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Unread 10-10-2002, 01:27 PM   #1
5420
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Join Date: Oct 2002
Location: Carson City, Nevada
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Premium Fuel - YJ - 4.2L Carb

So I went down to the Shell station yesterday, with a big "E" on my fuel gauge, and filled up my 4.2L 160,000mi YJ with Premium Fuel - and holy SMOKES!

What a difference! It idles smoother, runs stronger, and warms up faster! No more weird pings at low rpm to cruise, etc.

Anyone else notice this on their STOCK motors? I had no idea it made that big of a difference! I guess the $1.29 Cheapimart gas is no good, eh?

BTW - I pulled the old plugs a while back and they looked like Nuclear Testing victims - all sorts of detonation damage. Checked timing - it's spot on where it needs to be... weird

Shell 92 Octane $1.59/gal...

Dave

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4.2L, Weber, K&N, 31",
2" combo, cheapo 15" Chromies,
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Unread 10-10-2002, 02:08 PM   #2
Meister_jeep
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If I was you I would stay away from shell if you want your fuel pump to continue working fine. They have an additive in the gas that gums up your fuel pump. I have a 4.2 and did not really see a difference in the fuel that much except when I did the nutter bypass which made a difference not to throw myself off a bridge like most people seem to say but I saw a difference. I have no idea if my jeep is fine cause I get 300km out of a full tank.
__________________
1988 YJ 4.2l
____________________________________________________
WEBER CARB
NUTTER BYPASS
FIBERGLASS BODY TUB
BDS 3.5
SYE+CV SHAFT
FORD 8.8 WITH 4.10 GEARS, DISK BRAKES
33x12.50 GOODYEAR MT/R's ON AR767 15x8
CUSTOM STANLESS STEEL DISCO`s
JUICEBOX.
LED TAIL LIGHTS
$10 homemade POSILOCK
____________________________________________________
(IN THE WORKS THIS SUMMER)
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Unread 10-10-2002, 03:44 PM   #3
Bob K
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Join Date: Nov 2001
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Posts: 987
Said it before...i'll say it again. This is as true about Jeeps as it is about motorcycles. Save your money.

Wrenching with Rob--Chemical Soup: The Meaning of Gas.
By Robin Tuluie

In many high-performance situation, riders clamor for higher octane fuels, thinking this will give them additional horsepower and, thus, an advantage over the competition. But this is not the case--adding higher-octane race fuel to your motorcycle may actually produce less horsepower. Here's why: Octane, an arbitrary number which is calculated as the average of the Research Octane Number (RON) and the Motor Octane Number (MON), and is only an indic ation of a fuel's sensitivity to knock, which is typically pressure-induced self-ignition. (Of these two ratings, MON is more applicable to racing fuels as it is measured under high load and high speed conditions.)

Octane, as you can see, is not a measure of how much power--or, more correctly, specific energy--is contained in a fuel. And remember that leaded high-octane race fuels burn slower than most unleaded fuels, and may reduce performance in stock or lightly modified motorcycles. A high octane rating itself, however, does not mean that the fuel is slow burning. Hence, it has no direct bearing on the power characteristics of the fuel.

The knock tendency (and hence, the Octane rating) of a fuel is a function of the amount of free radicals present in the fuel prior to ignition and can be reduced by the addition of tetra ethyl lead, aromatics and other additives.

Although some racing organizations still use maximum octane number as the discriminating factor for fuel legality, it is really not appropriate for racing purposes.

Instead one should look at the amount of energy (heat) released in the burning of a particular fuel. This is described by the specific energy of the fuel. This quantity describes the amount of power one can obtain from the fuel much more accurately. The specific energy of the fuel is the product of the lower heating value (LHV) of the fuel and molecular weight of air (MW) divided by the air-fuel ratio (AF):

Specific Energy = LHV*MW/AF

For example, for gasoline LHV= 43 MJ/kg and AF=14.6, while for methanol LHV= 21.1MJ/kg (less "heat" than gasoline) and AF=6.46 (much richer jetting than gasoline). Using the above formula we see that methanol only has a 10% higher specific energy than g asoline! This means that the power increase obtained by running methanol, with no other changes except jetting, is only 10%. Comparing the specific energy of racing and premium pump gas you can see that there is not much, if any, difference. Only alcohol s (such as methanol or ethanol) have a slightly higher specific energy than racing or pump gas.

Other oxygen-bearing fuels, besides the alcohols and nitromethanes, such as the new ELF fuel, will also produce slightly more power once the bike is rejetted. However, at $15.00 to $20.00 at gallon for the fuel the reportedly minor (1% - 2%) improvement is hardly worth the cost for the average racer.

The real advantage of racing gasolines comes from the fact that they will tolerate higher compression ratios (due to their higher octane rating) and thus indirectly will produce more power since you can now build an engine with a higher compression rati o. Also, alcohols burn cooler than gasoline, meaning even higher compression ratios are possible with them, for even more power.

The bottom line here is that, in a given engine, a fuel that doesn't knock will produce the same power as most expensive racing gasolines.

However, it sometimes happens that when you use another fuel, the engine suddenly seems to run better. The reasons for this are indirect: First, the jetting may be more closely matched to the new fuel. Secondly, the new fuel may improve the volumetric e fficiency (that is, the "breathing") of the motor. This happens as follows: Basically a fuel that quickly evaporates upon contact with the hot cylinder wall and piston crown will create additional pressure inside the cylinder, which will reduce the amount of fresh air/fuel mix taken in. This important--but often overlooked--factor is described by the amount of heat required to vaporize the fuel, described by the 'enthalpy of vaporization' (H), or 'heat of vaporization' of the fuel.

A high value of H will improve engine breathing, but the catch is that it leads to a different operating temperature within the engine. This is most important with two-strokes, which rely on the incoming fuel/air mix to do much of the cooling--even mode rn water-cooled two-strokes rely on incoming charge to cool the piston. For two-strokes a fuel that vaporizes, drawing a maximum amount of heat from the engine, is essential--the small variations in horsepower produced by different fuels is only of second ary concern.

Also important is the flame speed: Power is maximized the faster the fuel burns because the combustion pressure rises more quickly and can do more useful work on the piston. Flame speed is typically between 35 and 50 cm/sec. This is rather low compared to the speed of sound, at which pressure waves travel, or even the average piston speed. It is important to note that the flame propagation is greatly enhanced by turbulence (as in a motor with a squish band combustion chamber).

The most amazing thing about all this is that you can get the relevant information from most racing gasoline manufacturers. Then, just look at the specification sheet to see what fuel suits you best: Hot running motors and 2-strokes should use fuels wit h a value of "H" that improves their cooling, while more power (and more heat) is obtained from fuels with a high specific energy.

By the way, pump gas has specific energies which are no better or worse than most racing gasolines. The power obtained from pump gas is therefore often identical to that of racing fuels, and the only reason to run racing fuels would be detonation probl ems, or, since racing fuels are often more consistent than pump gas--which racers call "chemical soup"--a consistent reading of the spark plugs and exhaust pipe.
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Other Tricks I won't tell to just anybody!

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Unread 10-10-2002, 04:02 PM   #4
turfman*
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Do a TFI Ignition upgrade it will help to burn all your fuel in your conbustion chambers and have better power stroke..

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Unread 10-10-2002, 04:11 PM   #5
5420
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Location: Carson City, Nevada
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Fuel + Air = Go!

Ok, well, other than
123:XYZ5/3.3345+4210.5-645.76YQ+ABCDEFG+12.0555E,

I'd say it made it run better! Seems to pick up better, idle better, etc.

Whatever...

Anyways, so what's this JuiceBox? Is that one of those pseudo-HEI kits? How are they? The JuiceBox looks good, but what do you do when you need another cap/rotor? Top looks like a regular ol' GM cap, but the base looks proprietary...

Let me know how it works for you out there with the Hunk-O-Iron 4.2L 6...


Dave
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4.2L, Weber, K&N, 31",
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Unread 10-10-2002, 04:14 PM   #6
Bob K
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Location: New Bedford, MA
Posts: 987
The Juice Box

http://www.driveajeep.com/tfi/index.html

is awesome. Best $130 I ever spent on my Jeep. Better starts, better warmups, smoother idle, better acceleration. Parts are available at any auto parts store.
__________________
'87 Wrangler YJ 4.2 I6 (sorry, sold)
JuiceBox ignition
2 1/2" ProComp Lift
31" BFG A/T's
K&N Filter
Custom Rock Guards
Turbo Muffler
Rear Track Bar in the shed
Other Tricks I won't tell to just anybody!

'99 Grand Cherokee 4.7 V8
Towing Package
K&N FIPK
ProComp MX6 shocks
Borla Exhaust
Tow Hooks
Alpine CD with Infinity+iPod connect
Just getting started!

If you're not living on the edge...
you're taking up too much space.
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Unread 10-10-2002, 05:19 PM   #7
GASPEDDLER
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Posts: 70
have to agree with bob, i don't think a higher octane will neccesarily help in a jeep-perhaps it might in a high performance application.

i will say as an owner operator of five texaco branded c-stores that your concern should be with additives.

i've made plenty of trips to the fuel terminal and have observed the loading of many fuel trucks.

gas is gas it all comes from the same bucket so to speak.

the difference comes after the truck is loaded and the cleaning additives are added to the loaded fuel.

each brand (texaco, shell, exxon, etc.) has its own cleaning additives-that is except for the big bag hypermarts (sam's, cosco, murphy oil, walmart, etc.).

they load, deliver, and sell what we in the industry call unbranded fuel.

this is part of the reason they can sell thier fuel at a lower price.

it's kind of like using a cheap motor oil as opposed to havoline, pennzoil, or quaker state, you would never do it!

this unbranded fuel has no additives to help keep your fuel system clean and lubricated.

which may be fine for your lawn mower but not your baby.

do yourself a favor and save your money choosing a lower octane instead of a lower quality fuel.

you get what you pay for...
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