Croc

i saw some thread over the years about adjusting AFR after Intake/Exhaust mods installed.

now i do understand that those make the engine breathe in and out more easily - but i don't see how they make the engine to breath in MORE air.
the displacement is still the same and air is not forced into cilinders.

so why would we need to change amount of fuel supplied?

splatter85

If it can breath easier it does breath more air. More air particles will make it into your motor so you need more fuel.

s2k dre

The 06+ runs a little lean compared to others with bolt ons. But 13.5 is a good afr accross the power band on an all motor engine.

hypforlife32

yes, this is true. because you have more direct air going in as well. suck through a small straw and suck through a large straw. which one give you better results?

my afr's on my ap1 changed about .5 to .7 with CAI, 70mm test pipe and greddy tic single. i was about 13.5-13.7 in the afr range at max untuned and i put down very good power. i had step 1 colder spark plugs and it ran absolutley fantastic. no detonation on the plugs or anything.

Croc

so do you say with a stock intake the engine fails to suck enough air to completely fill the cylinder?

with the brute force applied to inhale i can't see this happening...

then why exhaust mods affect AFR?
they doesn't add more air - so what's happening?

TruBluS2k

exhaust mods allow the air to flow out faster from the head

ahrmike

the more air you can get to the valves, the faster they will go through the valves. The more backpressure you have, the mroe the exhaust gasses will want to "stay and hang out" in the cylinder. When a cylinder is going through tis exhaust stroke, it cant exhaust EVERYTHING out of the cylinder, some gasses are left inside. The faster the intake air enters, the more old air it can push out, and the less backpressure there is, same thing.

The more "new air" you introduce, the more oxygen resides in the cylinder before combustion. assuming you throw in the same amount of fuel, the leaner it will burn.

Croc

this is exactly a type of responces that doesn't explain how AFR is affected....

Croc

[QUOTE=ikeyballz]
The more air you can get to the valves, the faster they will go through the valves.

Mike21

More violent explosion in combustion chamber = more power.
Aftermarket intakes & exhausts(usually) produce more power by increasing velocity of flow and by increasing the amount of air that flows into(and out of) the combustion chamber, altering your air/fuel ratio. You're introducing more air with the same amount of fuel. This is why tuning is so beneficial. Adjust the air/fuel ratio and timing and you'll get the most out of your bolt-ons. Some people have increased output by as much as 15% with just bolt-ons and a proper tune.