zedpapa, you and a couple of the racers here at work have convinced me to go back to a single on my truck. while I love the sound of dual smithy's, I got no bottom end torque. If I go with a single after the dual Dutras, I might gain some of it back. Plus, I will have an extra muffler for when (not if) this one burns out.

You guys here rock. I mean that.

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If it was easy, everybody would be doing it.

zedpapa,

Thanks. Nice list of upgrades need for optamizing engine performance with out going deaf. I'm taking all them under consideration.

Well, so those cool looking, evil sounding duals maybe preventing my car form lighting them up on clean dry bare pavement. Spit, or two pebbles under each wheel and she will spin'em up. With the unknown spec hot cam I have, my engine dose not seem to generate a lot of low end torque.

Your car is set up close to my build excepting my 904 & 3.55:1 rear, and I presume yours will spin the rear wheels. What length Flow Master are you running?

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

cocunuteater, you will gain a noticeable amount of power/torque when you switch back to a single.

wjajr, keep in mind that my setup was done before i had any of this knowledge/experience. unfortunately my car is not built the way that it should be(2.5" all the way with a 40-series). trust me when i say it will be the first thing i change/fix when i start driving it again. unfortunately it is parked at the moment.

mine won't spin the wheels for a couple of reasons; clutches don't like oil, first is not deep enough, 3.23 w/suregrip, sticky 225-60-15 tires. get some water under there and no problem. the 390 holley and clifford manifold kind of killed torque as well.

i was only ever able to get about 17 mpg with and that was on a 65 mile round-trip commute. but i haven't done anything to the ignition curve yet or dialed in the holley.

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1970 dodge dart w/225 /6 bored .040" over, holley 390cfm w/vac. sec., compcams 252s, clifford shorty headers w/2.5" exhaust w/flowmaster, f-body 11" front discs, aluminum A-833OD, 8 1/4 w/3.21 SG
soon to have 5 gears!!!

I found this article on exhaust systems a while back and they like the Walker Dynomax mufflers. Apparently they are high flow and quite.

http://www.pontiacstreetperformance.com ... haust.html

zedpapa,
Interesting fine tuning........

Ask your boss if my 2.5" FM40 (Thrush version) would benefit from cutting the 2.25" tailpipe off that ends at the bumper and going to a 2" tail pipe for the last 2 feet. The head pipe to the muffler is 2.25"

Would it flow any better? Thus reducing the resonance caused by the reflections going back up the head pipe from all the turbulence in the tail pipe?

It would be nice to lower the resonance 3dB or more if possible between 2600 and 2750 rpm (62 - 68 mph) on the freeway or when going over the mountain pass. Under a sustained load up the mountain pass it is pretty loud.

I have quite a definite burn line/transition after the "V" shaped baffle. The front half looks like my spark plug color, a very light beige. The back half of the muffler is still silver and like new.
Inside the tail pipe at the bumper it is very dark, not light colored like the front half of the muffler. So the gases must be cooling off quite allot at the exit and probably making allot of turbulence and restriction.

You mentioned a minimum pipe length of 18" after the muffler.

How small should I go with the tail pipe????? Just 2" or smaller?
After going over the axle bends with 2.25" pipe can I neck it down to 2" for the last 24" or so and experience less resonance and greater flow?
Or should I go to smaller pipe like 1 3/4"?

I am willing to do a little experimenting to prove out your/Flow Master tuning/training.

Or does this only work with the FM50?

If it isn't worth it, I will go ahead and install the 2.5" diam x 5x8x18 body MagnaFlow.

Let me know,

Thanks!!!!!!!!

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Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

ted, if you have a thrush muffler, its not a FM. the patent ran out on flowmaster which is why we are seeing copies of them. i can't vouch for thrush mufflers as we don't use them, not sure why. probably because its a copy and not the real thing.

when we build a system we usually step down in diameter at the muffler. easiest point to do so. my boss prides himself on being able to do things in one piece, manifold to muffler and muffler to bumper. so doing the step down in the middle of the tailpipe is something i am unfamiliar with. but i would guess that it would help.

let me get this straight. you have a stock manifold with 2.25" to a thrush muffler with a 2.5" inlet/outlet with a 2.25" tailpipe? how did you attach everything? i will definitely have to talk to my boss about this one.

maybe another thread should be started for this discussion. to the orignal poster, sorry for the hijack.

zedpapa

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1970 dodge dart w/225 /6 bored .040" over, holley 390cfm w/vac. sec., compcams 252s, clifford shorty headers w/2.5" exhaust w/flowmaster, f-body 11" front discs, aluminum A-833OD, 8 1/4 w/3.21 SG
soon to have 5 gears!!!

Physics are physics and the design concept is the same, even the material gauge. The name really doesn't do much for me but the design and price point does. If I have been using the design out of context, then shame on me for not knowing. I will have learned a lesson that may benefit others.

Basically yes.

The 2.25" pipe slides inside the Thrush muffler and the entire system is welded. The exhaust manifold has been reamed up inside to 2.25" for about 6". The ports at the head have also been reamed and gasket matched. No heat flapper either so it is fairly free flowing for a stock piece.

If there is a way to utilize your training, we could be saving the original poster some time and money and also help wjajr with his duals. I am willing to do some work to test your theory and Flow Master training.

Thanks!

_________________
Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

ted, you are right that physics are physics and the design concept is the same. but we have seen/removed many FM look-a-likes because they are noisy, resonate or just plain fell apart. also the FM is made of 16 gauge metal and they claim .004" tolerance on placement of the delta plates. i am not saying thrush makes a bad muffler, it is just not the same as a FM.

as you asked earlier, ted, the 18" minimum tailpipe i refered to is for the truck guys who like to dump in front of the rear tire.

if you were to come to our shop, we replace the entire tailpipe. a lot of times its easier and it looks better. just replacing the last 38" like you said would probably make a difference, i am just not sure how much. i ask my boss when i get to work this morning.

zedpapa

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1970 dodge dart w/225 /6 bored .040" over, holley 390cfm w/vac. sec., compcams 252s, clifford shorty headers w/2.5" exhaust w/flowmaster, f-body 11" front discs, aluminum A-833OD, 8 1/4 w/3.21 SG
soon to have 5 gears!!!

zedpapa,

As you know going over the axle are is the 90 degree bend and lots of restriction any way on the 2.25" pipe. They used super heavy gauge pipe and the bends look like mandrel bends, no crimping or wrinkling. I cut the back off right after the last bend. It is just straight pipe for about 3' and bent down at the end. That is the portion I would like to replace with the smaller 2" pipe.

Let me know what you find out. Our local shop is cutting me a piece today and swaging it up for a slip fit.

Thanks!

_________________
Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

i talked to my boss and he said that for best results do the whole tailpipe. while doing the last 3' will help, you won't get everything you could. the 2" should slip inside the 2.25".

we have a compression bender to bend everything with. mandrel bent pipe needs to be saved for building headers. my boss drives a 90 chevy SS pickup with a 454 and he used to drag race it. he thought mandrel was better than compression bent pipe. he switched the whole system out and there was zero difference. and its not stock. he's had some head work done, chipped, doug thorley headers, cold air intake, NOS. marketing is great isn't it?

zedpapa

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1970 dodge dart w/225 /6 bored .040" over, holley 390cfm w/vac. sec., compcams 252s, clifford shorty headers w/2.5" exhaust w/flowmaster, f-body 11" front discs, aluminum A-833OD, 8 1/4 w/3.21 SG
soon to have 5 gears!!!

Ok, tonight when I get home the piece they made should be ready to slide in and I will report my findings after driving to work tomorrow.

Thanks! If this works it will save allot of money doing additional trial error testing with other mufflers. It should provide a very cost effective system.

_________________
Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

zedpapa,

All I can say is wow and I am stunned :shrug:

The gases must really cool allot after the muffler, because the engine is not only 6 to 9 db quieter depending on the rpm but is much punchier. My wife can't believe it either! The bigger pipe must have let it cool too fast causing the turbulence leading to back pressure and resonance build up at various rpms.

The FlowMaster sound (knarly growl) is still there up to 50 mph (2000 rpm), but after that it starts to taper off and reduce in sound level where as before it just got louder and louder. Since my commutes are pretty long, this is a welcome relief.

The only thing I did was cut the last 36" of 2.25" tail pipe off at the last bend behind the axle and slid on a 2" diameter tail pipe and clamped it in place. I guess the Chrysler and Flow Master engineers have it down. I had been told this before but, I let the muffler shop install it with 2.25" all the way. I went back to the shop that did the install and they gave me the 2" pipe. When I took it back to show them, they were surprised. It will be interesting to see in the coming weeks the effect this will have on mileage.

_________________
Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

and you only did part of the tailpipe. imagine what would happen if you did the whole thing. glad it worked out for you.

zedpapa

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1970 dodge dart w/225 /6 bored .040" over, holley 390cfm w/vac. sec., compcams 252s, clifford shorty headers w/2.5" exhaust w/flowmaster, f-body 11" front discs, aluminum A-833OD, 8 1/4 w/3.21 SG
soon to have 5 gears!!!

zedpapa,
I would say that it was a very simple test with great results and definitely worth it. I am finding myself driving a little faster than normal on the freeway due to the lack on resonance.

In the next few weeks I will pay close attention to see if there is a change in the mileage. I keep a log book of all the changes between fill ups and limit the changes to one at a time per week.

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Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

So have you seen any increase in mileage?

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Rob M
'80 D100 SWB stepside, S6 4-spd OD