Alright so for my A4 T/A i recently got a set of the Edelbrock Victor race headers. They are stepped and huge, with a 3.5" collector. I got them because they were so damn cheap from Edelbrock.
My concern is that ideally I wanted 2.5" true duals,preferably over axle, but with a 3.5" collector on the header would it be stupid to shrink that down to the 2.5" exhaust? Would i be loosing power or have too much back pressure?
3" duals would be do able but much harder and so damn expensive. My other option was getting a nice 3" catback with a cutout.

On the side of duals(this may be a dumb question) but what is the point of an X/H pipe. Why not just run straight from the headers all the way back?
Does the crossover pipe help with scavenging or something?

Any feedback would be great or anyone with experience with the edelbrock victor headers who could chime in with their setup would be appreciated
Thanks

 

Imo, this would be a lot easier to do:
I'd run some reducers(3.5-3") right off the collectors, then 3" Y-pipe into a FM merger w/4" exit, then into a 4" Mufflex cat-back w/Magnaflow muffler. This will clearly have a higher flow then running 2.5" duals, but not close to 3" duals.
If you don't mind having slightly lower flow than dual 2.5" pipes then you could go with a 3.5" exit FM merger and a 3.5" catback.

With all else being equal, this is about what you'll get from different exhaust pipe sizes.

3” Single, good for 370hp eng. with 0 loss.
3.5” Single, good for 503hp eng. with 0 loss.
4” Single, good for 657hp eng. with 0 loss.
2.5” dual, good for 513hp eng. with 0 loss.
3” dual, good for 812hp eng. with 0 loss.

 

For any performance exhaust system, some type of crossover connecting the two sides of a dual exhaust system is important because it acts to balance the exhaust pulses/complex pressure waves from the two banks of the engine. The result is enhanced low-end torque, better overall performance, and better sound.

With a V8, there are always (2) cylinders on each side of the engine that fire within 90 degrees of each other. On a small-block Chevy, the firing order is 1-8-4-3-6-5-7-2, and the cylinders are numbered from front to back down the crankshaft. Odd numbers on one side and even numbers on the other. A cylinder fires every 45 degrees of crankshaft rotation. So by looking at the firing order, you can see that cylinders 4 and 8 fire 45 degrees apart on one side. Then later, cylinders 5 an 7 fire 45 degrees apart. This creates a high-pressure pulse that inhibits smooth flow and makes for a "choppy" exhaust sound.


> The common H-style crossover is good at balancing sound pulses between the two halves, but doesn't do much to promote scavenging because the exhaust gases tend to follow the path of least resistance, which is straight through each pipe rather than taking the 90-degree turn through the H-pipe into the other half of the system.

> In an X-pipe system, however, where the two sides of the system intersect, the gasses have no choice but to intermingle as they pass through the junction. This promotes improved scavenging effects by smoothing out uneven exhaust pulses from the engine's firing order. It also helps quiet down the exhaust, resulting in a mellower, less raspy tone.

> Faster acceleration of the gasses through an X-pipe causes them to flow in a linear fashion parallel to the walls of the tubing rather than tumbling. This 'laminar' flowing gas is much quieter than tumbling gas, resulting in an exhaust tone up to 8 decibels quieter than a traditional H-pipe.


H-tubes should be at least 3/4 the size of your exhaust pipes, and located in the "hot" area of the pipes behind the header outlets. Easiest way to find that hot area, is to spray a line of white paint down the pipes after the headers, and go for a good run. Install the H-pipe somewhere in the area where the paint burns off the pipes, equal distance from each header collector. Use the same technique to determine where to place an X-pipe.

I know, prolly more info than what you wanted

 

I also just got those headers. I am thinking about running a 3 inch Y in to a flowmaster merge with a 3.5 outlet. However one person recommended running a 2.5 inch Y-pipe to increase exhaust velocity and promote scavenging, is there any truth to that?

 

No, that's horrible advice, the ways to.improve velocity are with good merges in the collectors and a good y merge or crossover pipe

 

In essence that's really the biggest give-and-take problem for exhaust system designers: exhaust charge velocity vs. minimizing exhaust restriction.

If you have the clairvoyance to just KNOW the perfect balance for that in any setup to make the best power, you should be making the big bucks because that isn't something the common person just knows.

 

okey thanks, i like the chart of what size exhaust is good for what. but i dont really want the duals for the power loss ration i just love the mean *** sound of TD's ya know. Im sure in time ill be around 500rwhp but thats years down the road haha

 

Wow!! not not more than i wanted at all thats awesome. i ask questions hoping to get good feedback.Thnaks. So an x-pipe would be the "ultimate" of exhaust with the best results?

So in your opinion( or maybe backed by a page of info haha) ive got the stepped headers(which are good for scavenging) and they have a 3.5 collector....would you break it all the way down into a 2.5" xpipe? or would that make some sort of constriction?

 

As long as the transition is smooth no, it will be fine

 

nice write up, i like it

 

For a true dual exhaust setup - I would come off your headers with 3" pipes, to a 3" x-pipe located somewhere near the tranny tailshaft, 3" pipes back to 3" inlet mufflers.

Kooks Custom Headers’ has a true dual, 3-inch, X-pipe equipped, bolt-on Fourth-Gen F-body exhaust system for an excellent example (PN 65-9802-CX-DUAL)





















Tough part of the design/install is the area between the gas tank, axle tube, & upper panhard rod on PS which is tight for 3" but possible...

 

With all else being equal, this is about what you'll get from different exhaust pipe sizes.

3” Single, good for 370hp eng. with 0 loss.
3.5” Single, good for 503hp eng. with 0 loss.
4” Single, good for 657hp eng. with 0 loss.
2.5” dual, good for 513hp eng. with 0 loss.
3” dual, good for 812hp eng. with 0 loss.[/QUOTE]

Is this correct? How much of a percentage do you think is lost using 1 7/8 headers and 3" y with a cutout on say a 650-750 HP car?

 

Is this correct? How much of a percentage do you think is lost using 1 7/8 headers and 3" y with a cutout on say a 650-750 HP car?[/QUOTE]

Easliy 20/20