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#1 |
Import Slayer
Join Date: May 1999
Posts: 2,241
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![]() I recently heard that a stock engine will run worse with 93 octane fuel if it doesn't require it.
Is that true and if so what's the explanation behind it?
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'82 GT 351W (.060)Comp Cams 274* Extreme Energy cam, ported & polished heads w/ 1.94/1.60 valves 10.3:1 flat top pistons,stealth intake, Mallory dizzy,Holley 750dp carb, BBK shorties,Flowmaster exhaust,C-4 with 3700 stall converter, B&M pro shifter,8.8 rear, 4:10's, subframes, electric fan, powermaster alternator, 4 core radiator. |
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#2 |
Registered Member
Join Date: Oct 1999
Location: Pierre Part, La. U.S.A.
Posts: 1,850
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![]() A engine will run harder on the lowest octain that you can get away with. High octain is to make an engine live. It is like a cam, most people go way overboard with it.
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88workcar 1988 Mustang LX 342. 417rwhp @ 6800. 28 X 10 ET Drag, 4.30s, 10.69 @ 126.43 1.42 60ft. 11.13 @ 127.7 on BFGs 1.72 60ft Rice Hater # 42 To be old and wise, You must first be young and stupid ![]() |
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#3 |
Registered Member
Join Date: May 1999
Posts: 5,246
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![]() Octane rating tells you how long the fuel will burn.
In a high compression engine, you need a slow burning fuel that won't detonate. In that instance you sacrifice a little power by going to a higher octane fuel, but that power loss is insignificant to the power loss you'd experience from the mis-firing of the cylinder. For an engine that doesn't need the higher octane fuel, all you're doing is slowing the combustion process, and weakening the cylinder pressure because it's slowing the expansion from the burn. Since cylinder pressure is one of the main contributors to torque, it also directly effects the horsepower production from the engine. |
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#4 |
Registered Member
Join Date: Aug 2002
Location: SanAntonio, Tx
Posts: 957
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![]() I've done some testing, on different fuels, vp 103 motorsport, 93 pump, midgrade ect....I found my car ran best on midgrade, i do belive my motor is low compression because of the heads.
however My buddies 93 gt loves vp fuel.....so it depends on timing, mods, maybe even weather?
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X-Texas highway patrol ssp 1990 coupe - exploder Gt-40 iron heads, Explorer intake, 19 lber's. E-cam. crane 1.7 rollers. 190fp. 75mm maf. 65mm tb, tubular subframe connectors, mac cai, Asp crank pulley, T-5, king cobra clutch, flowtech 1-5/8 unequals, mac X-pipe Frpp driveshaft, lakewood Lca's. race weight 3,160 12.69 @ 107.35, 1.71 60' 26x8.5 drag's 3.90 gear 13.20 @ 106.91 - 235/60/15 firestones 2.3 60' 3.27 gear |
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#5 |
dude5l
Join Date: May 2001
Location: Grande Prairie, Alberta, Canada
Posts: 603
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![]() Like 5302 mentioned, octane is added to fuel to resist burning, the higher the rating the higher the resistance to burning, it basically provides a more controlled burn. In diesel fuel they use a "cetane" rating which works the exact opposite of an octane rating. Just some useless knowledge I had to release.
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Good luck! Brad R. 1992 L.X. 5.0 coupe MODS: A few little bolt ons ![]() New Best time ...11.60 @ 128 mph @ 2000+ ft altitude. Rice Haters Club member #39 Users rides #2542 |
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#6 |
Registered Member
Join Date: May 1999
Posts: 5,246
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![]() High compression is just one example (most common) for why vehicles require higher octane fuel from the factory. The further advanced your timing, again, the slower the burn needs to be. Carbon build ups, lean fuel mixtures, and hot running engines can also increase the need for greater octane rating.
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#7 |
Registered Member
Join Date: Apr 2001
Location: Staging lane
Posts: 4,337
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![]() My 01 cobra ran way better with regular unleaded fuel. I think the high altitude has something to do with it.
I also run regular unleaded in my 90 coupe and it traps 107
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92' LX-Big brakes, Lots and lots of suspension, GT40X heads, Ported cobra intake, stock cam, Vortech SC trim. 00' Lightning-Stock 88'CRX-13 second ego killer |
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#8 |
Junior Member
Join Date: Mar 1999
Location: Ventura, California
Posts: 8,981
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![]() Unfortunately, many people assume that higher octane fuel is better for all engines, no matter what. This, as I'm sure you know, is absolutely false. Ultimately, the best octane for any vehicle is the lowest one you can run without detonation (pinging) occuring.
Running too high of an octane will ultimately make it necessary to continue using that octane. Just to clarify, it's not the fuel that increases the performance, it's the fact that the timing has been advanced, compression has been increased, etc. The higher octane permits this to happen. Basically, the way it works is something like this: Octane represents a fuel's stability. When you compress an air fuel mixture, it becomes quite unstable, and explosive. In fact, this is why diesel engines don't require spark plugs. They commonly have compression ratios of 22:1 (as opposed to a stock Mustang with 9:1), which makes the air/fuel mixture so explosively unstable that it ignites itself when the piston reaches TDC. Octane, for all intents and purposes, is used to slow down, or control the burn rate. Modifications that increase performance, such as increased compression, or advanced ignition timing, will cause the mixture to become too unstable, and pre-ignition (aka: detonation, pinging) will occur. This is when the mixture fires on it's own, at the wrong time. Severe damage will occur if left untreated. Anyway, the only way to perform the mods that increase the power is to further slow down and control the burn rate of the air/fuel mixture, and the method used to do this is increased octane. People often think of high octane fuel as being more flammable, and easier to explode, whereas that is actually the opposite of the truth. 110 octane race gas is much tougher to light than low grade 87 octane. BUT, because of that fact, it is the use of 110 octane fuel that permits the compression to be increased to 12:1 without melting the pistons. Use of a fuel that has a higher octane than is required by the engine and the way it has been tuned will result in unburned deposits being created and left behind in the combustion chamber, and on top of the piston. Often a contributor to carbon deposits, these cause the combustion chamber to become very unstable, for several reasons, all of which will ultimately require you to use a higher octane fuel to restore stability. Among the reasons, are increased compression (the deposits take up space, and actually increase the compression enough to make it unstable), retained heat (deposits retain heat at times when those surfaces shouldn't, increasing the likelyhood of pre-ignition), and the development of sharp edges (like sand under the waves, carbon deposits can be "shaped" by their environment, and can develop sharp edges, which act to the compressing mixture like a hat pin would to a balloon.
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#9 |
Registered Member
Join Date: Oct 2004
Location: NEW JERSEY
Posts: 41
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![]() ok i got 1988 gt which fuel then i should use regualer mid or super please let me know because i'm really confuse i got stock engine ,
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#10 | |
Registered Member
Join Date: Jun 2000
Location: Pigeon Forge Tn
Posts: 611
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![]() Quote:
If your running regular and are not getting any knock/ping: Keep using regular. If you play with the timing, etc and the car starts to knock, then try the next grade up, repeat as needed. ![]() If the car is stock, more than likely regular is all you need. J *Edit* WOOT WOOT, 400 posts, and it only took me about 5 years! ![]()
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____________ '66 Mustang Coupe- AKA "Lenore" *on disability for a (long) bit* '93 GT Mostly stock AKA "Fawkes" Rice Haters Club Member #239 "I find your lack of faith...disturbing." "Every normal man must be tempted at times to spit on his hands, hoist the black flag, and begin to slit throats." H. L. Mencken |
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