I built a exhaust system for one of my old trucks and only could do a single system right now and thinking I might have a too small muffler,I used a turbo muffler that looks to be good for half of a dual system but I have eight cylinders going through it. I was wondering if there was a way to determine a good size of muffler for a system.
I had a muffler shop install a system on another truck years ago and the muffler choked the motor so it did not run as good and used way more gas.
Mufflers are for sound control, you can get free flowing mufflers at the expense of more noise, or you can get quiet mufflers at the expense of exhaust restriction. If you feel the muffler is restricting the flow, then you need a "free flowing" muffler, not necessarily a "bigger" muffler.
Just thinking about this off the top of my head: On a V-8 engine, only one exhaust pulse at a time will be traveling down the exhaust pipe at a time. I don't think they'll overlap, wether you have a single pipe, or dual exhaust. Therefore, i think you could use the same size muffler for either a single or dual exhaust. I'm no expert and I have no experience so someone correct me if I'm missing something.
It is the same as running too small a carb. You must have enough flow to get the smoke out of the holes as it were. There are dozens of flow computers for exhaust systems.
http://67-72chevytrucks.com/vboard/showthread.php?t=263014 Lots of stuff there to soak in. Here http://www.jalopyjournal.com/forum/threads/heres-some-really-good-exhaust-info.737874/ The first link has gone dead but maybe you can find it? It basically described the bottle neck created by the muffler. A 3" in and out muffler on a 2" pipe saw less restriction but still plenty of sound reduction. A while back I was at a muffler shop trying to fit mufflers the where there was no room. I suggested some small body mufflers that looked like they would fit. The guy said no they were for 3 liter 4 cylinder cars. 2-1/4 inlet and outlet. I said perfect, think of that engine as 2 4cyl @ 2.7 liters each and we're putting 2 of them on. He looked at me funny. They Worked perfect and sound pretty good too. No way 1 of them would handle the flow. You can easily check for a restriction with a cheap *** vacuume/fuel pressure gauge. Tap into the exhaust pipe, note idle pressure- your looking for about 1.5 or less. Get 2000 rpm and hold it, your watching for a "good" reading on most engines at 2000 rpm should be 3 psi or less. There may be some vehicles that will read a little higher that don't have a problem, but the reading should not be significantly higher than 3 psi. Pay close attention to what the backpressure reading does while you are holding it at 2000 rpm. If it remains steady, chances are there is no restriction. But if the reading gradually increases, it means backpressure is building up and there may be a restriction. If you want to rev the engine higher, say to 4000 rpm and hold it, the backpressure numbers will shoot up. Most stock exhaust systems will show backpressure readings from 4 to 8 psi (27 to 55 kPa), or even higher. As before, if the backpressure reading is unusually high or it continues to climb at a steady rpm, it usually means there is an abnormal restriction causing an unhealthy increase in backpressure. You can check on the intake vacuum too. With a throttle blip - A drop of 10 psi before it stabilizes again and you can bet it's restricted in the exhaust.
But gee whiz, judging by the threads I read on here almost daily, I thought running too small a carb was just the best thing ever...
Don't start, you'll be waisting your time. Then get pissed off, and the only one around that you can take it out on will be yourself.
Yes and the restorer ****s are moving in too. I always thought guys who restore cars older than they are suffer from sort of Edipious complex.
Naw, just check vacuum at idle...say you have (stockish engine) 18 inches/hg...now run the engine up to 2K or so, let it sit...vacuum lower?...restriction...no idea how you can tell from a "blip on the throttle", cause that will always drop a vacuum reading. Yes, back pressure is right on, but you are quoting GM factory spec...if I had 3 psi BP...I'd be digging in, looking at a rotted muffler, plugged Cat, crushed pipe, etc. Take a new car, all the cats, mufflers, etc...be surprised if you'd get 1 PSI of BP...really surprised. Yes, FWIW, did my dealership time, did my ...aw, never mind...3 PSI is too much.
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