Is there a known HP to be gained with exhaust cut outs?

I cannot find any good info this. I saw one YouTube post that said 60hp gain, but the car had cams (which I don't have), and nothing else. I have maxed out on bolt on's, and I have a Lito tune, Exedy Stage 1 clutch, and 4:10's (not interested in the cams; the selling point seems to be sound, loss of power on low end, and gain at the top). But, does anyone have any real world dyno data on HP gains with cut outs?

The first thing you will discover is opening the exhaust will effect your tune. Put the cutouts too close to the headers and the engine will run lean. Not a good thing.

Hmmm that sucks. The tune never crossed my mind, so I appreciate that.

I figured if they were amazing no issue HP gains, there would be a lot of talk about them. But the lack of has me concerned.

If you seen Engine Masters where they were dyno testing exhausts. They found that:
2 1/2 dual supports 500 HP easy. Bigger does not make more power.
A cross over does not make more power/torque.
So, unless you are making power well north of 500, the answer to your question is NO.

It’s less of a HP gain and more like removing restrictions to the exhaust system. The quicker and easier it is for the exhaust gases to exit the system, the faster the car can get going. However back pressure can also help the car in some cases. Less bends in the exhaust system helps in some cases.

If you look at F1 cars, Nascar, some super cars and hyper cars, they have short exhaust systems as they need to reach higher speeds faster. In a drag race, a F1 car isn’t that great on take off, however when it gets going, it’s gone.

xeninworx said:

However back pressure can also help the car in some cases.

Click to expand...

Back pressure is never good. That’s a old myth. You want a properly sized exhaust system that eliminates back pressure and promotes scavenging of exhaust gasses.

xeninworx said:

It’s less of a HP gain and more like removing restrictions to the exhaust system. The quicker and easier it is for the exhaust gases to exit the system, the faster the car can get going. However back pressure can also help the car in some cases. Less bends in the exhaust system helps in some cases.

If you look at F1 cars, Nascar, some super cars and hyper cars, they have short exhaust systems as they need to reach higher speeds faster. In a drag race, a F1 car isn’t that great on take off, however when it gets going, it’s gone.

Click to expand...

Ummmmmm.... nope to almost all of this.
If there is a legitimate restriction in the exhaust system and you remove it, the car accelerates faster because it gained HP, not because the exhaust gasses exited the pipes in less time. A properly designed full length exhaust system will make more power than a poorly designed fender exit despite the gasses from any given combustion event taking longer to reach atmosphere.
NASCAR actually uses a fairly long exhaust system and top fuel dragsters use about the shortest exhaust possible. You can bet neither of those setups is robbing any HP at the RPM range the cars race in. The reason F1 cars aren't great drag cars has pretty much nothing to do with their exhaust design and a 2011 Red Bull RB7 F1 car ran a 9.2 second 1/4 so I wouldn't go putting your pink slip on the line.

Jerry Stoneking said:

I saw one YouTube post that said 60hp gain, but the car had cams

Click to expand...

60 HP for cutting out the exhaust??? Don't think so.

Jerry Stoneking said:

I cannot find any good info this. I saw one YouTube post that said 60hp gain, but the car had cams (which I don't have), and nothing else. I have maxed out on bolt on's, and I have a Lito tune, Exedy Stage 1 clutch, and 4:10's (not interested in the cams; the selling point seems to be sound, loss of power on low end, and gain at the top). But, does anyone have any real world dyno data on HP gains with cut outs?

Click to expand...

At best maybe 6hp but your exhaust will become much louder with cutouts and annoy a lot of people unless you use them only on a race track. The pipes would need to exit in front of the rear wheels similar to the system used on the 12-13 Boss 302.

On the S197, Ford designed an awesome exhaust. Minimal gains will be seen unless you had already done crazy mods. Anyone claiming 60 hp from an exhaust change is going for click-bait.

On a bolt-on mustang, aftermarket exhaust is mainly for sound. From what I read and can remember? Cut-outs on bolt-on mustangs are pretty much the same.

Picked up a non-cat Pacesetter H-pipe, with no noticeable hp change. It was tuned. Loved the sound with the factory manifold and cat-back. Not obnoxious. Sounded so nice at WOT. Planned to leave it that way.

Until wifey saw another bad ars mustang. Before I knew it I had sidepipes. While it sounds amazingly crazy? No noticeable hp change. While i have not ran on a dyno, if my mustang pulls 300? I would be ecstatic.

I do have to returned it soon. While I do have lifetime tunes? Will be going to LITO next time. See what the man can do.

XJCasper said:

I do have to returned it soon. While I do have lifetime tunes? Will be going to LITO next time. See what the man can do.

Click to expand...

Lito will do a vastly better job than BAMA for sure.
The most restrictive parts of the stock exhaust are the stock manifolds and cats. Replacing anything after the cats will result in minimal HP gain.
@XJCasper do you still own a Jeep XJ? I sold my '92 XJ 5-1/2 years ago after more than 21 years of ownership. You might recognize it:

http://www.jeep4.0performance.4mg.com/

AHaze said:

Ummmmmm.... nope to almost all of this.
If there is a legitimate restriction in the exhaust system and you remove it, the car accelerates faster because it gained HP, not because the exhaust gasses exited the pipes in less time. A properly designed full length exhaust system will make more power than a poorly designed fender exit despite the gasses from any given combustion event taking longer to reach atmosphere.
NASCAR actually uses a fairly long exhaust system and top fuel dragsters use about the shortest exhaust possible. You can bet neither of those setups is robbing any HP at the RPM range the cars race in. The reason F1 cars aren't great drag cars has pretty much nothing to do with their exhaust design and a 2011 Red Bull RB7 F1 car ran a 9.2 second 1/4 so I wouldn't go putting your pink slip on the line.

Click to expand...

Okay now that I’ve wrapped my head around the concept, I understand now how it works. Length and diameter do play a factor for back pressure.

Nascar isn’t that long though. Theirs come out the sides before the rear wheels, like a Boss or Viper. I guess that’s a regulation for Nascar? The Mercedes McLaren SLR has the exhausts pipes coming out under the front fenders. That’s pretty short.

The only situation where a cut-out could gain that type of power is a high powered
turbo car where the exhaust post-turbine is extremely restrictive and negatively affects spool time.
Any other situation, they just create more noise.

RED09GT said:

The only situation where a cut-out could gain that type of power is a high powered
turbo car where the exhaust post-turbine is extremely restrictive and negatively affects spool time.
Any other situation, they just create more noise.

Click to expand...

I know zero about turbo cars. Assuming a single turbo used, how the heck do you get from 8 x exhausts...down to just one..to feed the hot side of the turbo ? Does it split back into dual exhausts after this ? It must be a plumbing nightmare. What is the back pressure, right at the input of the single turbo's hot side input ? One would think it must be off the charts, esp with the immense load on it via the cold side.

Pentalab said:

I know zero about turbo cars. Assuming a single turbo used, how the heck do you get from 8 x exhausts...down to just one..to feed the hot side of the turbo ? Does it split back into dual exhausts after this ? It must be a plumbing nightmare. What is the back pressure, right at the input of the single turbo's hot side input ? One would think it must be off the charts, esp with the immense load on it via the cold side.

Click to expand...

Your question made me curious. So I looked it up. This is an On3 kit. Looks like a freakin’ nightmare to me.

In the simplest terms, single turbo will be at the 8-1 merge.
The larger the pipe after the turbo, the quicker it will spool.
Turbo acts as muffler to boot.

Is that a rear mounted turbo kit? That has got to laaag.

I have full 2 1/2" bassani with their headers as well
I custom fabbed electric cutouts on my terminator hp gains are not worth mentioning 3hp but I didn't make them for hp I did it for cool factor which is a 10

Laga said:

Your question made me curious. So I looked it up. This is an On3 kit. Looks like a freakin’ nightmare to me.
View attachment 83513 View attachment 83514 View attachment 83515

Click to expand...

But it's a very effective nightmare.
This is a dyno chart of an On3 turbo on an otherwise stock 3V. The baseline run was with a CAI only.

Laga said:

Your question made me curious. So I looked it up. This is an On3 kit. Looks like a freakin’ nightmare to me.
View attachment 83513 View attachment 83514 View attachment 83515

Click to expand...

I can't see the actual turbo in any of these pix. Where is it ?

Dino Dino Bambino said:

But it's a very effective nightmare.
This is a dyno chart of an On3 turbo on an otherwise stock 3V. The baseline run was with a CAI only.View attachment 83524

Click to expand...

Interesting to note, it doesn't hit 300 ft lbs of TQ, till it gets to 3800 rpm. I'm > 300 ft lbs @ 2 krpm with a M90 and 5.7 psi boost..(with an automatic). The turbo setups appear to crank out globs of hp/tq at higher rpms...but doesn't have the big tq hit at the bottom end...like a PD blower does.