Dual Exaust

[Mach83]

Another dumb question for you all. Does true dual exaust increase HP. If so how much? What are better exaust systems, Borla or Corsa. Thanks for all the info guys/girls.

[95TransAm]

Another dumb question for you all. Does true dual exaust increase HP. If so how much? What are better exaust systems, Borla or Corsa. Thanks for all the info guys/girls.

I always figured that with a true dual setup it would flow better....but... I do remember reading on this forum a while back that on F-bodies, it actually robs you of a small amount of HP.

I'm not 100% sure though, never seen any dyno numbers comparing the two setups with my own two eyes.

As for better exhaust, Borla and Corsa are both excellent choices...but cost you mucho dinero.

Any aftermarket exhaust system will flow better than stock. I have heard debates about flowmaster in particular not putting up as good of numbers as some other systems. Personally, I think the loudmouth is one of the best bang for the buck catback systems. Flows awesome, as cheap as they come, and sounds SICK on an LT1

[fastTa]

Really depends on the setup and alot of other obvious engine power outputs. But generally speaking, the y-pipe is actually there for a reason. Basically, you have 2 banks. Bank 1(driver's side) and Bank 2(passenger side).

Obviously you have 4 cylinders emitting an independent exhaust pulse at each exhaust cycle of the motor. Each one of those 4 exhaust pulses is eventually "merged" into 1 passageway so to speak. So essentially you have 2 passageways coming off of the motor at the y-pipe point...one from each bank. Since there are no 2 cylinders that are fired at the exact same time, the exhaust pulses are always itermittent and simultaneously overlapping once they get to the y-pipe. What the y-pipe does, is it literally uses the exhaust pulse that just entered the y-pipe to "pull" on the exhaust pulse right behind it that is about to enter the y-pipe. This effect actually maximizes the efficiency of the scavenging effect within the cylinder during valve overlap.

So a properly set up y-pipe configuration has the potential to outperform and make more overall power than a traditional true dual setup.

Whew!

[97LT1Z28]

Very well Explained Kevin......

[Steel2686]

Awesome explanation, Kevin. I've always wondered about true-dual setups myself. I figured there was a reason most systems are sold with a y-pipe, but never knew exactly why. Nice job.

BTW - Here's another vote for the SLP Loudmouth exhuast. I just installed mine. Wow!

[DeWynter]

Would it not do the same thing with a properly tuned X pipe dual exhaust set up? Here is one for an LT1

[Injuneer]

I'm not convinced the X-pipe and H-pipe mods are worth the effort, unless thye are correctly designed and proven. Problem is, I don't think anyone has taken the time to evaluate various combo's on the same engine, to see what the advantage is.

Exhaust design is extremely complex. The best analysis I have seen breaks it down into several sections.... 1) the primaries, where diameter, velocity and length play a huge part, 2) the collector - which is in large part a transition from the primaries and where length is an important factor, 3) a "separation" to "end" the collector and separate it from the balance of the exhaust, and finally 4) "everything else" which comes down to eliminating pressure losses, with few other considerations. Once you get past the collector, you are so far removed from the exhaust port that there is little affect on scavenging from the rest of the exhaust. Extending the effective collector length to reach the "H" or the "X" may actually hurt you more than it helps. The collector needs to be "tuned" to the RPM, just like the primaries.

I saw an LT1 383 S/C engine make 1,125HP through a set of Hooker LT's, custom 3" Mufflex Y-pipe with a 3" Borla XR1 in each branch, and the Mufflex 4" catback with the Flowmaster single-in/single out muffler. When the Mufflex catback and Y-pipe was removed, leaving only the Hooker LT's with the Borlas bolted to them, there was "0" HP difference on the chassis dyno. Pushing all that exhaust through a Y-pipe/catback was NOT costing any HP loss. But the sytem weighed 50#, so there was a gain at the track without that 50#.

It would be interesting to test some "H" and "X" pipe systems to see if its really worth it.

There are some interesting thoughts on exhaust system design in the David Vizard "How TO Make HP" book, and whether you like what he writes in other areas or not, the "exhaust" stuff is pretty good. His approach to a fully phased exhaust, actually combining cylinders from opposite banks in each collector to get them in the correct firing sequence and maximize scavenging, is fascinating. Sort of the ultimate extension of the thoughts Kevin presented.

[DeWynter]

His approach to a fully phased exhaust, actually combining cylinders from opposite banks in each collector to get them in the correct firing sequence and maximize scavenging, is fascinating.

Can you imagine the length of the primaries and the complexity of the routing? Its a nice idea but it would be next to impossible to do something like that on a production car. I have enough problems with my f-body with LT headers, now imagine trying to phase all the primaries together for maximum scavenging, I imagine there would have to be some primaries running to the opposite side for this to be achieved

[fastTa]

I haven't read Dave's writeup in Circle Track on exhaust tuning, but I need to. I've heard it come up a few times. I've also read some other articles on the "opposite bank cylinder swapping" into the collector on each side. Pretty cool stuff to say the least.

Interesting on GB's ride how the removal of the y-pipe/catback netted a zero difference. The ZR1's are really made to function without any plumbing behind them. They are tuned for an atmospheric exit. Could be one reason. The other I was thinking about was this. Maybe the y-pipe actually did make slightly more HP, but when combined with the additional backpressure and likely less flow of the catback, it may have just essentially cancelled out any gains seen by the y-pipe leaving a net gain of zero. Just brainstorming out loud.

When HP levels start to exceed 1000HP, physics seems to wander from it's natural course.