How to tune for 87 octane?
10-28-2004, 01:41 PM
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How to tune for 87 octane? Say I wanted to run 87 octane rather than 91 in a cam only car (stock manifolds/cats), do I just take a bunch of timing out? What is the most RWHP someone has made NA with 87 octane? I can save around 10% on my fuel costs this way... 
10-28-2004, 02:05 PM
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You would definitely want to pull out spark and might
have to bring down the coolant temp ('stat, fans, even
a better radiator?) to keep from plain dieseling. I have
been thinking about going to 6.0 truck heads which
would bring down CR and make 87 octane a bit easier
to digest (though, not for that specific purpose; just
looking for airflow on the cheap and having enough ping
sensitivity in summer, on stock CR, not to want to go
up any). If you got a clean set of ready-to-swap used
heads for like $300, I figure it would only take, say,
30,000 miles of driving until break-even (discounting
labor, hardware and consumables).
I'm not sure I'd want to drive 30,000 miles of punked-
out performance though; question is, could you run 87
octane on a performance-neutral basis? Energy content
of fuel says "yes", but GM seems to have thought "no".
I haven't seen anybody go all the way on this, keep us
posted!
have to bring down the coolant temp ('stat, fans, even
a better radiator?) to keep from plain dieseling. I have
been thinking about going to 6.0 truck heads which
would bring down CR and make 87 octane a bit easier
to digest (though, not for that specific purpose; just
looking for airflow on the cheap and having enough ping
sensitivity in summer, on stock CR, not to want to go
up any). If you got a clean set of ready-to-swap used
heads for like $300, I figure it would only take, say,
30,000 miles of driving until break-even (discounting
labor, hardware and consumables).
I'm not sure I'd want to drive 30,000 miles of punked-
out performance though; question is, could you run 87
octane on a performance-neutral basis? Energy content
of fuel says "yes", but GM seems to have thought "no".
I haven't seen anybody go all the way on this, keep us
posted!
10-29-2004, 11:15 PM
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the stock low octane maps should handle 87 octane (or less). Otherwise a bad tank of gas and gm would be replacing a motor.
Perhaps you could copy the low octane stock map to the high octane map, add a few degrees across the board on a warm day. Then go log the KR histogram on hptuners and tweak the timing more.
keep in mind that your air fuel ratio will change a good bit if you retard the timing.
honestly there's other ways to make the car run leaner or more efficient. 91 octane+ good tune could yield that 10% right back, in which case you'd get the power and the safety and the same effective cost of fuel.
10% of 16mpg (city?) is 17.6mpg 10% of 22mpg is 24.2 mpg, not a whole lot imo.
20% yeah i'd probably go for it, but i hope your knock sensors are healthy, it would suck to buy a new motor. save a buck spend a few thousand?
i'm actually going to do this with my vw this weekend to try the idea. It's 8:1 factory supercharged so i can keep good timing off boost and **** it on boost to keep it safe, i think it would be more effective with less dynamic compression, i'm not ready to frag an ls1, but i've done 87 on my vw before with custom timing maps. Honestly i got tired of the lack of power, skip a big mac extra value meal one day and you'll have your money back
Perhaps you could copy the low octane stock map to the high octane map, add a few degrees across the board on a warm day. Then go log the KR histogram on hptuners and tweak the timing more.
keep in mind that your air fuel ratio will change a good bit if you retard the timing.
honestly there's other ways to make the car run leaner or more efficient. 91 octane+ good tune could yield that 10% right back, in which case you'd get the power and the safety and the same effective cost of fuel.
10% of 16mpg (city?) is 17.6mpg 10% of 22mpg is 24.2 mpg, not a whole lot imo.
20% yeah i'd probably go for it, but i hope your knock sensors are healthy, it would suck to buy a new motor. save a buck spend a few thousand?
i'm actually going to do this with my vw this weekend to try the idea. It's 8:1 factory supercharged so i can keep good timing off boost and **** it on boost to keep it safe, i think it would be more effective with less dynamic compression, i'm not ready to frag an ls1, but i've done 87 on my vw before with custom timing maps. Honestly i got tired of the lack of power, skip a big mac extra value meal one day and you'll have your money back
