Posted by Brian in Oregon on Tuesday, May 22, 2001 at 2:49AM :
In Reply to: Re: Ug. Wantum torque, no gettum from V6. posted by DAvid on Tuesday, May 22, 2001 at 1:18AM :
I don't have the specs for the big Dodge V-6. I think the one in the van was a 3.6 or 3.8 or something like that. It got up and ran when the van was empty, but with a heavy load, it dogged.
No experience with Holly fuel injection.
What I'd suggest doing is to get the torque and HP curves for the various engines you are considering and compare them to the curves for popular V-8's. In my experience, the V-6's make their power at high RPM and at WOT. The V-8 can make more power at lower RPMs and less than WOT.
Which brings up another point. Cylinder Pressure Loading. Ever hear of it? You want to strike abalance between power and cylinder pressure loading.
Many factors contribute to this - compression ratio, weight of vehicle, gearing, etc.
I'll explain it with an example. I have a 1970 Ford Econoline pop-top camper I bought from my parents, who bought it new. It got about 15 mpg at 65 mph on level highways due to 3.25 gears and it's little 302 V-8 engine.
When I drove it in steep mountain grades, I would often have to downshift to second gear, dropping to 50-55 mph WOT (Wide Open Throttle) and sending the temp gauge up. Fuel mileage went into the dumper. About 8 mpg at best.
I got fed up with this and dropped in a set of 3.70's. Not a huge change, but now I can do 60 mph on the same grades in third gear and the temp gauge barely moves. The fuel mileage dropped to 12-13 mpg on the flatway, but I still get 10-12 mpg in the mountains. Most of my driving is 1/2 and 1/2, so this worked out fine.
This is cylinder pressure loading. Notice the bit about the temp gauge. I was dumping a lot more fuel into the engine to try and get more power out of it. Yes, it was making power, but the engine was being pushed beyond its design limits for the application. You can change this by going to a bigger engine, smaller tires, lower gears, or shedding weight. You can, of course, add speed parts to the engine, but in reality, there comes a point where the fuel mileage and temp will come back to get you, plus reduced engine life, as rings, seals and gaskets are pushed to their design limit. Remember, moving a heavy truck puts stress on an engine far longer than a few runs at the drag strip would for the same engine.
The term Cylinder Pressure Loading pretty much can be summed up by the force the expanding gasses are exerting against the resistance of the piston. You can see how taller gears, smaller engine, and more weight in the above story provided the mechanical resistance of the piston against the expanding gasses.
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