the muffler and exhaust mod thread

[EF TuneRR]

Anyone interested in actually trying to calculate what size exhaust piping they should use should look into Flanno Flow. Should prove somewhat useful.

[hackish]

I spent 10 years tuning vehicles, everything from hyundai accents up to exotics any everything in between. I only skimmed the thread but I'll add a few details in here that will hopefully correct a few things and add in a bit of info.

Diesel Dave... Try not to think of your diesel in terms of AFR then compare to gasoline engines. Stoichometric refers to the mixture that a specific fuel totally burns with a given amount of oxygen. E85, Diesel, Propane, gasoline all have different ratios. Instead if you think about it as lambda you will be talking the same numbers as the gasoline people. I've found that Diesel tuning for fuel economy is quite counter-intuitive for the gasoline guys. You actually save fuel by adding fuel. Add fuel till it smokes then back off a bit works surprisingly well. The reason for this is that more fuel produces more torque and thus gets you up to speed (and the more efficient -compared to gasoline) cruise operating range of the engine. I just finished evaluating more than 16,000km of fuel economy data for a TDI we tuned. It made 40bhp more and consumed a tiny amount LESS fuel.

Turbos do not like more backpressure. The only engine that really likes any backpressure is a supercharged one with high overlap. Too little backpressure and the mixture blows right out the open exhaust valve. Do not confuse this with the OEM tuning your car may have.

Reducing the backpressure will improve fuel economy significantly while accelerating. Steady state operation will make more gains on some vehicles - especially the EGR equipped ones. If the engine wastes less energy pushing the exhaust down a restrictive pipe through a restrictive muffler then more energy is left to turn the wheels.

I had a 1993 Civic VX with a crappy restrictive 1.25" crush bent pipe. Finally it rotted off so I bought the cheapest stainless setup I could ($150 at shop cost). With no other changes in driving habits I picked up 7% and that was with at least 5000km of test data on either side.

At the moment I have a Subaru. Originally it had pretty poorly designed factory headers and a pretty restrictive exhaust. At the time (yes 12 years ago) I picked up 11-12% doing the exhaust on that. I don't have the data anymore but it was a good 30k of driving for comparison.

Hope that helps with some real world examples.

[mcrews]

not really...... but bear with me here.
When in your post does it change from turbo diesel to normal gas?
also, You gave no mention of what size you went with in either example. so we cant know what really helps.
Given your background I was looking for more factual information.
DO your 'examples' run contrary to the chart that was posted?

Sorry....more questions than answers.

you said "Reducing the backpressure will improve fuel economy significantly while accelerating."
That is a pretty broad statement. But I can guess that it means the 0 to XX acceleration.
Not the steady cruise.
And that is important. Much like WOT which occures MAYBE 7-10% of the time, how often are we really 'accelerating'?

[hackish]

The diesel dave section was the section on Diesel. The backpressure section applies to both.

In the civic it was from a 1.25 to 2.25". The size of the pipe gives you diminishing gains. For example a 2.5" or 3" would probably not have made a significant difference. The muffler is probably a more significant cause but I've never spent time measuring backpressure on just mufflers changes. Do whatever you need to reduce backpressure, whether it's a pipe or a muffler...

The subaru stocker was 2" (I think) and I put on a 2.5". At the time it had a 2.5" engine but the installation of a header did a lot for cylinder balance so its data was really combined gains from both. I do not have specific data on it anymore but I did run it for about 10,000 km with just the exhaust (no headers). From memory I think the headers made as much improvement as the exhaust which tells you that sometimes there is more going on than simple restriction.

I think I posted a lot more on cylinder balance somewhere else. If you get the time do some searching on GAMI injectors as they do a lot of work on cylinder balance for piston (AC) engines.

For the comments on accelerating you may only be accelerating 10% of the time but in city driving it accounts for a significant portion of the fuel used. It is more complex to compare the steady state fuel consumption because you have EGR flow and flow limits that all come into play which is to say you may see few gains on some vehicles but large gains on others where during acceleration you almost always see gains.

[hackish]

Originally Posted by mcrews

Given your background I was looking for more factual information.
DO your 'examples' run contrary to the chart that was posted?

Which chart?

There was a dyno chart posted some pages earlier but it really has nothing to do with this discussion. In fact it shows nothing more than the car happened to make X power and Y RPM. You would need to see a lot more data to draw anything conclusive.

Some of the details are left vague - I can't give out clients' data. If someone comes up with a contrary example I can try to look at it and explain why.

[mcrews]

my bad......
posted a pipe sizes chart on another thread here.
let me get it over here.

thanks for the clarification.

[mcrews]

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 for 1 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.

[hackish]

Your chart is wrong. Many factory vehicles produce more than your max hp figures.

http://www.youtube.com/watch?v=KYaEzsjXgVo

Simple example. That vehicle had a 3" exhaust with 2 resonators, 1 cat and a muffler. 512whp is somewhere getting close to 580bhp.

I've made 600whp on a single 2.5" exhaust. I've made over 1000bhp on a 3" single.

[serialk11r]

hackish are you saying that that chart significantly overestimates the piping size? Could you share some backpressure data that you may have? I'm curious

[Ladogaboy]

In the turbocharged tuning world, a 3" pipe is generally fine for any < 600 hp application (i.e., you don't need to exceed 3" unless you are planning to exceed 600 hp). A 2.5" pipe doesn't tend to be a bottleneck until you exceed 300 to 350 hp.

NA engines might be different, but everything I've read agrees with hackish. The "dual" system numbers mcrews has listed might be closer to what a single-pipe system is able to support.