JBSVT,

You lost boost because you incresead the volumetric efficiency of your engine....boost is a measure of back-pressure....not airflow. Your engine is flowing more air with the long tubes.....with less boost...With the right tune...that means more horsepower and Torque.....

 

If the exhaust valves are closed during the intake stroke, then how can you lose boost??

 

Boost is a measure of backpressure....i.e. resistance. your engine is a reservoir.......and the exhaust syetem is the drainage system. The more efficient the drainage system...the quicker the reservoir can empty.....which equates to horsepower in the case of an engine...not to mention there is a pump in the reservoir...

Scott
M.S. Thermodynamics and Fluid Dynamics..

 

BlackJack, sounds as if you know your shiznit I wish most people could understand that. I did however lose horsepower due to putting the longtubes on only because I have the wrong tune (chip or program) . I do feel when JL gets the right program for me I will have increased horsepower overall. I cant wait to get to the track wity mynew chip.

 

Boost may be a measure of back pressure, but that is only true if the "drainage system" , as you call it, is closed(during intake stroke). So how can a more efficient exhaust show a decrease in boost when the 2 cycles are shut off from each other ...unless cam overlap has something to do with it???

 

Mondo1-

I think you are assuming that all of the spent air was gone by the time the exhaust valve shut. There is always some left in the cylinder. Long tubes help evacuate more of this spent air out by making the exhaust pulses draw 'harder' as they leave the cylinder. This makes more room in the cylinder for when the intake valve opens and all that glorious boost starts packing in. If you have more space to pack into, and you're given the same amount of time to do it in, you get less boost pressure. There is little or no overlap in these 5.4L S/C cams for emissions reasons. This is one of the few times when less boost pressure is actually a good thing.

Capiche?

 

BTW-

You want a re-burn on the chip.

The stock computer can compensate for this, but the aggressive timing/fuel curves that the chips create can cause problems with lean mixtures when you add long tubes. Also, a two to four lb. pulley with long tubes and the correct chip should yield impressive results (60-70hp+?), with normal looking boost pressures.

Later,

 

Well...la dee friggin da !! Now that makes sense! Glad you pointed that out, Wrongday.

 

the pulley and chip will be adding most of the power imo,

as i stated, the dyno showed me minimal gains, we'll see about e.t.s once the weather is cool

 

Yo Beef. . .I agree. The pulley and chip are the heavy hitters.