Steve001

iTrader: (7)

I am lead to believe that the more cold air you can deliver to the area of the induction filter the better the power response!!?

So this is the question (flame suit on)

Is it possible to redirect some of the cold air from the air conditioning system say 30% or so?

slippyr4

The power gains you make would be offset by the load on the air conditioning. You're engine breathes a lot of air:

Assume a volumetric efficiency of 100%:

4 stroke engine= 2 strokes per revolution
2 litres per 4 stokes= 1 litre per 2 strokes = 1 litre per revolution.

Peak power at around 6000 rpm = 100 rps

Therefore you'd need about 100 litres of cold air every second. You're a/c can't effectively cool at this rate.

an a/c system big enough to do this would lose more power to run that you'd gain from the cold air.

It's a question of entropy.

Steve001

iTrader: (7)

Oh POO!

So much for that idea.....

Thanks anyway

Steve

CharlieWhiskey

You canna change the laws of physics cap'n!

or

You don't get owt for now't

Gordo

Out of interest, how much air does a 'normal' impreza engine actually breathe?

I appreciate that Slippy's assumed 100% air etc but this calculation appears fundamentally flawed in that most of the volume input into the engine is liquid, the gases in there are compressed, not added to that much? I guess I'm thinking about how much gas comes out of the exhaust - it's certainly not 100 litres per second - or am I braking as the air flows required for better performance in the cold are more cooling related and therefore sod all to do with combustion?

Apologies to all the technically minded out there for this piece of random incomprehensible ****!

Gordo

Lushman

Steve,
For better engine efficiency drive your car in the winter without the bonnet, grill (infact lose the entire front end).

But on a more serious note apparently you car will be more economical with cold air rushing into the engine.

Something to do with the increased amount of oxygen against the petrol/air mixture.

Bobfrog

What about tailoring a nitrous kit to just spray fuel + oxygen into the inlet manifold, the fuel serves as an additional injector (take a t-piece off the fuel line into a solenoid then into the inlet manifold) and to stop it running lean, then add compressed oxygen (don't know what the temperature is but nitrous oxide is -128'C), Robert's your father's brother, you have more cold oxygen and more fuel. This works out better than a nitrous kit because not many companies will sell nitrous for car usage, funny that!!! Failing that, stick the induction kit out of the bonnet, as seen on a Renault 5 Turbo!!

Sam Elassar

you could
relocate the air filter inside the wing,to avoid hot engine air. as per the APS kit

or use a shield around an air filter to isolate the hot air from the engine bay

or relocate the air filter behind the bumper. right behind those small air slits to the side of the fog lights. air their will be the coolest. i am not sure if this has been done though.

GavinP

Air intake varies depending on engine speed but I have read in a couple of places that for sizing intercooler capacity (air flow), you work on the equation:

BHP x 1.5 CFM (cubic feet per minute)

So 300BHP would be 450CFM.

Thanks

Gavin

Steve001

iTrader: (7)

Thanks guys

But without getting too technical I was just suggesting supplying colder air to the engine bay around the air filter.

I have a K&N fitted to my car and the engine response is very much effected when things get a bit warm under the bonnet.

Anyway it was just an idea

Steve

JKJ2

What I find odd is that people spend £1700 on a PPP fitted to their car, (+ 30 bhp), then run with aircon on,(- 30 bhp).

Floyd

iTrader: (9)

Air temps under the bonnet when above say 15mph are only 3-5degrees higher than outside temps. I've measured it with proper equipment. If you pull air from inside the wing you will get a small gain (but you would not know it). Best increase is from an induction kit that reduces pumping losses from a bigger surface area for the filter and less restrictive. Downside is that it is noisy IMHO and your dealer may get upset!

Warm air is better for economy, cold is better for power, so says David Visard.

F

dowser

IIRC, the aircon is switched off at anything above .7 bar boost

I ran for two days at Nurburgring with it on, so I hope so

Richard

orbv

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR>Originally posted by slippyr4:
<B>
Therefore you'd need about 100 litres of cold air every second.[/quote]

and what does the turbo do to this air?

For that amount of air being sucked into the engine the under bonnet
temperature would almost be the same as outside.

DavidRB

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR>Originally posted by JKJ2:
<B>What I find odd is that people spend £1700 on a PPP fitted to their car, (+ 30 bhp), then run with aircon on,(- 30 bhp).[/quote]Exactly how big an aircon system do you have???? Try 5-10 bhp.

Oh, and most people run A/C because they get hot inside the car!

slippyr4

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR>Originally posted by Gordo:
<B>...most of the volume input into the engine is liquid, the gases in there are compressed[/quote]

Not true... The air that goes in to the cylinders is air. There is very little fuel in comparison to the volume of air, and this fuel is vapourised, so is in fact gaseous as well.

As you all know, the power output of an engine is directly proportional to the amount of air that goes through it. Picture a "perfect" engine, and imagine the inlet stroke. The inlet valve opens, and the cylinder starts going down. the cyclinder draws its full volume of air (with the injection system having also squirted in the correct volume of fuel). Then the inlet valve shuts. When the cylinder is at Bottom Dead Center, after the inlet stroke, its whole volume is charge. That is called 100% volumetric efficiency. A well tuned car, nice exhaust, nice inlet system, etc, will never in practise reach 100% volumetric efficiency, and at this brief moment in time, the gas pressure in the cylinder is less that atmospheric pressure. A well tuned Normally aspirated engine would do well to get 80% VE. Now picture our turbo engines. the turbo squashes the gas before it enters the cylinder. This means that by the time the piston is at BDC, there is in fact more gas in the cylinder than the volume of the cylinder. The gas is already pressurised. And we've exceeded 100% VE.

Therefore, the engine, with a turbo, does in fact product more gas than my original example.

Gordo: you were thinking that no way does 100 litres of gas come out of the exhaust: you're right at idle... but how many times have you held your hand by the exhaust when the engine is at 6000 rpm?

At idle, the engine is doing no work, the revs are very low, and the throttle is almost completely closed. Volumetric efficiency is low... maybe 40%... so at 750rpm idle you're looking at about 5 litres per second... a twentieth of the fast, loaded engine figure.

orbv questioned about underbonnet temps... remember: the air intake on a standard scoob is at the front, the main flow is through a tube... also, the turbo makes much more heat the more work the engine is doing which heats things up, and finally, get yourself a temperature probe and measure it: your underbonnet temp when cruising won't be much more than 3 or 4 degrees up on the surroundings. except right next to the turbo which will be hot.

phew, i'm all typed out now.

Chris_Warburton

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR>Originally posted by Steve001:
<B>Oh POO!

So much for that idea.....

Thanks anyway

Steve[/quote]

You could always "save up" the cold air from the air-con in the cabin, then at the crucial moment somehow "release" it (through a trapdoor or something in the dashboard) into the engine bay - this would give a sort of "Nitro" style boost.

Chris

PS. This was my first post.

fast bloke

Chris_W - I think you will fit right in in the muppet forum

Adam M

If people are gonna get all flashy, the ideal would be to fit a front mounted intercooler and rotate the turbo so that it gets fed cold ram effect air from a filter in the air scoop. This will be as cold asd it gets, and also will reduce the pressure ratio across turbo. Which means greater efficiency which means less heating of the pressurised air. Compound advantage.

Wow, what a great idea. If only it hadnt been done a million times before .