reglar vs hight test gas 2

[zekeman]

Is it cost effective to use regular gas on an engine that is rated for high test? Is there any documentation around?
Thank you.

 

[patprimmer]

By my sums on energy content, 10% ethanol blend needs to be at least 3% cheaper, octane rating being the same.

Different octane rating, then it gets more complex due to many of the factors already covered as well as the different a:f and energy content.

I have a very unscientific test. Every time I refill, I reset the trip meter. I watch the mileage vs gauge. It is a pretty good indicator of whether I am doing better or worse than normal.

Occasionally I try private brand or independent fuel, sometimes ethanol blends, sometimes higher octane, but I guess about 95% of the time I use std unleaded which here I think is typically 89 to 91 depending on brand.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[ivymike]

http://autos.msn.com/research/vip/spec_engines.aspx?year=2003&make=MINI&model=Cooper&trimid=-1

1.6L 115 hp I4
10.6:1 compression ratio

 

[btrueblood]

"Pat, wouldn't you think that if one is shooting for max fuel mileage, there should be no high load component ?"

For the best (lowest) BSFC, you want the engine operating very near its maximum load, and typically at its peak torque. For any lower throttle setting, the engine will perform less efficiently (power produced by the engine is lowered, but all of the rotating friction losses are still there - think of an engine at idle speed, barely producing enough power to keep rotating, but still burning fuel: its efficiency is pretty much zero).

Unfortunately, most of us like to drive cars that can accelerate hard enough to be at freeway speed at the end of an on-ramp, thus the peak power we want is quite a bit more than is required for "cruise". Thus, we have systems that shut down part of an engine (one side of a v-8) or reduce pumping losses (Toyota VVT), or hybrid systems that use stored electrical power to provide acceleration, while the IC engine is sized for the cruise condition.

 

[thundair]

btrueblood
IMO the older engines had to spin up to become efficient, but my Z06 runs 1500 RPM at ~65 with 24MPG.
I run the 87 octane and have had no problems but I have not done a mileage check other that the computer trip mileage.

I don't know anything but the people that do.

 

[dcasto]

My 2zzge engine is 11.5 to 1 compression ratio and I would not dare to put a lower octane in it on purpose. One time I noticed the engine ran rough, had no acceleration and would not go into lift. The station or I myself must have gotten a lower octane fuel. I drove it very gingerly for a while and refilled with 91 octane. The engine still didn't run like it was suppose to so I disconnected the battery for 15 minutes to reset the ECU. It ran like it was suppose to.

As for price, I love it. The gap between low and high octane is a constant $.20/gallon. As gas has gone up, the % in price has declined.

 

[drwebb]

Hey- I'm not the only one who has noticed the fixed price gap means that 'high test' is a better value now.

Here's more anecdotal data- I have a Volvo V70 2.4T that 'recommends' high test (91 RON, if memory serves) but 'allows' regular. I understand that advanced timing theoretically should give marginally quicker accel and maybe even smoother run, so I wanted to justify fancy gas. On several trips to grandma's house I alternated fill-ups with 87 and 93 AKI and recorded mileage. The difference compared to standard deviation convinced me that I couldn't tell a mileage credit for fancy gas. Maybe now that premium is relatively cheaper I should try the experiment again using in-town service.

Is there a CAFE requirement that OEMs have to recommend the same fuel grade they qualify models with?? I'm still wondering what's in it for them to call out fancy gas unless they believe it reduces their warranty costs or customer complaints- but I doubt many average drivers would complain that their mileage or acceleration was noticeably different.

 

[TheTick]

With every car I've owned, I did a study of regular vs. premium gasoline and mileage. Generally, I got slightly better mileage from premium. On a cost-per-mile basis they were always equal within reasonable doubt.

That said, I tend to go with performance. In winter, the low-test fuel performed better. In older cars with knocking or dieseling tendencies, premium fuel in the hot summer helped avoid those difficulties.

 

[FoMoCoMoFo]

Should never have spoke of it.
Just bought fuel and for the first time in ages the spread was more than 10 cents. only 11 an 22 but still ...
I'm pretty sure there are vehicles that are more economical to operate on premium ( I hope so, I've put considerable effort into making it so.)
That said, I'm sure there are a thousand times as many wasting money on unnecessary octane

 

[btrueblood]

"IMO the older engines had to spin up to become efficient, but my Z06 runs 1500 RPM at ~65 with 24MPG."

Ok, you probably have me there, my numbers are from memory for 4-cylinders...

But my point is (was) that running an engine at a higher load gives best efficiency. Compare your numbers to my 4-cylinder 1.8L that runs ~2500 rpm at 65mph with 33-34 mpg. I would bet it puts out something a bit closer to its maximum load (as a percentage of its capability) at that speed, relative to a V8, thus it gives better mileage. Your motor would pretty much tear the shorts off mine in a drag race, but the little motor wins in efficiency, simply because it better matches the average driving power requirement.

 

[thundair]

If things keep going the way they have been, I will change to a turbo 4 Cly maybe a 3L twin turbo Eco tech engine.

I had a turbo T bird that I spent money on that my wife got 33 MPG and I got 16 MPG so driving a 4 Cly isn't the complete answer to good mileage. A side note; in 4 years I went through 3 turbos and 2 motors...also expensive..



I don't know anything but the people that do.

 

[evelrod]

Hmmmmm. A couple observations, nothing personal since I had a long relationship with a stock and modded Tcoup...
One...If your wife averaged 33mpg, she probably needs a new calculator or, a Hondayota something or other.
Two...Since you got 16mpg, I certainly can see why you went through three turbos and two engines. I approve but, you shoulda had me do your new engine. )

My wife and I averaged 22/26 mpg from new until 100k miles where she holed a piston...crapping the turbo, etc.
New engine (Evelrod Racing build @ 295hp at the rear wheels on the JBA dyno)...we managed 22mpg most of the time and that engine went over 200,000 miles! Sold it because we could not keep an AC compressor in it and it wouldn't pass smog last time. I liked that car!... "1983-1995 RIP" Sure was a fast car. Used it in many, many SCCA schools at RIR and Willow Springs...fast on the dry lakes too, 155mph on the rev limiter...clocked!

Rod

 

[Lou Scannon]

I'm still enjoying the Ford 2.3T in my daily driver, now heavily modded (in a streetable way).
I agree with Rod's mileage observations, but IMO a stock 2.3T has plenty of safety margin when maintained in tip-top condition, and as he notes, when judiciously modded, is capable of vastly increased power without sacrificing longevity.

 

[evelrod]

I just read the last post from hemi and it dawned on me that that 83 T-bird was one of the exceptions to the 87 octane rule. After it was modded (bigger turbo, ported head, hotter cam, bigger injectors, altered ECU, etc.), I could not retard the timing enough to keep it out of knock under full boost. Even with the 93 oct available in the early 90's, I needed water injection to keep out of knock on a hot day pulling the hill on I-15 out of San Diego. I used racing gas for much of the time...the cat was 'empty' and I was not too worried about the added cost of the race fuel...I think it was something like three bucks a gallon or therabouts.
I suppose I could have backed boost down to some 'reasonable' numbers...what fun would that have been.
I could spin the tires going into second gear (first was kinda doggy...low boost) and it would go plumb sideways into third. Coming out of T-9 at Willow, I could 'haze' the rear tires in 4th gear!!! I know. I'm too old for that...NOT.

Rod

 

[thundair]

I was naive (dumb) about turbos I killed the first one at a car wash when I accidentally hit it with the spray. It made a whimpering noise and started smoking. The dealer was close by and it was warrantied.
The next one just sucked in the impeller and contaminated everything.
And the last one; I was told to let the turbo idle down as there was no reserve oil to the bearing and should have listened, if I do it over again I would PAY attention its cheaper that way.

Cheers

I don't know anything but the people that do.

 

[Lou Scannon]

A water-cooled center section goes a long way to reduce coking after shutdown, in turbos that tend to run hot, e.g. those applied to spark-ignited engines.

 

[evelrod]

hemi, only the 83 Bird had a non water cooled center bearing. Water cooling helps but does not cure the coking problem. Cooling, along with quality lubricant changed at no greater than 3000 mile intervals and taking care to let the turbo spool down and cool for a few minutes will do the rest.

I doubt if I will ever buy another street driven car with a turbo unless there is some very large profit in it for me.

Rod

 

[Lou Scannon]

Rod, you've obviously had a bad first experience, but remember the '83 turbo Bird was engineered over 25 years ago. By now the European & Japanese brands especially have really figured out turbos in spark ignited engines, but the North American brands aren't afraid to dabble with them anymore either. Change the subject to diesels, and a non-turbo diesel is nowheresville these days.
In my case my DD has been the Ford 2.3T '85 vintage for the past 16 years and have never had a turbo failure. I've torn down & reassembled the turbo a few times, but only the first time was for maintenance (compressor seal passing oil), the rest were mods in pursuit of higher performance, so I'm just now on the third set of bearings/seals at 200,000 miles. Just to fill in the picture, I'm currently running 22psig boost (at 5000' elevation), and expect to have around 300 whp when tuning is complete.
Sorry for the thread hijack; we should start a new thread I guess if this turbo discussion has legs.

 

[evelrod]

Hemi, you misunderstand my posts. I have nothing against turbos, I loved that Bird, used the crap outa it for 12 years. Only sold it because I just got too old for a street hot rod and my wife (whose car it was, technically) was complaining about the AC always on the fritz. Incidentally, I used 18 psi on the street and 24 or so when I could get by with it. In 1988 (when I rebuilt the engine) the Bird was FAST!!! There were no Mustangs that could even touch it. It also was a 'ticket' magnet ;O( !!!

I have only lost one turbo due to ignorance, I guess. That was on my Corvair Spider in 1964. The first turbo in the Bird was cratered due to the molten Al from the piston failure at 100k miles. The turbo on my Dodge/Cummins, now at >200k miles and 17 years old, is doing just fine.

Rod

 

[Lou Scannon]

Understood.

Cheers!

 

[kevindurette]

Saturn ION owners with the 2.4L engine report that they achieve better fuel efficiency with 89 than 87, presumably because of the knock sensor. I don't recall whether the difference was significant enough to justify the most expensive fuel. Personally, if I had a car that recommended the higher fuel, I wouldn't mess around with the lower stuff. I'd be afraid of fouling the plugs and chamber with the extra carbon running rich, and I think one knock is one too many.