taking 1 of the 2 cats off the exhaust.

[mhn3773]

on the backpressure issue..if u ever get close to a top fuel dragster like a rail type one..look at the headers ull see a bunch of welds at the end of the headers tahts because they take off and add on little bits of pipe to tune the back pressure

to much and ur not making the power u should and to little back pressure and the engine is kinda of running animic

so if the back pressure on any giving car .truck is damn near perfect adding bigger exh pipe or a better flowing exh. wont do anything but if u add like a KKM or some kind of forced induction then that perfect BP is now way to much PM so u need to free it up a little

mustangs come from the factory with restrictive exh. so adding larger pipes and such really helps

 

[huskyfan23]

on the backpressure issue..if u ever get close to a top fuel dragster like a rail type one..look at the headers ull see a bunch of welds at the end of the headers tahts because they take off and add on little bits of pipe to tune the back pressure

to much and ur not making the power u should and to little back pressure and the engine is kinda of running animic

so if the back pressure on any giving car .truck is damn near perfect adding bigger exh pipe or a better flowing exh. wont do anything but if u add like a KKM or some kind of forced induction then that perfect BP is now way to much PM so u need to free it up a little

mustangs come from the factory with restrictive exh. so adding larger pipes and such really helps

You just have a way with words

 

[unclemeat]

You do not need to remove loose heat shields. You can get a big hose clamp or string together several small ones and use them to firmly connect the heat shields. Ford has actually issued a TSB on loose heat shields and hose clamp repairs.

 

[TheRookie]

*sigh* ok I have been trying to educate many on this board about exhaust and the myths there of.
Here we go. One more attempt to make this make sense. This is proven again and again and I personaly have also Dyno proven this.

First a little backround. I am a tech and bend custom exhausts all day long. My shop refers to me as the exhaust guy. ANything custom or odd comes directly to me. I have done performance exhausts on everything from motorcycles to powerstrokes. A few of them have been dyno'd before and directly after my work. One guy insisted we give him dyno sheets to prove a gain so we happily did.

There are several differences from car to car. Mainly they go like this.
Turbo car: Cant have too large or too free flowing of an exhaust. Literaly the bigger the pipe and the straighter the pipe the better. This is due to how a turbo works.

Naturaly aspirated. OK this is where the confusion lies. In the end backpressure is BAD. You dont want it. Some engines are indeed tuned to run with a certain amount of backpressure however eliminating this and retuning will make for some great gains. The problem is there is a difference between backpressure and flow. The two are Always confused. Backpressure is from restrictions like cats and mufflers. These also aid in flow to a certain extent due to how the gasses move through them. If the exhaust gasses flow through the pipeing fast they create something called scavenging. Scavenging is basicaly a vacuum that pulls spent gasses out of the combustion chamber. This is good. Backpressure wont let the spent gasses out of the combustion chamber this is bad. Problem is if you just go tearing out your muffler and cat or cats you alter the flow charecteristics of your exhaust. A GOOD exhaust guy can usualy figure out whats best for your specific aplication. Mandrell bent pipe is always the best choice. Ask the shop if they have one. If they dont know what it is dont go there. Even if they do not have a mandrell bender an exhaust guy that knows anything should know what one is.

Scavenging is what creates torque.

One last thing.
Gutting a cat.
This is bad for several reasons including power. Obviously legal reasons make it a poor choice. There is the debris issue. However a little known problem with this is turbulence. Once you gut the cat you have this big empty shell with small pipe leading into it and out of it. This will create a large amount of turbulence in the case that used to house the catalyst. Turbulence makes scavenging near impossible. This is yet another reason people think backpressure is good.

I hope all this helps clear up the confusion for a few people.
Feel free to ask questions. No one is perfect I have in fact done a few exhausts that lost a few ft lbs in the lower RPM range but more often than not I gain a few through the entire rpm range

 

[jake the snake]

ok ,

with all this being said, might i get the rookie or alec to make a recommendation to me for my rig, a 94 x sport. i am eventually going to fab a custom exhaust.
i want throaty sound.
should i go dual or single? is it a bad idea to use an inexpensive turbo muffler? what size pipe should i put behind it? can i just use the existing pipe and just replace the muffler itself?

 

[mhn3773]

that all makes sense the rookie..but running a car w.o even a header on the engine 0 backpressure right??? is a no no..right??

also i am not a certifed exh. tech or anything..but seems to reason that since NHRA top fuel dragsters dont agree with u..then well u have to be wrong at leased a tinny bit...and where i see u are wrong is in ur tuning state ment this whole thread started because of someone wanting to put a bolt on exh onto there ex..no tuning...

hell even with tunning u can just run 15" pipe off the collecter plain and simple..there might be some instances where it doesnt matter but thats very unlikely

 

[typhoon43]

Hmm, we have no emissions testing in my town. I've removed Cats before on Turbo's vehicles and that made a ton of difference. I think I may try this mod, even though I only have the SOHC V6. I would think you'd notice more on the 8's.

 

[TheRookie]

MHN, They are tuning flow on dragsters. Running no header is bad for several reasons. The loss of bottom end is due to the fact you will get NO scavenging with No exhaust. The NHRA guys agree with me just ask them. Also if you read my post you would understand why running huge pipe would be bad even with tuning. sorry if my post didnt make flow and scavenging clear for you or anyone else.

 

[TheRookie]

Typhoon, please read my description about turbo cars and NA cars.

 

[glfredrick]

Thanks Rookie - post was educated and good... I too was a tech and a racer... both motorcycle, truck and car... street, dirt, and drag. Scavaging is where it is at - thus a good set of quality exhaust headers versus the turbulent cast manifolds. The headers are grauated steps insuring laminar flow which in turn insures scavanging - but in turn you must also increase air flow into the engine to keep things balanced. Used to be more art then science, but nowadays we can just purchase tested parts.

On another front:

Just on the news tonight is info that SE MI does not pass Fed air standards. They are now talking of having emmision tests for the area.

Emissions tests will not do a thing to increase air quality. We are currently enduring a round of civil litigation in the city of Louisville against the EPA because our Mayor threw out the EPA tests. Turns out that over 92% of all cars passed with no problem each year - which means no reduction of any polutants but each car did have to pay $11.00 a year. When you factor that around 1 million people live in the metro area that is a lot of $11.00's for nothing.

I actually wrote the Mayor to encourage him in his fight to keep the testing out. My suggestion was that all the cars that had to "warm up the engine for a minimum of 15 minutes before the test" (to which you had to certify that you had - and to which they made you wait in line at least that long to insure compliance!) and the miles each car had to travel each year (plus the accumulated gasoline fumes, extra fuel consumed, etc.) in performing the test was indeed MORE harmful than any benefit the test entailed.

I was really suprised at the response I recieved. I got calls from the mayor's office twice, three times from the local air quality office, two letters, and at least a dozen emails from various people, all thanking me for pointing this fact out "that they had not previously considered!" Today I heard on the news that the Mayor's case had won in court and we would not resume testing. I hope I played a small role in that victory.

I was also asked if I favored removing "old vehicles" from legal use. In essence, I said h e double hockey sticks no. I am an older vehicle enthusiast and removal of old cars will ultimately do nothing for air quality. There are too few to matter and they are not driven regularly in most locals. Instead, I recommended that we examine the local factories - one of which is the single worst polluter in the entire county... and the city buses - which can choke you right out of your car...

 

[TheRookie]

thanks, you make an excelent point about air coming in. Exhaust is a mytery to many because of all the myths out there. I hope some of them get cleared up from all this. And thanks for standing behind old cars. It seems more and more are turning against classics these days. I can only hope they never get banned. Hell I just got a 66 GTO that thing has to stay around for years

 

[bates]

Great info! I think you sell yourself short with your name. Would blown motors fall under the turbo cars? Could you maybe talk a little bit about H-pipes and X-pipes??

 

[glfredrick]

You are probably asking the Rookie, but the genreral rule of thumb is that either an H-pipe or an X-pipe is the way to go. H-pipes tend to be eaiser to install -- especially in tight confines, but X-pipes tend to scavange better, and cause less flow restrictions and turbulence. Both work to balance the pulses from each bank of the exhaust to the other. The way you determine where to place an H-pipe for maximum efficiency is to spray some non-heat resistant paint onto your exhaust pipes, and then watch to see where it burns off. Right about the place where it stops burning off is where you want the cross over mounted. Of course, that is presuming that nothing is in the way... which on more modern vehicles is almost an impossiblilty.

Rookie will likely have some more words of wisdom for you, but this is how I normally do it. I would run an X-pipe if I could, and an H-pipe if the X doesn't work out space wise.

 

[bates]

Thanks glfredrick! While my questions were aimed at the rookie I like hearing from as many people as possible.

 

[TheRookie]

Could not have said it better. X pipes are always the way to go but its rare that you can fit one on most cars anymore. Superchargers are different than turbo's Reason being how a turbo works. The turbo mounts to the exhaust manifold, this is how the exhaust gasses spin the turbo. From there the turbo has an exhaust outlet. This is wher you want totaly free flowing. You arent going to affect scavenging at all at this point. The turbo also obvoiusly has a pressured outlet going through the intercooler (if equiped) and to the motor. Superchargers are not part of the exhaust system. Same rules aply as with NA cars except you do want to go a little bigger on average. (more air in more air out) Of course there are exceptions to every rule.

Thanks about the compliment about my name. I chose it because where I used to work there were 2 other techs. One that has almost 50 years experience and knows more than anyone I have met and a guy that has about 25 years experience and can do just about anything blindfolded

 

[LOGJOCKY]

Quick question. My rear cat was removed awhile ago and the front has a pipe through it. After this was done i think i lost some low end tourque, but the high end was really good. A month ago I cut my airbox and after resetting my computer I now have way way more low end power and like no high end. Why would this happen like this? Like when i accelerate it is useless to stomp on it because it will go faster if i only go to like 1500-2500rpm. very wierd to me.I do plan on a new exhaust set up soon, but i am curious why this has happened like this.

 

[glfredrick]

Logjockey,
I would think, based on the modifications you described, that you are now likely a bit lean on the fuel/air ratio. You have boosted airflow in and out, but haven't done anything to increase fuel flow. All these things work together in a balanced system. In the old days, we would just slap a bigger Holley carb on our engine and hope for the best (usually living with some huge bog off the line becaue we always over-carbed) but on today's computer controlled/injected engines it is a bit more difficult to increase fuel flow. You are now either going to need a good chip (not one of those $20 ones they sell on eBay - they are crap), and/or a modified fuel pressure regulator and injectors. That is the only way to bump fuel flow.

Bet that sort of makes you wish that you hadn't started messing with things... The motor can and will make more power, but power costs money and unless you are willing to go all the way and do what is needed (and have it power tuned at that) you are likely not getting the best bang for your modification buck.

I would start with an air/fuel meter that plugs into your oxygen sensors to moniter the fuel system for leaness or richness and take things from there.

 

[LOGJOCKY]

well actually i am getting like 2-4mpg better milage too. Ive tracked it for awhile now and because i dont go so high into the rpm's i guess i get better milage. as for the chip, i was gonna get one soon anyway, and also i do not regret tinkering with anything. thats the fun of it.

 

[bates]

Sort of off topic here, but GL, wouldn't you have been better off re-jetting the carb you had instead of putting a larger carb on a motor that's already lean, giving it even more airflow? I assume you meant you would go from a 750 cfm to an 800 cfm carb or something of the likes (I don't know how much motor you had).

If I assumed wrong just tell me as I do that a lot.

 

[glfredrick]

Yeah, you are definately right. I would have been better by far, but those were the good old days - just put bigger stuff on them and hope you go faster. My only chassis dyno back then was the seat of my pants and the neighbor's Mustang... I've learned a lot since then about cams, fuel systems, exhaust, etc. Now, making a 10 second street car isn't out of the question, and I could also probably make it get 20 MPG if I could keep my foot out of it.

Now, I'm about 30 years into this motorsports thing and though everything is a bit more complicated, it is still parts that go up and down as fast and as hard as possible. The trick is to do it for the least money and with stuff the other guy never expects... I love street sleepers! I once had a 69 Ford E 100 (shorty van) running a 302 with ported 351 Windsor heads, Racer Brown 292 duration cam, Holley 650, headers, dual exhause (everything polished, high vol oil, etc.). I built a full manual shift C-4 for that one and was runnig a 4.10 detroit locker. The ugliest machine East of the Mississippi, but what fun. Used to really love to play with the kids... With a 6800 RPM redline that thing would wail and no one ever expected it. Ever seen a Ford van pick up the front tires going into 2nd gear? Neither did most other people...