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Big Block Package

nebraskaairboater

Well-known member
My dad saw a boat climb the riverbank for the first time this past weekend and it helped me in my quest for him to upgrade to reduction. Just wondering what would be a good combo for a stock engine. He has a 455 Olds. I know the 454 Chevy would probably be better. He is looking for all around push more than anything. Sound is an issue out here (sort of) but with the push it should lower the sound. What ratio and prop would be best for a 16 x 8 fiberglass boat that will be used for fishing, and riding more than anything... top speed and snap not important just to drive up a ramp with 4 -6 people on board if possible. Would take being able to do it with only the driver as well. He want's me to figure out what it would cost to convert. I was thinking a 2.38 or 2.68 and a master blaster 3 blade.
 
I'm also doing the same think with my boat. Wondering if you would need to much RPM if you ran a 2.3 or 2.6 or would you just install bigger prop to keep you in operating range of motor. Because a stock engine can't run 4000 + RPM for too long. Looking foward in here your comments.

Swampdonkey
 
I was thinking of the master blaster or q series ultra wide to keep engine rpm to 4500 max and still get decent performance out of the boat.
 
With an adjustable prop you will be able to control your RPM's by adding more pitch so that shouldn't be a problem, I went with the 2.37 rotator but alot of people are goin with the 2.68. Just my 2 cents. SAFARI RICK
 
boxes are for torque multipliers not rpm enhancers. first thing you need to know is where your engine wants to run rpm wise and then put the most box on it and the most prop and turn it slow, lots of pitch, thats where the gears come in. It isn't rocket science unless you wnat quiet and power on a big barge. Then you need to think a little more but it still aint hard. Forget all the mess about turning you motor 9000 rpms and using a big box to bring the prop down to 3000. use the box to run a bigger prop slower, you save gas and engines, they live a lot longer at 5000 than at 9000. old time props were meant to run at 2800 rpms and some pushed them to 3000 or a little more and they were loud. now props are designed to generate power while turning slower so take advantage of it.

I was asked by alumitech to try the sensenitch super wide blades and got a heck of a deal on one because they needed some of them out there for folks to start talkin about them. I called them with my report and sensenitch told me they already knew what i had to say but no one else wanted to hear it from them so they were not bothering to tell anyone about the performance down slow speed. Yes there is another 100 lbs waiting on you if you will spin it on up but why, i was already making more than I really needed for normal airboating but I always say why be normal, but I still don't spin it up I kept it turning right in my motors band of power and even modified the motor to turn slower when I had a block rust in two. I never turn my prop over 1670 rpms and maybe slower on my new boat. time will tell.

And mufflers will give you more power and I dont mean tin can mufflers I mean real mufflers.
 
What RPM would you recommend for a stock 454? Steady cruising and max full throttle. Also what would a guy have to do to his engine in order to increase RPM without doing any damage to engine? After mods what RPM could a guy expect run at? I want to build a monster 454 airboat engine, but want to keep it reliable. IS THERE SUCH A THINK!!!!! My engine guy said that if your after torque you need heads with small intake ports. Are we on the right track, and if so what size intake ports sould we be getting. OH yah engine will be on a 18x8 panther with 2:1 gear box. Might need new gear box, would you recommend a 2.68?? Sorry for all the questions, just got carried away.

Thanks Swampdonkey
 
that is kind of my same question. On a stock engine what gear box ratio works best. Would the 2.68 be best because of the torque multiplying effect? Also would an 80 3-blade masterblaster be the best prop for the money when push and dry running is the main request. As everyone can read we in nebraska have 96db at 100 feet on plane and it is very difficult to enforce. I want to run the engine at no more than 4500 to keep the sound down and stay in the rpm band of the engine. I know that the reduction has nothing to do with rpm cause rpm usually gets you nothing but noise. Also can't imagine how much gas I would save cruising at less than 3000 rpm at a good clip. Now we curise at 24 to 2600 rpm and it isn't very fast being direct drive. Be nice to cruise at the same rpm but be going twice as fast. Maybe be like thunder and cruise at 1500 engine rpm. I would just like a starting point for a recomendation on what box and prop would be best. That way I can get out a pry bar to get dad to release some funds. He He
 
I would go with a 2.68 box over a 2 to 1 everytime myself. i like to keep engines turning slow, around 5000 rpms. I am not the best for info on engines on here. I would hate to reccomend something and whomever puts it together gets one thing wrong and it blows up. I definately build for tq. myself. all these mods are expensive and that is often a road block. So figure out what you wnat to do and be specific and take all advice with a grain of salt and get after it. it is always a work in progress.
 
Hey Guys, here's a topic I know a little about.
I have a 14' Diamondback with a 425hp 454 crate motor, Stinger "soft drive" 2.09-1 gear box, and a 78" 3B Powershift prop.
Overall I am satisfied with the performance, I go where the 2 seater 520/540 boats go it just takes more effort to do it. I can carry 5 or 6 passengers plus gear and don't have to worry much in deep water. I can run dry with 4 or 5 people and with just me on it it will climb the hill.
It is kind of heavy and doesn't move on dry until you rev up to about 4000, then you can ease off.
When I "get on it" it will spin up to 5000, but usually don't stay there very long because stuff starts to happen real quick.
top speed is 54.9 MPH , and it is very stable. Cruise (25-30 MPH) is about 3000 in deep water and 26-2800 in skinny water.
As far as reliability, the motor has been great. I bought the boat used and have put about 420 hours on it over the past 5 years with only minor problems (motor mounts, starter, alternator, batteries, nature-blocked radiator, and a small issue with a broken exhaust valve)
After several years with this package I would only change a couple of things,
I believe in the future I would like to add a MSD ignition and aluminum cylinder heads with a different intake (if 425hp is good then 500+ would be even better-right)
also I would go with a higher ratio gear box so I could put more pitch in the prop.
I am very happy with this boat, it has taken me everywhere I needed to go and some places I probably shouldn't have been. It doesn't slide or handle as well as some boats, but I think that has more to do with the hull.
The only thing I don't like is if you want performance out of a big-block you are going to have to FEED THE HORSES, and that takes FUEL. If I am playing HARD it can suck up 8-9 gallons an hour.
100_1391.JPG
 
I run an 18by8 daimondback with a 2.1 reduction and a 78in sensinech three blade composite with a crate 454. The boat runs grass small stretches of dry ground(stressing small sections of dry ground) with three people fairly easily but running up a riverbank is gonna require some real push on an 18 foot hull. I would look at a 502-502 with at least a 2.3 reduction and a superwide prop or I believe you will be dissapointed in your riverbank climbing abuiltys. We run mud,marsh grass,flats etc here so the 2.1 and 425 horse works great for me but sandy riverbanks are another story with such a large hull especially if your loaded. Calm Seas...
 
I'm glad to see you all are coming around to the 2.68 ratio. I have been using 2.68's for 6 or more years now. And 90% of everyone still say's I don't want to turn more RPM's so I would rather have a 2to1. Nobody believes the 2.68 is better until they try it and then the say I wish I got a 2.68 the first time. I run a 2.68 on a LS1 that will produce over 600HP and I set my prop where my max engine RPM is 5,400. And to top it all off my boat get's awesome fuel economy.
 
I went from a DD to a 2:38 gearbox on my 500 caddy with no major up grade. Needed to stay under 4000rpm. Ran dry ok. Have a 4 blade Stump puller and looking to step up to a Master Blaster 2.3 with the new rebuild 500.
You'll be happier with a 2:38 or 2:68 than a 2 to 1

If you need some info to wake up that Pontiac. This guy is the master of Pontiac 455. This is where I had my 500 just rebuilt. Check it out.

http://www.angelfire.com/fl4/pontiacdud ... eshop.html
 
waterthunder I like your reasoning behind the 2.68 gearbox but how fast does it push at idle? I worried about the boat moving too fast.
 
Well if our 2:1 gear box is done I will be going with a 2.68:1 Is there a particular type that you would suggest? Not looking to same money. Want to do right the first time. WATERTHUNDER I am going to build a 496 and my engine guy wants to know what RPM we want to develope our horse power and torque at. In other works will it make any difference weather we go with a 2.68 or a 2.1 as far as our engine goes. I'm certainly not an engine so the answer I am looking for is. At what RPM sould we expect to turn our engine? Because the higher you need to push those Big Blocks the more money it will take. Again just want to do it right the first time.
 
Mudpuppy, I wish you hadn't shown me that Pontiac website ..... I love big Pontiacs.

Now I gotta start a new quarter jar ..... 8) .
 
Your boat speed at idle will increase because you hav emore pitch but you get used to it soon enough. I have been shutting off to pull up to docks for a long time now.
 
On your big block tell the engine builder do not build a motor for peak power numbers tell him you want a broad motor that makes all it's steam before 6,500RPM also tell him not to run a cam with more then 108 lobe center. Then throw a 2.68 box on it and choke it down to where you like how it runs which will probably be around 5,000RPM to 5,500RPM max. If he builds a nasty 496 you will need a four blade but a good conservative 496 will like a 3 blade ultra wide Senseinch. Out of most big block combos for an airboat I prefer the 496 based on the mark IV block the best. I do not like the new scalloped mark V and VI Big Block Chevy's. The block decks are weak and the oiling system's are sub par compared to the original design. Plus I have seen well over a dozen new design BBC blow out the number 5 main cap when you throw an arm in them.
 
so on a stock 455 olds a 2.68:1 with a 3-blade 80" master blaster should work (for a start) with possible future mild engine builds later?


also what mod's did you do to the caddy to run the gear box? Just the rocker and spring upgrade? I'd like to possibly run a small box and a 3-blade stump puller on my boat some day.
 
I'm in the same situation as you are nebraska. I,m running a 455 olds and wonder what it would do with a gear box. I don't think I would like to go much over 3500 RPM for too long. I don't think they were made to turn that high. Correct me if I'm wrong. With a 2.68: 1 at 3000 rpm your prop would be turning at 1100 rpm. Is that enough to push a 18 x 8 boat ?

SD
 
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