Retrorod

Monster5601 has it 100% right about fuel octane. I have heard so much conversation from people who think they are getting "cleaner" or more efficient and powerful fuel in higher octanes. That just isn't correct. The difference is strictly to resist detonation in a higher octane fuel. My SS runs just fine on 87 octane fuel and I don't really notice any performance loss. Now, when the summer heat starts I will use higher octane or begin dumping a little "octane booster" in the tank to ward off the dreaded knock-retard. My old "real" hot rod has almost 11:1 compression and it is a little more prone to detonation but I run the same fueling theory with it also.

I suppose if you ran around with your foot buried in the carpet and the boost gauge over 14psi all the time......you might want to stick to the high octane!!

RussellM454

I'm with ya Retrorod at least in theory. Not being a chemist I wouldn't swear that 93 octane wouldn't squeeze out a tad bit more MPG due to it's burn rate.

Would be interesting to know for sure but for now I'm running 89 and may go to 87 when I have the ability to do a apples to apples mpg test between the 2.

I'm taking a 700 mile roadtrip this weekend. Filled up with 89 but will have a passengerm 2 chocolate labrador retriever's (total 160#) in crates and between 300 - 400 lbs of gear. I'll post the MPG on Monday.

Clevelandhhrss

This post is for c2vette and anyone else who is attempting to get better mileage and know a little bit more about me. I don't want to argue or have a


"spirited" discussion about who is right or wrong about efficency and fuel mileage. I just wanted to start a thread for those who do more than Pedal Mash.Yes


Pedal Mashing is fun, and the rush from the TURBO FEELS great, the BOOST WHISTLE sounds great, and the rapidly shrinking cars in the rearview mirror LOOK


great. This is why I bought an SS version of the HHR. I bought an HHR versus other small cars because of its cool modern but retro-in-a-good-way APPERANCE,


the PRATICALITY of throwing my mountain bike inside with the seats down, and carrying THREE GIRLS (they tend to travel in groups Downtown C-town) with the


seats up. My old faithful 2000 2dr s10 4CYL had a blue with red pearl PAINTED INTERIOR PLASTIC (91 ford probe color) with black and light grey CUSTOM LEATHER


seats. The HHR SS comes with a multi-color/material interior STANDARD OPTION. I always wanted 18 INCH WHEELS or larger on my truck, but responsibilities come


before bling. I love MANUALS becuase thats what my first truck had (98 sonoma 2dr 4cyl) and I can usually get at minimum the federally rated highway mileage


as an OVERALL MILEAGE. I like vehicles that have seating (or RIDE HEIGHT) high enough to see through the cars windshield infront of me. I took my drivers


test in an 96 ss Impala, you know the one, the cop car with the vette engine. My father owned all three orignal colors black, wine, green at different times


(the employee discount was great). He retired after 30 years with GM at the facility on CHEVROLET blvd. His first "SS" was a 1969 z28 with a 302CI small block, 4 inch bore 3


inch stroke, he drag raced back in the heyday. He chose auto mechanic as a trade. I was an engineeing intern, and production supervisor


for 4 years for GM also. When I pull up to my parents house, my HHR makes 5 total chevys in the driveway, NONE WITH BUTTERFLY DOORS THOUGH :0 .


I work now as a chemical and process engineer in the aerospace industry. I did not take physics untill senior high, my senior year, so I am not as smart


as c2vette. But I do try to apply what I learned in those 6 part time years at Cleveland State University getting my BS in chemical Engineering, minor in Math and chemistry.




But this is about gas mileage, SO.

FACT 1. Above 50-60 mph all cars (read-the ones regular folks like you and me drive) efficencies will go down.

Their are exceptions to this overly general fact,(like cars built for land speed records) but our beloved HHR does not meet any of the exceptions.

Fact 2. Your engine is not "lugging" on the highway in 5th gear, it isnt lugging at 40 either, infact I switch to 5th around 35 in the flats.

Exceptions would be uphill, into a tornado/hurricane, through deep water, rough roads, while towing etc...etc

Fact 3. The computers in our HHRs try to give us the best mileage without detonation and will learn and adjust to compensate varying conditions, altitudes and octane. This is


why our solstice/sky LNF friends have such a difficult time getting mods to work in the first place, and keep working indefinatly, without the CEL coming on. We will


too without a tune. So octane SHOULD NOT matter as to mileage, but WILL matter to performance at WOT. I can't tell you how long it takes the computer to learn, but the


engineers (accountants acctually) at GM do not want to warranty a bunch of HHRs before 100,000 miles because the computer took to long to prevent detonation when I go


from a tank of 94 to 87 octane and floor it.

Fact 4. Cotton clothes shrink in the washer, not the dryer (sorry girlfriend)

Fact 5. Removing the tailgate on your truck will not increase mileage (my dad believe this one)

Fact 6. Cold drafts, air conditioning in the summer, and all other versions of grandma's cold causes are untrue. (sorry grandma)

Fact 7. Speeding up to "get to highway speed" and then setting cruise IS NOT more efficent then slowly accelerating to 60. (my dad believes this one too)

Fact 8. You too can get better than 5mpg over the sticker in the city and on the highway if you TRY. For crying out loud I'm doing in the first 2000 miles, it's not like I've


had practice or trained for this. Just do it. HINT....keep the boost guage at -10 or lower if at all possible at all possible times PERIOD. Keep tires at 36+psi cold.


hit 5th at 35mpg on the flats, stay under 65 on the highway and in cruise, coast the steeper-long-downhills in neutral city or highway. Coast to red lights cause if you

get there first, its still RED. Accelerate slowly and don't warm your engine before leaving the house, unless it's cold INSIDE the car LOL BRRRRRR. Ill repost once i

test out the 87 octane vs 91+ on a long trip, but I'm betting for mileage it dosent matter at all driving like I do. Aggressive driving with WOT should see reduced

power and mileage with 87 for the reasons retrod rod said in the above post.



TURBO FEELS

BOOST WHISTLE

SHRINKING CARS IN THE REARVIEW

APPERANCE

PRACTICALITY

THREE GIRLS

4CYLINDER

CUSTOM LEATHER

STANDARD OPTIONS

18 INCH WHEELS

MANUAL

OVERALL MILEAGE

RIDE HEIGHT

CHEVROLET


BTW I had fun writing this, keep HHR lovin, Pedal mashin or Fuel Sippin. Bring on the mods, and the tune. My dad and I are read to rip into this LNF.

monster5601

Regarding fact 3, yes they do but the computers first priority is emissions control and this costs MPG because fuel is used to heat the cats. This is one reason why we see a decrease in MPG in cold weather. A rule of thumb is emissions control costs, on average, about 1.5 MPG depending of the vehicle and the engine.

I'm not a chemist but I worked with with emissions folks for a while and emission is a (very) high priority because emissions is under government control and recalls are very costly.

GM Powertrain design priorities are quality, reduced warranty, and customer satisfaction.

monster5601

Gee thanks.

I worked many years in GM powertrain as a software engineer and strategist and what I have learned over the years is just amazing. Most of my time was in premium 8 cylinder and diesel group bit I also spend time in transmission and shift control.

I'm just glad am I able to remember most of it.

Tyler HHR SS

Good posts, LMAO about the clothes in the dryer, I must have had the same conversation with my wife 3 times. Does the same hold true for all cars. It really seems like my WRX gets noticeably worse MPG when using 89 oct.. But it could be psychological or I could be driving it a bit harder to make up for the loss of power. By the way, the WRX does say it requires 91 right on the fuel door.

c2vette

I am not sure why adding more facts for critique is perceived by an affront to some folks as it seems to be, as it certainly not intended to be that. I am not denying that a vehicle should be able to get better MPG at 55 than at 65, but the facts are (honest!) that with my 2004 Silverado 4WD, I would consistently get 18.8 MPG at 65, and 18.2 MPG at 55. I did not believe this myself at first, but did many controlled runs over the same section of freeway. My humble opinion is that it has something to do with gearing, ignition timing, cam timing, overdrive lock-up, or software problem?, and factory optimization for epa hwy mileage testing. People are still a bit vague on whether their claimed 36 mpg in the SS is at 55mph, 62 mph, or 65 mph? BTW what was this original thread for?

NickHHRSS

My '03 Silverado with 3.42s got better mileage at higher speeds than my friends with 3.73s. Gearing, speed, CoD, and Volumetric Efficiency are key to how fast you go to get the 'best'MPG either in City or Hwy driving.

Please no more blanket generalizations the 55 is better than 65 or vise versa.

Clevelandhhrss

LOL, yeah please no blanket statements. I was just giving my experience, and the 30 years of data gathered by the department of transportation. LOL. As I said before, above 55 for MOST vehicles that NORMAL FOLKS drive (that includes all of us here) ABOVE 55-60 IS A LOSE LOSE. Gearing cannot overcome the parachutte, volumetric efficency has nothing to do with DRAG (read that in a nice soft voice because that is what im using right now). There are many trucking companies that govern their trucks to a maximum of 65. Some will soon move to 60, and then 55. Watch and see. I don't want to drive 55 anymore than the rest of you. But Drag is Drag, and unless your vehicle is shaped like those solor powered cars in the desert races each year, you will lose above 55-60. HHR's , Semi's, SUV's, Pick ups tailgate up or down. The root of the problem here is the drag, a much more aerodynamic car could be more efficient at 75, or 80 or maybe even 90. But not vehicles that are safe and practical for the road as of right now, that we look at as attractive. It is possible, but none are sitting at my local chevy dealarship to buy now.

An c2vette, sorry if i was vague before (you all know i like to babble by now)

I was driving on from Cleveland to Cincinnati, Cincinnati to Pittsburgh, an Pittsburgh to Cleveland on the 24th april.

For the 250 miles from Cle to Cinci leaving at 8pm arriving just ater midnight.

No stops, but a small detour around a bridge, off-ramp then back on the on-ramp, somewhere around Dayton. Lost 0.7 MPG there.

Set cruise at 60, looks like i stayed between 58-62 the entire way, bumped up to 62 to give the Semi's a break when the road went to two lanes.

My trip average was 58 MPH, i lost the 2 (58 aint 60) because of the detour.

I had a full tank of 94 octane ( i don't think this is a factor) and either a sunoco or shell, whichever has the 94.

I coasted some of the long downhills that were steep enough to maintain 60mph. I was not able to do this many times.

I accelerated around as many Semi's as went around me, 1-3 per hour.

Slow speed lane the entire way.

Tire pressure 34 at the start 36-37 by warm up due to road friction.

1250 miles at the start of the trip on my 5speed black SS all options, no roof rails.

No accesories on except the XM...lol windows up, sunroof on "vent"

Later in Pittsburgh, I had to fill up again, I had gone 515 miles, i could only fit 14.2 into the tank before the auto shut off clicked. I dont ever force more in.

Clevelandhhrss

And NickHHRss, i agree that the 3.42 will get better mileage than the 3.73 in your truck because both probably have v8 and have the torque to turn those low gears. Gearing will help if you engine is not working at its maximum efficiency at 55-60mph in your final gear ratio. I was able to get better mileage in my 3.73 1998 gmc sonoma 4cyl 2dr short bed manual zq8, than my 2000 s10 4.10 4cyl 2dr short bed automatic zq8. But the sonoma was slow as a honda insight. Volumetric efficiency will apply at all speeds , on all vehicles in all conditions. Low VE is like having an out of shape runner, at any speed he will get poor mileage.....This is where our ecotecs shine. They are like slight build kenyans.