93 octane gas only?

[Peer]

JackG wrote:
> In an engine optimized to burn 87, you don't make or lose HP by
> using 93. You just pay more money.

Well, actually the best matching octane/timing would be a compression that's just on the limit to ping. However, since pinging is bad for the engine, the manufacturers are usually exaggerating the recommended octane rating just to be on the safe side.

-- peer

[trube78]

For high compression high reving engines, advancing timing just before ping occurs is great for steady state driving on the flats. Anti knock sensors are inserted to ensure there are no instances where knock actually occurs in the transients although the use of High Octane gas ensures a reasonable engineering margin of safety. Continuing to retard timing to prevent knock will adversely affect both power and MPG. For many cars the computer will log instances where the anti knock sensor retards timing. Dealer Repair shop use it for troubleshooting to see if there is an engine management problem. In BMWs if there is consistent indications of knock onset without an accompanying engine problem they will assume low octane fuel is used (BMW also logs over-rev situations on their cars and has used the data in warranty claims in the past.) I do not know what the new Porsche computer logs but it does log more than they did in the past. Under current EPA rules and automotive engineering standards. Exagerating Octane requirements in order to squeeze additional performance is prohibited. The Mazda RX-8 performance was downgraded due to engineering sleigh of hand by mazda. When independent testing was conducted, the output was downgraded and Mazda had to compensate their new RX-8 owners. My personnel experience with high octane/high performance engines. Expect a decrease of about 10% in gas mileage and similar HP decrease from using regular vice the recommended premium gas. So you will loose in the end plus possibly put your engine's long-term life at risk during hard acceleration. while my 'test" were not scientific other folks experience concurs.

ATB,
Tom

[Peer]

trube78 wrote:
> Expect a decrease of about 10% in gas mileage and similar HP decrease from
> using regular vice the recommended premium gas.

A ping-free engine will not gain any power by increasing the octane rate.

-- peer