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Discussion Starter · #1 ·
ok this is gonna be a long one.
I'm posting this because im sick of people telling me that you lose power by removing cats, or mufflers, or adding or removing certain things from the intake and exhaust system and the real biggy the burns me up "your fuel system wont work right without some back pressure.

the key to excellent exhaust systems is tuning for both flow and sound pressure. when the exhaust valve closes, there is a high pressure wave running down the exhaust. it echos off any sudden change in pressure or volume (drastic change in pipe size/pipe exit). this wave is then sent back up the pipe to the valve.
the cat its self doesnt effect low end torque, the open chamber just before the media causes the pressure wave to be rammed back up the pipe hindering exit flow at the valve, in affect keeping fresh A/F in the cylinder.
this effect can be maintained by adjustment of runner length before collector. these adjustments when finely tuned will cause a high pressure sound wave to occur at the valve keeping fresh charge in while not reducing flow.
these adjustments can be optimized for a given RPM. most factory designs were intended for low end torque due to city driving conditions.
organ pipe theory (scientific design of exhaust & intake systems third ed)
the formula for obtaining the optimum pipe length to either adjust power band or compensate for modification (removal of cats) while improving performance is
V = velocity of sound in exhaust gas in FPS
L = length of pipe from valve to extreme end (to collector or step in pipe diameter)
T = time for pulse to travel the end of said pipe and back again

T = L/(6V)
in terms of crankshaft degrees this becomes T= (rpm*L)/V
for the speed of sound in exhaust 1700 fps is usually pretty close to accurate so i will use it for sake of demonstration.
lets say we've pulled a ME and ripped out or cats fabbed up own headers and ditched the muffler and are running duals with an ex pipe. in 3 inch pipe just because you had enough 3 inch layin around and didnt wanna buy pipe.
I like autocross so i usually want my power around 3000 rpm.
(1,700*120)/3,000=68
okay what that means is that for my power band to peak at 3000 rpm i will need a primary length of 68 inches from the back of the valve to next major rapid change in pipe volume or exit if you're using zoomies. but who uses zoomies on a bull?
so how do you pull this off? its not easy cramming fifteen feet in the spaces between our blocks and firewall and radiators. but thankfully we can build a set long tube headers JDM style for the front go down the block and turn back to the rear of the motor. as far as the oxygen sensors, the first problem you run into is them not heating up fast enough and triggering a CEL. to fix this you can either wrap your headers or wrap a length of pipe ahead of the O2s with ceramic coated heater wire... lot of work there. a common problem with wrapping headers is cracking. I've never had a set crack. but then i wrap them properly. EVERY set of cracked headers ive seen werent the fault of the wrap it was the fault of the "if a little works more must be better" way of thinking. too much wrap is not bad.. its horrible.
if you look around on the net like i did back when i built my intrepid you can actually tune your pipe diameters and lengths for a system without a muffler that still runs quiet. my 96 intrepid 3.3 V6 had a total of 49 inches of pipe from the number 1 cylinder to the exits in the trans mission tunnel. had X pipe and no muffler. sounded like single flowmaster 40 series with a resonator. rumbling but quiet.
intake time
remember all that up there *points up and apply here*
same principles but this time were looking at the reduction in pressure not the increase. the purpose before was to get a low gas pressure wave/high sound pressure wave at the valve upon its opening. if you want an explanation of that seemingly contradictory statement buy the book.
now were trying to get high gas pressure/high sound pressure at teh valve upon opening.
here the average pressure and temperature will make V=1100
again aiming for 3000 rpm
L= (90*1100)/3000=33 inches from valve face to atmosphere.
and that is why our intakes look a little goofy.
the math goes on for days but this is the basis of all my goofy hodge podge lookin parts.
these formula inputs should be adjusted for your average atmospheric conditions.
and remember next time some moron says "if you take your cats or muffler off it makes your car slower" remember thats only true for stock pipe lengths and ******** who believe everything they are told by the guy trying to build a faster car then them.
 

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Discussion Starter · #2 ·
today after pouring over a few of my newer text books i began considering a 3.0l plenum with a set of tapered runners. :coolgleam:
for the main plenum i would build it the same end to end length as the outside to outside length of the stock lower plenum (ported of course) and tapering from the lower plenum diameter (havent taken measurements yet) up to 3x1.5 inch ovals in the bottom of the plenum with a blended floor.
havent decided on runner length yet. any suggestions?
 

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Discussion Starter · #4 ·
the math isnt an issue, i wasn't clear on the question. I've never fooled around with runner shape at all, that was the part i was talking about to. I'm not really sure how the tapered intake runner will affect velocity at the intake valve. and all the info i can find suggest it would be beneficial, but are pretty vague as to the actual benefits to flow and how they effect other aspects. prime example, does it effect flow and velocity in such a fashion as to allow me to use a shorter runner for a higher power band, or would it widen the effective rpm range?
 

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Intake

There are a hand full of guys around TCCA that have truely done there homework and created intakes for the vulcan that would flow enough to accomplish 210-215 REAL dynoed horsepower. All the fabbed, same length runner intakes that have been built made no more horsepower than a ported, polished and extrude honed 1999 - 2001 Ranger intake - Fabbed intakes make a huge difference on forced induction vulcans BUT not naturally asperated vulcans.

I worked with Boss3.0 from the RPS for over a year to build a stout vulcan for my GL. Horsepower from a vulcan is pretty simple: modified and extrude honed Ranger intake (upper and lower), 60-70mm TB, 80mm maf, extrude honed and ported Alabama cylinder head blanks, new SI valves, Lunati lifters, 1.5 or 1.6 roller rockes, dual valve springs (custom), 19lb injectors, 155lph fuel pump, custom delta cam, 1996 or above vulcan crank, 1996 stock rods, .030-.060 over forged pistons (I used ROSS), good line bore, balancing and blueprinting, extrude honed 1996 or 1997 exhaust manifolds and a solid 2.5" exhaust system with a good y-pipe, cat and muffler - then just have a good tune. I'm sure I left a couple things out but you get the idea.

This formulla may have been what I came up with after hundreds of hours of research and asking questions of guys that have already done what I was looking to do - If you want vulcan performance - rogueperformance.com has everything you need to know and more. The guys over on the Ranger forums are into building stout vulcans and they are a great resource.
 

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I would add that your math and such does not really take the cam timing into account. While I agree, there are lots of improvements that can be made to get a lot more power out of any setup, the stock setup is designed to be a consistent and reliable setup with the stock equipment. The engineers that designed the factory system and designed the converters factored the same mathematics that you are displaying here into their designs.

These figures also do not take into account the induction that a cat can generate by burning the unspent fuel that is left behind. A while ago we built some space heaters using some propane fitting and the large cat substrate out of the old Ford torpedo type cats. The propane was dispersed by the stove pieces we were using and the mixture was drawn through the catalyst along with air (this was an open air design). The amount of draw these would develop was fairly impressive, considering that hte who system had no moving parts. We would use several of these to heat a shop. Of course we would not use these indoors, the amount of carbon dioxide a heater like this can generate could be dangerous without ventilation. We would use them when the doors were open. People claim that the expanding burning gas would create more backpressure, but based on what I saw these open air heaters we made do, I think the catalyst helps draw more spent exhaust from the cylinders. The catch is that the cats have to be properly sized, and they have to be working properly.

I have also seen a forced induction setup produce more power with cats than without. Buddy of mine built a 1988 Buick Grand Nation. Produced 755 hp at the wheels. He built it to be a daily driver, so he had some true high flow cats. One day, he forgot to take them off on track day. The result, it shaved 2 tenths of a second off his quart mile time consistently. After he realized his mistake, to cover the bases, he switched the cats out for the straight pipes, ran a few more pulls, again, he lost about 2 tenths of a second. Put the cats back on, he got his two tenths back. The cats were the only variable. Now granted, the cats were more free flowing than any OEM cat.

You math and figures are great, but they do not take everything into account. Thats why supercomputer models have to be used to get even remotely close to real world scenarios.
 

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Discussion Starter · #8 ·
yes the formulas do call for cam timing to be input. most people leave that out. i have a cam on order so before i even start on the intake i plan on gettin a cam card and degreeing the cam.
also yes diameter does have a profound effect, but lets be honest 99% of the people building intakes or exhausts for themselves will just match the runners to the ports.
the reason the forced induction set ups khan mentions made more power with cats is because with a poorly designed exhaust you have a problem with dumping raw fuel into the exhaust, the O2s then cut fuel to stop the rich condition they read.
as for the factory guys, you are mostly wrong. they run the numbers... then forget them. which is why there are so many variations on the intakes. they must consider space, cost, sound and emissions. we dont. i dont have a problem with cutting a hole in my hood, i dont mind my car being a bit louder to produce more power and i live in a non emissions regulated state.
in my case there is total freedom in design.
as for the rest of the formulas required there are way to many to list, im not going to get mean enough to the novice intake builder to bring up adiabatic process. nor am i going to point out that yes it does apply to NA as well as FI. i gave the title of the book that seems to be the most popular in the field of intake and exhaust design. if you guys like i can make a complete list of the formulas i use and post them all.
but that will take a few hours. and i would appreciate not being bashed for using general figures instead of plugging the exact values that apply to your engine, the post is for demonstration purposes after all.
 

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Discussion Starter · #9 ·
i just noticed that part about the super computers... they run the same formulas with the same numbers that humans do.. in fact they were programmed by humans, so it still comes down to the nerd with a calculator. besides those super computers are still programmed for generic parts. after all an intake manifold that works best in southern california would suck here in mississippi. our humidity and average temps are much different. so get what works best for you the best option is do like i have done in the past, run the numbers build a straight tube intake and use couplers so you can adjust your runners on the dyno. the point is no amount of math or super computer simulation will ever get you exactly what you want, but they will get you close enough to fine tune for what you want.
 

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Discussion Starter · #10 ·
intake runner diameter is the square root of the answer to(rpmxdisplacement in litersx0.95 )/3,330
for plenum size its a mass of equations pertaining to TB size and runner size and engine size, so i usually like to start with a base plate for the plenum and make a top plate as two pieces so i can use spacers to alter the volume untill
i get the numbers im lookin for.
and about those super computers you mentioned... i watched a development video for teh new 5.0 fords, and the plenum was resin plates that were stacked until they got the numbers they were looking for, if i recal properly the computer was 30 some odd percent off from the actual runner length and the runner diameter was a few thousandths off as well.
the humans with the dyno got it right the computer and formulas got them in the ball park.
 

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An experiment was done on the exhaust mainfolds on a 3.0 SHO motor. Extrude hone the intake manifold yielded 10 ft-lbs of torque all across the rpm band. So everyone though if we did the same, extrude hone, on the exhaust mainfold we would gain power. The dynojet showed a loss of 25ft-lbs of torque all across the rpm band. After lengthly discussions, the reason for the loss of power was because the larger diameters in the exhaust manifold decreased the velocity of the exhaust gases therefore the gases in the combustion chambers did not get scavenged as well. I found that I lost power at low rpms with the headers I installed for the same reasons. I did gain some power at the upper rpm range because of the larger cams I installed. I would need to go to stage 2 cams to get all the advantage of the headers. For like reasons, you can also potentially lose some power by having too large a diameter for the pipes in your exhaust.

Bob
 

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Discussion Starter · #12 ·
thats very true, and ive tried to make that very point in the past only to be laughed at "youre an idiot bigger increases flow and makes power"
these are the same people with four inch duals on a B18 equipped acura o_O
i have my pipes wrapped and they only run half the length of my car so im not concerned with the loss of velocity. our cars have a pretty impressive pressure decrease in the "transmission tunnel" it helps scavenge like crazy but makes the bottom of my car filthy as two dollar date. and i may be losing a bit of power for it, but its still faster than stock. but im still in the process of revamping the entire system including the intake.
 

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thats very true, and ive tried to make that very point in the past only to be laughed at "youre an idiot bigger increases flow and makes power"
these are the same people with four inch duals on a B18 equipped acura o_O
i have my pipes wrapped and they only run half the length of my car so im not concerned with the loss of velocity. our cars have a pretty impressive pressure decrease in the "transmission tunnel" it helps scavenge like crazy but makes the bottom of my car filthy as two dollar date. and i may be losing a bit of power for it, but its still faster than stock. but im still in the process of revamping the entire system including the intake.
:lol2: 4in pipes with neon lights makes a 16yr old proud
 
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