Repower I/O Qs.

Hammerhead said:
Wrench ( highly respected shop) found a rebuilt longblock for 1500.oo and will do all the labor for another grand. That's alot cheaper than I tho't it'd cost.
I should have it back in a week or so. ThanX guys.
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Put it in yourself and save a grand.
 
I'm doing the whole thing myself, I pulled my old 305 and am buying a 350 from Rapido marine and installing myself. They use car blocks versus a used marine block. $1450 + 150 for shipping.
 
I bet this one would push a V-20 plenty fast. 5.7L 315HP MAGNUM, would probably at least plane it ;D.

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ThanX for the links. I tho't about a 5.7 250hp but, went the cheap route with a rebuilt longblock replacement. Paid 1500.oo for it. Wrench is doin' the install for 1000.oo.

Motor is already out and parts off that need to be transferred to the new motor.
 
76GMC1500 said:
That motor has horrible torque.  220ftlbs at 2600 rpm?  Your oringinal engine made 350 ftlbs peak and would probably have been close to 300 ftlbs by the Cummins 2600 rpm peak rating.
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I seriously doubt a 250 straight 6 could develop that kind of torque. The 6.5 diesel V-8 in my SUBURBAN was factory rated at around 380-390 ft lbs of torque, and that's a V-8 diesel. The 255HP 5.7L VORTEC truck motors made 330 ft lbs of peak torque. I would say that 165HP straight 6 probably produces peak torque close to the peak HP number, that's normally a good rule of thumb.
 
I'm talking crankshaft ratings and I thought he was replacing a 260hp 350 Chevy, those are rated at 350 ftlbs at the crankshaft. Torque is kind of a meaningless number, though. If you ever look at a prop curve, the chart will make no mention of torque. Horsepower is all you need to know.
 
horsepower readings alone will get you into trouble, horsepower is the timed application of torque( hp=(torqueXrpm)/5250) you have to know what the rpm the hp is rated at. I've seen a 50 trawler with a single 125 hp engine make 7 knots, it would take two 5.7's to do that in this boat. Saw an model airplane engine that would make 5 hp( at something like 15,000 rpm), but I bet it wouldn't push my lawnmotor as well as my 5hp Briggs. Torque alone won't tell you much either, think of a torque wrench, you're applying torque, but you're not going anywhere. I've started to pay attention to Kw ratings(used on modern engines), I haven't made my self familure enough with them to know what I'm looking at.
 
kW ratings are identical to horsepower, it's just metric units.

But seriously, if you have 2 engines both turning props at the same speed and are both making the same horsepower, the torque seen at the props is the same, regardless of the torque output of the engine.  If the torque output of one engine was half, it would have to run double the rpm.  In order to spin the prop at the same speed, the transmission reduction ratio would also have to be doubled.  Because the transmission ratio is doubled, the torque output on the prop end is also doubled.  So, the engine that had half the torque at the crank still has the same torque at the prop after going through the reduction gear.  The difference between that 125hp motor and the 5.7L is that the 5.7 would have to be run balls to the wall while the other motor could just chug along.

P.S. I'm trying to be a little controversial to get everybody to think about things. Sure, they're are holes in my logic but there are also points to be made.
 
Simple way to think of it is torque is how much work an engine can do and horsepower is a measure of how fast an engine can do that work.
 
Chevy 250, in a boat puts out 165 HP at the motor, from a different came then stock, same motor in car gets 140 hp.
I believe that at the prop this is about 130 or so?? I forgot.
WOT on a cuddy 5000 rpm will get you low 30's But will rode nice in the mid 20's

Thats what I had when I got my boat, I have converted to outboard now by bracket and a 175 hp, I get wot 5500, 40 mph (light load) Ride around all day low 30's

I run 15 X15 1/4 prop on both the I/O and OB, gives me best out of hole with heavy loads, 3 guys + gas + 200 # fish, 100# ice

thats whats best for me.
 
that six runs much better proped at 4000 to 4400 rpm

GMC. my point was that without rpm information, horsepower ratings can be missleading
A couple of years ago, Mercruiser introduced the 5.0 MPI rated at 260 Hp at the prop, they were claiming it would do the same as a 5.7 carb, what they neglected to point out was the 5.0 needed to turn 4800 to 5200 rpm to make power( it had a peaky hp curve), while the 5.7 only had to turn 4400 to 4800 to make the same power. the 5.0 would run faster than the 5.7 in a light boat( checked it myself), but put the two in a medium to heavy boat, the 5.7 walked all over the 5.0, it wasn't even close, with out the torque curve referenced to rpm, most people wouold assume the 5.0 would do the same job(thats what they were telling the salesmen, who were telling the same to the customers).
 
Before the motor went...it'd go 40 mph tops. I usually ran it about 30. I expect the same performance with the new motor. It's turning a 19" SS prop.

A 5.7 sure would'a been nice tho'. :D
 
a 5.7 would have been nice, but if it will make you feel better, remind yourself that it would have taken a new inner transom plate, might as well replace the outer transom plate, you would have had to find the correct y-pipe, and you know it would be a shame to bolt up an old drive so might as well...when you're done it only cost you $$$$$$$$$$$$$
 
The boat being a '77...and NOW my wife wants us to move to the North Carolina MOUNTAINS !!!!! aacckkk.
( she's skeered of hurricanes ) ::) If I sell it it'll go eaiser at less a loss with less money dumped in it.

If the move happens...I'll list it here first. I'll hang onto the lil'Bonita for lake use up there...or if the river rises during a Hurricane. (There's Nooo escape) ;D
 
tell her that Hugo travel North West after making landfall in Charleston, SC, went right up thru Charlotte, NC, then skirted the NC mountains before turning back North East
 
Big diff is the winds get cut way down by the mountains. We hava place in Hendersonville and are all too aware of the hassle of rising rivers and creeks. The French Broad River rose about 15 ft high in the early 90s it washed thru Chimney Rock.
 
Hammerhead said:
Big diff is the winds get cut way down by the mountains. We hava place in Hendersonville and are all too aware of the hassle of rising rivers and creeks. The French Broad River rose about 15 ft high in the early 90s it washed thru Chimney Rock.
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If you move to H-ville you should keep the V to use on the lakes along SC Hwy 11 fishin for stripers with REEL.
 
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