[avalonandl]

Originally Posted by Village Idiot

CSP did tests that it's not a restriction until 850-900whp it's not costing anyone a race lol

This..... Thw 2005-2006 GTO's had the same pinch....ZERO loss

[HDRDTD]

It has been demonstrated in the past that even though the tube is 'crushed' a bit, the cross section area remains the same, resulting in 'no' loss of performance.

[L78toLT1]

Originally Posted by HDRDTD

It has been demonstrated in the past that even though the tube is 'crushed' a bit, the cross section area remains the same, resulting in 'no' loss of performance.

The cross section is reduced a bit, but not enough to affect performance

[BrianL]

I got rid of mine as it was just against my grain to have these in place. Just wasn't right in my mind.

I got the Hooker BlackHeart crush pipe delete kit and my cut off wheel and replaced them last year. No difference in performance is all I hear & read, but I would swear there is a bit of a difference in the NPP sound. To me, it was worth it. After all, modding a performance car is about personally getting your hands on it and tweaking, at least for me. I am an engineer and believe in the data shown, but fluid dynamics were on my mind and even though cross section remains the same, the turbulence is not. For the low cost of the kit, I decided to do it.

Measure twice or more before cutting though. The directions provided in the kit were not totally clear.

[JSH]

Originally Posted by BrianL

No difference in performance is all I hear & read, but I would swear there is a bit of a difference in the NPP sound.

The crimped section has been discussed here endlessly, but it bugs me that, even when you add, say, 50 to 100% more CFM to these high hp engines, that the crimp wouldn't add back pressure.

[UnknownJinX]

Originally Posted by BlaqWhole

ANYTHING that affects performance is a HUGE effect since it could potentially cost you a race. That pinch section is an abomination and should be removed imediately before it costs you a race.

If you lose a race and that's your excuse, I'd be shaking my head and thinking you are saltier than Dead Sea, even without knowing that the pinches don't affect the power unless your car is heavily modified.

What's next? Your engine air filter has a leaf on it? Tires have too many rocks on it? Didn't remove your back seats?

[L78toLT1]

Originally Posted by BrianL

I got rid of mine as it was just against my grain to have these in place. Just wasn't right in my mind.

I got the Hooker BlackHeart crush pipe delete kit and my cut off wheel and replaced them last year. No difference in performance is all I hear & read, but I would swear there is a bit of a difference in the NPP sound. To me, it was worth it. After all, modding a performance car is about personally getting your hands on it and tweaking, at least for me. I am an engineer and believe in the data shown, but fluid dynamics were on my mind and even though cross section remains the same, the turbulence is not. For the low cost of the kit, I decided to do it.

Measure twice or more before cutting though. The directions provided in the kit were not totally clear.

Think about it! You’re an engineer! The cross section isn't the same:


The exhaust pipe just before/after the crushed section is 2.75” which works out to a circumference of 8.64” and a cross sectional area of 5.94”. Ignoring any stretching of the pipe resulting from the forming process and discounting the radii at the corners, when considering rectangular sections, a square will give you the max possible cross-sectional area. In our case, we have 8.64 inches to work with, which gets you a 2.16 x 2.16 square with a cross sectional area of 4.67sqin. It gets worse the flatter the rectangle. Ex: a 3.5 x 1.32 rectangle (3.5 + 3.5 + 1.32 + 1.32 = 8.64) nets you a cross section of 4.62sqin. A really flat section of, say 4 x .32 is only 1.28sqin.

[JSH]

Confirming that the crimp has no impact on hp or torque https://www.mishimoto.com/engineerin...he-crimp-myth/

[CreeperRS]

Originally Posted by BrianL

I got rid of mine as it was just against my grain to have these in place. Just wasn't right in my mind.

I got the Hooker BlackHeart crush pipe delete kit and my cut off wheel and replaced them last year. No difference in performance is all I hear & read, but I would swear there is a bit of a difference in the NPP sound. To me, it was worth it. After all, modding a performance car is about personally getting your hands on it and tweaking, at least for me. I am an engineer and believe in the data shown, but fluid dynamics were on my mind and even though cross section remains the same, the turbulence is not. For the low cost of the kit, I decided to do it.

Measure twice or more before cutting though. The directions provided in the kit were not totally clear.

If anything gained is an increase in dB on the NPP, I think it’s worth it!
Seems to me it would offer better exhaust flow, I’m not an engineer.

[90503]

Drill a couple of small holes (1/4" or so) in the crimped area to compensate for the restriction. Good luck.

[3.8TransAM]

The farther u move a restriction from the exhaust the less of a restriction it is

[Idaho2018GTPremium]

Mechanical engineer here...Technically, the crimp adds a tiny bit of back pressure in the exhaust since there is a transition from round to...oval-ish, and back to round, and there is a slight reduction in cross sectional area which means the velocity will increase, and thus, so will the frictional/dynamic losses in that section compared to the rest of the round piping. That said, the crimped pipe segment is so short that it likely has a negligible effect on exhaust performance, and thus little to no effect on engine power.

[L78toLT1]

Originally Posted by Idaho2018GTPremium

Mechanical engineer here...Technically, the crimp adds a tiny bit of back pressure in the exhaust since there is a transition from round to...oval-ish, and back to round, and there is a slight reduction in cross sectional area which means the velocity will increase, and thus, so will the frictional/dynamic losses in that section compared to the rest of the round piping. That said, the crimped pipe segment is so short that it likely has a negligible effect on exhaust performance, and thus little to no effect on engine power.

I'll bet that of all of the mechanical engineers weighing in on this discussion, I'm the only one educated at a school that has played, and beat Saban and Bama! Gig 'em Aggies!!

[Norm Peterson]

Originally Posted by L78toLT1

Think about it! You’re an engineer! The cross section isn't the same:

The exhaust pipe just before/after the crushed section is 2.75” which works out to a circumference of 8.64” and a cross sectional area of 5.94”. Ignoring any stretching of the pipe resulting from the forming process and discounting the radii at the corners, when considering rectangular sections, a square will give you the max possible cross-sectional area. In our case, we have 8.64 inches to work with, which gets you a 2.16 x 2.16 square with a cross sectional area of 4.67sqin. It gets worse the flatter the rectangle. Ex: a 3.5 x 1.32 rectangle (3.5 + 3.5 + 1.32 + 1.32 = 8.64) nets you a cross section of 4.62sqin. A really flat section of, say 4 x .32 is only 1.28sqin.

I think your 3.5" wide rectangle would only be 0.82" high; a 3" wide rectangle would be 3 x 1.32.

You should probably be thinking a bit deeper than simply outside cross-sectional area (you did consider that inside areas are not based directly on the OD measurement?). But even running with outside 2.75" OD and 8.64" circumference dimensions, a 3 x 1.32 rectangle provides (3 + 3 + 1.32 + 1.32) = 3.96 in^2, or about 85% of the 2.16 x 2.16 square.

I don't blame you for not wading through the round to flat oval math, but I think that the inside area reductions don't happen as rapidly (I think the area loss going from a 2.75" circle down to a 2.2.5" x 3.75" flat oval runs a lot closer to 5%). Feel free to check this.


Beyond that, flow restriction is also a function of how long the restriction is, relative to the unrestricted length. This is at least part of the reason you can get away with dimpling header primary tubes for clearance without losing power until you've really choked the inside area down.


Norm