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What is the highest octane recommended for a supercharged engine

Fastrthnu5.0

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I have a 2021 gt. I got a roush stage 2 supercharger, midpipe delete and everything else is stock still has stock roush tune. I can barely find 93 here but have access to race fuel. Usually not unleaded but i am looking for sunoco 260gtx and usually can find VP C12. Question: will mixing either with 91 and getting my octane to 98 give me any benefit. I know lead is bad for o2 and cats but idc thats guna be gone eventuallyand i prefer the sunoco but i hafta take what i can. And i can find this easier and mix rather than travel 20 miles for 93 every 5 days.
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engineermike

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With a stage 2 Roush at the stock boost level, I think your best route would probably be a good octane booster like Boostane. It would only take a 1/4 can of professional per table of 91 to hit 97 octane, and you really shouldn’t meet more than that to clean up any knock you might have.

That said, I’d need to look at your log to know if it would really benefit. I don’t know if Roush caps the timing below knock. Most supercharger tunes run it right into knock and let the knock retard system manage it…but this has it knocking a little on every wot pull.
 

stanger1

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My 2017 Roush RS3 on a Roush Phase 2, 727hp and I watch the Knock activity with my N Gauge and my car does good with only 4oz of Boostane with 15 gallons of 91 Octane.
N Gauge shows - knock, so adding timing, so it's happy.
If I don't put any Boostane in and have just the 91 octane, it will show + knock sometimes.
We do have one Fuel Station here that has 93 octane, but my car did not like it.
Just because it says 93 does not mean it's Good Gas.
.
 

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engineermike

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@stanger1 just because it shows negative knock retard doesn’t mean it’s avoiding knock. You have to plot knock retard over time at wot and watch the behavior. If there are sudden increases in retard, even if it stays negative, then it recorded and responded to knock. This can happen whether the correction is positive OR negative. What’s your total timing?
 

stanger1

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I think the most I have seen with out the computer adding timing is around 17 degree's, but it is a Stock Roush 2.3 TVS on a Phase 2 tune, 80mm pulley.
I have see on the N Gauge add - 3.5-4 at the most, so Car seems happy with it adding the 3-4 degree's timing.
Have not data logged this as my laptop died, so I would not be able to read the log anyway.
Assuming Roush tuning is good!
 
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Fastrthnu5.0

Fastrthnu5.0

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Wow thanks for the reply guys. I didnt get rid of the O2 or cats. I did a dumb thing and ran some sunoco 110 it set off check engine light but man did it have more immediate response. Sometimes when i go WOT it seems to wait a second before it gives me full power but no hesitation on the race gas. I think i will take the advice and use boostane
 

96gt4.6

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I have ran Boostane in mine since the kit was installed 15k miles and 3 years ago. I primarily only run it during the summer months, and on race days just for the added safety net of the additional Octane.

I'm running a stage 1 Whipple kit/whipple tune.

Car has never skipped a beat, and knock retard has always been negative (adding timing). Stuff works. I change plugs every other year, Whipple recommends every 20k or so (need to reivew manual to know exact interval).

Seems to work great. Nice little 10 sec car I can drive anywhere. Did Rocky Mountain Race Week last year, and going this year. 1700 miles across 3 states and 4 tracks last year. Took 2 bottles of Boostane and just ran whatever 91 I could find along the way.
 

hlfbkd420

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4 years on a 2018+ roush p2 kit and running 91 in hot AF Arizona. I don’t really worry about it :)
 

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Cory S

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if stoich deviates too much from pump you’ll need a tune. Just use octane booster or go e85
Actually, you don’t need to worry about specific gravity effecting stoich on our platforms since they are closed loop fueling and lambda targeting.
 

SolarFlare

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Actually, you don’t need to worry about specific gravity effecting stoich on our platforms since they are closed loop fueling and lambda targeting.
so he can run E85 on a pump gas tune?
 

Cory S

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so he can run E85 on a pump gas tune?
No. Not E85. Race gas yes. With E85, STFT's would almost be out of range because E85 as you know has 30% less energy.
 

SolarFlare

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No. Not E85. Race gas yes. With E85, STFT's would almost be out of range because E85 as you know has 30% less energy.
To be honest highly doubt he'll get anything from mixing some race gas besides some knock suppression.
 

BrianH87

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I always wondered how this would work. Some race fuels have a stoic of 13.0 or so. How far off can the PCM account for?
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