Turbo Diesel Quicker Than Usual??

HPT

Hi All,

I meant to post this a week or two ago...

Recently (in Dublin at least) we've had consistently warm temperatures in the low to mid twenties. It's also been pretty humid at times.

I was driving my jeep, Landcruiser D4D, one night and noticed it was a bit quicker than it had been in the few days / weeks earlier. Nothing that would blow your socks off of course but it was noticeably quicker.

That particular evening the temperature had dropped to about 12-13 degrees after a fair bit of rain. Nothing else with the jeep had changed. Same load, same fuel etc.

So I'm wondering if a 10 degree drop in temperature could have caused a noticeable improvement in performance and is that the kind of benefit people get or expect when installing large front mounted intercoolers?

Lex Luthor

I think cooler air into the engine burns better

I've always noticed that my cars run better in winter time when its about 5-6 degrees outside

Gumbo

its the colder air temps being passed through the intercooler and hence feeding the turbo with colder more explosive air = more power (or at least recovery of the standard power thats lost due to high air temps)

thats why so many cars can be upgraded with cold air scoops etc etc the bonnet scoop on an impreza is actually there for a reason

Tefral

HPT wrote: »

Hi All,

I meant to post this a week or two ago...

Recently (in Dublin at least) we've had consistently warm temperatures in the low to mid twenties. It's also been pretty humid at times.

I was driving my jeep, Landcruiser D4D, one night and noticed it was a bit quicker than it had been in the few days / weeks earlier. Nothing that would blow your socks off of course but it was noticeably quicker.

That particular evening the temperature had dropped to about 12-13 degrees after a fair bit of rain. Nothing else with the jeep had changed. Same load, same fuel etc.

So I'm wondering if a 10 degree drop in temperature could have caused a noticeable improvement in performance and is that the kind of benefit people get or expect when installing large front mounted intercoolers?

Same with petrol cars and particularly affects turbos, the lower the temperatures the more power you get. At lower temps air and fuel is more dense and thus more gets into the engine.

A common problem that is experienced in the modified car world is "Heatsoak" this happens when you swap out the filter box for the open induction kit style filter. When the engine is warm it heats the air around it and this hotter air gets in and saps power. So the idea is to have the intake as close to the front of the car as possible and also as far away from the engine as possible.

With intercoolers a general rule was you gain about 1 horsepower for every 10degrees drop in temperature. How true this is im not sure...

gofaster_s13

kceire wrote: »

its the colder air temps being passed through the intercooler and hence feeding the turbo with colder more explosive air = more power (or at least recovery of the standard power thats lost due to high air temps)

thats why so many cars can be upgraded with cold air scoops etc etc the bonnet scoop on an impreza is actually there for a reason

Explosive air :eek::eek:

Saab Ed

gofaster_s13 wrote: »

Explosive air :eek::eek:

You get a lot of it in here thats for sure.......sorry.......sorry

Mr Benevolent

Hmmm. Could you get one of those plug-in minifridges (or an air conditioning unit) and stick it in front of the intake? :D

gofaster_s13

Confab wrote: »

Hmmm. Could you get one of those plug-in minifridges (or an air conditioning unit) and stick it in front of the intake? :D

Has been tried in various ways from simple systems like packing around the intercooler with ice or spraying CO2 accross the intercooler core to full on refrigerated intercooler pipework and core

ianobrien

The reason for the "quicker" than usual is down to air density.

Air density is dependent on atmospheric pressure and temperature (ideal gas law). Atmospheric pressure generally varied from 960hPa to 1030hPA in Ireland, and during the summer months is quite steady and is typically 1000 to 1030hPa. This can be seen every night on the weather forecast after the 9 o'clock news.

This means that air pressure is generally not much of an influence and can be considered to be constant for the purpose of this demonstration. Air temperature can be shown to be of influence on air density as a look at Steam Tables (a useful engineering book that has physical properties listed, in much the same as Log Tables has for maths) can show.

Below is an extract from Steam tables, showing the relationship between air temperature and air density, assuming a constant pressure (of 1013hPa)

Temperature Density of air
in °C ρ in kg·m−3
−25 1.423
−20 1.395
−15 1.368
−10 1.342
−5 1.317
0 1.292
+5 1.269
+10 1.247
+15 1.225
+20 1.204
+25 1.184
+30 1.164
+35 1.146

As you can see, air density changes with temperature.

Now the benefit for us is twofold. First, the more dense the air, the more oxygen is in it per unit volume (basic chemical stoichiometry) and the second in a lower intercooler outlet temperature, meaning more dense air, meaning more oxygen per unit volume.

The reason for the lower intercooler outlet temperature is basically the cooler air is cooling the intercooler more (basic heat transfer). This cooling of the intercooler outlet temperature gives a more noticeable effect to the drive than the cooler inlet temp in a normally aspirated car . This is because the intercooler outlet temp can be easily 40 to 50°C, so any drop in temp is of greater benefit due to the greater volume of air compared to a non-turbo car.

When manufacturers & rolling road operators are quoting vehicle horsepower, they correct their readings for atmospheric temperature and pressure to get a comparison figure.

Bet your sorry you asked......

Dartz

Confab wrote: »

Hmmm. Could you get one of those plug-in minifridges (or an air conditioning unit) and stick it in front of the intake? :D

No...

Basic thermodynamics prevents this.

It will take more energy from the engine to continuously cool the air, than you'd get back from the improved combustion efficiency.

Dry-ice will do it... because it's been cooled elsewhere, but running cooling off the cars own electrics won't

Mr Benevolent

Dartz wrote: »

No...

Basic thermodynamics prevents this.

Meh. Thermodynamics is a crock of shyte. Take entropy for example. Everything is getting more random, right?

Right.

So why aren't there Ford Fiestas appearing randomly in space?

(I do understand your point though. Just a semi-scientific rant on my part)

ianobrien

One other random thought...

OP, was the Landcruiser in 4WD before and now it's in 2WD? Transmission power losses would be less in 2WD compared to 4WD.

If anybody wants to see the power loss due to 4WD compared to 2WD, I can get my hands on a Subaru Vivo, 600cc and switchable 4WD. In 2WD, it goes reasonably well, but in 4WD, it's like a snail....

HPT

ianobrien wrote: »

OP, was the Landcruiser in 4WD before and now it's in 2WD? Transmission power losses would be less in 2WD compared to 4WD.

Thanks for all the replies!

@ianobrien Not sorry at all! Thanks for the detail

Nice to know I wasn't imagining it.

Re 4WD vs 2WD...

That model of LC (it's a 2006) is full time 4WD. It can't be switched into 2WD.
It's pretty thirsty!
It has low range and you can lock the centre diff in high or low range but that's about it. I didn't get it with the lockable rear diff