Quick octane question for Turbo [Archive] - GrandAmGT.com Forum

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redhotalero
03-12-2008, 04:53 PM
To those out there super/turbocharged, this question is for you guys! Wife and I just got a Turbo S Beetle with a 6-speed stick... Love it! Granted it wasn't my first choice, but we got it for a steal from my Uncle. :D Anyway, with the high output turbo recommended gas is 91+ octane, and I'm all down with that since my foot can be somewhat heavy at times, but would 89octane be okay if I didn't go screaming around town? 91 just hit $3.45 (89 $3.35 and 85 $3.15-20) here, up 28cents since a week and a half ago...

I realize that higher compression needs higher octane, but since were here at 4600ft in the mtns and 85 replaces 87, would 89 be okay if I didn't drive it like I stole it?

Thanks! Love the 3.4L, but I can't have it with a 6-speed stick.. :)

FromTheInside
03-12-2008, 05:36 PM
gosh, my 87 has been 3.49 for weeks. Sorry, I don't have an answer to your question... just passing through.

Malaclypse
03-12-2008, 10:59 PM
Noooo no no.

Run the highest octane you can get (93 or 91). Especially since you're at altitude. You're going to run slightly more lean than if you were at sea level.

Look at it this way. Its an extra $1 per 10 gallons. Might as well save the wear and tear on the engine for the cost of a few bucks a tank.

alerored04
03-12-2008, 11:02 PM
/\ You are backwards, same amount of fuel + less air density = rich. I don't know whether it would be ok to do or not but i would not chance it to save a couple bucks.

RooK
03-13-2008, 01:09 AM
It'll be fine if you accelerate slow and don't get into boost. However, if you forget and jab the throttle, you might wish you didn't. Remember, boosted apps have lower normal compression than a standard N/A engine. It's boost that increases that compression ratio and by slowly accelerating, you'll never get into it. However, remember that passing maneuvers that kick down the transmission result in boost as well. So, be careful on the passing if you're hell bent on doing this.

Moral of the story: You've got a boosted car, pay the extra $3/fillup and treat it right. Only run lower octane in emergencys. Too bad you don't have a supercharger like me... then you could just remove the belt off the blower. I suppose you could rig the wastegate to stay open, but good luck with that.

silvergtjrad
03-13-2008, 05:23 AM
You should be fine as long as you arent hammering on the throttle. How many old people do you see driving around in GTPs on the street? Do you think they all use premium fuel?

Slim
03-13-2008, 06:22 AM
Is it worth it to save 10 cents per gallon and have performance issues and possible detonation problems?

Malaclypse
03-13-2008, 07:00 AM
/\ You are backwards, same amount of fuel + less air density = rich. I don't know whether it would be ok to do or not but i would not chance it to save a couple bucks.

D'oh. Good catch.

AaronGTR
03-13-2008, 07:26 AM
You should be fine as long as you arent hammering on the throttle. How many old people do you see driving around in GTPs on the street? Do you think they all use premium fuel?


They're supposed to be using premium fuel though.



The rule of thumb is, always run the fuel that the car is designed for. Even if you aren't getting on the gas and getting into boost, the ignition timing maps in the low throttle areas are still tuned for the same gasoline you'd be running for boost. Granted, they probably don't have the low throttle ignition maps tuned on the ragged edge... they tend to leave a wide safety margin from the factory... so you might be able to run lower octane and not have detonation, but you are losing some of that safety margin.

If it was me in the turbo beetle I'd be springing for 91.

redhotalero
03-13-2008, 10:07 AM
Thanks for the feedback guys. We love it, beats the pants of our Alero in zip, yet still gets tons better gas mileage around town (got 24.8 on my last tank, even with my lead foot). Haven't tested freeway mpg yet...

Yeah, I've yet to put in anything less than 91octane, and I'm really ok paying for it -- my Uncle was doing some early 'spring cleaning' as he called it to his garage and got rid of his Suburban, Silverado, and the Beetle... Now they "only" have 3 cars for he and his wife to choose from... :D With it being a 2003 and only having 33k miles on it, we couldn't pass it up. Anyway, with the cash we saved I can afford the 91octane until we need a bigger car!

I'd forgotten that boosted cars aren't quite the same as others at altitude -- everyone around here can run 85octane and be fine. I do in our Alero around town, but if we're doing freeway with mtns or anything I put in 88...

RooK
03-13-2008, 11:38 AM
You should be fine as long as you arent hammering on the throttle. How many old people do you see driving around in GTPs on the street? Do you think they all use premium fuel?

Well, we occasionally get the story of someone who did that and forget the whole 'lay off the throttle' advice and they popped a piston.

redhotalero
03-13-2008, 12:38 PM
Yeah, not worth it - I would most likely forget!! :D My wife frequently points out that I have to be the first through the intersection at a red light... What can I say, it is a disease...

Actually I'm testing my city mileage (and my patience) by NOT doing a jackrabbit start everywhere. That isn't to say that I've stopped driving fast, I just take longer getting there... After 3 tanks I'm averaging about 24mpg!

SSRacer
03-13-2008, 01:49 PM
Lower octane = detonation = bad bad bad