CarMotorBarge wrote:Well car motor guys definitely don't pay high dollars for used parts like A/C guys do. With the competition in the SBC, BBC, and LS markets, car motor guys are able to buy NEW parts at COMPETITIVE prices. This definitely doesn't happen in the A/C market.
So adding a 1.5 ratio gearbox to an A/C engine so you can make 50% more prop shaft TORQUE is losing your balls? So is it all about TORQUE or not?
CMB, no doubt the AC market is used, but it is generally quality. Regardless, cost is not my primary driver, not even the cost of fuel. I'm 1 hour minimum from legal running, I want a boat that runs right when I get there and brings me home, reliability is #1 for me. My present motor ran 4 miles of ground with a quarter size hole in #6 cylinders 2 years ago, no skeeters around me then. Replaced the cylinder in 2 days and back running, just got all the parts out of the pan last weekend. That makes the balls feel larger.
Putting a 1.5 ratio gear box on my present AC motor would probably result in throwing a rod out the pan leaving me twiddling thumbs 1-1/2 hours from home on a Sunday night. Sounds like Experimental Ball Removal Surgery to me, EBRS for short, see how close to EPRB that is?
Real men think about stuff like this.
Seven3 wrote:This feud you guys are having is both hilarious and entertaining, lol. But it seems like it’s all in good fun. I know this is more of a HP vs TQ debate than a CM vs AC, but in the end that’s what it ends up being. IMO it all comes down to the size of the boat you need to power. 12 foot and under, generally speaking you need AC. 15 foot and over, generally speaking you need CM. 13-14 foot is really where you can go either way. I’m an AC guy, but I admit that if you need to spin a big prop on a big boat, you need a CM. Sure you get can go with an 0-720 or a GSO-540 or 480, but those things cost so much to run.
Seven3, Glad we could keep you entertained! On the CM vs. AV subject, that is exactly the reason I posted my thread in the Airboat Tech forum as opposed to the Aviation only forum. As the thread title says, I am building 2 boats, identical hulls. But I am not building 2 identical boats, Ghost is gonna be AV for sure, Boat #2 remains undecided. Your point about the 12-14 foot range being the "either way" range is pretty spot on in my case.
I love the hull, it's perfect for my primary use. The narrow width decreases the amount of ground it has to run over/through and 14 feet of length makes a huge difference on the ride vs. a 12 foot boat. The extra length also let's me haul extra weight up front, like dogs on the nose. It actually runs easy dry with 2 people at about the same RPM as on plane in deep water (2,000-2,300). So eliminating weight is driven more by the boat's performance in deep water, but it will help dry for sure too. Hull is 7' wide total, but it's only 5 feet of flat at the transom with 1 foot of roll on each side, so every pound on the transom sinks the rear a lot more than flat bottom, 7-1/2 - 8' boats. Everything is a trade off, in my case tilted more towards ground vs. deep water.
Ghost, Boat #1 is gonna be AV with a 500 Ft-Lbf straight valve 540 Engine that makes about 260 Hp at 2,800 on the prop. The original boat as is runs very well. But as I am trying to document, it has been hauling quite a load. Ghost is gonna run like the same boat less one of my larger buddies and his extra cooler.
Moving on to the future, I want more outa Boat #2. I think CMB really summarizes the argument well in this quote (stolen from his Low Torque thread):
CarMotorBarge wrote:The debate you get into on an airboat is whether you should shift the torque curve to the left or the right on a dyno sheet and what gear ratio you should use. The LOW TORQUE LS Engine build in this thread will be shifting the torque curve to the right. Max HSP will be at 7,000 RPMs and a 2.88 gear will be used.
Honestly, I have no idea why someone would build a 7,000 RPM motor and only make 400 Hp, if you just cut off the gas and leave the throttle open the damn thing will probably keeps pushing for a couple seconds just from crank inertia. It's probably gonna need a secondary containment diaper to keep the EBRS in check (see above). I Seriously, I hope CMB has plans to turn that egg beater into a 650 Hp machine soon after our competition (maybe for round #2), otherwise it seems like a hell of a lot of effort just to shut me up.
At the start of the thread I said that Boat #2 was going to be 600 Ft-lbf minimum and less than 400 Hp. I am gonna try to keep things down, but staying under 400 Hp may be an issue. I intend to make maximum use of the prop torque curve and explain why. I do not want #2 to weigh more than the Ugly Duck. Deleting 150 lbs or so of rigging and switching to a single rider rear gives me a good bit of weight to work with.
Maximum prop limited to 76" and torque roll limit maximum reasonable power. Reliability, range and running quiet are also big goals. I don't give a crap how much fuel the boat burns, as long as it meets my other goals. I love the sound of a muffled AV motor just doing it's thang. I have also seen some real quiet CM boats that impressed me. But those damn loud a** high RPM CM race boats are getting us all run off good land, now and in the future.
In summary, I have 2 hulls to compare power plants side by side. One may be a AV or a CM and it may or may not have a low ratio gear box on it. One is gonna be high Torque, the other is gonna be higher torque. Time to come up with a name for #2, "Torque Ghost", "TorqueAGator", "MomentArm". Hmm....