fueling and lean running

[jagman]

I have an idea for fueling the tuned supras at higher boost levels,and would like to see if anyone can fault the thinking;

As we know running the engine lean can be catastrophic,and running large injectors problematic with control of them at the lower rpms and expensive with fuel rails,ecus,etc

What if say 2 extra injectors were fitted in the maniflold equi-distant to allow an even fuel spread across the manifold (a simple tap and thread job) these extra injectors are not pulsed controlled ones but cold start injectors which are simply on or off as used by a variety of engines (12volt switched) the switching of these injectors in turn controlled by a boost switch which is set to say 14 psi (1 bar) ,so at high boost the cold start injectors open to send atomised fuel to the manifold (cold start injectors are available in a variety of sizes so lets just say 400 cc each) this extra fuel would enrichen the mixture for high boost conditions,but the lambda sensor would back off the standard injectors if it saw too rich so the stock ecu would still control within its parameters and thus you have extra fuel for the extra air from a single turbo - cold start injectors not prone to failure because they do not pulse only open -opinions please am I daft or is it feasible?

[b_have]

Old school stuff. Yes, it works, but effectively controlled larger injectors are better. Also, dumping a load of fuel in at (say) 1bar may be effective at 1bar, but less so at 1,1bar and so on. Remember, the oem lambda sensor only corrects fueling in closed loop (not on boost)

[SUPRALOOPY]

I have an idea for fueling the tuned supras at higher boost levels,and would like to see if anyone can fault the thinking;

As we know running the engine lean can be catastrophic,and running large injectors problematic with control of them at the lower rpms and expensive with fuel rails,ecus,etc

What if say 2 extra injectors were fitted in the maniflold equi-distant to allow an even fuel spread across the manifold (a simple tap and thread job) these extra injectors are not pulsed controlled ones but cold start injectors which are simply on or off as used by a variety of engines (12volt switched) the switching of these injectors in turn controlled by a boost switch which is set to say 14 psi (1 bar) ,so at high boost the cold start injectors open to send atomised fuel to the manifold (cold start injectors are available in a variety of sizes so lets just say 400 cc each) this extra fuel would enrichen the mixture for high boost conditions,but the lambda sensor would back off the standard injectors if it saw too rich so the stock ecu would still control within its parameters and thus you have extra fuel for the extra air from a single turbo - cold start injectors not prone to failure because they do not pulse only open -opinions please am I daft or is it feasible?

 

my mate has this setup on his fester..very good but no control:)

[jagman]

If you consider the times the ecu is in open loop except during start, ie WOT it is still controlling the injectors pulses,sothe additional injectors only need finer control, the first refinement is to use the feed fuel pressure to the coldstart injectors via a rising rate regulator thus they have greater flow at higher boost pressures,due to them being open at all times and not pulsed the effect on fuelflow is greater on them than normal injectors, so at 1 bar you would get x flow but on rising boost x+

Bearing in mind the low cost of components to further refine ;2 boost switches could be used one at 14psi and one at16psi each controlling its own injector. if it came to it 6 pressure switches could be used controlling 6 injectors at 1 psi intervals 14-20psi for testing purposes an AFR gauge and a few runs would be required to fine tune

[Ian C]

It sounds like a nasty halfway house towards proper staged injectors and a nod towards mechanical fuel injection.

 

You've got an indiscriminate dump of fuel, or an over-complex system of staged pressure sensors, neither of which are tuneable short of changing the fuel pressure or the size of the injectors, and all of this completely bollixes up the mapped engine management of the primary injectors because the outcome is hugely variable. Troubleshooting and mapping would be a nightmare.

 

You can control pretty big injectors with a piggyback, and massive ones with a standalone, if your power requirements go beyond that then a) I'd say you aren't interested in 1500rpm drivability any more and b) you don't want to be fuelling your incredibly expensive 1200bhp engine via cold start injectors or some other nonsense solution. You'd have a 12 injector rig with an ECU that can run them staged.

 

So I'd say it's not feasible but you aren't daft for bringing it up because we all like a good techie chat

 

-Ian

[jagman]

It not quite an indescriminate fuel dump ,its at a prescribed boost pressure and a quantified amount of fuel , the ecu as standard does a fine job of controlling injectors based on its parameters ,looking at throttle,speed,rpm,air flow etc ,it throws out economy when you floor it and maps accordingly but when you have modified the turbo ,cats,etc the standard injectors cannot cope with the increased air flow but only during the higher boost conditions at the higher rpms until then it is fine,large injectors also have their downsides rich running at the lower rpms ,foulling plugs,off idle stumbles,washing bores etc

I am not looking at a super high horsepower monster but say around 450-500 bhp where the stock injectors are only just light of the mark at the high boost and high rpm levels and adding the extra 50-100 bhp of fuel to match the extra air within the reqd afr range ie safe no I agree not precise but safe and there is quite a safe tolerance band to play erring on the rich side

[sdavies]

Where do the water injection systems fit into all tihs?

[Kranz]

Water injection can reduce the need for huge amounts of fuel (used to create over rich mixtures at full power in a crude detonation prevention method).

 

The excess fuel (down as low as 9 AFR) is used to slow the combustion flame path to prevent detonation. When water is added as well (up to almost the same volume as fuel and with methanol added 50/50 to the water for even better quenching/burning characteristics) the excess fuel is not needed, so the engine can run with nearer chemically correct air to fuel ratio. Its all to do with flame propogation, burn time, wavefronts and the speed of sound.... so I'm told

 

So in essence a good H2O injection system means you'll need slightly smaller injectors & will use less fuel at WOT on high boost to make the same power..... but who wants the same power when you can have more???

[jagman]

its a tech forum for discussion and any discussion can promote knowledge,so here we go ; the stock system control the injectors by voltage pulses the duration of which determine the time they are effectively open for and hence fuel flow ,for accurate fuel flow the fuel pressure must be tightly controlled ,first drawback of aftermarket fpr,s they can fail or become erratic and require a pressure sense line and ultimately its another link in a chain, The voltage pulse to the injector must be a "clean" signal ,that is one with constant voltage (bear in mind the cars voltage is constantly changing with load) and no interference (emi) The stock ecu does this (it monitors the battery voltage-please someone correct me if I am wrong) it also is well grounded and uses screened cables and internal bonding and impedence matched to the stock injectors ,the use of an aftermarket piggyback ecu firstly can corrupt the ecu signals both input and output,they are also another source for emi,grounding issues,and poor connections, another link in the chain- If we accept that the stock injectors "max out" ie the pulses to the injectors reach a speed that will not allow further opening/closing ,when does this happen? and what ecu signals determine this? TPS,RPM,MAP/MAF,TEMP would be the main culprits I suspect,and for how long do these conditions remain? I would think it is the point of boost cut plus a tad of safety margin,-thats the point we all overide:d to be continued...

[JohnA]

Jagman, what you propose does work, in fact it was the way it was done with older turbo conversions. But it is rough, and cylinder distribution is anyone's guess. It could vary by a lot more than the naked eye can see.

You will only see an averaged-out figure at the oxygen sensor, but a 12:1 there could be hiding 14:1 in two cylinders, 10:1 in two others and 12:1 in the remaining two.

So flame speed will be quite different in they cylinders, and the power they'll be making will be varying a lot (not a happy crank)

The iginition requirements will also be different, but they'll all be fed the same timing anyway.

 

The same stands for non-port Water Injection by the way, the (effectively) timing retardation it provides can vary a lot among cylinders.

 

On a supra engine I'd go for a bit bigger injectors controlled properly. At least the fuelling will be uniform.

[bignum]

I think thats cleared that 1 up then johna,

[jagman]

yes John I agree with the roughness of the mixture , but the stock ecu during large accel periods also gets rough and I think multi fires the injectors,the boost pressure /flow also gets unlinear and has rapid changes,and the rpm changes quicker,Yes a quality standalone can cope,but with such large variations and airflow speeds exceeding the design limits of the head/manifold/valves/cam even that will get out of shape ,its not that different from adding 100 shot of nos ,kinda best guess,the point is the cost of injectors,pumps,fuel lines,ecu upgrade,fuel rail,fpr,mapping,etc will run into many thousands of pounds,and is only required at the very high boost levels,not used that often,and these are road cars with the odd drag run, even with the £1000s spent on fuel/mapping etc they still fail and or can have reliability/longevity issues there are not many willing or able to justify thousands spent on a 13 year old car just for the odd times they nail it,sometimes engineering excellence is not required and the primative system that works is good enough,one glitch with the most advanced system and your engine is toast anyway! it would not take much to make a simple enrichening injector variable flow with boost and give an element of refinement during the peak demand times cheaply

[JohnA]

yes John I agree with the roughness of the mixture , but the stock ecu during large accel periods also gets rough and I think multi fires the injectors

You've lost me here:blink:

,the boost pressure /flow also gets unlinear and has rapid changes,and the rpm changes quicker,

Are you talking about the FPR boost compensation?

I'm not getting this either:blink:

Yes a quality standalone can cope,but with such large variations and airflow speeds exceeding the design limits of the head/manifold/valves/cam even that will get out of shape

What exactly exceeds the design limits of the head?

manifold? Valves? Cams?

Are you talking about revving at 15K rpm? If so, yes, there are design limits --- mechanical stresses and such.

But more boost doesn't really push any design limits on these components, not before we start talking silly boost numbers.

 

A different balance has to be struck perhaps, but what design limits are we talking about here?

 

,its not that different from adding 100 shot of nos ,kinda best guess,the point is the cost of injectors,pumps,fuel lines,ecu upgrade,fuel rail,fpr,mapping,etc will run into many thousands of pounds,and is only required at the very high boost levels,not used that often,and these are road cars with the odd drag run, even with the £1000s spent on fuel/mapping etc they still fail

 

I run on stock fuelingeverything mate, and still have a healthy headroom.

I was careful enough to start with a UKSpec, exactly for this reason.

 

..not many willing or able to justify thousands spent on a 13 year old car just for the odd times they nail it,sometimes engineering excellence is not required and the primative system that works is good enough,

I totally agree.

You don't need a tank full of race fuel just because may go full boost for 30 seconds. You want the extra octane (and fuel) just for those 30 seconds!

That's what I do.

Smart people start by eliminating the need for silly extra fuel in the first place. I ain't running 11:1 or 10:1, no way, that is pure waste and stupidity. I see anything richer than 12:1 as a pathetic attempt to cool the combustion chambers.

Fuel is not very good at this task.

 

Simplicity is the mother of reliability.

[Ian C]

I can't quite work out what you are trying to say. It's reading like, and I may be wrong, that all aftermarket stuff like ECUs and FPRs is far too inaccurate and we should use a cold start injector instead ?

 

To respond to a few points you made:

If we accept that the stock injectors "max out" ie the pulses to the injectors reach a speed that will not allow further opening/closing ,when does this happen? and what ecu signals determine this?

I know when the stock injectors max out, it's pretty simple - just before 1bar of boost. (about 0.98)

 

"large injectors also have their downsides rich running at the lower rpms ,foulling plugs,off idle stumbles,washing bores etc "Bigger injectors don't per se cause bore wash and overfuelling while off boost, it's unmapped injectors that do it. Your 440's would cheerfully overfuel if their duty cycle was too high.

 

first drawback of aftermarket fpr,s they can fail or become erratic and require a pressure sense line and ultimately its another link in a chain

Well, the stock FPR has a pressure sense line as well. And aftermarket FPRs vary in quality - Aeromotive ones are used in motorsport and although I've heard of many of them being tested when a problem with the car occurs, I've never heard of one being at fault. FSE's yes

 

the use of an aftermarket piggyback ecu firstly can corrupt the ecu signals both input and output,they are also another source for emi,grounding issues,and poor connections

This is an unreasonable argument - there may be EMI, grounding issues, and poor connections with your pressure sensor setup Which would be worse as it simply wouldn't fuel and you'd never know. You can't say a botched install of a piggyback = all piggyback are inherently bad.

 

one glitch with the most advanced system and your engine is toast anyway!

This is why I've got loads of monitoring gear staring me in the face on the dash I'm even thinking of a fuel cut mechanism coming out of a det monitor...

 

I don't really think that "one glitch and your engine is toast" is a reason to use a more basic and primitive setup, that just hugely increases the glitch-chance.

 

If it's not an uber-power engine you are on about and instead just a BPU+ type thing, stick in 550's and a cheapie air fuel controller and have done with it Much more accurate and it works

 

-Ian

[jagman]

by multi fire I believe the sequential injector system ,no longer is sequential under wot /high rpm conditions and the ecu fires more than one injector at a time ,this in itself removes the fine fuel control at high demand situations, the standard system also must surely cater for the cats that are fitted and cannot add too much fuel to knacker the cats, but if cats are removed and boost levels increased the ecu does not know that there are no cats to knacker. when I say the head etc design,lets say characteristics,all the factory fuel mapping is based on the standard conditions that the head/cams/valves see at pre determined levels of boost and airflow from the stock turbo,if the car is decatted or a different turbo used the quanity of air and the rpm that it is achieved is different so larger injectors alone would be out of whack 440-550cc with a decat would surely still have fuelling errors.yes the lambda sensor reads a "delayed" reading and the fuel ratio in the chamber may be different,precission fuelling is the goal but there are tolerances what AFR variations are normal on a mapped big injector set up? these variations allow the cold start thing to be feasable

[JohnA]

by multi fire I believe the sequential injector system ,no longer is sequential under wot /high rpm conditions and the ecu fires more than one injector at a time ,this in itself removes the fine fuel control at high demand situations,

I still don't understand this point.

So are you suspecting that the ECU activates the injectors differently under high load?

...the standard system also must surely cater for the cats that are fitted and cannot add too much fuel to knacker the cats, but if cats are removed and boost levels increased the ecu does not know that there are no cats to knacker.

That's why we can pull out fuel at full load with no detrimental effect (gaining power in fact)

when I say the head etc design,lets say characteristics,all the factory fuel mapping is based on the standard conditions that the head/cams/valves see at pre determined levels of boost and airflow from the stock turbo,if the car is decatted or a different turbo used the quanity of air and the rpm that it is achieved is different so larger injectors alone would be out of whack 440-550cc with a decat would surely still have fuelling errors.

A decatted stock system is well within the ECU's range of operation.

A different turbo is most probably outside that range. The ECU expects boost from 2K rpm almost, something which no aftermarket turbos can provide. It can adjust to some degree, but still the fuelling might be on the rich side and ignition will not be advanced properly. That's why it is a good practice to shell out for aftermarket ECU with a single.

yes the lambda sensor reads a "delayed" reading and the fuel ratio in the chamber may be different,precission fuelling is the goal but there are tolerances what AFR variations are normal on a mapped big injector set up? these variations allow the cold start thing to be feasable

You've lost me again. Where does the lambda delay come in?