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Hi guys, its been a long time. I had to put my 89 Daytona Shelby TII in storage for the past 2-3 years, due to the combination of my situation and the gas prices. Anyway, last Friday someone totalled my economical daily driver by rear-ending me at a stoplight, so I took my Daytona out of storage and I've been driving it since then. My situation is that I drive roughly 100-120 miles a day and buying 93 octane is killing me. My question is what would I have to lower my boost down to in order to safely use 87 octane? Its just a factory, unmodified engine with a BOV and a grainger valve. Any input would be good, any experience with this would be great. Thanks in advance! :thumb:
 

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The big question is? how much boost are you running. If you turn it down, you can safely run 87 octane. I run my mini with an intercooler at 12 psi on 89 octane with no issues. Try running lower boost, around 5 psi and listen for knock, or use a scanner and watch your plugs. Turn it up until you hear knock or you can retard your base timing a few degrees!
 

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Conidering youre wanting to run 87 to save money on gas, you probably care about your fuel economy, so you probably wont be beating on the gas pedal, in which case, light spirit driving would be fine on 87...
 

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I've got an '87 Shelby Z with a bonestock CB 2.2 T-II drivetrain out of an '89 Daytona Shelby.Believe it or not,I've got my G-valve set at 15 psi and I only run 87 octane!I've been driving this car like this for about the last 3 1/2 years and only recently did I break a ringland.I blew a heater hose and the car overheated a bit while out for a spirited run and I think the combination of high heat,bad gas and high boost is what killed my piston.I run a large intercooler that I made from a section of an intercooler from a Freightliner and I'm sure that helps to keep my charge temps down.


Frank
 

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I have the grainger valve set at around 14 psi. It was my understanding that if you're under boost and you hear it knocking or detonating its already too late. I'm uneasy about trying the trial and error method. Is that really safe? This is my only other car and if I screw it up, I'm down the river without a paddle.

Timmay2 is right, after driving a Honda Accord for the past 2 years I'm completely conditioned to light spirited driving, but the temptation of instant gratification is too great, and I find myself frequently spooling up the turbo and I just can't help it.
 

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What would happen if there was too much boost for the octane? Wouldn't that be fatal for the engine? Correct me if I'm wrong, but I thought there was no margin of error? You guys seem so relaxed about crossing into the red zone.
 

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Back your base timing off a couple degrees. I'm guessing if the car is unmodified, you do not have a grainger to set the boost lower. This is really the only thing you can do. 9-10 degrees initial should help quite a bit. The only other thing is to take the wastegate can vac hose and run it directly to the vacuum source. this will limit you to 5-7psi MAX boost.

When you think about it, 100-120 miles a day is roughly $1.00 more a day in gas (assuming 20mpg and $.20 more per gallon for premium) You really need to ask your self if that $1.00 is worth any risk you feel you are taking??
 

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But Ken, backing off ignition timing yields worse mileage! He said he was running a G valve at 14 PSI, my advice if you really want to run 87 octane is to back that off to 12 PSI and you'll be fine.
Ken is DEFINITELY right about running premium, stop and think about it and do the math, it's not much of a savings AT ALL and certainly not worth the cost of a rebuild on the engine! So, run the premium but bump your ignition advance to 15 degrees...that should give another 1 MPG and make it worth running the 93.
 

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Octane boost is a waste of money. Most bottles say they add 10 points, well a point is .1 octane....so 10 points is one octane. So if you run 93 you'll have a whopping 94 octane with the $5-10 bottle.
 

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moparzrule said:
Octane boost is a waste of money. Most bottles say they add 10 points, well a point is .1 octane....so 10 points is one octane. So if you run 93 you'll have a whopping 94 octane with the $5-10 bottle.

So true. The main ingredient in them is toluene, which can be purchased at a paint supply store, or perhaps home deopt for pretty cheap compared to octane boosters. Xenelene is another good alternative.
 

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turbovanman said:
Una, a few degrees won't effect gas mileage enough to worry about!
Sorry Simon but I must disagree, my mileage dropped 2 MPG when going from 12 to 8 degrees base ignition timing with no other changes whatsoever.
 

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when im poor, I run 87 in my 91 shadow and just dont floor it. the computer seems to be able to compensate.

Jake Bauer
 

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moparzrule said:
Sorry Simon but I must disagree, my mileage dropped 2 MPG when going from 12 to 8 degrees base ignition timing with no other changes whatsoever.
Were talking 2 degs, your talking 4. Mine didn't change from 12-15, just was more peppier. Each vehicle is different so he may or may not have a mileage change but probably will get more as he will be running less boost!
 

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turbovanman said:
Were talking 2 degs, your talking 4. Mine didn't change from 12-15, just was more peppier. Each vehicle is different so he may or may not have a mileage change but probably will get more as he will be running less boost!
Well, if you have your foot in it all the time :p your mileage probably won't change even if you dropped it to 4. I'm talking just driving to work and back with light throttle only.
 

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Una said:
Also, don't worry about listening for knock or ping. Your engine has a knock sensor, it'll do it's job just fine at only 7-9psi, if it has to.
So you should be safe either way? Even if your try and run 15psi, the knock sensor should catch anything before damage occurs, right??? Is this correct???
-mark
 
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