I am new here, and have enjoyed reading everyone's comments about exhaust options, and the pros and cons of various configurations. I am hoping someone here can put this "Loss of Low End Torque" issue into perspective for me (and perhaps for others with the same question).

I have read that installing dual exhaust and/or systems with inadequate backpressure and/or that are poorly designed can result in loss of low end torque. What are we talking about here? Is it something that would be readily apparent to someone who primarily drives on the highway at normal speeds and not towing anything? Does it mean that you could only pull a 24' travel trailer up a steep hill at 20 mph instead of 25 mph? Are we talking about something an average driver would not notice?

For comparison, I have seen the dyno sheets of the "improved" HP and torque when a magnaflow system is installed - but the same dyno sheet shows a premature decline in both of these stats at the top end when compared to the stock exhaust. One might respond to that observation (and rightfully so) that "Well, that's not something you are really going to notice at that point" so I would then ask in kind, is that the same kind of "something most people won't notice" when it comes to this often discussed "loss of low end torque?"

Thanks in advance for your insights.
Stu

 

Hi.

Well Stu, Welcome to the forums!

I would first ask that you to kindly point us in the direction of the dyno sheet.

It would seem to refute the following ( excerpted from Troyer Performance ):

---------------------------------------------
"Magnaflow Cat-Back Exhaust System for 1997-2004 Ford F-150 V8
15609 Magnaflow cat-back exhaust system for the 1997-2004 Ford F-150 with 4.6 or 5.4 V8 engines.(Note: On 2004 ,models, fits 2004 Heritage models ONLY - for new body style 2004 F-150 models, use Magnaflow system #15821.)


This is the F-150 exhaust system you've been hearing about. We spent 23 months testing virtually all of the "name brand" cat-back exhaust systems on the market for the Ford F-150 platform, in SISO, SIDO & DIDO configurations. This Magnaflow was the only F-150 system that showed positive torque gains at any throttle position tested, as well as at any rpm. There is NONE of the usual torque loss below 3000 rpm that is so common with almost all truck & SUV cat-back exhaust systems.

This 3" single Magnaflow cat-back exhaust even gained more peak HP than any true-dual exhaust system we tested, along with gaining torque *everywhere*, a clear demonstration of superior flow engineering specifically for these heavy trucks. Simply put, you can't get a better result with any other commercial cat-back or muffler shop system.

Power gains typically average about 15-17 HP (flywheel) on the 4.6 & 18-21 HP (flywheel) on the 5.4 motor. Thanks to the largest peak power gains as well as more torque at any throttle position or rpm, this cat-back system is literally perfect for any kind of use, typical daily driver, *great* for towing, all the way up to actual drag racing, this exhaust adds more power all the time in any situation."

------------------------------------------------------

So, given Mike's reputation and his testing, and from personal experience (my top end has never been better compared to stock), and from a simple extension of logic - an unbaffled, 3" efficient, ( as in sustained flow velocity - forget backpressure - it's not a factor here) exhaust system will not likley restrict top-end power compared to a stock 2.5" baffled system. Just does not make sense to me. Something else is up with that.

The link to the full text is here:

http://www.troyerperformance.com/cgi...atalogno=15609

Feel free to call Mike to get more info.

And, Kudos to you for taking the time to do the reasearch!

Cheers!
Vic

 

Hi Vic, thanks for the reply. I'll see if I can't find the dyno sheet and I'll post a link. It may have been an IMCO catback that showed the decline (?) but anyway I was more interested in getting some sort of perspective on this often discussed loss of torque and just how much one would notice it. I freeway commute in my 2005 F-150 4.6 and don't race nor tow. Thanks!

 

I guess it wasn't either, as the 2 Magnaflow products for my application (#16113 and/or #16114) don't offer a dyno sheet on their website. And I don't find IMCO Catback on their website, only mufflers. Maybe I was dreaming....but I am sure I saw dyno sheets from more than one source that showed positive torque and HP gains at lower RPM's compared to stock, but that fell below stock levels at higher RPM's. But again that was used only as a comparative example in my original post, and was not the crux of my inquiry.

 

I myself am particularly concerned with low-end torque as well, because one thing I know about my truck is that it seems to have a power band that complements the higher RPM ranges. When I had my 2003 Dodge Ram 4.7L, it routinely spanked Ford 4.6L's off the line, but then fell short in the upper RPM ranges, so we were about even. Now I'm on the other side of the coin, and I'd rather have a bit more torque up top, but when I installed my Flowmaster, I lost low-end torque, and am about to have a Magnaflow installed to gain it back.

 

I dont believe there is any loss of low end torque with a cat back install. There is plenty of back pressure from the small pipes, the y pipe and cats. I would love to see a before and after dyno. I bet your sotp meter only thinks there is a low end loss due the the upper gainning more. And if by any chance there was a Small loss i bet it is below the convertors rpm range any how.

 

01vert, you seem to be quite the expert for someone that just joined the site. Are you a mechanic or do you work for Ford. What truck do you have? Your profile does not show it. There have been dyno tests that show the loss of tourque at low rpms. Do a search. Welcome to the site.

 

I just started replying, I couldnt stand reading some of the replys. But have been watching this board for awile. I currently own a 04f150, 01 cobra, 89 5.0, 03 4.6 explorer. I have had many, many cars, and yes i used to have my license. As far as the low end loss what are we talking about 2,000 rpms?? These truck exhausts are so restictive i just cant imagine it can be anything worth even talking about. And thank you for the welcome, p.s. are you the same norm from blueovalnews...

 

If you're asking me about low-end loss, I'd say below about 2500 or so.

 

I installed a Gibson cat back system on my truck and I definatly lost low end torque over the stock system. Before I could spin the tires from a dead stop but not now. My 2 cents

 

The only thing I noticed that reduced my bottom end was putting larger tires on, and even then, not much change. I have installed dual exhaust pipes to one muffler with a single 3" tailpipe. I'm happy with the results and, once it gets going, it screams.

 

i have the delta force II flowmaster installed on my truck and it has lost nothing!.
it sounds very deep with no loud and crazy sounds .