Wasup guys? Today I was reading the manuel on my 04 gt and saw that it said that I was only supposed to use 87 octane. The thing is that I have always used 93 and was told it was better. So have I been messing up my engine by filling it up with 93 instead of 87 octane?

 

no... you've been wasting money hand over fist.

Last time... Octane ratings are an expression of the resistance of the specific blend to burning. This means that 93 octane takes a little bigger jolt to get it burning than 87, or if you like: 93 octane is more stable than 87 octane. The only reason to use anything higher than 87 is if your timing is advanced, you run a power adder, or your compression is high enough to justify it.

By using 93 you've wasted money and you may have given your engine (more over your ECU) a taste for the higher test stuff. Disconnect the battery for 10 minutes and then fill up with 87. You may have some minor drivability issues but nothing major and they'll pass. If it's too bad then wean the car off 93 by stepping down gradually through 89 and then to 87.

All else being equal you will make less power on 91 octane than on 87 octane but only marginally so.

 

Yep.

 

Thanks alot man. I still have half a tank of 93 to burn, will that be ok?

 

nope, i use 93 for my cobras too. Anything over 87 is fine to use, anything under, not good lol.

 

I did the same thing for awhile mostly cause I think I got a batch of bad gas once and my engine pinged like crazy on 87 so after that I ran 92 until i realized that it was just a waste of money I switched back to 87 and everything is all good. I just got custom grnd stage II cams installed and tuend and the best part they will only tune on 87 so even with 293 rwhp I still run 87... soon to be E85 though

 

It'll be fine.

 

Higher octane fuel burns slower then lower octane fuel. Also, lower octane fuel will combust at lower pressures then higher octane fuel w/o having to add spark. Think of higher octane fuel as meaning "more resistance to knock".

High compression motors need high octane fuel because otherwise the fuel will combust before spark (pre-ignition or knock).

You can allow a lower compression motor to take advantage of higher octane by advancing the timing further.

Unless your car is setup for higher octane fuel, there is no advantage to using it. In fact, you can loose power. UNLESS, the car has a lot of carbon build-up. When this ocurrs, the carbon decreases the compression space, which has the same affect of increase compression. When this happens, you will get knock. You can prevent the knock in these instances by either removing the carbon or by raising the octane.

 

Yep.

 

Using 93 will not do anything to your car...i have a 2001 V6 and i put 93 in since the day i bought it, and the car runs better, and also performs a little better. If your putting good 93 in such as Exon Mobile Shell, there 93 actually cleans your gas tank and takes care of it...93 won't hurt your car at all...

 

Same here! i have a 03 GT and the day i bought it till now i run 93 octane through it! I notice very little performance and throttle response. As long as its not going to hurt my engine then ill keep on running 93 through it!

 

If your going to run 93 octane atleast get your car tuned for 93 octane so you get your money worth.

 

Who would you take it for that?

 

You are wasting $5 a tank for no good reason by using too high a grade of gas. Apart from that you ARE losing power over what you'd get with 87. How much is lost is a bit variable based on your setup/tune.

The detergent packages that you get in 91/93 are present in 87 and 89 octane as well. The blend is octane rating specific so you'll never know how much is in there but it is in fact in there.

 

On last question, If I get the sct tuner and install the 93 octane tune would it then make it worth my money to pump up using 93?

Thanks in advance

 

Yes. Just make sure its not some BS mail order tune that comes on all of the tuners like Diablo does. Make sure the mail order tune is created based on your actual mods. And never use mail order tunes without putting the car on the dyno and checking a/f.

The only mail order tune for a power adder car I would ever use is one from Tim @ Modular Powerhouse, even then I would still bring it in to check a/f.

 

the cost benefit analysis between power output with a tight 87 tune and an equally tight 93 tune will only become evident on the dyno. There's sometimes 10-15hp to be had from advancing the timing and tinkering with the fuel enough to require higher octane like 93. In my car (every car is different) we noticed a 2 hp difference between the two. For 2hp... I went right back to 87 and decided I'll refine my tune rather than switch fuel grades. For my new motor... it'll be running in excess of 10:1 compression which is totally not 87 octane friendly. I'll be stuck with 91 becuase of requirement of that high compression. If it weren't for that factor... I'd probably always use 87 if possible. THe 10hp isn't worth 50 cents a gallon to me.

 

Welcome to my world of $3.09 a gallon for 91 octane! It sucks having to run premium fuel all the time. Although I'd love to have 93 octane. Speaking of that, have you ever tried Torco Race Fuel additive? I've been thinking about getting a bottle of it and mix it so my fuel would be 93 octane....just for ***** and giggles.

 

never tried it. I've used 104+ with varying results. Anymore if I want/need more I go to the 76 on Vasco and get a couple gallons of 100 from them. Usually only need that when I'm trying to blow up a lawn mower though.

 

How much does it cost for the 100 octane? Just wondering.

 

5 bucks a gallon last time I was there.

 

Oh I didn't know they sold 100 octane around here.....I heard of a place in Sunol that sold it for a bit, but I didn't know you could get it off Vasco. I'm going to put a couple of gallons in my car one day for the hell of it.

 

100 octane....ahh go bigger put some 116 in it and call it a day. Thats what I ran in my old '04 gt every weekend and she ran like a champ on it and even better with nitrous!! Actually it seemed to run x10 stronger with that race gas in it than 93 unleaded. Now during the normal work week it was on 87octane, but plenty of 116 still mixed in with it. The only down fall to running 116 was the cost of it $6.** a gallon, and the next day you would notice a blueish tint on the rear bumper around the exhaust tips.

 

That tint is from un-burnt fuel. If you were to have put that car on the dyno you would have seen a power loss. You can't run race gas like that in a street car not tuned for it. The power increase you noticed was from having a lighter wallet.

 

..Not exactly, had the car on the dyno..plenty of power NA while running 116. s far as making my wallet lighter...naaa it wasnt hurting me, I only had to pay for it the 1st time cause it was the last of it my friend had, from then on i got it from the shop for free cause i ran it soo much and used soo much N2o also! The blue tint I mainly noticed was from when the car had been sitting idling most of the time, but that was only with the 116. When i'de run 110 now and then i never saw it.

Oh and trust me, run your car on 116+Nitrous....she will impress you alot!! Especially when a close friend with the same mods and same size shot runs you and the Gas is the only difference between the two cars and mine would spank him.....even when he drove mine..my mustang will won with him driving it! So there wasnt any power loss.

 

With the nitrous it might be a different story, for all of you NA guys running 93+ without a tune for it, you're wasting you're money, any gains you feel like you're getting are in your head. End of story.

 

that's the scientific fact of the matter. 116 VP gas is optimized for power adders so making more power on nitrous is no surprise. using it just for giggles on a street compression motor without any actual need is just burning it...