308/328/Mondial performance exhaust development

I am considering upgrading my exhaust by adding European Larini headers and switching to a true dual system instead of the current both sides dump into a single 3" collector. Since I document all of the car's upgrades here, this is the new project since I am still waiting on my hero Mark Eberhart to discern if head porting is viable.

The big reason for a 180 degree flat crank is optimization of cylinder bank pulsing as we all know. It seems that if I kept both sides separate with approximate equal resistance I would better be able to utilize this attribute (The induction is already split with dual plenums). The mismatching of Ferrari exhaust is well known, but I am not sure of the amount of effect.

The first issue is with the headers is ceramic coating - I have heard that coating inside will keep the heat in and accelerate flow while and external coat will lower temperatures as well. Since I will be losing the stock insulation jackets around the headers, I do have concern about accesory heat soak and transfer (i.e. starter).

The second issue is sound volume while keeping performance as I use the car on longer trips and Grand Touring. My goal is to have a smooth low idle with lowest possible drone at about a 3750 rpm off throttle cruise, and a low "woom" when under accelleration more reminiscent of classic Ferraris that the high pitched wail of modern F1. I am pretty happy with the smooth low toned GT sound I have now with the bespoke single large Dynomax silencer followed by Ansa resonators (see old threads); this system was arrived at after multiple other solutions tried, including tubi. My experience shows that the fiber filled mufflers have a relatively nicer tone than an all metal acoustic box type. I am curious if two smaller silencers will have the same overall volume decrease as the one large, not to mention the size/space restrictions. The Lambo Urraco/Jalpa, reknown for being about the sweetest sounding V-8, uses a split system with two small silencers per side and resonators. The other option is to have them flow through one larger muffler, with separate non-communicating paths then terminating in the longest and widest resonators available. My experience has shown that tip resonators make a big difference in the smoothness of the sound. While the Ansas I use are 2.75" wide and 10" long, I have found a nice high quality unit from Hooker with dual 3" wide tips I may or may not try.

Questions for the group:

1. opinions on ceramic coating of s/s headers? Inside/outside?
2. two separate silencers or one large silencer with separate flows?
3. Will the true dual system make that much of a difference? If so, what difference?

Many thanks as I try to develop the best exhaust system possible for the car. Will keep everyone appraised of progress.

rt

 

excellent thread. all i can add is that my original thermo reactor on my car was a ticking bomb and i had it cut off. i now have a Magnaflow dual in, dual out. the exhaust on this black 77 GTB that had the TR is different from my old red GTB that had the factory Ansa on it. the Ansa system had longer mid pipes between the muffler and the manifold. my car has what look like headers straight off the head , so my connecting pipes to the muffler were very short. i paid $525 parts and labor to a local custom shop and i love both the sound, the weight loss and the performance gain from the Magnaflow. i am sure there are better "tuned" systems out there for the 308 though.
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Very nicely done system CR!

From my experience, here is a summary of lessons in doing your own exhaust, at least with fiber packed exhausts; all metal 'acoustic box' mufflers are more tinny and metallic and harsher (like a tubi or flowmaster)

The larger the muffler volume, the quieter and lower pitch;

Flat crank mufflers do NOT need a crossover or 'x-pipe'

Resonated tips have a huge effect (surprised me) - they very much smooth out the sound. That is to say a more pulsitile sound becomes more of a purr. I went from three inch non-resonated tips to 2.75 resonated with about 10" of resonator and the difference was immense, especially at idle and cruise (off-throttle).

Cats do make a difference, especially in weight and operating temperatures.

My simplified design criteria: you can roll a golf ball from one end to the other

All mufflers have a finite service life, even s/s

All natural metal mufflers heat stain, INCLUDING and especially s/s tubis; ergo, there is nothing wrong with a black silencer.

Haute couture mufflers do not have the monopoly on excellent fabricator/welders.

All additions or comments welcome!

 

Here is some good info.

http://www.ferrarichat.com/forum/showthread.php?t=103116

My car is in there somewhere (red/tan with the magnaflow dual set-up).

No real issues with heat so far in over a year.

No real "tunning" done per se, just some straight back pipes with magnaflows.

 

Which tips are these, as they're the best looking ones I've seen
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Went with Jet-Hot on the stock Euro headers, not sure what difference it would make to SS units. On the car here, the Jet-Hot coating allows for better cooling, are said to flow better due to the very smooth surface, and the coating will add life to the headers.

If it was me, i'd go with cherry bombs muffler, resonator tips, and adjustable Traps at the end. The Traps allow you to increase sound silencing when desired without causing much air flow reduction. During track days or when you want to hear the car more you can remove/reduce the Traps easily with a screwdriver.

Maybe, i can't say for sure as the PO did a true dual system on the Euro 308 here. More flow can be good, but remember that some back pressure may be good to keep torque in check. Am curious, have you dyno-tuned your car and if so, what were the #'s?

 

Best I remember, best rwhp was about 243 SAE hp and rw torque at 204 @ 5000 or so. Done on a Dyno-jet in 100 degree weather.

Rival - those are dual 3" open nonresonated tips bought OTC at a local race shop - will try to find the brand; If you want dual 3" resonated Hooker makes an exceptionally nice set.

 

i did a magnaflow tru dual exhaust on my euro carb 308 4 years ago. surely woke up the car, i do get some popping on deceleration tho. its the onlyway to go as far as i am concerned. a noticeable improvement over the stock or tubi design....

 

Here's a picture of one of many exhausts with the single inlet I tried - s/s Magnaflow with the dual 3" UNresonated tips as shown from the rear below. This s/s muffler is a bit smallish, and with the large tubing (3" in, 2 X 2.5" out)followed by unmuffled tips was very angry and pulsitile - however it was smoother and about as loud as a tubi - all for $500

This is followed by a nominative sketch of the proposed dual system, similar to the older Borla system, now N/A.
Note it passes the golfball test. I am using one large silencer instead of two to get the largest volume of silencer for the least weight.
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Here is a survey of V-8 systems that I have collected. Sorry if yours is in here and uncredited!

1. Borla 308 GT4 system
2. Ansa sport system
3. 246 Dino (note separate silencers)
4. Flowmaster
5. QV Tubi w/ cats
6. Wow - only cats and tips!
7. My old tubi showing heat dicolration and wear.
8. Lambo Jalpa - a dual can system producing a very nice sound
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Russ,

Muffler design is an art and science. I have years of experience designing and developing advanced free flow exhaust systems.

The idea is to get proper pulse timing and get the pulses in balance so that you yield a sweet sound throughout the range.

The well known high end systems do not do that regardless of what the makers say, and they are not quality free flow systems. Their goal is to yield an F1 sound in a specific frequency band. Who really cares about that based upon the multiple complaints folks have stated of their to be or not to be systems?

They achieve this by using smaller and restrictive tubing w/in the muffler. What kind of a free flow system is that? Since you can't see within the unit and since no one shows a cutaway, you don't know that.

However, if you dynoed the stock vs one of these, you would be surprised to discover that the replacement might be MORE restrictive than the OEM unit! All of that for sound? Big price to pay for little gain.

The design you show with the orange/red packing is a smart design, but if you can separate the mufflers per bank and then put two resonators in line rather than one large one, you can yield a very, very sweet sound. This arrangement would tend to better balance the exhaust pulses.

Keep the banks separate-no x-over pipes. OEM's do that because they only care about silencing the exhaust not augmenting it.

Of course, there is quite a bit of engineering that goes into this to get everything properly balanced.

As to packing, very high grade and high temp fiberglass packing makes the best silencer. Any internal metal has no ability to damp resonance. It is used primarily for support, but some use it to achieve the higher pitched sounds.

Keep playing with it, and you will result in a great product.

 

Greg -
Many thanks!!

You mention the use of two resonators - does that mean two separate cans or a can and a set of resonated tips?

I've sketched the two options below in Type A and Type B.

Type C is a variation that can be adapted to type A or B that splits the flo in the muffler instead of the tips.

The goal is a deep smooth sound, not loud but tolerable on long trips.

I have often noticed that the classic V-12 Ferraris almost always use two sets of resonators per side followed by resonated tips.

Any and all comments welcome.
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Russ,

Type "B" is what you want. You get balanced length in's and out's, and then you get a dual value resonance silencing. Type "C" does not give you that.

You also get a better weight distribution of the muffler itself which is easier on the hangers and vibrates less overall.

The whole idea with exhaust is to ensure that everything is as balanced as possible. Remember "equal length" headers from the 60's and 70's. They were then referred to on the Indy cars as "spaghetti".

V design engines are all about balance. You then want to keep the exhaust note in balance and keep the banks separate for exhaust. You mention what you have seen on the V-12 muffler designs. This is why.

Front engine cars are easier to work with, because you have tubing and room to layout the resonators. Tubing itself has some silencing capability but not much.

In the 60's we had flexible exhaust tubing that was great. It was itself almost a silencer. The problem was that it would collect the exhaust moisture and rust through quickly.

Another thing is to keep the ID of the piping the same all the way through.

I can't give away too much more as I am working backwards on exhaust designs for some of the 3X8 series.

 

Greg - many thanks for a terrific explanation.

Any comment on type of tone (low/high frequency) attenuation and the size of the packed silencers?

What is dual value resonance silencing?

Also - has anyone ever seen a ceramic coated mffler in addition to ceramic coated headers? Any value added in keeping in the heat? Velocity?

 

Russ,

We are dealing with simple physics here. It's referred to noise cancellation technology. You try to either a) dampen the resonances that cause the multiple resultant harmonics or b) you create the equal and opposite frequency to net a 0 value. This then cancels the wave.

For example, if you take a speaker driver and hold it in free air while it's playing you get little output. Put that same driver on a baffle whose length exceeds the longest wavelength that speaker can create, you then get substantial output.

The reason for this is that what comes out the rear of the speaker is 180 degrees out of phase of what comes out the front. In free air you are, therefore, getting the nearly full cancellation. On the baffle, you are separating the frequencies, and you then hear substantial output.

In proper muffler design (and I emphasize that) we are trying to get similar resonances out of balance so they cancel. This then creates the exhaust harmony. Proper design achieves silencing the entire spectrum of exhaust frequencies. it is not tuning to a specific resonance to emulate an F1 racer.

You are then left with the resonance of 1) the exhaust gas explosions and 2) the air under pressure that is escaping.

So, by using the multiple resonators, you cause the above to occur by breaking up the waves rather than by passing them all through one resonator in one pass. This then yields the dual value concept I mentioned.

A one can design is an inexpensive way to make a muffler. Think of this when you are asked to pay $4K for it!

Rear engine cars are difficult to exhaust tune due to 1) limited tube length, 2) limited resonator space, and 3) proximate engine heat.

The 3X8's have mufflers below the engine. The 355 on have them at engine height. Which models sound better to you?

BTW, removing cats is not the answer. They are silencers themselves.

Hope this helps.

 

Greg -

I really appreciate the great input! As you also said, there is the practical problem of space available. From my experience with the Mondial, accounting for tubing bends and fitting the exhaust through the original openings in the rear grill, the max side to side muffler that may go is 20". Typically, the smallest aftermarket universal fit silencer has a shell length from 11" to 14" (I use Dynomax and Magnaflow as the basis).

One option to get two silencers would be close staking of two straight through duals. This is Type D below (quickie sketch)

So, would this allow the dual value resonance silencing, or are the seperates better or required? I have seen 250 GT SWB with two twin in and twin out resonators per side, but not with opposing flows (although separated in in the packed muffler)

The other option where type b could be used would involve longer but smaller volumed mufflers and more 180 degree direction changes - we'll call this type E.

Both still pass the golf ball test, but I was taught that volume of the muffler brought the sound down, and Type E does not have very much volume although a large resonated area. Type D has good volume, but unsure of the effectiveness of the dual value resonance.

Many thanks for a great discussion. All opinions and comments welcome.
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one thing to consider is that the flow of gases like liquid do not like 90* bends. each bend will cause a 'stacking' of pulses and a hot spot. the less bends the better. the same goes for reducing the flow of gases, the energy pulse is transfered to heat. if you painted the stock exhaust system where the paint flakes is the location of restrictions due to the heat build up.

i've got a great physics book 'the refigerator and the universe' that handles gas and thermodynamics in a very understandable way, well at least if you've had a course or two in it. anycase as Greg has pointed out there is science and art in the design of exhaust systems. not to detract from Greg but if you've got the coin $$$$ Jack Burns is the guy who can fab up the best system for you. AKA Burns stainless. but get in line behind the NASCAR and NHRA boys he's a BUSY man! oh and he's done the F1 Ferrari inconel periscope headers.

i've got a great article by him about the design and layout of basic systems and what to look for, i'll try and scan it this weekend when i have more free time.

 

Russ,

You do not want to add any bends as Scott has mentioned. So, stay away from the recent designs you just did. That would defeat the whole purpose of your design.

BTW, the "golf ball" test is a way to tell you that you ahve no restrictions w/in the muffler, but it has no actual effect upon design.

Keep looking for small resonators. There are manufacturers other than the ones you mentioned who may be able to help you, and check with the one Scott mentioned as well.

Try: http://www.ansaautomotive.com/index.html They may be able to sell a few to you.

I am presently working with a European firm who will be making mufflers for me, and I will have smaller blanks available. I just don't have a time frame, however, on their availability.

Take your time with this design, and the results will pay off.

Any other help you need let me know.

 

here is the layout on my mondi 8, euro headers and test pipes with tubi muffler if you call it that.
warning crude dwg!
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Thanks Scott and Greg - will shelf Types D & E.

Scott - your Picasso exhaust resembles my initial thinking down in post number 9, only more modern artish

Greg - thanks for the link! I was noticing the Ansa sport muffler for the 328/Mondial also looks like a variation on the same design.

I'll keep working on more space ideas and look at other silencer options. My worry is with the two smaller resonators is that while the sound will be good, sound attenuation will not not be. The requirement is to be a street 2+2 GT and not a 'boy racer'.

Looking forward to the scanned article! It is quite interesting and enjoyable to understand how all of this works and solve the problems. Many thanks!

 

sorry - should be 'shelve'


Interestingly, Scott, your 'tubi' exhaust system as drawn has the same amount of 90 degree bends and same basic path and length as both types D & E which you say are bad.
Hmmmmmm.

 

great thread!!! wow!

my question: does the Magnaflow muffler keep the exhausts seperate in side the housing , or do both banks "mix"? from what Greg has said, this is not desireable.

there was a huge in crease in felt performance with the new exhaust from the old , swollen thermoreactor my car had. but i am wondering if there is something better out there. i will state that the $500 or so dollars i spent parts and labor for the local guys to put this Magnaflow on was a deal. i would however, consider another system if its a better design for a carb 308. we need all the help we can get, our cars are SLOW!!!!

 

mine acctually has only 1 90* and thats the one coming down the front of the motor. the rest are 'U' turns and there are only 3 in total. the D & E scketch show 5 with out the header turn connected. hopefully all that was clear as mudd

my caution was to avoid as many turns as possible, i'd change mine too since i don't have cats and cut out those extra two leangths. more like the GT4 system you posted up in the pics.

i'll say mine is loud and 'barks' everyone that hears it loves it and says it sounds great. doesn't sound like any other 308 i've ever heard. highway drone isn't too bad, it's low and rumbly. oddly with the cats on it was painfull to drive at highway speeds, i really mean it hurt your ears it was so bad! removed the cats tuned the motor back to run right and she now sings. i can get a F1 scream when ripping thru the gears but at idle sounds like a small block chevy with a bark.

 

not if you join me on the dark side, MUWAHAHAHAHAHA!

ohhhh a black darth 308, mmmmm

 

U turn = 2 x 90 bends

Both systems have a total of 8 where they meet the headers.

I agree we need to keep the degree turns to a minimum. I am still trying many permutations of muffler arrangements.

Will pulses in separate pipes in the same silencer effect the flow or the sound over seperate cans?

There is room for two single silencers and one shared (non-communicating pipes) - will that allow dual resonance?

Many thanks
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