muffler question

guys i need a new muffler in my flattie... I've got the stock flathead 4. any issue with me putting a cherry bomb (straight through style) on there or do i need something with more back pressure?

 

At least in these parts a straight through style is not legal on the trails, I am going to have to have an extra set for the trails around here

 

i use mine on both street and trail... i dont think the law will hassle me too much unless its ridiculously loud... im mostly wondering how it will affect the way the engine runs... i've heard that the L4 runs better with a bit more back pressure. any thoughts anyone?

 

I'd run a Flow Master myself.
Can't kill them.

 

get a repo from walcks..you needy the back pressure..repos have the correct baffles in them..

 

i wanted to put a glass pack on my 3b 4 cylinder. what does the back pressure do to help the engine?

 

It gives gas to be compressed along with the fresh air. Or at least thats the theory I have been given. Contrairy to what a lot of people think backpressure to a cirtain point is needed for most motors.

 

Wise man told me it also helps the valves from getting burned out..???
Makes since but everyone has there own ideas..I have burned valves testing(running) engines without an exhaust system before I have re-built them..

 

I believe as long as you have a manifold and a length of exhaust pipe you are fine. Exhaust gases will be drawn out properly. The muffler seems insignificant. I have seen flatheads run well with original, glasspack, and mufflerless exhaust. I think some newer computer controlled engines might throw error codes for EGR if there is not enough back pressure for a little exhaust to be returned. Those recirculated exhaust gases do lower combustion temperatures, but that is primarily used at cruising speeds, and many people (myself included) get rid of EGR valves. Engines like cool fuel and clean air.

 

I'm going to throw in my 2 cents on this if you don't mind. From what I know about exhaust, which is little, is that running an engine with no exhaust or only a manifold will allow the valves to cool to fast and bend. I think that is why the old timers alway say to run a manifold with some pipe or a header. That is all I've heard about an exhaust system, or the lack there of, damaging your valves. I've never understood the back pressure theory. If you think about what cam and head modifications do for your motor backpressure seems to contradict that. Bigger cams and better flowing heads and intakes move more air and than increases your volumetric efficiency. Your enigine is basically an air pump. Think about an air compressor as it builds pressure. As the pressure goes up in your tank the motor and compressor works harder. Maybe a bad analogy, not sure, I would like to hear some other therories on the back pressure thing.

 

Here a brief description:http://www.uucmotorwerks.com/html_product/sue462/backpressuretorquemyth.htmIt's on the internet, so it must be trueR) R) FWIW, you can still get the stock muffler at a Napa store locally. I'm not enuff of an engineer to have an opinion on going one way or the other. On a 70hp motor it comes down to your noise tolerance IMO.

 

Hey, I buy that theory. That makes total sense to me. I thought about this more after my post last night. Think about the header designed to produce a "scavenge" effect. That is when one header tube helps pull more air/fuel mix into another cylinder during valve overlap, at least I think thats how they work. Anyhow, this totally bebunks the backpressure idea. Heck, I don't know, maybe each one has its' benefits depending on the engine design. I've already put to much thought in to this. I usually just buy the muffler thats cheap and holds up well. We're talking about a Jeep muffler, not an F1 race car!

 

Once again that points to back pressure as being a load of B.S. Good article, thanks.

 

tell ya what guys... I'll be the guinea pig . I'm going to install the straight-through cherry bomb... I'll let you know what the results are. And hey, if i blow the motor, we can call it an excuse to finally swap in a 6. R)

 

Racecars and what we drive are not that much alike.
I think the cherybomb will work but a muffler would be better.
Not much advice out there for low rpm performance.

my .02 cents.

 

I have a 51 with the stock L head. I run a cherrybomb on mine with no problem. It runs smooth and I drive it daily. In Virginia as long as I keep antique plates theres no need for state inspections. (cherry bomb's are illegal on newer vehicles???)