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I didn't see anyone disputing that.
"Woodchuck" wrote in message .. . Tony, don't sound like anyone believes you with the 15hp = 1mph faster! I do! "tony thomas" wrote in message news:PiKpe.27752$x96.17450@attbi_s72... Unless you are rebuilding the engine anyway, I would not waist my money. It takes a lot of hp to gain any real benefit on the water. Most quote 15 hp to 1 mph. Spend your money on a 350 assuming your boat is 18' or bigger. A 17' will probably run sideways from the torque. Biggest bang for the buck is usually found by going to a good performance SS prop. You can see 5 mph gain with the right prop over a cheap aluminum one. -- Tony my boats and cars at http://t.thomas.home.mchsi.com - "Gorf" wrote in message ... I have done some research and heard you can put higher compression flat-top pistons in the 4.3 and gain a few HP. Who makes these pistons? I have done a bunch of searches and come up empty handed. A related question, I have also read that the 4.3 is a 350 minus two cylinders and that the pistons and rods are the same. Is this true or false? -- John WWW.Firewalk-NC.com "Be the change you wish to see in others" ----Gandhi |
I will. I added 15 hp to one of my boats and more than doubled my
speed. 9.8 HP outboard = 7~8 mph I switched to a 25 HP = 20~25MPH depending on load. 15HP increase = 13~17MPH speed increase. on an 16'6" aluminum boat. Paul JamesgangNC wrote: I didn't see anyone disputing that. "Woodchuck" wrote in message .. . Tony, don't sound like anyone believes you with the 15hp = 1mph faster! I do! "tony thomas" wrote in message news:PiKpe.27752$x96.17450@attbi_s72... Unless you are rebuilding the engine anyway, I would not waist my money. It takes a lot of hp to gain any real benefit on the water. Most quote 15 hp to 1 mph. Spend your money on a 350 assuming your boat is 18' or bigger. A 17' will probably run sideways from the torque. Biggest bang for the buck is usually found by going to a good performance SS prop. You can see 5 mph gain with the right prop over a cheap aluminum one. -- Tony my boats and cars at http://t.thomas.home.mchsi.com - "Gorf" wrote in message ... I have done some research and heard you can put higher compression flat-top pistons in the 4.3 and gain a few HP. Who makes these pistons? I have done a bunch of searches and come up empty handed. A related question, I have also read that the 4.3 is a 350 minus two cylinders and that the pistons and rods are the same. Is this true or false? -- John WWW.Firewalk-NC.com "Be the change you wish to see in others" ----Gandhi |
Probably enough power to get the boat to plane. Displacement speed before.
Bill "Paul" wrote in message oups.com... I will. I added 15 hp to one of my boats and more than doubled my speed. 9.8 HP outboard = 7~8 mph I switched to a 25 HP = 20~25MPH depending on load. 15HP increase = 13~17MPH speed increase. on an 16'6" aluminum boat. Paul JamesgangNC wrote: I didn't see anyone disputing that. "Woodchuck" wrote in message .. . Tony, don't sound like anyone believes you with the 15hp = 1mph faster! I do! "tony thomas" wrote in message news:PiKpe.27752$x96.17450@attbi_s72... Unless you are rebuilding the engine anyway, I would not waist my money. It takes a lot of hp to gain any real benefit on the water. Most quote 15 hp to 1 mph. Spend your money on a 350 assuming your boat is 18' or bigger. A 17' will probably run sideways from the torque. Biggest bang for the buck is usually found by going to a good performance SS prop. You can see 5 mph gain with the right prop over a cheap aluminum one. -- Tony my boats and cars at http://t.thomas.home.mchsi.com - "Gorf" wrote in message ... I have done some research and heard you can put higher compression flat-top pistons in the 4.3 and gain a few HP. Who makes these pistons? I have done a bunch of searches and come up empty handed. A related question, I have also read that the 4.3 is a 350 minus two cylinders and that the pistons and rods are the same. Is this true or false? -- John WWW.Firewalk-NC.com "Be the change you wish to see in others" ----Gandhi |
Your talking about a 1.5 times increase in hp. We are talking about adding
15 hp to an engine that has 190 hp to begin with. Going from 190 to 205 will not increase the speed by 13~17 MPH. It may increase it by 2 mph if your lucky. -- Tony my boats and cars at http://t.thomas.home.mchsi.com - "Paul" wrote in message oups.com... I will. I added 15 hp to one of my boats and more than doubled my speed. 9.8 HP outboard = 7~8 mph I switched to a 25 HP = 20~25MPH depending on load. 15HP increase = 13~17MPH speed increase. on an 16'6" aluminum boat. Paul JamesgangNC wrote: I didn't see anyone disputing that. "Woodchuck" wrote in message .. . Tony, don't sound like anyone believes you with the 15hp = 1mph faster! I do! "tony thomas" wrote in message news:PiKpe.27752$x96.17450@attbi_s72... Unless you are rebuilding the engine anyway, I would not waist my money. It takes a lot of hp to gain any real benefit on the water. Most quote 15 hp to 1 mph. Spend your money on a 350 assuming your boat is 18' or bigger. A 17' will probably run sideways from the torque. Biggest bang for the buck is usually found by going to a good performance SS prop. You can see 5 mph gain with the right prop over a cheap aluminum one. -- Tony my boats and cars at http://t.thomas.home.mchsi.com - "Gorf" wrote in message ... I have done some research and heard you can put higher compression flat-top pistons in the 4.3 and gain a few HP. Who makes these pistons? I have done a bunch of searches and come up empty handed. A related question, I have also read that the 4.3 is a 350 minus two cylinders and that the pistons and rods are the same. Is this true or false? -- John WWW.Firewalk-NC.com "Be the change you wish to see in others" ----Gandhi |
But with that increase in HP you should be able to run a higher pitch
prop. A 2" pitch increase at a prop speed of 2500 rpms should give you 4.7 MPH speed increase. My 9.8 would never be able to get to WOT with a 13" prop on my boat. But the 25 HP has no problem. If you do get more ponies from an engine upgrade. You should look at changing the prop. A prop turning at a certain speed is only going to go so fast not matter how much horse power is behind it. Paul |
You forgot to divide by the gear ratio. With a 1.87 gear and taking into
account an efficiency of 90% for a SS prop you get 2.2 MPH. But increasing from 190 to 205 hp is probably not enough to increase by 2" of pitch on top end. You could go 1" of pitch and get 1.1 MPH or the extra rpms w/ the same pitch will give you the same. Again - your comparing a 1500% increase to an increase of 8%. Don't come close to being the same. -- Tony my boats and cars at http://t.thomas.home.mchsi.com - "Paul" wrote in message ups.com... But with that increase in HP you should be able to run a higher pitch prop. A 2" pitch increase at a prop speed of 2500 rpms should give you 4.7 MPH speed increase. My 9.8 would never be able to get to WOT with a 13" prop on my boat. But the 25 HP has no problem. If you do get more ponies from an engine upgrade. You should look at changing the prop. A prop turning at a certain speed is only going to go so fast not matter how much horse power is behind it. Paul |
The 2500 RPM was the prop speed. That would be 5000 RPM on the engine.
I accounted for the gear reduction. So a 2" pitch increase would give you a 4.7 MPH increase. I know it is not a 100% efficient. And whether or not the extra 15 HP can turn a 2" bigger prop 2500 RPM I do not know. But if do several modifications that give you 15HP here, 5HP here and 10HP there it all adds up. You can do headers, Fuel injection, upgrade the ignition, camshaft, computer etc... The 4.3L motor is very a versatile motor. I personally have seen (out of vehicle on a dyno) a 10 hp increase just by adding a spacer (a $100 item http://www.jetchip.com/TBI/chevFSTBI.cfm) under a TBI unit on 4.3L motor. I would put one on my Blazer but I would not be able to close the hood. I have done a lot of work on the 4.3 in land vehicle applications. Limited, but expanding, in boating applications. Paul |
You have to remember how many of these add-ons are advertised. They use the
word "up to" a lot. They may claim a 15hp increase but the results may only be 2hp in real world. Granted the 4.3 can make some good power, but building one for marine use is different than a car/truck. You need to build and engine to make torque. "Paul" wrote in message ups.com... The 2500 RPM was the prop speed. That would be 5000 RPM on the engine. I accounted for the gear reduction. So a 2" pitch increase would give you a 4.7 MPH increase. I know it is not a 100% efficient. And whether or not the extra 15 HP can turn a 2" bigger prop 2500 RPM I do not know. But if do several modifications that give you 15HP here, 5HP here and 10HP there it all adds up. You can do headers, Fuel injection, upgrade the ignition, camshaft, computer etc... The 4.3L motor is very a versatile motor. I personally have seen (out of vehicle on a dyno) a 10 hp increase just by adding a spacer (a $100 item http://www.jetchip.com/TBI/chevFSTBI.cfm) under a TBI unit on 4.3L motor. I would put one on my Blazer but I would not be able to close the hood. I have done a lot of work on the 4.3 in land vehicle applications. Limited, but expanding, in boating applications. Paul |
I agree torque is a big factor in boat engines. That is where your
choice of cam shafts comes in. Just like the car world manufactures put "stock" components in a car for cost reasons. But with some tweaking and adding an after market computer, cam shaft, ignition or what ever else is out there. You can really boost your power and torque. I have learned a lot by putting a user programmable computer in a boat. You can change all kinds of settings. Dwell and timing for spark and fuel. With an MPI system that is really cool. There are many variables and there fore, very easy to mess up. You can even have presets, like a skiing and a just plain cruising. The preset for skiing changes to give you more torque to pull someone up. For cruising it can be to give the best economy at a comfortable speed. Grant it, not everyone likes, want or has time to tweak. With the people I know and the line of work I am in I get the chance to see and play with new technology. A lot of stuff is meant for the car world but can very easily be adapted to the boat world because boats do not have emissions standards, yet. Trying to find a place to put a threaded hole for an o2 sensor in a marine exhaust manifold was fun. Not. Paul |
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