Read a little bit on it, but still confused, and trying to find my ideal exhaust pipe size, dual or single...

http://www.exhaustvideos.com/faq/how...pipe-diameter/
http://www.eng-tips.com/viewthread.cfm?qid=104735

3.5 liters*7500rpm/2 = 13125 liters per minute

Guesstimating intake and exhaust temps (copy/pasted from second link)

So... 13125*4.185 = 54928.125 liters/minute

So... 54928.125 / 28.3 = 1940.9 CFM

Then...

So finally... 3.5 liters*7500rpm/2*4.185/28.3*1.0756 = 2087.6 CFM total?

I don't know what our engine's realistic intake and exhaust temperatures are though (so that bold number is an estimate. Also, I don't know know exactly how to translate pipe size to CFM excluding any crazy scientific scavenging designs like Motordyne's.

I keep getting hung up on converting pipe size to pipe area to CFM potential though. I see the chart in my first link, but it's saying a 3.5" pipe can flow 1029CFM? So I need dual 3.5" exhaust? This just doesn't seem to make much sense. Obviously HR's don't have dual 3.5" exhaust piping, and so my built NA DE shouldn't need that either lol. I was thinking dual between 2.25" and 2.5" would be ideal just based off their simplified "Quick and Dirty Exhaust System Math" of max HP per pipe single/dual.

Currently my exhaust is Bassani. Advertised specs are "2 1/4" dia. tube in, with resonators and "X" Crossover, dual 4x8 mufflers, 2 1/2" dia. out, 4" single wall dual slash cut polished stainless tips with billet inserts, stock location exit." So will this be ideal for ~300whp? It sounds super raspy though with the C8 cams, DC headers, and 60mm test pipes though, and I was thinking maybe it was a flow issue (thinking about trading it for something else). Also, anyone know specs on DC headers? Couldn't find them advertised.

Any thoughts/corrections/suggestions to suitable exhausts for an NA 11:1 comp, C8 cams (12.01lift/272dur) NA build?

 

our temp difference isnt that big expect closer to 1500 degrees for most people egt, that also dosnt take into account cooling down over the length of the exhaust which will be highly variable. also at peak power the engine isnt going to be a full 3.5L it could be higher or lower which is why each one has to be custom built for that specific setup. i know theres a few sites with calculators its best to just use those to be completely honest since all the hard work is already dont. have to figure in lengths as well, pressure drops and more. atmosphere box's/expansion chambers are pretty nice to use to help eliminate alot of variables.

 

based on some very basic info headers should be 26.19 length, 1.71 inchs dia, 3.4 inch collectors but dosnt list length wallace racing has some nice calculators sure they have a exhaust calc too or use expansion chambers.

 

Here's my 2 cents.

IMO, most of these calculations to come up with exhaust size are rubbish, and often inaccurate in the real world. There's just too many factors/variables that come into play on a combustion engine that make such calculations far from accurate.

A 2 1/4" dual like the Bassani should easily support 300whp without much restriction (power loss), if any at all...and isn't a bad pairing since the DC header collector is likely only 2 1/4" anyway. The only questionable part with the Bassani I can see is the affectiveness of the "x-pipe" though, as this is a part that can have a massive impact on scavenging, and moreso low to mid range power. Although it's a bit hard to tell what's going on inside the Bassani x-pipe, it does seem from outside appearance to be a bit crude compared to say a Burns or Vibrant X-pipe....and might also be attributing a bit to the rasp you speak of.

If I were you, and was really worried about maximizing your catback design, I would probably just have a good exhaust shop weld in a Burns/Vibrant 2 1/4" x-pipe and be done with it (unless you're just tired of the exhaust note). Of course a well designed 3" single exhaust (like the Tomei Expreme Ti) are proven to work quite well, but that would be a lot more money in the end (especially since a Y-pipe would be neccesary).

It's also worth mentioning that when sizing you're exhaust, it is strongly influenced by the intake side and the restrictions there as well.

 

I will look into these calculators. I'm thinking it doesn't make sense to buy generic mass produced aftermarket exhausts at this point now, material and fabrication cost should be much less than ~$1,500 if you can get most the variables just about right I think. Would be nice to build an exhaust from the vast selection of mufflers/resonators/piping, and sell the Bassani to cover the costs.

If I ever do figure out something, I'll post the recipe.

 

Hm true true. I too have always wondered what the hell is going on inside the square-ish x-pipe on the Bassani. I need to research a lot more on exhaust designs still to see how some of these different designs factor in.

 

I had done this sometime back and don't remember the numbers.

What are your goals with these calculations, are planning to modify your exhaust?

Also, since all cylinders do not scavenge at the same time, you need to figure out the firing order, lets say all 3 cylinders on 1 bank scavenge in x time, your true flowrate is x/3, which is called a pulse, for a true dual exhaust at the collectors. Then you need to find the K-FACTOR, which is the loss at bends.

 

Goals are a good flowing exhaust that is suited to my engine build at 7500RPM. For sure will be either chopping up this Bassani exhaust, selling it, or trading it in the future. Was great as a basic bolt-on, but with the higher rev range, cams, and such... just doesn't match well I think. Also, staying dual exhaust, debating h vs x pipe... need to research. Bazooka single exhaust mufflers will not clear my mastergrade cf diffuser.

 

The combustion of gases is not linear, with just numbers its difficult to achieve, by goals I meant do you wish to change the note or increase the volume?

 

Note, it's super raspy.

 

Here is another fact that will add confusion.

Exhaust gas is produced in pulses thus the determination of pipe size is governed by a much more complex resonance tuning. The parameters also vary with temperature.

Don't worry, you won't gain much out of it.

 

Ya, I got the gist of that. Read about it before, just thought this had more to do with headers than cat-back. Obviously everything is connected though right right.

 

Most manufacturers do lots of research, in your case, I suggest checking few Zs in person with exhaust mods or youtube. As far as gains go, there's not much to achieve.

Post a video of your exhaust and check at what rpms rasp occurs

 

I will once it's running again. I'm pretty sure the cams different lift & duration in combination with headers totally changed any sort of resonance tuning from the factory... if there really was much on an '03 DE lol. Rasp when I ran it seemed from about 2k to 6.6k lol... Going to be revving higher with the built motor now though. We'll see. Maybe slightly higher comp will change the note slightly.

 

That's impressivel, do you have any numbers for your mufflers? 3.5-6 is almost the entire range, may be your mufflers are not pairing/or shot?

 

Ya, I don't know muffler design or anything besides their advertised website. They've seen at least 5qts of oil in the last ~1.5k miles though... not sure how badly that might affect them. Exhaust was literally spitting oil on the rear bumper like mist lol.

Still, sounded fine before cams & headers/TPs though.

 

Mcarther, you’re treating the engine as if it has 100% Volumetric efficiently before any of your other calculations, which of course no engine (or even an air pump) has. You need to correct downward for this.

 

Did you get resonated test pipes? That could cause the rasp. Mufflers drenched in oil will not work well ny friends. They will no longer muffle the frequencies that they would if they were dry.

Here's a crazy idea, if they are still drenched, remove them and leave it in sun to dry for a few days, try them once they are dry

 

except these calculations are how every single pro race team builds there exhaust there isnt too many variables unless your lazy. also you talk about scavaging, for scavaging to be effective your exhaust needs to constantly step up in size. ALSO a short length of 2 1/4 collector is way different then a entire exhaust where it is going to see pressure drops and velocity drops over its entire length. a 2 1/4 collector will easily flow as much or more then a 2.5 inch full exhaust system even if its straight pipe simply due to this.

 

thats not true modified vq's do have in excess of 100% VE, the new ford 5.0 has 110% VE, pro mod/pro stock engines and f1 engines hit 120-124% VE. the theoretical maximum due to air speed limits is 125% VE. its possible due to exhaust savaging and intake pulse tuning, engines have been exceeding 100% VE since the 90's in pro race engines.