Hey guys, sorry for a crazy long thread, but please bear with me. I have a few exhaust questions pertaining to low end torque.

The only mods to my 1994 Z28 6-speed right now are Koni SA shocks in front, and bilsteins in back (stock springs). Now that my car handles nicely. I want to move on to exhaust.

A few months back I picked up a Borla catback, Pacesetter offroad long tube race headers, Pacesetter ORY, and a Magnaflow 14159 muffler to replace the cat (mostly to eliminate rasp and cut the noise down slightly). I did quite a bit of research and it seems the only thing I did wrong was buy a muffler to replace the cat instead of a resonator. Though it'll do the job I guess. Unfortunately my opti went out on me recently so I haven't had a chance to install the exhaust yet. Then again, this delay gives me more time to finalize my exhaust plans.

I was talking to one of my car buddies this weekend who has a '93 5.0 LX Mustang with long tube headers. He said that they definitely free up hp in the higher rpm. However, he noticed a loss of low end power due to a reduction of back pressure. I jumped on the internet and saw that he was right. So now I'm somewhat regretting getting the long tubes if I'm going to lose low end torque. He also says he scrapes on every speed bump. Though, I think I saw a picture of an LT1 Z28 with long tubes that didn't sit that low to the ground, but this was awhile ago. Since my Z28 is a daily driver for almost half the year, I care more about low end power and enough clearance to keep the car from rattling and scraping from casual driving. I am hoping for an increase of power and sound from stock, but not shifting the power band up.

His suggestion was to get shorty headers. Though to do this, I would need to buy a different ORY and sell my current long tubes. I rather not since I'd have to hassle with selling and shipping the parts I have now. So I apologize for my super long question, but is there a way to prevent loss of low end torque and scraping while using long tubes? I heard many great things about Pacesetters long tubes and also Borla. I was hoping to enjoy them, but not at a loss of low end tq. Will installing a high flow cat instead of the Magnaflow 14159 help create more back pressure to help?

My only future mods would be a K&N and a possible PCMforless mail tune.

Thank you guys. I would love suggestions for my predicament.

 

i wouldnt recomend shorty headers unless you have to for emmisions. Do you have to pass emmisions? if so then you would need to have a cat. and yes getting long tubes might cause you to take it easy over speed bumps and such. and the lt1 engine is a torquey engine as is. i dont think you have anything to worry about looseing torque. and i wouldnt want to buy parts and never even be able to install them and sell them. but thats just me though.

 

ya know i really dont think you will lose low end power. power range has more to do with the cam. i beleive u will gain high end power. im not real sure on the clearance with the pacesetters but the kooks i have are not that much different than the stock exhaust concerning ground clearance. the y pipe is the piece that will be lower and the kooks is a oval shape in the right areas. again not sure of what the pasesetters have. as you see the driver side is the low side and is not much different in clearance than where the cat would set. i do have problems with the crossbar for the torque bar that i added. it will hit on speed bumps if i have a load or its a really tall speed bump. my car is lowered about an inch by the way.

 

first, you bought an off road y so either you really don't have it yet, or don't realize that it deletes the cat. Seriously, why do you think it's called an "off road y" ?


according to your post, you have a 6 speed manny and worry about low end torque? Downshift if you aren't pulling hard enough

anyway, CAI/custom tune/airfoil/1.6 rr's/ORY/Pacesetter LT's/Maganflow' 4 speed 4L60E auto and 3.23's in the rear

shreds the tires if i want so low end torque is there.

 

It also depends on what size your header primary tubes are. Some guys think that bigger is better, so the engine can breathe more.
The fact is that smaller primaries give you more bottom end torque than large primaries do. Is it possible your buddy went with big toobs?

 

Wow, all good stuff to know. Thank you guys. Looks like I'll be running the long tubes after all . Hopefully there's still enough room to run the Magnaflow 14159 somewhere on the Y too. Do you think it'll fit anywhere?

 

Lack of back pressure will not hurt low end power as long as the engine is tuned properly. Longer tubes will increase low end torque, while shorter tubes will help the high end; again, assuming all parts such as cam, heads, compression, and tuning complement each other. What you don't want to do is to have a tube diameter that is too large for the size of the engine. You need to have the slug of exhaust gas travel fast enough to create a vacuum behind it and completely scavange the cylinder. A large tube will allow the exhaust slug to travel too slowly and the scavenging effect won't take place.
Back pressure prevents the exhaust to flow freely and prevents scavenging and causes reversion. Reversion forces exhaust back into cylinders that happen to have open exhaust valves diluting the fuel mixture and causing loss of power.

 

Pete, I thought you had a sticky on back pressure and scavenging? I can't find it, if there is one. It seems quite a few people confuse the two terms.
To simplify it...back pressure is BAD, period.
Scavenging is something altogether different, and has to do with how the exhaust is tuned to the output of the engine. Exhaust gases don't flow constant like water does. Exhaust comes out in pulses, behind each pulse is a vacuum, and behind that is chasing another pulse. Think about how Nascar works, with the car behind "drafting" the one in front. The car behind doesn't have to work as hard because the front car is pulling him along in a vacuum. And the front car has it easier too because the two cars are more or less "linked" together through a vacuum connection. That's the same basic principle behind exhaust scavenging. If the pipes are too big for the engine, the gases will more or less "fall" out (for lack of a better term) instead of each pulse being closely linked and helping each other to the end.

 

Hopefully that will clear it up. Thanx.

 

Maybe it will. But next myth will probably be saying something about stuffing matchbox cars in your exhaust to make it perform better!