RE:COLD AIR INDUCTION

jo proffi

jo proffi

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RE:COLD AIR INDUCTION

I've observed the sometimes heated debate on cold air induction,and am left puzzled about one thing.
Why is the inlet manifold heated on the fuego,and would this have much relationship to intake temp.
 
jo proffi said:
I've observed the sometimes heated debate on cold air induction,and am left puzzled about one thing.
Why is the inlet manifold heated on the fuego,and would this have much relationship to intake temp.
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The inlet manifold is heated on a Fuego (and other carby models) is to keep the fuel vapour from getting too cold, which leads to smoother running and prevents icing of the carby in cold damp conditions. The Fuego also has a thermostatic valve on the aircleaner (sometime erratic working) which also directs warmer air from the manifold into the aircleaner in very cold temperatures. In normal conditions the coolant heated manifold would not have much effect, but it does come into effect when the weather is cool or the car has made a cold start. Overall, influencing the coolant heated manifold by say placing a blocking thermostat on it (if there was such a thing) would probably have only a minimal effect.

Sometimes due to poor maintenance the coolant heated carby jacket corrodes up, leading to poor running when cold, and conking out in cold damp conditions because of the carby icing up from the water vapour in the air.

However on a modern fuel injected system, the fuel is generally injected right at the inlet valve and goes straight into the combustion chamber, so there is little chance of the car conking out on cold evenings. The denser air in cooler temperatures, leads to a likely increased fuel mixture from the engine management system and the car generally performs better. Probably more marked with turbo cars which run a lot better in cooler temperatures with dense air (as long as the altitude is not too high!).
 
Agree with Simon here. Seems like in multi point fuel injection, cold air induction provides a larger charge and power ;the ECU adjusts the fuel to maintain the correct air /fuel ratio to allow the cat to operate efficiently and reduce pollution.
Carby and single point injection can be adversly effected by the low air temp. If the evaporated fuel vapour reverts to a liquid and depending on inlet manifold design can lead to large variations in fuel supply and air/fuel mix to individual cyclinders which cause rough runnning and poor economy. :2cents:
 
Ok, so what about a car which has k-jet continous injection? Does it gain any benefit from cold air intake?.
I'm specifically thinking PRV engines here, on the R25 v6 the air intake is a rubber pipe leading down into the space between the bumper and the wheel arch. The pipe has a series of holes where it crosses the exhaust manifold.
I've often thought of blocking most of these holes to lower the intake temperature, but can't really see any benefit because the kjet doesn't measure intake air temperature and can't adjust the mixture based on temperature.
Will a cold air intake have any beneficial effect on the running of the engine under these conditions?. :confused:
 
Dave seems like you are in the perfect position to do a test and report back.
If you are in the lower Sth island you should have no problem getting some cool air for the test. :)
 
Dave, K-Jet should definitely benefit from cooler intake air. Even though some versions don't have intake air temperature sensors (I think KE-Jet was the first) the flow metering flap would deflect further because of the density of the colder air (the air having greater inertia because of its increased density). Therefore, it will provide more fuel to go with the greater oxygen in the charge, despite not having an air temp sensor.

Stuey
 
I was flicking through an old book earlier and just happened to read a paragraph on the 5 Turbo. According to Renault Engineers, there was a 1bhp loss in power for every 1 degree celcius increase in intake temperature, which was the reason why they used an intercooler on the 5 Turbo. No idea how it relates to the topic, but the temperature change I'd say would be less important for normal non forced induction, however the 5 Turbo is also fitted with K injection.
 
Simon said:
No idea how it relates to the topic, but the temperature change I'd say would be less important for normal non forced induction, however the 5 Turbo is also fitted with K injection.
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Would have thought that it is the same for a normally aspirated engine. A given weight of fuel requires a given weight of oxygen for complete combustion. Increases in temp. at a given pressure mean that both liquid and gas volumes increase. Gases far more noticably -throw a balloon in the fridge if you want to verify this - think it is something of the order of 10% between 0 degrees and 25 degree.
Elecronics now use a combination of flow(volume/time)sensors, oxygen sensors and tempurature sensors to enable the computer to tweek the injectors for maximum efficiency of burning.
As an aside petrol companies were pressured to change the way they sold fuel to servo's because of the volume problem. Years ago they would fill a tanker and the driver would sell it along his route - on a warm day he would still have some left over and could offer this at a very good rate (nudge, nudge, wink, wink) to his favourite operators on the return journey. Fitting load cells rather than volume measuring devices put an end to this practice. Of course with Bluetooth they now have the capability of telling the truck, not the driver how much fuel to put into any given servo, although I don't know if they have gone down this route.
 
I'm trying to work out how the fuel metering flap works with forced induction (ie. in the case of the 5 turbo)

My understanding of it is that the spring loaded flap lowers due to the vacuum created by the motor - if you apply forced induction, wouldn't that just push the flap to the bottom of its travel, thereby negating it's purpose as a fuel metering device?

Or do they just fit a stronger spring? ;)
 
Roughly speaking 5deg c change in air temp = 1% change in power. It's the same for NA and turbo/ supercharged engines, only turbos / schargers heat the air a lot over ambient so there is more to gain.
 
Europa said:
I'm trying to work out how the fuel metering flap works with forced induction (ie. in the case of the 5 turbo)

My understanding of it is that the spring loaded flap lowers due to the vacuum created by the motor - if you apply forced induction, wouldn't that just push the flap to the bottom of its travel, thereby negating it's purpose as a fuel metering device?

Or do they just fit a stronger spring? ;)
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The spring loaded flap will deflect a certain amount for a given air flow. It can't tell if it's getting sucked or blown, it just 'feels' a mass flow of air.
 
GavinS, yes, i will do some quick measurements of intake temperature, I'm still not totally sure how the car will react, or even what sort of temperature change to expect (5-10*c would be good).
From the points so far, it seems that geater fuel flow is expected- I'll have a look at that too - the trip computer on the r25 has a diagnostic function which gives fuel flow in L/h (even on a "gallons" car).
Europa, the flap on k-jet is counterbalanced in the airflow and "damped" by the fuel pressure against the top of the control plunger. Thus it reacts in the same way in a N/A car as in a turbo- the fuel pressure regulates.

Farmerdave
 
Dave I would not expect too much of a change in performance by blocking the holes in the air intake but evry little bit helps of course. The reason for the holes in the first place would be due to the lower ambient temps in the home market the car was designed for to help with cold starts. The CO level is adjustable with Kjet, I gather your 25 is pre cat converter?
 
Europa, the K-Jet flap raises with air flow. There's actually no spring - the fuel pressure doesn't just damp the movement, but causes it to spring back too. I assume the 5 uses a suck through setup, but I can't picture the engine bay...
 
Stuey said:
Europa, the K-Jet flap raises with air flow. There's actually no spring - the fuel pressure doesn't just damp the movement, but causes it to spring back too. I assume the 5 uses a suck through setup, but I can't picture the engine bay...
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Thanks for the advice guys.

Think I'll just bolt mine back on after my engine rebuild and hope it keeps working ;)
 
GavinS said:
The CO level is adjustable with Kjet, I gather your 25 is pre cat converter?
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Yes, no cat, leaded petrol car. K-jet on the v6 is the basic spec and has few of the electronic extras used on Ke and later versions of kjet.
Farmerdave
 
The CO level is adjustable on the basic K-Jet, but just in the same way it is on many fuel systems - by adjusting the idle mixture only. There's a hole in the unit where you insert a long key, from memory, to turn a screw. I think it just works like a carby in this respect (either adjusting fuel or air through a port) - it's been a long time since I had a K-Jet car (14 years or so).

Stu
 
Just to follow up, the temperature change resulting from blocking up the hot air holes is in the order of 2*c lower at idle, with engine at normal temperature and hot manifolds. This is measured with a pair of thermistor sensors, ex. egg incubator, 16*c ambient. Some improvement, but not really the sort of change I was expecting :confused:
The trip computer isn't sensitive enough to pick up any difference in GPH.

On a side note, one of the R25 RTA books shows an air preheater in the cooling system diagram- for really cold countries maybe?

Farmerdave
 
Good feedback Dave, an additional thought without knowing the size of the blocked holes would be if the airflow has been reduced in the process? Openings closer to the throttle body would flow a higher percentage of air and with them blocked the overall resistance would increase. May diminish any gain from closing the holes, who knows? :2cents:
 
GavinS said:
Openings closer to the throttle body would flow a higher percentage of air and with them blocked the overall resistance would increase.
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Good point, I'm not sure to go about testing this (airflow speed vs. volume with extra holes). Would there be any ram effect with the holes blocked?. any ideas?
The holes are (from memory) about 13mm diameter. :renplak:
 
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