white_lightning

I see that items like long tube headers will likely reduce boost on the 4.6 engines. I dont know why and it doesn't really matter. However it made made me wonder, will an X pipe with high flow cats and an axle back reduce boost any?

Any help would be greatly appreciated. I want to go Whipple or Edelbrock and am trying to figure out what size pulley to get.

Nick

liberty911

FWIW, with a Whipple, 3.25 pulley and OEM exhaust. I was at 12.4 lbs. boost. After Kooks LT w/cat'd x, and a 3.40 I am at 11.4. I had also upgraded to 8 ribs and the Thumper RRR tensioner due to belt slip. My understanding is the loss in boost comes from the LT and not the x-pipe or h-pipe or cats.

shanec

Get ready.....boost doesn't give you power. More air + more fuel in the engine = more power. Headers aren't a bad thing.

That said, I have the smaller of the two LT header pipes that Bassani makes. I got these before I knew what I was doing. Wish I'd have gone Kooks but that's a different story.

Anyway - no boost reduction for me.

TheRage

Doesn't more pressure = more air though?

GerRod

Just means more air is being supplied than what can flow through the valves, cylinder, and out through the exhaust, thus increasing pressure between supercharger and cylinder heads. When you put headers, this scavenage more flow from the cylinder, which reduces pressure between cylinder heads and supercharger.

shanec

Yes it does. But when you put on headers, if you lose boost you are not going to lose power.

fast64ranchero

Don't think of it as "Boost" think of it as "Pressure" and Pressure is caused by a Lack of Flow, so if you free up the Exhaust flow, it reduces pressure, a small amount of Exhaust back pressure is a good thing, when you add FI you increase that back pressure to a point it starts backing up though-out the engine (so to say) if you could measure "Air Flow" before and after the exhaust upgrade you would notice, that although the Boost pressure dropped the Air Flow increased, the same thing happens when you install good ported heads.

Jersey Stang

Should we bring up the water hose analogy?

A free flowing water hose will push out lots of water with very little pressure. Put your thumb over the end and the pressure will increase, but the amount of flowing water will decrease.

Plan and simple, LT will make your engine more efficient. Pressure will decrease and your engine will get more air = MORE POWER!!!

onederful100

not necessarily
you could run the same pulley at different psi, but still spinning the blower at the same rate, moving the same amount of air
but with a better free flowing exhaust lowering boost, you have made it more efficient moving the same amount of air in but scavenging out better
blower is spinning at the same rate but making more power with less pressure

breathegood

If you want to start picking at nits, anything you do to free up the exhaust from headers to axle backs will result in the loss of boost pressure. As others have stated, power shouldn't be reduced. You are just making the engine work more efficiently. More power with less boost is a good thing.