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Increase speed on 270 hp

G

going_east

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"I currenlty own a silverton w

"I currenlty own a silverton with twin 350 cursaders @ 270 hp, currently my boat is set up to run @3200 RPM it won't go above 3200 rpm, im thinking because any faster i will start bruning up my engines, my top speed is around 20 to 21 knots, is there anyelse i can do to increase my speed? the only option i have come accros without buying bigger motors is putting in high performance heads along with a new intake and camshaft, any suggestions thanks"
 
"The boat has the original pro

"The boat has the original props, what prop should she have to get the best speed? thanks"
 
"I have a Silverton 34c with t

"I have a Silverton 34c with the same engines, and I experienced a similar problem. After repowering with original factory GM 350 long blocks, and switching to pointless ignition, I was only able to get 3500 rpm with the original 18X20 props. I had the props repitched to 18X18 and now get approximately 4000rpm WOT. I would still like to get more, but reducing the pitch farther would only result in a lot of water churning without much forward thrust.

By the way, added equipment, family gear, full tanks etc. all add to boat weight and reduced performance. Also, how is the bottom? Slime and growth greatly reduce performance as the year progresses and waters warm up."
 
"well guys I think my boat may

"well guys I think my boat may have been over prop after all, here's how I did the test, i ran her last weekend gunned down the throttle sticks until it couldn't engines ran @ 3200RPM, when i got to the dock I opened up the the carb with the boat turned off and gunned the throttles to my surprise the carb valves where open all the way, so it my have been over propped, Im not sure why the previous boat owner would of done this, but I will say that due to the larger props the boat is always on plane, the bow never pitches up on take off. luke I had the marine mechanic tell me the same, he said he would pitch my props about an inch to get more speed of them, how did you determine that 2 inch was your max pitch? THe bottom is in pretty good shape very little growth on the anodes, I have also been looking at some new enginers @ Jegs with vortec 350's that put out 340hp would this work also work as a replacement engine? thanks"
 
"A pretty reliable rule of thu

"A pretty reliable rule of thumb is that a reduction of 2 inches of pitch = 500 rpm. However, once the props are less than what they call "square", that is the pitch becomes less than the diameter, any increase in rpm achieved is at the cost of proportional forward thrust. Thus less than square is no longer an efficient configuration.

As to engine repower, here is the BIG lesson that I learned. I chose to repower with long blocks, since all of my peripherals were in good shape. What my mechanic didn't fully explain was that the labor cost of transferring my peripherals to the new long blocks would equal or exceed the cost of brand new drop in engines with all current technology, with outputs and efficiencies far exceeding my OEM engines. In hindsight, what looked like a substantial cost,namely finding counter-rotating vortec engines that would mate up to my velvet drives, would have probably been comperable or cheaper than going the long block route.

A caution on significantly increased horsepower. My Silverton has 1 1/4" shafts and the supporting struts are not very beefy. If yours is similar, I could forsee that 25% hp increase might put a strain on the running gear. However, you could probably use your oversize props."
 
"Thanks for the info Luke, I h

"Thanks for the info Luke, I had a I/O boat that had 4.3 L. engines, did the same thing, thinking I was going to save money. ya right, now when I look for blocks I try to find them fully asembled, with the exception of the exhaust, intake man, and carb. The guy at jegs is telling me that the vortect won't work becuase of the high RPMS, so I asked him what the difference bewteen a Crusaders(GM) engine and a 350 JEGS 350 GM engine, that dude started blabing about the material the block is made off, man i put the phone in mute and laughed my ***off, anyways a while back we actually bought a auto 454( i think from PEPBOYS) and droped on a 23 ft I/0 that is still in use in california, we switched the cam and the heads works great, thanks for your help and your insight looks like we do have the same boat, be safe on the water"
 
trying to find bolt on upgrade

trying to find bolt on upgrades I can put on my 1985 270hp-350 crusader to get more hp
 
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