Piggyback qns

[Auto_ghost]

When we talk about car mod and ecu tuning, common sense say, we want power.

 

When we talk about close loop tuning, common sense say, fuel economy.

 

Power and fuel economy are two totally opposite objectives.

 

Normal close loop AFR (Air Fuel Ratio) is 14.7, if you can force close loop AFR using piggyback or whatever means to achieve, say AFR 15.5 of lean burn mode, fuel saving is 1-15.5/14.7=5.4%. Btw, driving at 15.5 AFR other then high speed cursing is an extreme torture.

 

A normal piggyback ecu cost about $800, and assume $2.0 per liter of petrol price, you need to pump 800/0.054=$14,814 of petrol to breakeven.

 

If your petrol consumption is $500 per month, means you need 14814/500/12=2.46yrs.

 

That means you need to light throttle, never rev your engine beyond 3k rpm to breakeven your piggyback investment in 2.46 yrs time.

 

What a boring life

[Zeee]

yup! i hv a fren who has tat xperience, but not on a "sophiscated" piggybck like e-manage... like those OEM stuff fr taiwan... where anyone cld slap a local brand on d pdt. yes... it's tat scary...

[Zeee]

i kno there r piggybck software where it cld control d efficiency of d fuel pump in closed loop mode. e.g. sending an electrical signal 2 d fuel pump 2 run @ 85% efficiency when in closed loop. it's all abt software & electronics... nowadays, local tuners dunno jackshit on both...

 

d most common fdbck i hv fr these tuners r like "...aiyah, d piggybck dun match d stage 3 cams lah...", "..u wan pwr, afr must b richer lah, so fc suffer loh...", "...bigger tarbo, must hv additional injectors lah, no nd 2 upgrade fuel pump wan..." more than 50% tuners out there dun even understand d workings btwn stock/aftermkt injectors w d stock fuel pump!!!

[Smhomie]

Well AG, a few points to think about...

 

If you are talking about NA cars where you are always operating in vacuum, typically 22InHg to 0psi atmospheric, then you are correct to tune close loop leaner aka AFR 15.5-16.0 because thats where you are mostly during cruise speeds of 80-110km/h

 

Problem for FI cars is PARTIAL THROTTLE BOOST. This is the problem area when close loop needs to be addressed. You can be cruising at 80km/h and rpms at approx. 2200rpm and just in vacuum. What happens when you depress your gas pedal to increase your speed to say 120km/h from your cruise speed? Thats where boost comes in. A responsive turbo can boost between 1psi to 10psi within the rpm range of 2200rpm to 3500rpm. You now have positive atmospheric of 14.7psi + 10psi boost = 24.7psi absolute atmospheric pressure in the intake plenum. All this happening while you are still in close loop from 0% to 60% (an example) throttle position. Open loop would start from 61% to 100%.

 

The close loop tuning is predominantly aimed at FI cars not NA. Partial throttle tune is extremely important aspect of total tune. It will make the car run like it was stock boosted car from factory, smooth and transient fuelling smooth not to mention avoiding detonation or timing retard by the ecu

 

The only gains for a NA car when using piggybacks are just better throttle response & better fuel consumption which you have rightly pointed out It is more advantageous to use any ecu hack for an FI car to gain more power as opposed to their stock settings.

 

So if you have an FI car, and if the tuner talks about close loop tuning, he is not wrong. Problem is whether can he tune it properly and if the hardware is capable of delivering such results

 

And yes, you need power to make power. Fuel consumption & horsepower is a difficult topic to harmonize

[Smhomie]

I agree with you on your observations, they don't know jack.

 

Additional injectors are so passe and outdated. The ideal is to have full control of ALL injectors and not add external injectors.

 

Your fuel pump is regulated by the ecu + relay. Lower voltage = lower volume pressure. All you need maybe just a voltage regulator to the fuel pump Our recent new cars from late 2003 to present all have a returnless fuel system ie. fuel travels one way and no longer do feeback loop unlike the old days pre-2003.

 

We have an intank fuel pressure regulator which bleeds the extra pressure back to the tank even before the fuel leaves the tank. Some bleed at 43psi while other bleed at 50psi. The returnless system was implemented by automakers worldwide to comply to newer and stricter emmission standards and to avoid the uneccessary heating of the fuel itself when returning to tank from the fuel rail.

 

The return system or positive feedback loop system is preferred for an FI car as it maintains equal fuel pressure to all fuel injectors hereby ensuring consistent delivery + AFR for each firing cylinder

[Imuya]

Woohoo! Finally some decent posts in MCF! Props for you guys.

 

A quick question regarding lean AFR at cruising RPM. How lean is lean? 15.5? 16?

Will extended period of cruise at this AFR overheat the engine, or does being on the move cools the engine enables it to cruise at this AFR?

 

As for the additional injectors, have seen some JDM (JB Domestic Market) modded cars with turbos running additional injectors. The proper way to go is to get bigger injectors sized to a fuel pump with the correct pressure and flowrate?

[Smhomie]

Well, to answer your question.... 15-16:1 AFR is ok.

 

I do not know what car you drive and hence the engine design but in general :

 

1) Modern aluminium engine blocks can dissipate heat better and most of the new engine designs are based on Ultra Lean Burn architecture ie. Mark X direct injection cylinder has a lean burn design of 22-25:1 AFR when fuel cut comes in when gas pedal is released during cruise drive. High compression + Lean Burn design = efficient & powerful 2.5 V6

 

2) Modern alum. block can withstand heat more than ever in comparison to previous designs. So yes, extended travel period pose no threat to engine longevity. Even on 15 or 16:1 AFRs (for cruise & vacuum, not WOT).

 

3) Use a colder plug like IK22 or BKR7E-11X (this I assume you are on IK20 now) to prevent pre-ignition by the plugs themselves since you intend to run lean. This allows the porcelain insulator nose of the plugs to transfer heat better to the cylinder thread wall since leaner mixtures also mean higher cylinder temps.

 

Johor Malu cars can do it doesn't mean you should do it too They don't know any better or couldn't care less. I supposed they grenade their engine and it costs RM2-3k to replace? Can we do this in SG? I don't think so, the laws of economy prevents us from dabbling in stupid practices

 

Injectors are more important than the fuel pump. Calculate the proper size using the formulae shown :

 

Expected Crank hp x 0.55 or 0.45 (brake specific fuel comsumption - typically 0.55 for FI and 0.45 for NA) divided by no. of cylinders x 10.5 to get cc/min size.

 

Example :

 

250 x 0.45 / 4 = 28.125

28.125 x 10.5 = 295.31

 

So you should get 295cc/min injectors if you are getting 250 flywheel hp. But do try to get additional volume if you can as it would serve as available buffer ie 310cc size injectors, should you need more fuel at a later stage. Do not be greedy and get too big an injector size ie 450cc or you will have a hard time tuning them for idle

 

Hope that was helpful to you

[Auto_ghost]

Heat is generated from chemical reaction between petrol and oxygen. The more efficient is the reaction, more heat is generated. Peak cylinder temperature typically happens at stoichiometry (14.7 AFR for petrol). It does not mean it get hotter as you go leaner. In fact, at AFR 15-16, it

[Auto_ghost]

Transition to open loop at 60% throttle sounds like EJ20 behavior. Different ecu transit to open loop on various conditions, can be and/or throttle, MAP, RPM, etc.

 

For TC engine, we typically want about 12.5 AFR during turbo spool up. In many cases this can happen when the original ecu is still in close loop and wants to run 14.7. Using the piggyback

Edited March 27, 2008 by Auto_ghost

[Imuya]

Hmm...that's something new. Never knew the reason why always hear engine will piang if run too lean.

 

So am i right to say that at AFR of >14.7, the engine gets hotter because there is no excess fuel to carry away the heat, compared to when running rich, the excess fuel helps to cool the engine by carrying away heat in the fuel molecules?

[Smhomie]

This is relatively new to me... Its something my course professor at Texas A & M automotive module had taught differently to our cell.

 

Based on my own observations using a wideband and EGT (cylinder) probe on both NA and FI cars in both countries ie US and Singapore and using RON 87,91,92,93,95,98,116 cylinder temps DO GO UP in lean burn ratios. We learn about MBT (minimum timing for best torque) amongst other topics in EFI.

 

Initial engine load will see temps on the rise if on lean burn. It will stabilise during cruise.

 

You are right to say heat is generated, but latent energy is what its all about.

 

No, more efficient reaction does not create more heat. ie. Retard timing creates higher EGTs or very rich mixtures can also create high temps but you do not achieve ideal combustion.

 

14.7:1 is the ideal chemical ratio for complete combustion based on weight. Are you also aware of the different AFRs of different RON fuels? 14.7 is not universal

 

Sorry if I offend you but I cannot agree with your opinions. To each their own and pls no arguments on this thread in defending ones pride. This thread is to allow fellow readers to perhaps understand the 4 stroke engine a little better and this would ultimately lead towards shop tuner independence

 

I'm just stating what I've understood.

[Smhomie]

As I have said in my post, the TPS values was an example. I do not drive a Subaru. I'm allergic to that jalopy.

 

The factory ecu is much more powerful and complicated than we think Even Motec with Motorola 32bit is nothing compared to your stock ecu. So it isn't "retarded" as you suggested. It has to look up the algorithm table and cell values based on the CAN loop feedback of coolant temp, TPS, MAF, AIT, RPM, oil temp, engine load to determine fuelling needs + variable valve cam technologies involved in the equation.

 

For FI application, an added module program controls a PWM boost solenoid that modulate the internal wastegate. This adds in the equation. Companies like Vextronic Mastertech are paid a hell lot of money for automotive ECU solutions to major manufacturers.

 

Your observation on STFT and LTFT is correct. AFR of 12.5 is not universal on FI cars, some run better on 13.5 and others 11.0. Throttle response is one consideration when factory tunes according to turbine compressor sizing and spooling characteristics

 

Standalones as I have mentioneed earlier are better equipped to reinstate all parameters but involve too much work and time and still won't run like stock factory car. Thats the honest truth

[Smhomie]

Partially correct and you are on the right track excess fuel DO carry heat away but only to a certain extent before it outlives its thermal usefulness for heat absorption.

 

You can run leaner but only to a certain upper limit threshold.

 

As stated earlier by AG, if lesser heat is created running leaner, then shouldn't we all be running at 18-20:1 AFR? this would save us all alot of $$ right?

 

He was half right to state engine runs cooler at cruise speed, what he failed to clarify was that the Intake Air Temps would have also accordingly dropped to 33c from 50c if driving at a constant speed of say 90-100km/h at ambient temps of say 30c

 

Driving off from a dig and ambient temps do make a difference in the density of air ingestion by the combustion chamber as compared to constant velocity, hence the need to adjust AFRs to suit your performance palate.

[Auto_ghost]

It

Edited March 27, 2008 by Auto_ghost

[Auto_ghost]

The original ecu is

[Auto_ghost]

Lean burn is a way for fuel economy but it can only push to certain extend that power drop is too much and it

[Auto_ghost]

When AFR goes richer than about 12, the extra fuel is not burned, but instead, it vaporized and absorb cylinder heat. However, too rich mixture also weaken the power. The petrol combustion consists of two major steps:

 

Step 1 : Petrol + oxygen to form water and carbon monoxide

 

Step 2 : Carbon monoxide + oxygen to form carbon dioxide

 

Majority of the heat energy is generated during the second step. If we have too reach mixture, the larger amount of petrol would had consumed almost all the oxygen available and it

[Smhomie]

Yes, it's slower since the 02 sensor in local cars are typically narrowband (0-1v) as compared to factory wideband in US because of CARB (0-5v). Response time and resolutions are different.

 

Yes, you are right in the factory boost controller concept.

 

Yes, 12.5 AFR is the textbook figure most books and websites like to use but bear in mind too the advanced developments in engine design since then. But yes, you can use the value as a starting yardstick.