I'd say my average before was 27-28mpg, now my average is 32-33 after the HAI, but I made the HAI the day I got my SGII. I didn't want to run the HAI w/o being able to monitor IAT. So I'd say 2mpg from HAI, and probably 2 mpg from SGII/drivnig habits.
I'm ultimately wondering if the HAI is advancing my oil burn issue though. Makes no sense to me because even if the cyl. was fed w/ hot air, you'd think it would thin the oil it came in contact w/, but then again, strange things can happen inside an engine. W/ the HAI you'll for sure notice power reduction after warm up.
I tried Rislone Ring seal and it made the car run like hell, but after I changed the oil I went about 2k w/ no oil burn... then all the sudden, massive oil burn came back. I'm looking hard for an SL1 or SC1, but if I can't find one in time and get one of my other cars back on the road, I'll do a nice write up on re-ringing the S-Series DOHC for everyone to enjoy.
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John
'09 Saturn Aura 2.4L
'94 Chevy Camaro Z28 (5.7L 6sp)
'96 Chevy C1500 (5.0L 5sp)
'08 Kawasaki Vulcan 900 Custom
'01 KTM Duke 2