MurrayZA

I'm trying to find out the difference between:

1) The std TD04L on a std ECU
2) A VF23 on a std ECU

Ok - I know about the compressor and wheel sizes, roller bearings, higher flow rate of air and different efficiency zones, spool up and charge temperature but is the 0.9 bar that gets into the combustion chamber the same pressure for the both or, because the VF23 flows more air, the pressure into the chamber is higher?

Basically, I guess, what I'd like to know - under hard driving (not insane, but say 6500 rpm changes on a 01 WRX) on a stock standard ECU (NO Dawes or the like), is the VF23 more or less hurtful on the engine than the stocker (TD04L). Is the VF23 or the
TD04L more likely to cause det ?

BruceWarne

1 bar is 1 bar. There won't suddenly be more air molecules in there because the turbo is larger. A larger turbo might run a bit cooler, but I reckon mechanical heat generated is very small compared to the heat generated due to compression.

A large turbo is able to generate higher pressure than a smaller one at a given RPM, though.

But, a larger turbo really comes into its own at higher revs. 'Cause a small turbo can't spin fast enough to generate high pressure at high revs, but a larger turbo can ('cause it moves more air per revolution than a smaller one).

MurrayZA

Thanks Adam. I'm aiming at a safe 270 BHP with a decat up-pipe,
VF23, PPP ECU, all on a MY01 WRX (new shape). We have really cr@p fuel here (dare I mention it - 93 octane @ about a mile above sea level) - so 280 is probably about the most upper limit. Our PPP here runs 1.15 bar boost max (16 PSI) and I plan to use no Dawes or the like, just the PPP ECU. Will probably run 1ml NF to
1l fuel. Any other mods anyone may think are necessary to lessen the chance of det without dropping boost and apart from a FMIC ?

dowser

Murray,

I've just gone from td04 to vf23 on my00 with PPP. I'm using manual boost control though.

I'm running the same boost (17psi-ish), but have a nice increase in power. I put this down to reduced charge heat on inlet side, and reduced back pressure on outlet (you notice more torque off boost). Downside is the lag - remap should help there a bit.

I consider the upgrade as is to be a safety mod...except the held boost above 6k gets addictive....something else for a remap to fix Not sure how you're OE boost control will cope with the bigger turbo though....

Richard

BruceWarne

Point taken. I actually wanted to start off with tha gas law, and show how it all fits together. Then I decided that over most of the OE turbo's operating band, the two turbos probably generate about the same amount of heat. And there is an intercooler in there too. And the gas is moving through the turbo quite fast.

So, from 3000 to 5500 RPM, things are probably very much equal (especially for short bursts). Above 5500 RPM the heat generated by the OE turbo can no longer be ignored, but this is also the point where the larger turbo's capacity to move a lot of air comes into the equation - the larger turbo being just so much better at moving air, and the small one just so pathetic, that for comparison purposes, you can almost ignore temperature (although both temperature and pressure is in favour of the larger turbo).

So, let me rephrase

In the normal OE turbo operating band (3000 - 5500 rpm), and for short bursts:
1 bar is 1 bar (give or take .01 bar).

Above that 1 bar from a larger turbo is much more than one bar from a smaller one.

I actually explicitly mentioned this, saying that the mechanical (turbo friction) heat generated (and transfered to the charge)is much less than the heat generated due to the compression of the air. And T is measured in Kelvin, after all. And there's an intercooler in there too.

nom

Well, 1 bar is always 1 bar, it's just that you can fit more oxygen in a cold 1 bar than in a hot 1 bar, and it's the amount of oxygen - not the pressure - which is important in the combustion process.
That was meant to be a clear way of putting it, but I don't think it's worked very well
You want flow, not pressure...

dowser

17psi from a vf23 at any revs feels much stronger than 17psi from a td04 - whether this is heat or back pressure related I can't say

Richard

john banks

The standard boost control will be naff at the bottom and top ends unless remapped. Use a manual boost controller if you are on a budget. Replace the fuel pump.

Adam M

1 bar is 1 bar?

there will suddenly be more molecules in there because the turbo is larger.

Larger turbos generate a cooler charger, cooler air is more dense.

PV=nRT (for an ideal gas) nR relates to the mass of gas for simplicity.


therefore PV/T=nR

therefore if pressure and volume are constant the mass of the gas is inversely proprtional to the temperature.

Ie. temp goes up/mass goes down hence how hot air baloons generate lift.


The pressure can be considered as particles colliding with the walls of the container.

one container has 5 particles at high temp therefore moving fast, the other 10 at low temp therefore moving slower.

overall they exert the same pressure on the walls of the container (if they are the same volume) because the higher speed means the fewer particles hit the walls more often than they would if travelling slowly and when they do hit, they hit with a greater impact force due to greater kinetic energy.


In short even though the pistons draws the same volume of air at the same pressure, the amount of oxygen in there is greater with a larger turbo meaning more power and also requiring more fuel.

If running a car with a maf sensor it will detect the greater airflow and provide more fuel up to a point, if you running as link or the like on your car, you will need to add fuel to maintain the air fuel ratio.




[Edited by Adam M - 7/9/2002 10:26:05 AM]

BruceWarne

The ideal would be an instrument that shows MAP*MAF...
Or would it?
Wouldn't the ideal be MAF output? No, the air can be measured, but go out the wastegate, and BOV...

PV=nRT
n=PV/RT
n=K*P/T
The ideal would be something that shows:
MAP/MT (Manifold Temperature)...



[Edited by BruceWarne - 7/9/2002 2:26:38 PM]