355 Exhaust Manifolds (Headers)

Oz, I did like the sound of your exhaust better than the Capristo bypass delete racing exhaust.


Jimmy

 

^^ speaking of twin valve ......... there will also be a gothspeed twin bypass Y-pipe delete for the 5.2 ........ judging from the performance of the 2.7 version I made ........ it should be quite a performer ....... while also keeping that famous F355 F1 sound .........

 

Mostly, when someone wants a different sound the replace the muffler, and when they need a enw header they replace the existing headers. So the manufactures are kind of placed into a mode where the header has to be independent of the muffler and use the std Ferrari connections. Only when you replace both headers and muffler have you obtained the freedome to re-architect the system.

The advantage to the F355 architecture is that it is quiet around town, and makes good nois when you get on it. The disadvantage is two separate paths that shed heat into the engine bay plus all the weight and components.

One Can get the sound advantage of the F355 architecture by putting a bypass valve inthe muffler, giving a short path through when the valve is open and a long path through when the valve is closed.

 

Yes the 360 style exhaust system for the 355 is the one on that video !

Yes!!! The whole idea behind that project was to get rid of the bypass valve and keep a factory shielded 4-2-1 header!! It added solid double digit RWHP across the entire RPM band ..... however at that time I had to care for my elderly father who has since passed ..... it was a very tough time .... that was the biggest thing kept me from making that set up for Rob .... I wish things would have worked out differently .............. I still have the cats I bought for that setup ............. I think it would be a great idea for someone who needs a system to get those NEW 360 CS manifolds from Rob and get that project back on track!!!

 

Oz, sorry about your father, it is never easy. I have been there as well. As far as the exhaust situation goes, I was talking about the bigger companies not addressing the design problems. You took matters into your own hands for a better solution. After I gave Carm a tip for your exhaust search on google, I did a search here after I asked Technut that question and found all the threads with your exhaust development.

Mitch, the question I asked was kind of rhetorical. The newest car being 13 years old and the exhaust problem is still being discussed.



Jimmy

 

Just sent you a PM. These manifolds need Goth's magic. It would be the monster system.

Feel free to email me at [email protected] or call at 805.680.0526

 

This is going to be a fun project. Goth, I may end up just dropping the 360 CS manifolds when I head down to get my 360 CS center lock wheel conversion project underway. I'll try to pm you to get contact info. and an address.

 

Thank you Jimmy!!! I very much appreciate the good thoughts!!

The future twin bypass is primarily for fitment of stock or stock compatible manifolds and will be a while before it is completed ...........

All things considered the 360 style is much simpler ...... cost and weight wise .......... the ignition pick-up on the dyno I use had intermittent issues but I was still able to get some useable data ....... calculated net minimum peak gain on the 360 style sytem was just over 18 RWHP ........ but the throttle response and character change was phenomenal!! partly because there were double digit gains at low RPMS all the way through redline .......... as I have mentioned, I had to adjust my shifting habits as the rev limiter came up a lot faster in every gear ........

+355 .........

 

Mitch, Do you know the diameter of the factory primary tubes? As soon as I can get my hands on a set of 2.7 headers I think I am going to have some made. I do not want to use my originals. Keeping the factory design, would increasing tube diameter and possibly having them stepped have any negative effects? If increased tube diameter does not hurt mid rpm hp and torque, what would the biggest diameter that can be used? Some of the master engine builders that compete in the Engine Masters Challenge have used stepped headers. All of these engines are American V8's with massive hp and torque. Do not know how that would effect a small European V8.




Thanks,
Jimmy

 

Mine measured OD 1.51 to 1.55 depending on where they were measured. Also note, they are NOT mandrel bent (or of particularly good quality--materials, welds, collectors,...).

As you increase the tube diameter, you need to increase the length of the tube. The relationship I found for a F355 is::

pipe_length = 15.2*pipe_diameter+21.66 //in millimeters.

For the F355, a tube ID of 40-t0-42mm is optimal in balancing midrange (5500-72000 RPMs) with high end (7200-9000). This corresponds to a tube OD of 1.70 to 1.78 or just about equal to the std american V8 with 400 HP header pipe diameters. Anything smaller than 38mm really starts to choke off the top end. Anything larger than 42mm starts to make the upper midrange flabby. {Caveat with std valve sizes.}

With a 41.25 (==1.75OD) tube, one want the primary pipes to be 637mm (25.1"). The merge collector has a join angle of 15 degrees included angle and is 6" long with an output of 50.77" (2" ID 2.125" OD). The primary merge collectors immediately run into secondary merge collectors. The length between the join point of the primary and secondary merge collectors is 150mm (6") The secondary merge collector has a merge angle of 15 degrees included from 2.125 tubes and exiting with 76.2" and into a 3" diameter expansion chamber at least 12" long.

My headers have a nozel which converts the effetive 38mm ID of the oval-ish exhaust port in the head to the 41.2 (==1.75"OD). The nozel is 10mm long. I may machine this nozel into mold for the flange to simplify construction. I suspect one would see litte difference with a step, but this nozel was chosen for gas flow (supersonic gas flow!) to slow it down a little without creating a shock wave. I'm not sure what a step would actually do.

 

Thanks Mitch. According to an article I read stepping the primary tubes was supposed to help midrange torque. Mitch, I think that 41.25mm is smaller than 1.75", if my stoichiometry is right it should be 1.62".





Jimmy

 

41.25mm Inner Diameter with 2 walls of 0.063 is 1.75" Outer Diameter.

 

Hi I just ordered Nouvalari manifolds from Glenn (thanks bud!). I was wondering what the power curve looks like with these manifolds? I am concerned about losing midrange power, since this is where I spend most of my RPM's. I have heard that they have the same configuration as the factory manifolds. Any feedback? Thanks!

 

You will have no issue they are real nice manifolds close to stock configuration

 

Can anyone answer the following questions regarding cracked manifolds?

I realized my LH manifold was cracked from the insulation dust all over the left side of the engine bay.

So: is it likely I did any damage to the engine whilst driving around with a cracked manifold? I would suppose I put 50 miles on it before I realized...but not really sure. It could have been 150 miles. The dust seemed abundant one day, all of a sudden, and so I drove it 5 miles home since I noticed the dust while at a friend's house, and haven't driven it since.

1) Do you think I did any damage?
2.) What actually happens to the motor when there is a cracked manifold?
3. I noticed throttle hesitation/ flutter under acceleration. Could a cracked manifold make the car do this?
4. Is this why my check-engine light came on? I ran the codes, and they pointed to the exhaust valve. Codes:
1448 Catalyst bypass valve circuit (sounds like it works fine)
1445 catalyst temperature range performance
0410 secondary air injection. (I replace the blown 15A fuse)

Thanks, been trying to get answers, but not too many have come back as of yet.

 

1)possibly. Valves can get damaged, for one. I had 2 bad exhaust valve seats and the head was re-worked in the seat area. Guides & valves replaced.
2)see above.
3)Yes, mine did same.
4)dunno

Good luck! Hopefully no big deal to get yours fixed & running properly again.

 

Thanks for the feedback. Do you know how many miles you put on your cracked headers? I had a compression test done 500 miles ago and everything looked fine, without any big fluctuations.

 

I prob drove 175 miles on mine. I was hoping it was bad gas, but it was truly "sick" in retrospect. I didn't drive it hard, just drove it.


Sent from my iPhone using Tapatalk

 

For the air pump, the factory fix is a 20amp fuse (really). They undersized the fuse.

 

thanks for the info. When your throttle hesitated ... would you attribute that to the fuel air mixture being affected by the air sneaking in through the cracked manifold or would you attribute the flutter to the bad valve seats? some have said the increased oxygen In the fuel/air mixture makes the ECU compensate for the extra air.apparently this makes the fuel wash through the cylinder while yet others say the insulation gets sucked into the cylinder. I am wondering what made my car hesitate? Fuel air mixture? Insulation from the headers? Bad valve seats? An electrical problem? STUMPED.

 

Well, you may have "lost" one cylinder as my car did-due to valve(s) being unseated. Or I suspect a lack of back pressure makes it feel fluttering/hesitating under acceleration. In my case, the altered sound could certainly add to this sensation.