Generally speaking, which one flows the best and worst? Either a converter in good condition, a converter that's been hollowed out, or just a piece of pipe?
A piece of pipe will flow the best. Gutting a cat will introduce turbulence that a straight pipe will not. But a full-on cat poses almost no restriction, 1-2%hp loss at most. On a 1000hp car, that might be a consideration. On a 100hp car? Not worth worrying about. Do the right thing for the environment. We only get one.
I think it was Magnaflow that published a white paper showing the flow characteristics of their cats versus test pipes, and the losses for normal cars are almost imperceptible. There was also a magazine article, maybe in Sport Compact Car, back in the day which did dynos on some high-strung motors with various exhaust equipment on them and, again, the differences were negligible - single digit hp losses on 200hp motors. It's not until you get into big horsepower numbers where the restriction becomes a legitimate problem and the losses become tangible. My own personal experience would be on a slightly tuned Saab - 260hp with cat, 264hp with test pipe, at the wheels.
I imagine there could be some sort of case made for using the shell of the cat like an expansion chamber or something that under the right circumstances could lead to a better result than a test pipe, but that relative improvement would be a fluke and not some sort of general truth.
Speaking of, don't buy into the "high flow" cats, either. Superb marketing there, reducing the substrate and thus the cost and then charging more for the part because it's special. When you've lost 5hp from a cat gaining back 2hp from a high flow part that won't last as long is pretty silly.
The straight pipe gives far better mileage and performance than a CAT. It also eliminates a dangerous fire hazard and costs only a fraction of a new CAT to use. However, Uncle Sam says that this modification is legal for off road use only.
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Flotech Afterburner Exhaust, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
The straight pipe gives far better mileage and performance than a CAT. It also eliminates a dangerous fire hazard and costs only a fraction of a new CAT to use.
A proper, working catalytic converter has a negligible effect on mileage and performance. Why is everyone stuck in 1971?? Come on... Also, are there are far more car fires caused by leaking fuel or oil than catalytic converters. They greatly reduce emissions and are proven technology. The debate has been over for decades.
A proper, working catalytic converter has a negligible effect on mileage and performance. Why is everyone stuck in 1971?? Come on... Also, are there are far more car fires caused by leaking fuel or oil than catalytic converters. They greatly reduce emissions and are proven technology. The debate has been over for decades.
well didn't take long for B/S to show up..
Original post wanted to know what flow better. Answer---Straight pipe.
Now if B/S is wanting to just bully Mr.LaGrua....Straight pipe gives better mileage and performance
And Im going by B/S on his statement..Quote "A proper, working catalytic converter has a negligible effect on mileage and performance." so it does right.
The Stuck in 1971 was just an attack with no reguard to the information,
His more fires by other stuff is just another sensless attack,the comparsion Mr.LaGrua made was at the fire hazard the cat vs straight pipe has.
And once again nothing in the original posted question and nothing in Mr.LaGrua response was about emissions.
That was just a Greenie response that they are trained to include.
And any time someone has to spew the "Debate is over" crap...well that's B/S for ya.
A piece of pipe will flow the best. Gutting a cat will introduce turbulence that a straight pipe will not. But a full-on cat poses almost no restriction, 1-2%hp loss at most. On a 1000hp car, that might be a consideration. On a 100hp car? Not worth worrying about. Do the right thing for the environment. We only get one.
Even on a 1000 HP car, it's not a problem. 10-20 HP when you're making that much, isn't really going to matter.
Originally posted by fireboss: well didn't take long for B/S to show up..
Original post wanted to know what flow better. Answer---Straight pipe.
Now if B/S is wanting to just bully Mr.LaGrua....Straight pipe gives better mileage and performance
And Im going by B/S on his statement..Quote "A proper, working catalytic converter has a negligible effect on mileage and performance." so it does right.
The Stuck in 1971 was just an attack with no reguard to the information,
His more fires by other stuff is just another sensless attack,the comparsion Mr.LaGrua made was at the fire hazard the cat vs straight pipe has.
And once again nothing in the original posted question and nothing in Mr.LaGrua response was about emissions.
That was just a Greenie response that they are trained to include.
And any time someone has to spew the "Debate is over" crap...well that's B/S for ya.
So which one of you is the March Hare, and whom is the Hatter?
Even on a 1000 HP car, it's not a problem. 10-20 HP when you're making that much, isn't really going to matter.
I guess it depends on what you're going for... if a cat turns your 1000hp into 980hp don't you lose bragging rights or something?
I cannot remember what site it's on, but one of the domestic tuners built a crazy Mustang and suffered 0hp loss up to like 800hp from the cat. Past 800hp it lost 2hp. Past 900hp it lost 5.
I'm sure the anti-cat mythology comes from those old ceramic ball cats which sucked. Modern monolith cats just don't provide any functional restriction in anything, and there are dozens and dozens of flowbench and dyno tests to prove it. Maybe I drank the Greenie Kool Aid at some point, but I definitely am not listening to 1950's Hot Rodder Guy for my "science." The actual science is that modern cats have been refined to a point that their interference is somewhere between negligible and utterly meaningless. I don't think there is a reputable tuner left in this country who recommends doing anything with the cat for gains. Because there aren't any, and dyno after dyno proves it.
ROFL. I did the same on my '84 Trans Am for a similar reason with similar results. I then gave Magnaflow $98 and they gave me a new cat. Same performance, no smell. All win.
Pulled the CAT last weekend and went with straight pipe. Sounds throaty but can really smell exhaust now.
What a surprise, eh?
I've got a new cat here that I've been delaying installing until I swapped in the rebuilt injectors that I bought a couple months ago. I finally got these "new" injectors in (and discovered in the process that my EGR tube was completely plugged with a "tarball" where it attaches to the intake plenum). Wow, after replacing the injectors and fixing the EGR system, what a difference in the smell... even before I swap in the new cat. I'm expecting my Formula to be basically odorless when I'm done... and have better gas mileage to boot.
Fire hazard? Probably true, but not for the reason that you'd expect. One of our guys at work burned down an F150 when he parked on the side of the road in some tall grass, and the cat lit it off. When cats were first installed (mid 1970s time frame) there were a number of cars burnt up when they parked in tall grass for the Masters tournament in Augusta. Again, that cats lit the grass off. Made headlines in Atlanta. Not to mention the Fiero engine fires. When the rods "air mailed" through the front of the block, the cats were right there, waiting to receive all the vital fluids.
Having said that... I hate being behind a car that has had the cat removed. In the days of leaded gas, it didn't seem so bad. But with the chemicals that are added to modern gas, an "un-catted" car makes my eyes burn.
Me? I have a cat on my 4.9. It's going to stay there, even though it's no longer tested. (I don't believe it hurts the performance, and it's already too effin' loud. ) My SD didn't have a cat when I got it, and I'm not putting one on it. (It's carbed. The cat would probably die in short order, since the fuel metering is not nearly as precise. It is what it is.) ------------------ Raydar 88 Formula IMSA Fastback. 4.9, NVG T550 Praise the Lowered!
[This message has been edited by Raydar (edited 06-02-2015).]
A piece of pipe will flow the best. Gutting a cat will introduce turbulence that a straight pipe will not. But a full-on cat poses almost no restriction, 1-2%hp loss at most. On a 1000hp car, that might be a consideration. On a 100hp car? Not worth worrying about. Do the right thing for the environment. We only get one.
quote
Originally posted by thesameguy:
I think it was Magnaflow that published a white paper showing the flow characteristics of their cats versus test pipes, and the losses for normal cars are almost imperceptible.
I agree with you here about 75%... however, I disagree with the idea that a factory catalytic converter is somehow within 1-2% optimal.
For the most part, the original Fiero catalytic converter is a "pellet style" charcoal filled catalytic converter which is basically total crap. It is a pretty significant power sap, and you see a fairly sizeable difference by replacing them with the ceramic honey-comb style catalytic converters that most new cars have today. On a stock or slightly modified Fiero, an "Ocelot" cat converter with the 2" pipe is probably optimal.
As for modern cars, we now have pre and aft catalytic converters. My Crown Victoria has 4 cats on it, and they definitely made a difference when I swapped them out with Magnaflow cats that had a higher CFM rating.
On my Pontiac Solstice, I replaced the 350 cfm factory cat with a 500cfm one, which was far more optimally sized, and the difference in performance was unbelievable. Power RUSHED from 3,500 to redline like it had never before.
Cars are required to meet VERY strict emissions standards today, and they also have to balance that with cost. Most cars will do well both in efficiency and overall power by properly matching the catalytic converter to meet their engine's true requirements. Something that is definitely not done anywhere near optimal on today's modern cars.
Well, read the tests. I believe there is going to be significant variables from one modern cat to the next, but there is PLENTY of documentation on all manner of cars from Honda to Mustangs to Corvettes where tuners have done dynos with and without cats and came up with almost no variance whatsoever. I don't necessarily doubt your Solstice or CV experiences, but unless you have dyno sheets of before and after, I can't take anything you've said to the bank. The butt dyno is unreliable and often tainted by expectation. Especially the Crown Vic - taking some old car and replacing parts with new parts will always yield some result. No five year old or ten year old cat is going to flow exactly as well as it did when new. I've taken cars in for tests with full expectation of amazing results only to find power loss all over the place and slight improvements in the top end. Without science quantifying experience, all we have are fun stories.
[This message has been edited by thesameguy (edited 06-02-2015).]
CHART #2:Comparison shows the difference that a complete header back system can make. Also note that our Mustang did not benefit from the 498 cfm flow of the UltraFlow "straight through" mufflers vs. the Pypes V-Force 304 cfm flow mufflers. Thus re-igniting the ongoing arguement that the better the flow, the higher the horsepower. We will continue to gather data on this subject but feel that in the final analysis, the cam will dictate whether a car needs the additional flow. Most stock lower-horsepower cars will be less likely to benefit from the additional flow. At this time, we recommend full-flow mufflers when engine horsepower exceeds 400-425 hp.
Admittedly it's talking about mufflers and not cats, but it shouldn't matter. If a 304cfm muffler is not a restriction in making 400hp, it seems unlikely a 350cfm cat would be. CFM is CFM.
“Hi Flo” cats? Really? Show us your flow tests. HP tests. Our 1000HP air flow bench reads 407 cfm stock and 549 cfm gutted and no HP gain at 775RWHP.
Still want to gut those cats - or buy some “Hi Flo’s?” We welcome any magazine to come to Kenne Bell and test back to back on any Mustang - ours or theirs. We’ll hook up the data logger and record back pressure, air flow, temperature, etc. and, of course, HP with and without cats. All at no cost - IF it’s printed in a magazine. And we promise the tests won’t be skewed by changing ignition timing, AF ratio, pulley (boost), x pipe, headers, exhaust etc. to increase HP. You know how that can go. “Cats and a tune,” Cats and a pulley,” “Cats and cat back . . . “ Just a typical Kenne Bell back to back cat test.
They seem to have managed 775hp on a 400cfm cat with no improvements sans cat. This seems contrary to the butt dyno, and they seem pretty convinced they can repeat it.
Your experience is, of course, your experience. But literally everything I have read in the past ten years suggests cats are not in your way. Even stock ones.
Edit: I lied. The Mustang has a dual exhaust, so they managed 387.5hp on 400cfm cats... half the hp on each side.
[This message has been edited by thesameguy (edited 06-02-2015).]
Originally posted by thesameguy: The butt dyno is unreliable and often tainted by expectation.
And perception. It's a very common misconception that simply because the exhaust is now louder, that the engine is making more power, and the car is now faster. And we all know a gutted cat or a straight pipe will make the exhaust louder. It however, does not necessarily make the engine more efficient or powerful.
Generally speaking, which one flows the best and worst? Either a converter in good condition, a converter that's been hollowed out, or just a piece of pipe?
I asked a similar question a few months ago and the same debate is starting again. Everyone has their own views on cats and when it comes down to it, do whatever you want. Keep in mind its technically illegal to have no cat on a vehicle for road use.
For better FLOW, no catalytic converter obviously is the answer, as a cat is a restriction on the exhaust; it's like drinking a soda through a straw. Hollowing out a cat so your car looks like it's legal for road use is TECHNICALLY just as good as a strait pipe; any differences between a strait pipe and a hollowed out cat is just splitting hairs TBH.
As for my Fiero with a cat on it I can tell you first hand the "differences".
I bought my Fiero a year ago now with a strait pipe and no cat thanks to a lie from the previous owner. I installed a cat to pass inspection two months ago and noticed a few things after it was put on. I installed the Fiero Store cat kit and passed with flying colors! I have an 88 GT with what leads me to believe is a bone stock six cylinder with 150,000 miles on it; unknown if ever rebuilt.
First hand experience with differences with cat installed:
A lot more quiet. Neighbors don't hate me as much when I get home at 2AM on a Friday night anymore. LOL
No more popping from the exhaust when letting off the throttle
SLIGHT difference in throttle response, seems like I have to press the throttle a little more to rev it up. Not a problem in the slightest.
Peace of mind that if I get pulled over and the cop wants to bust chops and check for a cat I am in the clear.
Honestly, there is no "HOLY CRAP" differences performance wise that you will ever notice; cat or no cat, unless you are an extremely technical, number crunching engineer that wants to get every ounce of performance out of my engine kind of guy.
If you want optimal exhaust flow, I would be more worried about getting a decent set aftermarket headers first.
------------------ "Discord" Red 1988 GT under restoration!
Let's Go Mets!
( ͡° ͜ʖ ͡°)
[This message has been edited by Shho13 (edited 06-03-2015).]
Originally posted by Shho13: Honestly, there is no "HOLY CRAP" differences performance wise that you will ever notice; cat or no cat, unless you are an extremely technical, number crunching engineer that wants to get every ounce of performance out of my engine kind of guy.
If you want optimal exhaust flow, I would be more worried about getting a decent set aftermarket headers first.
A) I'm an extremely technical number crunching engineer, and being very meticulous about my engine build. I'm still installing a cat, and even with crunching the numbers, the amount of difference with a cat or without is largely irrelevant. Unless you're building a Top Fuel or Funny car, arguing about having a cat or not is a waste of bandwidth.
B) If you want (truly) optimal exhaust flow, none of the headers on the market for a 60 degree V6 are going to give you that. You'd need to build a custom exhaust system, like the one guy in Taiwan did, that everyone wants to replicate, but nobody wants to invest the $100 in tubing to attempt doing.
A) I'm an extremely technical number crunching engineer, and being very meticulous about my engine build. I'm still installing a cat, and even with crunching the numbers, the amount of difference with a cat or without is largely irrelevant. Unless you're building a Top Fuel or Funny car, arguing about having a cat or not is a waste of bandwidth.
B) If you want (truly) optimal exhaust flow, none of the headers on the market for a 60 degree V6 are going to give you that. You'd need to build a custom exhaust system, like the one guy in Taiwan did, that everyone wants to replicate, but nobody wants to invest the $100 in tubing to attempt doing.
I hope you didn't take my post the wrong way. I agree with you. The difference between is mostly irrelevant.
As for the optimal exhaust flow, generally speaking, most if not all stock exhaust manifolds are a bigger factor in restriction; wayyy bigger than whether a cat will cause a big enough restriction to reduce performance considerably. There may be a few exceptions of course.
------------------ "Discord" Red 1988 GT under restoration!
Originally posted by Shho13: I hope you didn't take my post the wrong way. I agree with you. The difference between is mostly irrelevant.
As for the optimal exhaust flow, generally speaking, most if not all stock exhaust manifolds are a bigger factor in restriction; wayyy bigger than whether a cat will cause a big enough restriction to reduce performance considerably. There may be a few exceptions of course.
The stock 2.8 manifolds are known to be a horrible design. They are very simple exhaust logs. But to say that any arbitrary aftermarket headers will give you optimal flow is false. They might flow better than stock, but they are not optimal. Truly optimal flow would be a custom exhaust designed to match the displacement, any boost added, cam timing, and firing order, of the engine.
Modern engines tend to have stock exhaust that flows very well though, and installing aftermarket headers does more for tuning where the power band is, than necessarily improving flow.
When I had my Rotrex supercharger the PSI dropped about 2-3 on the boost gauge after I removed the CAT. Obviously it was a restriction. But, this was only under hard acceleration, which tells me that you will never really notice a difference driving around town, but at all out full throttle I believe it matters.
I didnt like the cat because of all the heat it created under the hood. Unlike some cars, the cat in the Fiero is in the engine bay. The 3800 SC does not have one and I have no plan on incorporating one.
When I had my Rotrex supercharger the PSI dropped about 2-3 on the boost gauge after I removed the CAT. Obviously it was a restriction. But, this was only under hard acceleration, which tells me that you will never really notice a difference driving around town, but at all out full throttle I believe it matters.
I didnt like the cat because of all the heat it created under the hood. Unlike some cars, the cat in the Fiero is in the engine bay. The 3800 SC does not have one and I have no plan on incorporating one.
Sorry man, but that is not good science. Removing the cat could have, as you note, just taken a bunch of heat out of the engine bay and resulted in lower intake temps and higher charge density resulting in lower charge pressures. Without a dyno sheet showing some improvement with the loss of the cat and a flow bench showing your exhaust produced more flow than the cat could handle, it's a fun story. *Even* with that information, the only thing you have proved is that the particular cat you had was wrong for the application. You could have had a bad or partially clogged cat or mis-sized cat. I run a 3" cat on my '86 XR4Ti because the stock 2" cat couldn't handle the 300hp the car makes. It doesn't mean cats are an obstacle to 300hp, it means that a stock 1980's 175hp cat can't flow 300hp. That's kinda "duh."
Eh? Cats address NOx which is a participant in both acid rain and the greenhouse effect. While it does result in the production of CO2 (another major greenhouse gas) it eliminates CO, and the ratios are VERY favorable. There is almost 100% reduction of CO with only a 10% increase in CO2. That's a pretty big win. Cats have nothing to do with the other major greenhouse gas, methane. You can blame at least some of that on meat eaters. Of which I am one. I'm sorry, I do try to keep my steaks & hamburgers to a minimum.
The actual downsides of catalytic converters are the precious metals needed to make them work. Those metals come from only a few places, and production of them is pretty awful. Norilsk, Russia is not a pretty place. It's somewhat unclear whether it's necessarily in bad shape because of the work, or because of the way the work is being done. I do believe there are two new technologies under development for these things which will reduce or eliminate the precious metals needed to make them work. I hope it pans out.
When a converter costs less than $100, it can't have that much precious metal in it. The new ones have been reducing the amount of metals needed for a long time.
My Fiero only had 24k on the odometer when I installed the Rotrex Supercharger. My Fiero was a mint car, garage kept when I purchased it in 1999. It was the original cat converter that was installed by GM. When I removed the cat it was not clogged. I did it because it was a restriction. I was doing some drag racing at the time and it served no use. I clearly remember the drop in boost because even on my little boost gauge I could tell the difference.
My 3800sc runs great with no cat and I have no plan on installing one. I'd be willing to bet it would pass emissions.
There is a world of difference between the 80's fuel injected engines, the technology was very new, and the engines of today. My 98 3800 has better engine management and I could never imagine going back to those old 80's engines. I had a 2.8, 3.2, and 3.4 all with turbos and they ran poorly. You could tune them forever and never get them to run correctly. Even the stock engine idled horribly.
[This message has been edited by RotrexFiero (edited 06-06-2015).]
I am sure you'd be surprised about exactly what a cat does even on modern engines. There are limits to what even the most advanced EFI can do, and there is no EFI on the planet that can address NOx emissions. The *only* thing that control NOx is a cat, and a 1975 engine drops as much NOx as a 2015 engine. Not running a cat on a street engine is flat-out irresponsible.It's no different than littering on the highway. It's dropping crap into the environment because you can.
But, hey, you do you. I don't have kids. If the world ends tomorrow, meh.
[This message has been edited by thesameguy (edited 06-06-2015).]
I am sure you'd be surprised about exactly what a cat does even on modern engines. There are limits to what even the most advanced EFI can do, and there is no EFI on the planet that can address NOx emissions. The *only* thing that control NOx is a cat, and a 1975 engine drops as much NOx as a 2015 engine. Not running a cat on a street engine is flat-out irresponsible.It's no different than littering on the highway. It's dropping crap into the environment because you can.
But, hey, you do you. I don't have kids. If the world ends tomorrow, meh.
For every day use I would agree that a CAT is necessary for clean air quality. However, most of us here have Fieros as hobby cars and only drive a couple of thousand miles per year, if that. IMO, a cat is not necessary with that minimal use. Many car collectors and hobbyists operate in straight pipe country! If you consider all the cat exempt internal combustion engines used in older show cars, vehicles for racing, in tractors, chain saws , generators, farm and power equipment; running a hobby car without a cat produces pollution that amounts to a drop in a bucket, and what do we do about the third world that operates without any pollution standards at all? Point is green is good but it has its limits.
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Flotech Afterburner Exhaust, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
[This message has been edited by Dennis LaGrua (edited 06-06-2015).]
Not wanting to start an argument over the environmental issues, but you cant kill an environment. The idea that the earth is a dying corpse is just absurd, being there are places on the earth, volcanos to name one, that emit many tons of noxious gases every day. My lawnmower is more a pollutant than my Fiero (with no cat). To live is to pollute, and it is all part of a larger system. The automobile is, if anything, a victim of its own success. Though be sure I am not advocating we go around removing all cats from cars, but for my application, as mentioned above, it is suitable. I seldom drive beyond 2k a year. I drive my lawnmower much less, probably around ten miles a year. My yard is pretty big.
The problem in our cars is it's placement, right below the engine, engine that when new, leaked oil.. it doesn't take much oil for it to turn the car into a ball of flames, These cars really need a belly pan above the converter to drain any oil that might leak away from the converter and pipe, cause you can stay on top of leaks, but it only take the oil sender to fail and up in smoke it go.. The newer converters are much smaller, but the replacement converters that are 100.00 are not going to last long.. oem has to last 100000 miles, that 100.00 converter 1 year. and no one ever knows it is going as most areas don't test these cars anymore, it's bought mostly for looks, i.e. so the inspector when he looks under the car see's one.. nothing more.. I still have the o.e.m. converter and it is a monster..
Todays pump gas smells like crap, I honestly think they add something to it so cops can tell easy enough if the converter is "missing" cause if you've ever smelt unleaded race gas.. AHHHHHHHHHHHHHH so much better..
I am sure you'd be surprised about exactly what a cat does even on modern engines. There are limits to what even the most advanced EFI can do, and there is no EFI on the planet that can address NOx emissions. The *only* thing that control NOx is a cat, and a 1975 engine drops as much NOx as a 2015 engine. Not running a cat on a street engine is flat-out irresponsible.It's no different than littering on the highway. It's dropping crap into the environment because you can.
But, hey, you do you. I don't have kids. If the world ends tomorrow, meh.
NOT A PERSONAL ATTACK, JUST AN OBSERVATION...
Funny. California wants to control the environment in the rest of the country, and has pretty much gotten its air regs passed at the federal level, but they can't even be responsible with their state taxpayers money. And their environmental laws run their businesses out of the state....
)
