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Thoughts on 87 octane on a low boosted car.


thorne

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I've been going over this in my head and I'm not sure if its a good idea or not. I know I can tune the car to not knock on 87 octane. But I don't know if my gas millage would go down by removing so much boost/timing.

 

I was just thinking of my money I spend on gas a month and figured If I could get better milage out of cheaper gas why not.

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If you were to tune the car on 87 octane but keep the same a/f numbers that you currently use, you would see a decrease in horsepower and you wouldn't gain any gas mileage.

To get better gas mileage, you would want to tune your cruising map to an a/f ratio around 15.7:1. You would be able to use any octane gas and see better fule mileage results.

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If you were to tune the car on 87 octane but keep the same a/f numbers that you currently use, you would see a decrease in horsepower and you wouldn't gain any gas mileage.

To get better gas mileage, you would want to tune your cruising map to an a/f ratio around 15.7:1. You would be able to use any octane gas and see better fule mileage results.

 

 

The car sits at 14.7 at cruise as it is.

 

I guesse it was a silly idea. ohhhhhh welll. I would prolly get pissed off at it anyways not having the power.

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You probably know this but I just wanted to add something. When the oem's run 14.7 at cruise, it's because they only care about emissions and not fuel economy. You can run it a little leaner and will see a gain in fuel economy and still be safe.
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RL, I had no problems tuning for 15:7:1 on a dyno and there was no driveability issues at all. It was tuned in real-time though.

 

The difference in BSFC between 15.7 and 14.6/14.7:1 is roughly 4-5%, which is a very small amount considering the torque output drop is roughly triple that. At this point you're going to need more torque - throttle, to maintain the speed of the vehicle against any drag. 15.4:1 is where most engine's hit peak thermal efficiency, and usually is cited as the outer most air/fuel boundry before torque drops off like it was paulie shore.

 

Tyrone - did you do the work on loaded dyno? I'm assuming since it was done in real time the answer is yes, in which case you should have seen some torque dips durning tip in with such a lean A/F ratio. I think that's what RL was trying to get at.

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Speaking of Tip in. I've yet to figure out on my subby why when I first get on it on the dyno or street it goes rich then comes to my AFR's I specified shit pisses me off

 

I'm not familiar with Subaru's controls but generally speaking regarding engine control strategy: non steady state fueling is mainly influenced by acceleration enrichment or dynamic airflow calculation parameters. Predicting airflow during transitions can utilize simple modifiers or complicated system response curves.

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Tyrone - did you do the work on loaded dyno? I'm assuming since it was done in real time the answer is yes, in which case you should have seen some torque dips durning tip in with such a lean A/F ratio. I think that's what RL was trying to get at.

 

Exactly.

 

You can see lean misfires in that range, heck mod motor fords will begin to lean misfire around 15.5:1, some motors wont until they are leaner, but you typically will never command anything that lean. You won't end up with perfect driveability, and depending on the control system you might not be able to accurately command that AF in closed loop.

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Exactly.

 

You can see lean misfires in that range, heck mod motor fords will begin to lean misfire around 15.5:1, some motors wont until they are leaner, but you typically will never command anything that lean. You won't end up with perfect driveability, and depending on the control system you might not be able to accurately command that AF in closed loop.

 

Hey Rob - dumb question - what kind of HP can you get out of the Ford EDIS systems on the V8's without any additions?

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I see your point and I guess I shouldn't have specified 15.7:1. I should have said lean it out more at cruise.

 

I did it using a Motec and Autronic stand-alone on the class cars, which were basically unmodified 4 cyl n/a vehicles.

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Hey Rob - dumb question - what kind of HP can you get out of the Ford EDIS systems on the V8's without any additions?

 

 

500-600rwhp. The gaps on the plugs end up being pretty tight though (like .020). They might even go higher than that.

 

I have a full EDIS 8 setup here for a 302 minus the coils if you need one! You can have it dirt cheap.

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I'm curious on how well I my tune on the wrx would stand up to a protuner. Would any protuner be willing to help with my expeirment. I'm really curious but not enough to pay a ton for a couple hp.

 

I think you'll see more "pro" tuners` portfolios shine in the stand-alone area. Most of OEM calibration revolves around the availabilty of options to calibrate versus the resources needed to calibrate them. If you have a control system that is popular and widely supported like the LSx or Mod Motors, you see the problem less, but your many times stuck within OEM maximums.

 

GM is making a push to use a standardized platform and the way they've done so is ingenious. I imagine the other domestics along with competing foreign platforms are doing the same.

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500-600rwhp. The gaps on the plugs end up being pretty tight though (like .020). They might even go higher than that.

 

I have a full EDIS 8 setup here for a 302 minus the coils if you need one! You can have it dirt cheap.

 

I appreciate the offer - mainly had read varying numbers, saw you post and it jogged the memory to find some clarity. The GM crew would crucify me.

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I know that the Omni was actually designed to run on 87, recommended in the owner's manual and on the gas flap. Even though it was a turbo, I saw very little difference in milage or anything of the sort from running cheap 87 to Sunoco 94.
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I know that the Omni was actually designed to run on 87, recommended in the owner's manual and on the gas flap. Even though it was a turbo, I saw very little difference in milage or anything of the sort from running cheap 87 to Sunoco 94.

Well if it was tuned for 87, you probably won't see much gain going to 94 without a retune. Whereas if you're tuned for 94 and go with 87 without a return you'll see a big difference (if the engine doens't knock itself to pieces.)

 

Thorne, have you thought of a 0% WGDC map to flash-in for when you won't be flogging the WRX? If anything, it'll help keep your lead foot from stepping on your wallet.

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