gas for 5.0

Jmet

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Jun 14, 2003
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Ok can you run regular 87 gasoline in a 87-93 GT?? no mods or anything completely stock. or do you HAVE to put a premiums gas in it? we run regular gas in our 03 GT is that bad??? someone fill me in here i've been getting alot of mixed opinions :shrug:
 
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Mine has a mild h/c/i combo with exhaust, 1.7's, upgrade maf/throttle body - stock bottom end, and a chip that controls wide open throttle timing so I can run 16-18 degrees initial and 32-34 degrees total. I run 87 octane - no detonation whatsoever. There's absolutely no benefit to running higher octane fuel UNLESS it allows you to run more timing, or you have high enough compression that detonation is an issue. Run the lowest octane you can and still avoid detonation. Higher octane fuel is more resistant to being ignited (that's why it resists detonation) and burns slightly more slowly than lower octane fuel. If you can run the same timing on low octane fuel that you do on higher octane fuel, you might actually notice a slight increase in fuel mileage on the lower octane stuff.
 
Jmet said:
Ok can you run regular 87 gasoline in a 87-93 GT?? no mods or anything completely stock. or do you HAVE to put a premiums gas in it? we run regular gas in our 03 GT is that bad??? someone fill me in here i've been getting alot of mixed opinions :shrug:


A 5.0 Mustang runs on 87 Octane from the factory. If you modify the car, or bump the timing up, you need to run higher octane to control detonation, but factory stock, use 87.

Same goes for the '03GT. They use 87 octane.

The myth about premium making cars run better is totally false. Cars actually make more power with lower octanes. The higher octane is for vehicles with higher compression motors and need the octane to help control detonation. Run the octane the motor was designed for. Don't listen to people who say running premium gives them better gas mileage and more power. It's all in their head.
 
I usally run 93oct , but the other day I whent to the gas station I was almost out and the only gas they had left was 87oct, so I say whatever and filled my tank. Well think it had just as much power as when I use 93oct. But what i did notice was that I only got abot 200ml to the tank full VS about 240-250 with the 93stuff what gives??
 
RiceCooker5.0 said:
I usally run 93oct , but the other day I whent to the gas station I was almost out and the only gas they had left was 87oct, so I say whatever and filled my tank. Well think it had just as much power as when I use 93oct. But what i did notice was that I only got abot 200ml to the tank full VS about 240-250 with the 93stuff what gives??
you kept your ass outta the gas.............
 
I think he's alluding to the possibility that while you were testing out the fact that it "had just as much power" you were busy getting worse gas mileage because of your right foot, not the gasoline octane rating.

Car and Driver tested this in an article a couple of years ago. At the bottom is the link. Here's their summary: "Our tests confirm that for most cars there is no compelling reason to buy more expensive fuel than the factory recommends, as any performance gain realized will surely be far less than the percentage hike in price. Cheapskates burning regular in cars designed to run on premium fuel can expect to trim performance by about the same percent they save at the pump. If the car is sufficiently new and sophisticated, it may not suffer any ill effects, but all such skinflints should be ready to switch back to premium at the first sign of knock or other drivability woes. And finally, if a car calibrated for regular fuel begins to knock on anything less than premium or midgrade, owners should invest in a tuneup, emissions-control-system repair, or detergent additives to solve, rather than bandage, the root problem. Class dismissed." The bottom line has been touched on already - even if modded, if your car will run without detonation on 87, there's no benefit to running a higher octane - it just wastes money.

http://www.caranddriver.com/article.asp?section_id=4&article_id=3604&page_number=1
 
Michael Yount said:
Mustang5L5 said - "If you modify the car, or bump the timing up, you need to run higher octane to control detonation"

Certainly not true in my case - see the post before yours above....

Well, hopefully by the time someone gets to the same point as you Michael, they know a thing or two about octane and tuning and such.

But for any newbie, i just made a general statement. It would be too complicated to get into the exceptions and "unless"es.
 
If Im running 10:1 compression and shooting 100hp dry shot,and I retard the timing 2.5* for each 50 shot, would I benifit from running 118 octane race fuel at the track only to make sure I dont detonate when spraying? What are your thought on this concept? Thanks for the help........
 
Higher octane will help prevent detonation -- in other words if all else is equal, you'll have less chance of detonation on 118 race gas than on pump 93 gas. However, whether it will keep your combo from detonating, I have no idea.
 
cjman15 said:
So if you've run 93 in your car for awhile, like i have, and you start puting 87 in it, will it make it ping or anything?
if your run little enough timing to not detonate/preignite, no. if you ping on 87, take some timing out and see.
there are quite a few anomolies that can lead to pinging. carbon build up in the chambers can artificially raise compression ratios or pieces of carbon can act like a glow plug and ignite the mixture without a spark. there are many things, but as a blanket answer, try the 87 and dial out timing if necessary. all motors are different and have different requirements. for me, i run 87 year round. timing is 15* in winter. 10-12 in summer (ambient temps ~110*).

good luck.
 
cjman-It's hard to know what will happen. As miles go by, carbon deposits build in the cylinder. They can be the source of hotspots which can contribute to detonation. So it's at least possible that the car is more prone to detonation now than it was before you switched to 93 octane fuel. If it's not detonating with 93, I'd step down to the in-between grade (91, 89 - it varies across the country), and try that. If all's well, then step down to 87 and see what happens. This is the worst time of the year for detonation because ambient temps are the highest - and the higher the intake air temp, the more possible detonation becomes. But if you haven't modded it since you started running 93, ease the octane down and see what happens. You can always go back to 93 or cut the timing back if it causes problems.