pinchvalve
pinchvalve MegaDork
4/1/20 8:23 a.m.

A comment in a towing thread got me thinking, my FiST puts out 300 ft/lb at the wheels from a 1.6l turbo. If I put that engine in a 1999 F-150 body it should match the performance of the 4.6 liter V8 with 290 ft lb of torque and offer better MPG. Torque at the rear wheels doesn't care where it came from or how it was made, it is an amount of twisting force.

But who would prefer the V8 over the I4? Me too.

Why is that? Is the 4 banger really more stressed than the V8? I have to believe that a modern turbo with advanced materials and engineering would be more reliable overall than a 20 year old V8. The power is lower in the RPM range in the V8 for sure, but a modern 10-speed would offset that. Is it all just ingrained mindset?

oldopelguy
oldopelguy UberDork
4/1/20 8:39 a.m.

My 4-cylinder '19 Silverado drives very much like the 4.8L '04 I had a few years back, and on paper the engine specs are pretty darn close. I think it only works as well as it does, though, because it is very much optimized for low end torque as opposed to the high rpm power band that car motor would have. 

Streetwiseguy
Streetwiseguy MegaDork
4/1/20 9:11 a.m.

Both engines have to create the same amount of power to provide the same amount of thrust.  To produce that much power, each engine has to burn the same amount of fuel and air.  The four cylinder engine has to create twice as much power in each cylinder, so cylinder pressures are twice what the V8 would be, con rod loading is twice, and so on down the line.  For a commuter, running easily, the concept has merit, although I will argue that the benefit is small, since you need to burn a certain number of pounds of fuel to create a certain amount  of work. 

The trouble comes when you need to use the engine at its higher rating for long periods.

My example:  A friend here sold Nautique ski boats.  In 1986ish, he bought a brand new Astro van with a throttle body injected 4.3, producing 165 horsepower.  He used it for over 300,000 km to drag boats back to Saskatchewan from Florida, and never had a moments trouble with the engine.  One transmission, and a couple of sets of pinion bearings, but the old 4.3 chugged along happy as a little clam.  He replaced it a decade or so later with the same van, sporting a 4.3 with port injection, creating a staggering 195 horsepower.  He barely made it home the first time he went south, and I had to pull the heads and change all the exhaust valves, several of which looked very much like tulips.  The second trip, he went easier.  That time, it needed valves and rod bearings.

There is a big difference between "passing" horsepower and "towing" horsepower.  I also agree that modern electronics are a lot better at managing power levels to prevent such issues, but I have seen a 3.5 Ford turbo burn up because of a large trailer, a headwind, and an impatient owner.

z31maniac
z31maniac MegaDork
4/1/20 9:18 a.m.
pinchvalve said:

Is it all just ingrained mindset?

Yes, that turbo 4 is going to be in boost non-stop. Imagine the heat.

Floating Doc
Floating Doc UltraDork
4/1/20 9:19 a.m.

Actually, the fiesta gets the torque in at a pretty low RPM. 

Edmund's dynoed the FiST and FoST, torque peak of the former was around 2500.

Heat dissipation is a big part of making a small boosted engine survive in a truck application where it could be on the boost for long periods of time. 

Toebra
Toebra Dork
4/1/20 1:13 p.m.

All torques are not created equal, the ones at the small end of the tach are better.

 

I presume those turbo trucks have an oil cooler, and a timer so you run it a bit before shut down.

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