Hi guys! Proud 2001 Prelude owner over here. Forgive my newbie question, but does using high octane gas really make a difference? Because I've been spending a hell of a lot of money on 94 octane. Thanks!
Preludes run a pretty high compression so you need a higher octane gas to prevent engine knock from detonation and overall better performance...go ahead and try a tank of 87 octane and see if you can't tell the difference performance-wise or if your idle is rough. There's a reason they say to use premium unleaded fuel only.
Yes, you will see a significant decrease in power if you run gas with octane lower than 91. You don't need to use 94 though--the owners manual says 91+ is just fine *I think*. I use 93 just because 91 is hard to find.
------------------ Prelude forum moderator Prelude FAQ
'97 Prelude Type-SH
As already posted, compression is the biggest factor in octane selection. 91+ is recommended in the manual, though a 92 or 93 + 89 blend (if I mix tanks) seems to do OK (no loss in power). I wouldn't recommend subsequent tanks of less than 91 or any 87; it won't harm the engine but it will cause the ECU to not advance spark (and subsequently lose power).
Stay away from octane booster (at least regularly) as the additives leave deposits that eventually damage O2 sensors and the catlytic converter. Same for most fuel system cleaners.
Using higher octane gas to get more power is the biggest misconception with gasoline. There is not one more BTU of energy in 93 octane gasoline than there is in 87 octane. The octane rating is how many additives have been added to make the gas burn slower. As stated before, high compression engines need a slower burning gas to prevent engine knock.
Detonation ocures when you have a hot spot left in the cylinder after the power stroke and when the next batch of air/fuel comes in, it ignites right away before it is compressed, but at the same time another cylinder is firing like normal, and so you now have two going and that means that a rod is going through the top of a piston. You shouldnt have to worry about this as todays gas doesnt leave too many hot carbon deposits in the cylinder.
Engine knock occurs with the compression ratio where some of the fuel burns, then when the piston is moving down more fuel ignites and you get the knock. This is bad as it will cause your piston heads to be sandblasted. With a highly volital gas which has a lower octane rating, this occurs easier in the higher compression cylinders because high compression cylinders are larger in volume. The solution, get a slower burning gasoline that is not subject to that second explosion which is what you get with a higher octane gasoline. However, with todays cars, the engines come with knock sensors that will retard your timing to prevent this knocking if it detects it from using a lower octane gas and this is where you will lose power, not because the 87 is lower in quality or has less power because is is the same in quality and has the same amount of energy in it. So because of this, you dont need to buy octane booster or a rediculously high octane gas. You only need enough octanes to keep your engine running at its optimal settings, which on a stock lude is 91 octane, thats all you need to run your car at its max as you wont get anymore power from anything higher. If you have mods and stuff, then you might want to get higher octane just to keep your engine from exploding as your knock sensor might not be able to compensate for it anymore with SERIOUS mods like turbos and such.
Sorry about the long post. The two most important things to take from it are:
1) There is not 1 more BTU of energy in 93 octane than there is in 87 octane, even if you add octane booster.
2) You can run lower octane, but your timing will probably be turned down and this is where you will lose some power.
Hope this helps ya out.
------------------
If you only knew the power of the Lude...
'98 Red Base Prelude
"Straights are for fast cars. Turns are for fast drivers." - SCCA Solo2
AEM CAI, APEX-i VAFC, Neuspeed Ft Up Strut Bar, 28 mm Neuspeed RR Sway Bar, Neuspeed Sport Springs, Koni Yellows, and SH RR Deck installed. Shock knock cure done. Installing Quaife ATB Differential.
The new built motor makes higher compression so the sensor backs off on the timing decreasing performance when I run lower grade gas, have to run 93 in it.
It ran better even, temporarily, with some octane boosters, but then the plugs foul very fast, so I stay away from using boosters now.
My dealer told me 91, its in my Owners manual, and its in the Service Manual that I got from Helm Inc.
------------------
If you only knew the power of the Lude...
'98 Red Base Prelude
"Straights are for fast cars. Turns are for fast drivers." - SCCA Solo2
AEM CAI, APEX-i VAFC, Neuspeed Ft Up Strut Bar, 28 mm Neuspeed RR Sway Bar, Neuspeed Sport Springs, Koni Yellows, and SH RR Deck installed. Shock knock cure done. Installing Quaife ATB Differential.
Premium Unleaded is usually at least 91 octane...go and check at any gas station. Anyways, the cleaner the fuel is, meaning it's less contaminated with particles that can cause early detonation, the higher the octane number. When low octane fuel like 87 is put in a 10:1 compression, it's more likely to detonate before it's supposed to due to contaminants. So just stop being a cheap ass and get the 91+ octane fuel, unless you don't give a rat's ass about performance.
You can get bad gas even when you use high octane. this is a result of the tanks at the station you use, sometimes they contain to much moisture or even worse, debris.
As for performance 87-89 actually gives you more power but increases the risk of detonation or knock from the volitility of the gas. So basically your car runs worse because its backing off on the timing.
Higher octane gas is harder to burn than the lower octane, but because the possibility of detonation is lower you car runs better because its not backing off on the timing to avoid it.
[This message has been edited by VeeTec (edited March 28, 2001).]
<font face="Verdana, Arial" size="2">Originally posted by VeeTec: You can get bad gas even when you use high octane. this is a result of the tanks at the station you use, sometimes they contain to much moisture or even worse, debris.
As for performance 87-89 actually gives you more power but increases the risk of detonation or knock from the volitility of the gas. So basically your car runs worse because its backing off on the timing.
Higher octane gas is harder to burn the lower octane, but because the possibility of detonation is lower you car runs better because its not backing off on the timing to avoid it.
Smoothy, read my post and veetec's and you will get a better understanding.
Not knockin on you or anything.
------------------
If you only knew the power of the Lude...
'98 Red Base Prelude
"Straights are for fast cars. Turns are for fast drivers." - SCCA Solo2
AEM CAI, APEX-i VAFC, Neuspeed Ft Up Strut Bar, 28 mm Neuspeed RR Sway Bar, Neuspeed Sport Springs, Koni Yellows, and SH RR Deck installed. Shock knock cure done. Installing Quaife ATB Differential.
My prelude specifically says "high octain only" so I have been puttin in the 93 octain stuff all the time? Would it make a difference if I were to put in mid grade? thanks
<font face="Verdana, Arial" size="2">Originally posted by smoothludey: Premium Unleaded is usually at least 91 octane...go and check at any gas station. Anyways, the cleaner the fuel is, meaning it's less contaminated with particles that can cause early detonation, the higher the octane number. When low octane fuel like 87 is put in a 10:1 compression, it's more likely to detonate before it's supposed to due to contaminants. So just stop being a cheap ass and get the 91+ octane fuel, unless you don't give a rat's ass about performance.</font>
Disregard this post, i just realized it's total bunk...hehe
Basically if you are running higher compression you want more octane. Say 91 octane fuel contains 91% octane and 9% heptane. Heptane is the volatile fuel that cannot take high compression before igniting...it's what causes knock. I apologize for the misinfo.
[This message has been edited by smoothludey (edited March 28, 2001).]
<font face="Verdana, Arial" size="2">Originally posted by smoothludey:
Originally posted by smoothludey: Premium Unleaded is usually at least 91 octane...go and check at any gas station. Anyways, the cleaner the fuel is, meaning it's less contaminated with particles that can cause early detonation, the higher the octane number. When low octane fuel like 87 is put in a 10:1 compression, it's more likely to detonate before it's supposed to due to contaminants. So just stop being a cheap ass and get the 91+ octane fuel, unless you don't give a rat's ass about performance.</font>
Disregard this post, i just realized it's total bunk...hehe
Basically if you are running higher compression you want more octane. Say 91 octane fuel contains 91% octane and 9% heptane. Heptane is the volatile fuel that cannot take high compression before igniting...it's what causes knock. I apologize for the misinfo.
[This message has been edited by smoothludey (edited March 28, 2001).]
------------------
If you only knew the power of the Lude...
'98 Red Base Prelude
"Straights are for fast cars. Turns are for fast drivers." - SCCA Solo2
AEM CAI, APEX-i VAFC, Neuspeed Ft Up Strut Bar, 28 mm Neuspeed RR Sway Bar, Neuspeed Sport Springs, Koni Yellows, and SH RR Deck installed. Shock knock cure done. Installing Quaife ATB Differential.
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