questions a while back about tuning for 87 octane
Thread Starter
Joined: Mar 2003
Posts: 8,319
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From: North Carolina
questions a while back about tuning for 87 octane well i know some guys were asking about it, i saw in hp tuners Qc (q sub c) which is the heat of combustion. 87 octane has a lower "heat capacity" than 93 octane so that needs to be edited. i dont have my thermo papers with this information anymore unfortunately, but its fairly easy to find out.
i never read anyone that posted this up, dont know how much it effects the tune but its something that needs to be altered if you run lower grade fuel i would think. this may have been stated already, if so sorry, i just never saw it up so i figured i would put it up.
i never read anyone that posted this up, dont know how much it effects the tune but its something that needs to be altered if you run lower grade fuel i would think. this may have been stated already, if so sorry, i just never saw it up so i figured i would put it up.
I've always read that 87 has more energy content
(heat of combustion) than high octane. But heat
capacity is another sort of thing, that's heat input
to vaporize & raise temp. I figure 87 -is- probably
lighter fractions and lower heat capacity. But
would like to see good info on heat of combustion.
Well, both.
George, what made you change VE table when the
fuels are "supposed" to be same stoichiometry?
Just throwing down some extra enrichment for ping
suppression, or did you see an actual mixture
difference coming from 87 vs 93?
(heat of combustion) than high octane. But heat
capacity is another sort of thing, that's heat input
to vaporize & raise temp. I figure 87 -is- probably
lighter fractions and lower heat capacity. But
would like to see good info on heat of combustion.
Well, both.
George, what made you change VE table when the
fuels are "supposed" to be same stoichiometry?
Just throwing down some extra enrichment for ping
suppression, or did you see an actual mixture
difference coming from 87 vs 93?
Last edited by jimmyblue; Oct 3, 2005 at 01:29 PM.
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Joined: Aug 2002
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From: Hartsdale, NY
Since the price of fuel has climed to around $3, the difference in cost between 87 and 93 has become much smaller - like 6%.
Since, I think you will go further on a gallon of 93 than 87, I don't beleive there is a cost advantage to using 87 octane. Can anyone shed some light on this?
$3.20 = 93
$3.00 = 87
$0.20 = difference
6.7% = percentage difference in price
Since, I think you will go further on a gallon of 93 than 87, I don't beleive there is a cost advantage to using 87 octane. Can anyone shed some light on this?
$3.20 = 93
$3.00 = 87
$0.20 = difference
6.7% = percentage difference in price
Originally Posted by jimmyblue
George, what made you change VE table when the
fuels are "supposed" to be same stoichiometry?
Just throwing down some extra enrichment for ping
suppression, or did you see an actual mixture
difference coming from 87 vs 93?
fuels are "supposed" to be same stoichiometry?
Just throwing down some extra enrichment for ping
suppression, or did you see an actual mixture
difference coming from 87 vs 93?
Let me look through my logs ... I believe it was running a tad rich. I run SD, so the MAF is not an issue. I verified it with my wideband, which is fairly new, and I was puzzled at the difference. But since timing also affects fueling, I can kind of understand the change. I will look it up for you guys ...
Mind you, for those wondering why I am using 87 Octane ... simple, we are "EFI Tuners" and it would be wrong of me not to experiement with different octane levels.
More info equals more knowledge equals ... well we all know. Thread Starter
Joined: Mar 2003
Posts: 8,319
Likes: 1
From: North Carolina
around here 93 is about the same price at regular at some places since we are running out or regular every now and then at some stations. i dont plan on doing this just wanted to put some info up that i saw that may need changing to run 87 for those who want to do it. if you fill up once a week you only pay about 2-3 bucks more for 93, thats nothing when you pay about 45-50 bucks to fill up anyway. like you said a very small percentage. but now if you drive a whoel lot, that little bit can add up fast
I would be very, very interested to see dyno (or other
quantitative comparison) of a car well-tweaked for 93
and same car well-tweaked for 87.
My pile of someday mods includes a pair of truck heads
(on the shelves). Which make 87 more of a reasonable
proposition I think.
A year of running 87 would probably pay for the install.
quantitative comparison) of a car well-tweaked for 93
and same car well-tweaked for 87.
My pile of someday mods includes a pair of truck heads
(on the shelves). Which make 87 more of a reasonable
proposition I think.
A year of running 87 would probably pay for the install.
