Finding torque specs for I/O engines

[KD4UPL]

I just test drove a 25' Four Wins with a VP 5.7GSi. This is supposed to be 280 HP I think. The boat felt pretty slow coming up on plane with only 4 adults and half a tank of fuel. I know the GXI is supposed to be 320 HP but I've heard that both engines have about the same torque and thus the GXI really doesn't have any better hole shot. I'm set to test drive a 23' Rinker next weekend with a Merc 350 Mag. It's rated 300 HP but I have no idea how it's torque compares to a VP engine. The there's the Merc 6.2L at 320 HP. I would have to assume this larger engine has more torque than the 5.7L GXI even though they both make the same HP. Or, maybe I'm wrong. Are the torque specs even available for these engines? How much difference that really make in the hole shot of a boat. I'm assuming that HP gets me speed and torque gets me hole shot. Maybe I'm wrong.
I really want a big block but they are hard to find and even harder to afford. Is it just not realistic to expect a 23 to 25' boat with a bunch of adults on board to perform well without a big block? Which of the engiens I listed above should give the best hole shot?
By the way, I'm only even looking at boats with dual props. We take a lot of people along boating, normally 10 or more people. Often 4 adults and 6 little kids. We don't go fast, just lots of tow sports in the 30 MPH range and some cruising around at roughly minimum planning speed.

 

[KD4UPL]

In reading back over my post I don't think my question is very clear.
Am I correct that torque is more important for hole shot than HP?
If so, I need to find out what engines has more torque. How do I do that since the manufacturers don't list it?

 

[Scott Danforth]

If you dont care about speed, only towing, use a prop for your needs. A V6 with a 13 pitch prop will out hole-shot a big block with a 25 pitch prop.

torque and the shape of the torque curve is what determines pulling capabilities of the motor. Gear ratio and prop pitch determine how the torque is delivered to the water as thrust

 

[HT32BSX115]

I just test drove a 25' Four Wins with a VP 5.7GSi. This is supposed to be 280 HP I think. The boat felt pretty slow coming up on plane with only 4 adults and half a tank of fuel.------------------I'm assuming that HP gets me speed and torque gets me hole shot. Maybe I'm wrong.

There's always an argument about torque vs HP. (but there's only a mathematical relationship between the two......this means, on a Dyno, you get 1 and you can calculate the other.

None of it really means much because neither Mercruiser, VP, or OMC really mentioned torque in their specs and nowadays, Mercruiser and VP ONLY rate PROP HP.

And for our purposes it's the only thing we're going to need to compare anyway.

If you're considering (approx) 25ft day-cruising type boats, and any of them DO NOT have dual Contra-Rotating props (Bravo III or VP DUO-Prop) even when "propped" correctly they're going to be "slow" coming up on plane.

I had a single prop OMC King Cobra 460 in my 1987 21ft Four Winns Liberator (Sport type, cuddy cabin) It was pretty fast (60+) for a boat that size (considering 340hp crankshaft in those days) But it was a REAL DOG "outta the hole" even when new (my brother bought it new)

After I put the 1997 454+ Bravo III in it (literally the same hp .......actually 330 crankshaft hp) the top speed was only a few mph less but the hole-shot was (is) spectacular.

I wouldn't consider any boat over 20-21ft in length with a single prop drive.

Mercruiser touted the 320hp 6.2L engine as a replacement for the 454. I would expect my boat to perform approx the same with a 6.2.........maybe better since they're a little lighter. (my desired engine would be an all aluminum 6.2 with aluminum manifolds and risers and full closed cooling!) (A Four Winns 261 with twin 6.2 aluminum engines and twin Bravo III's !!!)

Nothing wrong with Volvo for any boat you want to get.......but get a DUO-PROP drive that's rated at least 300HP (PROP SHAFT HP)

Just stay away (RUN Will Robinson!!!!) from a Volvo Penta XDP composite drive though........veddy bad. And a boat with one will be priced low (just make sure it's priced low enough to get a replacement [NOT XDP] drive.
(Do a search for "Am I a fool to buy a boat with an XDP drive?")


If it were me and I was planning to work on my own stuff , (and I do) I would get a Mercuiser powered boat. FAR more (used) parts and services out there than for a VP. (but, there's nothing wrong with VP either)

73/Rick

 

[KD4UPL]

Thanks for the advice. I am definitely ruling out any boat with a single prop. I'm also ignoring anything with the 5.0 or a carb. The 5.7 GSI I thought might do okay with the DP drive in the 25' boat but I guess not. Saturday I'll be testing a 23' Rinker with a Mag 350 and a B3. I hope it does better. It is likely I could prop anything differently for better hole shot but 2 new SS props are kind of pricey.

 

[HT32BSX115]

Thanks for the advice. I am definitely ruling out any boat with a single prop. I'm also ignoring anything with the 5.0 or a carb. The 5.7 GSI I thought might do okay with the DP drive in the 25' boat but I guess not. Saturday I'll be testing a 23' Rinker with a Mag 350 and a B3. I hope it does better. It is likely I could prop anything differently for better hole shot but 2 new SS props are kind of pricey.

I have 3 propsets for mine. 24p, 26p (3x3 props) and 24p (4x3 ) I bought all of them used from eBay for about $500-600 each set. (I didn't see much advantage in the 4x3 props btw.

You select props for WOT RPM in the max range for the engine. (preferably at or near the top RPM if you want the best hole-shot)

(my 454 is 4200-4600) I think the Mag 350 is 4600-5000 RPM max. So when you test drive it, if it makes 5000 RPM at WOT, it's propped about right. If it won't make it to at least the recommended range, it's either not propped right or the engine is not making rated power.