Open Headers versus Mufflers

I'm playing around with DynoSim6 seeing what my new motor could/should do. I'm curious, does using mufflers move up your HP and torque to occur earlier in the RPM range? Do these numbers and curves seem reasonable in the way mufflers are affecting power?

Not if the collectors are the correct length.

A bad muffler will really hurt the performance, a good one, (straight through design and big pipes) not so much
Been, there done that, both ways

Exhaust choices can have a significant impact on power. I use electric cut-outs so that I can concentrate on the tone and amount of the exhaust that I hear. Loud, quiet, X pipe, H pipe, straight through, baffled, 2 1/2", 3", 3 1/2" , brand X, brand Y, or brand Z don't have much, if any, impact on power with cut-outs. Get the right collector length with cut-outs and most of the other issues guys struggle with when it comes to the exhaust are mute.

www.youtube.com/watch?v=eLceqIoTMvo

www.youtube.com/watch?v=_PVXvHkr-Vs

There are many, many more muffler/exhaust shoot-outs/tests on the 'tube.

You'll need to consider fine tuning your jetting once you determine whether you want to optimize open headers or full exhaust. There will likely be a difference. In my particular 360 application, going from 3" open headers & collectors to 3" X-pipe & straight thru bullet mufflers, it ran even better when jetted down 2 #'s all around, I'm assuming that the X-pipe helped efficiency. Your results may vary.

just now going from 3 1/2" collectors, 3" long, to a 10" extension [3 1/2"] reduced to a 3" x pipe to 3" race bullets.
446, 11 : 1 [measured compression] slightly worked RPM heads, RPM dual plane intake, big thermo-quad [? !!], 2" to 2 1/8" step TTI headers. [with the above mentioned 3 1/2" collectors]
i have a vast selection of jets and metering rods for the thermo-quad, so i should be able to get a good tune on it.

An engine with a large enough overlap triangle area* (from Vizard: OL area ~ OL Degrees^2) to benefit significantly from tuned exhaust will experience less pressure differential to the chamber with any disturbance to the exhaust return wave (diametric change, more volume, restriction).

Very mild engines may not notice any change.

* For OL area comparison using nominal valve events (IO @ BTDC + XC @ ATDC), 70 degrees is not 40% greater area than 50 degrees (70 / 50), but 70^2 / 50^2, or 96% greater (4,900 / 2,500).

Engine masters did a couple shows about exhaust systems. Worth checking out in regards to your question.

Like the links I posted above.

No.

Mufflers gain 100ft/lbs 3500-4000?

And then lose 80hp 60ft/lbs at 7000?

Hell no.

As madscientist stated, no real comparison unless you have the right collector length. Still...


Said in a different way, I think you can build an exhaust system to the bumper that performs closely to open headers/optimized collector with then the only downside weight.


I use pypes race flow mufflers. Despite the name they are very quiet and straight through. Made 595 rwhp @7200 through those mufflers, tailpipes (dual 3") and stock exit size tips.


I think it will be 610-620rwhp after a few changes I've made.

Can certainly test it but don't think there would be more than a -couple- of HP difference between the exhaust I'm running VS dropped before mufflers/tailpipes.



For the wheel hp levels originally posted, dual 2.5" would efficiently cover it, and those pipes would dictate velocity.

At that point, -no- muffler is picking up 100ft/lbs.

And no muffler is -losing- 80hp to open headers unless total junk.



So, choose exhaust pipe size to be capable of supporting max HP and pair it with a straight through/non restrictive muffler (like the race flow) and I think you've done your best.

I don't know the exact mufflers (they are big) that are on the 589ci wedge RR I crewed on but its a full 3" system to the bumper. Has 2.1/8" TTI step hdrs with 4" collector.

Engine dyno'd@694.2hp@5500, 693@5900, same carb dyno to track, car weighs 3800@line and has been a best of 130mph on a no headwind day.

Thats 679fwhp and shows a 10.34 with a 1.44 60, cars gone 10.30@1.421 60.best. Never been run on open hdrs. Perhaps the dyno was a bit stingy?

My 2 penneth. We have a 120db max sound level for 9.00 cars / classes and slower. They are regularly checked at race meeting but there no sound level in place at a RWYB's . I ran a true dual (no H or X) 4" system with bullet muffler to the axle with turn downs. No noticeable effect on ET or MPH, db dropped from 124.9 (open headers) to 120.4 close enough for the tech guys to pass. I later made an X pipe using the same 4" dyno max mufflers, again no noticeable effect on ET or MPH db dropped to 119.8 when tested. I've since welded V clamps to the pipes to make swapping stuff out easy, we've ran with the x pipe but no mufflers, again no noticeable effect on ET or MPH. I've yet to be tested for sound level in this configuration but to the ear it is a little louder. For the street we have a pair of old super trapps which are v clamped on to the end of the bullet mufflers in place of the turn downs. Never ran on the strip with these, I'm guessing they woukd really hurt the performance. Last time I ran with just open headers, I burnt all the candy paint off the trans crossmember

[There are a lot of people on this forum that are A LOT smarter than me. I still scratch my head from time to time thinking about my results, I probably just built a poor system. These are the results from my 605 Hemi on my dyno. My dyno exhaust system is two 5" pipes attached to two 5" diesel mufflers. I have adapters that slip fit over the header collectors so the system is sealed tight while making pulls. The headers on the motor may be a bit small for the application, they are 2-1/8x36x3-1/2, bolted to 18" 3-1/2" collectors.
Through the dyno exhaust it made 816.9hp@6059&752.6ftlbs@5383. I tried everything I could think of and this was the best it would do. Finally I I unhooked it from the dyno exhaust turned it and pointed the open collectors out the door. I made 3 pulls like that and it netted 852.8hp@5782&818.4ftlbs@4818. Finally I hooked the street exhaust up to it 3-1/2" pipes with X pipe hooked to 3-1/2 Ultra Flows. It killed the hp, 735.7hp@5405&748.5ftlbs@4274. I unhooked the exhaust and it went right back to the previous numbers.