- Thread starter rustred
- Start date
Huh ? What ? I can't hear you !
I think a really short pipe or straight out the manifold can cause valve warpage as cold air rushes in upon shut down. I have seen engines like pullers and racers where they put covers on the short pipes as soon as they turn them off.
Some engines (mainly stock) will run better with some back pressure.
I think a really short pipe or straight out the manifold can cause valve warpage as cold air rushes in upon shut down. I have seen engines like pullers and racers where they put covers on the short pipes as soon as they turn them off.
Some engines (mainly stock) will run better with some back pressure.
Butch(OH)
Well-known Member
The muffler is there to quiet the engine and is a restriction, and restrictions limit HP,, period. The reason a short pipe might make more HP than no pipe is not back pressure but quite the opposite. Exhaust out of an engine is not steady flow but pulses and a pipe of the correct diameter and length will take advantage of the pulses timing them to provide a scavenging effect that lowers pressure the port. I have never seen any evidence of valve warping from short pipes as a matter of fact I once ground an exhaust valve true and repeatedly heated it red hot and let it cool in open air and it never warped. It didnt even warp when I threw water on it, I call that one BS too. Racers are the biggest bunch of monkey see monkey do types you will ever run across and I dont doubt that some of themc over headers thinking they are preventing valve warpage. However the original reason for covers on dragsters with zoomie headers was to keep the hot sticky tires from picking up gravel and debri and pitching it in the headers when they were being towed back the return road. They also keep things out of the headers that others might throw in there AND they provide protection for the body when working over them.
rustyfarmall
Well-known Member
If you idle down the engine after working it hard, and allow it to cool slightly, there will be no warping of valves. Most of the older tractor engines do not care if there is a muffler or a straight pipe. The choice is strictly operator preference.
restrictions limit HP,, period
Not gonna get in to a big thing about it,but they claim on the 2 cycle GMs in the Oliver Super 99s and 990s,they'll actually put out more power with a muffler than they will with a straight pipe. Something to do with the blower pushing the exhaust out and fresh air in on the same stroke I would think.
Not gonna get in to a big thing about it,but they claim on the 2 cycle GMs in the Oliver Super 99s and 990s,they'll actually put out more power with a muffler than they will with a straight pipe. Something to do with the blower pushing the exhaust out and fresh air in on the same stroke I would think.
My nieghbor asked why no car type muffler on my tractor. I said how else would you know I was cleaning the snow from your driveway at 430am. He doesn't leave for work till 830 and once asked if I had plowed that morning (during a snow storm).
I tried a glass pack and a oval car muffler. Oval got tore off in the woods easier so it was back to glass pack. Never noticed a power difference.
I tried a glass pack and a oval car muffler. Oval got tore off in the woods easier so it was back to glass pack. Never noticed a power difference.
Steve@Advance
Well-known Member
I don't believe it will warp the valves.
What's the difference in a straight pipe and a straight through glass pack? Nothing to stop air from coming back up that!
Changing the exhaust back pressure will change the mixture though. It makes little difference on a carb with an adjustable main jet, just reset the main. But with fixed mains, carbs with power valves, secondaries, and some fuel injections, it can be quite a process getting it tuned properly.
And depending on the cam, head design, carb CFM, changing the back pressure can move the power band. If interested in low end torque, some back pressure may be preferable. Only a dyno will tell for sure.
What's the difference in a straight pipe and a straight through glass pack? Nothing to stop air from coming back up that!
Changing the exhaust back pressure will change the mixture though. It makes little difference on a carb with an adjustable main jet, just reset the main. But with fixed mains, carbs with power valves, secondaries, and some fuel injections, it can be quite a process getting it tuned properly.
And depending on the cam, head design, carb CFM, changing the back pressure can move the power band. If interested in low end torque, some back pressure may be preferable. Only a dyno will tell for sure.
jimg.allentown
Well-known Member
The valves will work just fine with or without a muffler. Mufflers can affect things like power output, power band, and the like, but the effects are minimal.
How fine do you want to split hairs?
Also, when an engine is running, hot gases are flowing OUT of the engine at high velocity and under some pressure. Air is not coming back into any engine I have ever seen. Maybe when you shut it down, some air might come back into the pipe, but certainly not while running.
How fine do you want to split hairs?
Also, when an engine is running, hot gases are flowing OUT of the engine at high velocity and under some pressure. Air is not coming back into any engine I have ever seen. Maybe when you shut it down, some air might come back into the pipe, but certainly not while running.
Phil in Pa
Member
An old helicopter mechanic told me once when I asked him that, he said look at the drag racers, who want max horsepower. One short, straight pipe and that's it. The back pressure thing is baloney except maybe some unique cases like Randy mentioned.
OP
OP
rustred
Well-known Member
ya, i figured it was a here nor there thing which didnt matter one bit. just that guys start in with this back pressure thing and valves warping by cooling too fast. but i can keep telling them they are full of it. i never could figure how cold air would zoom down a hot exhaust pipe when the engine was shut down. i would think the hot air from the engine would be rising out the exhaust pipe. so ya its a big wives tale. lol.
Have seen dyno test on a superM and 450 and can gain from 2 to 5 HP with straight pipe. I have a 3 1/2" stainless steel straight pipe on my 450 and if you had to use it all day you would go deaf. I have a allis Chalmers WD45 with 3 1/2" stainless steel straight pipe with a modified muffler inside of it and you could use it all day and has a nice tone to it.
buickanddeere
Well-known Member
Who ever told you that the engine needs back pressure or a pipe to protect the valves from cold air . I suggest you firmly and swiftly apply your boot to the seat of their stupid pants and never talk to them again.
buickanddeere
Well-known Member
Bull Crap
kcm.MN
Well-known Member
- Location
- NW Minnesota
D beatty - Those are some beautiful machines!
Texasmark1
Well-known Member
My Ford diesels will not run with back pressure. I got the wrong muffler at TSC once, made for an IH tractor and you couldn't see through the muffler from end to end. Knocked the baffle out where I could see through it to get it to work but it was useless as a muffler and found the right Ford spec. muffler (you could see through) and the engine ran fine.
When I had my cosmetically restored '79 JD 4230, it had a stupid little 1 ? outlet on the muffler for a 100hp, 400 cu in engine. Drove me nuts. So I took it off and installed a 4" dia chrome after market pipe without a muffler. The exhaust manifold outlet on that tractor was large because the 4430, the 125 hp version of that machine used a turbo to get the extra 25 ponies.
Loved to take that big 6 to parades with flags all over it, idling along listening to that sweet music. Bystanders liked it too. Got a lot of thumbs up. When working it, I usually wore ear protection even though the Sound Guard cab helped. Sold it when I downsized my farming operation.
When I was a teen growing up, my mechanical mentor said the same thing about not to run the engine hard without exhaust manifolds attached and told me a story about having it happen to him. I never attempted to prove him wrong. Wasn't worth it.
When I had my cosmetically restored '79 JD 4230, it had a stupid little 1 ? outlet on the muffler for a 100hp, 400 cu in engine. Drove me nuts. So I took it off and installed a 4" dia chrome after market pipe without a muffler. The exhaust manifold outlet on that tractor was large because the 4430, the 125 hp version of that machine used a turbo to get the extra 25 ponies.
Loved to take that big 6 to parades with flags all over it, idling along listening to that sweet music. Bystanders liked it too. Got a lot of thumbs up. When working it, I usually wore ear protection even though the Sound Guard cab helped. Sold it when I downsized my farming operation.
When I was a teen growing up, my mechanical mentor said the same thing about not to run the engine hard without exhaust manifolds attached and told me a story about having it happen to him. I never attempted to prove him wrong. Wasn't worth it.
If you want to live in a quiet world in the future and I mean quiet world where you cannot even hear them ask what you want to eat then run that straight pipe. I even quit going to my tractor club meetings because I could no longer hear what was said. And have been told by the hearing examinor that sells the hearing aids DO NOT THROW AWAY YOUR MONEY ON HEARING AIDS, THEY WILL DO YOU NO GOOD. Do you want to hear that fire truck comming screaming at you so you can get out of its way?
T in NE
Well-known Member
- Location
- Cambridge, Nebraska
As long as there is something on the exhaust port, you won't get fresh air into the back side of a hot exhaust valve, reducing the chances of burning said valve.
Like the exhaust manifold.
The less pressure in the pipe, the less parasitic power loss. It is harder for a 350 to push exhaust gasses through a 1 inch pipe than a 2 inch pipe. Keeping more heat inside the pipe also keeps the gasses more fluid (less resistant to flowing). That's the principle behind header tape.
A properly built header and exhaust can actually start to pull a fresh charge into the cylinder before the piston starts back down the bore. "Scavenging" but you won't get it much with a low rpm motor with a manifold.
Like the exhaust manifold.
The less pressure in the pipe, the less parasitic power loss. It is harder for a 350 to push exhaust gasses through a 1 inch pipe than a 2 inch pipe. Keeping more heat inside the pipe also keeps the gasses more fluid (less resistant to flowing). That's the principle behind header tape.
A properly built header and exhaust can actually start to pull a fresh charge into the cylinder before the piston starts back down the bore. "Scavenging" but you won't get it much with a low rpm motor with a manifold.
buickanddeere
Well-known Member
Fresh air will not warp or burn an exhaust valve although too lean of an air/fuel mixture will increase exhaust gas temperature.
How about the exposure of "cold fresh air and cold droplets of fuel " during valve over lap when both valves are open together .
How about that blast of cold ar and fuel full on the exhaust valve with the intake valve full open and the mixture hitting it full on?
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