experiment in power and fuel economy

[woodrowskis]

Time to overhaul/upgrade 96 Explorer/old friend.
I have a 96 Explorer 4 dr 2wd with the 5.0 L that I purchased new. It is not worth much to sale so I have decided to put some money into it and make it worth keeping another dozen years or so. However, I feel where I want to go is a bit unusual.
I am interested in bumping the hp above 300 (maybe the 350 range) but intend to drive it to work a lot. Therefore I do not really want it loud and I want to upgrade the hp in a way that will leave me the most fuel efficient manner as can be for stop and go commuting, 30 miles to work and 30 back every day.

It has 260K miles with no overhauls (or even a timing chain) on engine or transmission. So both need overhauled and therefore can be considered expendable.
The only money I have spent is for a pair of ford motorsport headers to fix that ticking noise (not yet installed) as this is what started this project. And no I do not know if they are sufficent yet. Original plan was to fix the truck period and plan changed to upgrading afer ordering them. I saw that Ford Motorsports catalog.

Engine: Seems the most fuel efficient power would be turbocharged but I am curious how turbocharging or supercharging affects mileage in stop and go traffic. Is one better than the other? Should I stick with this engine or consider a more modern one like the 4.6L if I want efficiency? I do seem to lean towards the nostalgia of keeping the 5.0L. But it seems that a smaller but turbocharged engine might be the better anser for what I want. Is there a hp number I can reach before the efficency really declines? I do want more than what a cold air intake, larger exhaust, and chip are going to give me.

Transmission: Should I start with a completely different model or can it be rebuilt in a better fashion? I have an Expedition that is already better on the Hwy but a good deal worse(and sluggish) in stop and go. It seems I could possibly gear for best fuel economy for 50 and under (which would probably speed up the low end) and dedicate it as the intown vehicle and the expedition as the hwy vehicle. Don't know what data there might be on that.

I do a lot of engineering work with large industrial engines so I understand the theory of turbocharging, economy, sizing exhaust, transmissions, etc. pretty well but my hands on experience is not so good. Never been a racer or had a hot rod. Too busy waterskiing. I figured it was about time to learn. Example, I know turbocharged with exhaust or belt driven supercharger is more fuel efficent at high hp than naturally apsirated but have no idea what happens to the efficiency at low load.

 

[Smythe302]

In theory, a turbo only "works" when the engine is experiencing load. When the engine has little to no load, such as at idle, or possibly even a constant speed on the highway, the turbo is not producing any boost. boost is (for the purposes of this oversimplified explanation) the addition of extra air into the engine. its accompanied by extra fuel and thus extra power. without extra air, there would be no need for the extra fuel and the economy "should" stay in an acceptable range under these conditions.

now there is often load in stop and go driving, hence lower economy with any car in general. a turbo would be no different. more load, more extra air and fuel, less economy.

in some degree of contrast a supercharger makes boost and power in a relationship with RPM(i'm not super duper sure of this statement, tho i know there are losses in HP due to the paracitic drag of the SC). this is rather than the turbo that makes boost and power with respect to load (actually thermal energy transfer)


i like the 5.0 and the large aftermarket following it has currently. However, the 4.6 is now very plentiful and the "higher technology" has the potential for increased benefits. space considerations could become an issue with the width of OHC motors. i still like it better. 350 is an easy goal to achieve with a power adder on a V8.

 

[woodrowskis]

thanks for the response. I am in agreement with you. i am intersted in the unloading mechanisms if any on the turbo and belt driven. that is going to determine the no load economy. large industrial engines have a wastegate so the turbo only makes as much boost as is required. This works verywell for 60% load and above. Thats the only range these engines need to work in. How well does this work at minimal load? Exhaust going through the turbo is going to make some extra back pressure. At speeds as low is idle, is it a measurable number as far as fuel economy? I do not know. And I know the belt driven gives more power from low speed, but the compressor is turning all of the time (direct linked with belt). How well does that system unload? Those are the answers I am looking for. I do know that when turbocharged engines came out they touted fuel economy. I have never heard a supercharger make any such claim.

Also, Iwas tired that night when I wrote. Really meant to ask about comparing a 6 cylinder (not the 4.6 V8) with some charging to get to 350 HP versus the 302 with would not be hard to get there without charging.

 

[steveofire]

I'll throw a little in on superchargers i don't know much about turbos. The supercharger that i have on my ex only throws boost when i pull a lot of vacuum so when i am cursing down the road the supercharger is only pulling 3hp until i pull enough vacuum to engage the supercharger and with a tune they are awesome through out the rpm band with instant low end torque.

 

[Smythe302]

ok so SC has the same type of deal as TC when making boost is concerned. there is some loss with the SC though.

Load is directly linked to your right foot as it turns out. Which is great news! It means that each and every one of us already posesses the hard to find and even harder to use... load limiting switch. up hill climbs will increase load and downhill will decrease in kind. removing or diminishing accessories will help decrease load. removing weight will also decrease load.

my dad tales of "back in the day" when people would hook up a vacuum guage and monitor it for best economy... this should read "boost guage" on forced air motors... i think i've seen them with +/- 0 psi

there's a really good website for the v6's called v6power.net its a forum like this and you'll find out that its actually not that hard to glean 350 from a 6

 

[Cobraguy]

Difference between SC and Turbos are many...but the best argument for the Turbo is it takes wasted energy out the exhaust and turns it into power. So in the grand scheme of things, the turbo is always more efficient for that reason. But, a properly designed positive displacement SC is so much more fun to drive on the streets because of the bottom end grunt that even the best turbos can't compete with. But if you take each system, and put the same amount of boost in each (i.e. 10 psi), the turbo will always have more power. Significantly so. The turbo doesn't have any parasitic losses the SC does.