[78w72]

Originally Posted by CROCIE JR

I have tested a lot of complete exhaust systems on engine dynos and chassis dynos. Thats why I say what I say. All engines are different. To paint with a broad brush here and say it works for this guy or that guy is cool with me. So are you saying that hotter gasses take up more room than colder gasses? BTW, did I try to put smaller tail pipes on the dyno, no. Did I baseline with open headers and a collector extension, yes. Havnt seen a complete exhaust make more power than open headers. Have I done back pressure testing at multiple spots along a system, yes. I simply use this dyno info to jet accordingly, and say to myself " that system only sucked X of the top." I dont know why other people say what they say or do. I test in a controlled environment and use math and stuff. You guys do what you want to do. Most of the time your minds are already made up. I'll just stick to my book learnin'.

yes, i am saying, based on numerous info & testing i have read from reputable sources, that hotter gasses expand more & therefore need bigger pipes compared to cooler gasses. makes sense to me & sounds like its based on facts of physics. are you saying that's wrong? nobody is saying a complete exhaust will make more power than open headers... where did that come from?

my reply to your initial post was simply asking for more info on your statement that a 2.5" exhaust is ok on 550+hp engines... i asked what a 3" would have done in comparison. please elaborate on that with "math & stuff" & "book learnin."

not sure why the negativity in your reply, "you guys do what you want to do. most the time your minds are already made up." i wasn't doubting you, i was asking for more information based on your statements. sorry if that offended you.

thanks everyone for the help & pics.

[Skip Fix]

Open header vs exhaust personal experience with 10.95 @ 124/6.91 @ 99.1 1/8 mile 3750 lbs car. initially had 3" head pipe and H pipe into 3" 2 chamber Flowmaster mufflers and 2.5 tail pipes(class requirement from previous class racing). Would loose 0.3 with exhaust hooked up compared to dropping a 12" section in the collector headpipes.Tailpipes were getting thin so we dropped entire exahust system with a tranny swap. Took to track and dialed in with new tranny/convertor and got the 1/8 mile times. Added a 3" Dr Gax X Ultraflow 3", 3" Torque Tech tailpipes and even with all that additional weight the car ran identical 1/8 times. So that car ran identical even adding a little weight open headers to exhaust system.

Theoretically with the same number of air molecules hot air will displace more volume than the same amount of molecules at a lower temp because the molecules are moving around more with more "gaps" between them. Same with a liquid having more volume at a higher temp than a lower temp.Thermodynamics and how a thermometer (non digital) works. So theoretically cooler exhaust should displace less volume and could ue a smaller pipe to keep the same velocity as hotter gas. Probably some formula you could figure.How much I can't tell you, or if it would be enough that a 2.5" woul dbe OK vs a 3" can't tell you either, and I would keep a system the same pipe diamter

The pipes system looks real similar to my Dr Gax X and Torque Tech tail pipe system.

[tpssonic]

The relationship between pressure, volume, and temperature of a gas is most simply decribed by the Ideal Gas Law; PV = nRT, where P is the absolute pressure of the gas, V is the volume of the gas, n is the amount of substance of gas (measured in moles), T is the absolute temperature of the gas and R is the ideal, or universal, gas constant. If you increase the temp, you increase the product of the pressure and volume. Bottom line, if the volume remains the same (as in a car's exhaust system), if you increase the temp, you proportionally increase the volume as "n" and "R" are, for all intents and purposes, constants in this scenario.

[mnfatcat]

Had the exact same result as Skip on a Nova. Same 3" full system exits behind the tire, Flowmaster Super 40's. System is built with flanges, took out the sections ahead of the mufflers 11.86/111.68 full exhaust, 11.63/114.88 open. I was stunned, I made my 1st pass down a dragstrip in 1960, and seeing a 3+ mph increase on a system that I felt was very efficient was jaw dropping.

Have a couple 9" bullet mufflers I'm going to put on the Catalina in the spring, that and an aluminum flywheel might be just enough to get by an old friend who has a max wedge 63 Plymouth that outruns me by about 3 tenths.

[CROCIE JR]

Wrote a lenthly dissertation in responce to 78w72. Lost the data before I could post. Tired now. Not offended. Do your own testing. Forums are for advise not fact. Including my own. You got some pix. Not a big deal here. Take it or leave it. Its the internet. Just here to help. Posting my experiences.

[TransAm525]

I also went with a side exit oval tube exhaust system. I purchased mine from Ram Air Restorations. The system is their UXO-30 universal oval tube side exit exhaust system with 3" diameter tubes, X-pipe, and dual Spintech Sportsman series mufflers ($749.00 plus shipping). It's also available in 3.5" if you prefer. My 1978 Trans Am is lowered just over two inches from stock, and I have plenty of clearance between the exhaust and road. Being the non-conformist I am, I wanted something unlike any 2nd gen Firebird out there. The look and sound is unreal! Just another option to consider...

http://www.ramairrestoration.com/pon...th-x-over.html

[tpssonic]

"...if you increase the temp, you proportionally increase the volume"

I should add, if you decrease the temp of the gasses (as they cool passing thorugh the exhaust system), they proportionally decrease in volume. The big question is "how much do they cool...and how fast"? Factors that affect this are: surface area (larger diameter pipe and/or mufflers, the ambient temperature, the velocity of air passing over the pipe, fuel mixture, and timing. There are other factors that affect the rate, but are less influencial.

[78w72]

Originally Posted by CROCIE JR

Wrote a lenthly dissertation in responce to 78w72. Lost the data before I could post. Tired now. Not offended. Do your own testing. Forums are for advise not fact. Including my own. You got some pix. Not a big deal here. Take it or leave it. Its the internet. Just here to help. Posting my experiences.

no hard feelings. i appreciate the help & advice... some of it just sounded kind of negative, or like you were mad for some reason & i wasn't sure where all that came from.... & it seemed like you were doubting or questioning some of what was reiterated about hot exhaust gases &/or using smaller tails. all backed up by tests at the track, & others even used math & science & stuff to support it. & yes forums are for advice, but that advice should usually be based on some type of fact. no?

t/a525: that ram air system looks very nice, i've "heard of" spintechs but never actually heard them. however at $749 + s/h they are way out of my budget.

based on the info & pics here i have decided to go with the 3" pypes system. any other info, advice or pics are welcome though.

thanks again!

[CROCIE JR]

tpssonic. That is the big question. The dyno loops at 200rpm per second from 2500-6000 tend to get the whole exhaust system pretty toasty. Most of the exhaust is pretty straight untill you put the multiple bends after the muffs. Inducing some restriction. Airspeed under the car helps cool, I'm sure. The Westech Dyno rooms are pretty "windy". Next time if time permits I would like to install 3" inch tails on a 2.5" system. Maybe create some extra "pull" on the gas column.

[Skip Fix]

I should add, if you decrease the temp of the gasses (as they cool passing thorugh the exhaust system), they proportionally decrease in volume. The big question is "how much do they cool...and how fast"? Factors that affect this are: surface area (larger diameter pipe and/or mufflers, the ambient temperature, the velocity of air passing over the pipe, fuel mixture, and timing. There are other factors that affect the rate, but are less influencial.


That was my comment on hard to figure how much without an A vs B trial.

Another factor often overlooked in the whole equation is header tube diameter. Too big can decrease the velocity into the exhaust system and even my 2 chamber Flowmasters caused reversion until I dropped to a smaller tube size. This also decreased the open header to exhaust system difference on that motor.

[oville]

Trans Am 525 how noisy is that system sitting in the car?
I like the idea of not having to run the pipes out the back, just wondering about sound level.


Also anybody ever used a fuel cell and moved the mufflers to where the original gas tank would locate?

Got this idea in my head from reading the Jim Hand book and how is exhaust is setup on the wagon. That and hoping to maximize ground clearance. Have never seen it before myself, guess it would have to be custom or cobbled from a kit and some extra parts or something.

[TransAm525]

The sound is similar to a Flowmaster without the drone during cruise. At idle, the exhaust note is throaty, but not overly loud. It's when you put your foot into it where the Spintechs really shine. At wide open throttle, the sound is extremely strong (aggressively speaking, not loudness), and makes the engine sound as if it's turning 1000 rpm higher than actual. In the car, the exhaust tone is a bit loud, as the mufflers sit right under the rear seats, but nothing that an ordinary muscle car enthusiast wouldn't enjoy.

Overall, your results will vary depending on your camshaft. I recently made the switch from a very small hydraulic cam to an aggressive solid with a large exhaust duration. Following the switch, the exhaust note at idle was slightly louder, but not much. You should be able to find some YouTube video clips of various cars using the Spintechs. If you like the sound of a Flowmaster, you'll love the sound of a Spintech.

[tpssonic]

One of the ways I check pipe temps on my 2-stroke race sleds (snowmobiles) is by using an infrared thermometer, like those that can be purchased inexpensively at Harbor Freight. When tuning two-stroke sleds, pipe temperature (in particular, the tuned pipe center section positioned between the divergent and convergent cones) is crucial in determining CVT clutch calibration, from engagement through full shift. Hot pipe and cool pipe peak horsepower can vary dramatically (up to 1000 rpm) ON THE SAME ACCELERATION RUN. Pipe temp at the holeshot can make or break the acceleration run. The ability to retard ignition timing on the starting line can "put more heat in the pipes, thereby aligning engine's ability to "close the clutch" without "bogging" the engine (much like a stall converter on a car). These little devices have taken much of the guesswork out of tuning two stroke motors. Yes, we also use probe-type pyrometers (EGTs) to constant monitor air/fuel mixtures as well as ignition timing. They are also very helpful in letting you know when you get a load of sub-par (not as-advertised octane) fuel as well.