How to get the most hp from exhaust

midpipe.

open headers = loss of tq.

backpressure robs you of power, but not enough backpressure kills your bottom end. like he said, get a free flowing mid-pipe.

what are you current mods? where do you want to be with your car? if you're looking for something for the 1/4, go w/ an o/r xpipe.

have some dumps welded in before you mufflers. Like this http://store.summitracing.com/partd...4+310245&N=4294923429+4294920534&autoview=sku or http://store.summitracing.com/defau...4+310245&N=4294923429+4294920534&autoview=sku . Check Summit under exhaust cutouts.


+1 on the some backpressure is good too.

Are you ready for this???

5.O STANG said:

Would open headers be the most gains in hp since there is no restrictions? If it does increase your topend hp would it hurt your low end torque? Would it be worth it? Is there some kind of switch that opens and closes the flow of exhaust for our cars that you can have regular use through the mufflers then when you arrive at the track or want to scare people just flip the switch and have open headers. Would running open headers hurt anything? If there is a swtich with a set up like that and if so where can I get one.

Click to expand...

I've recently been doing a lot of research on exhausts and basically it's a big area. To get the best setup is complex and likely not cheep. However to get good setup is very easy. I'll highlight some of the areas, but if you want more info, ask and I'll copy or post the link to it (it's very long and detailed though).

Basically you need to look at 3 areas:

1. flow rate
2. exhaust pressure wave
3. scavenging

1 & 2 are concerned with not reducing power (i.e. freeing up lost power), where as 3 actually increases power. However 2 (pressure wave) is rather complex and in many cases way beyond what most people need to know about.

1. Flow rate:

Basically you need enough flow so as to let the engine breath at high rpms without any restriction. However if you have too much flow you may not be able to ake use of the potential and you will loose low rpm toque. So as others have stated, you want free flowing, but still retain some back pressure to keep stronger bottom torque.

Use this formula as a guide:

2.2cfm for every 1hp

So estimate your expected BHP level (engine) and go from there. Example:

350bhp would require (350 x 2.2) 770cfm flow rate. Now on a dual system, each bank only has to deal with half that (385cfm).

So you need to pick you mufflers and/or CATS to flow a minimal of that amount. Most performance mufflers should exceed this, but it's worth checking. Especially if a supercharger is in your future plans.

Then two the exhaust tubing, 2.5" duals will easily flow well enough for 500bhp, 3" would be OTT and compromise low end torque. If you do exceed 500bhp 2.5" duals should still flow pretty good, I suspect you would need to be producing over 700bhp to really see the gains of 3" tubing.

N.B. A Highflow Metal Matrix CAT will flow upto 580cfm, even ceramic CATS can exceed 440cfm, so in terms of backpressure there really is no reason not to run CATS on a road going car.

3. Scavenging.

Long Tube headers are the answer, bore size and lenght will have a bearing on their ability to scavenge and equalise the pressure wave. However I would recommend just buying a well know/respected brand off of the shelf.

Then there's X and H mid pipes. These also promote scavenging. In a test 50% of the setups saw a BHP gain with a H/X the other 50% did not. However there was no drop in BHP at all. So you may not pick up any BHP, but you certainly won't loose any.

In addition X/H pipes also reduce the DB noise level which can certainly be of benefit on the road.

2. Pressure wave, as I said this complex in calculating it. But things to note. Glass Pack and Chambered mufflers affect the pressure wave differently.

Also location of the muffler or straight pipe (from open headers) can have a dramatic affect on the pressure wave. All of these will affect BHP.


You mentioned cut-outs, to bypass the mufflers. If you design a low/zero loss system in terms of flow. A cut out will yeild no gain in BHP only noise, as the exhaust will not actually flow better when bypassing the mufflers. Also you may affect the pressure wave for the worse, thus producing lower BHP numbers.

If you plan on running open headers, I recommen you look into the pressure wave (PM me for a link) as it will have a major affect. Personally I'd just design a low loss, low restriction exhaust system. It will produce good power, be streetable in noise levels and with CATS even emissions friendly. And on only a mildly modified car I doubt there would be much in the way of BHP difference it and an ultimate setup (10rwhp or less) and probably 1-2rwhp over open headers.

Hope this helps.