silverbullet

I don't understand the relationship between higher octane fuel and how it effects the a/f ratio. If you have chips for 15psi on 93 octane, and then run 18psi on 97-100 octane, does the a/f change?

Ex: you run your 15psi chips at 18psi, you normally would go lean and thus detonate. To safely do this you would have to increase the fuel. How can you raise the boost on high octane without increasing the fuel?

I have to be missing something!

Porsche-O-Phile

Absolutely! I encountered (for the first time) knocking issues with my 951 last week. The cause of this is still as yet unknown and I have to spend some time analyzing it this weekend. Might've been crap gas possibly related to the dropping of blend restrictions in wake of Hurricane Katrina, possibly not. Also might be some slop in the boost controller, or a loose pipe or a leak somewhere. Who knows - I need to check. Since that incident it's been reassuringly knock-free, but 've also noticed more rough running, occasional misfires and what seems to be less power than I used to get even a few weeks ago. I just replaced all the plugs, cap & rotor, etc. recently so I'm wondering. . . I'll throw my rocket fuel blend in there soon and see if it clears up but in any case, I agree gas just keeps getting ****tier and ****tier with every passing year. . .

Pretty soon a $10 can of Xylene won't be appreciably more than a gallon of regular gas anyway!

toddk911

"Since that incident it's been reassuringly knock-free, but 've also noticed more rough running, occasional misfires "

I have noticed some of the same in the last few weeks, i.e. intermitten misfires at high revs. Could be a gas issue.

Can bad gas cause misfire though??? I would think it would have to be really bad or gotten water in the tank/lines to misfire.

I also just ordered new cap and rotor. Plugs and wires are new.

If cap and rotor are not the fix I will let you know as it may be a gas issue.

toddk911

"you run your 15psi chips at 18psi, you normally would go lean and thus detonate. To safely do this you would have to increase the fuel."

OR increase your knock threshold by adding additional octane.

Bill

dlr944,

Are the stock lines capable of using aromatics? yes.....for a while. Toulene is a solvent, thus you find it in a paint store. It will eventually eat the rubber and you will have a leak. When I work on particularly messy areas of my car (draining tranny fluid, greasing bearings, etc) I use the latex gloves. When I take an CV shaft to my solvent tank for cleaning, the latex may last 1 minute in the solvent. It litterly blows up and melts. Just an example that you may have seen, and what is going on inside your fuel lines. This also applies to the MTBE's and other additives that gas companies are putting in pump gas.

What fuel lines are more suitable for aromatics? Rigid lines, the factory steel lines are fine. Flex lines, use Teflon. I bought Earls, "speed flex" stainless braided teflon lines. I made up my own lengths and had to modify the stock fuel rail. I cut the stock fittings and TIG welded AN fittings so I could attach the teflon lines. Lindsey Racing makes a fuel rail with braided lines/AN fittings, but I do not know if they are rubber or teflon lines. The teflon Earl lines are more expensive that the rubber Earl lines. You can do a google search on "Earls fuel lines" and get more information. By the way, in Earls description of teflon, they mention its resistance to the nasties in fuel. I believe teflon lines were developed for F1 when they were using toulene and running 50+ psi of boost.

Bill

Silverbullet,

I am not a chemist but I can give you my simple explaination.

Higher octane in application, does not affect the a/f ratio. Your computer montors the air entering the intake, and per a program (chip) adds fuel to achieve the optimum a/f ratio. So the a/f ratio is just a factor of how much air is flowing in the engine and how much fuel is added to that air.

What octane does is raises the knock index. Knock or detonation is when the heat inside the combustion chamber raises to the point that the fuel ignites without the need of a spark plug. This is how a diesel engine operates. A diesel uses high compression (thus high heat) and no spark plugs. In the case of a 951, we achieve high compression (or high heat) via high boost. In the case of a diesel, fuel detonation is part of the normal combustion cycle. Where it becomes a problem is when pre-detonation occurs. This is when the a/f mix ignites before it is designed to ignite. Like when the piston is still on the upstroke before top dead center. Knock is more complex, and there are many factors that can cause the fuel mix to pre-ignite, hot spots in the combustion chamber, timing, ambient air temps, coolant temps, cylinder configurations, carbon build-up, etc. But the above gives you a very basic explanation and hopefully helps your understanding of pre-ignition.

toddk911

Octane Shootout
Can Cheap Gas Make Power With Booster?
By Steve Magnante
Photography: Steve Magnante

Ever since high-octane leaded gasoline vanished from the scene, there’s been an undercurrent of concern among hot rodders every time they fill up at the pump. For the most part, daily driven hot rods have adapted to greatly reduced fuel quality by embracing stroker kits, nitrous oxide, specialized camshaft grinds, aluminum heads, and lower static compression ratios. It must be working; cars just keep getting faster.

To explore the impact of fuel quality on engine performance, we stuck a 10.4:1-compression-ratio 360 Mopar on the DTS dyno at Joe Jill’s Superior Automotive. Then we beat it up, making 40 power pulls to see if octane rating has a significant impact on power and if ignition timing can be effectively manipulated to ward off detonation without heavily penalizing output. Does fuel additive really increase the octane of pump gas? And does boosting the fuel’s octane really make more power on a typical street engine? The results are surprising.

87-Octane Unleaded: 396.0 hp/401.3 lb-ft

You pull up to the pump in your hot street whip; the needle’s on E. You’ve only got 20 bucks, and you have to make it count. Premium is 30 cents a gallon more expensive than the cheap stuff. You roll the dice, grab the nozzle marked “Regular,” and start filling.

Approximating this scenario, we filled our 2-gallon fuel cell with a dose of 87 octane and set the total ignition timing at 31 degrees BTDC. Despite the sleazy gas and heavy dyno loading, the smooth power curves indicated no sign of detonation. Then we tried 34 degrees and still no sign of detonation. Yet another counter-clockwise twist of the Accel Billetproof electronic distributor gave the Mopar 36 degrees total; despite the lousy gas, the motor liked the additional timing.

Could it take more? Pushing the envelope further, we dialed it up to 38. Detonation had found us. The most telling evidence of detonation was seen in the 300-rpm drop where peak horsepower was made and in the way the smooth power curves of the previous tests had become a jagged mess at 4,200 rpm all the way up to our self-imposed 6,000-rpm limit. The peaks and valleys on the dyno chart reveal uncontrolled combustion causing fluctuations in peak cylinder pressure and, as a result, hiccups in the force delivered to the business end of the crankshaft. See Test 1 in the sidebar below.



87-Octane Unleaded With 104+ Octane Booster: 397.9 hp/403.1 lb-ft

The rent is due and the kid needs new sneakers, so you’re running the cheap stuff… again. You add one 16-ounce bottle of octane boost to your 20-gallon tank, cross your fingers and hit the road.

To see if we could turn sow’s-ear 87- octane into silk-purse go-juice, we shut off the dyno’s fuel pump and let the test motor drain the Edelbrock 750’s bowl dry at idle. Then we added 2 ounces of Super 104+ additive to the 2 gallons of 87 in the fuel cell. With timing set at a conservative 31 degrees, we saw no appreciable difference, but we’d only just begun. Twisting the sparker up to 34 degrees BTDC delivered 6 hp, and we were still far from the motor’s likely detonation zone. At 36 degrees we noted that more peak horsepower was made at a higher engine speed, a clear sign that the chemical enhancement was keeping detonation at bay. Further proof of the benefit came when we cranked it well into what should have been rattle city with 38 degrees of timing. Power readings were on their way down due to mechanical factors related to the efficiency limits of the heads, cam, and induction rather than fuel quality. Despite this, the motor still made peak power at 5,800 rpm, a full 400 rpm more than without booster. Convincing proof that the Super 104+ was thwarting detonation.

If some is good, then more must be better, right? Doubling the dose of octane booster to 4 ounces in the 2-gallon fuel cell (like putting two 16-ounce bottles in a 20-gallon tank), and leaving the timing set at 38, we gained 1.5 hp. While power wasn’t improved significantly, the 5,700-rpm horsepower peak and smooth torque and horsepower curves indicated continued protection against abnormal combustion. Octane booster works, but double-dosing an engine like ours wasn’t worth the added expense. See Test 2 in the sidebar below..

91-Octane Unleaded: 402.1 hp/409.4 lb-ft

The bills are paid and you’ve got a few extra coins rolling around in your pockets, so you give your motor what it should have had in the first place—the good stuff: 91 octane.

While some parts of the country can brag about as much as 94 octane, left-coasters must make do with 91. With the timing set conservatively at 31 degrees BTDC, the sturdy 360 surpassed the best 87-octane numbers by 2 hp and 5 lb-ft. At 34 degrees, the numbers dipped, but recovered when we bumped timing to 36 degrees, delivering our highest numbers yet and breaking the 400hp mark.

There was no doubt that the higher octane fuel was good for a few extra ticks on both the torque and horsepower charts, but would it finally allow us to advance timing to 38 degrees BTDC without losing power? No dice: At 38 degrees, the numbers fell by 8.2 hp and 11.9 lb-ft, illuminating the reality that there is a difference between chemical potential and mechanical potential. If testing reveals that an engine is most efficient with timing set at 36 degrees BTDC, it will not necessarily produce more power even if high-octane fuel allows the use of more ignition advance. Still, our testing was far from over. See Test 3 in the sidebar below.



91-Octane Unleaded With 104+ Octane Booster: 399.8 hp/403.6 lb-ft

You’re off to the local bracket races. You know your pump-gas motor will be flogged pretty hard, so for insurance, you pour a bottle of octane booster in the tank and roll into the staging lanes.

Once again, Jill shut off the dyno fuel pump and let the 360 idle itself dry. Then the customary 2 ounces of Super 104+ were added to 2 gallons of 91-octane, and the torture test resumed. Starting again at 31 degrees of timing, the motor dropped a few points. It recovered some ground at 34 degrees, and just like the other tests, made best power at 36 degrees total. Going further, we advanced timing to 38 and lost a little more power; double-dosing the booster with the timing set at 38 brought a slight improvement. The power numbers generated with the boosted 91-octane are lower than those made with non-boosted 91, an indication that the fuel additive may have slowed the burn speed and reduced cylinder pressure. One thing is certain, there was no detonation present or we’d have seen it on the dyno charts and in reduced peak crank speed numbers. See Test 4 in the sidebar below.

100-Octane Unleaded: 403.5 hp/407.5 lb-ft

You’ve heard some of the local street rats whisper about 100-octane unleaded being sold straight from the pump. Its like some flashback to the ‘60s, but is it too good to be true? You just have to try some.

Even though we were pretty sure detonation wouldn’t be a problem with so much octane coursing through our 10.4:1 360’s veins, we began with the 31-degree setting to maintain consistency and to see if any noteworthy patterns emerged.

The dyno video monitor flashed just over 400 hp. Moving up to 34 degrees BTDC delivered virtually identical results, and 36 degrees bought almost 3 hp while torque remained nearly constant. At 38 degrees, the numbers were largely unaffected. The motor seemed indifferent to the increased timing, but in contrast to previous cycles run using the lower fuel grades, the amount of power sacrificed with timing set at 38 was negligible. To see if more timing would translate into more power, we did the unthinkable and moved up to 40 BTDC and let it rip. The results amazed and confounded us. Testing thus far confirmed that this particular motor combination really liked 36 degrees total, regardless of fuel quality. Any more or any less cost power—not much, but the numbers consistently fell. But now with 100-octane, the power seemed to remain stable despite the substantial 4-degree jump in timing. What’s more impressive is the fact that the 100-octane fuel was the only grade tested thus far producing maximum torque and horsepower numbers that never fell below the 400 mark. Our conclusion was that octane was not the sole factor at play, and that the 100-octane had superior burn characteristics to the MTBE-laden pump gas available here in California. See Test 5 in the sidebar below.



114-Octane Leaded: 408.3 hp/414.7 lb-ft

You love to watch professional drag racing on TV and jump with joy when the Pro Stockers run. So why shouldn’t you also jump at the chance to run the very same gasoline in your hot rod? It’s gotta run faster, right?

Taking our motor through its now well-established paces, we rang up our highest numbers yet at the 31-degree setting. We couldn’t wait to get to the 36-degree sweet spot, but exercised restraint and followed the plan, dialing in 34 degrees. What? Power was dropping? A backup run at 34 BTDC confirmed it. “Gotta be some kind of fluke. We’ll get it all back and then some at 36 degrees.” Or so we thought. We saw another drop at 36 degrees, and crumbs of no significance at 38 degrees. Through it all there were no signs of detonation. To rule out the possibility of error, we restored the timing to 31 degrees and watched the output jump back up to 406.6 hp at 5,700 and 413.7 lb-ft at 4,500. Further exploring the apparent benefit of retarded timing, Jill cranked in a mere 29-degree setting and output began sliding downward, losing 5.1 hp and 4.2 lb-ft. Why hadn’t more timing increased power? Probably because the 114 had even better burn characteristics than the 100. Its hydrocarbons vaporized and burned more readily, releasing energy sooner and accounting for why it required less spark lead to reach complete combustion. The octane level was not the operative here—rather it was the superior hydrocarbon content and vaporization characteristics of the racing fuel. See Test 6 in the sidebar below.

Conclusion

Frankly, the results of our test were a bit confounding. We consulted the chemists at Super 104+ and our pal Tim Wusz at 76 to help figure out what had happened. Here’s what we learned:

First, the octane booster did work. However, we saw that octane alone does not deliver horsepower; it only allows more complete utilization of the hard parts in the engine. Wusz said, “An engine does not know what the octane rating of the fuel is, unless it is too low”; note that we made less power by adding booster to 91-octane fuel. The lower the octane of the base fuel, the more benefit you’ll get from octane booster.

Also, the Edelbrock heads on our test motor have high-efficiency combustion chambers that are very tolerant of low octane levels, and their aluminum construction helps, too. Older chamber designs may not be as efficient and may succumb to abnormal combustion more easily.

But most of all, we discovered that our presumption that higher-octane fuels burn slower than lower-octane fuels (and therefore require more ignition lead) is largely incorrect. There are too many other fuel-formulation issues at work to assign a general rule about octane. Race fuel tends to have a more powerful formulation than pump gas, regardless of octane rating, because it is denser and can release more power and heat. (Note that we made the best power with 114 octane with the least ignition lead, indicating it had the fastest burn time.) California pump gas is blended with methyl tertiary-butyl ether (MTBE), alcohol, and other ingredients damaging to performance. Knowing what we know now, we’ll always experiment with ignition timing—both higher and lower settings—when we change fuels rather than presuming that more power can be made with more octane due to more timing.


SIDEBAR ARTICLES
Octane Alley: The Test Results

How Does Booster Work?

What Is Octane?

HIGHBOOST

"higher heating value of toluene also means that the exhaust gases contain more kinetic energy, which in turn means that there is more energy to drive turbocharger vanes."

This is a quote I read in that article posted a while back in the 2nd post on this thread. How does the higher heating value lead to more kinetic energy? kinetic energy is mv^2/2. Is it because the molecules move faster due to the higher heating value or what? I am interested because maybe this can relate to what I am learning right now in Thermodynamics

If anybody can shed some light on this, it would be a great help. Thank you

JAred

special tool

Todd - thanks for that post.
Unfortunately - a 5.8 liter engine making a laughable 400 HP is not pushing the limit of anything. It certainly doesn't need 114

If you were to put a 600+ 2.5 liter engine through the same test, we would see some relevant results.

Bill

Todd/Lutjens,

Also that test appears to be on a normally aspirated engine and they are just using timing in the search for power/detonation. A turbo engine is a whole other animal as Highboost points out.

Highboost,

Great point. The hotter the exhaust, the more excited the gas molecules are. The more excited the molecules are the faster they expand. The faster they expand, the faster they push out the cooler molecules in front of them. The faster they exit the exhaust system, the faster they turn the turbine blades. The quicker the turbine blades spin up, the more the "turbo lag" is reduced. Does this increase boost, no the wastegate controls boost. So, what it does do, is give you boost sooner.

Tomas L

I don't know how your experience found the figure 6.45:1 but it definately not correct for ethanol which is stoich at around 9:1 as Tommy said.
As for how much richer than that you should be I can only say that although I didn't do extensive test I haven't found any noticable power increase beyond lambda 0.85. This is with constant boost.

As for practicality, A mixture of 85% ethanol and 15% gasoline is sold in Swedish gas stations at a cost around 2/3 of gasoline. This makes it economical to use compared to gasoline even when you calculate with the increased consumption.

As I said before I've used this ethanol mixture (which is sold under the name E85) for a couple of months now in my 951 which is a daily driver.
I've setup my DME with one mapset for normal gasoline and one mapset with fuel and timing values for E85. I switch between them with the code plug. I've tested both open loop and closed loop operation without any problems.
The only real problem is cold starting, even with normal air temperature. To get acceptable cold start properties I have worked quite a lot with the DME cold start parameters, I even had to rewrite some of the DME program code to be able to have cold start setups for both gas and E85 in the same chip.

For me this is a superior fuel compared to the xylene/toulene - gas mixtures as it gives me 10-20% increase in power at constant boost level! I still have the stock K26/8 which I max out at the boost levels I can run with pump gas. Therefore I have no room to increase boost to take advantage of a fuel with higher octane rating. E85 both have higher octane rating and gives a power increase with the same boost level.

Apart from a little degradation in cold start properties I have not noticed any downside yet. And in my world filling up a car at the gas station at a reasonable cost beats messing around with hazardous liquids in my garage any day.

I'm glad that you despite your success in the dyno room have stayed such a nice and humble man

Corleone

I can just agree 100%. I have used E85 for about 3 months now and its far superior to gas+Xylene that I used before. Moore power all over the rpm, much lower exhaust tmep, about 20%. A much smother run. As Tomas says only harder to start, you have to do a few (4-5) short starter runs and then it will run. I love it!

Duke

Hmm you should really stop tempting me to join the E85-club

And I don't get this additive/race fuel madness, A 1000 hp glory dyno run wouldn't mean jack to me if I can't fill it up at a regular gas station.
I can just imagine the scene where one is waving dyno run printouts in front of the laughing GT2-owner who just blew your doors off

special tool

I was talkng about meth - I should have quoted ethanol, sorry.

I took for granted that everyone would assume I meant Meth because I said 6.45.

lart951

Meth?