Stillen's site states that the headers will impede the performance of their roots blower. I don't understand at all. I have a procharger on my other car and 36" long tube headers with a 3" collector yada yada on the back side. Before adding the headers it showed 8# of boost. After it showed 6-7# before a pulley swap put it back at 8# to.--this is on an LS1

Here's why I don't understand--even though the boost didn't measure as high (because the exhaust flow was increased) it still dynoed 30 rwhp/tq higher with less boost adn even more back at 8#.

Is it different with V6s???

 

yeah i don't understand the deal with the stillen either in that regard. Headers should shift the power band up higher giving the top end more power and with possibly losing some low end.

The boost pressure is kinda meaningless on a SC. It isn't really boost pressure that gives you power, it's air volume and speed. You can apply 8 lbs of pressure to a coke can or you can apply 8 lbs of pressure on a barrel of water - the barrel has more water even though they can both sustain 8 lbs of pressure.

Usually opening up the exhaust will do what you described - lose boost pressure, but gain power. It's all about power anyway. With a SC who cares about boost pressure. It's different with a turbo though where you have a wastegate regulating boost

 

stillens view on this is yes it will lose boost .but what they dont say is you will lose torque down low but you will gain horsepower up top.they want all there power down low and midrange and really dont care about upper powerband.thats why they are devoloping the m90 supercharger,so it will gain all that is lost up top and a lot more.

 

I would like to do headers, but damn they seem like a pain! After putting in the S/C though it may be not as bad. I like Alphawerks. Stillen is wierd with thier "recommendations" (SP? Im drinking, lol) arent they?

 

If I go with Headers I'll go with Crawford... I don't want to lose the TQ down low tho, I am on the fence on this one.

 

Stillen's instructions for headers don't seem that complicated.

I'm itching so bad to mod my 06 Z, but I don't know which way to go. I love my peak power with my vette and procharger and the loss some low end is welcome as traction is a challenge, but I've ridden in magnacharged Z06s and GTOs too so 470 rwtp at 2200-2500 is INSANE! Then there is Shariff who is 3 hours away with the TN setups!!! I'm not familiar at all with the turbos though.

 

I have read a lot of anecdotal discussions on "loosing low end power when opening exhaust" but have yet seen or read of why.. Anyone actually know why you loose low end Tq when either adding Headers or Dual Exhaust??

 

it's backpressure

 

Sorry but saying backpressure does not do it for me.. Elaboration with some facts and figures would be helpful..Freeing up exhaust flows more combustion products while also developing more power output by the engine but somehow the Tq is reduced down low..? And it's due to backpressure! If backpressure goes up , does it not follow less combustion products go out the exhaust and a reduction in power results.. But why does backpressure go up with a freer flowing exhaust.. Sorry I don't get it !! What's the physics involved?

 

it's as simple as if you were to try drinking a soda thru a 6mm diameter straw or a 2 inch straw

you don't have enough suction to use a 2 inch diameter straw

 

Let's take this one question at a time and I think you can help me understand .. I have a problem with straws.. Do we agree we are flowing more air/fuel thru the engine with a freer flowing exhaust.. Yes/No?

 

HKS and DC headers here.... I was also told it would decress backpressure and drop some boost. why I dont know

 

This explantion doesnt cut it. You're doing the same amount of work for either straw. No one is more efficient than the other. Lower pressure also allows the engine to spin more free, not have to work against the exhaust valves.

 

it's like this,

having a smaller exhaust forces the air to compress more as it gets backed up and that denser compressed air helps with low end power. When it goes thru the exhaust, it does it with more force (FI cars will notice they're boost gauge is higher) When you open up the exhaust with test pipes, headers, cams, exhaust etc the air doesn't compress as much, it just comes out with not as much density

this is the difference between hp and torque. Torque is a big guy hitting a punching bag slowly but really hard and hp is the small guy hitting it more often, but not as fast

When you throttle the engine hard, only so much air can flow through because of how restrictive and how little rpms the engine is moving at. The air condenses a little and it comes thru with more force or density

When you get up into the higher powerband, more air flows thru because the engine is spinning faster, though the air isn't as compressed and thus doesn't hit as hard - well it will hit as hard if the exhaust isn't open.

it's one factor out of many why torque starts dropping off at a certain point in the upper power band. So the air doesn't hit as hard, but it does move faster due to the engine speed, and having an open exhaust helps to reduce the restriction of letting the higher volumes of air go thru the engine

When you put a full throttle load on the engine at low rpms, the engine just can't work fast enough to get the air out. Big liter V8's have way bigger cylinders and they can get more air volume into the chamber and get it out at low rpms. On a small displacement engine you don't have that luxury and the engine just can't do it until you get the revs up so it can do more work (hp)

 

Boost loss I totally understand..The engine will flow more combustion products with less resistance to that flow with a freer flowing exhaust. The pressure drop accross the engine is less when opening the exhaust.. The problem I have is understanding why with more air/fuel and hence greater power developed by the engine does the Tq decrease as has been indicated..Does less air/fuel flow thru when the exhaust is opened up??

 

as rpms rise, another reason torque decreases is the engine becomes less efficient. It's harder to fill up those cylinders really fast than it is to do it really slow. Also combustion has a harder time happening at faster speeds unless you start getting into expensive exotic spark plug setups like F1 race cars.

A lot of F1 engines are around 3 liters but will work at 18,000 rpms. They're constantly near redline so having a bigger displacement with lower reving engine won't help them at all, because they're not going to be hanging around the low/mid powerband very long at all. Yet a big liter diesel engine that reves up to 3000 rpms is awesome in the lower and midrange of it's powerband and can pull a train, but isn't usually very fast

this is why high reving engines usually are smaller displacement engines. Small cylinders are easier to fill up at faster and faster rpms

the engine is the most efficient where it's peak torque is - usually in the midrange for most engines. For honda vtec engines it's in the upper end though because of the camshaft change

but you have to understand that hp is the exact same thing as torque only rpms are factored in. Rpms start playing a bigger role than torque does in the upper powerband. Well they're linked, but the rpms start becoming the primary reason the engine is able to generate more power at redline than earlier

 

When it goes thru the exhaust, it does it with more force" ??

 

if the engine and exhaust is restictive, it's going to try to pump the air thru but it's going to end up bottlenecking and the air will compress a little more than it would with a big open exhaust.

it'll only compress so much though on it's own though because the engine isn't spinning very fast and it'll go thru the engine being more dense

 

Theres a big difference between a push and a pull when it comes to pressure and gasses. You can infinately push a gas, but you can't infinately pull a gas against something (think of a gas in a tube, you can only hit 0 pressure (pull) however, you can approach infinate pressure (push)). With that in mind, explain how having 0 pressure in the exhaust manifold is a bad thing? If it sucks air out and allows it to expand (1st and 2nd low of thermodynamics, as well as charles law), the engine has to do less work pushing the air out of the cylinder at the 1st step of the 4 step combustion process. This directly increases the LEAST efficient part of an engine. For most engines, thats the upper RPM range- which happens to produce the most power.
For larger engines, a better exhasut collector and larger piping, will increase power down low as well as up high, but not as much down low because those engines have cams which are far more efficient below 5000 RPM because of the mass of the parts. Also, at those sizes (7 liters of air for example, in a LS7), the mass of the air also becomes important in the absoulte power of the engines.
Although its already known you can't have a 100% efficient chemical/combustion motor, which has a net heat production of 0, net work output = 100% of the engergy in the gasoline, you have to realize this is a result of not only friction, but heat of work, and negative effects of the mass of the reagents, and the dynamics of non-adiabatic compressions.
Basically, a larger exhaust will always make power where the engine is least efficient because the mass of the air, moving parts and airflow between the valves becomes more important then.

More flow will always make more power, where it is needed in high RPM, low efficiency regions

 

a simplified explanation is a highway and rush hour.

there's only so many cars on the road (amount of air)

a 2 lane highway will clog up easier than a 8 lane highway (how restrictive the exhaust is)

when rush hour happens (throttle) , the cars bunch up and get pissed off (condensed air)

when those pissed off cars finally get out of rush hour, they speed up beyond normal because they're pissed off (air wants to decompress and moves faster due to the barometric pressure difference to get outside to where the air is normal density again)

if you had a 8 lane highway, the cars would just pass right thru at their normal speed