POM HB

Let's say you have your car tuned at A/F of 11.5 wot. Everything is fine and daddy. One day, you have upgrade a lot of ignition components, such as great plugs, wires, coil, something like HKS' Twin Power, and etc. (Well, on a different car, I noticed better acc & faster reving just changing to great plug wires from NGK)

So, that got me thinking that better spark ==> more power ... because the fuel was burned more. That must effect the A/F ratio on the tuned map. It might have changed from 11.5 to 12.5 wot.

So, the question is... Should the map be re-tuned to keep A/F ratio at 11.5 again? Is it necessary to do so when it was proven that that the fuel map (hence fuel for given rpm ) was enough for the engine? Or, should we re-tuned the engine to A/F of 11.5 for safty purpose (and waste a little more gas :-) ).

Any insight is appreciate, Thanks.

Pom HB

spanner

iTrader: (2)

Hi, in my humble opinion I think it would be wise to re-tune to your 11.5 A/F or maybe 11.0 A/F , a lil extra rich won't hurt the motor...jus the pocket, but better off in the long run.

arghx

iTrader: (3)

I see your point but the safest thing to do is retune. At that AFR range in my experience adding a little more fuel doesn't cost that much power. In terms of power loss there's a much bigger difference between going from from 11:1 to 10:1 compared to richening up 12:1 to 11:1.

blue87

iTrader: (2)

If you are only changing ignition hardware I don't see why the A/F would change to begin with. The same amount of air and fuel are entering the engine. *IF* you make more power from the upgraded ignition it is because you are burning the A/F more completely increasing efficiency. The same amount of Air and Fuel are being combined though. You may have different reading on a wideband if you were misfiring before the ignition upgrade due to unevenly mixed and un burned fuel in the exhaust. If that was the case your actual A/F ratio in the engine combustion chamber might have been closer to 12.5 to begin with but looked richer due to the raw fuel. But like arghx said, you should re-tune either way...

But if I read the OP correctly this is only a theoretical exercise right? you didn't actually do this and see the difference?

POM HB

hee hee hee.

First of all, I'm surprised that all poster in this thread are long-time member. I must confess that, after being away for a period of time, I expected to see newer members.

blue87 really hit the spot that was on my mind. The same amount of air and fuel are still used altho A/F ratio measured at the exhaust is different. So, is it safe not to get the car tuned (at least, I'm sure the engine will run hotter)? It's not the question about money, but rather, I'd love definite answers in theory, so I can apply.

cewrx7r1

iTrader: (2)

Still not one correct answers to the real question. It means many of you do not know what a O2 sensor really measures. Go find the truth on the web.

A misfire will cause AFRs to go leaner as fuel is not burning and consuming oxygen.
Thus there is more oxygen in the exhaust gases.

If a better ignition causes better fuel burn and more power, that means more oxygen was consumed and AFRs go richer. There is less oxygen in the exhaust gases.

blue87

iTrader: (2)

There is no "real" question it is all in theory... misfire certainly can cause a rich reading depending on the mixing of the unburt fuel in the exhaust and the posistion of the A/F sensor. I do know that an A/F sensor measures the ratio of O2 in the exhaust compared to a reference usully ambient air through the wiring harness... that is not the question, if fuel is not burnt and is on the sensor it will read rich, if the unburnt fuel is not on the sensor it will read lean...

But the original point was the actual A/F ratio does NOT change due to ignition, just what you are reading changes... so either way you need to re-tune becuase basically you were out of tune to begin with before the ignition upgrade you just didn't realize it becuase the wideband reading was actually in error...

cewrx7r1

iTrader: (2)

The real question was:
"better spark ==> more power ... because the fuel was burned more. That must effect the A/F ratio on the tuned map. It might have changed from 11.5 to 12.5 wot. So, the question is... Should the map be re-tuned to keep A/F ratio at 11.5 again?"

Burning the fuel better reduces the O2 level and the result in a richer AFR due to less oxygen. He was assuming it would go lean. His premise was wrong.

Always tune to your goal AFRs when everything is working correctly.

POM HB

Chuck was right that I assumed about the A/F after ignition upgrade. I was making that assumption based on the thought that leaner AFR (closer to 14.7) = more power. And, since I felt more power after changing the wires, I guessed the fuel was burned more without thinking about the oxygen.

Now, if oxygen is actually reduce and AFR is richer, then my understanding of leaner AFR = more power is also wrong?

But, I'll get the car retuned for sure now.

cewrx7r1

iTrader: (2)

A leaner AFR than what most of us run will make more power.
Best power is made with around 12.2-12.5 AFR.

But due to high heat and hot spots in the combustion chamber, our engines and many others would detonate with this AFR range. Thus we run richer AFRs to cool the engine.
All at a loss of power to make the engine survive.

This is where water or water/alky injection comes into play. Great cooling within the combustion chamber and flame front stabilization.

You need to do more research into all of these subjects.