My performance gains from superchips and 5.38's
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When we gonna run them JKERR? LOL. Let me know when you get that RIPP kit, i would love to check it out and take a ride in it. i am in woodridge. Be curious to see what your zero to 60 times are now and when you get ripped!
My posted times are 5 run averages. There was a 10th of a second difference or more in alot of my runs. So unless your gains from tow tune to 93 tune are based on averages i wouldnt consider them very acurate.
My posted times are 5 run averages. There was a 10th of a second difference or more in alot of my runs. So unless your gains from tow tune to 93 tune are based on averages i wouldnt consider them very acurate.
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I think you've got the idea of octane wrong. The engine can "handle" any octane. Higher octane gas does not contain more energy, it detonates at a higher temperature. Engines that have more power run higher octane because they have a higher compression ratio. In those engines, the gas is compressed more before the spark is ignited so it heats up more. If you compress it enough it gets hot the air/fuel explodes before TDC and before the spark goes off, forcing the piston down while it is trying to come up.
A tune isn't going to change any variable enough to require more than 87.
A tune isn't going to change any variable enough to require more than 87.
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I think you've got the idea of octane wrong. The engine can "handle" any octane. Higher octane gas does not contain more energy, it detonates at a higher temperature. Engines that have more power run higher octane because they have a higher compression ratio. In those engines, the gas is compressed more before the spark is ignited so it heats up more. If you compress it enough it gets hot the air/fuel explodes before TDC and before the spark goes off, forcing the piston down while it is trying to come up.
A tune isn't going to change any variable enough to require more than 87.
A tune isn't going to change any variable enough to require more than 87.
I mean, seriously, if you were at sea level, put a 93 tune on your Jeep, left your Colorado 85 octane in it (or my 87 for that matter), and floored it in top gear at 1500 RPM uphill it would rattle like a coffee can full of rocks.
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Before knock sensors and computerized engine management systems you couldn't even dream of running 87 octane fuel in a 9.6:1 compression ratio engine (which is the compression ratio of the JKs 3.8L engine). Modern engine management systems keeps the engine on the verge of detonation and pinging as that is where an engine makes the most power and provides the greatest efficiency. To suggest that there isn't room for additional timing advance, slower flame front, longer flame propagation and use of higher octane fuels by way of tuning would be incorrect.
The ECU/PCM and knock sensors will retard timing if pre-detonation is detected. That alone suggests the use of higher octane fuel can be utilized to it's full extent with tuning as timing won't need to be retarded to prevent knock. While timing advance alone doesn't mean more power or efficiency, as fuel formulations also play a role, we certainly have a platform for broader experimentation and use of custom tuning. Also, keep in mind that as a marketing objective Chrysler will want the vehicle to perform with the cheapest fuel available at the pumps despite what gains can be brought from higher octane and accordingly sets the parameters of the PCM.
Anyway, there is far too much to get into here and it takes away from the intent of this thread from the OP. What Superchips has done with higher octane fuel is pretty well documented by lots of happy customers. My findings were significant improvements running 91 octane and nominal efficiency and power gains bumping to 93. Superchips enjoys the luxury of the enthusiast who wants to put the fuel in their tank that makes the engine perform the best while Chrysler is saddled with the low end of the market who just wants to put the cheapest fuel possible in the tank.
The ECU/PCM and knock sensors will retard timing if pre-detonation is detected. That alone suggests the use of higher octane fuel can be utilized to it's full extent with tuning as timing won't need to be retarded to prevent knock. While timing advance alone doesn't mean more power or efficiency, as fuel formulations also play a role, we certainly have a platform for broader experimentation and use of custom tuning. Also, keep in mind that as a marketing objective Chrysler will want the vehicle to perform with the cheapest fuel available at the pumps despite what gains can be brought from higher octane and accordingly sets the parameters of the PCM.
Anyway, there is far too much to get into here and it takes away from the intent of this thread from the OP. What Superchips has done with higher octane fuel is pretty well documented by lots of happy customers. My findings were significant improvements running 91 octane and nominal efficiency and power gains bumping to 93. Superchips enjoys the luxury of the enthusiast who wants to put the fuel in their tank that makes the engine perform the best while Chrysler is saddled with the low end of the market who just wants to put the cheapest fuel possible in the tank.
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Ok, I'm going to make one last point then I'm done with this subject. We'll have to agree to disagree. IF there were more power to be had out of this engine, Chrysler would do what so many other manufactures have already done, recommend 93 octane and say that lower octanes are fine but will reduce performance. Especially considering how many complaints there are about the power of this engine.
I will not believe that cylinder temperatures are increasing enough to require the same fuel as a Honda Civic Si with a higher compression ratio running 8,000 RPM's or a Subaru WRX that is running 5ish pounds of boost AND a higher compression ratio.
I do believe that there is some performance to be had from a tuner but it's extremely limited. Most of those tuners change shift points and make automatic drivers feel better about how their cars run.
I for the life of me cannot find a chart or article that lists the behavior of different octane fuels at different temperatures and density's. I believe that is the only way anyone could take this discussion further.
I will not believe that cylinder temperatures are increasing enough to require the same fuel as a Honda Civic Si with a higher compression ratio running 8,000 RPM's or a Subaru WRX that is running 5ish pounds of boost AND a higher compression ratio.
I do believe that there is some performance to be had from a tuner but it's extremely limited. Most of those tuners change shift points and make automatic drivers feel better about how their cars run.
I for the life of me cannot find a chart or article that lists the behavior of different octane fuels at different temperatures and density's. I believe that is the only way anyone could take this discussion further.
It isn't cylinder temperatures that would promote the use of higher octane fuel, but timing, flame front and flame propagation. Higher Octane fuels available at the pump burn slower and therefore can take more timing advance. This is very common knowledge for anyone who has twisted a distributor in the days before PCMs and ECUs. I routinely change the advance on my '67 Chevelle when I don't have the inclination to mix race fuel or make the 20 mile trip to buy 100 octane fuel and opt for 93 at the pump, and yes there is a significant increase in power. The power stored in the fuel doesn't change, just how the engine is utilizing it over time on the power stroke.
If you can't find an article that discusses timing and octane ratings you aren't looking hard enough.
Here's a quick one from a former usenet article.
h t t p://www.faqs.org/faqs/autos/gasoline-faq/part3/section-1.html
7.4 What is the effect of changing the ignition timing?
The tendency to knock increases as spark advance is increased. For an engine
with recommended 6 degrees BTDC ( Before Top Dead Centre ) timing and 93
octane fuel, retarding the spark 4 degrees lowers the octane requirement to
91, whereas advancing it 8 degrees requires 96 octane fuel [27]. It should
be noted this requirement depends on engine design. If you advance the spark,
the flame front starts earlier, and the end gases start forming earlier in
the cycle, providing more time for the autoigniting species to form before
the piston reaches the optimum position for power delivery, as determined by
the normal flame front propagation. It becomes a race between the flame front
and decomposition of the increasingly-squashed end gases. High octane fuels
produce end gases that take longer to autoignite, so the good flame front
reaches and consumes them properly.
The ignition advance map is partly determined by the fuel the engine is
intended to use. The timing of the spark is advanced sufficiently to ensure
that the fuel-air mixture burns in such a way that maximum pressure of the
burning charge is about 15-20 degree after TDC. Knock will occur before
this point, usually in the late compression - early power stroke period.
The engine management system uses ignition timing as one of the major
variables that is adjusted if knock is detected. If very low octane fuels
are used ( several octane numbers below the vehicle's requirement at optimal
settings ), both performance and fuel economy will decrease.
The actual Octane Number Requirement depends on the engine design, but for
some 1978 vehicles using standard fuels, the following (R+M)/2 Octane
Requirements were measured. "Standard" is the recommended ignition timing
for the engine, probably a few degrees BTDC [38].
Basic Ignition Timing
![](http://farm5.static.flickr.com/4091/5191781035_e15a568649_b.jpg)
The actual ignition timing to achieve the maximum pressure from normal
combustion of gasoline will depend mainly on the speed of the engine and the
flame propagation rates in the engine. Knock increases the rate of the
pressure rise, thus superimposing additional pressure on the normal
combustion pressure rise. The knock actually rapidly resonates around the
chamber, creating a series of abnormal sharp spikes on the pressure diagram.
The normal flame speed is fairly consistent for most gasoline HCs, regardless
of octane rating, but the flame speed is affected by stoichiometry. Note that
the flame speeds in this FAQ are not the actual engine flame speeds. A 12:1
CR gasoline engine at 1500 rpm would have a flame speed of about 16.5 m/s,
and a similar hydrogen engine yields 48.3 m/s, but such engine flame speeds
are also very dependent on stoichiometry.
Last edited by JPop; 11-20-2010 at 06:50 AM. Reason: Better display of data
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Jpop you or I know the best way to show this is on an older vehicle with a distributor cap and just yank up the timing until ping then add higher octane and see no ping and greater power. Unfortunately I don't believe Cbloyer81 has seen or knows what a distributor cap is yet alone ever adjusted one therefore the ease of understanding is out the window and you can now just blame everything on computers as there is no easy mechanical adjustment - it's now tuning the computer using a programer as your wrench, hands, timing light, and pushing a few buttons as apposed to using you wrench, hands (hopefully not getting shocked) , timing light, and turning the cap - people can not perceive it doing a similar thing
Last edited by scoped; 11-20-2010 at 09:35 AM.
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I believe for any of us our experiences become our reality. If I hadn't lived through making my first vehicle, a late 60s muscle car, work with the fairly new at the time lower octane unleaded fuels I might not have a clue. From there and doing a fair amount of racing on vehicles that aren't controlled by a computer I continued to learn a lot. A four stroke engine is still a four stroke engine and the physics of what makes it work hasn't changed, just the technology to deliver it.
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