looking for 100hp 10 mph
02-16-2012, 05:48 PM
#22
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wrong button aparently when you hit enter on quick reply it submits it instad of dropping a line still new to this forum stuff
but on the subject at hand i mean it seems to be pretty split between building or finding a better engine and throwing blower on it and yes all you safety guy i am preparing for add on steering for the safety part of it wouldn want it to swap ends at speed
but on the subject at hand i mean it seems to be pretty split between building or finding a better engine and throwing blower on it and yes all you safety guy i am preparing for add on steering for the safety part of it wouldn want it to swap ends at speed
02-16-2012, 08:55 PM
#23
Prop change for TOP Speed
first actual forum question gents please help
the boat 96 baja 208 islander 61 gps 1.36 bravo drive 20p 4 blade with 310 454 carb gen v flat tappet engine
from what i can find online it has cast pistons at 8.0 to 1 and a whimpy cam but a steel gm crank 4 bolt block and the smaller gm forged rods
i already have a 1.36 x upper laying in the shop for it and got 12x16 tabs laying next to that all for the boat now my question to you fellows is should i put a 177 blower on it with about 4-5 lbs or try and find a 502 or something take out engine for it looking to spend least amount of money and keep turn key reliable and dock idle friendly so big cams and heads not really an option asking the local engine guys they seem very confidant it will hold 4 lbs especially if i do better springs in heads fact or fiction?
the boat 96 baja 208 islander 61 gps 1.36 bravo drive 20p 4 blade with 310 454 carb gen v flat tappet engine
from what i can find online it has cast pistons at 8.0 to 1 and a whimpy cam but a steel gm crank 4 bolt block and the smaller gm forged rods
i already have a 1.36 x upper laying in the shop for it and got 12x16 tabs laying next to that all for the boat now my question to you fellows is should i put a 177 blower on it with about 4-5 lbs or try and find a 502 or something take out engine for it looking to spend least amount of money and keep turn key reliable and dock idle friendly so big cams and heads not really an option asking the local engine guys they seem very confidant it will hold 4 lbs especially if i do better springs in heads fact or fiction?
You are looking at 15HP to 20 Hp per MPH depending on hull beam and weight design. I would look into a better set of heads, matching cam, intake and carb which will put you in the mid 60s for sure. Keep the rpms in the 5200 rpm range the the cast pistons and cast crank will survive.
I also doubt the 502 putting most 25 to 28 ft boats into the 68 to 70 mph range more like in the mid 60s at best in my experience.
02-17-2012, 03:52 AM
#24
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Having a 208 I bought new for 8 yrs mine came with a 1:50 bravo 1 and 23 Mirage same engine best I saw was 63 gps I could spin the mirage up to 5000 rpm. I will say that you want the tabs on because mine was a little squirrely at that speed on anything but flat water would start 2 chine walk
02-18-2012, 11:09 AM
#25
Butteboy I'm with the guys that suggested getting a complete motor to drop in.
BTW I have found this calculator to be very accurate IF you put in accurate current data and then calculate the constant. Keep in mind that your current engine is prop shaft hp.
Both of the boats I added hp was 11.6 hp per mph. There is no set number as hull design and current speed are important factors and the hp needed goes up as speed increases. It takes a lot more hp to fo from 80 to 90 than it does 60 to 70 even though they are both 10mph.
BTW I have found this calculator to be very accurate IF you put in accurate current data and then calculate the constant. Keep in mind that your current engine is prop shaft hp.
Both of the boats I added hp was 11.6 hp per mph. There is no set number as hull design and current speed are important factors and the hp needed goes up as speed increases. It takes a lot more hp to fo from 80 to 90 than it does 60 to 70 even though they are both 10mph.
02-18-2012, 03:20 PM
#26
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Butteboy I'm with the guys that suggested getting a complete motor to drop in.
BTW I have found this calculator to be very accurate IF you put in accurate current data and then calculate the constant. Keep in mind that your current engine is prop shaft hp.
Both of the boats I added hp was 11.6 hp per mph. There is no set number as hull design and current speed are important factors and the hp needed goes up as speed increases. It takes a lot more hp to fo from 80 to 90 than it does 60 to 70 even though they are both 10mph.
BTW I have found this calculator to be very accurate IF you put in accurate current data and then calculate the constant. Keep in mind that your current engine is prop shaft hp.
Both of the boats I added hp was 11.6 hp per mph. There is no set number as hull design and current speed are important factors and the hp needed goes up as speed increases. It takes a lot more hp to fo from 80 to 90 than it does 60 to 70 even though they are both 10mph.
Just remember the 502MPI 415 and 300 motor in question here are rated the same way. This motor is rated 300 hp the same way the 310, 330, 350, 365 and 385, 454s are. This particular boat is about 2 an-a-bit mph slower with the 7.4L 300 than with the 7.4LX EFI 330 hp. Call it prop shaft or call it crank shaft SAE J1349 hp, dosen't matter. And correct, you cannot generalize about how much hp 10 mph takes, your number of 11-12 from 61-71 is pretty spot on. Just look at how fast a 24OL or 25OL is with a 502MPI.
02-20-2012, 01:41 PM
#27
Bingo, right on.
Just remember the 502MPI 415 and 300 motor in question here are rated the same way. This motor is rated 300 hp the same way the 310, 330, 350, 365 and 385, 454s are. This particular boat is about 2 an-a-bit mph slower with the 7.4L 300 than with the 7.4LX EFI 330 hp. Call it prop shaft or call it crank shaft SAE J1349 hp, dosen't matter. And correct, you cannot generalize about how much hp 10 mph takes, your number of 11-12 from 61-71 is pretty spot on. Just look at how fast a 24OL or 25OL is with a 502MPI.
Just remember the 502MPI 415 and 300 motor in question here are rated the same way. This motor is rated 300 hp the same way the 310, 330, 350, 365 and 385, 454s are. This particular boat is about 2 an-a-bit mph slower with the 7.4L 300 than with the 7.4LX EFI 330 hp. Call it prop shaft or call it crank shaft SAE J1349 hp, dosen't matter. And correct, you cannot generalize about how much hp 10 mph takes, your number of 11-12 from 61-71 is pretty spot on. Just look at how fast a 24OL or 25OL is with a 502MPI.
02-26-2012, 09:46 AM
#28
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ok guys i thank you for all the info and opinions but 
unfortunately it has came to my attention that my hull cant handle ANY more power the starboard [right] stringer that the engine mounts to is soft and flexing cracking the fiberglass and twisting. according to a trusted local fiberglass repair guy the boat will be fine at 300-350 horse/ft pounds but doesnt suggest any more than that without replacing that stringer. so boats up for sale here locally
but i am taking it as a sign to move into a little bigger and better boat gotta stay positive 
unfortunately it has came to my attention that my hull cant handle ANY more power the starboard [right] stringer that the engine mounts to is soft and flexing cracking the fiberglass and twisting. according to a trusted local fiberglass repair guy the boat will be fine at 300-350 horse/ft pounds but doesnt suggest any more than that without replacing that stringer. so boats up for sale here locally but i am taking it as a sign to move into a little bigger and better boat gotta stay positive
02-26-2012, 05:06 PM
#29
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at least patch it. layup 5 or 6 layers of heavy mat over the stringer. right one isn't as crucial as the left, since engine torque pulls up on the left one. but if the stringer is flexing, so is the hull...
04-27-2013, 07:46 AM
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Interesting, I gotta ask
I have a 1993 Baja Islander 454, I was told 330 hp when I bought it. With the age I'm guessing the 330 has relaxed to 300hp. I get 63mpg on the GPS, at 4600rpm. The exhaust is running thru the prop today, and running a mirage 23. I've been told labing the prop should get me 2 to 3 mph, thru hull exhaust 1 or 2 mph. GIL headers 1 to 2 mph. So 4 to 7 mph, I'm getting some of it used for $1400 which should bring the boat 67 to 70 mph. Seems like a great trade off, without jeopardizing reliability. I wondering what your opinions are about the suggested mpg gains I've been told? Also wondering how many horsepower you guys think I'll be running, the stern of the boat has a "330hp" sticker on it, thinking of replacing it.
l'd really appreciate your opinions!
l'd really appreciate your opinions!
