOT. WOT was definitely not the max HP. And realistically that does make sense. If you look at ANY Dyno chart out there, there is a drop in hp (and torque) at the end. It's distinctly called the "HP curve".

Dyno was at the prop shaft running in a run tank.

There were certain rpm ranges were it barely made 135hp and then up to 150, to 175ish (for a very short RPM range) , back down to I think around 145-150ish at WOT.

I really don't care if you believe me or not. I know what my experience is and Im just sharing it to the group.

[BQUICK]

Mine is PROV 150 all stock......5.6 compression vs 200s 5.9. It runs 28 deg timing vs 22 deg for the 200. Yamaha was playing around with these motors....
Doesn't always seem to make sense....why lower compression then run more timing? Seems like a wash....

[99yam40]

maybe the higher compression makes the fuel/air charge burn faster

[Masonmobilemarine]

maybe the higher compression makes the fuel/air charge burn faster

probably. More compression more potential for kinetic energy.

[zenoahphobic]

Sorry, yes I was talking about a 4 stroke.

I don't remember the exact RPM number, it may have been 5k. But I do distinctly remember it was a bit before WOT. WOT was definitely not the max HP. And realistically that does make sense. If you look at ANY Dyno chart out there, there is a drop in hp (and torque) at the end. It's distinctly called the "HP curve".

Dyno was at the prop shaft running in a run tank.

There were certain rpm ranges were it barely made 135hp and then up to 150, to 175ish (for a very short RPM range) , back down to I think around 145-150ish at WOT.

I really don't care if you believe me or not. I know what my experience is and Im just sharing it to the group.

It's not a question of believing you. We are curious and trying to understand what you are saying.
I take it in your second last paragraph the rpm ranges are within the manufacturers recommended WOT range you found the hp wavering with a peak not at the maximum. I see it now. It is very typical when seeing graphic representation to see all manner of bumps, spikes and dips (like a rugged mountain range). This does not mean it actually can be felt , as you implied the 175 figure was for a very short range.

That hp drop off on a dyno is when the practical maximum rpm has been reached, not necessarily WOT. An outboard test you would not rev it limitlessly to see what the max hp may be, you are only revving it to the manufacturer set limit; so it is interesting that you observed that hp drop off you presume at that set limit revs.

I say you presume that it was going to continue to drop, but you did not continue to rev it past 5000 (not sure which figure you now are using).

I therefore find it hard to see how anyone can design an engine hp and immediate drop off of that hp, to a specified (arbitrary) rpm range . Seeing the internal friction would not be significant at 5000rpm to cause this rapid drop off (I think that would be closer to 8000rpm, it can only come from the exhaust tuning, a very radical tuning that will also severely limit the horsepower at the same time earlier prior to these revs. I don't believe so in these outboards, the exhaust tuning must be broader than that otherwise you have this for example, getting a boat to get up on, and stay on the plane difficulties.

[Masonmobilemarine]

We ran the dynos around 5500 with a few shots up to 6 momentarily.

It would hit about 175 around 4500, and then settle into 150ish at the max rpm rpm around 5500. Im assuming that's why it's rated a 150 and not a 175.

[BQUICK]

Well I finally got around to putting the big 200 carbs on and it definitely helped despite the small exhaust tuner. Went from 67 mph to 70. Rpms are up to 5700 now so I could run 1-2 in more pitch. I suspect it would make best power at 5300-5500 due to the small exhaust Rather than 5800-6000 with better exhaust.
So if you are looking for speed or you are in need of carbs for a 150 I wouldn't hesitate to put 200 carbs on. Downside is I'm sure fuel consumption will be up going from 24 to 32mm carbs. (127 vs 146 main jets)