[dgman2]

I would like to hear from someone who really knows the theory on this. I'm very frustrated with the attempts to make a decison on what to do about inproving my intake & exhaust.

I don't quite understand that one one hand whe need more flow for performance but yet need backpressure on the other hand. I think it makes sense that, depending on your engine's state of tune, you need a specific amount/pattern of flow and backpressure and that more is not always better for performance. Please let me know if my thought in this first paragraph is correct.

If there is to much restriction on flow going through our stock engines (obviously that is the case because there is power to be gained by increasing flow without changing anything other than intake and exhaust), than it stands to reason that if all we do is changing intake and exhaust (& I don't mean internal changes such as heads, cams, etc) there has to be one ideal set of mods that is the best....anything different would be less effective. This has to be true if the first paragraph is correct.

So here is my problem. After reading a good bit and listening to others, I've heard so many opinions on what mods are the best, but there are to many different opinions for me to find the correct answer.

FOR MY STOCK ENGINE, I want the best available CAI (if this is really better than just replacing with a K&N filter). Next I want to change my exhuast with the best available option for the dollar amount. If headers and the best pipes you can get are perfect for a fully modified, say 600+ HP engine, than this should be to much flow for a stock engine (according to my thoughts in the first paragraph).

So, if somewhat more flow is needed, why would headers be better than say a muffler delete. Exhaust flow is hindered by several obstickles such as restrive manifolds, cats, mufflers, etc. Doesn't removal of any of those restrictions cause improved flow & thus better performance up to the point that flow is excessive for a stock engine?.....OR, is it the placement of the restriction that makes the difference? (e.g. headers and muffler delete are pretty much oposite ends of the exhaust).

How does nitrous fit in this picture? Does a normally aspirated 600HP LS2, for example, need the exact same exhaust flow as say a 450HP LS2 with 150 HP shot of Nitrous. Are their needs the same or is there a difference in exhaust pressures due to the nitrous induction vs 100% ambient air?

Finally the magic question. What intake & exhaust combo is the best for a stock LS2 GTO with 150 shot of nitrous & what other changes are essential to make with such a combo (e.g. plugs, thermostat, etc)?

I'd very much appreciate some good info.

 

[Licit]

Not naming brands but I'd say it's pretty heavily weighed towards LongTube headers, a CAI and most important, a tune. Want cost effective you could go with a set of Pacesetters and look for a used CAI in the for sale, then tune. Would put you at roughly $1100 for 30-40hp, little more or less just all depends.

 

[svede1212]

well you really don't want back pressure but you need flow velocity. the reason you don't want a long, too big exhaust is that the gases can cool off and lose speed. that acts as a plug to the gases that follow it. the right dia keeps the gases hot and the flow going. you need to tune for the best power. exhaust is also not a continuous flow but a series of pulses. headers use the pulses and the vacuum that follows the pulse to pull the next pulse along helping evacuate the gases. x-pipes interleave the pulses from the left and right banks and do the same type of scavaging as headers. it also better utilizes the following pipes because they're not "resting" as much in the pulse voids.
i've written alot about intakes. most of the data on them is very misleading. claims of HP gains are of course done on a dyno. on the dyno the hood is raised and a fan is placed facing the engine bay to cool the engine. the side benefit to the HP claim is that you're providing cool air that you don't see on the street. the only way to rate an intake is to monitor your MAP (manifold absolute pressure) and IAT (intake air temperature) under "street" conditions, with the hood closed. the MAP will tell you if you're seeing a restriction (by not approaching atmosphere at high RPM). the IAT is important because 1. cooler air is denser thus providing more oxygen per cylinder load and 2. because to prevent knock the computer pulls timing (and thus power) when the IAT achieves 86*.
claims of acceptable IATs are misleading because they are achieved after several minutes of driving at speed. that doesn't cut it if you're leaving the line and making it to the end of the strip in 12-14 seconds or when you're leaving a rustang in the dust at a light. you need cool, clean, abundant air. click on SS Intake in sig for further musings.

 

[machinistone]

You want minimal backpressure - scavanging is what makes power, and why you loose power when removing a well designed exhaust system.

Svede made a good post...just backing his up

 

[Licit]

I agree with both of you guys, but would you advise him to go with the setup like svede's SS or goat-ee's cold box(can't remember what he called it last) with the drop-in K&N? Myself I was thinking about just trying both and deciding what I like better. Guess I would like to be like dgman2 and know ahead of time what the best bet is but damn I really need to get on this one way or the other. One thing; my tuner told me while we were street tuning with hptuner, that my car was running less power under 3000rpm than the guys who had cai's and similar other mods that he tuned. I told him it made no sense since as far as I knew cai's that are out don't make their gains until above the 2500 to 3000rpm level. But hey he was the one looking at the numbers. I also figured with a p&p TB and UDpulley, that they would have put me ahead of the guys who had typical cai's but no p&p TB or UDpulley. Somehow the shorties with catless mids were in need of more on the intake side as far as flow is concerned. Sorry dgman2 for going on a rant here but these are probably things that will help you ahead of time with modding. I have also debated trying the MAF-less tune when I do tune next but am still debating where I am going after the more "true" CAI route.

 

[dgman2]

Thank you for your info guys. I'm still working on getting the right combination of mods before I put my plan into action.