Performance exhaust bullet summary

Thought this may be interesting to a wider audience than the several thread this came from. The claculation examples we will use are based on a 320 hp 3.2 liter normally aspirated engine.

Base facts and Assumptions:
Required flow capacity is about 2.2 CFM (@1.5") per hp
A straight pipe will flow average about 115 CFM/sqin area
Areas of common exhaust pipe:
2" = 3.1 sqin
2.25" = 3.97 sqin
2.5" = 4.91 sqin
3" = 7.0 sqin

So, for our 320 hp V-8 engine,
Flow required " 320 x 2.2 = 704 cfm total, or 352 CFM per side for that side's 160 hp.

1. Headers.

The important things are the length prior to the collector, and the collector characteristics. Some say the individual lengths do not have to be equal, some do.

Requirements for flow In out engine, each cylinder makes 40 hp per cylinder, requiring 88 CFM per cylinder (40 x 2.2) - so header primary tube diameter required is 0.8 sqinch, or about a 0.78 inch pipe. The final collector on each side the volume must increase over the tube diameter to generate the scavenger wave and carry the combined flow volume, so it must exceed 352/115, or about 3 sqin - so a 2.25" pipe is good on each side in our example, and is in fact about what Ferrari uses.

The famous mismatch in header/ exhaust system lengths from front to back on the transverse V-8s is actually deliberate - it will spread a the torque and powwer curve widely through averaging. Exactly matched lengths will give you a higher final number, but it will be more peaky and narrow. Again, the Ferrari stock system gives a wide power band.

Similarly, in racing engines all four collecting tubes generally drop into one collector before the exhaust also give the maximal power, but at the expense of a comparatively peaky power band. Ferrari uses the "Tri-Y" design, or a 4 into two into one design which again is best at delivering a wide flat torque and power band for a street driven car.

Ceramic coating gives excellent heat insulative properties to the header, which keeps heat in with high gas velocity and lower underhood temperatures. There are several types of ceramic coating available.

Since the Ferrari has a flat crank V-8 w/ even firing banks , no crossover tube is neccesary between sides = that's the beauty of it - each side is already balanced and responds well to a true dual exhaust

2. Exhaust system

Most folks say that as long as it flows enough CFM, the exhaust aft of the collector is primarily responsible for tone quality and not so much hp increases. There are two primary types, acoustic boxes with noise cancellation chambers and absorptive with usually glass packing. Each has pros and cons, but I like the lower deeper tone of the absorptive mufflers, they are readily available and inexpensive.

The greater volume of the absorptive muffler, the lower the sound and deeper the tone. Does not matter if round or oval - the volume is the thing

One of the major determining factors is just what space constraints exist under the car - for transverse V-8s the room is VERY restrictive; for example, the room available in the Mondial 3.2 is a transvese area 35"w x18"l x 10"h. In the transverse engined cars, the lack or room and orientation of the engine is the largest challence to exhaust design - there's just not a lot of room to silence without adding flow restriction (which also can cancel noise).

According to separate textbooks and the thread discussion on dual resonance noise cancellation I've read, two mufflers of equal volume will provide more noise cancellation than one muffler of twice the volume of one small muffler, i.e, it is a non-linear relationship.

A cat acts as a muffler/silencer to some degree

Bends and flow direction changes should be kept to a minimum and use the largest available center line radius (e.g. 1.5 times tubing radius) . If a tighter bend is unavoidable, try to use more than adequate width of tubing to reduce the flow resistance.

In contrast to the headers, the primary advantage of ceramic coating of muffler systems is keeping external temps down and muffler protection.

According to Arvin Meritor engineers and BMW, to meet current legal sound silencing requirements, an absorptive muffler must have a volume equal to 12X the swept area of the engine. This sugests why many 3.0 and 3.2 liter V-12 Ferraris have at least two 14" mufflers per side.

You can "cheat" a little bit by flowing one side through double pipes through a muffler where the sound "sees" two volumes.

Exhaust tips have a large impact on final sound, with resonated tips making a large impact in smoothing the final tone. Older V-12s which also used the doule pipes per side all had singlr resonators at the end of each pipe

So, taking everything in consideration, for our 3.2 liter 320 hp engine (let's just say it's in a Mondial) driven on the street have :

1. ) s/s ceramic coated headers of at least .8 - 1" tubing diameter in Tri-Y design (e.g. Tubistyle Euro header)
2.) mounting flanges port - matched
3.) collectors opening into a single 2.5 pipe leading to the exhaust
4.) Two Dual flow mufflers per side (total of 4) maximizing silencing and tonal smoothing per length in a confined mounting space
5.) Dual resonated exhaust tips; final sound character can be tuned by differnt spec resonated/non-resonated tips.
6. To allow better fit, more silencing capability, less flow obstruction, use reduced tubing radii, going to twin 2.25 inch tubing for each side after splitting from the 2,5" single from the collector

Will continue to modify and tweak - while this may fit on paper, the area is extremely tight.

I'd be very appreciative for other pearls of wisdom folks may have.

Many thanks to everyone in the Tech, Vintage and 308/328/Mondial sections - a terrific bunch of enthusiasts.
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Ordered the parts for the exhaust system today.

4 x Magnaflow #11378 s/s mufflers @ $83 apiece
4 x #770225 reonated s/s resonated tips at $360 from Stainless Works in Ohio

Will use standard 2.5" and 4" centerline radius mandrel bent tubing.

Will connect to the tubi header with a single 2.25" pipe before splitting.

all advice welcome
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Thanks all - I do think about this too much indeed!

There will be some signifigant shortening of the straight sections of tubing as the Mondial exhaust centerline seperation is 28" to keep the original rear grill and the entire 'exhaust bay' is 35" wide between frame members. This is the challenge with this whole system - what can fit to give the desired result. Yes, it's a bit heavier than I'd like, but I chose trading a few pounds for what will hopefully be a smooth sweet sound, and very 'trip-friendly'. I lost quite a bit of weight removing the FI and stock springs, so I hope that helps cover.

Although not stated in the drawing, it's now 2.25" all the way through as the header ends in 2.25". I looked for a small enough 1 in/ 2 out muffler, but there are none that I can find, so we are doing it this way.

As said before, I'm actually not being too terribly original on this -- it is basically a 250 GT TdF or 275 GTB/4 exhaust system a bit shorter, overlapped and folded to fit.

I really appreciate everyone's advice and support. If this doesn't work well, I'll just try something else.

Thanks to all

 

Yes, and front to rear is about 18".
Height is about 10", a bit more if you remove the lower grating.
Many, many thanks!

 

The headers are for more hp, as is the complete true dual system
The rest of the exhaust system is for a high flow that gives a fuller, richer, sweeter sound that is quiet enough to be tolerable on long trips and daily use.
This in not so much a track use car, but a GT, so that's the hope.

My current single 3" in / 2 x 2.5" out 20" muffler has a volume of about 563 cu. inches to work on the entire exhaust. With this system EACH SIDE sees two 316 cu inch silencers that are also dual resonant ( not present in the Ansa I do not believe) which gives greater than linear additive silencing effect and makes for a smoother tone, also further sweetened by the dual resonated tips. Notice also that there are minimal change of gas flow direction.
If you look at older Ferrari V-12 systems, you start to notice they look liked tuned organ pipes with resonators- I have tried to duplicate this somewhat. A bit of a wag, but will be interesting to see the result.
Like I said, this system is not wholly original but combines elements of existing systems and some theory, and uprates the flow to allow for higher power. Is it hard to make - yes. Will it do what I hope? - I hope!

Scott -
As GCalo and Harmony said, it's tough fitting much back there. What I eventually used were scale sized styrofoam blocks to model. One has to cut the stubs off of the mufflers to get the 11" duals to fit, as shown in my scale drawing below. It will take a bit of skill to do it, but the guy doing it is James at Norwood's. He will not use a stock y-tube, but basically fabricate the splice where the pipes split going into the muffler. My rough design suggests that standard 2.5" CLR pieces will fit. There will also be a little hokey-pokey at the exit side, but not too much. One trick will be to connect the duals with only an inch between them. Again, no substitute for skill and artistry.

I do have some back-up plans if this simply will not fit, but we'll see!

Many thanks

rt
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