Best budget/MPG engine for RWD project
 

I'm going to put together a Lotus 7 replica or similarly light RWD project car and am sorting through engine options. I'd prefer something that is relatively common (so newer than 1990.... newer than 2000 would be even better) and affordable. I'd entertain the idea of <60-80hp motors but am looking at some feasible 130-150hp options that would be much more entertaining.

I'd like to focus on gasoline engines right now, I know a VW TDI 3 / 4 cyl would meet all of my goals but unless I find a steal on one, it's going to take a long time to pay off. I also believe that CNG is something that I'll be able to use locally in the near future and I think once that crazy-cheap fuel cost is factored in, the diesel loses most of the advantages it has.

Whatever I pick, if necessary I'd run it on standalone EFI and have no problem adapting whatever motor it is to my RWD longitudinal transmission of choice.

I have Datsun 70's model A12/A15 motors and parts and could stick multiport injection on one, but don't think it's going to stretch the economy too much and will certainly not get past 80-90hp without adding a turbo... and replacement parts have gotten higher.
Suzuki/Geo Metro 3/4cyl are interesting but getting to be a bit long in the tooth.

Honda: L series, R series. Certainly getting cheap enough and spin the correct direction. Then I see that K motors have come way down in price and I know I could take the project in another direction by going gonzo power with one of those. So right now my favorite seems to be the R18, the simple Vtec on it and it's psuedo-atkinson cycle really seem promising.

Turbo Japan Kei car ~667cc engines could work, but USA availability is certainly an issue.

If there were more BSFC charts (one of the best collections I found was certainly here on the forum! Thanks!) I would have more to debate with but for now, I'm open to more thoughts and suggestions!

I would use a Honda D15z1 from a Civic VX or a D15 from Japan, it's pretty close to the D15z1 only it has the 3 stage V-tec head and a different intake but I think it is otherwise pretty close to being the same engine block, the D15z1 is around 92hp at 5,500rpm and the D15 is said to be 128hp at 7,000rpm.
These engines tend to last 300,000 miles, unlike some of your other options, this also makes them cheap and common.

Honda D, B, H, etc.... older engines spin the wrong direction for me to hook to a regular RWD transmission. :(

1.6 from an early Miata? Parts availability is very good, especially weight-reducing and performance enhancing mods if you want more than the original 115 horsepower. Online community is very helpful as well.

The NA Miata, with a .38 Cd, was rated at 30 highway (old number), so it seems like the potential is there for some very good mileage, especially in a light car with a higher-geared differential &/or bigger diameter tires.

1.8 from the NB Miata makes ~140hp stock, returned the same mileage rating.

The Miata transmission is a real sweetie as well, short throws & good feel. 6-speed is available on the some of the later ones.

Certainly a possibility, and I do like the gearboxes. (Coincidentally my gearbox of choice could be turbo mazda rotary) I do think it's going to be behind in MPG compared to like a Honda R18 and for no major gains (except that it's ready to go RWD, which is one)

I may inject one of the old datsun motors and see where that gets me, if they got the best epa highway mpg for the years they were made, certainly I could inject it and get a BIT better? But it's still going to be turd slow (<70hp) unless it sprouts a turbo.

Have you considered motorcycle engines?

If that's not where you want to go, maybe GMs Ecotec line. I believe any Ecotec engine will mate up to the RWD trannies in the Solstice/Sky and this would give a wide range of sizes/performance to choose from.

Look to small pickups? 4cyl out of an S10, Ranger, Tacoma, etc. Very common and inexpensive.

Nissan 240SX motor?

Suzuki sidekick 16v 1.6 engine. Can do 15psi boost with very little mods. I could hit close to 30 mpg keeping up with traffic with stock tires and stock 5.12:1 gears, revving high and the tracker / sidekick is not very aero dynamic

knew a guy to run 15s with stock drietrain and 33 inch tires with a turbo

The more I think about it, the more I think that anything >2 liters is going to have to be a very well designed motor to do anything near what the honda R18 does. Since it has very high compression yet has the economy cam profile to reduce pumping losses, it should sip fuel like a motor even smaller than a 1.8 at cruise. Yet still makes ~140hp! If some other great BSFC numbers come up or if someone can highlight some great highway MPG feat of some engine that suggests that it must be approaching the best of the best BSFC.... That's what I'm looking for.


I'm not going to run a motorcycle engine. I'll keep the ecotec in mind, as I certainly can pick up a bolt on transmission for it but I still think the R18 honda is going to get better fuel economy. Once I get to play more with direct injection gas motors, the Ecotec and Mazda stuff could be ones that I would deal with in a swap scenerio but right now they're a bit pricey and I'm afraid of parts costs.

The later Ranger's mazda MZR motor is one I've thought some on. Aluminum block and modern fuel economy oriented cylinder head is a plus and I believe I could run a smaller 2.0 from a car. I don't think the S10 stuff is going to eek out quite the fuel economy the more modern designs will. I've seen what the tacoma 2rz/3rz motors can do, big big power under boost, but they don't seem to be as economy oriented as the other newer car-designed motors.


I have a bunch of 240SX stuff but they are certainly not too exceptional on fuel economy. Giant stroke "truck motor" .... If I get some parts together and the project seems to be moving along quickly, I may actually drop the new drivetrain into an extra 240sx I have instead of the older lighter car. I'd focus more on the 240sx if I had a taller geared diff for it as I know the aero is pretty good and I could take a bit of the weight penalty considering how much less work it will be to get finished than the older car!

If I run into one.... I'd certainly like to give it a try over the older 3/4cyl Suzuki aluminum block motors. Looks like they make ~95hp to begin with? Not bad, wish it made the ~120hp of the 1.8 liter version. At least it should be on the very light weight end of things like the earlier ones, and 1.6 liters is nice and small.

An Insight I engine without the battery ?

Lotus 7 is very popular with the Zetec 2.0L, and I say that not just because I have one in my ZX2. In that light of a car, 50+ mpg would be easy with better gearing.