Jump to content

Welcome to Autoworld Forum !

Sign In or Register to gain full access to our forums. By registering with us, you'll be able to discuss, share and private message with other members of our community.

Close
Photo

Necessary Or Not


  • Please log in to reply

#11
jonlsl

Posted 14 June 2012 - 01:59 PM

jonlsl

    Fast & Furious

  • Members
  • PipPipPip
  • 2,013 posts
QUOTE (drexchan @ Jun 14 2012, 01:06 PM) <{POST_SNAPBACK}>
How about cars with performance cams and exhaust?

What's a slightly rich mixture when 14.7:1 is the most efficient ratio?

How about finer spray at the same duty cycle but higher pressure?


Cars with performance cams and exhaust will lean the mixture out. By how much depends on the cam angles and lift used and the size of the exhaust and type of air filter fitted. You will only know by how much when you dyno the car with A/F ratio readings and graph. If you going that route always use Dynojet as its the most accurate and repeatable.

14.7:1 ratio is only applicable with idle mixture and light load or light throttle mixtures below 3000rpm. Any more load with higher rpm needs more fuel increasing in demand till you get to full throttle high rpm, you will need about 13.2:1 to 12.5:1 depending on engine type, design and manufacturer. Figures quoted are only for N.A. engine turbo engines are different.

Most 100% stock cars unmodified at full throttle dyno run at high rpm usually will show a 12.0-12.5:1 A/F ratio. That is why when you add an open air filter and exhaust you can usually just get away without needing to add more fuel but gain more power. But always check on the dyno because you might be having a car which is tuned just right for stock conditions. That is why always dyno the car first with A/F ratio graph so you know where you stand rather than guessing all the time.

With higher pressure you will only get a marginal or no increase increase in finer spray basically negligible. Most of the time even with standard pressures the fuel is quite well atomized already. Some injectors don't really atomize the fuel at all, it almost comes out like a straight stream as its designed to hit a plate and then the resulting spray atomizes the fuel, usually found in older continental models. In order to get a finer spray you need really high pressure and small duty cycle. Thus DI high pressure fuel systems

So when you increase the fuel pressure even slightly, alot more fuel goes into the engine without affecting spray pattern and atomization. So the slight increase in fuel pressure will not affect the spray pattern.

If you want to do a test. Take out the injectors and get them serviced. On the injector machine you can see the spray pattern. Ask them to increase the pressure by 0.2-0.5kg/cm (usually standards pressure is about 3.0-3.5kg/cm). Then ask them to run the injector you will see little or no difference in the spray pattern but in a timed test you will see flow has increased dramatically. Most injectors and fuel systems are designed to atomize and spray properly at 3-3.5kg/cm pressure, that is why any more pressure will not create a finer spray. But a decrease in pressure will affect the spray pattern and atomization as will occur in a faulty pump or clogged fuel filter.

If life was so simple everybody would just buy a F/P regulator and crank up the pressure. But as I said when you crank up the pressure fuel feed is increased everywhere. So you might get the A/F ratio right at full throttle but idle, compensation, start maps and parts throttle maps will be running rich, so you need to retune all those.

Moreover more and more cars are using returnless systems so its out of the question already to add a F/P regulator.

#12
drexchan

Posted 14 June 2012 - 11:35 PM

drexchan

    Hot Rod

  • Members
  • PipPipPipPip
  • 14,758 posts
In most graphs that I read, even on those old tech 4Gs, lightly upgraded, 60-70% of the ratio from 2.5k to 6.5k is quite linear, hovering around 14, except a small dip around the peak torque. Some engines, such as mine, even went leanest at peak power.

The way I see it is, crank up the pressure slightly to touch 13.5 with an regulator, and spend minimal time with the laptop, just to touch up the area around the peak torque to get a pretty flat line.

Another engine that I stroked, even gave us a surprising flat 13.8 AF line from 2k to redline. All I did was JUST a regulator to push it down to 13.5. RM500 max, gained 3Nm and 3HP on the wheel. No hanky panky tuning session on the roller, just a LM-2, a few spanners on the road, and I will call it a day.

#13
jonlsl

Posted 15 June 2012 - 08:39 AM

jonlsl

    Fast & Furious

  • Members
  • PipPipPip
  • 2,013 posts
QUOTE (drexchan @ Jun 14 2012, 11:35 PM) <{POST_SNAPBACK}>
In most graphs that I read, even on those old tech 4Gs, lightly upgraded, 60-70% of the ratio from 2.5k to 6.5k is quite linear, hovering around 14, except a small dip around the peak torque. Some engines, such as mine, even went leanest at peak power.

The way I see it is, crank up the pressure slightly to touch 13.5 with an regulator, and spend minimal time with the laptop, just to touch up the area around the peak torque to get a pretty flat line.

Another engine that I stroked, even gave us a surprising flat 13.8 AF line from 2k to redline. All I did was JUST a regulator to push it down to 13.5. RM500 max, gained 3Nm and 3HP on the wheel. No hanky panky tuning session on the roller, just a LM-2, a few spanners on the road, and I will call it a day.


What you described is the quick and easy way and it works no doubt, that is why I said when you increase the pressure you increase everywhere including idle, startup, temp compensation and part throttle and light throttle maps. So then you have to check how much richer did those parts get.

#14
drexchan

Posted 18 June 2012 - 07:01 PM

drexchan

    Hot Rod

  • Members
  • PipPipPipPip
  • 14,758 posts
QUOTE (jonlsl @ Jun 15 2012, 08:39 AM) <{POST_SNAPBACK}>
What you described is the quick and easy way and it works no doubt, that is why I said when you increase the pressure you increase everywhere including idle, startup, temp compensation and part throttle and light throttle maps. So then you have to check how much richer did those parts get.

Idle, part throttle and even anything below 2.5k rpm has been taken cared by the close loop operation as long as it's hot. Cold start, don't care lah... It is already rich anyway

#15
jonlsl

Posted 19 June 2012 - 09:16 AM

jonlsl

    Fast & Furious

  • Members
  • PipPipPip
  • 2,013 posts
QUOTE (drexchan @ Jun 18 2012, 07:01 PM) <{POST_SNAPBACK}>
Idle, part throttle and even anything below 2.5k rpm has been taken cared by the close loop operation as long as it's hot. Cold start, don't care lah... It is already rich anyway


Yah the close loop can take care of that usually it have the ability to add or cut about 15%-25% fuel. But if you are really sensitive and you have a silky smooth engine and car and you do this you can feel the engine not so smooth. you can feel the ECU cutting back the fuel. I tried it before. Still drivable and most people might not be able to feel it. Until you get used to it and sensitive then its obvious.

That is why its not a perfect method but its a cheap and reasonable method. Its one of those "Can Lah" methods but not the perfect or correct method. But in Malaysia because most of use don't have deep pokets "can lah" will do. smile_big.gif

#16
drexchan

Posted 19 June 2012 - 11:44 PM

drexchan

    Hot Rod

  • Members
  • PipPipPipPip
  • 14,758 posts
Let's draw a conclusion? =]

#17
jonlsl

Posted 20 June 2012 - 08:40 AM

jonlsl

    Fast & Furious

  • Members
  • PipPipPip
  • 2,013 posts
QUOTE (drexchan @ Jun 19 2012, 11:44 PM) <{POST_SNAPBACK}>
Let's draw a conclusion? =]


Simple, if you have money, do it properly with proper ECU tuning bigger fuel pump and/or injectors with FP regulator depending on level of mods to the car, if you don't have money, not much choice but to use a FP regulator if you are running lean because of your mods. If you have a stock standard car with no mods don't bother as it will do nothing but make it worse and you will most likely complain about fuel economy.

#18
drexchan

Posted 20 June 2012 - 02:21 PM

drexchan

    Hot Rod

  • Members
  • PipPipPipPip
  • 14,758 posts
Spot on!

Build up the muscle before feeding you car with steroid.