Running mid grade gas????

Jacob_Royer

Jacob_Royer

SCCoA Member
What mods could be done to get away with running mid grade(89/90) octane in my s/c it is completely stock and i don't plan on running anymore boost than what I already have. Will an I/C fan help a bit perhaps a double i/c or the snow kit? 92 is rediculous right now! I can get 90 octane for the same price as 87 ($2.29) right now... Or would 89/90 be fine if i kept my foot out of it?
 
im thinking the best way to run regular gas is colder thermostat and colder plugs and gutted cats my 89 5 speed runs great on regular gas no pinging even wide open. my 90 all stock will ping even with 89 i try to keep my foot outof it when i hear it so i dont blow a headgasket
 
Last edited:
When my milage dropped to 10mpg, it got my attention.
(plugs had a huge gap, say .09 - .10)
So I changed the plugs and wires, and it added 2 mpg.
Then changed O2 sensor and that added 2.
Then lost the original supercharger and that added 2 mpg.
(tied the bypass valve open)
I now got about 16.5 mpg in the city.
Now with reman SC, I'm back down to 13-14 city driving.
 
Last edited:
Jacob_Royer said:
What mods could be done to get away with running mid grade(89/90) octane in my s/c it is completely stock and i don't plan on running anymore boost than what I already have. Will an I/C fan help a bit perhaps a double i/c or the snow kit? 92 is rediculous right now! I can get 90 octane for the same price as 87 ($2.29) right now... Or would 89/90 be fine if i kept my foot out of it?
Click to expand...
If you remove the octane plug you would probably be fine. The octane plug removes timing. You should be able to find more info on the octane plug by doing a search.
 
I just put in a 1/2 tank of 89 this week just to see how it would do. So far even with with 3/4 throttle, I haven't heard any bad noises. It didn't used to be like that.. many years ago, 89 used to make it sound like a can of marbles under the hood. But that was also when going up a long grade in O/D with the engine spinning slow. :)
 
Knock Sensor

How much timing will the Knock Sensor pull, before you actually HEAR the pinging?

68COUGAR
 
I thought about running mid grade but even at today's prices it's not worth the difference. I filled up today with premium at $2.569 a gallon. Mid grade was 2.509, only 6 cents a gallon less.... the difference is a dime a gallon at most places. so if you drive 15,000 mile/yr and average 20 mpg (very realistic from my experience) you're gonna use 750 gallons of gas every year. so you are gonna save $75.00 a year ( or $6.25 a month) by using midgrade gas instead of premium. even if it was 20 cents a gallon cheaper you are only gonna save $12.50 a month! In my opinion it's not worth the risk so I just run premium.
 
dime a gallon difference

kevenj90sc said:
I thought about running mid grade but even at today's prices it's not worth the difference. I filled up today with premium at $2.569 a gallon. Mid grade was 2.509, only 6 cents a gallon less.... the difference is a dime a gallon at most places. so if you drive 15,000 mile/yr and average 20 mpg (very realistic from my experience) you're gonna use 750 gallons of gas every year. so you are gonna save $75.00 a year ( or $6.25 a month) by using midgrade gas instead of premium. even if it was 20 cents a gallon cheaper you are only gonna save $12.50 a month! In my opinion it's not worth the risk so I just run premium.
Click to expand...


Lucky for you guys !
Up in the north where people don't notice much, the pump difference between 87 and 91 (not even 92 anymore) is a dime a litre thats 3.56L/usgallon x $.10 = $.356/gallon
None of the big dealers cut this differential ever, a few VERY small players bump 91 up by $.25
Dollars and units aside, at least you get better value for the premium fuel.
This drives me nuts because I like the 91 in my SC, but I hate paying into the rip off!!!
Pete
BTW Octane plug pulls 4deg out of timing, it is located back passenger side firewall VERY close to EEC test connector.
 
The summer is the worst time to try and run low octane gas. Remove the SC belt and wire the bypass open, and then buy cheap gas if money is that tight.

Might be time for a 4 banger.
 
Peterdroy, i was talking about the difference between mid (89 here) and premium (92)....not the difference between regular (87) and premium. but even at 36 cents a gallon you are lookin' at $20 a month difference..... more substantial than the $6 or $12 in my example but still not worth risking in my opinion. To me the SC gets fantastic gas mileage considering it's a nice comfortable car too.... I average well over 20...... have gotten 26 on road trips.
 
kevenj90sc said:
....To me the SC gets fantastic gas mileage considering it's a nice comfortable car too.... I average well over 20...... have gotten 26 on road trips.
Click to expand...
The good 'ol days. I remember getting 28 mpg one year heading to Carlisle. Now, with all of my mods and non-lockup convertor, I'm happy if I get 17 mpg on long trips. Around town is only about 14 or 15 mpg.

Oh well, I still drove my car all weekend.
 
Who has actually run cheap gas with the octane plug removed?

I am thiking it could be worth it if you were making a several hundred mile trip or more....

Does it make it run like a dog???
 
Pull the octane plug. That retards timing 10degrees automagically and should let you run the lower octane stuff and not hit any detonation that the EEC can't deal with.

Paid 2.769/gal for 90 octane crap on the way home tonight. (only put in 5 gal)
 
I kinda wish I was where some of you are. Here gas has gone up about .40 since last Thursday. I filled my SC up Saturday night for $2.87 per gallon and right at 16 gallons for a grand total of $46.00. When me ex-husband bought it new in '88 we were able to fill it for $19.00. Now here I am 17 years and 315K miles later and can't bring myself to get rid of the car. It's just too damn fun to drive plus, no car payment!
 
Mike8675309 said:
Pull the octane plug. That retards timing 10degrees automagically and should let you run the lower octane stuff and not hit any detonation that the EEC can't deal with.

Paid 2.769/gal for 90 octane crap on the way home tonight. (only put in 5 gal)
Click to expand...


OK, I have alway heard 4degrees being the magic number, but now you say 10...

Do you have a source for this figure???

I'm curious....
 
sizemoremk said:
OK, I have alway heard 4degrees being the magic number, but now you say 10...

Do you have a source for this figure???

I'm curious....
Click to expand...
I'm 95% sure that it's 4°, but I'll wait for someone to confirm.
 
my tuner file says minus 4 degrees when spout plug removed and minus 8 degrees taken out for knock snsor so im guessing minus 4
 
Mea culpa...

PURPOSE
The octane adjustment switch is used to retard the ignition timing three to four degrees.

OPERATION
When the switch jumper is INSTALLED, the timing is normal. With the jumper "REMOVED", the timing is retarded. This is done to allow for optimum spark advance for effective combustion of the air/fuel mixture.
Click to expand...

i was getting it confused with the base timing set which is 10degrees BTDC.. Sorry folks.

SCT Tuners can modify the behavior of the EEC based on if that jumper is installed or not as well, increase the timing retard, or using that to signal when to go to a more advanced setting for the track.
 
premium

kevenj90sc said:
Peterdroy, i was talking about the difference between mid (89 here) and premium (92)....not the difference between regular (87) and premium. but even at 36 cents a gallon you are lookin' at $20 a month difference..... more substantial than the $6 or $12 in my example but still not worth risking in my opinion. To me the SC gets fantastic gas mileage considering it's a nice comfortable car too.... I average well over 20...... have gotten 26 on road trips.
Click to expand...

My beef is that after all the conversions and exchange, the value of the difference in cost between 87 and 91 here is not justified.

I agree, the SC is quite good on fuel, I have driven Toronto to Hastings Mi (350 miles), relatively flat, steady 70mph and recoreded 34mile per imperial gallong, thats about 27.2mpusgallon.

Regards
 
You must log in or register to reply here.
Back
Top