FUEL

[dj10]

I wanted to get some opinions and I'm sure there are many, between using pump Sunoco Fuel 94 and 100 Octane racing fuel. Does anyone have any supporting data between the two, one making sufficently more power than the other? This would be in ITS class. Does the higher Octane have any effect on rotarys?
dj

[Andy Bettencourt]

Does the higher Octane have any effect on rotarys?
dj [/b]

The ITS rotaries run 87 octane regular unleaded.

AB

[charrbq]

I've heard, and adhere to those who relayed the advice, that 93 octane is perfect for eveything except long, long straights at extended periods of extremely high rpms. Then it would be advisable to use 100+.

[C. Ludwig]

An octane rating theoretically has nothing to do with an engines power production. Octane is simply a measurement of the engines ability to resist detonation. Every engine has an octane requirement. Using more octane could, again theoretically, hurt power. Geeks speak on gasoline.
http://www.faqs.org/faqs/autos/gasoline-fa...3/preamble.html

The point in the rev range where the engine is most susceptible to detonation is at peak torque (peak cylinder pressure). So the adage of using higher octane for protection in an extended high rpm situation isn't all together valid.

There is a difference between detonation and pre-ignition. And for the record there is no such thing as pre-detonation if you've ever heard the term thrown around. Check out this link for a clear description of each.
http://www.germanmotorcars.com/Detonation.htm

The engine run at extended high rpm is more likely to experience pre-ignition than detonation. Since the engine is obviously being loaded for an extended period and not being given the chance to cool there can be heat buildup. Spark plugs of the wrong heat range and casting flash on a piston or cylinder head can become heat risers that ignite the air fuel mixture before the ignition event. Octane won't help you in this situtation. Octane won't make the engine run cooler and it won't make more power. It will resist detonation and that's all.

Yes, most of the guys that run rotarys are using the cheapest swill they can find. It's a perk. With 9.7:1 compression there's no need for more octane. The rotary's inherit design makes compression ratios of over 10:1 yield no more power so there's never been that push for high compression ratios.

Having said all of that, I've heard anecdotal accounts of some "race" fuels producing more power simply because it's a hotter blend. Dyno time would be required to verify this and IMO a couple horsepower doesn't justify the expense and PITA to purchase fuel. Race fuels are usually devoid of detergents as well making them better to use when reading spark plugs if you're in to that sort of thing.

So Dan, if you're not getting knock on 94 stick with it. That's my .02 anyway.

[dj10]

An octane rating theoretically has nothing to do with an engines power production. Octane is simply a measurement of the engines ability to resist detonation. Every engine has an octane requirement. Using more octane could, again theoretically, hurt power. Geeks speak on gasoline.
http://www.faqs.org/faqs/autos/gasoline-fa...3/preamble.html

The point in the rev range where the engine is most susceptible to detonation is at peak torque (peak cylinder pressure). So the adage of using higher octane for protection in an extended high rpm situation isn't all together valid.

There is a difference between detonation and pre-ignition. And for the record there is no such thing as pre-detonation if you've ever heard the term thrown around. Check out this link for a clear description of each.
http://www.germanmotorcars.com/Detonation.htm

The engine run at extended high rpm is more likely to experience pre-ignition than detonation. Since the engine is obviously being loaded for an extended period and not being given the chance to cool there can be heat buildup. Spark plugs of the wrong heat range and casting flash on a piston or cylinder head can become heat risers that ignite the air fuel mixture before the ignition event. Octane won't help you in this situtation. Octane won't make the engine run cooler and it won't make more power. It will resist detonation and that's all.

Yes, most of the guys that run rotarys are using the cheapest swill they can find. It's a perk. With 9.7:1 compression there's no need for more octane. The rotary's inherit design makes compression ratios of over 10:1 yield no more power so there's never been that push for high compression ratios.

Having said all of that, I've heard anecdotal accounts of some "race" fuels producing more power simply because it's a hotter blend. Dyno time would be required to verify this and IMO a couple horsepower doesn't justify the expense and PITA to purchase fuel. Race fuels are usually devoid of detergents as well making them better to use when reading spark plugs if you're in to that sort of thing.

So Dan, if you're not getting knock on 94 stick with it. That's my .02 anyway. [/b]

Chris, I knew I liked you for some damn reason . Just to kill my curiosity, I have some dyno time coming up...won't hurt to test some 100 Turbo Blue.
Thanks, very informative and easy to understand, good writer.
Dan

[C. Ludwig]

Anyone wanna guess why I haven't had a date in months?

[Geo]

An octane rating theoretically has nothing to do with an engines power production. Octane is simply a measurement of the engines ability to resist detonation. [/b]

Correct.

Every engine has an octane requirement. Using more octane could, again theoretically, hurt power. Geeks speak on gasoline.
http://www.faqs.org/faqs/autos/gasoline-fa...3/preamble.html
[/b]

A very good read.

The point in the rev range where the engine is most susceptible to detonation is at peak torque (peak cylinder pressure). So the adage of using higher octane for protection in an extended high rpm situation isn't all together valid.[/b]

IIRC Motor Octane Number (MON) was developed as a direct result of Research Octane Number (RON) not being useful in situations that contained sustained high speed running, i.e., the Autobahn. It's covered in the Gasoline FAQ.

[JimLill]

I would think that if the higher octane was to provide for more power via a "hotter blend", it would provide have a different "Heat of something or other" due to the blend of aromatic hydrocarbons used. If true, then I would also think that would be reflected in the effective AFR and might be noted in plug color.... (just thinking out loud)

-Jim

[joeg]

The "Hotter Blend" could have been a reference to Oxygenates in the fuel--a completely different subject than Octane.

[dj10]

The "Hotter Blend" could have been a reference to Oxygenates in the fuel--a completely different subject than Octane. [/b]

Turbo Blue 100 unleded has a Oxygen/ Wt. of 3.5%. Wouldn't a oxygenated fuel burn better, thus producing more power?

[DavidM]

I think it may depend on how built is your motor. The more built, the more you may want to use race gas. When I talked to Bob, he said the only time he ran 93 in the 240 he blew the motor. Coincidence, maybe, but I don't want to find out. I've only run race gas in the car.

I have a related question. I usually see 110 and 112 race gas along with the 100. I believe the 110 and 112 are leaded whereas the 100 is unleaded. The 110 is usually the same price as the 100. Can we run the 110 in our cars if all the emissions stuff is removed? I'm always thinking I might as well get the 110 if it's the same price as the 100, but don't know if it's ok or not.

David

[dj10]

I think it may depend on how built is your motor. The more built, the more you may want to use race gas. When I talked to Bob, he said the only time he ran 93 in the 240 he blew the motor. Coincidence, maybe, but I don't want to find out. I've only run race gas in the car.

I have a related question. I usually see 110 and 112 race gas along with the 100. I believe the 110 and 112 are leaded whereas the 100 is unleaded. The 110 is usually the same price as the 100. Can we run the 110 in our cars if all the emissions stuff is removed? I'm always thinking I might as well get the 110 if it's the same price as the 100, but don't know if it's ok or not.

David [/b]

Dave,
If you have a Oxygen Sensor, you have to run unleaded. I believe the rules state we have to use unleaded also......somewhere. Correct me if I'm wrong.

[Fastfred92]

Dave,
If you have a Oxygen Sensor, you have to run unleaded. I believe the rules state we have to use unleaded also......somewhere. Correct me if I'm wrong.
[/b]

I am not sure anything prohibits you from using leaded gas, a few years back many IT'ers considered Avgas all the rage and while the most common Avgas is 100 LL (or low lead), it does contain lead. I am not sure if that was carb guys or what but I do know a few years back I crewed on a Trans Am team that was testing the new FI engines (with O2 sensors) and we still used the same leaded race gas we used with the carb engine.. ( not sure if there was something different about the sensors )

[joeg]

You can use pure race leaded gas in IT--as long as it meets testing specs (it will as long as it is not heavily oxygenated) and the car is not registered for the street.

I use it for two reasons--VP has an infinite shelf life and lead helps your valves.

It may have a bit too much octane--meaning it is wasteful--but I will err on the side of caution any time when it comes to detonation.

[jc836]

For what it is truly worth-I have used both and found little difference. Then again the car has not been on a dyno and is completely stock (emissions still connected too). We do have the distributor set at 18 degrees and either fuel is fine with this. For the difference in price versus high RPM use you may well want the 100 just to be on the safere side from a heat standpoint.

[dj10]

You can use pure race leaded gas in IT--as long as it meets testing specs (it will as long as it is not heavily oxygenated) and the car is not registered for the street.

I use it for two reasons--VP has an infinite shelf life and lead helps your valves.

It may have a bit too much octane--meaning it is wasteful--but I will err on the side of caution any time when it comes to detonation. [/b]

If your running a car that needs the O2 sensor to give the computer data, I was told, that at least on stock O2 sensors leaded fuel will cause the O2 sensor to malfunction.

[C. Ludwig]

If your running a car that needs the O2 sensor to give the computer data, I was told, that at least on stock O2 sensors leaded fuel will cause the O2 sensor to malfunction.
[/b]

It won't cause the sensor to malfunction. Lead can lead (isn't the english language wonderful?) to the early demise of O2 sensors and catalytic converters though. Your mileage may vary but I've racked up thousands of miles of leaded race gas on wideband sensors before they finally failed. How to tell if one fails? The failure mode is generally to read full lean all the time.

FWIW, no stock ECU that I'm aware of uses O2 feedback at WOT. Closed loop is only used at light throttle. Cruising situations. When you go to WOT the ECU reverts to open loop and runs off a map with no regard to O2 correction. IMO there is very little to worry about in an IT car with a dead O2 sensor. Fuel mileage around the paddock maybe?

[dj10]

It won't cause the sensor to malfunction. Lead can lead (isn't the english language wonderful?) to the early demise of O2 sensors and catalytic converters though. Your mileage may vary but I've racked up thousands of miles of leaded race gas on wideband sensors before they finally failed. How to tell if one fails? The failure mode is generally to read full lean all the time.

FWIW, no stock ECU that I'm aware of uses O2 feedback at WOT. Closed loop is only used at light throttle. Cruising situations. When you go to WOT the ECU reverts to open loop and runs off a map with no regard to O2 correction. IMO there is very little to worry about in an IT car with a dead O2 sensor. Fuel mileage around the paddock maybe? [/b]

Well I guess I was told wrong. Then this brings up 2 questions. 1. being if you are on a dyno, burning a chip, why does the guy who is burning the chip want the O2 sensor connected or need it connected? And 2, If you are going to burn racing fuel with a slightly compression ratio (as allowed by the rules) should you burn leaded or unleaded. Is this a leading question?
Chris, if you lived in Globblers Knob, Pa you'd probably get a date, or at least a prune.

[C. Ludwig]

Well I guess I was told wrong. Then this brings up 2 questions. 1. being if you are on a dyno, burning a chip, why does the guy who is burning the chip want the O2 sensor connected or need it connected? And 2, If you are going to burn racing fuel with a slightly compression ratio (as allowed by the rules) should you burn leaded or unleaded. Is this a leading question?
Chris, if you lived in Turkey Knob, Pa you'd probably get a date, or at least a prune.
[/b]

The narrow band sensor that most cars use is what I'm referring to. Some makes, and more and more, are starting to use wideband sensors that are more capable but, again, every car I'm aware of only uses O2 correction for less than full throttle correction. That combined with the fact that you'll usually only see about 10% max correction is why so many completely stock cars show overly rich mixtures at WOT. The WOT map is safe rich (low warranty costs) and those throttle settings are never used for EPA ratings (good CAFE numbers for the manufacturer and, oh yeah, your mileage may vary).

The O2 sensor you are probably thinking of that the tuner is using is the wideband sensor. Sometimes called Lambda sensors. Check out this thread for wideband v. narrowband info. http://itforum.improvedtouring.com/forums/...?showtopic=7635 The tuner is using the wideband sensor to see what the actual a/f ratio is in order to know what corrections to make to the tune. It's the high tech way to read plugs and change jets. If he is tuning part throttle settings where there is O2 correction he'd need to see what the base tune is and know the correction factor.

No idea on the lead v. no-lead debate. With modern engines there is no need for lead afaik. However, like has been said, no-lead high octane fuel is expensive. Don't give a hoot and pollute?

[dj10]

No idea on the lead v. no-lead debate. With modern engines there is no need for lead afaik. However, like has been said, no-lead high octane fuel is expensive. Don't give a hoot and pollute?
[/b]

The only advantage of using the 100 unleaded is the O2/WT =3%, where as the leaded has none.