How much dose the exhaust play in the cam profile.

Make this with LTheaders 3 y pipe

if you have standard 3" cat back vs 3 1/2" vs 4" would there be any change to the ex side of the cam.

What about duals same LTheaders

2 1/2" with "X" pipe vs 3" with "X" pipe..

same but with H pipe

thx

 

My short answer is that total exhaust system back pressure is more important in chosing camshaft timing.

The biggest restriction in a typical street F-car system is probably the muffler, so that should be the primary focus.

 

There are two things that come into play here: total system backpressure and tuning effect.

1) Total system backpressure: As you probably know, exhaust valve opening (EVO) occurs during the power stroke. This is a trade-off because you are releasing energy out the exhaust that could otherwise be used to push the crank. But, for best power, you need to allow the exhaust to "blow down" to near zero pressure before the exhaust stroke begins. With less backpressure, "blow down" occurs quicker, so you can wait until later to open the exhaust valve, thus taking advantage of more of the power stroke. So, less backpressure means later EVO, which translates into less exhaust duration, narrower LSA, and slightly less advance.

2) Tuning effect: Long tube headers, if correctly designed, can pull a vacuum on the chamber towards the end of the exhaust stroke. This helps to pull in fresh air/fuel. To take full advantage of this, however, you have to close the exhaust valve late in the cycle, creating more overlap and more opportunity for this vacuum to take effect. So, tuned exhaust means later EVC, which translates into more exhaust duration, narrower LSA, and slightly less advance.

So, if you take a car with stock exhaust and add full length headers and dual exhaust, you could take better advantage of it by simply retarding the exhaust lobe 4 - 8 degrees.

Of course, better tuned exhaust with less backpressure will allow the engine to breathe to a higher rpm. To take full advantage of this, you would also monkey with the intake lobe by adding duration for more horsepower.

Mike

 

So if i was going to get a custom cam done , What exhaust i have on the can would play a part in the cam,..

Is there any diff with 4" vs 3" duals X pipe with the same muffler.

 

I'd be willing to bet that there is very little difference in backpressure of a single 4" versus dual 3", providing you have a good muffler(s), i.e. NOT SlowMaster or SpinTech.

Mike

 

Absolutely!