Gear ratio question

[wca_tim]

I dont agree with your HP theory on top speed thats why small blocks are a flop in boats. They can have plenty of HP but no torque.

sorry man, not a "theory". What rpm was your wot? and it bears mention that you can't have horsepower without torque nor movement without horsepower. They're inherently linked.

 

[mkhammer]

A mild 450 hp 502 will produce 500 ft lbs of torque at 3800 rpm.
A 500 hp 383 may see 500 ft lbs of torque closer to 5000 rpm.and peak hp over 6000 rpm
Do I have to go into what that means?

If this post has turned in to which is a better boat engine small block or big block.

There is no comparison the big block wins hands down.

Offshore,GN,ski race, and drag Boats don't win races with small blocks.

Small blocks can be made to run pretty darn good but there is a cut off point for power and reliability where they just can't touch a big block. I can sell you a Dart 500 hp 406 ci 512 ft lbs of torque at 4800 rpm Marine engine that's reliable for 10K. For a few bucks more I can sell you a dart 750 hp 598ci with over 780 ft lbs of torque at 4800 rpm and that's the mild one. show me a naturally aspirated SB that does that on pump gas.

Dollar for dollar a small block can't match the hp and torque of a big block.

Build to build there is no substitute for displacement.

This is no theory it's real world running


MKHammer

 

[wca_tim]

No question regarding your post!!! I was ONLY referring to the part about propping for wot at peak horsepower and which dictated max speed! and it's horsepower because that is the point where there is the most ability to provide forward motion (work!) against resistance (drag).

...and no you don't have to go into what it means. I get it - big time.

For ANY engine, if you have the dyno curve and a a stab at where you think it's going to hit for top end, isn;t the sweet spot for performance going to be right where peak horsepower is at wot? peak torque is lower and where you get the strongest mid range accelleration - horsepower corresponds to the ability to move at a given speed against drag, torque translates into the ability to accellerate to that speed.

to your point - the ONLY reason I have a small block in my current little beater is because I wanteed it to go a good bit faster and there's no substitute for displacement - the biggest engine it was offered with was a 4.3! I went with more cubes rather than try to squeeze much more than say 220 or so horse out of the v6. A big block woult be fun... however, it already sits kinda low in the ass end, the risers clear the engine hatch by a half inch as does the flame arrestor - that's with the hatch shimmed up about 1/4 - 1/2 inch with an extra thick gasket...

A mild 450 hp 502 will produce 500 ft lbs of torque at 3800 rpm.
A 500 hp 383 may see 500 ft lbs of torque closer to 5000 rpm.and peak hp over 6000 rpm
Do I have to go into what that means?

If this post has turned in to which is a better boat engine small block or big block.

There is no comparison the big block wins hands down.

Offshore,GN,ski race, and drag Boats don't win races with small blocks.

Small blocks can be made to run pretty darn good but there is a cut off point for power and reliability where they just can't touch a big block. I can sell you a Dart 500 hp 406 ci 512 ft lbs of torque at 4800 rpm Marine engine that's reliable for 10K. For a few bucks more I can sell you a dart 750 hp 598ci with over 780 ft lbs of torque at 4800 rpm and that's the mild one. show me a naturally aspirated SB that does that on pump gas.

Dollar for dollar a small block can't match the hp and torque of a big block.

Build to build there is no substitute for displacement.

This is no theory it's real world running


MKHammer

 

[mkhammer]

No question regarding your post!!! I was ONLY referring to the part about propping for wot at peak horsepower and which dictated max speed! and it's horsepower because that is the point where there is the most ability to provide forward motion (work!) against resistance (drag).

...and no you don't have to go into what it means. I get it - big time.

The big problem with a small block that's built to make "a lot" of horsepower is that it gives up a ton of torque on the bottom end - to prop it to take advantage of the max horsepower at wot, it may not even have enough ass down low to get on plane!

For ANY engine, if you have the dyno curve and a a stab at where you think it's goig to hit for top end, isn;t the sweet spot for performance going to be right where peak horsepower is at wot? peak torque is lower and where you get the strongest mid range accelleration - horsepower corresponds to the ability to move at a given speed against drag, torque translates into the ability to accellerate to that speed.

I'm not sure what your point is. But this I can tell you, If you have a small block set up already. It would be fun and rewarding to build it up to put it to some mild big block set ups.
The draw back is most have to do it with a Alpha drive.

 

[wca_tim]

The main point I was making was that Peak horsepower is what dictates maximum speed - even though it's a broad, strong torque curve that dictates performance everywhere else, ie ability to accellerate.

The original topic of the thread was gear ratios. The answer for a "starting point" in the pursuit of best top end is to choose a gear ratio based on expected max speed that puts prop pitch to diamever ratio around 2 - for 14-15" props, that's

To be honest, I bought this boat to learn on and plan in the next year or so to buy something a good bit bigger and faster. if I wind up with something in the 24-27 ft class, I would talk to Joey about building a blown big block, a bigger boat and it would be two I assume (depending on what I wind up with). I'll look for a "project" when I have enough cash saved that I can afford to pay for power (assuming 15k++ per engine) and any other work or mods needed to get it done and on the water.

I love to go fast on or in anything and I always get chills when I've been by the shop and they're running big power / race engines on the dyno. I also (used to?) love to watch the Fountain crew wet testing boats out on the river.

The screaming outboard / tunnel hull crowd that hangs upriver have some cool, extremely fast toys, but I doubt I'll never get over the sound of big block power on dry pipes...

Speaking of which, I better get some work done toward that goal..

I do very much appreciate (everyones) patience and teaching.

I'm not sure what your point is. But this I can tell you, If you have a small block set up already. It would be fun and rewarding to build it up to put it to some mild big block set ups.
The draw back is most have to do it with a Alpha drive.