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  #16 (permalink)  
Old 09-19-2008, 01:51 PM
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Quote:
Originally Posted by jbvcw71
"Bolt on" modifications that increase real world low speed torque are non-existant.
Except this



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  #17 (permalink)  
Old 09-19-2008, 02:07 PM
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That bolt on would not fit under my Engine compartment lol. It would rip the 305 block to shreads also, I believe.

Bryan
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  #18 (permalink)  
Old 09-19-2008, 04:54 PM
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Yeah, but that first trip up the lake would be worth it. Then you'd have an excuse for a 350

For now I would focus on getting a good, low-RPM suited intake. An edelbrock performer (not RPM) would be a great addition. Do you do fresh water or salt? If you do fresh then you can get away with aluminum. Look on Ebay for an aluminum intake from a GM crate engine. Its a PERFECT intake. It flows almost as well as an Edelbrock performer and would be more than enough for your 305. Its the same intake as can be found on GM crate engines and they plate the water passages with bronze or brass for the marine version. Many guys buy the crate engines and upgrade the intake, so they go cheap in new condition

10185063 is the part number from GM; its the ZZ intake. Try to find one on Ebay if you're doing fresh water. Its an EGR intake, but you can just block it off. If you're doing salt, the marine version is the same casting (minus the EGR passage) and the water passages have been plated to prevent corrosion.
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  #19 (permalink)  
Old 09-19-2008, 05:41 PM
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Quote:
Originally Posted by bry21317
(split off from another thread. )


I have a boat, that is a 94 Model with a Chevy 305 Installed in it. It is a Inboard/Outboard with 4 inch thru hull exhaust. I Upgraded the Intake last winter and the carb from a 2bbl up to a Edelbrock 1409 with a High Rise RPM Airgap Intake.

I am looking for some more low end, I can run this motor no problem up to 5000rpms but its supposed to redline at 4600 RPMS and have changed the props and all to get it down to correct this, which I did. I then lost some Low end torque.

So what I am wondering is if I were to find some Vortec Heads to put on it, what type of difference would this make? I know that right now this engine should be around 220 hp, or maybe 240. Also, would 350 Heads work on a 305 or not. If you can't tell, I am pretty new to this stuff, just like it and want to learn it. So if you could tell me what might give me some boost in power, that would be great. The cams are hard to change on the marine stuff, to make sure that you do not get water inversion through the exhaust. They also say the inconnel valve seats are the best for Marine applications. Any ideas would be greatly apreciated.

Thanks,
Bryan
The problem with a boat is that you can't divorce what you do to the engine's power curve from the prop as you already found out. The prop is very much like an open torque converter. Like a car with an automatic, if you do things that run the power band up to higher RPMs, the prop needs more slip to get you going. In that regard, since you already increased the pitch to bring it into the engine's rev range, the best thing to do is to increase the size of the engine without changing cam timing nor the relative amount of carburation it has in proportion to its displacement.

Things that slow the port velocity reduce mid range power and move the power band peaks further up the RPM band, such things are larger carbs, larger manifold passages, larger head passages, larger valves, more cam duration, lift, and less LSA. All these things add power, in many cases lots of power, but they push the place where that power is camping up 1000 - 2000 RPM or more. That means a different prop, and certainly different boat handling as a result of the prop change.

A larger displacement engine will not reduce low speed tractability and boat handling characteristics, but will improve upper end performance without having to change the prop. In a perfect world where cost isn't a consideration if you could belly up to the bar and order a variable pitch prop, a whole nuther world opens up. Then you can re-cam and carb the engine till the cows come home and still retain cool bottom end characteristics that are nice in the marina.

If you're running in fresh water, I don't see inconel seats as necessary especially if the boats on a trailer rather than floating all the time at the marina.

Bogie
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  #20 (permalink)  
Old 09-19-2008, 09:14 PM
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Quote:
Originally Posted by bry21317
(split off from another thread. )


I have a boat, that is a 94 Model with a Chevy 305 Installed in it. It is a Inboard/Outboard with 4 inch thru hull exhaust. I Upgraded the Intake last winter and the carb from a 2bbl up to a Edelbrock 1409 with a High Rise RPM Airgap Intake.

I am looking for some more low end, I can run this motor no problem up to 5000rpms but its supposed to redline at 4600 RPMS and have changed the props and all to get it down to correct this, which I did. I then lost some Low end torque.

So what I am wondering is if I were to find some Vortec Heads to put on it, what type of difference would this make? I know that right now this engine should be around 220 hp, or maybe 240. Also, would 350 Heads work on a 305 or not. If you can't tell, I am pretty new to this stuff, just like it and want to learn it. So if you could tell me what might give me some boost in power, that would be great. The cams are hard to change on the marine stuff, to make sure that you do not get water inversion through the exhaust. They also say the inconnel valve seats are the best for Marine applications. Any ideas would be greatly apreciated.

Thanks,
Bryan
What kinds of props have you tried, pitch and type are important. Have you tried a prop with more rake or less?

I just spent the last 2 days trying various props on my 90 HP Merc outboard and I can tell you there is a huge difference amongst the brands and models even in the same pitch.

I think that if you found a dealer who would let you experiment you would eventually find one that was a good compromise for your situation.

Just remember if your prop let your engine rev to 5000 with the boat empty no load then it was probably the right prop with a boat load of people and tanks full of fuel on a hot day.

This is how you should prop your boat, sounds to me like you had the right prop and now you have the wrong one for your application. Typically one inch of pitch will drop rpm 150-200 rpm, if you went up more than one inch of pitch from your last prop then you have sacrificed holeshot for top speed.

You can't have both!

FYI I finally got the right prop selected for my boat (16.' Tuffy Sportsman 160, 90 HP Merc) and going from a 21" pitch stainless factory Merc prop with a huge amount of cupping to a 22" Laser II with no cup dropped my rpm 400 and raised my top speed from 72 KPH to 82 KPH. This amount of speed change and rpm drop is not typical for a prop change but each of these props had completely different characteristics. Now the boat literally flies on the water bow high and only the rear pad is in the water, I originally was going to raise the motor one more hole but the new prop likes it where it is. I even played aorund with weight distribution and found my boat likes all the weight in the rear which is not typical for most boats, most boats start to porpoise with too much weight in the rear, mine did the exact opposite.

There are many variables not engine related that will affect the performance of your boat/motor combination.

Here is a good forum that may help you with prop selection etc. I read it daily!

Scream And Fly, High Performance Boating Forums
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  #21 (permalink)  
Old 09-20-2008, 12:45 PM
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We did alot of experiments on my boat as well which is a 1997 21 foot Gambler with a 200 mercury pro max EFI outboard. It has a 4 blade trophy prop, we moved the engine up and down a good bit on the jack plate to find the comfy spot. it planes in the snap of a finger and has killer midrange power. I`ve not had it up to top speed as I don`t go over 55 on the water, when it goes to chine walking around 65 I get uncomfortable. However I have ridden with my brother with him driving doing a top end blast, I think he got it up to 77 with me hollering slow down.
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  #22 (permalink)  
Old 09-20-2008, 05:11 PM
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Reynolds Racing, Boat and Prop Selection Guide

Just remember every site I visited that had prop recommendations said not to exceed the max rpm of the motor, in my experience if the prop doesn't allow the motor to rev a little past max rpm of the motor a little it will perform poorly with max load. The key here is everyone is covering their butt with recommendations, you are the one controlling the throttle and not exceed the max rpm of the motor.

Besides having a little extra throttle left at max rpm empty, lets the motor breathe and leaves some room for high wind loads etc.

Of course I don't recommend you exceed your engine manufacturers label specifications at any time!

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  #23 (permalink)  
Old 09-21-2008, 08:32 AM
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I have 2 identical props, one is a Rev 4 21 pitch prop and the other is a Rev 4 23 Pitch prop. They both work ok, but my hole shot is much quicker with the 21 pitch prop for sure.

The Top end was also the fastest with the 21 pitch, so I got both with this prop, over the 23 pitch. My RPMS just seem to be a few hundred over even with it fully loaded. It will run the same loaded or empty with only me and a low amount of gas.

The boat is a 94 Cronwline 196br, it weighs in around 2900lbs dry. So it is a heavy boat, for a 19 footer the nice thing about this is it rides great and takes chop really good. Just no speed demon for sure due to the weight, but that is ok, the better ride is worth it.

I just like to try to mess with it, to make it faster, quicker. Just like you guys are, but I am still learning all the Hot Rodding stuff, and what to do to make the engine run better/stronger.

So I am taking all of this information in for sure, like a huge sponge. I know all about the props for sure, and have been thinking of trying a Laser II prop anyways. I love the Rev 4 4 Blade props, they are awesome, but I think for speed, you can't beat a 3 blade. For handling and pulling the 4 blade is great.

Bryan
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  #24 (permalink)  
Old 09-21-2008, 08:23 PM
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I think you will much prefer a 3 blade, the added weight and drag of a 4 blade sucks out the motor. I tried a 4 blade 22" pitch Ballistic on my 16" boat and couldn't break 4900 rpm empty. With the 22" pitch Laser II it hits exactly 5650 empty and 5400 with 5 people and two tanks of fuel plus all the fishing gear. This is a 2003 90 Merc classic outboard so its not apples to apples but unless you really need the extra blade to pull a skier I don't think its worth it from a speed guys perspective.

The factory round ear SS 21" no-name factory Merc prop (lots of cup but only a little rake) had a better holeshot but not by much, it might be a better choice for a heavier boat but mine only weighs 1100 pds empty. It did pop the boat out of the water like a torpedo though.

I might add that the Laser II likes to run close to the waters surface which I got by raising the motor 2 holes so the anticav plate sits right at the waters surface, not sure what you would have to do to accomplish that on your I/O. The factory SS Merc prop didn't care where it ran from my testing.

I just finished syncing the carbs and setting the timing an hour ago and hit 85KPH (53mph) with me and two kids and one tank of fuel, she sure purrs now and didn't get passed once!

There were many that tried!
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Old 09-27-2008, 03:37 PM
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Been there done that. I started with a 305 in my 18' deep V, tried to improve the performance with 4bbl and intake. Very little difference. Went to a 350, and had quite a bit of difference, but not what I wanted. I then built a 383 from scratch. Big difference except I had severe prop torque coming on at 4000RPM. Put on a duo prop lower with a C6 ss prop to get rid of the prop torque The boat comes out of the hole instantaneously and accelerates like a scalded cat. You gotta have everything off the dash or it is all over the boat if you 3/4 throttle hole shot it.
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