Premium gas?
 

I just bought a 91 rx7 N/A and i was juat wondering if i should use premium gas or what? What do you guys use? thanx.

Howdy and welcome to the rotary world!

I also live in Colorado Springs and here is what I use currently and have used on my other 3 rx7's I owned over the past 15 years.

Winter use: 85 octane, however the rx7 sucks in winter driving and I would advise against using anything other than studded tires and about 100 lbs of weight in trunk. I've spun out twice on I-25 when I drove my newest addition home. Luckily no damage.


Summer use: 87 octane.


Rationale: Naturally aspirated (non-turbo) RX-7's don't have a problem with detonation. The risk of detonation at high altitudes is virtually nil considering that you can drop 2 pts in octane for every 1,000 feet in altitude gain. As a side note, I used to burn 77 octane gas in a Toyota Landcruiser in the mountainous regions of Afghanistan with no problem.


However, if you have a turbo engine, I'd run the highest octane you can find in the summer and mid-grade in winter. Its too easy to blow an engine (actually apex seal) with detonation.


Detonation can be aggravated by the following:
Improper air/fuel mixture
Carbon buildup in engine or on spark plugs
Heavy load on engine/not sufficient cooling/hot weather

Typically running too high of an octane fuel (low compression engine on high octane fuel) is a waste of money and can actually contribute to carbon buildup. However, the rotary engine is an exception since detonation is more fatal to it than a piston engine.

I run 87 octane in mine because I premix two stroke oil in each fuel tank. Premixing oil tends to lower the octane ratio a little and using 87 midgrade is a good compromise.

Andy

PS For all of you lowlanders, 85 octane is regular gas in colorado, 87 is midgrade, and 89 is premium.