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For those of you with a dyno........


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Out of curiosity, have you ever experimented muffler vs straight pipe just to see if it "actually" made a hp difference? Or did it just rattle your ear drums

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There are other benefits in addition to a possible boost on horsepower. There is the benefit of the engine breathing easier resulting in lower egt's, and IT JUST SOUNDS FREAKING AWESOME!!!

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Ive been running straights on the bike since '85, it sounds fast, it feels fast, but from what I understand with no backpressure it is less power, my intake and carb was changed but what do I know this is just one instance for me, I know with the truck that the straight through 4" exits exhaust faster and with the cold air intake it breathes really well, and the smarty jr regulates fuel/air on three levels, dats all I know.

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48 minutes ago, TractormanMike.mb said:

There are other benefits in addition to a possible boost on horsepower. There is the benefit of the engine breathing easier resulting in lower egt's, and IT JUST SOUNDS FREAKING AWESOME!!!

WHAT DID YOU SAY? I ran a straight pipe on a D21 Allis as a kid, as well as straight pipes on my pickups until I was in my 40’s. I can’t hear a stinking thing especially in a crowd. 

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About 30 years ago my BIL had a JD 4555 with a straight pipe. He lives a mile from me. I could sit on my deck and hear him disking.

I was just curious if anyone with a dyno had experimented just to see if there was a hp gain. 

ps (Chrome pipes don't count. Everybody knows they give an extra 25 hp.)

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If the muffler was restricting then yes 

But not necessarily at all rpms....

Exhaust back pressure is just part of a system....

My opinion is if you want/need more power get a bigger tractor .....

 

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Should ask the nitromethane drag guys if mufflers make more power, I think they tried it and they blew them off the engine so far they picked them up at the next track the next weekend 

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Wish I could remember where, but there was a guy I believe here with a 656 that he highly modded the motor. He did dyno it with various exhaust strategies even to split manifolds. Results were interesting.

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2 hours ago, VacDaddyt said:

Wish I could remember where, but there was a guy I believe here with a 656 that he highly modded the motor. He did dyno it with various exhaust strategies even to split manifolds. Results were interesting.

This the one you're thinking of?

 

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7 hours ago, Dasnake said:

Ive been running straights on the bike since '85, it sounds fast, it feels fast, but from what I understand with no backpressure it is less power, my intake and carb was changed but what do I know this is just one instance for me, I know with the truck that the straight through 4" exits exhaust faster and with the cold air intake it breathes really well, and the smarty jr regulates fuel/air on three levels, dats all I know.

Back pressure is not good at all. Muffler and header/pipe system is a compromise. Better systems will be set up to create negative pressure at exhaust port or valve opening at certain rpm. A downside is positive or backpressure at other rpm.   Power loss will be noticeable at some rpms without muffler but will gain at other rpm     Saw a big block 502 Chevy lose nearly 100hp on a Dyno after a header swap. They reckoned the headers were really rusty inside. Swapped another set on and picked up the lost hp. 
good book on the subject is the scientific design of intake and exhaust systems by Morrison I think. It’s a fairly old book but was used by a lot of motor racing guys. Theory in there is good today just heavy reading. 
 

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Good topic

I am working on exhaust on my '19 6.2

I have reduced the back pressure with single glass pack. 

But I have some drone and harmonic(?) noises that are annoying at certain rpm's and engine loads. 

I need to figure out a plan to add back resonator(s) to manage the exhaust note. 

I think shift points may be affected by the reduced back pressure but this pu is still pretty new to me and not sure if that is the case or not. 

The last pickups I did were. 

Straight piped the 99 Cummins.....great!

Duals and glasspacks on 89 351........great!

This pickup is a whole different animal. Trying to stay with the single 3 1/2 exh it came with. 

 

 

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3 hours ago, VacDaddyt said:

DT, Yes

 

Just looked it up the other day myself. After watching that 460 at the county fair pull it had me thinking. Always thinking about building a puller, never have time to get started!

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9 hours ago, England806 said:

Back pressure is not good at all. Muffler and header/pipe system is a compromise. Better systems will be set up to create negative pressure at exhaust port or valve opening at certain rpm. A downside is positive or backpressure at other rpm.   Power loss will be noticeable at some rpms without muffler but will gain at other rpm     Saw a big block 502 Chevy lose nearly 100hp on a Dyno after a header swap. They reckoned the headers were really rusty inside. Swapped another set on and picked up the lost hp. 
good book on the subject is the scientific design of intake and exhaust systems by Morrison I think. It’s a fairly old book but was used by a lot of motor racing guys. Theory in there is good today just heavy reading. 
 

I don't remember the instigator of the HD back pressure theory, maybe hardtail might remember, he's into the bike scene forever also, the drag pipes I run are different lengths as you can see in the pic, but that point is naught when compared to engine headers which are staggered lengths to have them all exit at the main flange at the same time, the only other thing with twin pipes is the crossover tube, now would that create a benefit from backpressure?

As stated with my truck it is an I6 and it exits through a 14" straight through muffler, now this takes gases into an area that is hollow but the outside round is perforated to a fiberglass interior, when I first put it in I thought no way it would kill any noise, it does and it also removes the dreaded 2000 rpm drone.

I'm exhausted from talking about this subject, going to lay my header down for a nap.

Does anyone know how to leave a handle so the member is aware of me mentioning them as I did hardtail?

2020-01-26_06-17-13.jpg

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1 hour ago, Dasnake said:

I don't remember the instigator of the HD back pressure theory, maybe hardtail might remember, he's into the bike scene forever also, the drag pipes I run are different lengths as you can see in the pic, but that point is naught when compared to engine headers which are staggered lengths to have them all exit at the main flange at the same time, the only other thing with twin pipes is the crossover tube, now would that create a benefit from backpressure?

As stated with my truck it is an I6 and it exits through a 14" straight through muffler, now this takes gases into an area that is hollow but the outside round is perforated to a fiberglass interior, when I first put it in I thought no way it would kill any noise, it does and it also removes the dreaded 2000 rpm drone.

I'm exhausted from talking about this subject, going to lay my header down for a nap.

Does anyone know how to leave a handle so the member is aware of me mentioning them as I did hardtail? @hardtail

2020-01-26_06-17-13.jpg

 

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Back pressure bad. Scavenging good. Engines with back pressure in the exhaust are going to loose power. What you are really gaining from headers is the flow. Equal length headers are the elite. Each tube is the same length so the exhaust pulse reaches the collector flange as the previous one just left. Camshafts are designed with the overlay of exhaust and intake so the intake valve is opening just as the exhaust is shutting. The escaping hot exhaust gases are rushing out pulling in freshly atomized fuel. You want that pulse from the moment the exhaust valve opens to be the same on each cylinder so there is an even smooth flow out of the head, through the exhaust manifold and the rest of the system. You can play with torque curves by moving the mufflers away and toward of the exhaust headers to raise or lower the curve in the rpm range. Also, smooth gradual bends flow the best. 

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A friend pulled a diesel 560 years ago, it had the pump turned up and different injectors put in it, maybe more I can't remember.  They pulled it twice one night at the same settings once with muffler and once with a straight pipe.  It actually went farther with the muffler, not a lot,5-10 feet and I suppose many other things could have caused the difference.

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The original Ramchargers. These guys were all engineers. Their test track was Graciet (sp) Avenue at 2AM. I've read stories about them. I may be wrong, but I think NHRA banned these headers. They had different headers for different intake combinations. I believe they were tuned to each individual cylinder. They were racers at heart but engineers who in the early days, spent more time playing around with intakes and exhausts than they did at the track. You Mopar guys probably know all about them.

 

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There are many poorly designed exhaust ports from the late 60's into the 80's.  I have heard more then once of restrictions in the exhaust improved output.

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4 minutes ago, 460 said:

There are many poorly designed exhaust ports from the late 60's into the 80's.  I have heard more then once of restrictions in the exhaust improved output.

Exactly, never have I ever heard of someone putting mufflers on and gaining hp or torque. Free flowing is the key. I can see where some mufflers do not hurt, but I definitely don't see of or hear of gains by putting back pressure on an engine. 

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Now, that being said, there is some magic in pipe diameter. Say someone goes from 2.5 mufflers to 3 inch straights, then you are losing your velocity out of the tailpipe and your scavenging effects. The flow becomes lazy and loses it's effective "pull" I guess for lack of knowledge for better word. That's why people pay good money like the thread started off with, people with a Dyno to fine tune their engines. 

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When I was looking into changing my exhaust my thoughts was go from 4" to 5", reading up I found my staying with 4 was fine as I wasn't going over 550 hp flywheel, and with my thought of staying at that point why bother with the extra change needed to go bigger then I went home, get it? Go big or go home, Bwahahahahahahahaha.

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54 minutes ago, MinnesotaFarmall said:

Now, that being said, there is some magic in pipe diameter. Say someone goes from 2.5 mufflers to 3 inch straights, then you are losing your velocity out of the tailpipe and your scavenging effects. The flow becomes lazy and loses it's effective "pull" I guess for lack of knowledge for better word. That's why people pay good money like the thread started off with, people with a Dyno to fine tune their engines. 

So, if remember right an 806 has a 2 3/4" manifold pipe coming up. What would be the correct size straight pipe to put on there? 

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