Stavros

Summat from a quick convo on MSN last night...

Say if a car was live mapped, but on normal unleaded rather than super, how much power (id guess as a %) do you think youd lose compared to if it was mapped on super?

Was put to me that a turbo car with say 250bhp will probably only lose around 10bhp mapped on normal unleaded compared to on super, and could always run super afterwards anyhow if you wished as it gives you a bit of a safety margin to take into account possible poor fuel etc, as live maps are quite close to the limit (ie mapped to the edge of det then taken back a lil).

That sound about right but im no expert on the fuel/ign side of things, i can see the logic, providing you dont lose much horsepower, or is there a better way?

Rick

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 rations. 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 impiact on power and if ignition timing can be effectively manipulated to ward off detonation without heavily penalizing output. Does fuel additive really increawse 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 stret 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 34degrees and still no sign of detonation. Yet another counter-clock-sisw 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.

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 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 1.5hp. 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.

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.

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.

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 unthinkalbe 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.

114-Octane Unleaded: 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.

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 tertiarybutyl ether (MTBE), alcohol, and other ingrediaents 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.

How does Booster Work?

Knowing that density is at the core of power potential in gasoline, it is hard to imagine that the addition of 16 ounces of chemical additive could have any significant impact on the density of 20 gallons of gas. But that's not how octane boosters work. Rather, they bolster the host gasoline's ability to resist abnormal combustion through the inclusion of manganese. Like tetra-ethyl lead, manganese releases vapors when combusted that surround and protect the end gases in the combustion chamber (those farthest from the spark plug) from being ignited by hot spots or pressure spikes. This suppression of uncontrolled ignition is responsible for any observed power increases. As our testing revealed, power drops off quickly when abnormal combustion begins. By improving the quality of the base gasoline, octane boosters don't actually make power in and of themselves. Rather they allow the full utilization of what is already in place by helping to maintain controlled combustion.

Octane Alley

TEST 1: 87-Octane Power Pulls
Total Ignition Timing Peak Horsepower Peak Torque
31 degrees BTDC 392.2 @ 5,600 404.7 @ 4,500
34 degrees BTDC 394.6 @ 5,700 401.4 @ 4,500
36 degrees BTDC 396.0 @ 5,700 401.3 @ 4,400
38 degrees BTDC 393.5 @ 5,400 402.8 @ 4,300



TEST 2: 87-Octane With Booster Power Pulls
Total Ignition Timing Peak Horsepower Peak Torque
31 degrees BTDC 390.5 @ 5,300 406.8 @ 4,500
34 degrees BTDC 396.3 @ 5,500 404.7 @ 4,600
36 degrees BTDC 397.9 @ 5,700 403.1 @ 4,500
38 degrees BTDC 395.1 @ 5,800 400.6 @ 4,500
38 degrees BTDC* 396.5 @ 5,700 400.1 @ 4,600
* double-dose of 104+ booster



TEST 3: 91-Octane Power Pulls
Total Ignition Timing Peak Horsepower Peak Torque
31 degrees BTDC 399.9 @ 5,700 408.4 @ 4,600
34 degrees BTDC 398.6 @ 5,600 403.2 @ 4,800
36 degrees BTDC 402.1 @ 5,600 409.4 @ 4,400
38 degrees BTDC 393.9 @ 5,500 397.5 @ 4,400



TEST 4: 91-Octane With Booster Power Pulls
Total Ignition Timing Peak Horsepower Peak Torque
31 degrees BTDC 396.3 @ 5,700 401.0 @ 4,600
34 degrees BTDC 398.0 @ 5,800 404.4 @ 4,400
36 degrees BTDC 399.4 @ 5,700 404.2 @ 4,400
38 degrees BTDC 396.7 @ 5,600 401.1 @ 4,700
38 degrees BTDC* 399.8 @ 5,700 403.6 @ 4,500
* double-dose of 104+ booster



TEST 5: 100-Octane Power Pulls
Total Ignition Timing Peak Horsepower Peak Torque
31 degrees BTDC 400.8 @ 5,700 406.9 @ 4,500
34 degrees BTDC 400.7 @ 5,500 407.8 @ 4,600
36 degrees BTDC 403.5 @ 5,600 407.5 @ 4,500
38 degrees BTDC 403.2 @ 5,600 406.9 @ 4,500
40 degrees BTDC 402.1 @ 5,600 404.7 @ 4,500



TEST 6: 114-Octane Power Pulls
Total Ignition Timing Peak Horsepower Peak Torque
29 degrees BTDC 403.2 @ 5,600 409.8 @ 4,500
31 degrees BTDC 408.3 @ 5,600 414.7 @ 4,500
34 degrees BTDC 405.0 @ 5,600 408.7 @ 4,500
36 degrees BTDC 403.3 @ 5,700 404.9 @ 4,500
38 degrees BTDC 402.7 @ 5,600 405.2 @ 4,600


What is Octane?

Octane is the rating of the fuel's ability to resist abnormal combustion due to heat or pressure. Abnormal combustion is defined as any burning that is not initiated by the spark plug. Octane has nothing to do with the fuel's ability to make power other than the fact that, properly selected, it allows the engine-builder the use of high-compression, aggressive cam timing and any other trick that elevates cylinder pressure. The power potential of gasoline is related directly to its density. Density is determined by the grade and quality of the crude petroleum, the refining process, and whatever chemical additives are included before shipment to the retailer.


--------------------------------------------------------------------------------

Diabolical Critique:

The test engine had "only" 10.4:1 compression. The higher the compression, the greater the need for high-octane fuel.

The test engine used aluminum heads with "modern design" fastburn chambers. Fastburn chambers, with a squoosh area to provide turbulence and therefore prevent detonation, allow a greater compression ratio for a given octane level. Alternatively, you could say they allow the use of lower octane for a given compression ratio.

If they had used a 12:1 engine with old style cast iron heads, they would have seen a much greater advantage from the octane booster.

If your engine is performing fine with no pinging, then adding octane booster (without adjusting the timing) will just dilute your fuel and reduce your performance.

In the real world, you set your timing and then go through dozens or hundreds of tanks of different gasolines from different oil companies, without adjusting the timing again. Real world gas sometimes has other impurities in it. Your timing has to be set for "worst case" gas quality. (Of course, new cars actually have knock sensors which adjust the timing when detonation is sensed.)

Don't build a high-compression engine (>10:1) with some old cast iron double-hump heads and expect to get maximum power out of 87-octane gas. On the other hand, by using new aluminum heads with modern fastburn chambers, you might get by with 87 octane gas, with more compression than you would have guessed. Technology comes to the rescue again! A generalization of the results of their test would be to say that using some good heads, you can run 10:1 on the street and run 87 octane and set your timing to around 34 or 36 total and probably be OK without any detonation and only give up 5 to 10 hp compared to using 114 octane racing fuel with idealized timing. For the street, that sounds like the way to go. Why pay 20 to 30 cents per gallon more for gas when you don't have to? If your engine is built with aluminum fastburn heads, decide which octane you're willing to pay for and then adjust your timing to eliminate detonation.

Note that we use "good heads" on our engines.

When we dyno our engines, we use 92 octane and find the timing the engine wants. If you are going to run less octane, you'll possibly need to back off the timing a few degrees.

Rick

had sommat on turbo cars but lost it

Stavros

Well thats pretty much saying theres fuck all real difference and may as well set it up for unleaded, isnt it?

TBH even if i did have a car setup for unleaded, id always run super as a safety margin thing anyhow, cost of the fuel isnt an issue.

LOL@the way some of that post is worded tho

EscortWRC

You'd be amazed at what is in a can of octane booster

Mostly Toluene (around 98%)
A little Xylene (like 2%)
A tiny bit of ATF (for injector lube)

So...if you need octane boost and don't want to pay STUPID prices for it, just get a gallon of Toluene at your local paint store and pour it in the tank

I mixed it @ 40% with 92 Unleaded (98 in UK ratings) and it worked out to about 103 octane (around 110 in UK) and had no problems whatsoever

However....you need to re-tune to take advantage of this. I think I ended up putting a few more degrees of timing in from the midrange all the way up on the Autronic in the rally car.

As always....YMMV

PhilM

Confirms what i was thinking I suppose, not really a great HP loss, so may aswell map for shite 95 ron (worse case scenario), and then when ragging it, youll run 98 and not have to worry on the top speed runs etc. Least then you can still give it full chat on 95 ron too if you are caught out with no higher RON fuel at local garages.

EIL132

Octane Number
Octane is a measure of resistance to knock in a spark ignition engine on a scale where iso-octane is taken as having a value of 100. It is a measure of the speed of spontaneous combustion (not spark-ignited combustion) - higher octane means lower spontaneous combustion speed. Research Octane Number (RON) is used to identify a grade of fuel at the dispenser and is often associated with performance. Higher compression engines give a better performance and/or better fuel consumption than otherwise identical lower compression engines but require a gasoline of higher octane quality. The fuel itself doesn't contain more energy per kg than a lower octane fuel but does require more energy to manufacture.

Markets with several grades of fuel usually differentiate these by octane, eg a 91, 95 and 98 RON fuel. In Europe, the 95 grade has become the standard or premium grade. In markets with only two grades, surveys are carried out to determine the minimum acceptable quality of the higher octane grade. The lower grade is self-selecting.

Octane is also measured using Motor Octane Number (MON). RON measures knock resistance during acceleration and hill climbing and MON at high speeds.

Matt

in karls absence...

Karl

Rick

Steve it does affect turbo motors more - and we need to look at the MON number too.

Spiky

iTrader: (1)

i'm sure i heard if u map a car for a low octane, you cant nesecially just put a high octane fuel in

and PMSL at matt and karl

Rick

you can - wont go any better though.

Matt

optimax makes your drive smoother and pull better according to certain people

mines mapped on 97ron but always runs a splash of nf cos a) it will account for a bad batch of fuel b) its a fuckin expensive engine to melt and c) i get it fuckin cheap off ding

whitneyd

To much octane hurts performance. Don't go putting 150 octane in there expecting to run 9's. It'll make your engine run worse if it even runs.