MainePorsche

Your thoughts ?

worf928

Context? Lawn mowers? N.A. 928s? Twin-turbo 928s?

MainePorsche

Just for our standard 928's.

MainePorsche

Is ethanol really problematic ?

FredR

Craig,

You chaps over the pond rate your octane in a slightly different way to the "enlightened" rest of us [ha ha]! You use the average of RON and MON that gives slighly lower numbers. For this reason I get a bit confused as to what your numbers actually mean but I have it in my noddle that your 91 is what we refer to as 95 RON octane.

My work with sharktuner suggested to me that some degree of knock was taking place with the stock maps around the flappy transition rpms and at around 5.5k rpm and to stop it I had to pull about 2 degrees of advance. Members of the local Porsche club often commented that they felt their cars [911's, Coxsters and my 928] ran better when fuelled with Super 98 that is available up in Dubai.

The knock control system in our cars seems to handle this well and even though ST2 was telling me retard was being applied I had no sense of such happening within the car itself [no rattles etc etc]. However a friend of mine who had a new GTS back around 1993 reckoned his 928 audibly was knocking on the local 95 RON gasoline - I think the GTS compression ratio is slightly higher than that on my 90 S4 motor.

I suspect your 93 gas is equivalent to 98 RON and if so would be preferable I would suggest but you can safely run on 91 assuming my comparisons are correct.

Rgds

Fred

Bertrand Daoust

I always use 91 octane fuel here. No Ethanol (I think).

Running good.

hacker-pschorr

I'm assuming you meant to ask about 93 with ethanol vs 91 without?

Define problematic.

The gas station a few blocks from my house has 91 ethanol free. I fill up at Costco which is 93 with 10% ethanol. Why? Costco has top tier gasoline and it's cheaper.

In regular driving, 10% ethanol will harm nothing, ever. Long term storage.....just out of paranoia I would try filling up with 100% gasoline but now we need to define "long term". I have yet to experience a fuel related issue after storing a 928 with a tank full of 10% ethanol gasoline.

My small engines get the 100% stuff, not even sure that's necessary but running to Costco to fill up my ATV would get annoying, and carbs are a bit more sensitive to what sits in them long term, I think.

The issue people get concerned about is water absorption. It's an internet fact ethanol will absorb water and ruin your car. Right up there with facts that gasoline more than 3 months old is varnish and your car will explode if you try to start it.

BC is our resident expert on this.

FredR

What is the issue here- performance of the gasoline or material degradation issues purportedly caused by the ethanol content?

Red Flash

I avoid ethanol whenever possible with my 928 simply because of the intake pump internal hose.

If you talk to Europeans, they don't seem to have nearly the same trouble with fuel lines failing as we do. This could be related to ethanol, or it could be related to other factors like generally hotter conditions in the US than in say Germany. I really don't know.

In the meantime I have GB's fuel lines and GB's in-tank pump fuel hose, so I expect no real problems due to material degration. Nonetheless I still avoid the use of ethanol thinking that it is more likely to draw water and I don't want a rusty fuel sender again...

GlenL

Doesn't it all depend?

First off, there's a 17-year span of cars to consider. I don't think any of them have had problems with ethanol. I'm sure someone will come up with a horror story. Back, back, back when it was coming into the market there were problems. Some vehicles had seals and gaskets that swelled or softened and ethanol would get contaminated in distribution.

That's all past.

The questions now become:

Is that the right octane for your car?
Do your want the extra power that pure gas has over a blend?

I'll spare you all the internal thoughts on which octane is right for which car at any one time. In general, I pick the octane the manufacturer suggested and pump the ethanol blend.

When I'm going to track the car, I'll pick alcohol-free gas. Let's argue, but ethanol has roughly 1/2 the energy, per unit volume, than pure gas. At the track, I do hold the loud pedal fully down for extended period of time. On the street, a 5% power drop means opening the throttle 5% more as I rarely use it fully open.

To Fred's point: US octane ratings are different and roughly 3 points lower than European ratings. If your RoW car calls for 95 it'll be plainly happy with 92 in the US.

hacker-pschorr

Glen, good points but to play devils advocate for your track days, ethanol is an excellent anti-knock additive which may be better for your car when going WOT for extended periods of time. Especially in a EuroS without knock sensors.

Wisconsin Joe

I always thought it was 2/3 (approx 66%) of the energy. Could be wrong, but that's what I find with a quick search. And when we are talking E10 (10% ethanol) that changes the power from 5% less to 3.33% less. I highly doubt anyone's "butt dyno" could detect that difference. Kinda doubt that anyone's "butt dyno" could detect the 3% difference between pure gas and E10.

Personal experiences:

97 Blazer: Purchased new. Sold two years ago with ~90k on it. Ran 87 octane E10 all it's life. After '00, It spent alternating weeks sitting while I was at work. After 04, it spent most of the summers sitting because I had acquired a "summer car" after that. There were times I would fill it up in June and not again until August. I ended up having battery issues because I would drive it a couple miles to work, park it, drive a couple miles back, park it and drive the other car. No gas issues at all.

83 Porsche 944: Purchased in 05. Always used 87 octane E10. Drove it alternating weeks during the summer through 2012. Stored it every winter with E10 and Seafoam. No issues. It sat the entire summer of 2013, with a "For Sale" sign. Started it a few times to charge up the battery, but when I parked it that winter, it still had 3/4 of the tank of gas from the previous winter. Started it up the spring of 2014 with no issues (so much for "old E10 problems"). I don't drive it anywhere near as much since I got the 928, but still have fun with it from time to time.

85 928 Euro: Purchased in 13. Always used to use 93 octane E10, but that station closed (had the cheapest premium around too). Have bounced around trying to find the lowest priced premium this year, varies between 91 (no ethanol), 91 E10 and 93 E10. No issues. Parked each winter (usually Thanksgiving to end of March) with Seafoam.

As a side note: I am always amazed at the variance in premium gas prices. All the stations are the same price for regular 87 E10 (they may take a day or two to all agree after a price change, but that's it), but premium runs between $0.65 and $0.85 over that price. With no apparent correlation between 91 pure, 91 E10 and 93 E10. The place that closed where I used to get it had 93 E10 for $0.45 or so above.

One thing I have noticed. Gas line freeze up has virtually disappeared. Old school rule was to never let the tank go below half (to minimize airspace and condensation), but even so, I'd get a "no start" or a "runs for 2 or 3 minutes and quits" from gas line freeze every so often. A bottle of "Heet" was standard equipment, right next to the jumper cables and snow brush.

I haven't had it happen since E10 became widespread. I don't even see much "Heet" for sale anymore.

GlenL

I blend 110 race gas 50/50 with "non-oxy" premium to get ~100 octane. No cats on the car.

hacker-pschorr

Last time I was tuning my 79 for the track I purposely used 87 since premium in Elkhart was over $5 a gallon

Shows how long it has been since I did a track event....

GlenL

Stations near tracks will charge extortionate prices for special fuels. I've got jugs in the trailer for that reason. I still haven't gone to an airport to get 110 leaded where, I'm told, it's much cheaper than the $7-$8 gas station price.

No track time? I've posted a couple of times about a Midwest 928 Track Fest but it hasn't caught on. Maybe if someone who knows more people better took the lead then just maybe...