Instead of premium can I use regular unleaded gas without any negative impact.

 

I can't address the negative impact, but you surely will notice a performance difference.

 

From my understanding you must use the premium gas. The compression pressures these cars use can cause the lower octane gasolene to pre-detonate(IE the pressure, the heat of the engine, and other energy formed will cause the vapor to detoate before the spark is fired.)

In extreme cases this can cause a knock in the engine because there is downward force on the piston while it is still traveling up. Most fuel injected cars like these have sensors that detect this and adjust the timing for the engine etc so that it will run with the lower octane gas.

So the result is lower performance, excess buildup and eventually excess wear on the engine. Now I don't know what octane they designed these engines for 88 or 92 etc. The Jag dealer once said you can get away with a odd fill up of 86 now and then or alternate fillups but by then...how much money are you really saving?

I don't know the effect of homemade octane boosters in jaguar engines but if that would work that is where I might go. http://www.ehow.com/how_6615290_home...e-booster.html Apparently this is what is used in standard over the counter booster but you must use quite a bit to raise the octane from 88 to 92 etc. I hear Xylene works as well...

 

In the UK a JAG would use Super, 97+ octane. Back in the sixties I used 101+ in my 'E Type', of course no knock detectors then. Very risky to use anything other than the manufacturers recommended grade......Roger.

 

Been running regular unleaded in my '91 Sovereign for 165000 miles now, with an occasional premium fill up along with a can of fuel system/injector cleaner at the change of every season...have had zero runability problems or failures to start. I live in central Indiana (grew up near Buffalo, NY) where we have all four seasons (sometimes all in one day!) and have had no trouble with regular. Keep in mind that I do not drag race with the car (I have a '68 'Cuda for that) as that is not what it was designed for, but I don't baby the old girl either. 75-80 MPH highway cruising (or faster if you can afford the gas) is a regular pastime in this car. If you make a habit of heavy acceleration, then follow the mfr. recommendation for octane, but if you're a happy cruiser like me then regular works just fine.

 

Because it's automatically retarding the ignition........Roger.