RIWWP

iTrader: (2)

Then you hope your ECU has enough safeguards in place.... or you lose your engine I would like to think that I have enough presence of mind to know what button I'm hitting at the pump, and to double check before pumping in case I made a mistake. It's a very expensive mistake

A 93 octane safe tune that has been tuned for max power at that octane will indeed have severe problems from losing 2 points of octane.

In order to be safe for 91 octane.... I would have to tune for 91 octane. Which is clearly what I would have to do, but certainly not something that I want to do.

blackenedwings

2 octane points is a huge difference, particularly for boosted engines. If you have a tune for 93 octane that wouldn't notice a change to 91 octane that tune is **** not the other way around. Have a highly tuned boosted car? Don't hit the wrong button at the pump. Buy your gas from known good suppliers. If you have enough invested in your motor, do fuel tests regularly on your fuel supplier or buy directly from VP.

j9fd3s

really? i'm supposed to buy 91 octane right from VP for a street car?

color me lazy, but that's ridiculous.

j9fd3s

i think this is part of good tune... i didn't google it, but i can't think of one OEM car that blows up in CA vs the rest of the 93 octane world.

RIWWP

iTrader: (2)

j9, i think you are missing my point

Yes, stock cars, even highly moddified N/A cars can deal with 91 octane just fine.

BOOSTED cars that are professionally tuned for a specific octane will not be able to tolerate lower octane than they were tuned for.

As noted previously, my daily IS boosted, on an aftermarket ECU, and will shortly be tuned for 93 octane. If I then fill up with 91 octane, I could indeed be in serious trouble.

No, this doesn't even affect 1% of cars out there. No, I never claimed it would be pervasive. I simply stated that I care heavily, and don't want the CA craptane on the east coast.

blackenedwings

No, because 91 octane is ****. You would buy something good like oxegenated E85. Also some of our "street" cars are only street tagged for classing purposes for racing.

nycgps

iTrader: (1)

I feel sorry for the guys in California and their 91 bullshit ...

j9fd3s

if your engine blows up on 91, then it might have blown up because it was cold out, or the moon was full, or it was windy or something....

if you're only safety margin is an octane point, you're in trouble...

my friend makes 500rwhp on 89pump, in his FC....

RIWWP

iTrader: (2)

Air pressure, temperature, humidity, etc... can all be measured and adjusted for on the fly by any competent ECU. The only way octane can be adjusted for on the fly is with a FLEX fuel setup. Period. (well, maybe 1 caveat, if you let your knock sensor do all the work and retard timing like crazy 100% of the time, but that isn't "tuned")

Your friend's 500whp FC on 89 octane is tuned for 89 octane or lower. He isn't "running on 89 octane while tuned for 93 octane". Even if he didn't do anything but throw some gas in it before getting it tuned, he is tuned for the octane he runs.

It's simple tuning principle. I admit to not really being sure why this is difficult to understand?

blackenedwings

Because I'm a glutton for punishment... if your friend is tuned on 89 pump its because he A) has nothing better locally available to him B) doesn't have the storage or funds to ship something better and store it and C) had the car tuned for that octane. If he got a watered down batch of 89 pump gas... yes, he would be spitting seals like a 12 year old spitting teeth after taking a right hook from a young Tyson.

Environmental variables CAN effect a tune, particularly a boosted motor and do need to be accounted for. This can include temperature, altitude, seasonal fuel blends... etc. We aren't talking about a stock car you pick up from a dealer. Stock cars are made intentionally with huge margins of safety and ECUs that can account for some environmental factors. Factory turbocharged cars are tuned for 91, run very low timing values, and low boost pressures. They generally run MAF which is pretty adept at handing minor changes.

A built motor with a performance tune, particularly if its been converted to speed density (like my car) requires more handholding. I test my fuel carefully before using it to ensure it has the right amount of ethanol for my tune, I run a mild tune with low boost pressures to ensure reliability for 20-25 min of WOT on the track. When its particularly cold out I have to adjust my boost pressure to make sure I'm not overboosting. Is it extra work? Sure some... but I have more invested in my motor alone than most people on this forum paid for their entire cars. RIWWP isn't saying the average car driven off the lot cares much between 91/93 octane, but enthusiasts DO.

Edit: Btw, I'm going to go ahead and call bullshit on a 500 whp car on 89 octane. I'm running 105+ octane fuel with a 57 lb/min turbo and just over 500 whp. Your average AWD car tuned on 93 vs. the same mods on 91 octane loses ~40 whp. Even with a gargantuan turbo I seriously doubt 500 whp is possible with fuel as bad as 89 octane.

j9fd3s

whoops, sorry its on 91, Pump gas 502 rwhp - RX7Club.com

he did one about 5 years ago on 89, yes the engine has been together that long

blackenedwings

Even on 91 octane that is insanely risky. I'm with the other people in that thread. I think its incredibly foolish to push a car to that limit. There are guys in the Evo community who do crap like that too. Pushing stock pistons/rods to 700 awhp. It might hold together for a while, but it probably won't for long.

In the context of this thread however, if the guy in that thread goes to fill up with 91 octane and gets a tank of 89 octane... that motor is going to pop like a grape. Which is exactly what we are talking about.

rotarygod

I would personally tune for 87 or 89 octane just to be safe and forego the extra few hp that is lost by doing so. It's a street car. If you need every last bit of hp for any particular octane you should probably just use a bigger engine instead to play it safe. Rotaries are already finicky. Stupid tuning is the biggest reason they have the poor reputation that they do.

Razz1

Umm.. I thought gasoline octane at the pump could vary as much as 2 points.

I know, I know, it's supposed to be what the pump says but it can vary.