355 - disconnect exhaust Bypass

You have 2 choices:

1) use mechanics wire and just hold the valve open.
2) remove valve and insert pipe of same diameter and end fittings.

 

why would you want to do this anyway!

less torque, more noise ( an not a pleasant one) the 360 is a different story for 355 not something you should do

 

Its not so much that you get less TQ, what happens is that there is a hole in the TQ curve in the 2500 RPM-3000 RPM band when the positive pressure wave from the headers arrives with the exhaust and intake valves open. This positive pressure wave blows the fresh mixture out of the cylinder and back up the inatake. The result is noting positive with respect to performance. Away from the hole, the TQ curve is not really hurt.

Closing the valve prevents the collector (Y-pipe to third muffler port) part of the headers from functioning like a tuned pipe and results in a much lessened pressure pulse (both negative and positive) reducing the ability of bad harmonics from impacting the TQ curve.

 

Thanks for the explanation!! I just noticed when using a 'sports exhaust I seemed to loose low down torque and when I wired open the valve it was worse.

I suppose why would Ferrari go to all this trouble to produce this system only for individuals to wire it open!!

 

Keep the revs over 5k

PS Sorry. Thought you said "what's a good 'well established' way of increasing performance and 'good' noise."

Not convinced you're going to get anything massively noticeable just by ditching cats, although I guess they weigh a bit.

 

Hello 355f,

we did that on a '95 and on a '96, both EURO Spec GTS with stock exhaust.
We couldn't notice less torque.
But the "noise" at low revs is to enjoy. (Matter of taste)
With open roof you won't really suffer in the cockpit
It's a cheap trick to lift the outlet throttle.
Every 355 driver can test it for a while. Way back is easy.
Someone already tested torque with this config on a dynojet?

forza

cinquevalvole

 

well ive done dyno results with and without cats on my 355 and have the benefit of many people who have done the same thing on this site.

Removing them makes no difference and if you have a 96 on car may trigger engine check lights but more worriyingly on the dyno results we had the computer did not substitute the ideal values required for best running efficiency. The only way of doing it correctly is to use OBD11 repicators to trick the computer. To the best of my knowledge no one does box for this application.



If you have a 348 or earlier, yes remove the cats - on a lter 355 DEF not and it makes it noisier as well.

Whatever you do I can assure you there is NO difference in performance- just as they isnt with K&n filters.

 

Hello Ade,

1. Do not touch hot exhaust parts
You cant't let it be done ambulantly at your shop because the system needs
too much time to cool down.
Usually the gate opens when a certain pressure relation is reached.
This is around 4.000 revs, but it depends.
By reducing the cross section it prevents the exhaust gas to go in the muffler
immediately. We have a barrier/congestion for gas, sound, temperatur.

2. As you can lift the central gate with your own fingers (upside) you can fix
it at this complete full open position. (you need much power in your fingers!)
For testing purposes we use a long strong hose clip. Don't try plastic! Only heavy metal
Later, when decided to keep it forever, you can fix it with a bolt at the lower
end of the construction where nobody can see it. A simple bolt has to prevent the mechanism to go back in close position.
Maybe I can take some pics of this issue in a few weeks from my buddy's car.
But today a have only some pics of my car done.
On the picture you see what we call "under-inflation-can" (Unterdruckdose)
with the hose clip applied around. (355 '95 EURO)
The poor man's sport exhaust is ready to go
Each gas station can do it for you in some minutes.
What you get is a fine bass at ideling and at rolling between 2500 and 3000 revs.
You can enjoy the reaction of the engine under every little load.
If you use a Tubi or a Fuchs behind the "under-inflation-can" you will harvest
something shocking for your neighbours. No way to find home discreetly

good luck

cinquevalvole
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