What would it take to get an RX8 to get 30 mpg on the highway?

Realistically, what would it take? First thing HAS to be an engine swap. I like the rotary but they are too thirsty and moody for me to consider DDing. So the easy button is the LS1, probably a 4.8l or 5.3L because of the lower displacement. Maybe using a Displacement on Demand motor... Next I am thinking that swapping to a Ford or Getrag Diff with a taller ratio. Would that get me there? What would I be out, dollar wise, to make this happen. The kit from V8R is 2K+ another 1k. Then the motor and trans is 3k. Rear end kit is probably 2K right? So 10k with my labor all and all?

I'd say the LFX is the easy button. Dump it in with a good tune and that should be all you need.

No engine swap. Tune the engine to run lean of stoich under cruise (the side port engine has really weenie port timing so it should be okay), remove all exhaust restriction, premix some 2 cycle oil in the tank (believe it: increases compression and reduces internal friction) get rid of the speed rated gumball tires for some nice low rolling resistance narrow all-seasons.

Don't discount the latter. My RX-7 dropped a ton of fuel economy going from all-seasons to performance tires. On went the all-seasons again.

If I may point at the elephant in the room: Why spend 10k on an RX-8 for fuel economy?

I am guessing it is because you still want something sporty that handles well. I'd think tuning a BMW 3 series, a Pontiac G8 or GTO would be a better bet.

That is a fair question Brett. Any of the engine options that are mentioned would probably end up being more powerful. I like the rotary but I drive 85 miles a day and they tend to make that a painfully expensive drive. This is mainly a thought exercise.

Sell car by GTO, Fbody, C5.

Dont get me wrong, I love the idea of V8 power in an RX8, but you are saying this is for an 85 mile commute, dont know if I'd want to rely on a car with an engine swapped from another manufacturer as a DD for that long of a commute.

If you want to keep the rotary, check ecomodder to see if anyone has done anything.

Like stated tires are a big deal. LRR tires can make a huge difference, dont know what size you have but they may not make a true LRR tire in your size if you have the 18s or other performance oriented tires, BUT if you have some crappy performance tires on there a switch to a good tire can help sometimes to. Many times the premium performance tires from people like michelin/pirelli/bridgestone get decent mileage, you can check tirerack tests to get some ideas, and that way you dont lose performance.

Lowering can help.

remove spoiler and pass side mirror.

good synthetic fluids in all positions can help some cars. I know a rotary isnt supposed to run synth because of the OMP but I have been told you can block it off, run two cycle oil in the gas tank and put synthetic oil in it. I HAVE NO IDEA IF THIS IS TRUE, JUST WHAT IVE BEEN TOLD.

Check maintenance items to make sure it is in good running shape, and check the alignment.

Mentioning synthetic oil and rotaries in the same sentence is likely to start another holy war . I know people who are successfully running Royal Purple in their RX8s and they don't seem to explode more often than usual.

Either way you're not going to get 30mpg out of an RX8 with the rotary in there easily. Well, unless you tow it with a TDI or something.

I am going to go out on a limb and guess you have never done an engine swap?

Engine swaps are way harder and more expensive than you want to think. And the real scary part is that right about the time you think you are done (cause its running) the real work of sorting the new Chimera is just started.

Bottom line, you can buy a lot of fuel for what it is going to cost to complete any swap.

Now, if you just like to berkeley with stuff and this is your excuse, then party on!

buy a prius and average the two'd MPGs

MZR from NC Miata.

You might not be able to get 30mpg on the highway, but the savings between say 25mpg and 30mpg is fairly small. To maximize fuel economy drive a bit slower. I find fuel economy is a fair bit better around 60mpg than say 70mpg. You might not like the idea of driving slower, etc. but the time lost there is probably small compared to the effort involved in a swap. Draft transport trucks, increase the air pressure in the tires. I noticed a small fuel economy hit going from 225 to 245 tires.

Another idea would be to try running lower octane fuel. It might not help with economy, but it can represent a ~10% savings on fuel.

You guys are taking this way too seriously. I already drive an Insight and wanted to see what you thought about making something like this happen.

NOHOME wrote: Now, if you just like to berkeley with stuff and this is your excuse, then party on!

This is pretty much it. I like the idea of a mildly efficient (when I need it) RX8 is pretty sweet.

I thought there wasn't a LSx swap kit available for the RX8? I echo the swap is a lot harder than you think, I've had an LS swap in my 951 for 5 years now and while it's been running that entire time, I've been continually evolving it, "finished" is a moving target...

Tow it behind a Prius

This makes me think of the old Joe Isuzu commercial. How many of you remember that one? He says something like "The I-Mark gets 70mpg", then the little disclaimer on the screen says "Downhill in a hurricane".

Mazda 2.5 engine and 3.73 final drive.

Rx-8 has a drag coefficient of 0.31. Step one would be reduce that (and drag area as well).

Step 2:

DaveEstey wrote: Mazda 2.5 engine and 3.73 final drive.

Its a RWD sports car, so don't expect any miracles. Very few RWD sports cars are rated >30mpg highway.

Put a hydraulic claw on the front and latch it to semi trailers rear bumper...... You'll be able to say you're getting better mileage out of a rx8 than people are getting from their solar racers....

what would it take ?

A miracle.

Gas is $2.50/gal. Daily driving an Rx-8 85 miles/day - priceless.

Doesn't Swank Force One (the car) get surprisingly good MPG? What would it take to put an F2T in one of these? Swank Force One (the person)?

Snrub wrote: You might not be able to get 30mpg on the highway, but the savings between say 25mpg and 30mpg is fairly small. To maximize fuel economy drive a bit slower. I find fuel economy is a fair bit better around 60mpg than say 70mpg.

When the RX-8 was new, a forum member tried driving at different speeds on cruise control. 60, 70, and 80mph were all within a half MPG of each other. (All around 23-24mpg)

The difference between 25 and 30mpg is huge. Another way to see it is, over 150mi, 30mpg is one gallon ahead of 25mpg. Over 3000mi, it is twenty gallons ahead...

Another idea would be to try running lower octane fuel. It might not help with economy, but it can represent a ~10% savings on fuel.

In all cases but two where I've experimented, higher octane fuel netted better fuel economy because the computer was able to take better advantage of it. On one where it didn't, the engine was a scrody no-compression pre-knock sensing POS. The other was my RX-7 that runs better the LESS timing you give it, so it would probably get best fuel economy at ATDC timing and running on kerosene and lacquer thinner

In reply to NONACK:

I think the recepie is the same for anything RWD; the transmission from a Turbo II RX-7, the bellhousing from a B2600, random aftermarket clutch parts, and home done motor mounts and such. You'd probably want aftermarket engine management to get rid of the flappy-door vain airflow meter and to get distributorless ignition. As it is the distributor and the firewall may try to occupy the same space like what happens on B-series/F2T swaps.

My 626 Turbo pulled 30mpg very easily and once did 40mpg and everything was completely stock. I think there's some padding in the fuel curves with the factory ECU and I don't think it's the most accurate thing around so there's probably some points on the table with better hardware and tuning.

That's really what I think the OP should do; get an RX-SEVEN and an F2T swap instead of the -8. There isn't an RX-7 made that's as dorky as the -8.

I'm getting over 30mpg from my 175hp 4AGE....... if it is a early RX8 then you can keep the 6 speed, add a LEEN adapter and bolt in a 4AGE... managment isn't all that tough... you can likely keep the suspension the way it is.....

In reply to pres589:

The primary reason that I like the RX8 is the rear door assembly. I expect kids in the VERY near future and have been told that my next DD must accomidate this fact. The likelyhood of this ever happening is low but I get bored easily and look at the fun ideas here!

In reply to oldeskewltoy:

Does the 8 and the IS200 have the same transmission? I am guessing yes. The 4age is an interesting option...