If this site, had a member of the month. I would choose you 007 for your outstanding courtesy and respect for other members lmao .....I always felt like a badass buying octane booster for my other car

 

Well, if you were tuned for 91 or 93, it would be because you were advancing the timing in order to increase the cylinder pressure to increase horsepower. If you were to go back to 87, you would be running more unstable fuel with the increased heat of the added timing which could detonate.

So, no you could not go back to 87 unless you got retuned and retarded the timing back down.

 

The reason you have 91 rather than 93 octane is because of the elevation you are at. Higher elevations do not need as high of octane levels

 

I do have a question of my own though (this question probably belongs in the hypermiling section, but oh well).

My plans are solely for fuel economy (K&N drop-in for now...will get an intake later, LSJ DP, LSJ cat-back, and either leave the manifold alone or go with something like the Racing Solutions header) and fun in the curves (front strut tower, rear sway, SS/TC struts/shocks).

Can I get a Trifecta tune done and not increase the required octane (this probably doesn't make sense...I'm thinking, what's the point in getting a tune if you're not going to run higher octane fuel)? Or, can I get the same kind of MPG with 91/93 as I would with 87 (assuming I drive the same)?

Thanks for the clarification, I wasn't sure if the computer would automatically take the lower octane into account and retard the timing or not (since there was mention of the 2 tables). I have a lot to learn in terms of fuel and timing and what not.

 

In 90% of cases, a tune will yield better fuel economy by leaning the mixture and getting more out of the fuel you burn, instead of running rich from factory tune. If you really wanted, you could get him to tune you specifically for MPG. It would probably be not too far from his bolt on tune, but he's a great tuner and could definitely work something out for you.

One word of advice, stay away from the 2.4 manifold if you want to keep good mileage. I used to get 39/40 mpg hwy with bolt ons and a careful watch of the rpms, afterwords I was seeing maybe 32 at most. It REALLY shifts the powerband up, you want all the low end grunt you can get for fuel economy.

 

After all is said and done, if I can get at least a 15% gain in economy, I'll be happy. In the winter I'm getting ~25 because of warming my car up and the additives they put in the gas....summer time I average 28-30 (this is mixed with a bit more city driving). I think the only highway trip I did, I averaged almost 33/34. So If I can get about 3 MPG more in my mixed driving, I'll be happy.

 

subd...for good info

 

On 87 octane I dyno'd at 360WHP,91 octane I dyno'd 393WHP. just kidding my car will prolly never see the rollers haha.I use 91 just cause I feel it burns cleaner.I scoped my cylinders and they look purty @ 38,000 miles.

 

I use 93 octane, but im running stage 2 cams. So the timing is advanced quite a bit.

 

glad someone cleared this up. gonna get trifecta tuned and was gonna ask about what the difference would be.

 

easy answer...no longer answer, you can, but you'd have to avoid going into PE mode which means no heavy throttle at all...in which case i have to ask why you would get a tune that you cant use

or perhaps they just dont sell it there? They dont have 93 in a LOT of states/cities. Its incredibly difficult to find a station in socal that sells higher than 91.

you can get a trifecta tune and stick with the stock 87, however, since you will be running additional timing, a 91 octane tune will increase mpg, since you will need less fuel to make the same horsepower. the question however is this: is it cheaper to run 87octane and go heavier on the throttle? or is going lighter on the throttle with 91octane going to be cheaper, even though it costs $2 more per fill up?
If you really want MPG mods, get an underdrive pulley, lightweight rims, and tires with a low rolling resistance. if manual, get a lightweight flywheel as well.

 

If they are a fairly decent tuner you will see increased mpg on a higher octane spark table but only if they also increase spark during closed loop conditions. I've seen some hack jobs only increase during WOT which will usually result in decreased fuel economy during driving conditions in which you desire better fuel economy (closed loop). It has to do more with the spark table cells used during closed loop conditions than anything, these are usually increased in higher octane tunes.

As far as the computer learning down octane levels, some will throw you completely into a low octane table which is much lower than a reduced 87 octane tune. Other PCMs can learn values between the low and high octane tunes in order to achieve the best spark conditions for the fuel present.

 

thank you capt obvious. :-P doesn't change there are two tables for the capability of tuning both high octane and low octane.

And Sentry, for bolt-ons including intake mani, you can run 87 just fine after tune. Got this info from Vince himself.

 

did he say after a 91oct tune? or just after a tune....theres a difference

 

i'm tuned for 93 and i can go back to 87 with a loss in performance. even sprayed on 87 by accident one time, the car was fine. i use 93 all the time these days though.

 

When Trifecta does the tune, they mess w/ the high octane table. anyone that gets the trifecta tune is getting their high octane table changed as part of the process. So are you talking about a tune minus one of the fundamental portions of a ecm tune?

 

vince told me that I should run 93 Octane for best performance gains...makes sence to me

 

ill talk to vince about it and see what he says...