Black C5

When I first got my HHR SS I ran NOTHING but 93 octane for many fillups. Everything ran fine. I wanted to experiment with 89 octane to see if there was a performance hit. GM recommends 93, but it is not required. There is no engine damage that results from the use of 89 octane fuel, the computer prevents it.

I noticed a couple of things: Acceleration was down slightly (seat of the pants) and I noticed that if I got on it hard the instant mileage readout went down considerably for a few miles. I think that was because of the aggressive timing retard to suppress pre-ignition. After a couple of miles the timing stepped up and mileage returned. The overall mileage was down a couple of mpg for a couple of tanks and then crept up to about the same as with 93 octane (26-27mpg in town and 35+ with cruise set to 65). I don’t get on it hard very often, so 89 octane seems to work fine for me.

I currently have 40 miles left on my first tank of 104 octane E85. I think it will be my last unless I take my SS to the track. First, after about 9 miles on the full tank, the Check Engine Light came on and is still on. My SS usually runs at 199 water temp and it jumped to 207 for a while on the E85 driving sanely in town. The average mpg has come down to 22 and the highway mpg is down about 10mpg @ 65 with cruise set.

Seat of the pants acceleration, on the other hand, is really up and my full boost, which is usually 15 pounds, was reading 17 psi! I don’t know how that is possible unless using a larger volume of E85 pushed the boost up (not likely because peak boost is usually controlled by the computer). It ran much stronger and was more fun to drive with my foot planted to the floor however! Impressive performance increase, but for daily driving on the street it is not worth the cost to me.

I plan on filling up with gasoline tonight or tomorrow morning.

Tyler Harvey

Oh ya, I love having premium fuel in my baby. You're lucky you get 93, here in Canada we only get 91. Runs great still, but it would be nice to get the extra octane.

ThatChevy

Just out of curiosity did your HHR SS have a yellow fuel cap or a Flexfuel badge located on the rear? Cause as far as I know only the 2009+ HHR's with either the 2.2L LE8 or 2.4L LE9 are E85 compatible and the 2.0L LNF used in the SS is not E85 compatible, which would explain why your check engine light came on after filling up with E85.

KissMy08SS

your running E85...in your SS...without a tune???

Snoopy

Kind of wondered about the E85 use, when I read it. I guess the other posters are thinking the same. The 2008 HHR SS 2.0 ltr. was NOT made for E85 fuel. So you MAY experience some problems, either initially or down the road.

A tune would be a good thing if you continue to use E85. But if it were me, I'd stick to 91-93 octane...(owners manual says 91, I believe).

Your car, your choice.

Black C5

Yes. It is not a flex fuel HHR. One tank will not cause any damage. All late model cars are designed to run on a percent alcohol. Using 70-85% (which is what pump E85 is) will not affect the motor much more than the 10-15% that most 93 octane contains. The problem with alcohol is that it damages gaskets and rubber seals in older cars. Since the government has required the use of ethanol in our gasoline all the manufactures have used materials to resist deterioration of seals because even a little alcohol, especially if the car is stored for a while can cause damage.

I filled up this morning with normal gasoline and the mileage, after about 25 miles, was back up to where it should be. When my SS is running right it gets 40mpg or better at 40mph. With the E85 it was getting 32mpg or less at 40mph. The check engine light is still on and was likely tripped somehow by the E85.

In regards to an E85 tune: the purpose of this special tune is to take advantage of the 104 octane by providing more advanced timing. I could feel a difference because my computer did not have to back any timing out at full throttle as it does on lower octane fuel.

It was an interesting experiment using E85, but it is not worth the extra expense for street driving.

JoeSchmoe

Chevron has 94 octane where I live....

Tyler Harvey

That's great Joe, I didn't know that. Here in Manitoba, we don't have Chevron. You're lucky.

JoeSchmoe

Oh darn!! That sucks!!

Black C5

Filled up with the second tank of gasoline yesterday. Mixed driving average for the tank is 27.0 mpg average, about 40 @ 40 and the check engine light went out after about 1/2 of the first tank.

Power is good, but the 104 E85 had a little more seat of the pants performance...

When I get my new shifter I will get some numbers from the track.