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backpressure questions....

C

compudude86

CEG'er
Joined
Apr 28, 2011
Messages
414
Location
Algonquin, IL
I have been thinking of upgrading my exhaust, switching from the single exhaust to something a lot less restrictive and a bit louder, and a lot more......dual. I have seen other setups, where people have gone from the individual headers directly to individual mufflers on a v6, but I have also seen the same setup with an "H" pipe, a pipe crossing between the two exhausts.

will either of these cause problems with my engine? I remember reading something about backpressure, but I thought that was only an issue on 4 cylinder cars. would my stock precat headers gutted give me enough backpressure?
 
yea dont worry about back pressure. just make sure u dont throw on a full 4" straight pipe . and if you go true dual (1 exhaust per header) i think u should but a pipe between the two(H-pipe). and you can also go dual where it splits up in the back.

iv just heard usually its better to have the true duals connected with at least one pipe somewhere in the exhaust. obviously this is more towards street cars
 
Thanks to that thread, i understand "back pressure". I have not ran a true dual on my contour, but i know you NEED some sort of muffler/restrictive exhaust piece. On my SVT with pre cats, RaceBits Y pipe and decat pipe, and a custom dump (no mufflers/resonator), i lost so much power and torque with it i removed it. And i noticed close to 4-5 average MPG loss with it as well. So, you do need a muffler or resonator. Just letting you know so you don't waste money having a custom exhaust made and finding out you need something else welded in:blackeye:.
 
ok, so an H pipe is a good idea. thinking about skipping the resonator, having flanged cats that can be swapped for test pipes? is there any real reason to have test pipes? also, in theory, does just a glasspack provide enough restriction? and if I went with header back, with resonators, cats, and glasspacks, would I still want just 2 inch?
 
If you remove main cat id put a hollowed out dummy cat and put a straight pipe through it,just for looks since this setup might be hella loud and attract cops in a bad mood, becasue its highly illegal in most states and the tickets arent cheap like 1200 bucks in some places lol....i dont have a main cat from previous owner im trying to put a catco cat on mine but im broke atm. lol
 
silver rocket said:
Thanks to that thread, i understand "back pressure"...you NEED some sort of muffler/restrictive exhaust piece.

On my SVT with pre cats, RaceBits Y pipe and decat pipe, and a custom dump (no mufflers/resonator), i lost so much power and torque with it i removed it. And i noticed close to 4-5 average MPG loss with it as well. So, you do need a muffler or resonator. Just letting you know so you don't waste money having a custom exhaust made and finding out you need something else welded in:blackeye:.
Click to expand...

Based on those statements, I dont think you understand what that other thread was trying to tell you at all. Backpressure bad. High velocity good. What size were your pipes?
compudude86 said:
...does just a glasspack provide enough restriction?
Click to expand...
See above. Backpressure bad, high velocity good.
The purpose of the muffler is noise reduction, not restriction. Look for a muffler that maximizes flow while offering a sound you like.
The purpose of the cat is pollution controls, not restriction.
The purpose of the crossover is to create the scavenging effect whereby the pulse from one cylinder helps to accelerate the pulse behind it.
The purpose of a test pipe is to fill the gap left when the cat is removed...if you have a cat, then you dont need a test pipe.
 
does just a glasspack provide enough restriction?
Click to expand...
a glasspack is a straight through muffler. meaning nothing to slow down the exhaust gases. the purpose of a glasspack is to reduce the high decibel noises with the fiberglass that surrounds the pipe.
 
They did a test on a magnaflow high flow real cat and it isnt much difference than a straight pipe i think 2 whp with cat removed vs magnaflow,not worth it unless you are on boost lol.....i would just stay legal and put i high flow magnaflow cat it will sound less raspy also but this is just my opinion my car takes off slow with cat removed but i didnt remove it. Id rather have low end and mid power for around town driving im never in the high rpms i dont want to damage my engine lol
 
The idea of necessary back pressure is just plain goofy. I've built plenty of motors of various types and not once did I ever see one that didn't run better with LESS pressure. Having said that you cannot just open everything up and expect it to run better. ALL engines rune better with some degree of sonic wave tuning applied to them, that means some sort of multiple tube header of correct length. After that we always got best result with straight through type mufflers, any that made turns did not work as well. I don't care WHO makes fantastic claims for them and the prerequisite stack of dyno tests can be tossed in the trash as far as my concern. On RWD cars best setup was short muffler after header only, any full tailpipe setup generally threw away 50 or more horepower. You CAN run full tailpipe but you need to understand that doing so negates much of the tuned power achieved with true equal length headers. That loss will get worse and worse as the motor tune gets more radical in terms of cam timing. Radical race only type cam timing requires as close to header as possible and then open exhaust, any extra pipe just kills the wave tuning and the motor then runs like a dog.

The absolute ONLY way an engine could run better with more back pressure would be for it to have something majorly wrong with the exhaust design to begin with.
 
I like Back pressure for daily driving the complete stock svt cat back is perfect for me.....and wouldnt less back pressure benefit with a tune instead of stock ecu setting....because they tune the ecu from the factory with the exhaust that was put on im probably wrong someone can correct me ? Because ive noticed when messing with exhausts on some obd 1 and 2 cars makes them slower but oldschool carburated engines would be better with less back pressure but again i could be wrong just my experience with cars that ive messed with.....My 91 thunderbird supercoupe had flowmasters on it and 2.5 pipes some type of resonator,and i wanted it louder so i removed the resonator and man that thing ran slower instantly
 
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