Front engine V12 exhaust question

On my Daytona, I removed the center mufflers and substituted straight pipes, and just used the resonators. When I had the engine rebuilt by Carobu engineering, they advised me to have crossovers put in between the dual pipes running on each side.

They took dyno runs before and after the change, and it showed significant gain in torque between 3500 and 5500 RPM.

I could post a picture of the crossovers, and of the dyno results if you need them.

 

Please do.

 

Look at you 12 cylinder as two 6 cylinder engines which are beautifully harmonically balanced.

Forget the X pipe and run them through on each side.

You will gain more engine efficiency and you'll have a nicer sound.

 

Guys on the 550M section have proven on dyne that the 550M makes more power with straight pipes not H or X. However, it is known that the H or X does something to cut the drone in the 2800-3400rpm range when first gen tubis were used. I just recently put straight pipes in my 550 center section left the stock cats and left the stock mufflers and the sound is way better with no drone. So there is another datapoint on what the 550 guys are doing. Also, on the 348/55 board we have a resident exhaust expert who not only fabs his own stuff but worked as an exhaust engineer if I remember correctly. We talked once and he was saying that H and X works on V8's but straight pipes make more poswer on paper on V12's for some reason that is beyond me. Anyway in the end it may just take some experimenting to find the sound you want and or dyno time to fine the power too unless others with your exact car have done the modifications before you. I was lucky with the 550 that many guys before me did all the work.

 

I just got done, and I mean 2 days ago, putting a Strebo system on my 400i. This system has no crossover pipes of any kind. Basically, I am running 4 separate exhaust systems. The sound is unpleasant with very harsh resonance from 2800 RPM and up. For what it is worth, a while back I had a 1996 Jaguar 6 liter v-12, it used an x crossover from bank to bank and it made way more than enough power. I am goin to post a realted question on the 400 section now

 

Carl,

As I stated a front engined 12 cylinder is the best to design a muffler. It has inherent excellent damping characteristics, and the lengths of tubing add to that.

The X pipes are a gimic that car manufacturers use to cut down development costs. They do not always cause harmonic harmony as some have said.

For all the 12 cyclinder cars for which I have designed exhaust systems, they were separate pipes front to back. Always a small resonator just after the cats (or headers depending on the year) to balace the harmonics up front, then usually a center section, and then rear resonators. All muffler sizes determined by considerable experimentation.

The final tuning was always done at the tips. Some were with packing, some w/o, some large diameter, some small diameter, and then the length of the tips was critical.

There is more of a science then thought but that's how good exhausts are done.

I cannot speak to the current Stebro. I knew of them from the 70's when the comapny was run by Peter Broeker who started it. He always reminded me of Dan Gurney.

Good muffler desing is an art.

Russ Turner built a great muffler for his Mondial with my advice. He had a sound clip of it that was very nice.

Oh and BTW, every muffler I designed provided daylight all the way through - No baffles and no restrictions.

 

i closed off the little bypass pipes on my headers and here is what Stebro did for me to replace the OEM center sections on my carbed 400...

no crossover pipes, no flat spots in the rev range (but it is an auto...), Ansa silencers and a sound to die for...exactly what i was looking for.

but, as you can notice at the front, they took some 'work' to make them fit...buyer beware with Stebro but, again, the sound is perfect, IMHO.

the pics are from '06 but i've run this setup since '04...no resonance, 'drone', 'thrum'...it's perfectly civilized, even over long distances.
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As requested, here are the dyno graphs for my engine, with and without the crossovers seen in the picture. Note the sizeable torque "hole" from 3500 to 4500 rpm without the x pipes. HP is slightly higher without the xpipes in the range from 4500 to 6000, but falls off faster above that. (Thanks to Carobu Engineering for the curves and the photograph).
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So your crossover is for one bank? Meaning you still have bank to bank isolation? Does that still support the twin or dual six comment that crossing over the banks is not recommended? Or did I miss something?

 

Ah ha!!!
What you really have is acting like long secondary header tubes - that is where your torque is coming from vice the original setup my good man. Well known behavior in header design.

I think what most are speaking of here are bank to bank H- or X- tubes, which are not neccesary.

Very nice installation, obtw.

 

That example is a band-aid redesign because the header design is ancient. Those collectors are a really terrible. This is a lot more modern (except the sidepipes )

http://www.thebestemployee.com/forum/showthread.php?t=178691

3-1 collectors should look like this with smooth transitions:
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Crossover works between the front 3 cylinders and rear 3 cylinders on each side. No side to side connection.

FWIW, Burns Stainless made the X-pipe sections, and then welded them into my straight pipes.

Car was designed 40 years ago, technology has changed! But I didn't want to rework the fine Euro headers on my car.

Besides, 415 hp is plenty of power.

 

Works for me- I think it's awesome and I'd love to have an strong old lady like that! Great job!

 

Why anyone would want to take a V12 and turn it into four three cylinder engines is beyond me. A simple set of six cylinder headers going into one collector with straight pipes and central or rear mufflers would provide better scavenging and more horsepower and torque all through the rev range. Guess us late model V12 owners with catalytic converters lucked out, because the single collector is the only way they could economically make the converters work.

Yes, I owned a Daytona, and electrically it was four three cylinder engines. Would like to see what the competition Daytona exhausts were like as a comparison.

Taz
Terry Phillips

 

The benefit of the x-pipes was first shown to me with dyno results on a 365 GTC/4. The C/4 was stock, I believe. Then they demonstrated the results on my car.

I don't know about the relationship to what was done to my car, which is not really that much. We went to 10:1 compression pistons, flow matched the intake and exhaust porting, and replaced the points with an optical system.

I think everything else such as cam timing, ignition advance curves were set to stock specifications. The carburetors were tuned via dyno runs, as was initial ignition timing. Being a Euro car, it already had the nice headers.

Yes, the youtube video is of my car. Note that these runs were taken with my entire exhaust in place. So the car sounds just like that on the street.

Reasonably quiet around town, but when you get on it, it screams.