Here's the deal, I have a 355 in my 86 bird, about 9.4:1 compression. My car ALWAYS runs 14.1-14.16 at the track, this week I tried experimenting with bad results and I want some theories. Changed for a 45 to a 43 AC Delco plug, gap also changed from .55-.45, swithced from Valvoline 10-40 oil to Valvoline 10-30 synthetic, AND switched to 87 octane from 91 octane. I made 3 passes and the car was all over 14.26, 14.33, 14.20, checked the plugs after 3 TT and 1st round elimins and they were whiter than when I pulled them new out of the box. Got a 750 VS Holley, so we pulled the 75's out and stuck in 79's (the 75 jets with the hotter 45 plug burns ideal) then we had a nice 2.5 hour intermission as not 1 guy but 2 guys back to back oiled the track the FULL length with the synthetic stuff. Now car is cooler, so of course the dart board dial in as now it's also dark car runs a 14.5? slowest ever WTF. So, do you guys blame the cooler spark plugs, lower octane fuel, switch to synthetic oil. Was'nt the air as everyone was their usual numbers. We all racked our brains, but could'nt come up with much, regardless everything I changed is going back to my original set-up, except of course the oil, 8 qts @ 4.88ea, yeah I'll run it for a while!

 

I would say the lower octane fuel, and the plug gap played a big role in your time loss. I would try the setup on high octane fuel. YOu can' t really change a bunch of things and wonder which one played the biggest part in it. I would have changed one thing at a time, like change somethin every pass down the track.

 

Damn, I pay a little less than that for Mobil 1.
I doubt 9.4:1 compression requires more than 87 octane, but I could be wrong.

 

I know I don't need any higher octane than 87 with my low compression, but I like to use just because, actually theory would say with a lower octane I should have picked up speed cause it has more btu's than higher octanes. I looked at the Mobil 1, but I've run Valvoline in all my vehicles since I was old enough to drive and never had problems. We were thinking it's the colder plug that had the greatest effect, they say in a 9:1 motor use the 45's 10:1 44's and 11:1 43's. I preach the same thing to people, make 1 change at a time, at least with the few things I did they're easily undone, I was just surprised how inconsistent the car became, race night I could give a **** about speed (running 14's that's obvious) but when this thing was jumping up and down like that it's hard to get in the money.

 

Mark, I went to the parts store and got my new plugs and fuel filter, I had the purolator glass filter and everyone said it would starve the motor on the big end, so I replaced with a FAT Fram one that everybodies running. Anyway I priced the Mobil 1 after I read your post and here it is 3.99 a quart. Synthetic just is'nt cheap any way you look at it. So I changed the plugs back to the 45's, gapped them at .50, changed the jets back to the 75's that were in it, sucked all the gas back out of the tank and filled er back up with 91 octane. Now as much as I hate going on Friday TT (track guys could give a **** about track prep when all the kids are out there playing around) I want to make sure I'm running the numbers again for Sat racing.

 

could be your "performance package".........or lack of one....

 

you should only change one thing at a time a nd you wouldn't be guessing now. one of your changes might of been a big gain and got cancled out by another change. if you switch everything back you'll never know. you also need to factor in weather conditions, you only lost a tenth or so and weather cound of been it.