Exhaust bypass valve on a 500?

[RobXjcoupe]

Was having a chat recently to an owner of a new Aston that sounded like it had a de-cat exhaust. Owner of Aston then demonstrated exhaust bypass via a switch on the dash.
So just wondering is this possible to fit to a cat exhaust Griff 500? So for mot, valve shut exhaust gas via cat and emission pass, then flick a switch to bypass cat and have that wonderful straight through v8 noise.
Has anyone any knowledge of fitting something like this?

[RobXjcoupe]

phillpot said:

Given that the "cats" are in the manifolds it could be tricky

I have the act manifolds with the 2 separate cats. I suppose even if a bypass pipe could be fitted the valve would get too hot being that close to the engine?

[RobXjcoupe]

Belle427 said:

Most I've seen just bypass a silencer or two.
Can't see how it can bypass cats if it's a factory option.

I’ve had a little read up and the Aston does just bypass a silencer or two as you say. It did sound rather angry when bypassed though. When I run the cats on my 500 it is noticeable quieter. Put the straight through pipes on and it sounds angry. I do have a small silencer on the rear so maybe it’s that I should be looking to bypass? I think the rear silencer is a jp sports silencer

[RobXjcoupe]

Yes these are very raw and bolt on.
I suppose I’m looking for a more factory fit. Something that still uses the original exhaust outlet but switches inside a silencer.
Looks like I’ve just given myself another project

[RobXjcoupe]

Oldwolf said:

Let us know how you get on please

I've got a Chim 500 and wouldn't want to have it permanently louder as it would make long distance tiring but switchable might be fun!

Early days yet. It doesn’t look like it’s a tried and tested mod on a TVR.
So picture below is of how I thought it would look like in my head. The picture is of an Aston part so prohibitively expensive new.
So if I can modify the rear silencer currently on my Griff to something similar it looks fairly straight forward. Probably not an absolute performance enhancement but would be great to simply hit a button for extra noise and again to mute it. Then the cats can stay permanently fitted and no carbon monoxide poisoning headache when driving.

[RobXjcoupe]

Belle427 said:

The Act cherry bomb system is the best sound I've heard on a RV8.
Is this not an option?

The initial idea was something to flip between a cats exhaust for mot and then straight through for a bit of extra noise. But without the hassle of unbolting and bolting up different parts.
To do that requires a bit more engineering than I’m willing to do as exhaust manifolds are a little expensive to chop up and weld to try out something.
Then we have the bypass valve. So the cat works as a silencer which legally needs to be fitted on a 500. I also have a small rear sports silencer fitted. It sounds nice but better without the cats. If I bypass the rear silencer via a valve I have the option of nothing after the cats and quieter when on a longer constant run.
The body is off my car having the chassis restored. Could be the ideal time to measure up and convert the rear silencer. That’s what I was thinking.

[RobXjcoupe]

Belle427 said:

The valve in the front pipe somewhere would be the easiest option, the yanks do it a lot on their cars.
Exhaust fumes would be my only concern, not sure how it would sound though.

Exhaust fumes would be my concern also with just a cut out under the car. It needs to cut out within a silencer or loop around a silencer.
Since looking into this I’ve started to noticed you can see a valve throttle from the bigger engined new cars. Today a new bmw 1 series had twin exhaust pipes either side of the rear bumper. Left hand exhaust I could see a valve. Right hand exhaust was open. So I would imagine the valve opens as the revs rise to give more of a performance growl sound.
I think I can modify a rear silencer similar to the Aston db9 one. So my TVR silencer has two inputs. I need to remove the top of the silencer, create a loop with a straight through part and silenced part. Then manually open the straight through loop when more sound is desired. Sounds relatively simple. I think the space constraint is where the engineering is required.