Question on Mixing fuels

[KB Viper]

Car is stock and I live in CA where 91 is premium. I am lucky enough to live down the street from a vp race station with 100 octane at the pump and I started by mixing 4 gallons of 100 and 12 gallons of 91 to get to a blend of 93. I didn't feel much difference but now I'm mixing 8 gallons of 100 and 8 gallons of 91 to get a blend of 95 and its a noticable difference. The car accelerates faster and is much smoother. My question is how high of a octane rating can you put in these cars stock before you start hurting them. I called driveSRT and they told me I could fill it up with 100 as long as its unleaded and the car will adjust to it and run great and that it will not hurt the cats. Anyone else mixing gas or have plans to? Thoughts please.

 

[mnc2886]

This would be a great thread for the SRT Engineers to respond to.....

 

[KB Viper]

This would be a great thread for the SRT Engineers to respond to.....

I agree. Do I need to move it to another section?

 

[mnc2886]

I agree. Do I need to move it to another section?

No. I wouldn't think so. They've responded here before....

 

[Jack B]

You can increase the octane without any problems. I believe these cars can use a minimum of 91. Octane would only play a role if you were to increase the compression ratio, add boost and/or add timing. Since none of those are possible at this time, octane is a none issue as long as you use the minimum requered value. As an example, on my Gen II with increased compression I use 93 on the street. If I go to the drag strip and add more advance (timing) i use 108 as a safety factor. That left over 108 does not hurt anything when I then run it on the street - it sure smells funny.

 

[uvbnbit]

Me loves the smell of Race gas.....

 

[bluesrt]

i use race gas in my **** eater and lawn mower, i feel if i have to breathe it, im going to snort the good stuff

 

[Voice of Reason]

You can increase the octane without any problems. I believe these cars can use a minimum of 91. Octane would only play a role if you were to increase the compression ratio, add boost and/or add timing. Since none of those are possible at this time, octane is a none issue as long as you use the minimum requered value. As an example, on my Gen II with increased compression I use 93 on the street. If I go to the drag strip and add more advance (timing) i use 108 as a safety factor. That left over 108 does not hurt anything when I then run it on the street - it sure smells funny.

To confirm then, you don't think they made any programming changes that would allow the PCM to increase timing on it's own past the minimum 91 octane? I've always filled my cars up w/ 93 but there's a station about 10 miles away with 100. If SRT was smart with the new PCMs and it would take advantage of it I'll start making the drive to gas up immediately.

 

[MoparMap]

I think you'd be treading a fine line as a factory if you built the computer around higher octanes since the car would have to constantly adjust to lower octane and would always be correcting. Easier to build it to a minimum and still have the safety factor if you just get a bad tank or fill up with the wrong stuff. 91 is the highest I can find around me easily for my 04 but I accidentally filled it with 89 once. Looked up as the pump clicked off and realized what happened. Went ahead and tossed a bottle of octane booster in it as a precaution, but if you don't push it real hard it will probably run on lower stuff just fine. The higher octane is going to make a bigger difference at higher output conditions like WOT. Your higher octance fuel might run better for other reasons than just octance too (like different additives or maybe even lack of additives for race fuel).

 

[Bruce H.]

Does the engine ECU not constantly adjust timing and fuel based on a knock response system? The ECU would receive inputs from various sensors, including various temps, air/fuel and knock sensors, and constantly advance timing and lean fuel to maintain optimal performance, fuel economy and emissions. When any operating conditions start to approach knock the ECU would start pulling timing to prevent it by lowering power. If condition exists whenever going WOT, or WOT under higher temps, then higher octane would at the very least prevent the ECU from reducing power, and at best allow for more power under all conditions. Dyno testing could answer the question, as might SRT. My "guess" is 94 will make more power than 91 on the gen V.

 

[MoparMap]

That's mostly true, but I think there's usually an upper limit built into the timing curves that the computer will never exceed, regardless of fuel choice. The question is how high is that limit. I wouldn't think the engineers would bother testing race fuels for a production engine, but then again SRT has a bit of a reputation for being gearheads.

 

[redtanrt10]

Kris, you can fill 100% unleaded 100 octane. Maybe the SRT engineers can comment on real hp/trq improvements going beyond 91 octane on the stock Gen IV and V computers??

On the Gen IV motors, with the venom ECU, the computer wants 93 or better. They run fine on 91 and just pull back timing. Seems from speaking to Dan Cragin at SPT in LA, the octane level power increase on the dyno (with venom controller), hits the wall at 95/96 octane.

Lot's of folks here track Gen IV's with headers and the venom ecu so lot's of fuel mixing going. Most mix to 95 though some with big $$$ just run 100.

Much better to mix using fuel jugs, 1-2 gallons of 91 followed by 1-2 gallons of 100.

As far as feel, you may be more sensitive and aware than me. On a base of 602 at the wheels in my viper (with 95+ octane), I don't feel a difference when I run 91 and hammer the throttle on the 5.

Best deal in the OC is $8.95 in Fullerton, most up here are $9.50. What are you paying down in SD?? Best wishes, Mike

 

[KB Viper]

Kris, you can fill 100% unleaded 100 octane. Maybe the SRT engineers can comment on real hp/trq improvements going beyond 91 octane on the stock Gen IV and V computers??

On the Gen IV motors, with the venom ECU, the computer wants 93 or better. They run fine on 91 and just pull back timing. Seems from speaking to Dan Cragin at SPT in LA, the octane level power increase on the dyno (with venom controller), hits the wall at 95/96 octane.

Lot's of folks here track Gen IV's with headers and the venom ecu so lot's of fuel mixing going. Most mix to 95 though some with big $$$ just run 100.

Much better to mix using fuel jugs, 1-2 gallons of 91 followed by 1-2 gallons of 100.

As far as feel, you may be more sensitive and aware than me. On a base of 602 at the wheels in my viper (with 95+ octane), I don't feel a difference when I run 91 and hammer the throttle on the 5.

Best deal in the OC is $8.95 in Fullerton, most up here are $9.50. What are you paying down in SD?? Best wishes, Mike

we have 3 vp fuel stations in SD that have 100 for 8.98 and 1 has 95.5 octane for 6.98. off subject question but do you know of guys who run the stock computer with headers on the gen IV? if so do they have issues leaning out or throwing the check engine light on? i want headers but the mopar race computer for the gen V isn't out yet and eveyone i've called doesn't know when it will be released. I'm new to the viper world but i know if you ran headers on a Vette without adjusting the A/F ratio it would lean out and throw a code.

 

[redtanrt10]

The CEL without the controller is when, not if with headers on a Gen IV. I lasted 200 miles? As soon as you moderately cruise for 10-15 minutes your done. (Issue is heat levels in the cats). Hopefully the controller for the G5 will be out soon. I don't keep up with the G5 developments like you owners do, but I also thought there isn't a G5 header available yet either?

Wish we had that 95.5 octane option here. My current cost is $4.20 (91) and $8.95 (100) so it costs me about $6.60 for 95 and I have to do the mixing. $0.40 a gallon more for .5 octane and no mixing, I'm in!

 

[Jack B]

In general, codes are thrown during closed loop (partial throttle) operation. One exception would be exceeding the mass air flow limit on a GM product. It would be extremely unlikely that headers would throw a code, a CEl after a header change is more likely due to the new placement of the O2 sensor (if it is moved) A high flow cat or cat delete will throw a code unless the tuner uses an available counter measure. Again, your air fuel is controlled by the O2 sensors, unless that system is defective your a/f will try to stay near 14.7 in closed loop. When you go WOT that a/f is controlled by a fixed table (with ambient conditions multipliers) and in general no CEL will be initiated during WOT.

In short, the high octane fuel willnot hurt you and will not change the a/f ratio. the above paragraph is a short description of general issues, there could always be an exception for a specific model, the viper, probably not.

we have 3 vp fuel stations in SD that have 100 for 8.98 and 1 has 95.5 octane for 6.98. off subject question but do you know of guys who run the stock computer with headers on the gen IV? if so do they have issues leaning out or throwing the check engine light on? i want headers but the mopar race computer for the gen V isn't out yet and eveyone i've called doesn't know when it will be released. I'm new to the viper world but i know if you ran headers on a Vette without adjusting the A/F ratio it would lean out and throw a code.

 

[SADVIPER]

This would be a great thread for the SRT Engineers to respond to.....

We can dream...

 

[345s-bspinnin]

In short, the high octane fuel will not hurt you and will not change the a/f ratio.

No offense, but your comment is inaccurate and offers horrible advise with potentially high dollar repercussions!!!

High octange fuels have different stoichiometric ratios and will absolutely change your a/f ratio!!!!!

I am not going to get deep into the chemistry in this post, but please find your chemist buddy to explain or do a quick search on-line.

Here is a quick excerpt from Sunoco racing fuels website:

"Due to its high oxygen content, Sunoco EXO2 requires a richer air/fuel mixture. Using EXO2 without proper air/fuel mixture changes can lean out your engine. Please consult the Stoichiometric Air/Fuel Ratio data in the table below. Since non-oxygenated race fuels typically have a stoichiometric air/fuel ratio of 14.6:1 to 15.0:1, you may need to richen your fuel mixture by 10 to 15 percent when using EXO2." By the way, most non-leaded fuels are oxygentated.

Here is thorough and well educated post on another board: CLICK ME

 

[KB Viper]

The CEL without the controller is when, not if with headers on a Gen IV. I lasted 200 miles? As soon as you moderately cruise for 10-15 minutes your done. (Issue is heat levels in the cats). Hopefully the controller for the G5 will be out soon. I don't keep up with the G5 developments like you owners do, but I also thought there isn't a G5 header available yet either?

Wish we had that 95.5 octane option here. My current cost is $4.20 (91) and $8.95 (100) so it costs me about $6.60 for 95 and I have to do the mixing. $0.40 a gallon more for .5 octane and no mixing, I'm in!

Mopar, american racing, and belanger have all told me the gen IV headers are the same for gen V.

 

[KB Viper]

No offense, but your comment is inaccurate and offers horrible advise with potentially high dollar repercussions!!!

High octange fuels have different stoichiometric ratios and will absolutely change your a/f ratio!!!!!

I am not going to get deep into the chemistry in this post, but please find your chemist buddy to explain or do a quick search on-line.

Here is a quick excerpt from Sunoco racing fuels website:

"Due to its high oxygen content, Sunoco EXO2 requires a richer air/fuel mixture. Using EXO2 without proper air/fuel mixture changes can lean out your engine. Please consult the Stoichiometric Air/Fuel Ratio data in the table below. Since non-oxygenated race fuels typically have a stoichiometric air/fuel ratio of 14.6:1 to 15.0:1, you may need to richen your fuel mixture by 10 to 15 percent when using EXO2." By the way, most non-leaded fuels are oxygentated.

Here is thorough and well educated post on another board: CLICK ME

thanks for the info, i'll stick with a blend of 93 on the stock computer and go up to 94 when i get the mopar race computer (hopefully it's released soon).

 

[Jack B]

Lets us start again, if you are in closed loop the O2 sensors keep your a/f at or near 14.7, that is not going to change no matter what the octane rating is.

Next step, I run dual 02 sensors and do extensive logging on my 97 viper. Whether I run 108 or 93 octane, the a/f changes little if any. That same car has had many/many gallons of 108 thru the engine and it runs consistent 128-129mph in the quarter mile - that is one strong engine, how is it surviving on this wide range of octanes??

Third step, typical available octane ratings go from 97 to 103, according to your thesis, with a range of octanes available one would think there would be seized motors all over the highway.

Step four, do you really believe that fuel distribution centers with blended octane ratings distribute exactly the advertised octanes, again, I still do not see all those seized engines along the highway.

Let me keep going, my daily driver runs on an advertised octane range of 89 to 93, I have put over 200,000 miles on the same series of vehicle - it has not seized yet?? Maybe there is middle ground somewhere?? The only issue that could manifest itself would be that some of the higher octane race fuels might not have the correct additives for long term usage. My guess is that your articles are in reference to carbureted engines. I will read your links and then we can discuss/ Lastly no one is advocating any extended deviations on daily drivers.

No offense, but your comment is inaccurate and offers horrible advise with potentially high dollar repercussions!!!

High octange fuels have different stoichiometric ratios and will absolutely change your a/f ratio!!!!!

I am not going to get deep into the chemistry in this post, but please find your chemist buddy to explain or do a quick search on-line.

Here is a quick excerpt from Sunoco racing fuels website:

"Due to its high oxygen content, Sunoco EXO2 requires a richer air/fuel mixture. Using EXO2 without proper air/fuel mixture changes can lean out your engine. Please consult the Stoichiometric Air/Fuel Ratio data in the table below. Since non-oxygenated race fuels typically have a stoichiometric air/fuel ratio of 14.6:1 to 15.0:1, you may need to richen your fuel mixture by 10 to 15 percent when using EXO2." By the way, most non-leaded fuels are oxygentated.

Here is thorough and well educated post on another board: CLICK ME

 

[PeerBlock]

The thing about octane ratings on gasoline is that you want to go with the lowest octane possible that avoids knock. The Viper's engine has a compression ratio of 10.2:1, and as the manufacturer recommends you can use 91 octane. You can get by with even lower octane at higher elevations. Higher octane fuel burns slower than lower octane fuel, so running a higher than necessary octane on a stock motor which was designed for 91-93 could result in carbon buildup over time, plus unburnt fuel shooting out with the exhaust. Most ECUs advance timing using data from the MAF and temperature sensors, up to the point where slight knock is detected and then the timing is backed off slightly. I would not expect an NA engine to see any substantial benefit (perhaps even no benefit at all) from running 95-100 octane when it was intended for 91-93, though maybe the 8.4L has some tricks up its sleeve that I am not aware of.

 

[Jack B]

If you are trying to increase hp one of the easiest methods is to add timing advance. Dodge has always been protective of the viper engine by pulling timing near peak torque. The PCM also forces the viper engine to run extremely rich at peak rpm, this is also intended to protect the engine from detonation. The theory is that on a hot day at the track the car will not detonate.

The problem is that you are giving away a lot of hp. It is all too easy to add timing and pull fuel on a Gen 1, II and III and get back some of that hp. There is no MAF sensor on the viper engine it is air density control. A lot of tuning was done with both the VEC and SCT, a large part of the tuning is an increase in the timing, in general that requires a higher octane. To go one step further tremendous hp increases can be had in boosted applications, when higher octanes are used used. With my Gen II, I have both 93 octane tunes and 108 octane tunes.

On a stock Gen V for daily driving, at this point any octane over 93 is not going to result in any positive gains. For long track events on a a hot day, I would not want anything less than 93.

The thing about octane ratings on gasoline is that you want to go with the lowest octane possible that avoids knock. The Viper's engine has a compression ratio of 10.2:1, and as the manufacturer recommends you can use 91 octane. You can get by with even lower octane at higher elevations. Higher octane fuel burns slower than lower octane fuel, so running a higher than necessary octane on a stock motor which was designed for 91-93 could result in carbon buildup over time, plus unburnt fuel shooting out with the exhaust. Most ECUs advance timing using data from the MAF and temperature sensors, up to the point where slight knock is detected and then the timing is backed off slightly. I would not expect an NA engine to see any substantial benefit (perhaps even no benefit at all) from running 95-100 octane when it was intended for 91-93, though maybe the 8.4L has some tricks up its sleeve that I am not aware of.

 

[345s-bspinnin]

Lets us start again, if you are in closed loop the O2 sensors keep your a/f at or near 14.7, that is not going to change no matter what the octane rating is.

Sure, the O2 sensors still target 14.7, but it doesn't mean you are running stoichiometric. An air fuel ratio at 14.7:1 is the stoichiometric ratio for pump gas only. Period. The stoichiometric ratio for VP109 is 13.4. So guess what, you computer is still targeting 14.7:1 despite that fact that the high octane fuel's stoich ratio is 13.4. It's dumb system that doesn't know what fuel its burning. It just assumes pump gas. Take another good glance at your a/f ratio manufacturer's users guide and I am sure that you will find a table for proper adjustment (based on lambda) for different race fuel and their respective stoich ratios.

In simple terms, the equivalent would be for your to be cruising down the highway on pump gas and your a/f is reading 16.0:1. The difference between 14.7:1 and 16 is the same as VP109 13.4 to 14.7. Tell me that makes you comfortable?

 

[Jack B]

I understand that totally and you make a good point, however, the most common race fuels for weekend warriors run between 14.0 and 15.0 stoichiometric, Take a look at the Sunoco GT series of fuels. If you consider there was 93 already in the tank, the resultant blend is going to be a stoichiomeric of approx 14.5. That is the reaason I have never seen a log that shows an a/f at WOT that deviates from the norm when using race gas.

Sure, the O2 sensors still target 14.7, but it doesn't mean you are running stoichiometric. An air fuel ratio at 14.7:1 is the stoichiometric ratio for pump gas only. Period. The stoichiometric ratio for VP109 is 13.4. So guess what, you computer is still targeting 14.7:1 despite that fact that the high octane fuel's stoich ratio is 13.4. It's dumb system that doesn't know what fuel its burning. It just assumes pump gas. Take another good glance at your a/f ratio manufacturer's users guide and I am sure that you will find a table for proper adjustment (based on lambda) for different race fuel and their respective stoich ratios.

In simple terms, the equivalent would be for your to be cruising down the highway on pump gas and your a/f is reading 16.0:1. The difference between 14.7:1 and 16 is the same as VP109 13.4 to 14.7. Tell me that makes you comfortable?

 

[Steve M]

If you are trying to increase hp one of the easiest methods is to add timing advance. Dodge has always been protective of the viper engine by pulling timing near peak torque. The PCM also forces the viper engine to run extremely rich at peak rpm, this is also intended to protect the engine from detonation. The theory is that on a hot day at the track the car will not detonate.

The problem is that you are giving away a lot of hp. It is all too easy to add timing and pull fuel on a Gen 1, II and III and get back some of that hp. There is no MAF sensor on the viper engine it is air density control. A lot of tuning was done with both the VEC and SCT, a large part of the tuning is an increase in the timing, in general that requires a higher octane. To go one step further tremendous hp increases can be had in boosted applications, when higher octanes are used used. With my Gen II, I have both 93 octane tunes and 108 octane tunes.

On a stock Gen V for daily driving, at this point any octane over 93 is not going to result in any positive gains. For long track events on a a hot day, I would not want anything less than 93.

There was no MAF sensor on the Gen I-III Vipers...there is on a Gen IV/V.

Sure, the O2 sensors still target 14.7, but it doesn't mean you are running stoichiometric. An air fuel ratio at 14.7:1 is the stoichiometric ratio for pump gas only. Period. The stoichiometric ratio for VP109 is 13.4. So guess what, you computer is still targeting 14.7:1 despite that fact that the high octane fuel's stoich ratio is 13.4. It's dumb system that doesn't know what fuel its burning. It just assumes pump gas. Take another good glance at your a/f ratio manufacturer's users guide and I am sure that you will find a table for proper adjustment (based on lambda) for different race fuel and their respective stoich ratios.

In simple terms, the equivalent would be for your to be cruising down the highway on pump gas and your a/f is reading 16.0:1. The difference between 14.7:1 and 16 is the same as VP109 13.4 to 14.7. Tell me that makes you comfortable?

O2 sensors are lambda sensors...in closed loop, they aim for a lambda of 1.0. Lambda is fuel agnostic...doesn't matter if it is E85 or good old 93 octane, it will get you to stoich either way - that's how flex fuel cars can still do fuel trims even when there is a mix of regular gas and E85. Now, that would fall apart in open loop, but by how much I'm not sure.

 

[Jack B]

Two very good points - but we should define that sensor as a narrow band device.

There was no MAF sensor on the Gen I-III Vipers...there is on a Gen IV/V.



O2 sensors are lambda sensors...in closed loop, they aim for a lambda of 1.0. Lambda is fuel agnostic...doesn't matter if it is E85 or good old 93 octane, it will get you to stoich either way - that's how flex fuel cars can still do fuel trims even when there is a mix of regular gas and E85. Now, that would fall apart in open loop, but by how much I'm not sure.

 

[Steve M]

Two very good points - but we should define that sensor as a narrow band device.

It wouldn't matter if it was narrow (0-1V) or wide (0-5V)...either will operate on the same principle.

 

[KB Viper]

so i'll continue to mix 4 gallons of 100 octane unleaded from VP with 12ish gallons of 91 to get a mix of 93 until they release a mopar race computer for the gen 5 and then i'll mix 6 gallons of 100 and 10 gallons 91 to get a 94 ocatne blend. I"m honeslty more worried about getting a bad tank of hippie gas so i always mix a minium amount of 100 just in case.

 

[VENOM V]

I don't know if you really need to be concerned with a stock, undertressed normally aspirated engine like the Viper's V10. It's rare that anyone gets a bad tank of gas these days. Even the small mom and pop gas stations get their gas from excess supply from Chevron, 76,... the big boys. The knock sensors will prevent any damage in the unlikely event of bad gas. I don't believe you'll see any difference in 1/4 mile or 0 to 60 times either, because the system is conservatively tuned. And unless the technology has changed the past few years, the stock computer won't advance the timing because it won't know that you're running higher octane. Our crappy California 91 octane should work fine.

 

[Steve M]

I don't know if you really need to be concerned with a stock, undertressed normally aspirated engine like the Viper's V10. It's rare that anyone gets a bad tank of gas these days. Even the small mom and pop gas stations get their gas from excess supply from Chevron, 76,... the big boys. The knock sensors will prevent any damage in the unlikely event of bad gas. I don't believe you'll see any difference in 1/4 mile or 0 to 60 times either, because the system is conservatively tuned. And unless the technology has changed the past few years, the stock computer won't advance the timing because it won't know that you're running higher octane. Our crappy California 91 octane should work fine.

Will they advance timing? No. Will they pull it in a big hurry? Yes. The Gen IV computers are very sensitive to anything even remotely resembling knock, and they'll adjust accordingly at the expense of power. I'd expect no less from the Gen V given they use the same engine (mostly).