Balance of mpg and fun for a swap

If you were looking to build a commuter and wanted a good balance of fun to drive but yet get "good" mpg on regular (non-premium) fuel. 
 

Let's say we want the end result to be RWD and a manual transmission. 
 

Start with a light weight chassis but what engine and transmission combo do you use? 
 

Kswap from a RSX? 
ecotec from a cobalt? 
is there a rwd transmission for a Chevy Cruze engine? 
tdi swap? 
 

Seems like all those engines in their stock forms get hwy mileage into the mid 30s. 

Light weight and RWD unfortunately are pretty limited. Obviously this depends on what your idea of "light weight" is.

Assuming under 3k lbs, the main cars I see are the subaru/toyota/scion twins (triplets?) and Miatas. 

Without a doubt, the most popular swaps for these are the typical LS swaps and the potent Honda K swap. 

Budget,goals, and available skills are the key factors in making any of these decisions. 

Want a Miata that looks like it came from the factory with a warrantied 500 LS ponies under the hood? Call up V8 Roadsters and send them your car and ~$50k.

I do realize you mentioned "good" mpg and you might think I'm crazy for mentioning a v8 right off the bat. You also might be surprised how good the mpg can be with an under worked v8 vs an over worked 4 cylinder. 

Lots of variables left unknown in your equation. Define the following and we can probably help even more. Budget? Lightweight? Fun? Good MPG? More specific goal?

In reply to JAdams :

Good points

light weight sub 3,000 sounds good. 

Budget let's say sub 10k, I am more just day dreaming about this so no real specific project planned. 
 

Target mpg mid 30's highway.
 

Fun is responsive throttle and would be something fun to run through the gears on a highway on-ramp.  

You already know The Answer.

If I needed a commuter/sporty combo the 2011+ Mustang w/ 3.7L V6 is rated for 30 mpg hyw.  

I'd stay out of the game of making more hp, it already makes 300 hp, but you could go endlessly deep into mods for more brakes and more handling. 

John Welsh said:

If I needed a commuter/sporty combo the 2011+ Mustang w/ 3.7L V6 is rated for 30 mpg hyw.  

I'd stay out of the game of making more hp, it already makes 300 hp, but you could go endlessly deep into mods for more brakes and more handling. 

And way less weight without sacrificing much.

If I didn't care about safety I'd put a Honda Fit engine in a Datsun 1200 chassis.

When you say "commuter," does that mean you need A/C, a top and windows, or is a Lotus  7 kit car is okay?

In reply to John Welsh :

Great idea. I guess there is also the cadillacs  with the lfx. I was thinking they are close to 30's hwy mpg as well.  Maybe a bit heavier than the mustangs though. 

In reply to Toebra :

It would need heat, windows and a roof. Wouldn't need ac though. 

In reply to Tom1200 :

Is there a rwd transmission for the fit engine? 

I've had two of The Answer- one '95 and the '99 I have- and I was getting 30mpg commuting to work and back.  And I've dreamed of doing a trans/rear end swap.  Back when the swap page existed, one could put together a trans from an RX7 and one of the oddball rear ends which would end up with 1-3 being almost the same wheel rate as the original, 4 being well lower, and 5th dropping 70 mph from 4000 to 3000 rpm.  Given I would get the same mileage top up or down or hard top on- the root fuel economy problem would be engine spinning losses.

Not sure how hard that would be, but a boosted Miata with those kind of gears would probably be a great package.

In reply to Somebeach (Forum Supporter) :

They are currently in Formula Fords; there's an adapter plate for a hewland box which can easily be modified to fit various transmissions.

Whatever engine came with the car.  $10k buys a lot of fuel.

Somebeach (Forum Supporter) said:

In reply to Tom1200 :

Is there a rwd transmission for the fit engine? 

Yes, but you have to put the motor in the back.

One thing to consider is the fuel economy will be worse.  Hypoid gears (such as in a rearend) have much more losses than normal gears.  Mounting the engine longitudinally is an instant efficiency hit.

C5 Corvettes already get high 20s-low 30s. Remove LS1, install LR4. Profit.

Toebra said:

Somebeach (Forum Supporter) said:

In reply to Tom1200 :

Is there a rwd transmission for the fit engine? 

Yes, but you have to put the motor in the back.

Actually no, I can't remember which one but one of the Ford boxes will work.

Pete. (l33t FS) said:

Whatever engine came with the car.  $10k buys a lot of fuel.

Similarly, if you're set on doing a swap, the cost increase of 93 octane is basically a rounding error in total cost, so use whatever engine you want. Most modern engines are happy running on any fuel, 87 octane drops a bit of top end and maybe very low end power. At current prices, 30mpg on 93 octane is comparable to upper 20s mpg on 87 octane, which is still pretty good.

K Swap Miata?