Sunday was a sunny day and I had planned on going on a tour. However once on the tour I had a problem, my muffler came apart and I had a big loss of power. I would like to understand the reason for no power when running a straight pipe.
Thanks in advance for your help.
ps: here is a short video, where you can hear the exhaust sound (I don't like the passion of the camera in this video)
Mufflers provide a certain amount of back pressure to keep the charge burning completely in the cylinder. Without getting too complex; lacking the correct amount of back pressure (assuming you have a stock or slightly modified camshaft), the fresh fuel/air charge will roll into the cylinder once the intake valve opens. That fresh charge should fill the cylinder from the bottom up as the expended charge is hot and the incoming charge is cool. Without enough back pressure, that incoming charge can roll the old charge out and some of it will exit past the open intake valve thanks to the overlap of the cam (when both valves are slightly open). Hope that makes sense.
My '17 has a cutout. When you step on the pedal it eliminates the muffler and the last two feet of pipe. The engine is more powerful, not less.
I suspect you had a failed muffler that resulted in more noise in spite of blocked or partly blocked flow. What does it look like?
Warren...yesterday must have been "muffler day"! When my wife & I were out on a little tour of our own the same thing happened to me, only doesn't sound like ours was quite as extensive. The rear plate nut was a bit loose, allowing the plate to move a bit, so a small section of the outer shell popped out. No big deal, as I tightened the nut after pulling over, to keep things from falling completely apart. No real loss of power, just a bit noisier. Once we got home later that afternoon I put her on the lift and in 10 minutes had it all back together properly. Nice and quiet once again. Hope yours turned out as easily.
Years ago I experienced a muffler failure in a non-model-T and I thought I had lost a lot of power. Careful testing revealed that the "loss of power" was an acoustic illusion. The loud exhaust made me think I was giving more throttle than I actually was. But I think at least some engines do actually benefit from the correct amount of back pressure. I suspect it depends on valve timing.
Along with Lester's thoughts, I believe you were subconsciously backing off the throttle due to the excessive noise of the open exhaust.
Our '14 roadster pickup, Otis, has a cut-out, just like what Royce mentions above. When I step on the cut out there seems to be a little more energy. When going up a slight incline I often use the cut-out.
Interesting. The TT that found its way to my garage has an apco muffler that is backfire proof. Cast iron with a built in cutout that also is a sort of relief valve. Don't know how quiet it is as I haven't started it yet but it looks really cool. Was wondering if it was noticeable HP difference on a 20 HP engine?
Thank you, everyone, for sharing your thoughts on my problem. I have experienced this problem ( nut backing, causing the muffler to separate), so I added a lock washer to keep this from happening. Yesterday the threaded rod, lock washer, and nut were missing, so I took the rest of the muffler parts off before I lost them. This left me with only the exhaust pipe that the muffler attaches to, see photo. I hope that helps clear things up about my problem.
exhaust pipe without the muffler
With all due respect you are mixing the airflow properties of 2 stroke cycle engines with 4 stroke cycle engines in your explanation. True, four strokes do use some intake and exhaust valve overlap and that varies with cam grind. But in general, high performance 4 strokes use exhaust systems with as little exhaust restriction as possible all the way up to include straight pipes with essentially no restriction whatsoever. Along with that, they tend to use cam grinds with more overlap along with higher lift and longer duration (which in part provides the greater overlap) among many other changes to the induction and exhaust systems. These changes are intended to work together at higher RPM to enable the increases in horsepower desired. They often work very poorly outside of that RPM sweet spot, which is why they often idle very poorly. They don't idle poorly because of a lack of restriction in the exhaust.
In a 2 stoke (no valves) the piston IS the valve, uncovering the exhaust ports and intake ports as it rises and falls. There can be much loss of air/fuel charge through the exhaust at non-optimal RPM. Much more than during the valve overlap period in 4 strokes which is why 2 strokes have been effectively banned from cars and motorcycles due to emissions regulations. In a 2 stroke cycle engine the exhaust is tuned to provide a degree of backpressure, although it is quite a bit more complicated than simply calling it backpressure. That backpressure does help to hold the intake charge in the cylinder as you describe. The most extreme examples of this are exhausts known as expansion chambers. Expansion chambers in 2 strokes are like racing cams in 4 strokes and usually work in a fairly narrow rpm band. In racing applications the term "on the pipe" in a 2 stroke is equivalent to "on the cam" in 4 strokes. In both cases the reference is to the RPM, usually very high RPM, where all of the variables come together to make the most power/torque.
The loss of fuel air mixture out the exhaust you describe is just wasted fuel, as the airflow into the engine has only just started since the overlap period takes place at the beginning of the intake stroke. There's another 180 degrees of crankshaft rotation and a full downstroke of the piston to ensure the cylinder gets it's fill. Exhaust backpressure will only reduce the effectiveness of the valve overlap in a 4 stroke engine.
One of mine split a muffler when the fiber timing gear lost a few teeth. What type timing gear are you running?
If not sure, shine a flashlight down through the oil-fill hole for a look-see.
You'd probably have a long argument coming from the instructors that taught me auto mech. at the tech school I attended years ago. Hard to equate a Model T as high performance engine unless it is substantially modified from its original configuration to truly take advantage of a straight pipe under most operating conditions. Most vehicles are engineered to operate with a certain amount of back pressure in the exhaust. Your arguments are certainly true for high performance applications. However, I never regarded my T as a "muscle car". I've been down the high performance path in my life and much prefer to see the world glide by at 35 rather than 95 mph. Thanks for your input!
Drill the bolt for a cotter pin and use a castle nut.
I didn't mean to suggest a Model T was a muscle car. I only wanted to illustrate that valve overlap is useful in any poppet valve engine. I disagree with the statement that: "most vehicles are engineered to operate with a certain amount of back pressure in the exhaust" if by that you mean to imply that backpressure is somehow beneficial on stock engines. Millions of cars have been modified with lower restriction exhausts alone (no changes to cams or carburetors) and the owners have experienced increased performance, not a loss.
I think others on this string have provided better explanations, that's all.
Thanks again to all those who made suggestions. Royce, I believe that my solution (using a lock washer) worked well until it must have rusted out (because, when I looked under the car, the threaded rod, lock washer and nut were missing). I appreciate your suggestion using a castle nut, but find (contradictory to Henry Ford) using castle nuts and cotter pins troublesome. I do have another muffler (that the nut kept loosing up) that I have had welded up and plan on installing it this week.
Fortunately I had no trouble the entire day today after mine became loose yesterday. (see my Nov. Tour post earlier this evening) as LizzieBelle ran smooth and quiet the whole day. Guess I need to check that stupid little nut more often!
Double nut it.
That happened to my Touring also. It's not about the nut coming loose, (but that happens too), it's about the whole stud coming out of the end of the exhaust pipe. The two folded over tabs in the exhaust pipe, that the stud mounts to, break off and let the stud come out.
Thanks Jerry, I'm sure that's what happened to it. If you look closely, you will see a small weld on the end of the exhaust pipe. Should I lay on the floor under my T and try to grind it of with my small Dremel grinder, or should I take the exhaust pipe off and grind it with my bench grinder.
Whichever way you decide to do it, but especially If you decide to grind on it from underneath the car, be sure to wear eye protection!
Thanks for your advice Mark, I was planning on doing that. Here's a short video demonstrating the power of Seabiscuit's newly rebuilt engine. I thought that I could hear a police siren so I turned down a dirt road.
I agree with Dave, use a double nut. I had lots of problems on my 17 touring until I used two nuts locked together. Lock washers seem to loose their spring and the whole thing falls off.