What Gas should I use?

red82gt · 07-11-2002, 12:32 AM

I'm going racing this weekend and the weather's gonna be very hot (37C or 101F) and very dry ~20% humdity. My mods are in my sig and my C/R is a bit over 10:1 and my heads are iron.
Should I mix a few galons of 103 octane with 94 pump gas? I read somewhere that in hot, dry conditions octane requireets increase.
Any opinions on this?

Mach 1 · 07-11-2002, 01:47 AM

experiment for best results

PKRWUD · 07-11-2002, 05:53 AM

Agreed. Ultimately, you want the lowest octane you can use without causing detonation.

Take care,
-Chris

Mustang_289 · 07-11-2002, 06:11 AM

Chris:

I'm curious to why you would want lower octane. I'm not challenging you here I simply don't know enough, just trying to understand more. When I watch drag races on TV I always got the impression these dudes crank the octane up in the pro-stock and higher classes.

PKRWUD · 07-11-2002, 08:32 AM

Quote:

Originally posted by Mustang_289
Chris:

I'm curious to why you would want lower octane. I'm not challenging you here I simply don't know enough, just trying to understand more. When I watch drag races on TV I always got the impression these dudes crank the octane up in the pro-stock and higher classes.

No problem. In short, the octane rating basically tells you the burn rate of the fuel. The higher the octane, the slower the burn rate / the lower the octane, the faster the burn rate. You want the fuel to burn as fast as possible, but still be stable enough to not burn faster than you want, which would create detonation. There has been a misconception that higher octane fuel is more powerful, when in fact it is actually harder to ignite.

When you do things like advancing the ignition timing, or raising the compression, you make the air/fuel mixture less stable, which can cause detonation. In order to stablize the mixture, you add a higher octane fuel.

The ultimate octane for any combination is one that results in stability with the mods and adjustments that engine has, without making the mixture any more difficult to ignite than is necessary. In otherwords, the best octane is the lowest you can use, without resulting in detonation.

Take care,
-Chris

302 LX Eric · 07-11-2002, 08:43 AM

Exactly.

High octane gas will 'resist' combustion more than a lower octane level - all things equal.

I find it amusing when you see kids pickup a can of SUPEROUTLAW OCTANE BOOSTER 104+ OCTANE!!!! for their Honda Civic that has been 'modified' with wires and a fart can.
The car was made to run on 87, so the super octane boost crap is most likely slowing them down. And actaully, with diliution on a full tank of gas, it would take several bottles of octane boost to really move the octane levels up that much anyways.

Bottom line is that in most cases this stuff is worthless. You're better off getting 89, 92, 93 or 94 octane from your local gas station - choosing the grade that your car really needs.

E

89 Cobra LX · 07-11-2002, 02:46 PM

Chris,

After reading this post I'm wondering if using a lower octane gas would solve some of my problems. My car always smells a little rich, even though when we tuned it on the dyno, we got it in the right range. I've always thought the higher the octane the better. I usually put in 91 or 92 octane (depending what the station carries). I'm going to try 87 octane next time and see if it pings.

What are your thoughts on ethanol?

Thanks,

PKRWUD · 07-11-2002, 03:06 PM

I'm not fond of ethanol. It tends to be too unstable, and tends to cause the rubber needle tips to swell shut, preventing fuel from getting into the bowl of older carbs.

As far as your idea, try 89 first. Don't jump to 87 first. Go in steps.

Take care,
-Chris

89 Cobra LX · 07-11-2002, 03:17 PM

hmmm.... around here 89 = ethanol. That's why I asked.

Mach 1 · 07-11-2002, 03:35 PM

Quote:

Originally posted by 89 Cobra LX
Chris,

My car always smells a little rich,
Thanks,

Are you running an off road H-pipe?

Mine smells terrible, and I think this is the main cause.

302 LX Eric · 07-11-2002, 03:42 PM

An off-road H pipe will definitely smell 'richer' than a Mustang with cats intact.

I noticed it immediately when I put on my H pipe.

E

89 Cobra LX · 07-11-2002, 03:43 PM

Quote:

Originally posted by Mach 1

Are you running an off road H-pipe?

Mine smells terrible, and I think this is the main cause.

Yes, I am. It never smelled this badly until I installed the new motor last summer. I'm sure the cam and heads are part of the reason, but this cam doesn't have any overlap and I was expecting to get a better burn.

I really need to install my new ignition coil.

stevstum · 07-11-2002, 04:26 PM

What about with NO2? I was thinking of buying a ZEKS nitros kit was wondering if I would have to run a higher octane.

red82gt · 07-11-2002, 06:48 PM

I know that for pump gas using the lowest octane you can run on is generally true, but I've also read that a well blended race fuel will result in a denser, cooler mixture and on a hot day I would think that to be worth some power, especially when the air is hot and dry enough to start a fire with snapping your fingers.
I'm going to make a couple runs with 94 pump gas and then try mixing in a couple of gallons of 103 and see how it goes.
It'll also be my first time running on M/T Sportsman pros, so I'm pretty excited.

07-11-2002, 12:32 AM	#1
red82gt Sober voice of Reason Join Date: Nov 1998 Location: Kelowna, B.C., Canada Posts: 1,514	What Gas should I use? I'm going racing this weekend and the weather's gonna be very hot (37C or 101F) and very dry ~20% humdity. My mods are in my sig and my C/R is a bit over 10:1 and my heads are iron. Should I mix a few galons of 103 octane with 94 pump gas? I read somewhere that in hot, dry conditions octane requireets increase. Any opinions on this? __________________ 393W: AFR 205's, hydraulic roller, TKO600.

07-11-2002, 01:47 AM	#2
Mach 1 Registered Member Join Date: May 1999 Location: Georgia Posts: 3,866	experiment for best results __________________ 2002 GT 1993 GT (SOLD) '93 Mustang GT RHC member #142

07-11-2002, 05:53 AM	#3
PKRWUD Junior Member Join Date: Mar 1999 Location: Ventura, California Posts: 8,981	Agreed. Ultimately, you want the lowest octane you can use without causing detonation. Take care, -Chris __________________ Webmaster: Rice Haters Club Jim Porter Racing Peckerwoods Pit Stop Support Your Local RED & WHITE!

07-11-2002, 08:43 AM	#6
302 LX Eric or '331 LX Eric' Join Date: Jan 1999 Location: Columbus, Ohio Posts: 2,142	Exactly. High octane gas will 'resist' combustion more than a lower octane level - all things equal. I find it amusing when you see kids pickup a can of SUPEROUTLAW OCTANE BOOSTER 104+ OCTANE!!!! for their Honda Civic that has been 'modified' with wires and a fart can. The car was made to run on 87, so the super octane boost crap is most likely slowing them down. And actaully, with diliution on a full tank of gas, it would take several bottles of octane boost to really move the octane levels up that much anyways. Bottom line is that in most cases this stuff is worthless. You're better off getting 89, 92, 93 or 94 octane from your local gas station - choosing the grade that your car really needs. E __________________ 1991 5.0 LX Coupe - 40,750 miles 331 cu. in. / Tremec 3550 / BFG Drag Radials 12.22 @ 114.31 mph - w/1.89 60'

07-11-2002, 02:46 PM	#7
89 Cobra LX Don Corlione Join Date: Jun 2001 Location: Omaha NE USA Posts: 491	Chris, After reading this post I'm wondering if using a lower octane gas would solve some of my problems. My car always smells a little rich, even though when we tuned it on the dyno, we got it in the right range. I've always thought the higher the octane the better. I usually put in 91 or 92 octane (depending what the station carries). I'm going to try 87 octane next time and see if it pings. What are your thoughts on ethanol? Thanks, __________________ Eric - 89 Mustang LX coupe 5 speed 302-Cobra Intake-GT40p heads-TFS stage 1 cam-FRPP 1.6 roller rockers-3:73 gears-KYB shocks and struts-Eibach Pro-kit-HPM Mega-bite upper and lower control arms-FRPP aluminum driveshaft-16x8 Chrome Cobra Rs R.H.C. #14

07-11-2002, 06:11 AM	#4
Mustang_289 Registered Member Join Date: Sep 2001 Posts: 512	Chris: I'm curious to why you would want lower octane. I'm not challenging you here I simply don't know enough, just trying to understand more. When I watch drag races on TV I always got the impression these dudes crank the octane up in the pro-stock and higher classes.

07-11-2002, 03:06 PM	#8
PKRWUD Junior Member Join Date: Mar 1999 Location: Ventura, California Posts: 8,981	I'm not fond of ethanol. It tends to be too unstable, and tends to cause the rubber needle tips to swell shut, preventing fuel from getting into the bowl of older carbs. As far as your idea, try 89 first. Don't jump to 87 first. Go in steps. Take care, -Chris __________________ Webmaster: Rice Haters Club Jim Porter Racing Peckerwoods Pit Stop Support Your Local RED & WHITE!

07-11-2002, 03:17 PM	#9
89 Cobra LX Don Corlione Join Date: Jun 2001 Location: Omaha NE USA Posts: 491	hmmm.... around here 89 = ethanol. That's why I asked. __________________ Eric - 89 Mustang LX coupe 5 speed 302-Cobra Intake-GT40p heads-TFS stage 1 cam-FRPP 1.6 roller rockers-3:73 gears-KYB shocks and struts-Eibach Pro-kit-HPM Mega-bite upper and lower control arms-FRPP aluminum driveshaft-16x8 Chrome Cobra Rs R.H.C. #14

07-11-2002, 03:42 PM	#11
302 LX Eric or '331 LX Eric' Join Date: Jan 1999 Location: Columbus, Ohio Posts: 2,142	An off-road H pipe will definitely smell 'richer' than a Mustang with cats intact. I noticed it immediately when I put on my H pipe. E __________________ 1991 5.0 LX Coupe - 40,750 miles 331 cu. in. / Tremec 3550 / BFG Drag Radials 12.22 @ 114.31 mph - w/1.89 60'

07-11-2002, 04:26 PM	#13
stevstum Registered Member Join Date: Mar 2000 Location: Salem, Or. USA Posts: 233	What about with NO2? I was thinking of buying a ZEKS nitros kit was wondering if I would have to run a higher octane. __________________ Steve Stumbaugh 89 LX 5.0 5sp, Removed air silencer Mac High Flow Air Filter Motorcraft 8mm wires Autolite platinum plugs Mac O/R h-pipe Flowmaster American Thunder 3:55 gears Accel Super Coil (42,000) 75 mm Mass Air Meter

07-11-2002, 06:48 PM	#14
red82gt Sober voice of Reason Join Date: Nov 1998 Location: Kelowna, B.C., Canada Posts: 1,514	I know that for pump gas using the lowest octane you can run on is generally true, but I've also read that a well blended race fuel will result in a denser, cooler mixture and on a hot day I would think that to be worth some power, especially when the air is hot and dry enough to start a fire with snapping your fingers. I'm going to make a couple runs with 94 pump gas and then try mixing in a couple of gallons of 103 and see how it goes. It'll also be my first time running on M/T Sportsman pros, so I'm pretty excited. __________________ 393W: AFR 205's, hydraulic roller, TKO600.