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.

 

Weld in a melted cat to restore backpressure?

 

Long tubes produce more low end than short tubes.... that's the whole purpose of the longer tube length. Read any good writeup on exhaust system design. Where you lose low end would be going to an excessivley large primary tube diameter, which slows down gas velocity in the primaries and reduces scavenging.

Once you get past the collectors, the exhaust system diameter is relatively unimportant. You don't want to build "backpressure" past the collectors - that will reduce HP. The "you lose low end torque when you reduce backpressure" is a myth. Its a carryover from the days when people ran carbs, the reduced back pressure improved air flow to the extent that it leaned out the mixture and you lost torque. If they had rejetted the carb correctly, they would have seen an improvement.

With a modern electronic fuel injection system, mass air and closed loop control, the computer takes care of the adjustments (within reason). You do not want to add backpressure to your exhaust.

 

Wow, good stuff to know. Thank you guys. Injuneer knows his stuff!

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. If not, any suggestions on a high flowing cat that'll fit?

 

My car is lowered (but not slammed).


I have SSW longtubes and have never scraped them or the Y pipe.




Here's your low end torque.


Original owner. 111K miles. Bone stock / original engine (well, with fresh OEM valve springs). Just the usual exhaust, CAI, 160 thermostat, tune.