So I'm making my own valved exhaust for the 348

I've been beavering away at this exhaust for a while. Struck it up for the first time yesterday and am so far pleased with the sound! I've only tested no load revving up to about 3 or 4krpm though.

Next phase is to build two bypass pipes with extra silencers that will come into use with the valve closed. I'll update as I produce those parts as it'll be easier than explaining the way I plan to make this work.

Please ignore my terrible welding I'm not a professional it will all be hidden in heat wrap eventually anyway!

My aim for this exhaust is to have the valve open for the majority of the time and only use the more silenced bypass route for when it really needs to be quieter. Valve is on a remote controlled on/off using an EP valve and engine vacuum.
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Yes I wanted to keep the original heat shielding but just couldn't get it all in :/ so I'm going with exhaust heat wrap. Are you going to run the bypass into a cross pipe or keep them separate?

 

Electrical Engineer, this is what happens when we're let loose with a welder!

 

Like this? I'd expect this to be almost as loud as open manifolds! It does have a cross connecting balance pipe, although so close to the end not sure it would do anything.
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Just as food for thought I ran mine with separate open pipes straight out of the original cats just as an experiment, it was loud but didn't sound nice. I figure to get the best sound it needs some form of cross pipe or H section.

Look at the RareFab design with the associated videos, although that exhaust is totally straight without silencing so is a little bit harsh.

 

The oem pipe pre and post cat is 2.25" so that is what I have used.

I've then gone to 3" for the merge pipe which results in a very small reduction in overall cross section area, then back out to 2 x 2.25".

 

Yes it will reduce back pressure, mainly due to removal of the cats. Whether it will burn valves is like asking if a cambelt will snap, there won't be a definitive answer.

In the manual there are different specs for catalyst and non catalyst vehicles for valve clearance and valve timing. I'll be checking these to the non cat specs during the engine out soon.

I guess if you were really concerned you could have individual cylinder lambda checked on the dyno to check for a dangerously lean conditions.

 

No dyno tests, I'd expect some benefits from ditching the cats but beyond that I'm not really concerned about power gains on this car, will just see if it feels any different and maybe do a dyno run in the future just for the hell of it

 

Agreed, however the car had an Ansa sport exhaust fitted when I got it so there is no real baseline for a standard setup anyway.

One thing I'd be interested in trying is with the valve open and closed, it should generate more torque at the lower end with the valve closed in the same way as the yamaha ex-up system.

My plan is to link the exhaust valve to the central intake valve so they both open at the same time at the top end. Then have an override to open just the exhaust valve on the remote for the loud setting at all engine loads. Really I'd expect it to lose a bit of bottom end on the loud setting.

It'll still be a few weeks before its all finished due to limited time, but will just have to see how it turns out.