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Ratios vs RPM of engines

C

Cadillac Performance Pts.

Well-known member
I'll be the first to tell you, I don't know much about the gearboxes other than I can build an engine to handle the rpms they add. One customer uses a 1.7 and a stroker engine and can pull it to 4800 with some prop, a big 80" 4 blade something, anyway, what kind of rpm can you spin with a 2.68 or more? Or does the pitch have more to do with it like a fat, tall tire? We can do engine that make peak torque at 5200 and go 7000 rpm for long periods of time, but I'm not sure if it'd do any good in a boat, unless it's a V drive, then I KNOW it will. I guess what I'm asking is will it benefit for pulling power and speed or is cruise at a good pace what you guys are after? Never rode in one so I'm not sure what you like to do with them. My stroker dude takes oil millionaires bow fishing. I think they actually shoot the fish and have a string to reel em in. Now that sounds like a sport to me. Kinda like hitting a baseball and running the bases....still carrying the bat! Ultimate Baseball Fighting Championship!
 
One of you guys with experience should explain to the Cad Guy how the higher ratio gearbox and big prop work together to get big push etc. He may have some good ideas on the cheap for us.
I have a mostly stock 472 Cadillac and bought a gearbox(2.37:1) and don't have a whole lot of $ to spend on engine upgrades.Sure would like to know where I need to put my money.
 
No sir, they claimed 400 hp, but I don't see it being possible at the rpm they operated at. over 500 ft lbs....yes. They just didn't move enough air through them to obtain it. Our crate engines are making over 500 ft lbs by 2000 rpm and peak with 600 by aound 4200 with peak hp at 4900. That's all the 2115 Edelbrock will allow. Smallest area in the intake port (known as cross sectional area) dictate when peak power occurs. It's in the middle of the 2115 and can't really be gotten to with a grinder. You can extrudeahone with the most aggressive aggrigate they have for about 450 bucks. By that time, a single plane is much cheaper along with a solid lift cam for a 6000 rpm peak. intake,cam and springs are about the only difference in a 600 hp crate engine other than a main girdle and ARP goodies. Keep in mind, the more you gain up top, it comes right off of the bottom! That can be bad in a boat.
 
Cadillac Performance Pts.":2086ns23 said:
...Or does the pitch have more to do with it like a fat, tall tire?
Click to expand...

Exactly. The idea is use the gear box like lower axle gears to turn the bigger prop (bigger tires), but at a slower RPM, and still have a ton of throttle response

I think your engines are close to ideal with the idle-up, flat-line torque curve. There is not much need to go above 5500 RPM on the engine, but it needs to have a lot of torque up to that point so that it can make the big props "snap"
 
Cadillac Performance I'm sure your big into drag racing! Look at it this way you know how all the Radial class and 10'' tire classes the stuff like NMCA. Well everyone is trying to run the tallest tire to get the car to hook then they run more gear because the tire is taller but end up turning the same RPM's thru the traps. It's the same principals we use more gear to turn more prop! U can run a 2to1 and turn your motor max RPM of 4,800 or run a 2.68 and turn your motor max RPM of 4,800. But with the 2.68 your swinging a hell of a lot more prop and if it where in a car you would be turning a hell of a lot more tire.
 
2.68 is multiplying your torque by 2.68 times

2:1 box only doubles the torque

Kinda like being in first gear with the 2.68 vs being in 2nd gear with the 2:1

2.68 will be more snappy; we call throttle response "snap"
 
The 2.68's tend to be snappier just like a gear in a car! The main issue which will eventually rear it's ugly head is when we keep building these brutal torque motors and adding more gear that there will not be a prop that can harness it. I expect to have to run a 5 blade super Wide on my next project. I'm sure a nasty Caddy with a 2.68 will require the same prop! Right now a Caddy with a 3.21 box would need a 5 blade but I don't like the 3.21 it's just like everything else there becomes a threshold of diminishing returns!
 
speeking of gearbox upgrades i talked to vaughan at precision he makes a bigger gear now or can redo a box to a bigger gear he does not recomend a bigger gear and he says it takes allitle time to machine.but it is another option for those with precisions so riggin modifications arent needed.
 
Are you talking about "bigger" like larger in physical size or a different gear ratio like 2.68?
 
Red Dwarf":qxryfj6i said:
Kinda like being in first gear with the 2.68 vs being in 2nd gear with the 2:1

2.68 will be more snappy; we call throttle response "snap"
Click to expand...
However if you were to run a taller tire in first gear the car will turn the same RPM's as a shorter tire car in second gear! The main thing the Caddy guy's are worried about is engine RPM. So I would run a bigger prop with a 2.68. Me personally If I ever built a Caddy it would have a 2.68 gearbox with a 82 inch 4 blade super wide. It wouldn't be to nimble but you could pull your house to your campsite if you wanted! You could also haul 20 people around if you cared to!
 
How can I simplify this. OK all the Caddy guy's are worried about engine RPM's. So no matter what you do that limits you. OK let's say the CADDY motor can only turn 4,000RPM if it turns 4,100 it blows up. Now if you run a Caddy with a 1.7 ratio which everyone thought was the ticket a decade ago you can only turn 4,000RPM right. I have seen dozens of Caddy's with a 1.7 ratio drive only swinging a 8 or ten blade Warp Drive. Now take that same exact motor put a 2.68 on it and only turn it the 4,000RPM guess what you better put a hell of a lot more prop a darn 12 blade Warp Drive ain't gonna be enough! The 2.68 gearbox turn the exact same RPM will allow you to swing a hell of allot more prop thus make a hell of a lot more thrust. Forget about engine RPM's get that out of your head and look at work performed after the gearbox. The 2.68 will perform more work then the 2to1 with both at the same engine RPM.
 
To take Dave's example to the extreme, in theory you could put a 5:1 reduction on your Caddy and at 4000 rpm you could turn a prop 10 ft in diameter. Of course you wouldn't do that, but in theory you could. One of the obvious things limiting you is the width of your hull, but you probably could if it was important to you.

There comes a point when there are diminishing returns though. A 10' prop would be turning so slow that it would be a lot less efficient than one 82" in dia. but turning at close to it's design speed.
 
I have spent a fair amount of time at STINGERS shop. I have not seen any broken shafts. I did strip a keyway but it was predicted because the gears were cut wrong but I said I would give it a go anyways, and STINGER WAS RIGHT. They fixed it with the correct cut gears when they got them and guaranteed I wouldn't break it and I haven't. I had my four blade super wide at the 3 mark and was over turning my engine and was going to the 5 blade super wide but it wouldn't fit in my boat.

As for diminishing returns well I never noticed any, I was getting more performance from a small block than most big blocks. I was running a 3.12 and I highly recommend them. You need a prop designed to turn slow and make an acceptable amount of thrust, I found the only one capable of doing it was the super wides. The optimum rpm for a prop is not always the maximum recommended rpm for that prop, the max is a safety factor. The super wides were designed to be most efficient in the 1600 to 1800 rpm range. I didn't test any water walker props so I can't address them. But as for gear boxes taking a lickin and keepin on tickin the only choice for me will be a STINGER, I don't care if it costs more i don't care if you need an adapter to run it with an LS1, I still will only run STINGERS PERIOD. But that is just me.

I have seen STINGERS boxes where they were run dry, I have seen them where the oil was never changed in them, I myself went two years without changing the oil in one because the dealer who sold it to me never said to change it. I have seen them run with out the mounting bolts tightened up on them BUT I HAVE never seen one with a broken shaft ,maybe they have one up there I don't know for sure but when I wanted one for a mockup I was making I had to wait three months to get one that was run with the mounting bolts loose until the case was worn out and it was still running on the boat.

Higher numerically gears and slower turning props are the ticket. I will run a five blade super wide on a small block and make it work very well, actually i will do it on my 396 small block once I repair it from the damage done testing the horizontal radiator, and the damage done by the demon carb gaskets dissolving and clogging the jets and runnin it lean and the damage done by the water inlet being porous enough to allow water to pass thru at operating temperature.

So if you want big boxes go to STINGER BOXES and be done with it, bolt it on and give it hell, change the oil every other time you change the oil on your engine, keep the mounting bolts tight and you are good to go no matter what ratio you run.
 
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