I have a basically stock 305 HO engine with an auto and 3.73s. the exaust is a little overkill,headers,borla (run with 2.5" open plate,because steam from just the left pipe in the morning just doesn't look right)anyways..it seems to have much better throttle response with 93 and uses less gas,is this just my imagination or does it really compensate for the lack of low-end back pressure?

 

open exhaust will often lean an engine (especially a carb'd engine), and higher octane burns slower which acts like a richer A/F ratio. Many cars need to lean down when raising octane (same specific gravity), and of course richen back up with lower octane. So maybe it's your imagination and maybe not. Borrow someones vericom or g-tech and find out what the car likes for sure. Run some tests, then go pump a several gallons of 87 octane in and run some more tests. Most streetcars will run faster with less octane... unless they were already at the lean limit (rare).
good luck

 

I've noticed my truck getting better milage with 91 octane compared to 87 but I never calculated if the extra cost of the fuel compensates for the better milage.

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Follow my racing progress on Stephen's racing page
and check out the race car

87 IROC-Z Pro ET Bracket Race Car
383 stroker (carbed) with double hump cast iron heads and pump gas
461 Big Block installed and ready for the 2001 racing season

Best results before the 383 blew up
Best ET on a time slip: 11.857 altitude corrected to 11.163
Best MPH on a time slip: 117.87 altitude corrected to 126.10
Altitude corrected rear wheel HP based on power to weight ratio: 476.5
Best 60 foot: 1.662

Racing at 3500 feet elevation but most race days it's over 5000 feet density altitude!
Member of the Calgary Drag Racing Association

87 IROC bracket car, 91 454SS daily driver, 95 Homebuilt Harley