Loss of Power w/Cutouts Open

[typicalmarine]

Long story short, one of my electric cutouts was either ripped off or wasnt welded on completely. I waited from early June until last Friday to receive the replacement.

I always felt that my power felt "flat" at best with the cutouts open. Back in May during a dyno run I opened them up just to see what happens and sure enough my hp/tq dropped by about 45 ponies.

Well with both cutouts on and closed I finally have that "snap" back! Chugging around town for so long with them open I forgot what its like to have that power....

So for those of you who want to go straight pipes - all I can say is I wouldnt do it. Pick up a set of cutouts and have the best of both worlds.

Strange thing is my tuner (ForeignMuscle) said he had an SRT8 on the dyno and when it's cutouts were opened it actually gained hp! Who knows but it just goes to show how easily the addition or removal of something can drastically change your power.

[Redfox0099]

They will cost you low in Torque but gain on the top end... at least they did on my N/A 426.

[MAN WGN]

I can feel the difference from when mine are open and when they are closed. But I love the sound of when they are open

[CoolVanilla]

I ran back to back on the dyno closed vs open and was unable to detect a difference in the curve.

And I understand exactly what your saying; my SOTP dyno tells me that I'm giving up low end torque also. Although, I question how much. I think the perceived difference with them open is huge, because there's so much damn noise and grunt associated with the same acceleration when compared to them closed. It just *feels* like you should be hauling ass given the car's attitude. But how much of that is real? I dunno. I'm betting not much (based on my totally informal testing).

[8yourM5]

U need a big motor to use cut outs. I only lost 5 up and tq with them open.

[BrianG]

I also did a back to back dyno pull and saw very minimal change maybe 2hp gain.

[sinistersix]

i just got my cutouts put on, and it feels that at WOT at higher highway speeds it seems a tad bit more power, but the butt dyno feels liek it is way flat from a stop or dig. Much more throttle response and quickness with them closed from a stop I think

[typicalmarine]

Oh hell ya the cutouts sound MEAN! I really enjoy them but going a couple months not having the ability to close them was rough. I had strep throat for a month and my 45 minute comute to and from work was horrible....

[dacaman12]

It isn't such much the fact that you have cutouts as WHERE the cutouts are. Whether on purpose, or by accident, your exhaust produces wave pulses that "tune in" at various RPMS. These wave pulses traverse you exhaust multiple times, creating peaks and troughs in your torque/hp curve. Consequently, you can "tune" for a certain RPM using more than one length, although the strength of the reflections decay as you go up in "order"...

....The cutouts are changing your "tuned length". In effect, they are making your exhaust shorter. THe shorter exhaust means you can take advantage of fewer "tuning points", but also have fewer "out of tune " points in the RPM band.

...If your cutouts are at such a spot that you are "out of tune" at peak hp, then a drop in the raw # only makes sense.

FWIW, to capture the initial pulse, which is the strongest, you would need an exhaust that is longer than your car, lol. You would also have a more pronounced "dip" before and after the RPM you are "tuning" for.

[HemiRedMagnum]

Well all that I have heard is that you loose the down low torque but gain about 8-11 hp. There is a member here with QTP cutouts that has a closed to open dyno with about that gain. Here is the link:

http://lxforums.com/board/showthread.php?t=160776

[Popeye's Hemi]

Good to see some new blood here and it may be fortified with some "Hemi Magic", but time will tell.

It isn't such much the fact that you have cutouts as WHERE the cutouts are. Whether on purpose, or by accident, your exhaust produces wave pulses that "tune in" at various RPMS. These wave pulses traverse you exhaust multiple times, creating peaks and troughs in your torque/hp curve. Consequently, you can "tune" for a certain RPM using more than one length, although the strength of the reflections decay as you go up in "order"...

....The cutouts are changing your "tuned length". In effect, they are making your exhaust shorter. THe shorter exhaust means you can take advantage of fewer "tuning points", but also have fewer "out of tune " points in the RPM band.

...If your cutouts are at such a spot that you are "out of tune" at peak hp, then a drop in the raw # only makes sense.

FWIW, to capture the initial pulse, which is the strongest, you would need an exhaust that is longer than your car, lol. You would also have a more pronounced "dip" before and after the RPM you are "tuning" for.

[dacaman12]

I punched the #s for a typical 5.7L performance package into Pipemax. How do these figures compare to what everyone is running?

-------------------------------------

"Chrysler late model 5.7L engine (calc'd 450 flywheel hp @ 5500 rpm)

__________________________________________________ __________________________


--- Single Primary Pipe Specs --- for 353.216 CID from 4000 to 6500 RPM
Diameter= 1.538 Length= 31.3 to 34.5 also 22.7 to 25.9 inches long
Note> Maximum Primary's Tuned Length= 50.2 to 53.4 inches long

--- Header Collector Specs (Conventional Straight Tube) ---
Diameter= 2.848 Tuned Lengths= 18.1 best and 9.1 or 36.3

H-Pipe= 18.1 X-Pipe= 72.5 distance behind end of Primary Tube ends

-- Total Exhaust System Tuned Lengths (Primary ends to TailPipe end) --
Best HP/TQ Tuned Collector Lengths= 18.1 , 36.3 , 72.5 , 145.0 inches long

Worst HP/TQ Loss Collector Lengths= 27.2 , 54.4 , 108.8 , 217.5 inches long

Note=> measured from where the Primary Pipes end inside the Collector to
the point the tailpipe exits into the atmosphere.
H-Pipe is located at end of Collector, and X-Pipe is located
usually half-way between end of Primary Pipes -to- tailpipe end

Note-> all Pipe Diameters are OD and based-off .0625 inch Pipe thickness

---- Primary Pipe's Harmonics ----
1st Harmonic = 127.5 inches long ... typically never used
2nd Harmonic = 50.2 inches long ... longest recommended
3rd Harmonic = 31.3 inches long ... highly recommended , best Torque Curve
4th Harmonic = 22.7 inches long ... shortest recommended
5th Harmonic = 17.8 inches long ... typically never used
6th Harmonic = 14.7 inches long ... typically never used
7th Harmonic = 12.5 inches long ... typically never used
8th Harmonic = 10.8 inches long ... typically never used

---- Collector's Harmonics (includes Intermediate, Muffler , TailPipe) ----
1st Harmonic = 145.0 inches long ... longest with Mufflers and TailPipes
2nd Harmonic = 72.5 inches long ... longest recommended with Mufflers
3rd Harmonic = 36.3 inches long ... more bottom-end Torque
4th Harmonic = 18.1 inches long ... highly recommended , best Torque Curve
5th Harmonic = 9.1 inches long ... reduced Torque , more top-end HP sometimes
6th Harmonic = 4.5 inches long ... reduced Torque , not recommended

[dudeiwin86]

so a reccomend length of a long tube primary would be 31.3"

and when it says reccomended "collector harmonic" length.. is that distance from the header collector to the tail pipe?
so if you run a cutout, you would want it 18.1" from the header collector?

just trying to get a handle on the Jargin used here,,,,

where does exhaust pipe diameter (excluding header primaries) fall into line?
will having a 2.5" pipe change the harmonics from a 3" pipe?
or is it all based on length?

looks like its time to bust out the tape measure

[lou1355]

I lost boost and power back to back on the dyno with them open. 2-3 psi and 40 hp, as I recall.

[dacaman12]

so a reccomend length of a long tube primary would be 31.3"

and when it says reccomended "collector harmonic" length.. is that distance from the header collector to the tail pipe?
so if you run a cutout, you would want it 18.1" from the header collector?

just trying to get a handle on the Jargin used here,,,,

where does exhaust pipe diameter (excluding header primaries) fall into line?
will having a 2.5" pipe change the harmonics from a 3" pipe?
or is it all based on length?

looks like its time to bust out the tape measure

If I understand correctly, "collector length" is from the end of your primaries to atmosphere. whether it be the end of your tailpipe, or your cut-outs.

......primary length includes the length of your port......

The exhaust waves travel at the speed of sound, which changes with temperature (THAT'S why my exhaust valve is smaller than my intake!!!!!!)

IMO, a change in pipe dia. will change the velocity more than anything else....but I could see where letting the gas expand into a larger pipe would affect the temperature of the gas, resulting in slightly different "tuned lengths". Of course, you would need to run the rpms higher, or increase displacement, to get the velocity back to where it should be with the larger pipes, which may/may not call for different "tuned lengths".

Wave tuning is quite a complex subject...(bows to the experts)

Calvin Elston of Elston exhausts done a test, comparing the latest stepped, tri-y race headers against 8 individual 6" long pipes. The results where posted on speedtalk dot com.


.............Headers where about 15 hp better, lol. If anything can be learned from that, is you can't loss anymore than 15, unless you are making things worse, right?

I guess the "accurate" answer lies on thought that more of something helps only if you ain't got enough to start with...............


It would be interesting to see if the location of the cut-outs fall into one of pipemax's "worse tuned lengths".............

P.S. Forced induction will definately change things. The exhaust temps, if nothing else will be different. i used 113.5% for volumetric efficiency, which will typically produce EGTs in the 1350° range.