Remove Resonator for Intake Or Change Exhaust?

[johnunit]

There is a very real restriction in most factory exhaust systems, even as low as 1500RPM.


A general guideline among hotrodders is that 1PSI is about where exhaust backpressure causes measurable efficiency/power loss at a given RPM. In performance circles, logically, this means that about 1psi is the max you want to see at redline/shift point. People here rightly point out that restriction at high RPMs is not an issue in most economy builds. However, I've personally seen 3-5 PSI on STOCK engines being free-revved (in neutral) at below 2500RPM. What does this mean? These engines WERE seeing a significant restriction at cruising RPM. One I remember vividly was a Nissan 350Z, which has a decent-looking exhaust system.

An even more in-person example is the CLEAR seat-of-the-pants difference to everyone who had known the car in my 1985 Crown Victoria going from 2 inch dual exhaust, iron exhaust manifolds, and stock mufflers to 1 5/8 inch primary headers and 2 1/2 inch with relatively free flowing mufflers. The gains were evident as low as 2000RPM in terms of acceleration. I also saw fuel economy improvements, especially on the highway, but I don't keep close enough track on that car to give you numbers. That's not even that restrictive a setup I had to begin with but the gains were still clear and WERE present at lower RPM's.



As for talking about exhaust tuning pulses and the like? Generally you need longtube (think 35 inches minimum) headers, and the ability to to choose primary tube diameter and preferrably collector diameter and length. Without that, the odds of exhaust resonant pulses lining up to give you a significant boost at cruising RPMs is very low.


I'd bet large amounts of money that virtually every car on the road, driven the same way before and after, would see fuel economy improvements from going to a larger diameter exhaust system than stock with less-restrictive mufflers. The only caveats to this would be:
1. Cars that can't self-adjust to compensate for more flow and where the owner can't/won't tune it to compensate themselves. Mostly an issue on early EFI setups.

2. If you went with such an absurdly larger exhaust system that the extra weight or aerodynamic drag negated the positives.


For further proof, go to almost any forum for a specific vehicle, be it the aformentioned 350Z, Crown Victoria, TDI VW's, anything, and ask whether people see fuel economy improvements with less restrictive exhausts.

In all honesty, I think removing restrictions to the exhaust and intake tract are probably where most of the people on this forum are missing out on gains. Not a shot at anyone in particular, but if you've spent 100 hours on coroplast aero experiments and you still have a stock 1 1/2 inch tailpipe on, you're really going about this game the hard way.

[mcrews]

john,
I could also go to other car sites and read about how wonderful their CIA induction or oiled air filter or XXXXXX or YYYYYYYYY gives better mileage or bettter response or better ZZZZZZZZZ
OR
I could stay here and look for ABA testing and documents.

oh life is full of easier choices!!!!!!!
If we follow your logic, then that crown vic had over 400hp.........

you said "In all honesty, I think removing restrictions to the exhaust and intake tract are probably where most of the people on this forum are missing out on gains. Not a shot at anyone in particular, but if you've spent 100 hours on coroplast aero experiments and you still have a stock 1 1/2 inch tailpipe on, you're really going about this game the hard way."
you comment is reflective of your 'tendancy' to exagerate. "100 hours"........
maybe.....you should spend 10 minutes using the search function. try aba testing first.

How To Calculate Muffler Size and Exhaust Pipe Diameter | Exhaust Videos
"Easy Way To Estimate: Your intake system needs to flow 1.5 CFM per engine horsepower, and your exhaust system needs to flow 2.2 CFM per engine horsepower.

Good Way To Estimate: Take engine RPM x engine displacement, then divide by two. This is the intake volume. Use this same volume of air for the exhaust system, but then correct for thermal expansion (you need to know exhaust temps to figure things out).

Exhaust Pipe Size Estimate: A good section of straight pipe will flow about 115 CFM per square inch of area. Here’s a quick table that shows how many CFM each common pipe size will flow, as well as the estimated max horsepower for each pipe size:

Pipe Dia. (inches).....Total CFM (est.)....Max HP/ Pipe........ Max HP For Dual System
1 1/2 .......................171.................... 78........................... 155
1 5/8 .......................203 ....................92 ..........................185
1 3/4 .......................239 ...................108 .........................217
2 ............................ 318 ...................144 ........................289
2 1/4........................ 408 ...................185 ........................371
2 1/2 ........................ 509 ...................232 ......................463
2 3/4 .........................622 ...................283....................... 566
3.............................. 747 ....................339...................... 679
3 1/4........................ 882................... 401 ........................802
3 1/2.........................1029 ..................468 ......................935

NOTE: These numbers are just estimates. All pipes are assumed to be 16 gauge steel.

The table above is probably over-estimating pipe size, but you can see that a 400 hp vehicle with a dual exhaust system only needs 2 1/4 – 2 1/2 inch pipes. Anything larger is overkill.

you do understand that this chart is refering to hp at wot?
so if you REALLY understand eco-driving, you understand that we arent at wot.
So why do we need larger exhaust?
But that is a retorical question...I don't want another post about 'how you feel'. do some research and proof what you have to say.(and not with references to what others 'say'. PROOF. tested proof.

[toc]

Ok, so if it's at WOT, the engine in my car according to wikipedia is capable of 126hp @ 6000 RPM

The table linked shows the exhaust to suit is 2", I know it's smaller than that - but I'm not at 6000 RPM, so the exhaust pipes should be fine.

Good thing I'm not going to touch the exhaust at the moment, the intake on the other hand, I might try a WAI if I can't break 600 kMs on this tank. A tune for economy would be nice (at 98 RON), but the cost outweighs any benefit, aftermarket ECU, then a fuel map and time - huge expense for what I perceive won't be much of a gain.

So Intake mods and driving technique must be where it's at.

[mcrews]

no 2 inches is 144
at 126 MAX your really closer to 1 3/4.

[Canary5_0]

So, is my 2 1/2 exhaust on my Mustang to large or does the column on the right represent 'true' dual exhaust, meaning no x or h-pipe crossover. BTW my cars max hp is 215 hp @ 4200 RPM & 285 lb-ft @ 3400 RPM. And yes i know thats horrible.

[mcrews]

Dual pipes should be no larger than 1 3/4 each
singlr pipe should be smaller than 2 1/2.
realize you hardly ever are at 4200 rpm for 5% of total drive time.
So being 'undersize' is only 'undersized' at 4200 rpms.

I'm not an exhaust expert and these charts are really basic.

[RH77]

I have a resonator question...

My exhaust leak has gotten a LOT worse (yet another failed spark plug wire shook the exhaust system violently during vibration and rocking). From the best I can tell, it looks like the rusty resonator failed more from the shaking and has gotten to the point that it needs replaced (1 -- because inspection is coming up; 2 -- CO concentrations are definitely an issue). I'm hoping the B-Pipe is solid. It's all post-cat, so it wasn't an issue until lately.

So, I hope maybe the shop can put a straight-pipe in place of a more-costly resonator? I assume it only "adjusts" the exhaust pulse to make the exhaust note "more pleasant". The remaining system looks good enough to go. It buzzes and rattles, but it wouldn't be right without those!

On the most basic of principles (and as I understand it), unless the header is replaced, it doesn't matter much downstream unless you restrict considerably.

RH77

[mcrews]

I had replaced my resonator when it developed a crack at the weld.
I replaced it with a x pipe sine I had factory duals past the single resonator.
I did notice a tad bit more buzzzing or humming from the exhaust since the resonator was right under the front seats.
(but only for a couple of days)
so I thing you will be fine!



Cant say wether the x pipe helped my mpg because I did this pre-ecomodder.
BUT, It didnt hurt my mpg because I was always paying attention to it.

But if I had a resonator now, and it had cracked, I'd still do the x pipe.

[gone-ot]

..."optimum" pipe diameter depends upon "where & how" you want that optimization to occur & do:

1) If you want the optimization to enhance torque and fuel economy, then you want smaller pipe diameter to coincide with engine speed where maximum torque is desired, roughly 3000-4000 rpm.

2) Conversely, if you want the optization to ehance HP (and FE be damned) then you want larger pipe diameter to coincide with engine speed where maximum HP is achieved, typically just beyond OEM HP-peak but below engine redline RPM.

[RH77]

Originally Posted by mcrews

I had replaced my resonator when it developed a crack at the weld.
I replaced it with a x pipe sine I had factory duals past the single resonator.
I did notice a tad bit more buzzzing or humming from the exhaust since the resonator was right under the front seats.
(but only for a couple of days)
so I thing you will be fine!

Good info. The rez had the only lower heat shield left, which rusted closed, trapped salt/moisture, and Chemistry finished the story. With a straight pipe, I wouldn't imagine that any adverse sounds would be a big deal (it fits the age of the car).

Aside from the inner A-pipe buzz, I'm really satisfied with the stock design of the system (perhaps a 4-2-1 header would help low RPM efficiency). But as Daox mentioned earlier in the thread, exhaust mods are costly and rather permanent for the EcoModding experimenter. As it continues to erode, I might consider a smaller pipe diameter -- I'm sure that most Honda B-Series products were tuned for high-rev performance... even still, any change is cautiously considered once other things are dialed-in.

On a side note, I'm wondering if anyone has info regarding VW's new lineup. I drove a 2012 VW Jetta this week (2.5 SE 5-Cyl / 6-speed auto). It had loads of useable power at 1000-2000 RPM (yet tended to get a bit wheezy at top-end) -- exhaust design? 1st gear was used less than 5% of starts -- way too low (6th gear could be manually hit at 50 km/h and offered 30-32 avg MPG with mostly highway operation). 70 mph registered just over 2000 on the tach.

RH77