From reading the archives, I see that the reproduction mufflers not welded together can blow out on some backfires. I understand there is something about the manufacturing process that is different and weaker than the original mufflers. I am not trying to discuss that. But the fact a backfire blows apart a muffler seems to indicate that there is a lot of back pressure from the reproduction muffler.
I have seen this FO-11 muffler mentioned numerous times: https://www.ruralking.com/ford-new-holland-tractor-muffler-8.html Would this FO-11 have a lot less back pressure? Will using the original vs. the FO-11 even matter with a Z-head (í24 motor)?
I would like to use original, but donít want to sacrifice power to do so. Can anyone comment on this?
I seriously doubt that the reproduction mufflers are significantly weaker than original mufflers. (Larry Smith may offer an opinion.) I have had original mufflers blow out with backfires.
As to your concern regarding back pressure caused by the original muffler: The pressed steel muffler has little back pressure. The earlier mufflers, those with a tailpipe, are more restrictive.
My two cents worth, perhaps overvalued, Bill
It not the back pressure it's when they load up with gas and it ignites. If the key is bumped off and turned back on while the engine is running or there is a pause between switching from battery to magneto the unburnt gas builds up in the muffler and when the first hot flame hits it, boom! Generally this happens when the engine is at operating temp but can happen at other times. The original outer tube was spot welded along the seam, at least in the later cars and had a tighter crimp to seal.
I have used many of the FO-11 mufflers and like them a lot. I figure they must be more free-flowing, which is a good thing. Your engine is basically an air pump. The more air it can move, the more efficient it is. My car has a Simmons straight-through carb, an '09-10 intake manifold, and an FO-11 muffler. And bigger valves and a high-lift cam to move more air.
First of all, my T's don't backfire. Second, what is an FO-11? All of my T's have original stock mufflers. Most of them have reproduction outer shells. What's all the concern?
I took an repro muffler that had blown out apart
and cut a piece of 5" truck exhaust pipe to replace the outer shell. Works great, has not blown out yet.
Ever see the inside of one of these repop mufflers Tom? There's basically nothing in there to restrict any thing. so back pressure isn't the answer. Mark is correct. It's collected fuel that's ignited.
The dynamics of a Model T exhaust system is not as cut and dried as "free-flow=good/back-pressure=bad".
Back pressure can change the power-band to a lower RPM level which can be useful, especially in a T, which spends most of its time in lower RPM's.
I know of several Montana 500 drivers who have won using mufflers, including the reproduction stock kind. (Yourn truly among them).
Besides a few blown out mufflers , I noticed that too much back pressure was slowing me down, My car with 280 cam and Zhead. I added two more holes on the inner pipes of muffler and on the muffler end for better breathing. A little louder but not too bad and engine works well.
When I ran my T engine without a muffler and tail pipe just the manifold, it just didn't (by the seat of my pants) run the same, just seemed to run better with the parts in place. (not a noise thing) Doesn't some back pressure come into play as part of the scavenger effect, helping pull the next charge in, or something like that.
Thanks guys, very interesting. Since your comments, I'm most likely going with the original/reproduction. I like the looks of the original, I like the sound, I now see there isn't that much inside the original.
Larry, the FO-11 that Mike is referring to has a link in my first post.
Suggest picking up a copy of:
Scientific Design of Exhaust and Intake Systems
Third Edition, by Philip H. Smith
with John C. Morrison
For years, engineers, engine designers, high-performance tuners and racers have depended on the Scientific Design of Exhaust and Intake Systems to develop maximim potential from their engines.
Dr. John C. Morrison is one of the foremost authorities on the analysis of the induction and exhaust processes of high-speed engines. Together with Philip Smith, he gives a thorough explanation of the physics that govern the behavior of gases as they pass through an engine, and the theories and practical research methods used in designing more efficient induction manifolds and exhaust systems, for both competition and street use.
Chapter topics range from Simple Flow Problems and Sound and its Energy to Designing a System for Racing. This authoritative book will lead you through the complex theory to an understanding of how to design high-performance exhaust and intake systems for your own particular application.