High Fuel Economy (MPG) Rx7 Ideas
 

I know most of us don't buy/drive/own Rx7's and other rotary powered vehicles for their fuel economy, or lack of :lol:

But it seems all Rx7's, specifically the FC, (fairly cheap + better aero than SA/FB) would make a great base vehicle for High MPG mods, because according to Mazda the FC w/sport aero pkg has a Cd of .29 (the fuel sipping Honda Insight has a Cd of .25) and all the champions of fuel economy have extremely slippery aero.

Mod ideas: using stock size wheels + tires should work well = less rolling resistance + "hellasunk" therefore easier to fully-fair the rear wheel openings (removable of course), fully flat-bottom the entire chassis (panels attached w/DZUS fasteners for quick maintenance removal) add some aero-channeling function for more win, strategically place micro vortex generators for better aero adhesion (like the middle back edge of the roof-line, immediately before the rear hatch), full-fairings on front wheels (very space limited, possibly attached to hub, very challenging...) w/removable cover, crop the side view mirrors w/better aero fairings or replace completely w/camera's, small fairing to "hide" the windshield wipers..

13B w/Turbocompound set-up:
VanDyne SuperTurbo
Join
35 MPG RX8
http://www.rotaryeng.net/NASA-Paper-...und-rotary.pdf

Or and I HATE, yes-HATE to even suggest a piston conversion...but a small industrial diesel engine...like this guy did...
turbo-diesel rx7 47 mpg - Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com

Or this guy (check the "garage" of OP in linked thread)
Kubota - RX7 - Diesel Place : Chevrolet and GMC Diesel Truck Forums

Just some food for thought..

If you want high fuel economy buy an economy vehicle (like a Camry)... People don't buy Sports Cars so they can have 30mpg+..

Camry's are NOT high fuel economy. I didn't buy my Rx7(s) for HFE/MPG either, just think it'd be interesting to see what someone can achieve.

the FC chassis isn't a bad start, for the reasons you mention. it does need to loose a few pounds, an S4 GXL is over 2800lbs stock, Mazda made it fairly easy, AL hood, loose the AC/PS, the stock exhaust weighs a TON.

if you keep the stock rotary, there are a lot of pumping losses, the exhaust could be more free flowing, the intake is not great...

there is some to be gained with an ECU, as its tuned around the air pump, and 87 octane, the Rx8 runs much more aggressive timing.

you have a few gearing choices too, in normal driving i prefer the S5 NA/turbo 5th, over the S4 NA's really tall 5th...

i dunno you could probably eek out like 26.5mpg...

The only time My car doesn't burn any gas is when it is on the flatbed..!
(sorry..I had to throw in a "ha-ha moment"!)

The N/A's I had seemed to get about 24ish..which I really didn't think was too bad.All the N/A's I had were thoroughly touched up with all the tuning parts,etc you could think of.(plugs,filters,wires,etc).
I figured they would last longer.I was right.The Guys I sold the cars to were still running strong!
(well Except for ITSFUN who had a Lead foot and Effed up a good car!)

I get 24-29mpg with a bridge port. It's all in tuning and how you drive it.

Also, don't use low profile gumball tires. That can be 5mpg right there with the additional rolling resistance.

What's a bridge port ?

when you add an eyebrow cut to the intake ports.

eg on turbo plates

http://xtremerotaries.com/images/ser...-port-na-2.jpg

Hey, Ace Convoy: This should help..:nod:

Something that everyone says should get half the fuel economy I get... :)

I also got as high as 33mpg with a stockport 12A.

That was your Polk High School moment.

By the way, congrats on your ten grand post count. May your rotary rev that high as well. https://www.rx7club.com/images/icons/icon14.gif

whats a gumball tire? lol

Another name is street sweeper. They are tires that are so sticky that everything on the road sticks to them and flies off making pinging noises in your fenders. You hear it a TON at autox when folks pull off the course that was swept and the parking area was not.

In other words the suggestion is: run the hardest tire you can or use a high mileage tire that is designed for high MPG.

Yeah I know :) But it was definitely interesting getting to that point, playing with ignition timing and such. The kicker is that the car has 4.78 gears and an FB trans and 185/70-13 tires so it was revving at 5000+ under cruise at times. So much for the idea that lower RPM = better economy... well on an engine that will run smoothly at light load, anyway :) Definitely can't do that with the bridge port. Gotta load that sucker down. If i had taller gears, I could run more ignition advance and less fuel and it would still run smoothly. As it is, at ~2900rpm cruise I have to have ignition timing way back and 12.5:1 to keep it from bucking, at over 75mph it starts bucking again because there isn't enough load on the engine so I can't go very fast.

But the short gears make it accelerate better with those 65cm rally tires on the back, so compromises :)

I was at 10K about five or six years ago, but that's when the posts started getting culled :) IIRC at one point I was top five poster.

Yeah, you gotta load down the vacuum secondary hitachis on old school 13Bs too, otherwise they don't open reliably in REPUs with their stock low gears of 4.625 and a stock 30 pound boat anchor flywheel. Basically if free reving won't open the secondaries, and normally it shouldn't, they won't open in 1st gear either. It takes so long to rev up a 30 pounder while free reving that it matches the acceleration in 1st gear so the secondaries will never open. You bascially need a steep hill, lots of weight in the truck, and second gear at least, for them to open, or you need to wait for 3rd gear if on a more level grade. REPU owners call 3rd their "power gear" or the "ever-lasting 3rd gear" because of this. Sad, I know. I've changed all this since then and should have decent power in 1st gear now. Trying two very different approaches in two REPUs. Well, one per REPU. :)

My post count went down only a little back then. I think it's because I had less posts in the lounge and FS threads. Now I'm kinda wondering if I should start posting a lot again. I'm very actively trying new things these days (turbo, which is completely foreign to me, and stock NA EFI crap) but I only rarely post about any of it.

As soon as a file transfer is done, I'm heading out to continue work on this funny engine I have... it has five things that boing up and down and they spin an exhaust pinwheel and the fuel injection is some weird air door controlled hydraulic thing.

I have one RX-7, and *three* CIS-equipped VWs. Much of my time is spent haunting clubGTI and motorgeek :) I still don't know what I am going to do with the GTI (a 12/82 build), but I had to buy it, you know? The fuel injection is severely crudded up and it also has the fusebox issues typical of models with leaky aftermarket sunroofs. I'm thinking end-run around everything and put a 1.6 Diesel in it because I hate Diesels and I think it would be fun if I could get better fuel economy in the RX-7 than a diesel VW. Plus it's cheaper to buy a complete engine than it would be to build a Megasquirt to put in the thing.

So it's an inline 5? Ever notice the sound of the lightcycles on the original Tron movie sounds a lot like them? Yeah, check out videos of Audi 5 cylinder dyno runs on youtube. :)

Improving Wankel intake
 

Hi!: you may like the patents US3514235 by R Yamanouchi, and CA1032477 by Ford, on means for improving intake and exhaust in Wankel RCEs; as a basic concept, you know that the lower the exhaust back-pressure, the better MEP and SFC are, and that for low rpm torque, a long intake duct is preferred.
Somebody patented long time ago a thick gasket to be put between the engine block and the intake manifold, in order to prevent ducts to heat, a hot induction tube would worsen volumetric efficiency.
It was proposed also to improve combustion, heating the incoming fuel by passing it through a coil-shaped tube inside a cylinder where hot water from the enegine cooling system enters in the output side of cylinder, and goes out in the place where cool fuel comes in from the tank, this system was implemented in a training jet plane, the 'Iskra'.

The attachments below summarize possible 'feasible' improvements in Intake and Exhaust. Kawasaki patent US3848574 proposed a change in plug hole for improved emissions and fuel economy. The SAE paper 790435 by T Kohno describes the Toyota research on ways to improve part load performance of RCEs, they claim a 7% improvement just by substituting the leading site spark plug for a glow plug, as in model engines.
Kevin Landers from RotaryResurrection, tuned for me a 1987 NA 13B engine, he's a kind and expert worker in this field. Enjoy season. Best regards. Salut †

Fuel economizers
 

Here it comes an image of two devices patented in the 70's, plus an ad in a 1916 issue of "Ladies' Home Journal", selling a Willys six-in-line engined car. Prices have changed since then! Salut †

Exhaust Port timing
 

This is a chart on the subject. Salut †

I'm getting only 13mpg on my 1987 NA GXL automatic (132k miles) even with driving with Overdrive. I have new o2 sensors, done a tune up of fluids and spark plugs when I bought the car. So what is the problem? I should be getting 17/21 hwy.

2 things.
1st thing:It's an automatic.
2nd thing: it's a Rx7.

Improving fuel economy?
 

There are some old proposals to improve mileage and reduce emissions in Wankel RCEs, one is a patent by Kawasaki -US3848574-, they drilled a cone/triangle shaped prolongation of the plug hole, with the tail pointing to the rear/trailing side of the Rotor/Combustion chamber; if someone tests this in an old housing and works, you may consider implementing the change in a housing in better condition.

Toyota presented another way in a SAE paper, nº 790435, they substituted a glow plug for the common plug in the leading site, and claimed a 7% gasoline economy improvement.

Paul Lamar of Rotaryeng.net is producing a continuous spark ignition system for RCEs that may act in a similar way as the glow-plug Toyota experimented, but Toyota also added a not-return, hydraulic ram effect, Reed-Valve system in an Intake Peripheral Port, the same as professor Teluan Chen in the Chinese Wankel Engine Project (SAE 1988-02-01).

no love for the LPG turbo rotary ??

rotary = bad HC and bad CO,, good NOx
LPG = good HC and good CO, bad N0x

anybody see what i see?


lambda 1 cruise and idle , even on large extend ports , minimal power differences under boost to petrol setups
.. 100+ RON octane ...


10 years and counting,, daily driver

i don't know why i don't do LPG, its smog exempt here....