Engine swap questions possibilities.

[cRiPpLe_rOoStEr]

There are many things that could be taken into account, such as the air-to-fuel ratio, compression, RPM range and how the cam profiling and the headers can lead to an optimized low-end output. Sometimes I actually consider doing a similar project to tune an apparently "oversized" and "outdated" engine and fit it into an econobox.

[ar5boosted]

So I'd be looking at putting in a Ford Turbo Diesel engine from Europe. Go with the same brand of engine because it makes things a lot simpler. Make sure you get the wiring harness and ECU as well.

Specifically the 2.0 tdci from the Ford Mondeo

Look here for the fuel consumptions:

- 2011 Ford Mondeo MPG - Actual MPG from 9 2011 Ford Mondeo owners

This 2.0tdi should easily have the torque of the old 3.5 petrol engine and it's more likely to feel more powerful than the original engine.

You can see people are getting 41-48mpg from those engines.

[Ecky]

Taking an engine from a 5000lb, 15.0 CdA 20mpg vehicle and putting it into a 2500lb, 7.5CdA vehicle will not automatically result in 40mpg, which many vehicles that size already get. When I first got into ecomodding I actually thought the opposite - why did the F150 I was driving have a 5 liter engine producing 170HP, when Honda was building 1.6L engines which also peaked at 170HP? Wouldn't swapping the huge engine for a smaller one improve economy, without losing any peak power, even if gearing needed to be different?

Neither is strictly correct, because all engines have an RPM and load range in which they're most efficient, and it's best to pair an engine with a vehicle whose weight and drag put a load on the engine which is most often in that ideal range.

Take for example the 3 cylinder 1.0L engine in my Insight. It's most efficient between 1700 and 2300RPM, at about 75% load. In my car, I can cruise on the highway in excess of 100mpg because the engine is perfectly sized to stay in that range. If I were to put that engine into another heavier and let aero vehicle, I would need to regear it. In a typical econobox (weighing about 50% more) it would likely need to be spinning at 3000-3500RPM, where it's significantly less efficient, so despite the new car only needing maybe 50% more power to go down the road, it would almost certainly take more than 50% more fuel, resulting in a lot less than an ideal 33% lower MPG.

The same is true of dropping a big V6 into my tiny aluminum car. To produce the power needed to go down the highway at high load, the engine would likely only need to be spinning at something like 6-800rpm, where it's extremely inefficient. Alternately, it would be running at low load, where it's also a lot less efficient. Putting a bigger engine in this car, even with the same peak BSFC, would be guaranteed to result in worse economy.

[cRiPpLe_rOoStEr]

Even though a higher-displacement engine might seem overkill when fitted to a small econobox since it would eventually not operate at a load that would lead it to reach its best BSFC figures, it still doesn't sound totally unjustifiable. I'm just not sure if the Cologne V6 has enough aftermarket support to provide cams and headers that would improve its low-end output and make it less rev-happy in order to match the requirements of a lighter and more aerodynamic econobox that would have it matched to a higher gearing.

BTW sometimes I actually feel tempted to do a quite similar project, even though I would want to go even further and try a flathead engine since they're noticeably less rev-happy, and the inherently lower compression on them would easily enable lean-burn.

[Ecky]

Maybe not unjustifiable, but most of the time it's exactly the opposite of what would help improve economy, if that's your goal. Generally speaking, downsizing (a little, at least) improves economy. That, or re-gearing. Downsize too far though and you're pushing a small engine out of its efficient zone.

[cRiPpLe_rOoStEr]

Downsizing vs. downrevving, that's somewhat of a great dillema. I'm not totally unfavorable to downsizing, but it's more than simply dropping a smaller engine and leaving all else equal. There were times when subcompact cars fitted with naturally-aspirated 1.0L engines held over 70% of market share in my country, basically due to fiscal benefits, but it was not unusual for the very same cars to get better mileage in export markets where displacements around 40% to 60% higher were the standard, since it enabled the usage of higher differential ratios and a decrease to the engine speed while cruising.

OTOH a truly-downsized engine, fitted with forced-induction and direct injection, is likely to fare better than a naturally-aspirated one with a larger displacement and port-injection, mostly because direct injection enables it to run leaner, but there are also some concerns about long-term reliability that still favors old-school engines and downrevving among some conservative folks.

[Ecky]

In the 'states we have the opposite issue, with most cars coming with far more displacement than is necessary.

[cRiPpLe_rOoStEr]

Originally Posted by Ecky

In the 'states we have the opposite issue, with most cars coming with far more displacement than is necessary.

Considering that certain trucks made in Brazil and Argentina had smaller engines than their American counterparts, I could agree with you on that matter, even though it's still quite arguable.