Asking for advice: how to size an engine for an "economy car"?

[ssgtbaloo]

I have noticed that when I try to make a small, fuel-efficient car, if I use too-small of an engine, it gets worse gas mileage. My only fix so far has been to try a bunch of engines with increasingly-larger displacement until I find one that gives the best mileage,

Does anyone know of an easier way to match an engine to a car for maximum fuel-efficiency?

[Swartkin]

Well, economy cars have smaller engines, nowadays they have between a 1.0L turbo/NA i3/i4 engine or a 1.6L N/A i4 engine, but to make an economy car is the compression ratio, Cam profile, fuel mixture and ignition timing, read the descriptions and you will get it.

[Admiral Obvious]

It's a combination of quite a lot of things, mainly the specific efficiency of the engine, power and gearing.

Really, you want a car with enough engins power to actually achieve a reasonable speed for the weight of the vehicle, then you optimize the gearing so the car runs at peak efficiency at the target speed (with 90 km/h being the best target generally).

[Nick Fish]

Originally posted by Swartkin:

Well, economy cars have smaller engines, nowadays they have between a 1.0L turbo/NA i3/i4 engine or a 1.6L N/A i4 engine, but to make an economy car is the compression ratio, Cam profile, fuel mixture and ignition timing, read the descriptions and you will get it.

or na 1.0 or 1.4 engines

[Swartkin]

Originally posted by Nick Fish:

Originally posted by Swartkin:

Well, economy cars have smaller engines, nowadays they have between a 1.0L turbo/NA i3/i4 engine or a 1.6L N/A i4 engine, but to make an economy car is the compression ratio, Cam profile, fuel mixture and ignition timing, read the descriptions and you will get it.

or na 1.0 or 1.4 engines

My Renault Sandero is 1.6, and it's quite economical, also the chevy onix is a 1.0 turbo

[ssgtbaloo]

Originally posted by Admiral Obvious:

It's a combination of quite a lot of things, mainly the specific efficiency of the engine, power and gearing.

Really, you want a car with enough engins power to actually achieve a reasonable speed for the weight of the vehicle, then you optimize the gearing so the car runs at peak efficiency at the target speed (with 90 km/h being the best target generally).

I get the gist of what you are saying, but what "peak efficiency" am I aiming for? Am I trying to ensure that cruising speed (90 kph) coincides with peak torque or peak horsepower? Or something else?

[Admiral Obvious]

Originally posted by ssgtbaloo:

Originally posted by Admiral Obvious:

It's a combination of quite a lot of things, mainly the specific efficiency of the engine, power and gearing.

Really, you want a car with enough engins power to actually achieve a reasonable speed for the weight of the vehicle, then you optimize the gearing so the car runs at peak efficiency at the target speed (with 90 km/h being the best target generally).

I get the gist of what you are saying, but what "peak efficiency" am I aiming for? Am I trying to ensure that cruising speed (90 kph) coincides with peak torque or peak horsepower? Or something else?

There's a graph in the engine designer which shows efficiency, so each engine will be different, but in most non boosted cases, the engine will be more efficient at lower RPM unless you use a lot of cam. The balance is actually having an engine that can get to speed without having to burn through lots of fuel to get to speed (acceleration test) and then sustaining the speed at the best economy by dropping down a gear or more (cruise test).

[ssgtbaloo]

Originally posted by Admiral Obvious:

Originally posted by ssgtbaloo:

I get the gist of what you are saying, but what "peak efficiency" am I aiming for? Am I trying to ensure that cruising speed (90 kph) coincides with peak torque or peak horsepower? Or something else?

There's a graph in the engine designer which shows efficiency, so each engine will be different, but in most non boosted cases, the engine will be more efficient at lower RPM unless you use a lot of cam. The balance is actually having an engine that can get to speed without having to burn through lots of fuel to get to speed (acceleration test) and then sustaining the speed at the best economy by dropping down a gear or more (cruise test).

Thanks. It'll still take some experimentation, but this might make it a bit easier.

Thanks.

[sand hanitizer]

2 cylinder diesel boxer.

[Durolith]

you can even get a 5.0 I6 fuel efficient if you aim for it

[RiftHunter4]

1.6L is the sweet spot IMO. You can tune for economy or speed around that size. 2.0L is usually kinda big and 1.3 tends to be too small.

This is all assuming you're using an i3 or an i4.

[ssgtbaloo]

Originally posted by RiftHunter4:

1.6L is the sweet spot IMO. You can tune for economy or speed around that size. 2.0L is usually kinda big and 1.3 tends to be too small.

This is all assuming you're using an i3 or an i4.

I'm usually using a flat four, an inline four, or occasionally, a very small-displacement inline or flat six. I've been keeping the cams set to around 17 (mild) because the fuel efficiency seems to peak around there (sometimes it needs to be a bit higher or lower, for a particular car/engine combination, but it's a good starting point. I've been playuing around with 1952 tech, for the most part. I figure if I can get satisfactory results at a low tech level, then getting satisfactory results should be relatively easy when I advance further up the timeline.

[Duuvian]

In 1955 a very nice minicar body opens up. You can get it under 1000lbs finished without too much difficulty. I was able to get it to yellow power warning under 1000lbs with a tiny engine that IIRC had good fuel efficiency. It was a really fancy tiny engine though, in a 1946 campaign start. I had aluminum gubbins so I had at least 3 or so tech points in engines. I might have been able to put a cheaper engine on it, but I might have had to use more engine weight so I guess it depends on what you are trying to do.

The engine was tiny and was sort of cheap for that so I was still easily able to outprice the competition in the campaign even using an engine contractor, though since I had to bump up the difficulty slider for all the fancy starting tech and to maintain score multiplier, my car was basically selling on price alone rather than beating the competition I think.

That was 9 points in body tech and at least 3 in one of the engine tech lines for that combination I think. You can get that pretty easily with a no factory and no money start, but you might have to take dealerships too or or a plot or you go bankrupt on your first tiny car factory, I haven't figured out yet what the bare minimum start would be yet. I've managed to survive on preorders the 7 months it takes to build the first tiny car factory but I'm pretty sure I had also set dealerships to 5 as well.