Cutouts before or after the cats????

[Mikes_Slow5oh]

So I have a 2015 whipped supercharged 5.0. I’m having long tube headers and high flow cars installed next week(parts on order). I was thinking about doing exhaust cutouts and was wondering if anyone has installed cutouts BEFORE the cats and how that worked for you. I know it would make the car very loud but would it be worth it?

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[Temovic55]

The headers will be loud enough even catted ! Mine is cattless and NASCAR loud with the Roush full exhaust! Try the headers first then think of the cutout!
I even have installed cutout on the muffler tips to quiten it in cold starts or in the presence of Police and that costed me to blow off my factory mid-resonator and had to weld those cracks as it was leaking badly! So in your case it won't be an issue as you would use it to increase the noise level and there won't be any risk of having back pressure and in worst case headlift!

 

[sk47]

Hello; I just rewatched episode 13 of season 7 of the series ENGINE MASTERS. Title "Exhaust Cutouts".

Episode compared a somewhat restrictive full length dual exhaust to open headers then to a capped cutout on the full exhaust. Of course the full exhaust killed a lot of HP.

The engine was run with the cutouts installed near headers but capped. Compared to the full exhaust Peak HP was not much changed less than half a HP. However, HP was down a lot at lower RPMS, around 25 HP at 4000 RPM. ( note the dyno chart did not show below 4000 RPMs so cannot know below that) Power was killed up to about 5200 RPM.

Run with cutouts near headers and open on full exhaust. Got much of the HP back across the RPM range. Maybe only 5 HP difference.

They moved cutouts back along the exhaust to right in front of the mufflers . Ran it open. Lost 13 peak HP compared to position near header and open. Loss of HP was even greater at lower RPM's but a loss all across the RPM range. So location matters.

A thing I have learned from watching this series is the results of one series of dyno runs does not necessarily translate to a different engine, header and exhaust setup. Only way to know for sure is to dyno a bunch of different configurations on a particular vehicle. They use an engine dyno. A chassis dyno might give different but closer to real world results at some expense to do.
That said my wild guess is to put a cutout close to the headers and in front of the cats.

 

[Mikes_Slow5oh]

The headers will be loud enough even catted ! Mine is cattless and NASCAR loud with the Roush full exhaust! Try the headers first then think of the cutout!
I even have installed cutout on the muffler tips to quiten it in cold starts or in the presence of Police and that costed me to blow off my factory mid-resonator and had to weld those cracks as it was leaking badly! So in your case it won't be an issue as you would use it to increase the noise level and there won't be any risk of having back pressure and in worst case headlift!

So I was wondering more about performance benefits than anything.

 

[Mikes_Slow5oh]

Hello; I just rewatched episode 13 of season 7 of the series ENGINE MASTERS. Title "Exhaust Cutouts".

Episode compared a somewhat restrictive full length dual exhaust to open headers then to a capped cutout on the full exhaust. Of course the full exhaust killed a lot of HP.

The engine was run with the cutouts installed near headers but capped. Compared to the full exhaust Peak HP was not much changed less than half a HP. However, HP was down a lot at lower RPMS, around 25 HP at 4000 RPM. ( note the dyno chart did not show below 4000 RPMs so cannot know below that) Power was killed up to about 5200 RPM.

Run with cutouts near headers and open on full exhaust. Got much of the HP back across the RPM range. Maybe only 5 HP difference.

They moved cutouts back along the exhaust to right in front of the mufflers . Ran it open. Lost 13 peak HP compared to position near header and open. Loss of HP was even greater at lower RPM's but a loss all across the RPM range. So location matters.

A thing I have learned from watching this series is the results of one series of dyno runs does not necessarily translate to a different engine, header and exhaust setup. Only way to know for sure is to dyno a bunch of different configurations on a particular vehicle. They use an engine dyno. A chassis dyno might give different but closer to real world results at some expense to do.
That said my wild guess is to put a cutout close to the headers and in front of the cats.

Now that’s some great information!!!

 

[illtal]

Hello; I just rewatched episode 13 of season 7 of the series ENGINE MASTERS. Title "Exhaust Cutouts".

Episode compared a somewhat restrictive full length dual exhaust to open headers then to a capped cutout on the full exhaust. Of course the full exhaust killed a lot of HP.

The engine was run with the cutouts installed near headers but capped. Compared to the full exhaust Peak HP was not much changed less than half a HP. However, HP was down a lot at lower RPMS, around 25 HP at 4000 RPM. ( note the dyno chart did not show below 4000 RPMs so cannot know below that) Power was killed up to about 5200 RPM.

Run with cutouts near headers and open on full exhaust. Got much of the HP back across the RPM range. Maybe only 5 HP difference.

They moved cutouts back along the exhaust to right in front of the mufflers . Ran it open. Lost 13 peak HP compared to position near header and open. Loss of HP was even greater at lower RPM's but a loss all across the RPM range. So location matters.

A thing I have learned from watching this series is the results of one series of dyno runs does not necessarily translate to a different engine, header and exhaust setup. Only way to know for sure is to dyno a bunch of different configurations on a particular vehicle. They use an engine dyno. A chassis dyno might give different but closer to real world results at some expense to do.
That said my wild guess is to put a cutout close to the headers and in front of the cats.

This was an NA setup right? Location would probably matter less on an SC car and probably more on a turbo car. I would like to see those differences.

On an NA car, exhaust scavenging matters more so that only fresh "cool" air is in the chamber for ignition. This is probably why there's a pumping efficiency loss at a lower RPM.

 

[sk47]

This was an NA setup right? Location would probably matter less on an SC car and probably more on a turbo car. I would like to see those differences.

On an NA car, exhaust scavenging matters more so that only fresh "cool" air is in the chamber for ignition. This is probably why there's a pumping efficiency loss at a lower RPM.

Hello; The engine was a 598 cu in big block which made in the past 850 HP on pump gas with idealized (larger) header tubes. This test header was a Hooker under chassis with a 2-inch tube to mimic what might be used in a car and is restrictive. Exhaust was 3 inch and also considered restrictive.

Stock deck height for big block Chevy. 4.6 in bore. 4.5 in stroke. 10.5 compression and runs on pump gas. Custom comp camshaft solid roller Duration of 2.74 intake & 2.84 exhaust at 50 thousandths tappet lift. 110 degree lobe separation angle. Brodix cylinder head. Brodix single plane intake manifold. 1150 holly dominator carb.
With this setup and running restrictive open headers only made 832.2 HP @ 6100 RPM & 789.3 torque @ 4700 RPM. So around 18 HP down from past runs in other episodes.

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