Reg or Hi test
Road Captain
Joined: Apr 2005
Posts: 535
Likes: 14
From: Highspire Pa
RE: Reg or Hi test
I need the higher octane in the '90 Harley Ultra (higher compression) but our '05 Buell Blast will run lower octane gas - but using higher octane gives me more mpg on the Blast, so I use Hi test in that as well. With Hi test I can get about 60 mpg with the Blast but with regular it is about 55 mpg. Not a very big change but considering the difference in price per gallon, I prefer more miles per gallon.
Ultimate HDF Member
Joined: May 2006
Posts: 6,590
Likes: 444
From: Ohio
RE: Reg or Hi test
ORIGINAL: 96 Wide Glide
Sorry for the late post. Getting my post count up for the BOTM contest
!
Sorry for the late post. Getting my post count up for the BOTM contest
!
SE heads, 9.5 compression, I need the hi-test.
Lots of the yuppie SUVs use it too, so I'm not worried about old gas.
Outstanding HDF Member
Joined: Jun 2007
Posts: 3,306
Likes: 5
From: Bellville, Tx
RE: Reg or Hi test
The physics of it are, the higher the octane, the slower the burn. It's not the comp ratio so much as the long stroke that benefits. I ran Sunoco Blue in both a knuck and pan because of the percieved increase in power and smoothness. Can't get it here but run Shell 93 for the same reasons in my EVO. I don't spare the throttle and do get a kick out of nailing my *** to the seat at times. Pull 39-40 mpg on the unfettered backroads around my house in east Texas @65+++ mph. If you don't often grab a whole handfull, you may not notice the difference.
Cruiser
Joined: Nov 2006
Posts: 193
Likes: 1
From: Arnold, MO
RE: Reg or Hi test
The higher the octane the greater the resistance to pre-ignition due to heat or pressure. If your running a basically stock bike with stock tuning then the 87 should be ok. Since an engine is an air pump, changes from the stock configuration is going to affect octane requirements. Getting the most out of any engine requires creating the maximum cyclinder pressure that the fuel will tolerate. Changes in timing curves and cam timing make huge differences in the pressures present in the cyclinder.
That said my 93 Evo runs best on 93 octane. The 93 allows me to run a more agressive timing curve than the factory ignition. My .02
That said my 93 Evo runs best on 93 octane. The 93 allows me to run a more agressive timing curve than the factory ignition. My .02
Outstanding HDF Member
Joined: May 2006
Posts: 3,273
Likes: 7
From:
RE: Reg or Hi test
I believe the octane rating to use is sometimes dependent upon the air and road temperature. Higher temps offer less cooling to the engine. So depending on conditions; to prevent detonation you may need to run 89 or 93. cooler days 87 will do fine. Also you may need to check your timing and advance.
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Road Captain
Joined: Apr 2005
Posts: 535
Likes: 14
From: Highspire Pa
RE: Reg or Hi test
We had a pleasant surprise yesterday filling up the car at the new, local Citgo station, their pumps were broken and they only had premium but priced it at the same price as regular at the Sunoco station across the street.....