jkerr

I was running the speed tests so I had a baseline for the RIPP. I will definitely post the results when I have them. I did several full stop idle to full throttle runs (no pre-loading the torque converter) and had the same results every time. It was surprisingly consistent. Good traction, zero grade, straight run, same temp, etc. and I was getting the exact same time run after run. The Tow Tune keeps the Torque Converter locked a bit longer and the sift is firmer, which is probably why it performs a bit better.

JPop

Higher octane fuel also burns slower and the flame front can and does start before TDC. What this means is piston speed is outpacing the flame front and with higher octane fuels you are able to add more timing advance because the fuel is burning slower.

tslewisz

Youŕe correct in that JPop made an error...which he clarified above this post. However, I can´t believe you still don´t acknowledge that more BTDC timing would require more octane. Is it because youŕe from Denver where thereś little air, less cylinder pressure, and octane levels can be had as low as 85?

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.

JPop

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.

JPop

It's pretty obvious the people on this forum aren't the primary target of who this vehicle is being marketed to. Even here there is a substantial portion of the users who don't want to have the need to use higher octane fuels and are concerned more about fuel mileage and efficiency than performance. The crunchy granola eating soccer Mom that wants to be portrayed as the healthy outdoorsy type driving there unlimited as an SUV isn't dropping the extra $3 or $4 a tankful when it means the difference between putting free range chicken on the dinner table as opposed to Mr Perdue's steroid induced genetically altered chicken. That is a very real consideration for the marketing people at Chrysler and the window sticker needs to reflect the ability to run regular octane and have the best efficiency numbers possible posted.

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


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.

scoped

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

AK4Dave

Oh......so now you're saying the added performance I'm getting from my Flaspaq is all in my head because I have an automatic?.......ooooookaaaaay

JPop

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.

JPop

Hey Dave, please come back to your room, I'll give you a cookie and turn on the Price is Right for you.

AK4Dave