urquiola

I had a 1987 NA RX-7 13B reviewed and tuned by Kevin at Rotaryresurrection, including bridge porting, and I'm pending to install it in a 1975 AMC Pacer X, including a 1987 4 speed, automatic Mazda RX-7 tranmission, when it's completed, I'll tell you about economy.
Drag coefficient of Pacer at .43 is worse than RX-7 at .31, also the Pacer frontal area is bigger, weight after extracting the AMC 6 in line would be the same as an RX-7, 1250 kg, the Mazda 13B is more 200 pounds lighter than the AMC engine.
Final axle ratio in Pacer is 3.08 or 2.73, for 39.2 km/h at 1'000 rpm, with a tire diameter of 641 mm, top speed around 4'000 rpm, values for 1987 RX-7 are an axle ratio of 3.909, with a tire diameter of 627 mm and 41.2 km/h at 1'000 rpm.

urquiola

I had a 1987 NA RX-7 13B restored and tuned by Kevin at Rotaryresurrection, including bridge porting, and I'm pending to install it in a 1975 AMC Pacer X, attached to an automatic 1987 Mazda RX-7 4 speed transmission, when it's completed, I'll tell you about economy.
Drag coefficient of Pacer at .43 is worse than RX-7 at .31, also the Pacer frontal area is bigger, Pacer weight is 1'400 kg, after extracting the AMC 6 in line would be almost the same as an RX-7, 1250 kg, the Mazda 13B is 200 pounds lighter than the AMC engine.
Final axle ratio in Pacer is 3.08 or 2.73, for 39.2 km/h at 1'000 rpm, with a tire diameter of 641 mm, top speed around 4'000 rpm, values for 1987 RX-7 are an axle ratio of 3.909, with a tire diameter of 627 mm and 41.2 km/h at 1'000 rpm.

urquiola

This is the ad in 1916 Ladies' Home Journal. Have a nice season. Regards

rx7 SE

iTrader: (5)

Managed 24+ mpg in my 6266 FC just by pulling fuel while cruising on the highway with the PFC until the engine starts to stumble then adding a couple ms of injector pulse back. AFRs were in the 16-18s.

fbse7en

I have feeling that w/the Pacer body annnnd automatic tranny (worst thing ever to put behind a rotary) your fuel economy will be much worse.. :-/

urquiola

Copyrights on images and pictures such as an: 'oil on canvas', are supposed to expire 70 years after the author's death. Is this up to date?

Vicoor

I think fuel economy and rotary engines aren't really compatible. The bottom line is Brake Specific Fuel Consumption. And compared to piston engines the rotary just can't compete.

urquiola

You may be right, I may be crazy (Billy Joel), when I test it, I'll tell you. The advantage of an auto trans with a RCEs is that loads on engine internal gears are much lower. Mazda reduced in 1978 the final axle ratio to 3.6, and they expected more, I don't know how late models did, as many had one or two turbos, and this differs completely from a NA engine. Thanks for your interest.

arran

I did a highway run few weeks ago over the Christmas break. 75% of the 300km was in the rain, so it was a very steady trip at 80, 90 kph.

I brimmed it again at the end of the trip and it worked out at 10.5 litres per 100km, or about 26mpg. This is all highway driving and I was trying hard to be light on the throttle. The wideband is reading about stoic at cruise, engine is extend ported 13b turbo run by a Megasquirt, 1000cc injectors x 4

Just turning on the AC brings the instantaneous up to 11.5.

I could pull a little more fuel out of it at cruise but I don't think there is going to be much real world improvement left in it. Congats to you guys getting over 30mpg!

If I get stuck into it there is no problem emptying the tank in under 100km !

j9fd3s

iTrader: (3)

i have some data points, but here are the most interesting three.

1. i had a gsl-se with an Rb street port exhaust, and it would do ~26mpg on the freeway, if not a little more, when the car was in closed loop it was basically turning on and off...
2. my STOCK 100% original 79 Rx7 would do 23-25mpg on the freeway. the idle mixture screw had a way bigger impact on fuel economy than one would have thought.

3. my friend and i swapped cars last week, his was an 03 Civic Si, mine is an 04 Rx8. the Rx8 gets 24mpg freeway (mpg is better at 80mph than 65, oddly), the civic only got 26mpg, although it was about half a tank of city driving.

so we can conclude that removing gas flow restrictions is good, and anything over rich is bad.. we've also learned that the rotary can get better mileage in higher RPMs than you'd expect.

for instance the Rx8 get better mileage at 80mph than at 65mph, and the 79 got better mileage in the 3500-4000rpm area than in the 3000-3500area

Akagis_white_comet

iTrader: (4)

This is very interesting. At first glance, it makes no sense that going FASTER gives BETTER fuel efficiency. But if you think about it with regard to engine load and a dyno chart, higher rpms means more power is able to be produced while higher road speeduses the power properly. The ECU just adjusts the fueling to match the load (aka road speed).

Got more data on it j9? This is sticky worthy!

rx7 SE

iTrader: (5)

I think this is soley the case for the rotary as it's VE (volumetric efficiency) is so poor in lower rpms that increasing rpms more than offsets the reductions in mpg due to air drag. I imagine that 3500-5000 rpms is about the sweet spot for what I can tell from my testing of mpg. Whereas my piston DD is anywhere below 2000 rpms.

j9fd3s

iTrader: (3)

not really, i wanna go to Blue Tii's dyno, as it lets you hold speed, and vary load, and you could really figure out the best combo of gears/afrs, etc.

i think with the Rx8, the engine doesn't get more efficient, it just covers more miles.

with the SA my impression is that its jetted really rich under 3500rpm to get the thermal reactor to work, and over that it EGT's are high enough they don't need to be over rich.

fbse7en

Paul Lamar (RIP), IIRC, with all of his engineer number crunching stated that 5,000 rpm was the sweet spot for the least internal loads (least amount of bearing wear & such) of the Mazda rotary, could that also factor into better MPG?

j9fd3s

iTrader: (3)

it must. since this thread was posted, i don't have a lot of new info.
so the Rx8 got better mileage the faster you went, i'm assuming there is some point where that stopped being true, but 80mph was better than 65mph. obviously the penalty for aero drag and friction is less than covering more ground

the FD has an injector air bleed system, and it works! my FC would get 11-13mpg (its fun), and hooking the thing up gave me 17+ mpg, which is pretty huge

peejay

What is interesting about the Paul Lamar info is that I'd done 32mpg with my first FB, when it had short tires and 4.78 gearing. So the 12A was spinning at about 5000 at speed. (75-80?)

I also had done some ignition timing tweaks, I believe I had the leading at 22 total, trailing maxed out, and ported vacuum advance connected to trailing only, because I did fuel economy testing that showed that provided the best economy. (100 mile topoff to topoff testing) I also did some very minor tweaks to the carb, mainly dropping the fuel pressure until it felt right. Hard to explain, but you can feel when the engine is getting too much fuel under cruise. It "lightens up" a lot when you drop pressure.