Some things everyone should know (but may not)
Some things everyone should know (but may not)
While this post is in no way a replacement of our FAQ section, there are a few general bits of information that any car owner that cares about their car at all should know. Some of this info is useful, and some is more of "Huh, I didn't know that. I learned something today." kind of stuff. So here we go...
First, Read The FAQs! <-----Yes, it's a link.
Octane Ratings
Our cars are designed to run on a certian octane fuel. Regular Neons are designed to run on 87 octane, R/Ts and ACRs on 91 (but the computer will pull ignition timing if 87 is run at the sacrifice of power), and SRT-4s at 91. The reason 91 is the highest listed is because that is the limit in CA.
If you run a higher octane in your car (excluding running 93 instead of 91 since the computers are capable of running it), you will not burn all of the fuel that enters the combustion chamber. The unburnt fuel will be dumped into the exhaust and flow right to the cat, which will try to burn it there. The cat isn't made to do this and will over time clog up.
The reason your car cannot burn the higher octane gas is because your computer controls the time and duration of your spark. Higher octane fuels take longer time to burn completly. Your PCM will not allow you to make use of the higher octane, sorry.
So, when using a higher octane gas than is recomended, you are...
Spending more in gas than you have to
Not using all the gas you paid for
Slowly killing your converter by dumping un-burnt fuel into it.
Still sound like a good idea?
Now, to those who say that the more expensive gas is better for the engine...BS. That is a marketing gimmick only. Each brand of fuel retailer has their own additive package that they add to the gas, but all grades get it. The only thing you need to worry about when it comes to fuel is getting clean gas. Not gas from a station that has 25 year old tanks that have 6-12" of water in the bottom of them.
So there you have it. Don't fall for the placebo effect and stop wasting your money. Enjoy.
Speed Limiters (This applies to all cars sold in the US)
Most Neons have their top speed limited to 118mph. The R/T and ACR are limited to 130mph, and the SRT is limited to 149mph (IIRC). This is not because the car can't go faster or that it is bad for the engine, but rather because of the tires the car comes equiped with. DOT regulations state that a car or truck sold in the US will not exceed the speed that the tires are rated for. Yep, that's the whole reason. If your SXT came with better tires from the factory, you could go faster. Of course this is a moot point really since you aren't going to be able to go that fast on public roads anyway. Right?
Component Clearances
Ever wonder why your stock wheels and tires sit so far inside the wheel wells? Do you still get pissed at the fact that the SRT has 6" wide wheels from the factory and has the turning radius of a bus? Or that the exhaust tips sit so far away from the bumper. DOT regs are your answer yet again. The DOT regulates clearance measurements for every part of a car that has to do with the supension, steering, and exhaust. So if having a 7" wide wheel on a SRT would put the tire too close to the body or control arm when at full lock while turning, it does not get DOT appoval. This is the reason for many last minute changes to a cars design or equipment choices. The wheels the SRT was supposed to have were much cooler (TSW VX1 17x7) but didn't cut the mustard with the regs. This is also way the steering rack had to be limited so much. Sad really.
Exhaust Back Pressure
This comes up a lot. Too many people have a mis-understanding on how much back pressure is best for their car. Here is the answer. You ready?
No back pressure is best. Any engine. Any car. Always.
The myth that some back pressure was good for an efficient exhaust was started sometime in the 50s or 60s by some people that didn't know what they were talking about. But enough other people heard this mis-information and it still exsits for some reason.
The one factor that makes a good exhaust system is proper flow. This is dictated by the path the exhaust has to follow, which will be dictated by the number, degree, and quality of the tubing bends and by pipe diameter. Too small a diameter and the flow is restricted, which does not let the engine breathe properly. Too large a diameter and it will actually cool the exhaust gases too quickly and create back pressure (by reducing flow). This is probably where the mis-conception that some engines need back pressure comes from. People throw a large exhaust on and they lose power so they assume that the lack of back pressure caused the problem when they actually created back pressure in the system.
The best exhaust will be designed to evacuate the gases as quickly as possible while maintaining flow, reducing back presure, keeping sufficient temperature and adequate scavenging. Scavenging will actually pull the exhaust gas out of the combustion chamber, helping the engine breathe even better.
Remember, an engine is basiclly an air pump. The more air you can get into and out of it, the more power it can make. Now forget about getting the right amount of back pressure and breathe.
Thanks to Frank for filling in the too large exhaust info.
I'll add more to this as time goes on. Thanks for reading
First, Read The FAQs! <-----Yes, it's a link.
Octane Ratings
Our cars are designed to run on a certian octane fuel. Regular Neons are designed to run on 87 octane, R/Ts and ACRs on 91 (but the computer will pull ignition timing if 87 is run at the sacrifice of power), and SRT-4s at 91. The reason 91 is the highest listed is because that is the limit in CA.
If you run a higher octane in your car (excluding running 93 instead of 91 since the computers are capable of running it), you will not burn all of the fuel that enters the combustion chamber. The unburnt fuel will be dumped into the exhaust and flow right to the cat, which will try to burn it there. The cat isn't made to do this and will over time clog up.
The reason your car cannot burn the higher octane gas is because your computer controls the time and duration of your spark. Higher octane fuels take longer time to burn completly. Your PCM will not allow you to make use of the higher octane, sorry.
So, when using a higher octane gas than is recomended, you are...
Spending more in gas than you have to
Not using all the gas you paid for
Slowly killing your converter by dumping un-burnt fuel into it.
Still sound like a good idea?
Now, to those who say that the more expensive gas is better for the engine...BS. That is a marketing gimmick only. Each brand of fuel retailer has their own additive package that they add to the gas, but all grades get it. The only thing you need to worry about when it comes to fuel is getting clean gas. Not gas from a station that has 25 year old tanks that have 6-12" of water in the bottom of them.
So there you have it. Don't fall for the placebo effect and stop wasting your money. Enjoy.
Speed Limiters (This applies to all cars sold in the US)
Most Neons have their top speed limited to 118mph. The R/T and ACR are limited to 130mph, and the SRT is limited to 149mph (IIRC). This is not because the car can't go faster or that it is bad for the engine, but rather because of the tires the car comes equiped with. DOT regulations state that a car or truck sold in the US will not exceed the speed that the tires are rated for. Yep, that's the whole reason. If your SXT came with better tires from the factory, you could go faster. Of course this is a moot point really since you aren't going to be able to go that fast on public roads anyway. Right?
Component Clearances
Ever wonder why your stock wheels and tires sit so far inside the wheel wells? Do you still get pissed at the fact that the SRT has 6" wide wheels from the factory and has the turning radius of a bus? Or that the exhaust tips sit so far away from the bumper. DOT regs are your answer yet again. The DOT regulates clearance measurements for every part of a car that has to do with the supension, steering, and exhaust. So if having a 7" wide wheel on a SRT would put the tire too close to the body or control arm when at full lock while turning, it does not get DOT appoval. This is the reason for many last minute changes to a cars design or equipment choices. The wheels the SRT was supposed to have were much cooler (TSW VX1 17x7) but didn't cut the mustard with the regs. This is also way the steering rack had to be limited so much. Sad really.
Exhaust Back Pressure
This comes up a lot. Too many people have a mis-understanding on how much back pressure is best for their car. Here is the answer. You ready?
No back pressure is best. Any engine. Any car. Always.
The myth that some back pressure was good for an efficient exhaust was started sometime in the 50s or 60s by some people that didn't know what they were talking about. But enough other people heard this mis-information and it still exsits for some reason.
The one factor that makes a good exhaust system is proper flow. This is dictated by the path the exhaust has to follow, which will be dictated by the number, degree, and quality of the tubing bends and by pipe diameter. Too small a diameter and the flow is restricted, which does not let the engine breathe properly. Too large a diameter and it will actually cool the exhaust gases too quickly and create back pressure (by reducing flow). This is probably where the mis-conception that some engines need back pressure comes from. People throw a large exhaust on and they lose power so they assume that the lack of back pressure caused the problem when they actually created back pressure in the system.
The best exhaust will be designed to evacuate the gases as quickly as possible while maintaining flow, reducing back presure, keeping sufficient temperature and adequate scavenging. Scavenging will actually pull the exhaust gas out of the combustion chamber, helping the engine breathe even better.
Remember, an engine is basiclly an air pump. The more air you can get into and out of it, the more power it can make. Now forget about getting the right amount of back pressure and breathe.
Thanks to Frank for filling in the too large exhaust info.
I'll add more to this as time goes on. Thanks for reading
Last edited by Danteneon on Wed Jun 15, 2011 8:12 am, edited 5 times in total.
If I could just figure out how to meld the Outback and the Neon into one car...
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I'm going to work on getting some of this kind of stuff added to the FAQ section. The octane discussion has been driving me nuts for years, I just want a hot link to send the noobs for schooling. Looks like you're right there with me eh John?
-Derek
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To be honest, I don't think the average 2gn user cares much about why modern cars are built the way they are. The tire/speed topic is an obvious exception, but beyond that I can't see us needing an entire section dedicated to DOT regs.
-Derek
|Donate to 2gn|Feedback || OB's | GozziFab | All Business |
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Dante, you are such a
I used that one because I don't think it's ever been used before
I used that one because I don't think it's ever been used before
occasional demons wrote:So maybe a FuzzyDanteHagan sammich might just beat a FuzzyHagan.
Danteneon wrote:My advice is to fight those urges and enjoy the fact that you have both X and Y chromosomes. And an SRT. And your hand. You don't need a girl.
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Re: Some things everyone should know (but may not)
Danteneon wrote:The R/T and ACR are limited to 130mph
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With boost, or an R/T, the higher the better. With what's available to the public at the filling stations, you really can't get anything with enough octane to do any damage.
Bill
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1999 neon coupe 2.4 swap
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Thank you for the info about the back pressure. I've been telling this to people forever now. You also mention scavenging which is what you want, not back pressure. A++ thread!
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Maybe add that if the pipe is too big it will actually cool the exhaust gases too quickly and create back pressure (by reducing flow). This is probably where the mis-conception that some engines need back pressure comes from. People throw a large exhaust on and they lose power so they assume that the lack of back pressure caused the problem when they actually created back pressure in the system.
The best exhaust will be designed to evacuate the gases as quickly as possible while maintaining flow, reducing back presure, keeping sufficient temperature and adequate scavenging.
In the end...
Back pressure is always bad, increased flow is always good.
The best exhaust will be designed to evacuate the gases as quickly as possible while maintaining flow, reducing back presure, keeping sufficient temperature and adequate scavenging.
In the end...
Back pressure is always bad, increased flow is always good.
-Frank
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A note concerning fuel octane. My local station(BP) recently went from 93 octane to 91 octane. He explained that when the state inspecters show up un-announced the gas must test the same or higher than what is posted on the pump. His change was due to that particular batch and has since gone back to 93. He told me that the 91 octane tests at 92 or 93. Remember this when the pump is labeled 93.