Gas In Grand Prix Gtp's

[mr314]

will anything happen to my car if I put in regular gas? Cause gas is high....LOL

[GTP Dad]

There has been a lot of discussion on this topic. For short periods or in an emergency you can run 87 but stay out of the supercharger. The 87 will cause a lot of knock which if excessive can damage your engine. Mid grade 89 is a little better but 91 or greater is still the best type to run in these engines.

[n2racingcars]

Long term use will clog your cat.

[mr314]

I don't get it

[tblake]

Bottom Line, Dont run anything less that 91 octane or possible internal engine damage could result. If you HAVE to run anything lower, its ok to do so ONLY in emergency situations. If you have 87, then you need to keep off the throttle and keep the supercharger from boosting.

[BNaylor]

Visit our Grand Prix Tips & Maintenance forum which has an FAQ on the issue of premium fuel in a L67 GTP. See link below.

Click here

[gob 455]

I have a 98 GTP that I run off 87 octane. But I live at 4500ft elevation. I also have acces to 85 octane but it pings with barley any boost, so I stick to 87. As a side note (because I'm not as hard on the throttle) my MPG went from 22.3 to 25.6. Every little thing helps.

[BNaylor]

Originally Posted by gob 455

I have a 98 GTP that I run off 87 octane. But I live at 4500ft elevation. I also have acces to 85 octane but it pings with barley any boost, so I stick to 87. As a side note (because I'm not as hard on the throttle) my MPG went from 22.3 to 25.6. Every little thing helps.

If your GTP is pinging or getting detonation at 85 octane then what makes you so sure it is not getting detonation running 87 octane gas? Are you a certified or calibrated human knock detector? Run a KR test with a full function scan tool capable of detecting KR and see what you get. You can run 87 octane regular unleaded all you want since it is your car but we recommend using only 91 octane or better premium unleaded as good sound advice in this auto forum. So what if you have to spend 20 cents more per gallon. I'd rather be safe than sorry.

BTW - I'm at 4,000 feet and have to use premium unleaded at least 91 octane since the KR levels are unacceptable based on my testing. In my GTP my mileage drops a few miles per gallon with regular unleaded and so does my Regal GS notable in both city or highway driving or combined. The bottom line is most L67 owners get better gas mileage with 91 octane or better even with a heavy foot.

[Highbeamz]

At 2500 feet with 91 octane I still get about 2* of KR at WOT...I'd hate to see it at 87 octane...

[doctorhrdware]

Originally Posted by n2racingcars

Long term use will clog your cat.

I have just 1 question, how is it possible by useing a lower octane gas to clog the cat.

[BNaylor]

Originally Posted by doctorhrdware

I have just 1 question, how is it possible by useing a lower octane gas to clog the cat.

I recall most likely because he experienced the issue. Anecdotal at best or draw your own conclusion. See link below.

Click here

[doctorhrdware]

I understand now, due to the raw fuel going into the cat, and being ignited in the cat causing, the cat to over heat and melting the substrate.

[gob 455]

I've been a mechanic for 15 years. I know what ping sounds like. I also know that you can have ping that you can't hear. This was not a scientific test, just things I've tried to try and save money. So take it for what it is, anecdotal evidence.

[BNaylor]

Originally Posted by gob 455

I've been a mechanic for 15 years. I know what ping sounds like. I also know that you can have ping that you can't hear. This was not a scientific test, just things I've tried to try and save money. So take it for what it is, anecdotal evidence.

Well, if it were a scientific test and due to your background as an auto mechanic technically you should have run a test with a scan tool capable of reading out knock retard (KR) and provided the results.

However, the problem with so called anecdotal evidence is if there is any doubt to its veracity or methodology then the evidence if you want to call it that is untrustworthy and wide open to dispute.

What you do with your car and what octane gas or type you run is your business but if your advice is it is OK to run 87 octane regular unleaded in a L67 engine without any second thoughts about it or deviating from the norms of acceptable advice to include contra-indicating the manufacturer's guidelines then I for one would take issue with it and as you can see other members see it in that respect.

[wafrederick]

Premuim gasoline is only recomended for the supercharged 3800s.The supercharged 38000s are only made to run on premium gasoline only.