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Pick my next mufflers *VOTE*

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fad2blk99, If I'm reading yours and Tim's posts correctly you agree with each other. /forums/images/graemlins/dunno.gif /forums/images/graemlins/ears.gif

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In the end... almost. The part being over looked is when you have a relatively mildly built engine (i.e. not a dragster) you can OVER scavenge your engine, damaging your off idle torque, an effect seen on the dyno with a set of Doug Thorley tri-y (this can happen at other points on the RPM band depending on how your entire exhaust is tuned). This is, I assume, why some people see a drop in 60’ and overall ETs due to lose of torque at critical points along the RPM band. It is my contention that you ABSOLUTELY want mufflers in your application. In fact, I wouldn't go with any thing bigger than a single 3" or a dual 2.5” pipe. Believe it or not, there is a formula for calculating pipe size.
 
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Combustion engines are only 25% efficient if I remember correctly.

-Chris

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The 100% efficient engine is a perpetual motion machine, only created in a vacuum. Jet Turbine engines are less than 50% efficient, and Pratt & Whitney makes one that produces over 100,000 ft/lbs of thrust! /forums/images/graemlins/yikes.gif

...volumetric efficiency... now thats a whole 'nother story....
 
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tim explain to me how a 2 stroke exhaust works. it REQUIRES backpressure to even run.

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This is what I found about two-stroke exhausts:
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The more asstute among you will of realised that it is possible for some of the fresh charge to get sucked out along with the spent charge, this means that some power is getting wasted. What we need is a method to keep all the fresh charge in the cylinder, so we can have as big an explosion as possible. To do this you use a tuned pipe. I tuned pipe fits on the exhaust of the engine much like a silencer. What a tuned pipe does is restrict the exhaust gases so they create a back pressure standing wave, that stops then fresh charge from getting out. Tuned pipes are great for giving you engine a power boost.

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This isn't an issue with 4-stroke engines because they have valves.
That's my take anyways.

fad2blk99, I can see your point, but I wouldn't think the engine would be able to over-scavenge down low.
Like you said earlier, this stuff can make a fella's head hurt.
 
You are almost correct... only you forgot to account for valve overlap, when both the intake and exhaust valves are open at the same time. Its another one of those obscure cam specs many don't consider.
Overscavanging isn't a made up term. It is real and is reflected on the dyno.
 
back pressure does not hold the valve open, thats the cams job. you want it to close when the cam says to.

i think i AM confusing back pressure with the venturi effect. but you do need backpressure to create torque
 
This post gives me gas... :farting: excuse me /forums/images/graemlins/blush.gif I released some back-pressure /forums/images/graemlins/whistling.gif
 
Volumetric efficiency is how close the engine comes to drawing in the amount of air that it theoretically would based on displacement. Since there are restrictions in the carb, throttle, manifolds, valves, etc., you get slightly less air than this. That is where the 80-something percent number comes from. On a 350cu engine, you would pump .8x350 cubic inches of air every 2 engine revolutions. Increasing this improves power by getting more air and fuel through the engine. That's where reducing restrictions and getting a bigger cam come in.

The overall efficiency of converting gasoline into mechanical power is very low. Of the energy that you do get out of the gas, more goes to the radiator than to the wheels. Sad but true, but it looks much better when you know that all of the batteries in an electric car store less energy than 2 gallons of gasoline!
 
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i think i AM confusing back pressure with the venturi effect. but you do need backpressure to create torque

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Nope.

Adding backpressure can do nothing but cut your engines power.

Inevitably every exhaust system and even the ports themselves have some sort of backpressure so zero backpressure is nearly impossible.

Glad to see that we're finally agree. Main point is backpressure = bad. High velocity = good. More backpressure = less power. Less backpressure without reducing velocity significantly = more power.

I think that it is possible to have an overly efficient exhaust system but I don't think that anything that will fit under your truck can manage to be too efficient.
 
I have only had one time when i didnt have enough backpressure. That was in my toyota, right after i got the motor reassembled, and i drove it arround town with an open head. No header, nothing. This is the only time i have ever experienced a power loss due to decreased backpressure, and its already been stated why that happens.

I run as large of an exhaust as i can, and get backpressure as low as possible, because as tim said, backpressure = bad.
 
boy its funny how an innocent thread about muffler choice can turn into a heated discussion about exhaust theories. gotta love it /forums/images/graemlins/thumb.gif

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So which mufflers did we pick???

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it looks like its gonna be magnaflows we'll see what kind of price mudfrog can get for me.

backcountry , thanks for the link to the muffler soundclips.
i kinda like the sound of those purple hornies /forums/images/graemlins/smile.gif

the magnaflows sound alot better in that clip than i've heard in person. i'd still like to hear those dynomax race mufflers, they are straight thru similar to magnaflows. they should sound alot better than the dynomax superturbos.too bad they arent very common.
 
one of my friends ran open headers in his mudder. after a few runs he put 3" dual exhaust out just infront of the rear tires. you can feel a difference in the take off.

here is what im thinking each exhaust valve has it own small tube, they dump into the collector at the same spot. then in 4" it ends. i think the pipe after the collector did the same thing that each header tube did for the valve. when i think of backpressure i think of a pipe to get of all the exhaust gases
 
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one of my friends ran open headers in his mudder. after a few runs he put 3" dual exhaust out just infront of the rear tires. you can feel a difference in the take off.

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Yep, because his fuel mixture was too lean. What we have here is a lack of engine tuning, not additional power due to backpressure.

Next?
 
How much lift do I need to clear 37's? I have 2.73's in my 10 bolts, will this be ok?
 
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How much lift do I need to clear 37's? I have 2.73's in my 10 bolts, will this be ok?

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i would go with at least a 12" lift, minimum.

your gonna lose all your ground clearance with those 10 bolts, too much beef.

a dana 30/35 would be a better choice.

with 2.73's you should go ahead and get at least 40's. you'll have plenty of power.

if you need more, just hack the exhaust off at the manifolds. you'll probly double the horsepower.
 
Good point on the clearance, I have some axles from a GEO Tracker I could use. I think I will go with the 12" lift and just take my manifolds off for ultimate power. /forums/images/graemlins/thumb.gif
 
ohhh, score!. i've been looking for a set of those badboys for awhile. what did you pay for them>? i havent seen anything under 10 grand.
 
i've got a 82 buick regal and it makes a "frr frr ka ka ka brrr" sound when i try to pass. whats wrong with it?
 
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