Car with turbo..requires 91 octane gas..

what if I put regular 87 in it? Will it destroy the engine? Run like garbage? No difference at all? Slight power loss?

If you’ve got a late-model car it may be equipped with a knock sensor and the ability to retard timing and/or dump boost to avoid engine-wrecking knock.

If not, well, there’s a fair chance you’ll encounter engine-wrecking knock.

If your car says something like "for optimum performance, 91 octane gas is recommended," you can run safely with something less.

If your car says something like “91 octane gas is required,” you’re likely to do damage if you put in something less.

After checking, it is recommended.

So what would the performance difference be with 87 v. 91 gas? Would it be noticeable?

on 87, it will knock and ping sometimes (and maybe not be audible to you), but the engine computer will do a fair job of retarding the timing to stop it. You will lose power.

The internal health of your engine and the longevity should be shorter on 87 than 91, because no engine management system can prevent all pre-detonation (knocking).

Higher octane fuels are harder to detonate, so there is less risk it will explode before the piston is at the proper point in the stroke/cycle.

Generally, turbo and supercharger equipped cars are the ones that should run on premium fuel. Many discussions about ‘do my cars need premium gas’ wind up with the conclusion that turbos and superchargers need it, as do very high performance cars (and the manuals will state that is is “required”).

If it is ‘recommended’, I’d use it.

I’d check the message board for your particular car at About a year ago I was car shopping and a couple models I was considering had turbo and recommended higher octane gas. I remember there was some discussion from people who had tried a tank or two of regular to see the difference. There are also probably several message boards for [your model car] owners/enthusiasts. Just do a search of your car name and a key word like “forum.”

If an engine does not knock/ping, it does not need the higher octane. If it does knowck/ping, you better spend the xtra $.

A co-worker ruined the engine in his turbo PT Cruiser by running a lower octane gas in it. The car only had 24,000 miles on it. The dealer was nice and picked up about a $1000 of the $3000 it cost to rebuild the engine, the damage was not covered under the warranty.

As Joe Frickin Friday points out, you may not be able to detect knocking or pinging caused by the low octane fuel, because the sensor will try to minimize it. You’ll still lose power, and perhaps suffer some damage, because of not using premium fuel, though.

My truck has a 5.7 liter Hemi, and it really needs the midgrade gas. We were once in a pinch and needed gas, but no midgrade was available. The engine computer did a fine job of retarding knock and cutting power to the point that it felt like we were driving in oatmeal.

I had the same question, so I ran some tests. The results can be found here: Mileage test results - Cecil's Columns/Staff Reports - Straight Dope Message Board

My conclusion was while you might pay less for a tank of gas if you use 87 octane, and you will pay less per mile driven than if you fill up with 93 and 89 octane at half tank intervals, the loss of performance was not worth the dollar savings over 500 miles.

Unless your friend ran sub-grade gas, or had modified the PT Cruiser (say with a Stage 1 PCM upgrade from MOPAR), this is not true. The PT Cruiser turbo engines are made to de-tune themselves when running on lower octane gas, in fact the sub-GT models with turbo engines, like the Touring and Limited where turbo was an option, did not require premium fuel and would not run any better on it, because the PCM was permanently adjusted to retard timing for regular gasoline.