Rotary power! 1988 rx7 convertible

[13B_88FC]

Probably not alot of people with my kind of car on this forum, but I joined because I love the idea of efficiency and reaching and exceeding a car's potential.

I've got the 1.3 L 13B wankel rotary engine in my car. It was rebuilt about 10k ago and was street ported during the process, as well as some other improvements. It now has a racing beat header and presilencer replacing all cats.

I have a best of 27 mpg on the freeway in california heat going 70-80mph, and a worst of 15 (because reasons). In reality my worst is about 19 (15 was an extreme outlier). Here is a link to my mpg spreadsheet if anyone is interested: [nevermind, can't post that yet apparently, will when I have 5 posts]

You'd expect a 0 cylinder car to do better than 27mpg :P

My planned future mods for fuel efficiency is a good tune, synthetic tranny and dif oil, and maybe a power steering delete.

[wmjinman]

I always loved the aerodynamic look of those RX-7s. In fact, I have a friend who once had one. My understanding is that while the rotary engines have an amazingly high level of condensed power for their physical size, fuel economy was never their strong suite. Not sure why - something inherent with the design, I think.

[doclees]

I think 27 mpg is great out of the rotary. Had a 74 rx3. The little hole shot! Don't think I ever got better than 21mpg. But I could cruise at 110 mph all day long. Love the engine whine. I wish this site, and the internet, was around then. I bet I could have gotten 22.5 mpg then! Rotarys are like inverse Jeeps wranglers. Aerodynamic body with gas sucking engines.

[13B_88FC]

Originally Posted by wmjinman

I always loved the aerodynamic look of those RX-7s. In fact, I have a friend who once had one. My understanding is that while the rotary engines have an amazingly high level of condensed power for their physical size, fuel economy was never their strong suite. Not sure why - something inherent with the design, I think.

If you think of the combustion chamber of a rotary engine compared to a piston engine, the rotary engine has a higher ratio or surface area to volume. A cylinder is a nice regular space with minimal heat loss through the inside surface area compared to it's volume while the rotary engine's combustion chamber is a more irregular space that loses more through it's inside surface relative to it's volume.

[13B_88FC]

Originally Posted by doclees

I think 27 mpg is great out of the rotary. Had a 74 rx3. The little hole shot! Don't think I ever got better than 21mpg. But I could cruise at 110 mph all day long. Love the engine whine. I wish this site, and the internet, was around then. I bet I could have gotten 22.5 mpg then! Rotarys are like inverse Jeeps wranglers. Aerodynamic body with gas sucking engines.

They're great fun. The sound is even better without a roof

Best thing about the 27 is that I wasn't trying, but I swear that car get's the best mileage when you drive fast and hard without even considering mileage.

[13B_88FC]

There we go. 5 posts.

https://dl.dropbox.com/u/5310442/198...%20mileage.xls

[Sporty Modder]

Excellent. We need pictures. And a video of this car.

[13B_88FC]

RX7Club.com - livevil904's Album: My car

Here are some old pics of my car.

[cRiPpLe_rOoStEr]

The only problem with Wankels is the apex seals at the rotor, leading to the ocurrence of the "Devil nails", which Mazda managed to overcome very efficiently. In theory it's a cool engine, but not everybody knows how to properly deal with them...

[13B_88FC]

A well maintained rotary will not have reliability issues with apex seals. Most of the time, they don't last over 200k miles, but I've seen original engine cars with 300+ on them.

Apex seals fail due to oil starvation. The engine injects oil into the engine (purposely consuming crankcase oil) to lubricate them. I put a little 2 stroke oil in my gas to help. I've also heard it's good to redline them regularly because that helps burn off any carbon deposits - this is no problem for me.

My engine failed due to blown coolant seals. The previous owner seemed to think pure water is ok to use in the coolant system. Then my thermostat stuck closed and I didn't notice and it overheated.

Coolant seals seem to be a more common problem with the engines than apex seals.