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Arcias
01-02-2005, 07:37 AM
We all know them. Myths about cars that drive us crazy. Some are absolutely insane, but others just might be true. Then there are those that only ignorant people believe but are so stubborn that they won't be proven otherwise...

I was just thinking of a thread that can be filled with myths and the truth (and lies) behind them. It'd be nice if we could get some discussion on some of the more tricky ones.

Here's one to start this off: octane rating.

This one drives me absolutely bonkers. Everyone around me seems convinced that just by putting in 92 octane gas is going to make my car, which is designed for 87, faster. Not only that, but it will also make it more fuel efficient and pollute less. Now, if it really did all that, I wouldn't mind paying the extra $.10/L.

From what I understand, octane is a burn inhibitor. That it increases the temperature of combustion of gas. I've heard that owners of older cars might want to use that since carbon deposits in the combustion chamber can get hot and cause detonation. I know that cars with advanced timing can make use of higher octane to increase gains and lessen detonation.

But of course, I could be wrong :saythat:

What are the real pros and cons to higher octane gas?

MrWOT
01-02-2005, 09:13 PM
Unless your car has a knock sensor defined ignition curve adding octane will make you slower. Some cars use the knock sensor to define the ignition advance by automatically advancing timing until trace knock is detected then backing off 2 degrees, in this case adding octane will give more performance, but usually it's worthless. Though you will get slightly better mileage because the gas won't burn all the way and that will tell the O2 sensor to lean out slightly. But you will be down on power.

irfrugus
01-05-2005, 12:10 AM
that myth is wierd some experts say yes to some extent
others so no diff
all depends on which expert u listen to

last time i read a myth like that was in motor trend and they did a whole write up
saying if car was designed for 86 and u put in 97+ yes would diff but
86 and placing 92 wont be that much differnce

EvilSpeeder
01-05-2005, 12:44 AM
The one that drives me nuts is that engines 'need backpressure'. Thats complete hogwash. Engines need exhaust gas velocity which helps with scavenging, but backpressure has nothing at all do with it and only costs power.

ST162MECH
01-07-2005, 10:31 PM
Ha backpressure what a crack hear that one all the time. The faster it gets out the better.

Luis C
01-07-2005, 10:46 PM
Octane is NOT a burn inhibitor is a detonation inhibitor, the higher the octane the less the fuel is prone to detonate before it's meant to (TDC).

GT4Dreams
01-08-2005, 04:28 AM
How about driving in 5th gear when you're only going let's say 35+ to "save" gas. I think that if you accelerate, it will use more gas because it's working harder in 5th @ 35mph than 4th gear would.

Rayme
01-08-2005, 04:46 AM
How about driving in 5th gear when you're only going let's say 35+ to "save" gas. I think that if you accelerate, it will use more gas because it's working harder in 5th @ 35mph than 4th gear would.

once the car is moving it requires less power and at a steady rate if you don't bog the engine it shouldnt be that bad... I mean that slow 4th of 5th its only a couple hundred RPM less. its about how much the throttle is applied too.

a small example would be letting your car rolling on idle in 1st and 2nd gear, the engine gets the same amount of gas and air and the revolutions are the same, but you go faster in 2nd gear, thus you save gas buy going faster.

Theres probably a threshold, hard to say :)

Beej
01-09-2005, 09:44 AM
hang on, im confused......how can an engine need the same amount of gas, if its doing far less revolutions per minute, thus less firing per cylinder and less fuel used to make that firing?

under load/throttle there may be a diff, but at constant speed, if ur in 5th at 1200RPM or second at 4500, u cant tell me that its the same amount of fuel being used

Jaemus
01-09-2005, 09:58 AM
lets say ur going up a slight hill, with what ur saying beej i imagine that in second at 4500 youve got the throttle nearly closed, so the computer knows it and isnt injecting much fuel, but if you go to fifth at 1200, you need to open the throttle right up to maintain the same speed up the hill, so the computer is injecting all the fuel it needs to do that

re: octane, MrWoT - is a celica such a car?

Mr E
01-09-2005, 12:11 PM
A ST205 WRC is somehow faster than the non WRC model.

It's not. If anything, not lugging the silly wing about makes the standard car a bit quicker in a straight line.

Cheap aftermarket wheels are always better than stock.
Lower is better.
Harder is better.

Etc.

Luni
01-09-2005, 03:19 PM
lets say ur going up a slight hill, with what ur saying beej i imagine that in second at 4500 youve got the throttle nearly closed, so the computer knows it and isnt injecting much fuel, but if you go to fifth at 1200, you need to open the throttle right up to maintain the same speed up the hill, so the computer is injecting all the fuel it needs to do that

re: octane, MrWoT - is a celica such a car?
The celica is NOT such a car unless you are talking about a GT4/Alltrac or a 7th gen GTS.

Its been speculated that a 93 and above 5SFE which has a knock sensor also has the knock/knock response built in, which if it does, it could potentially under ideal conditions take advantage of higher octane fuel.


Oh and E, that may be true on the celica, but with alot of newer modern rally cars, the WRC model is faster because its lighter and it also has a lower center of gravity so it should handle better and be more agile. Im using the WRX WRC model as an example. I dunno if its the same with the celica tho.

Mr E
01-09-2005, 04:05 PM
Oh and E, that may be true on the celica, but with alot of newer modern rally cars, the WRC model is faster because its lighter and it also has a lower center of gravity so it should handle better and be more agile. Im using the WRX WRC model as an example. I dunno if its the same with the celica tho.


I meant specifically the ST205 to be honest. I get irritated by the near mythical status the very few homogation special WRC edition has obtained on some places. It's exactly the same as the standard car except for some deactivated extra bits and a whale tail.

Sean
01-09-2005, 09:50 PM
Gas mileage is directly related to throttle pressure, conrad schooled me on that a long time ago.

85gtsblackman
01-09-2005, 11:58 PM
myth, honda 4cylinder engines make torque


myth: "i need to add this wing to my car to give it downforce, especailly going 45-70 mph daily"

red_94gts
01-10-2005, 03:37 AM
myth, honda 4cylinder engines make torque
the h22 makes some decent torque. 180 hp/ 180tq.
decent but it doesnt use it as well as it could