Mythbuster: LT headers/PP on forced induction. Gain or no gain?

[EvasiveS197]

So I sit here, pencil in hand, writing away my wallet to the automotive gods contemplating what I want my "dream mustang" to end up being. (Shoot past the moon and aim for the stars...it's the only way you'll make it to the moon).

LT headers make a difference on an NA motor. However, I wanna say in the past I read that LT headers and/or port/polish on the heads (not the supercharger itself) make SMALL changes at the dyno for a supercharged motor. I've heard that they only REALLY affect NA motors. True, false, proof?

 

[o0Dan0o]

I don't have any proof, but as you increase the overall airflow reducing any restriction should make a bigger difference. Meaning that anything that makes power on an N/A car should make more on an FI car (if it is applicable).
Dan

 

[SpartaPerformance]

+1. An engine is a big air pump, anytime air goes in and out with less restriction it make power whether it's N/A or F/I. A big problem with small gains is the wrong parts.

 

[EvasiveS197]

That'll vouch for the P/P, but what about exhaust? Same theory of "less backpressure"? Or would the engine not have a problem pushing out the excess of this additional air with (for example) stock headers?

 

[o0Dan0o]

That'll vouch for the P/P, but what about exhaust? Same theory of "less backpressure"? Or would the engine not have a problem pushing out the excess of this additional air with (for example) stock headers?

It shouldn't get easier with boost, it should get harder.

Think of an exhaust this way, it's essentially a parasitic loss. The engine has to force the exhaust gases through the exhaust which is power lost. The reason why we don't just run the things through the hood as open headers is we need back pressure at lower RPM for exhaust scavenging. As you gain RPM you need a similar amount of back pressure but a less restrictive exhaust to produce it (at 6K RPM you're forcing roughly twice as much gas through the exhaust compared to 3k RPM). The same is true when you up the HP in general (if its N2O or FI), you pushing more exhaust gas through the exhaust so you don't need a system capable of producing the same back pressure, thus you want a freer flowing exhaust.
Dan

 

[EvasiveS197]

It shouldn't get easier with boost, it should get harder.

Think of an exhaust this way, it's essentially a parasitic loss. The engine has to force the exhaust gases through the exhaust which is power lost. The reason why we don't just run the things through the hood as open headers is we need back pressure at lower RPM for exhaust scavenging. As you gain RPM you need a similar amount of back pressure but a less restrictive exhaust to produce it (at 6K RPM you're forcing roughly twice as much gas through the exhaust compared to 3k RPM). The same is true when you up the HP in general (if its N2O or FI), you pushing more exhaust gas through the exhaust so you don't need a system capable of producing the same back pressure, thus you want a freer flowing exhaust.
Dan

My B. Head got ahead of my fingers. I mean "less backpressure with aftermarket headers" for that sentence...

 

[NastyStang113]

LTs will make more power on a F/I motor. It will reduce PSI but it doesn't mean it's going to give up power at all. It's only becoming more efficient.

 

[EvasiveS197]

I think that answers the street-talk rumors.

 

[o0Dan0o]

That brings up a question I had, does the 500 RWHP on the stock bottom end rule of tumb stay with ported heads and cams? Those combined with headers should lower you boost readings a decent amount, but I'm guessing it would still increase cylinder pressures beyond what the stock rods can take.
Dan

 

[EvasiveS197]

That brings up a question I had, does the 500 RWHP on the stock bottom end rule of tumb stay with ported heads and cams? Those combined with headers should lower you boost readings a decent amount, but I'm guessing it would still increase cylinder pressures beyond what the stock rods can take.
Dan

I would think the improvement of of the head would need to be calculated in the "500limit". Simply because the bottom end is only meant to take so much pressure from the combustion. More air means more combustion no matter how you get it...

 

[stangzilla100]

i have a friend w/ a whippled terminator and stock exhaust except for borla catback. he put in some LT's and o/r x pipe. he gained 10 rwhp and lost 2 psi, went from 17 to 15. he has less compression and less strain on the engine w/ a slight increase in power. i would say that is a good deal, more efficient and less wear on the engine.

i already had LT's and o/r x pipe when my whipple went on. i have the 3.5 pulley which is supposed to be 10 psi but i only see 9 on the gauge. i will take better efficiency over more psi any day. cam and heads would make it even more efficient.

 

[EvasiveS197]

i have a friend w/ a whippled terminator and stock exhaust except for borla catback. he put in some LT's and o/r x pipe. he gained 10 rwhp and lost 2 psi, went from 17 to 15. he has less compression and less strain on the engine w/ a slight increase in power. i would say that is a good deal, more efficient and less wear on the engine.

i already had LT's and o/r x pipe when my whipple went on. i have the 3.5 pulley which is supposed to be 10 psi but i only see 9 on the gauge. i will take better efficiency over more psi any day. cam and heads would make it even more efficient.

Best post of the thread!

 

[NastyStang113]

Best post of the thread!

WTF !! I said the same thing !!

 

[EvasiveS197]

WTF !! I said the same thing !!

He had an example.