It'll only work for diesels, as petrol engines run at or near a stoichiometric mix, so any extra fuel won't get burned. Unless I've got this wrong, it'd be no different to running with the choke in all the time on a petrol car with a manual choke.

I think I know how to do the sums to get the effect on power output, but I don't know how the specific weight of diesel varies with temperature. Anyone know a website or that that would give those data?

I don't think the specific gravity will change hardly any with temperature (assuming it doesn't freeze or evaporate!) For the few liquids recorded in my copy of Perry's Chemical Engineers' Handbook, the variation in density (sg) ranges from about 0.008% and 0.015% per degC. These are liquid elements, admittedly, but I suspect it has more to do with the thermal effects of injecting cold fuel into the cylinder...

I don't think the specific gravity will change hardly any with temperature (assuming it doesn't freeze or evaporate!) For the few liquids recorded in my copy of Perry's Chemical Engineers' Handbook, the variation in density (sg) ranges from about 0.008% and 0.015% per degC. These are liquid elements, admittedly, but I suspect it has more to do with the thermal effects of injecting cold fuel into the cylinder...

Heres your statement

Heres my head

Heres your statement

Heres my head

I don't think the specific gravity will change hardly any with temperature (assuming it doesn't freeze or evaporate!) For the few liquids recorded in my copy of Perry's Chemical Engineers' Handbook, the variation in density (sg) ranges from about 0.008% and 0.015% per degC. These are liquid elements, admittedly, but I suspect it has more to do with the thermal effects of injecting cold fuel into the cylinder...

Well, I think the effects of this mod are pretty much directly proportional to the change in SG, so, even if the ECU allows a ridiculous range on non-error values of fuel temperature, that would indicate that a change in believed fuel temperature of 100Cdegrees would give me an maximum increase in power output of 1.65bhp!

I'm struggling to keep up, too!

i love the tech talk...i think i got lost there also.....:confused:

A certain mass of fuel contains a certain amount of energy.

The volume that that mass occupies varies directly with temperature (assuming we remain in the liquid state).

Fuel injectors inject fuel by volume, not mass (with me so far)?

So, if we tell the ECU the fuel temperature is different to what it is, it will inject a different volume of fuel, in order to obtain a certain mass.

The difference between the fuel mass which should have been injected, and that which has actually been injected, is the amount of extra energy which is available in the cylinder. (still with me?)

Ap0gee kindly supplied the likely range of change of specific gravity with temperature of a fuel. I took the "best case" value (for the mod) of 0.015% increase in volume per Celcius degree of temperature increase. I then multipled that figure by 100 (easy to do sum), and by the nominal output of my car (110bhp). (make sense now?)

I'll have to read it 3 or 4 times, but it beginning to make sense. Thanks on behalf of all us less educated folk.

As far as this mod goes my understanding of it is that the mod doesn't base itself on fuel temperature it interfers with the coolant temperature signal on pins 2 and 3 and fools the ECU into thinking the engine is colder therefore the ECU injects more fuel more by increasing the injector opening time. The fuel temp , as far as far as this mod is concerned, is irrelevant, the SG of the fuel will still behave over its normal operating range as you are not playing around with actual fuel temp or its signal.

just my take on how it works..

I still think it's more to do with the specific heat of the fuel. According to this table, the specific heat of diesel equates to 0.32kJ/kg.degC, so assuming each injection cycle puts in 0.1g of fuel and a 10 degC temperature difference, there would be 0.00032 kJ less energy available per injection, which (I think) works out at about 15bhp at 3000rpm.

AIUI, that's about the kind of bhp increase a resistor mod will give you. But I could be (and probably am) wrong...

A certain mass of fuel contains a certain amount of energy.

The volume that that mass occupies varies directly with temperature (assuming we remain in the liquid state).

Fuel injectors inject fuel by volume, not mass (with me so far)?

So, if we tell the ECU the fuel temperature is different to what it is, it will inject a different volume of fuel, in order to obtain a certain mass.

The difference between the fuel mass which should have been injected, and that which has actually been injected, is the amount of extra energy which is available in the cylinder. (still with me?)

Ap0gee kindly supplied the likely range of change of specific gravity with temperature of a fuel. I took the "best case" value (for the mod) of 0.015% increase in volume per Celcius degree of temperature increase. I then multipled that figure by 100 (easy to do sum), and by the nominal output of my car (110bhp). (make sense now?)

Which is why an engine use's less fuel on a hot day (or have I just made a tit of myself)

As far as this mod goes my understanding of it is that the mod doesn't base itself on fuel temperature it interfers with the coolant temperature signal on pins 2 and 3 and fools the ECU into thinking the engine is colder therefore the ECU injects more fuel more by increasing the injector opening time. The fuel temp , as far as far as this mod is concerned, is irrelevant, the SG of the fuel will still behave over its normal operating range as you are not playing around with actual fuel temp or its signal.

just my take on how it works..

If it's messing with the coolant temperature, it's just the fleabay resistor mod again, isn't it?

I still think it's more to do with the specific heat of the fuel. According to this table, the specific heat of diesel equates to 0.32kJ/kg.degC, so assuming each injection cycle puts in 0.1g of fuel and a 10 degC temperature difference, there would be 0.00032 kJ less energy available per injection, which (I think) works out at about 15bhp at 3000rpm.

AIUI, that's about the kind of bhp increase a resistor mod will give you. But I could be (and probably am) wrong...

We're not changing the actual temperature of the fuel, so the specific heat energy is a constant.

Which is why an engine use's less fuel on a hot day (or have I just made a tit of myself)

Not as such, although it's more complicated than that. It would be, wouldn't it.

On a hot day, you get less air into the engine (irrespective of fuel used and natural or forced induction) because air expands markedly with small changes in temperature (at least one order of magnitude more than liquid IIRC, so maybe 0.1% rather than 0.01% per Celsius degree). With a diesel engine, this is further complicated by the fact that "summer" diesel is chemically different to "winter" diesel, and burns better, so you need less fuel to achieve a given power output.

LOL at this thread and this mod

SIN BIN

Not as such, although it's more complicated than that. It would be, wouldn't it.

On a hot day, you get less air into the engine (irrespective of fuel used and natural or forced induction) because air expands markedly with small changes in temperature (at least one order of magnitude more than liquid IIRC, so maybe 0.1% rather than 0.01% per Celsius degree). With a diesel engine, this is further complicated by the fact that "summer" diesel is chemically different to "winter" diesel, and burns better, so you need less fuel to achieve a given power output.

Ah I see, kind of

Thanks for the retard versions

Being able to explain something complex to novices is the real test of whether or not you understand it yourself, so no problem.

Not as such, although it's more complicated than that. It would be, wouldn't it.

On a hot day, you get less air into the engine (irrespective of fuel used and natural or forced induction) because air expands markedly with small changes in temperature (at least one order of magnitude more than liquid IIRC, so maybe 0.1% rather than 0.01% per Celsius degree). With a diesel engine, this is further complicated by the fact that "summer" diesel is chemically different to "winter" diesel, and burns better, so you need less fuel to achieve a given power output.

That's the thing I don't get: the effect of temperature on air density is massive, hence the need to measure it to ensure peak performance. But the effect of temperature on fuel density is so small as to make no difference (certainly within the bounds of normal environmental temperatures). That table I linked to shows that the only thing that varies to any great degree with temperature is viscosity, but then once the fuel's in the injector (in PD engines anyway), it gets compressed to such a massive degree that I can't imagine its inlet temperature will be particularly relevant... :confused:

That's the thing I don't get: the effect of temperature on air density is massive, hence the need to measure it to ensure peak performance. But the effect of temperature on fuel density is so small as to make no difference (certainly within the bounds of normal environmental temperatures). That table I linked to shows that the only thing that varies to any great degree with temperature is viscosity, but then once the fuel's in the injector (in PD engines anyway), it gets compressed to such a massive degree that I can't imagine its inlet temperature will be particularly relevant... :confused:

Agreed; that's why I wanted the expansion co-efficient. I could use that to work out how much extra fuel you'd add, and hence how much extra power you could develop (in a diesel, and on part-throttle; on full throttle you may not be in a lean burn any more).

so.....the fuel mod makes the ecu think fuel is hotter.....[less mass] so injects more volume to make up for perceived loss of mass!!......... more bph!

the opposite then.....if we fool the ecu thinking fuel is colder then less volume would be injected...less bhp..but more fuel economy![great for around town]

or am i an idiot altogether??:confused::eek:

The crux of the technical discussion is that the chemists believe that the theory is correct, but some practical engineering and computer programming indicate that the claims for the mod are greatly exaggerated. You might be able to spoof the engine into reducing power, as described, but only fractionally, and I'd not want to make any claim that reduced power would actually mean reduced fuel consumption, simply because you'd probably find yourself having to accelerate harder and/or for longer to achieve "keeping up with the traffic".

Guys , just going back to the Evry mod ,the idea is that the resistor mod fools the ECU into thinking that the COOLANT[ ie. the engine] is colder NOT the fuel .

The low resistance caused by the presence of the resistor in the 'resistor mod box' fools the ECU into thinking the engine is still cold like at a cold start up and injects fuel for a longer time period [higher vol of fuel] . Measuring / bu66ering around with FUEL temps has nothing to do with this mod.

EDIT: Beginning to wonder on this point.... since the PD ones plug into the fuel temp sensor. Perhaps pins 2 and 3 come from the fuel temp sensor on the non-pd engine as well..anyway as far as this mod goes its still just a resistor inferferring with a temp signal.

The Evry mod is a resistor mod but the e-bay ones are just a resistor in a box and they are active all the time they are plugged in and can give engine management warning light issues. The whole purpose of the evry mod is to allow the resistor mod to be activated/deactivated at will by a switch on the dash..it is in effect a fancy on/off switch so you don't have to run with permanent over-fuelling....you just use it when you need it and don't have to fart about plugging/unplugging the box..

The e-bay resistor mods also have to be fitted inline with the connectors on the fuel pump ..easy to spot by plod or whoever.,wereas the evry mod you only have to run two wires to piggyback the pins 2 and 3 on the existing connecting block [if you are being a bit naughty re. insurance / plod you can bury them inside the existing loom and are dfficult to spot unless you are actively looking for them.] This method of wiring also makes it easier to site and use a variable resistor that you can adjust from the dash without going under the bonnet every time you want to make an adjustment.