right, but your word means absolutely nothing without the charts so that doesn't help him

 

..less time for the air to enter as opposed to using stock cams? please explain this one...the valve lift/duration doesnt change with rpms...

 

at 1000 rpms, each cylinder chamber has ample time to fully fill up then ignite.
At 8000 rpms, it has 1/8 the time to fill up.

The cylinder chamber is only as big as it is. It can only hold so much air at a natural ambient pressure. To hold more air would require larger displacement or FI

Gasses (air) can only move so fast naturally. When under pressure via FI, it's a little different story since the air can then be actively forced in

The valve lift usually doesn't change on most engines, unless it has VTEC.
Just as much air gets sucked into an engine with small exhaust/cams as a large exhaust/cams. What the difference is, is that small exhaust/cams make that air heat up more via friction and making the air more compressed

Having high lift/duration cams at first seems it's going to suck in more air, but what's really happening is at high rpms it's letting the fast moving air to pass through easier with less heat building up from friction and compressing. At low rpms, it's releasing some of the air so the ignition is less potent. Without high rpms, the engine isn't spinning fast enough to maintain an incoming high pressure of air

What you're really doing is changing the efficiency of the engine at different areas of the rpms. The only way to physically run MORE air through an engine is to either go FI, or increase the displacement via a larger bore and/or stroke.

 

that makes absolutely no sense..along with most of the stuff you just said..you know hot air expands right? the colder the air the more compressed it is..heat has nothing to do with it...the bottom line is aftermarket cams will make more power up top than stock ones..theres no way around it..and rpms also have absolutely no effect on how much air enters the engine...if what you are saying is correct then power should fall off up top since LESS air??? enters the engine....fuel+air+spark makes power..the more air and fuel the more power....and cams allow more air to enter the engine at any given point than the stock ones do.

 

power does fall off the top though if you reved high enough. Just look at any dyno curve, especially NA ones. The way to combat that is with a larger exhaust/cams. The tq curve always drops up high unless the engine is specifically tuned to make efficient power at high rpms. It's a little easier to understand if you just look at the tq curve and not the hp curve.

Fuel+air+spark = a bunch of burning fire, not power.
More air = a larger and brighter flame, not power
Add in some compression to those ingredients and then you'll get a violent explosion or released energy that has the capability to move something and create power.

higher lift, more duration cams are leaving the cylinder chamber open longer. You're going to lose compression at low rpms without high rpms keeping the air velocity high. It's great for high rpms, but loses power at low rpms unless the stock cams were not tuned well for the engine in the first place

hot air expands, but it doesn't have a free environment to expand into inside an engine, so it creates more heat via friction or the air molecules moving faster and that heat gets absorbed into the engine. With large cams/exhaust, that heat can just exit instead of getting stuck to warm up future incoming air

 

been following this out of a morbid curiosity. As rude as the OP seems from your advice, are you trying to defend credibility with this guy sentry? He only seems to use your often seeked advice to be more arrogant with each reply.

Let him make his own mistakes or do his own homework, rather than beg for quick answers then complain they arent good enough.

Edit*
Sorry OP, Snyperz just being the trouble maker

 

Are you retarded? I'm the OP and I have only made two posts in the whole thread. The original one asking which set-up is good and a follow up confirming what his advice was. Learn to read. It's not me arguing with him.

 

Back to the original question and the OP.........I agree with sentry65 and Jeremy that it is not simply a matter of getting a larger exhaust to get more power.
For most SC builds the only fixed parameter is the bore and stroke (most of us use the stock block) while the intake, plenum, cams, headers, injectors, catalytic convertors, exhaust and which kit/pulley used are all variables that must be balanced to achieved the best results over the broadest rpm range. This is where experience and intuition make a big difference as there is no effective way to completely 'model' the environment that occurs in our engines during daily operation. Which gear, what temperature, the barometric pressure, humidity, state of 'tune', speed, etc., etc., etc. all change the nature of the explosion that generates power in a motor. 400 dyno sheets is a good start on building a statistical universe but it won't answer everyone's questions.

Talk to Jeremy, Sharif, MRC, GTM, SGP and any of the other respected tuners in the community about what YOU want your build to do, weigh their advice and then spend your money. It's always a compromise and there are no guarantees.

The point of this long-winded diatribe is that, of course, I recommend the HKS exhaust because it's what I know and has worked very well (with the other equipment listed in my sig) on a daily driver for over 5,000 miles. And here's my dyno.

Good luck.

 

The OP basically asked the question relative to dual exhaust and power.. The responses seem to be all over the terrain relative to his question..The issue I am raising is with those who that say dual will reduce low end power. I am challenging those who believe it does by asking for DATA that verifies it. Simple as that..Changing an exhaust is expensive and anyone deciding on it should have some credible reliable info as to what he may be sacrificing vs gain..

 

I friend of mine has an Eaton M62 (twin screw) supercharger on his 1997 Ford Probe GT. It's virtually the same setup that I have except exhaust. He has a Borla 2.25" exhaust and I have a pacesetter 2.5" exhaust. I make a bit more power though. He recently got an electric exhaust cutout and installed it just down from the collector pipe. So it was back to the dyno, net result after two pulls on the same dyno was a 12whp gain when the cutout was open.

So a larger exhaust in this case would yield more power. No othere changes were done to the car between the two pulls on the dyno.

 

no car, no matter, FI, or NA, needs backpressue. People too often confuse backpressure for velocity...they are not the same. Backpressure is bad, velocity is good.

 

[QUOTE=Z1 Performance]no car, no matter, FI, or NA, needs backpressue. People too often confuse backpressure for velocity...they are not the same. Backpressure is bad, velocity is good.[/QUOTE


The question remains does a dual exhaust vs a single reduce low end Tq for a centrifugal S/C?

 

There is no magic answer...it will depend on the exact exhaust, the exact modifications. All too often people are looking for the easy answer where none exists. This is one such example

 

Not looking for any magic, do you have any experience with centrifugal S/C's that show low end power loss w/dual any dual? This low end power loss is often stated on this forum with no specific reliable supporting data..

 

So while we are on this topic I have to ask about my setup. I kept my stock exhaust and just did test pipes because I didn't want to lose any low end power. I was told by Sharif that I was losing power with my stock exhaust when he tuned it and I am only making 330whp on a DD. I was considering a new exhaust per his advice but haven't pulled the trigger yet. Even though I have test pipes is the stock exhaust too restrictive here? I was considering a Borla but now it seems like the true dual is not the way to go with a supercharger.

 

I should be able find a dyno to show gain from a true dual to X Pipe Dual.

 

This is exactly what I'm trying to understand...Urban legends will automatically tell you, you will lose low end Tq. But no one seems to have any definitive data that shows this to be the case..There may be a loss but where has it been shown to be true..

 

I didn't make any such claim. All I am trying to say is that there is not automatically 1 right or wrong answer. If you search around, I am sure you can find plenty of examples of various exhaust setups on various Vortech equipped cars, for you, or anyone else, to make their own decision from.

 

I have searched and only find urban legend B.S.

 

I agree with this, but it's the "backpressure" (notice the quotes) that helps create a high velocity when the rpms are low because the air isn't already moving fast. But yeah, there isn't going to be an exhaust that does everything well



Yeah I dunno. If I'm wrong, I'd just like to know where so I can learn from my mistakes. A lot of people know I love dyno charts and comparing dynos of different setups. As far as collecting data, aside from a shop that owns a dyno, I'm probably one of the people who has the most data collected over the years. So it seems funny he wants data, I offer him data, and he doesn't respond to it. I get it though, people have pride just like I do. That and I'm just killing some time at work while I wait on my computers to finish something

you're on an internet forum. There's not many scientists here running around dynoing individual parts for every setup. It's pointless since everyone has a different setup anyway. All you can do is collect dyno sheets and read people's impresssions and try to read between the lines and find an overall pattern


I still don't think dual or single matters at all really. What matters is your overall flow between your plenum, heads, cams, headers, cats, and exhaust as a whole. Changing one of those parts isn't going to be a magic answer. You could change a combo of those parts and get pretty much the same overall result if you changed a different combo of parts.

I think having the two sides connected has some benefits for NA and supercharged setups, but being dual or single isn't what really matters.
Centrifugals don't create a lot of boost at low rpms but do a lot of boost at high rpms. Most people that get centrifugal SC's opt to optimize their high rpm range by getting higher flowing exhaust parts. I've never seen someone gain low end power from changing an exhaust part on the exhaust side. I have on the intake side of things - plenum, supercharger pulley, etc




I'm still offering you all the data I've collected over the years, but you haven't said how I can send it to you...I have 697 megs worth of dyno data that follows people's cars as they've added parts and redynoed