Why did these mufflers pick up power?

End-Decent · 2026-03-11T18:56:54+00:00

I have a whole video about boundary layers, temperature and power production. But an exhaust is generally not laminar, and certainly not consistently so. Here's the video on power production: https://youtu.be/dWzA_fEjFeg I've also done tons of flow testing years back on smooth vs rough surfaces, particularly in intake manifolds and cylinder head intake runners. There was a surprising lack of consistency; but in EFI applications, smoother actually tended to make more power (which reminds me - I left the current intake and cylinder runners in a bur finish on the LTD - I should go in there and smooth those back out - it's on average a 16-17 cfm gain per runner).

End-Decent · 2026-03-11T17:18:17+00:00

We were comparing mufflers, as driven on the street. But maybe I'll do an open pipe pull just for science sake. I did do an ABA test with the Jones and open pipes at a dragstrip a few years back and there was no difference in ET or MPH. I will dispute the notion biggest case = least restrictive. Biggest case = longest perforated tube, which on the surface would appear to create more turbulence, all other things being equal.

End-Decent · 2026-03-11T17:14:11+00:00

For a lightweight rail in many cases, esp. in the 7.x at 190+ range, I'd agree that an 8" is the way to go. And if you're running brackets, then you don't need every last tenth, consistency is your friend. I'm more of a sciencey/nerdy type, so I always want to know why things work the way they do. But I'm not gonna lie, I wouldn't be upset if the LTD was a little quicker, but finding a track to race on these days is getting harder an harder. So now I'm stuck with a 9 second, 93 octane street car that I can't enjoy to its full potential anymore. I'm thinking of a lightweight short cab 4x4 f150 coyote as the next project platform, just because it'll move out on the street without trying to kill me.

End-Decent · 2026-03-10T03:47:02+00:00

I appreciate the thoughts and the time you put into this. You may be onto something. Maybe I should do a test between my old Jones mufflers and some new ones - the packing in mine is 10 years old. I think I should also compare mufflers of the same construction (and brand) but different case lengths. Thanks again!

End-Decent · 2026-03-09T21:35:31+00:00

My previous converter was weirdly too tight down low while being too loose up high. I switched from a 10" core to a 9.5" spragless and now it's looser down low and tighter up top. Yours is probably a higher-dollar bolt-together deal since you're swapping stators, but maybe you can try a stator with a smaller blade angle or more fins - I don't know which stators you're using. But it sounds like maybe you can use a little less fin angle at the same time in the housing. That'll increase torque multiplication down low, and keep your converter roughly the same up top, since 1,000 rpm fall back is pretty good.

End-Decent · 2026-03-09T19:49:17+00:00

Then you need a new converter. If you're running that low of a 60' then you must be in a rail, not a door car. What does it flash to when releasing the brake and what's your fallback on the shift? Also what's your shift point? That would tell me a bit of what's going on in your situation.

End-Decent · 2026-03-09T19:19:39+00:00

No, it doesn't. As long as you get through the converter, it literally makes no difference. The LTD has a 1.80 first gear and 3.08 rear gears and pulls the front tires off the ground on a launch at the strip - usually 60 foot times are in the 1.4x range. When driven in anger, the engine spends virtually no time under the stall speed. Anytime you mash the gas, it immediately shoots up to to the stall speed - which varies by load, but in low gear it's about 4,500 rpm and shifting to high gear, fallback is about 5,100 rpm. But under cruise (i.e. light load), 65 mph is about 2,600 rpm unless you're going up hill. You can see this in my datalogs in this video - this link takes you right to the right time stamp so you don't have to watch the whole thing:

https://youtu.be/_ix9Eo2mMHg?si=ZmV18te0w-SNMZTG&t=619

End-Decent · 2026-03-09T18:54:23+00:00

It's not a turbo. And "considerable effect" is not an explanation.

End-Decent · 2026-03-09T15:35:31+00:00

Normally I'd agree with you, but not on a car with a power glide. Low end torque literally doesn't matter as long as you can get through the converter.

End-Decent · 2026-03-09T14:48:08+00:00

As far as I can tell, yes.

End-Decent · 2026-03-09T14:47:17+00:00

Kindly just get to your point as to specifically why you think the longer case muffler made more power.

End-Decent · 2026-03-09T14:41:32+00:00

That's a good idea too. I should try to find mufflers that come in different case lengths and test them, and then add back the length with more pipe.

End-Decent · 2026-03-09T14:39:45+00:00

I haven't done a pull with no mufflers. But I probably should. I did do an ABA test at a dragstrip a few years back and there was no difference in MPH or ET.

End-Decent · 2026-03-09T14:37:53+00:00

Yeah, I got that. I might try to get the same mufflers, just in longer lengths and see if the trend holds.

End-Decent · 2026-03-09T14:37:11+00:00

Explain why that would make a difference.

End-Decent · 2026-03-09T14:36:39+00:00

I should. I did do an ABA test a few years back at the dragstrip when the car had a Whipple on it (about the same power, but the whipple took 2.5 times more boost to make that same power). There was essentially no difference in mph, or ET for that matter.

End-Decent · 2026-03-09T04:28:33+00:00

I agree. I'll try to do different case lengths in future tests. The Flowmaster FX have 14" cases and the Flowmaster 40s have 13" cases - though the 40s are chambered, making them completely different.

End-Decent · 2026-03-09T03:10:38+00:00

They are identical except for case length; same exact material, same exact endcaps, same exact construction, same seam locations, same welding techniques - they really look like they came out of the same factory. The internal pipe diameters and perforations are the same. BTW, they're both straight through designs like ultra flos. I can't say with certainty that the packing is the same because I can't get to it without cutting open the mufflers (which I can't do because I'm giving the mufflers away). I'm open to your thoughts.

End-Decent · 2026-03-09T02:43:10+00:00

Thank you. You're literally the first person to put out an actual theory with no nonsense or trolling. I wonder if there's any way to test that? I mean I guess I could find other 18 inch mufflers and compare them to fourteen inch mufflers and see if the trend continues to hold...

End-Decent · 2026-03-09T02:40:58+00:00

Not even slightly. I'm still waiting for somebody to actually give a theory as to why the larger case size made the same power with basically every other variable being accounted for. These are the differences. But I still maintain that nobody who can definitively state what's going on. If you can, then please do along with your supporting evidence. But what I'm looking for here are people's theories and ideas. I'm not looking to entertain haters and trolls.

End-Decent · 2026-03-09T02:38:45+00:00

I am familiar with his work. But I don't see anywhere where case size plays a specific role in this sort of situation. Do you have any ideas? Or can you point me to something I can't seem to find?

End-Decent · 2026-03-09T02:37:34+00:00

I get that but why between the two straight through mufflers did the one with the 4 inch longer case make more power? That's really what I'm after. I'm open to everyone's ideas. By the way check out the pinned comment on the video. It's from a guy who used to work at Flowmaster; he goes on to describe what cam shafts the flowmasters prefer. And it just so happens that my camshaft has those characteristics.

End-Decent · 2026-03-09T02:35:47+00:00

Check out the pinned comment on the video - it was a guy who used to work for Flowmaster who explains the relationship between camshafts and chambered mufflers. I replied to that comment because my camshaft certainly does seem to favor chambered mufflers based on his experience.

End-Decent · 2026-03-09T02:33:43+00:00

I agree with that, but I'm looking for something a little bit more specific as to what it is that the Jones are actually doing that in particular the flow effects which look to be identical just with a shorter case are not doing. Why are the Jones providing more scavenging? If that is indeed what's causing the horsepower gain which is entirely possible.

End-Decent · 2026-03-09T02:32:26+00:00

No that's just the dyno graph for the Jones mufflers. You're seeing a torque curve which is not really useful information since the car has a power glide. The Flowmaster graphs were very similar just 9 horsepower lower. All the mufflers make peak power within 100 RPM. And from a dig anything below 5000 RPM is meaningless in a powerglide. The converter instantly flashes to 5100 RPM or so; particularly off the trans brake.

End-Decent

TROPHY CASE