Best Gas for a 3.8V6??

mustardjohn · 09-19-2003, 05:26 PM

I have read several posts around the web that seem to indicate that you are better off using the lowest octane grade of gas, "regular", in a late model 3.8 V6, even with most mods. On one post about reducing 1/4 mile times and expert said it would actually slow you down to use the high octane racing gas. Any opinions on this board about gas? Does it matter? I have been burning premium in my 2003 3.8 mustang. My Contour SVT actually says to use premium on the fuel gage amd owner's manual in its 2.6 Duratec 2.5 V6. But then the Contour is a 24 valve with special cam, etc. What's up with the 3.8 regular or Premium?

GodStang · 09-22-2003, 08:14 AM

I would use 87. No higher than 89. If you go too high you can burn up your valves. You can get your computer redone to use higher octane gas but I do not think it is worth it unless you have a blower new heads new intake and all that good stuff.

84LX89GT · 09-23-2003, 12:31 AM

Higher octane gas burns slower and with less BTU's of energy, therefore it needs more heat to burn efficiently. In order to do this you must increase the compression ratio of the engine and have timing based on the increased burn time (higher compression ratio engines or engines with "fast burn" chambers require less total timing advance). Higher octane fuels burn more completely than lower octane fuels but the engine has to be designed or modified to take advantage of the higher octane fuel (some people advance their timing and run higher octane and may see a little bit more power and possibly better gas mileage).

In a vehicle designed for 87 octane, when you put in 92 octane without changing anything, it burns slower and as a result doesn't burn as completely which leaves more raw fuel in the oil, on the valves and on the pistons. This leads to carbon deposits and further problems down the line. In some cases you can see fuel mileage drop or power go down a little.

I personally would use whatever gas the manufacturer recommends you use for the vehicle unless you raise compression, add nitrous or boost, advance timing or change to more efficient cylinder heads.

mustardjohn · 09-24-2003, 07:45 PM

WOW, thanks for the advice. I love advice that saves me money. I also have a 1996 T-bird 4.6 V8 but I don't have the manual. I wonder what kind of gas would be best for that engine. Again I have been burning premium or high octane thinking it was the best thing to do. The T-bird was a really sweet buy. I got it this July with only 38K miles. I mean the head lights were still clear plastic it had spent so much time in the garage.

09-19-2003, 05:26 PM	#1
mustardjohn Registered Member Join Date: Sep 2003 Location: Orange, TX Posts: 360	Best Gas for a 3.8V6?? I have read several posts around the web that seem to indicate that you are better off using the lowest octane grade of gas, "regular", in a late model 3.8 V6, even with most mods. On one post about reducing 1/4 mile times and expert said it would actually slow you down to use the high octane racing gas. Any opinions on this board about gas? Does it matter? I have been burning premium in my 2003 3.8 mustang. My Contour SVT actually says to use premium on the fuel gage amd owner's manual in its 2.6 Duratec 2.5 V6. But then the Contour is a 24 valve with special cam, etc. What's up with the 3.8 regular or Premium?

09-22-2003, 08:14 AM	#2
GodStang College Stanger Join Date: May 1999 Location: Aiken,south carolina, usa Posts: 1,097	I would use 87. No higher than 89. If you go too high you can burn up your valves. You can get your computer redone to use higher octane gas but I do not think it is worth it unless you have a blower new heads new intake and all that good stuff. __________________ 2003 Sonic Blue Cobra

09-23-2003, 12:31 AM	#3
84LX89GT Mustangs Join Date: Jul 2000 Posts: 1,938	Higher octane gas burns slower and with less BTU's of energy, therefore it needs more heat to burn efficiently. In order to do this you must increase the compression ratio of the engine and have timing based on the increased burn time (higher compression ratio engines or engines with "fast burn" chambers require less total timing advance). Higher octane fuels burn more completely than lower octane fuels but the engine has to be designed or modified to take advantage of the higher octane fuel (some people advance their timing and run higher octane and may see a little bit more power and possibly better gas mileage). In a vehicle designed for 87 octane, when you put in 92 octane without changing anything, it burns slower and as a result doesn't burn as completely which leaves more raw fuel in the oil, on the valves and on the pistons. This leads to carbon deposits and further problems down the line. In some cases you can see fuel mileage drop or power go down a little. I personally would use whatever gas the manufacturer recommends you use for the vehicle unless you raise compression, add nitrous or boost, advance timing or change to more efficient cylinder heads. __________________ 2005 Suzuki Hayabusa GSX1300-R 1980 Ford Thunderbird - 255 V8 ported heads, 5.0L ported stock headers, O.R. H-pipe and Flowmaster 2-chambers, dual roller timing chain hi-po Mack Truck hood emblem 1985 Mustang GT 5.0L T5, F-303, GT40p, headers, off-road h, flowmasters, MSD stuff, etc. Sold 02/06/04 1989 Mustang GT ET: 13.304@102.29 mph (5-24-03) Sold - 1998 Mustang Cobra coupe, 1/4 mile - street tires: 13.843@103.41 (bone stock)

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09-24-2003, 07:45 PM	#4
mustardjohn Registered Member Join Date: Sep 2003 Location: Orange, TX Posts: 360	WOW, thanks for the advice. I love advice that saves me money. I also have a 1996 T-bird 4.6 V8 but I don't have the manual. I wonder what kind of gas would be best for that engine. Again I have been burning premium or high octane thinking it was the best thing to do. The T-bird was a really sweet buy. I got it this July with only 38K miles. I mean the head lights were still clear plastic it had spent so much time in the garage.