355 vs 360 Exhaust Differences

For my sins I am building a car which is a replica (not a recreation, so don't beat me up for not using a V12) of Mr Glickenhaus' 412P 0854, the using the engine and transaxle from an F355 which met with a tree. For clarity, its not porporting to be a 412P, it just looks a bit like one, no MR2 parts are used, in fact it is based loosely on a Prosports/Ultima chassis. Hopefuly I won't get flamed now!

I've got to the point where its time to design the exhaust and its causing me some problems understanding why the F355 has an active H type exhaust when the 360 does not.

The F355 uses an H pipe (linkiing the exhausts on both banks) which is unusual on an engine with a flat plane crank, as the exhaust pulses are an even 180deg apart on each individual cylinder bank already. It is this which gives Ferrari engines their unigue sound. (H or crossover pipe principles were also famously used on Ford GT40s to balance the exhaust pulses by using 2 cyls from each bank per manifold. - this making the Ford two plane crank sound much more like a single plane - listen to a real GT40 or a decent replica which uses a "bundle of snakes" as they were known exhaust - sounds familiar.....

Back to my point, I intend to use this car mainly on track, and hence it has to be reaosnably quiet, as much as I would love to use straight through pipes, I need to get it quiet.

There is not much room for silencers.....

Theory states that an H pattern exhaust knocks a couple of dB's of the sound, but my research shows the 360 does not have the H pipe. Does anyone know why the F355 has this and the 360 (and also 348) does not?

My assumption is that the F355 was the first steps into catalytic convertors for Ferrari, and early designs may have been a bit power sapping. Instead of using two actuators to bypass the cats, the H pipe and 3rd inlet into the silencer was perhaps a design signed off on grounds of lower production costs?

This point aside does anyone have any confirmation of the pipe layout within an F355 back box? Anyone with one lying around who could provide some rough dimensions would also be usedul.

Many thanks

 

For this project, I suspect that the F355-style exhaust system will be significantly harder to fit than a 360-style (prue dual) exhaust.

To this end you have 4 choices:
A) block off one of the exits on F355 headers
B) modify F355 headers
C) use 360 headers
D) fab up custom headers (actualy, probably the least expensive of B,C,D)

As you suspect the y-pipe design of the F355 system is for noise (low in the city at low RPMs) big in the country (with the foot down). The 360 system uses larger pipes from the header to the muffler and uses bigger cats. Finally note: the 2.7 system is a LOT easier to perform this kind of surgery than the 5.2.

I suspect that somewhere in the 360 muffler is an area (chamber) where left and right flows merge before going out all 4 tail pipes.

In the F355 muffler, left and right sides pass through a couple of chambers with swiss-cheese pipes before arriving in the center chamber where the y-pipe enters. At the bottom of this central chamber left and right diverge to another chamber and then their individual tail pipes. Mostly the chambers are connected with swiss-cheese pipes to allow the higher pressure waves to disipate but the momentum of the flow to continue unrestricted.

If you just use 4 glass-pack kind of mufflers you will remain at or above 92dB (my guestimate) so if you need real streetable sound levels, a real muffler with diversion (tone) chambers is going to be required. 4 glass packs, 2 before an x-pipe and 2 after will put you near the legal limit for most tracks, and an anoyance on the street.

A big part of he problem is the lack of length you can fit in the mid-engine configuration. The ideal length is 3 times the header length ("Design and Tuning of Competition Engines") with X-pipe at the 1/4 point, a resonator in the middle of the entire system, and muffler at the 3/4 points. These are relly difficult to package in a mid-engine engine bay.

The second problem is keeping all the heat away from thing that don't like heat.

 

Thanks for your reply Mitch.

The only way to do the headers is a custom fab as they need to run through and around the chassis to get decent length (say 30") before the collector. I'm planning on 1/3/4 OD primaries. 2.25 inch post collector.

Having done a bit more research today I have established that an X pipe configuration is going to enhance silencing efforts and also mask the fact that the car contains a V8 not a V12.

Space is very limited - there may be slightly more room behind the clutch for the silencers than in a 355 as there are non of the gizmos - the car runs no airboxes, air pump etc. and I have spoken with a few exhaust specialists and they have reccomended an X-pipe configuration inside a single box.

The 412P has 4 outlets - my idea is to use 2 full time and have 2 which have either no baffles or less baffles which are actuated by some solenoid valves. This means the car is loud when it needs to be and quieter (hopefully >98dB) for the fussy tracks (Goodwood etc.).

Length is the biggest issue. I might set the system up so the headers gather forwards before taking a 180 degree bend back to the collectors and onto the rear. Getting the X-pipe anywhere near the manifolds is near impossible. GT40 approaches this without abiding by the rules though.


Heat is less of an issue - I'll get the finished system Camcoated, and also its possible to duct lost of cold air around the maniflds from inside the rear wheel arches - no liners like a modern car.

 

Suggestion: Since you are going to run 2.25 (or maybe 2.5) tubes, you might be able to mock-up the system using flexible hose (like from a vacuum cleaner) to get an idea as to where the bends need to be and how to route this and that before ordering mandrel bent tubing.

In the car mentionied earlier, the X-pipe crossover is right above the clutch housing with glass packs before and after. This puts the X-pipe closer to the 2/3rds point than the 1/4 point, but for the challenge car it works. Noise level is track tollerable.