Transitioning 89 to 87 Octane...Comments?

OK-944 · 04:42 AM

I've been fueling up with mid-grade (89 octane) gas, which has been working fine for my (stock) '87NA, the engine of which I've recently rebuilt and its running beautifully, but as I plan to do a bit more driving this summer...some trips planned as well as having just joined the Green Mountain chapter of the PCA (nice group!), and want to participate in group drives, I'd like to drop down to 87 octane to save some dough. (savings would equal about 15.00 per tank in my neck of the woods...which could really add up over time)

Questions:
One - Should I make this transition gradually? In other words, start topping off with 87 a bit more with each fill-up? Or go "cold turkey" with a full tank of 87?
Two - Even if I find running 87 octane gas to be fine...should I go back to 89 for winter (cold weather) use?
And Three - How have others on this forum who drive a stock NA fared with straight 87 octane? And for those who've made a similar (89 to 87 octane) transition...any comments on noticeable performance changes/differences, plus and/or minus? Thanks!

944 Ecology · 04-19-2023, 04:57 AM

87 works fine. No transition needed. If you happen to get a bunch of lower octane gas, your knock sensor will retard the ignition until the knock goes away.

I used 87 exclusively on my 83 944 track car and successfully completed over 1000 laps at speed at Lime Rock and Watkins Glen, among others.

v2rocket_aka944 · 04-19-2023, 09:31 AM

A US model, non-turbo 8-valve 944 is designed for 87 octane anyways.
So if you've been running 89 the whole time, it's been for nothing.

There will be no difference in running or performance.

OK-944 · 04-19-2023, 10:09 AM

Many thanks gentlemen...looking forward to saving some coin!

Monkey Wrench · Monkey Wrench's Garage

Ive heard two viewpoints one is that high octane in a car that doesn't need it is like buying shoes that are too big for you. the other is that the chevron 91 stores better. I tend to go for the 91 just because it's the only one without alcohol and stores better. I'd fill up with a higher grade and add a bit of fuel stabilizer if you are storing it.

found a video where a guy buys gasohol from the pump , adds water, shakes the can , lets it separate then drains off the water and results in more water than he started with.
He's effectively removing the alcohol using water.
water can combine with alcohol but not gasoline . I'm not suggesting doing this , just found it interesting.

you know hen we remove the gasoline screen from the tank and it is all rotten, is the alcohol attacking the plastic? I see that effect in screens in wiper water bottles too , they degrade in a similar way and there is alcohol in the water.

brake fluid is similar, it has the ability to absorb water into the solution, alcohol does that too. perhaps adding some alcohol to the tank is a way of extracting water that separates and sits at the bottom of the tank, if it's running gasoline. maybe if you just use gasohol then it can remove that separated water so it may not collect there at the bottom of the tank.

anyone that is old enough to have had a car with a clear glass sediment bowl will remember how water used to drop out of the fuel, which was gasoline, and sit there in the bottom of the sediment bowl. people used to go - oh I giot some fuel with wate r in it then they would drain the sediment bowl to get rid of it.

I bet if you saw that and ran a bunch of gasohol you'd see the water dissapear as it gets absorbed into the alcohol in the fuel.

djnolan · djnolan's Garage

Can 87 octane be run safely in an 87-S 16v?

944 Ecology · 04-19-2023, 03:43 PM

Quote:

Originally Posted by djnolan

Can 87 octane be run safely in an 87-S 16v?

The knock sensor should take care of it. To be certain, try a tank or two and see if you have any problem.

v2rocket_aka944 · 04-20-2023, 03:37 AM

Quote:

Originally Posted by djnolan

Can 87 octane be run safely in an 87-S 16v?

I wouldn't.
an S does want premium because of the high compression. this is in the owners manual.

the knock sensor (Does a 944S have one?) will pick up and cut timing a little but for how much a typical 944 gets driven, the mpg, and the typical price spread between 87-91 it's not worth a lot to go down.