How air goes thru your engine.....(basic)

Great post Smooth flowing manifold runners made a big difference in the old carburetor (and throttle body injection) systems as coarse passages and abrupt angles actually de-suspend fuel from the fuel air mixture, costing power while increasing emmissions. With fuel injection systems, this is a non-issue.

 

Makes sense how forced induction just crams more air and fuel into the cylinders, so a free-flow/low backpressure exhaust suits these applications best. Easy to read and understand. Thanks
EDIT: Looks like someone's been watching "Two Guys' Garage"

 

No! Video's that violate do not have validity!

 

Hi guys. I have a question. My truck is up for a smog Check and I have a trd cold air intake and an aftermarket exhaust. I'm afraid I could have trouble at the smog check place. Do any of u know if that would affect my truck passing the check ? Thx

 

For normally aspirated engines, exhaust pulse timing and exhaust tuning is critical to obtaining maximum power from the engine. For turbocharged engines, it's a lot simpler...just have as free-flowing an exhaust as possible for maximum power. The ideal exhaust for a turbocharged engine would be a conical or horn-shaped pipe going straight to the atmosphere. While impractical for a street car, you see them on race cars all the time.

 

I only read the first page, but the "myth" of engines needing back pressure might have come from 2strokes (first internal combustion engines). A back pressure wave can really help compress air entering the cylinder depending on the exhaust valve location (or open engine hole). I know if I take off the expansion chamber on my 2stroke - it gets absolutely no power in comparison (maybe a 50% drop or more). So 2 strokes is definitely a different story.

Tuning the flow is right though. After a warm engine, I found about 1/8" bigger helped me get 1-2mph more top end and quicker response (i just drilled in some extra small ventilation holes - ie: not everything has to come out the very end of the pipe). But after only 1/8" + on exhaust size I started losing power. I would've thought 1/2" + or more would do better. Bigger definitely is not always better until you change the cams or turbo, etc.

The best advice is:
-just to leave it stock
-only mod it a little (<1")
-or keep trying stuff until you find what works right, but this can be pretty time consuming. Took me about 2 weeks on a small motor (tuning the carbs / intake size / etc. too though). I also had to tune while driving, cause it was completely different verse stationary tuning (dealing with 25mph+ i found much different throttle responses compared to stationary). I probably needed a fan on the intake to tune parked.


I think this is a cool topic, because I see a lot of people immediately jump to the 4" pipes. My buddy with an old Wrangler got the 4" pipes. It's funny to watch him take off in 1st gear. He has to rev soooo much to avoid stalling. It's so bad off road - especially crawling on fire access routes.

 

life on factory battery of 2007 tacoma

 

Chris4x4 or any others can explain a smog pump or air injector?

I believe it's now on 13's

 

secondary air injection? like in emissions control. fresh air is injected into the ehaust stream to allow a fuller combustion of gases. thank for this great thread. can really learn a lot.

 

^ this, and
the fresh air injected into the exhaust stream provides oxygen to allow any unburned fuel in the exaust gases to burn. In other words, the exhaust gases are still hot enough that the unburned fuel will combust when it finds this injected air/oxygen, that is the theory.

 

Excellent write-up Chris. You could also incorporate the effect of high-temp thermal coatings that are often applied to aftermarket long tube headers. Keeping the heat "in" lowers under hood temperatures and protects surrounding components, which is widely believed as the main benefit. However, keeping the exhaust gasses hot is also very important with a properly sized primary tube diameter for the reasons you have covered.

 

So how do you explains something like an air intake manifold spacer. Don't they lower the torque peak? Wouldn't they limit the back flow ,from the closing of valves, from getting to a different cylinder like mentioned in the op?

 

Ok so with all this said, why would a truck that has perfect fuel trims and timing run lean or rich? I just replaced my exhaust manifold about 3 months ago and I just found out that the new one is cracked. I'm about ready to ditch this truck.

 

Great writeup