Hemi Test-drives

I took out two Hemi 1500s for a test drive over the weekend. ?The first one the Dodge dealer had put on cat back duals on it with a FM40. ?I took it on the freeway; up a steep over pass and did some WOT starts on some empty back streets. ?It sounded great but boy was it disappointing, would not even chirp the tires. ? Kind of felt like it had TM! ?I swear my Z66 is faster! ?

I was getting ready to leave the dealership when I though about how Jack always warns that duals drop low end torque on the 5.3 so I asked the salesman if I could drive one with out the duals. ?He looked at me like I was nuts but went and got another 1500 Hemi with the stock exhaust. ? I rolled it on the feeder road, came to a dead stop and floored it. ?Both tires lite up! ?I ran the same test route and it was much faster than the 1st one. ?The salesman even noticed the different. ?

So if a new Dodge 1500 Hemi with duals pulls up along side of you and wants to run, your AV can take him! ?But watch out for the ones that are stock! ?

I've been wondering about exactly what happens between the stock exhaust and the various add-on exhausts. So, thanks Jonny_D for the bit of insight.

Ever since I joined this club, I've read every post that seemed to discuss various exhaust systems, but my brain just hasn't been able to put all the info together and make sense of it, nor do I think I've even been able to find any info on some of the systems at all. Can anybody out there please direct me to any threads or links that would, in one place, explain the effects (horsepower/torque gained or lost) of each type of system? I hear about dual tips, true dual exhausts, single tips, single in-dual out mufflers, cat-backs, etc., etc. That's the kind of stuff I'm wondering about, not so much the specific brands. To be honest with you, I haven't even been able to figure out for sure what I want to do with back pressure. I've gotten the impression that you want less back pressure for best performance gains; so it seems to me as if a dual exhaust would be more free-flowing than a single tip, but obviously that's not really what I'm reading
Of all the brands, I had previously settled on the Borla catback because I like the sound of it so much more than the others, but since they don't really advertise its performance gains, I would take that to mean there may even be lost low end? Is that actually the case? The Borla is a dual side exit, which I really like the looks of, but if it isn't going to give me torque gains, is there anything I can do to improve it without changing the way it looks from the road? I imagine if I did some kind of modification to it, that it would change the tone, ? so if tone is no longer a factor, does anyone else make a dual side exit sysytem that I should consider?

I'm sorry for going on so long, but I'm a real newbie at this, and I just wanted to make sure you know what I'm trying to get figured out. Thanks a whole lot for any help you guys can offer, I've already learned SO much stuff through this club, I'm amazed. With the likes of such performane gurus as 11H, Butch, Gandolphxx, etc. on here, this is the hottest forum I have ever been on, by far my favorite.

Dave

Hey Johnny, did the hemi feel faster than your AV? and if so hom much quicker do you think it was. Thanks

Alex

MisterGreen,

I'm no pro and perhaps one of those will help answer your question. What I've gathered though is that every engine needs a certain amount of back pressure to help it perform the way it's supposed to and the 5.3 especially loses low-end torque if the back pressure is too low.

So what it GENERALLY means is, don't put less restrictive exhaust on your stock vehicle without first opening up the intake side so that more air is coming IN to the engine too. Once you do that, THEN you need a better flowing exhaust to help it flow all the way through.

The back pressure on your engine is affected by the smallest diameter opening that the exhaust has to pass through on it's way out the end of your tail pipe, and also to some extent how long of a pipe that small diameter section is.

So... people who are doing Cat-Back systems (changing everything from Catalytic Converter to tail pipe tip) are basically changing everything except the headers. If your muffler is single-in, dual out, then your restrictive section will be before the muffler but the wider exit shortens the length of the small diameter passage. Hope that helps and that someone who knows more than me can correct any mistakes I might have made.

MisterGreen17 said:

Can anybody out there please direct me to any threads or links that would, in one place, explain the effects (horsepower/torque gained or lost) of each type of system?

Click to expand...

Paging 11H, where are you? This topic was made for you!

In the mean time, while we wait for him to chime in, I would suggest that you look at 11H's profile, list his posts, and then use your browser's "find on this page" feature to search for "exhaust" and you'll probably find that he talks about some of this.

I do agree, however, that a single place to find all of this information would be a great resource.

-- SS

02_2500avalanche said:

Hey Johnny, did the hemi feel faster than your AV? and if so hom much quicker do you think it was. Thanks

Alex

Click to expand...

Alex,

The Hemi with the stock exhaust was definitely quicker than my Z66 with the 3:73. With about 800 less pounds, 60 more HP and 50 more lbs of torque, a 3:92 rear end and a 5 speed tranny, it should be. The 5 speed on the Hemi doesn?t have the dead zone my 3:73 has between 1500 to 2000 rpm in first gear and in the higher gears it seemed a little quicker to kick down. The Hemi was quick, but it is not in the same league as Ford Lighting and, just my guess, not quite as quick as a Silverado SS. But you can get the Hemi for a whole lot less than the other two.

TxAvy is correct about the possibility of having too "free-flowing" ans exhaust. A larger bore/less restrictive system is beneficial at higher RPM, but robs you of power at the lower end. A more restrictive system, however, strangles the engine at the higher end. A smaller pipe actually causes the speed of the gases to be higher, and this promotes "scavenging" where the velocity is high enough to create a partial vaccuum and help draw the next batch of gas out of the combustion chamber. Too large a bore promotes volume but decreases gas speed and reduces this scavenging. You have to try for a balance, and one that is matched to the RPM range of the engine. It doesn't sound like the Cat-Back system mates well w/ the Hemi.

Thanks ShapeShifter, that was a good suggestion. I looked through 11H's many posts, and it turns out he did already discuss exhaust systems with several people, (and one them did a better job than I did of asking him what I wanted to know) so I put the links to those threads at the bottom. Unfortunately, the consensus seemed to be that currently, there probably isn't an exhaust sytem out there that's tops in every single respect for my picky self. (Unless I want to try doing a custom exhaust.) The thing that kept running through my head though, was "wouldn't it be cool if there was some way--either automatically, or manually--that I could constantly change the exhaust flow to be the most ideal for whatever application or RPM I need the power for. Is there any device out there that could do this? Maybe hook up to the PCM somehow?? That would be so cool, maybe I should even start a new thread on that, to find out if anybody's heard of such a thing.
Thanks also to TXAVy and Strigil for your comments, they made some stuff start to click in my head.
While I won't say I'm satisfied as far as finding all the info in one place, these threads (below) were very informative regarding some stuff that seems to work. If 11H or anybody else has something more, or some good links, to add here, please do!! I can use all the help I can get!

Still confused after researching...[11H has some very comprehensive stuff in here, excellent reading]

Magnaflow 1 in 2 out duals - enough backpressure? [More of 11H's wisdom in here]