Anonymous
01-21-2003, 11:35 PM
group
normal member in standard member. 1. Repowering/Anticipating performance
Just found this web site-looks great If anybody might be able to help me with the following questions I would truly appreciate your honest opinion. I am thinking of repowering a 1987 26 foot Shamrock center console-it presently has a 351ci 250hp pleasurecraft engine with a 2bbl carb and turns a 15x17 three bladed prop and uses a 1.5:1 transmission. It runs 23mph @ 3100rpm and 29mph @ 4200rpm under my desired loads. If I repowered this boat with the new 310hp 351ci motor from pleasurecraft and used the existing transmission what size prop would I need to match it with and what kind of performance could I expect out of it. Thanking you in advance for your help. Group
Date: 08:12 a.m. on 02-02-2001
Engineman
2. Re:Repowering/Anticipating performance
This not an easy question. First horsepower. Your engine was rated at 240hp @ 4200 rpm's. The newer engine is rated at 310 hp @ 4800 rpm's. The new engine will net you about 50 lb-ft of torque. What does this mean?
It means that you will probably only need to add 1" of pitch to the wheel. You will want the new engine to turn right at 4800rpm's to get the best performance and longest life. The advantages of the fuel injection are fast starts, great throttle response, and fuel efficiency.
The best way to get an accurate read on proposed prop size is to give a good prop shop the details and let them run a computer annalysis for size. They will need the weight of the boat, the horsepower of the engine and the max rpm's of the engine and the reduction ratio on the transmission.
My opinion is that you will increase the pitch by 1" and add a modified cup to the prop tip.
Date: 12:14 p.m. on 02-02-2001
Leprechaun
premium member in standard member. 3. Re:Repowering/Anticipating performance
No increase in performance anticipated with the new engine - you are drag-limited with these keel boats, its not a horsepower/torque limitation. Too much wetted surface for any significant speed increases - even with a 454 engine. See it with the local Boat U.S. towing group who use a Pilothouse 26 with 454 - same speed/more fuel used than with the 350/351s. You could try the same prop - shd be O.K. - maybe an increase to 16x17 uncupped - which is what i have on my 351/250hp now. Leprechaun
Date: 12:16 p.m. on 02-02-2001
kenny
4. Re:Repowering/Anticipating performance
it should run stronger. however if you want to sell the old eng. give me a call/email.
i'm looking for a project engine.
Date: 10:37 a.m. on 02-25-2001
kenny
5. Re:Repowering/Anticipating performance
i have 20 CC model w/351 4bbl. i run at 44 kts. clocked! 4500 rpm.
Date: 10:40 a.m. on 02-25-2001
little toot
6. Re:Re:Repowering/Anticipating performance
--------------------------------------------------------------------------------
kenny (02-25-2001 10:40 a.m.):
i have 20 CC model w/351 4bbl. i run at 44 kts. clocked! 4500 rpm.
--------------------------------------------------------------------------------
kenny,
what kind of project was putting the 351 in. does it fit under the engine box? how is it to work on? are all the engine parts acceccible? I just put a 5.7 mercruiser in my 20 pilothouse and ran into alot of little problems. For one i had to cut and add 4" to the engine box. It also looks like it may be a little tricky when it comes time to change the plugs. the performance was definetly noticed. I just picked up a 20 cuddy that needs a repower and am undecided which way to go . My considerations are 302 long block, 351 complete, 350 mercruiser.
Date: 05:37 p.m. on 02-25-2001
Leprechaun
premium member in standard member. 7. Re:Repowering/Anticipating performance
Toot - go with the 302 long block. With the shallow inner hull you can't use a redux gear box and you are forced to pretty much stay with the stock diameter prop due to insufficient hull-to-prop-tip clearance. With these two constraints you cannot really put much more power into the water than the 302 can make. My dock-mate Screamineagle, who posts here regularly, spent much money and time replacing his 302 2-bbl with a spanking new 351 H.O. Net result more fuel used and no real increase in useable hull speed. I think the factory got it right in the 20 footers. Maybe he can add to this post thread. Billy, you out there? Rgds, Leprechaun
Date: 06:07 p.m. on 02-25-2001
normal member in standard member. 1. Repowering/Anticipating performance
Just found this web site-looks great If anybody might be able to help me with the following questions I would truly appreciate your honest opinion. I am thinking of repowering a 1987 26 foot Shamrock center console-it presently has a 351ci 250hp pleasurecraft engine with a 2bbl carb and turns a 15x17 three bladed prop and uses a 1.5:1 transmission. It runs 23mph @ 3100rpm and 29mph @ 4200rpm under my desired loads. If I repowered this boat with the new 310hp 351ci motor from pleasurecraft and used the existing transmission what size prop would I need to match it with and what kind of performance could I expect out of it. Thanking you in advance for your help. Group
Date: 08:12 a.m. on 02-02-2001
Engineman
2. Re:Repowering/Anticipating performance
This not an easy question. First horsepower. Your engine was rated at 240hp @ 4200 rpm's. The newer engine is rated at 310 hp @ 4800 rpm's. The new engine will net you about 50 lb-ft of torque. What does this mean?
It means that you will probably only need to add 1" of pitch to the wheel. You will want the new engine to turn right at 4800rpm's to get the best performance and longest life. The advantages of the fuel injection are fast starts, great throttle response, and fuel efficiency.
The best way to get an accurate read on proposed prop size is to give a good prop shop the details and let them run a computer annalysis for size. They will need the weight of the boat, the horsepower of the engine and the max rpm's of the engine and the reduction ratio on the transmission.
My opinion is that you will increase the pitch by 1" and add a modified cup to the prop tip.
Date: 12:14 p.m. on 02-02-2001
Leprechaun
premium member in standard member. 3. Re:Repowering/Anticipating performance
No increase in performance anticipated with the new engine - you are drag-limited with these keel boats, its not a horsepower/torque limitation. Too much wetted surface for any significant speed increases - even with a 454 engine. See it with the local Boat U.S. towing group who use a Pilothouse 26 with 454 - same speed/more fuel used than with the 350/351s. You could try the same prop - shd be O.K. - maybe an increase to 16x17 uncupped - which is what i have on my 351/250hp now. Leprechaun
Date: 12:16 p.m. on 02-02-2001
kenny
4. Re:Repowering/Anticipating performance
it should run stronger. however if you want to sell the old eng. give me a call/email.
i'm looking for a project engine.
Date: 10:37 a.m. on 02-25-2001
kenny
5. Re:Repowering/Anticipating performance
i have 20 CC model w/351 4bbl. i run at 44 kts. clocked! 4500 rpm.
Date: 10:40 a.m. on 02-25-2001
little toot
6. Re:Re:Repowering/Anticipating performance
--------------------------------------------------------------------------------
kenny (02-25-2001 10:40 a.m.):
i have 20 CC model w/351 4bbl. i run at 44 kts. clocked! 4500 rpm.
--------------------------------------------------------------------------------
kenny,
what kind of project was putting the 351 in. does it fit under the engine box? how is it to work on? are all the engine parts acceccible? I just put a 5.7 mercruiser in my 20 pilothouse and ran into alot of little problems. For one i had to cut and add 4" to the engine box. It also looks like it may be a little tricky when it comes time to change the plugs. the performance was definetly noticed. I just picked up a 20 cuddy that needs a repower and am undecided which way to go . My considerations are 302 long block, 351 complete, 350 mercruiser.
Date: 05:37 p.m. on 02-25-2001
Leprechaun
premium member in standard member. 7. Re:Repowering/Anticipating performance
Toot - go with the 302 long block. With the shallow inner hull you can't use a redux gear box and you are forced to pretty much stay with the stock diameter prop due to insufficient hull-to-prop-tip clearance. With these two constraints you cannot really put much more power into the water than the 302 can make. My dock-mate Screamineagle, who posts here regularly, spent much money and time replacing his 302 2-bbl with a spanking new 351 H.O. Net result more fuel used and no real increase in useable hull speed. I think the factory got it right in the 20 footers. Maybe he can add to this post thread. Billy, you out there? Rgds, Leprechaun
Date: 06:07 p.m. on 02-25-2001