Aluminum Camper Forum

Boattest.com, a boat review site that I subscribe to, just published this article on tow vehicle selection: http://www.boattest.com/view-news/5349_how-to-choose-the-right-tow-vehicle

Although it is a bit oriented to heavier trailers- you don't need a V8 to tow most LL campers (but not at all towards boats), it has a nice analysis of the various factors in selecting a tow vehicle for a given trailer. It defines all of the weight terms like GVWR and GCWR and notes that staying within the GCWR often means that you cannot tow at the rated tow weight. I also like that they say up front: pick a tow vehicle with 25% more tow rating than your trailer for safety and GCWR considerations. You won't hear that from trailer sales people ;-).

David

Thanks for posting that. Good info and I like what it has to say about torque (mostly because I agree with it!).

With all due respect to the boating mag, and without starting a long online argument, I'd like to disagree on torque vs HP. Torque is important only when it is delivered to the wheels and is required when starting or accelerating. Torque at the wheels is engine torque times gear ratio so increased torque at the wheels is just a matter of using a lower (higher ratio) gear. OTOH, HP is required to get you down the road, through the wind, and up the hill in a reasonable time. No amount of torque will let you climb the hill at 40-60 MPH if you're out of HP. So, look for HP first. If two engines have the same HP then go with the higher torque. If two engines have the same peak torque go with the higher HP.

In general I agree with you Charlie, and physics is physics.

But since autos were first invented, drivers have appreciated the immediate kick in the pants when the throttle is pressed, WITHOUT HEARING THE ENGINE REV UP UNNECESSARILY. It takes torque to do that and until the recent advent of high boost turbochargers, it also takes a lot of cubic inches.

David

Quote from: DavidM on April 07, 2017, 02:54:54 PM
In general I agree with you Charlie, and physics is physics.

But since autos were first invented, drivers have appreciated the immediate kick in the pants when the throttle is pressed, WITHOUT HEARING THE ENGINE REV UP UNNECESSARILY. It takes torque to do that and until the recent advent of high boost turbochargers, it also takes a lot of cubic inches.

David

Ah yes. The rumble of the Chevy 350s and the Pontiac 400. That's as big as I ever got. But now I've grown older, wider and deafer so I'm stuck with the Pfsst of the 6 bangers. I still believe there ain't no substitute for cubes  .

Quote from: charliem on April 07, 2017, 12:37:23 PM
With all due respect to the boating mag, and without starting a long online argument, I'd like to disagree on torque vs HP. Torque is important only when it is delivered to the wheels and is required when starting or accelerating. Torque at the wheels is engine torque times gear ratio so increased torque at the wheels is just a matter of using a lower (higher ratio) gear. OTOH, HP is required to get you down the road, through the wind, and up the hill in a reasonable time. No amount of torque will let you climb the hill at 40-60 MPH if you're out of HP. So, look for HP first. If two engines have the same HP then go with the higher torque. If two engines have the same peak torque go with the higher HP.

Your reasoning is right on, so no argument from me. I just found it refreshing to read that torque is an important number. I find it pretty disingenuous the way manufacturers are now pushing their engine HP ratings in ads, because the HP is often achieved only at very high and not really usable rpms. I also agree with DavidM that the turbos and supers are a game-changer in relation to cubes. In all of this, I can't help but think of the old make-or-break engines with their 200 lb flywheels. Torque out the wazoo but only just enough HP at one speed.

Merlin,

Over the years I've become resigned to the fact that there's no perfect solution to the car/SUV/truck problem. I'm still looking for that 400 HP red sports car that hauls 5 kids with gear, an old sofa, 1000# of bricks, a sheet of plywood, pulls a trailer, is comfortable for the family vacation, gets 40 MPG and parks on a dime. Ain't no such thing. It does concern me that auto builders are rating HP at increasing and insane RPMs. I guess there is some benefit to age related loss of high frequency hearing  . I like the superchargers and turbos for altitude  performance but I worry about the durability of those small overworked engines. Time will tell. Now, what were those make-or-break engines?

I think that the high revving, high boost, low displacement engines that are in some of our cars are not all bad.

Our new little Mini convertible has a turbocharged 1.3 liter, 134 hp engine and is a blast to drive. Twenty five years ago we had a Miata with about the same hp but at 2 liters. The Mini gets much better mileage than the Miata did and they perform the same, but hey my right foot is also older.

Time will tell how they hold up. I think that better lube oils, better metallurgy and better design will let the Mini engine hold up well. Fifty years ago 100 hp per liter was not available in a production engine. Heck Grand Prix engines of that day barely made it. Our 1968 Triumph had a 2 liter engine which only made 60 hp per liter. Today 100 hp per liter engines are everywhere.

But the foregoing applies only to cars not towing a heavy trailer where the need for a hp hit is only at freeway entrances and passing and it only lasts a few seconds. Towing a trailer generally requires double the hp than without (the gas mileage drops in half) and it is continuous- hours and days at a time. So towing a heavy (more than 50% of the TV weight) trailer puts continuous stress on the engine and more cubic inches or liters of displacement is really the only way to cope.

David

David,

Can you even buy a cubic inch engine anymore? Seems like they're all liters now.