Diesel tuning facts

[monsterer]

Hi there,

I'm after some facts about tuning diesels:

If you run lean by cooling the charge (e.g. through intercooler or WI), do you risk engine damage without upping the fuel?

If not do you actually gain power without adding fuel?

Cheers, Paul.

[TonyN]

Diesels just want more fuel, pump it in till it smokes like a tyre fire!!!



But yeah, to lean and you'll eat pistons, but it dosn't seem as critical as petrol motors.

Intercoolers work great on Surfs for getting a better burn, more air= bigger bang. Uprated injectors are the next step after.

plus all the usual junk like air filters and fat exhausts.

Don't get to excited about the boost pressure, I've been told upping the boost to much will ruin the bottom end on these motors.

[da SLUG man]

if you do run lean, will the ECU not add extra fuel anyway?

[TonyN]

if you do run lean, will the ECU not add extra fuel anyway?

It won't know, don't have a 02 sensor like petrol motors.

[monsterer]

It won't know, don't have a 02 sensor like petrol motors, although the knock sensor will help lean pinking issues.

Now i'm really confused!

Why would you need a knock sensor on a diesel engine which is powered by compression ignition?

Cheers, Paul.

[TonyN]

Now i'm really confused!

Why would you need a knock sensor on a diesel engine which is powered by compression ignition?

Cheers, Paul.

Yeah, I was thinking of the crank position sensor was the knock sensor, wrong motor! oops.

[monsterer]

Also, i read that a leaner mixture with a diesel leads to a cooler combustion, but i fail to see how that would make more power.

Surely the equation is more air + more fuel = bigger bang, rather than simply more of one or the other?

Cheers, Paul.

[da SLUG man]

cooler air is denser so you can get more air fuel mix in the same space... heat it up and it expands... far more expansion from a denser gas.


i'm gonna fit a cryogenic system... ultra cool, and the extra ability to store deceased relatives!

[monsterer]

cooler air is denser so you can get more air fuel mix in the same space... heat it up and it expands... far more expansion from a denser gas.

Sure, i understand that, but what about just more air? What'll it do for a diesel engine?

Cheers, Paul.

[TonyN]

Its the Oxygen, you need it to aid combustion, like blowing on a smolding fire, it leaps in to flames, same in a motor, add oxygen and you get better combustion, thats why a motor running lean melts pistons.

Its also why leaning out a motor improves your emissions for the MOT, its burning everything completely. Unfortunatly it burns your pistons over time cause its to hot.

Now because your getting better combustion, you can add more fuel, lowering the temps but getting more power from the bigger explosion.

Toyota don't want you melting engines, so the engine is tuned to meet emissions and gettign the power they want while not being hard on the internals. Any performance upgrade you do by just adjusting the mixture is using up the safty margin built in. You can gain some without to many dramas, but over do it and BANG!

[monsterer]

Its the Oxygen, you need it to aid combustion, like blowing on a smolding fire, it leaps in to flames, same in a motor, add oxygen and you get better combustion, thats why a motor running lean melts pistons.

Its also why leaning out a motor improves your emissions for the MOT, its burning everything completely. Unfortunatly it burns your pistons over time cause its to hot.

Now because your getting better combustion, you can add more fuel, lowering the temps but getting more power from the bigger explosion.

Toyota don't want you melting engines, so the engine is tuned to meet emissions and gettign the power they want while not being hard on the internals. Any performance upgrade you do by just adjusting the mixture is using up the safty margin built in. You can gain some without to many dramas, but over do it and BANG!

Okey, i can see how that makes sense. The only thing which worries me (and i've been trying to get confirmation on this), is that i've read a diesel engine responds totally differently to air / fuel than a petrol engine.

I've read (for diesels) that a lean mixtures means a cooler combustion. And i've read that adding more fuel (like you might do on a petrol engine to cool the cylinders as a safety measure) will actually have the opposite effect on a diesel and could melt your pistons.

But then i get stuck because, how can a cooler combustion (i.e. leaner) produce more power?

Answers on a postcard, plz!



Cheers, Paul.

[monsterer]

Heres some good diesel tuning info which is not biased by some product (most of my web searching resulted in pages selling tuning chips):

http://bankspower.com/im_HotRod_Sept05.cfm

[lclascaris]

Now i'm really confused!

Why would you need a knock sensor on a diesel engine which is powered by compression ignition?

Cheers, Paul.

Most common rail diesel engines have knock sensors fitted now, don't ask me what they do I just sell car parts.

[monsterer]

thats becoz they dont have fuel injection pumps,its a pressure pump,

Whats a fuel injection pump got to do with knock sensors, you've lost me!?

[surfenstein]

Whats a fuel injection pump got to do with knock sensors, you've lost me!?

sorry most of that post is missing.
A knock sensor is a piezoelectric microphone that generates a 0-5mV signal to the ignition controller (knock box). When a millivolt input is received to the knock box the ignition timing is retarded to suppress ignition timing. Ignition timing is advanced to the most degrees without knock for optimum performance.