Air Fuel Ratio

[grips]

AFR were always important in tuning or optimizing an engine. One of the Quickest ways to find if carburetor and fuel injection is optimized.
Most of the top engine tuners will read AFR and we all know that a petrol engine is happy around 14.7.

Now what about turbo diesels or normal aspirated diesels . There are variables due to engine application but non turbo diesel are set at around 19-20.
Turbo diesels around 18 to 24 under load. At around 15 to 16 turbo diesel engines start to smoke and rise EGT.
We also knows that for 1 point lower AFR on the scale you score around 15 to 25kw.

Fact is AFR and EGT is directly related. The lower the AFR the higher EGT. Now my question why does the guys tuning turbo diesels not take AFR readings on the dyno`s while tuning ?

In my many years of building engines and many high performance v8`s I have always checked AFR readings with a simple AFR gauge and sensor. Simple home made setup.

Now back to turbo diesels. First I hate it to drive with my eyes glued to EGT gauges. Secondly if EGT becomes a problem then you are overfueling to make extra power. Overfueling is what chip tuners does in the end.

Ok so I owns the V8 Cruiser for almost three years. During my days with normal aspirated petrol v8`s I know that intake and exhaust flow is critical and several ways of improving this will provide more horse power.

So I started out with the diesel v8 in just doing that. My first step were port matched intakes and a free flow exhaust. I then started to play with boost.
Have designed my own boost controller to set boost mechanical as the Cruiser have a VVT turbo that is vacuum controlled. Problem now is ECU settings like max boost settings. That is sorted with a program were I can alter boost pressure settings. Going to push boost and see with the aid of AFR how far the stock ECU can keep up with the fueling.

I have ordered an AFR gauge to check AFR readings. This will be joined by an Avionics EGT gauge. Madman systems are nice but I do not see the reason to duplicate readings that can be very accurately taken from the ECU.

The correct way of tuning a diesel will be to increase boost and fuel keeping AFR in check thus controlling EGT in the same time.
Seems that tuners are chasing the quick buck by only increasing fuel and left the damage that might occur as a result of high EGT`s to the customer.

I think it is wise to fit a EGT gauge at least after chip tuning or an aggressive map.

[henris]

I totally agree. I fitted a "Tuning Box". Belgian device. Actually works well bit EGT was running away. So I upped the boost(after fitting the intercooler) to 1bar and things are a lot happier. Std 100vx is 1bar.

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[grips]

Henri to this day there are some things I battle to express myself in metric terms. When talking boost on engines I prefer psi. So you are running around 14 psi of boost

[henris]

Had to go check.
Yes, 14,5psi

My boost guage is in bar

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[david bfreesani]

Had to go check.
Yes, 14,5psi

My boost guage is in bar

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Lol, I also can't seem to get used to working PSI. My Madman is set to bar as well.

I have just put my turbo back about an hour ago after having to go look for the piece of my EGT probe that broke off when I was trying to replace it after the cable broke off the top. It had melted a big blob on the inside of the manifold, and would not come back out through its hole. Decided to move it slightly as the darn taper thread keeps letting my probe come lose.

Why do they use taper thread?

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[grips]

I am metricated in everything else. Found that even Japanese manufacturers quote boost in psi. So yes it is sort of personal preference

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[grips]

Now for the clever guys. Do you run the same EGT and AFR on an indirect pre-chamber engine than on a Direct Injection engine?

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[david bfreesani]

Does Pre Combustion refer to Non Common Rail?

[grips]

Nope. Indirect injection have pre cambers in the head. Very common on the older normal aspirated diesel engines. Direct Injection have the combustion chambers in the pistons.

[david bfreesani]

Thanks for that. I thought it had more to do with "pre ECU" controlled injection type systems. Manual pumps with nothing more than a compensator for when boost is achieved. The mechanic that looks after my old diesel, refuses to set the pump to anything more than what the manufacturers book tells him, and that gets done on the bench. The only thing he took into consideration for me, was that I was fitting an Inter Cooler, and he gave a bit more fuel.

After that, any AFR/Performance gains that I could make or achieve, came from what I can do on the air intake and exhaust. We never fiddled again with the pump.

I live by watching my EGT and Boost on the Madman, and the seat of my pants feel. Things that dropped my EGT was the Snorkel and bigger intake pipes, water injection (for a while), and the 3" exhaust. As the exhaust got shorter, the EGT's also seemed to drop slightly, but I think it had more to do with the boost that would come up much faster. Right now busy with the Inter Cooler. Hopefully that will be installed next weekend.