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Do you need 500 HP to run a 3B Maximus?

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John C

John C

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I am new to this site,so I apologize in advance if this question has already been answered. It seems that the latest buzz in props is wider, slower, quieter. I have been running a 15x8 Apache with a 500 caddy/gearbox for approx. 4 yrs now. Gearbox is a 2.12:1 Rotator. Upgrades on motor are from Cad Company. Pro/Street Heads, CTA/SS300+ Cam (Grind for gearbox airboat) with performance valve springs,lifters. Stage 3 (1.72:1) shaft rocker assembly W/special pushrods. Edelbrock alum. intake W/holly 850 Double Pumper carb. Cloyes true-roller timing chain set. Per Chris @ Cad Company, he says I am making an honest 450 HP & 575 Ft-Lbs Torque. I have been told that you need a min. of 500 HP to turn those wide blades. If my gearbox is truly a torque multiplier, and my math is correct. my torque # should be 1219 Ft-Lbs. Is that not enough to turn a 3B Maximus? Or do I need to develope 50 more HP?
 
John, I'm going to leave answering this question to the several Caddy experts on here, but I gotta tell ya ..... that sounds like one kick a$$ motor to me ..... :lol: !

Bf
 
Much easier to go with a lower ratio gear box, like a 2.68
 
the gearbox change would be to move your rpm higher so you can get into your horse power and your higher torque numbers so you can turn a bigger prop. with 450 horse you will be able to turn a three blade maximus but you will never hit max prop rpm. but do you need to no.you can get alot of push just turning the prop 2000 rpm.2.68 ratio is overkill imo for a caddy unless you modify your motor your torque curve starts to fall out after 4800rpm and by then you have already passed peak horsepower.but i would be safe to assume you could turn an 82inch maximus two blade with a 2.12 gearbox.than if you needed 2200 rpm you could have it.i run a three blade whirlwind on my caddy 78inch lots of pitch and it pushes like a monster.you have good mods on your caddy and with that box i would say a 3 blade 80inch falcon or 80inch whirlwind or sensenich what ever your preferance will satisfy you alot. but these are just my opinions you have to choose for yourself.
 
Bondsman thank you for your reply. I am running a 3B falcon series now, 80 in. the boat runs fine now. I am turning it up to 5200 rpm set at the factory mark in the center of the hub. I can run dry loaded. but I would like to quiet it down. I have mufflers, but they are the ones that blow straight thru. I must admit they do not do a very good job. Boat is still loud. Thats why I wanted some input on slowing down prop speed. If I went to a wider slower blade, would I get more push? Or would the boat perform the same, only quieter.
 
First off I know nothing of Caddies and don't want to. Pea brain will not hold anymore.

I would agree with what Bondsman said. You might not be able to reach peak rpms, but at 200 below max ratings you will still be pushing alot of air.

With Lycomings 540s I have seen them set with too much pitch on powershift and senseniches both and they still push great. With most of them the 2600 RPMs pushes fine until you really are in tough stuff or loaded for the bear. You get more thrust at 2800 (max) but how often will you need that extra.

Call Patty at powershift. If she cannot answer it, the old man (engineer who develops them) her dad can.
 
John C.,
As far as mufflers I would recommend Magnaflo XL turbo's, the biggist you can put on. As far as prop, try putting a little more pitch in it. Only go 1 degree at a time.
 
Well here we go i have to add my 2 cents......... the best box to run is the 2:68 yes it is a torque multiplyer this is how i was explaned how it works every one has been told by the air boat manufactures that you want to run a 2:12 box.. for them it is to keep them from having to replace or warrenty engines.

Now with a 2:68 if you think about it you will not over rev your engine if you set it up right.... All you have to do is ADD MORE PITCH!!!!!!!!!!!!!!!WITH MORE PITCH , COMES MORE WIND, WITCH ========= MORE PUSH, SO THE BOAT WILL PREFORM ALOT BETTER. The boat will plane at a lower rpm and you crusing speed rpm will be less because you have alot of pitch in the prop witch also save on you fuel because of the lower rpm your running and the snap is alot better you will be alot less likely to get stuck with all that wind.
 
I'm wondering the same thing. I'm thinking my 454 will probably put out 400HP with pretty close to 400 fp at 1500 with max around 500 fp, I hope that flat. Do you think I can get by with a 2 blade or do I need the three?
 
Oh yeah, important information for the equation. I am building the engine for a 5500 redline. ratio is still negotiable depending on prop but I would like wide and slow!
 
A Buddy of mine just put on a2.68 w/3b max prop on his 502 carb motor. He is turning it 5000 and the prop is set at the start marks.Sounds like he may need more horse power.
 
A Buddy of mine just put on a2.68 w/3b max prop on his 502 carb motor. He is turning it 5000 and the prop is set at the start marks.Sounds like he may need more horse power.
 
Thanks for the help. I did some searching last night as to not repeat to many questions. Alot of great info here.Going to a lower gear ratio does make sense, but I still have a few questions.It seems that the guys running a 2.68 also have high RPM motors. Im talking a caddy here. I also keep reading more pitch, lots of pitch, tons of pitch. Per powershift they say you can only go 1/8 in. in either direction. How much pitch is tons of pitch? Have any of you caddy guys here Changed to a gear ratio lower than 2:1. And if so how did that work for you?
 
You are getting a lot of excellent help with the prop sound . But for the exhaust sound two sweep ninety degree elbows pointing as much towards each other as you can will help with the boat sound for those that are watching you but it will put the sound in the drivers seat... This is fine for me because I'm not the one complaining about the airboat sound. You can go to the FORUM page --down to Airboat sound Research then to Exhaust Sound an their are several post explaining this topic. with pics. of this type of set up.
 
I agree Cold,If your not going to spend any money on horsepower.Why would you change to a prop you cant get off the start marks withs :( My buddy had a 2.1 with 3b regular wide PS to start with.I would propably go with a 4b sensinch 84".
 
I agree Cold,If your not going to spend any money on horsepower.Why would you change to a prop you cant get off the start marks withs :( My buddy had a 2.1 with 3b regular wide PS to start with.I would propably go with a 4b sensinch 84".
 
hey jon c i have talked to patty at powershift and she said you can ease it up to 1/4 inch past the referance mark which will drop your rpms down i am guessing around a 400rpm drop by what she called fooling the sweet spot on your prop which would give you tons more pitch and tons more push quieting your prop down.as far as a 2.68 you can run it but unless you have the high dollar mods on your caddy trying to hit 5500 is possible but you would not want to keep it there for long.a caddy which you are familliar with and how you set it up really does not need to leave the 5000 rpm mark. more pitch to lower your rpm is fine the caddy is not like a small block chevy or a nice ls1 rpm's are a caddy killer. before you spend money pitch it 1/4inch passed referance mark and see where that puts you.my caddy is similliarly built i have my props at 60degrees in pitch 78inch long and three blades.i hit 4200 engine rpm with a 1.9 to 1 box.it moves me where i need to go and is not even as close to beeing as loud as it was as a direct drive.
 
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