408 exhaust questions
 

My 408 with Chrysler 360 fitted has a custom made exhaust that is very loud. it uses 2.25" OD pipe and no mufflers / silencers to speak of. Just straight through glasspacks. The glasspacks are 3" diameter and fitted below the original heatshields. Each pipe is suspended at only two points - just before the rear axle and just before the tailpipe. However, the hangers are metal, not rubber and not flexible.

I am planning to change this system but probably cut short and keep the downpipes that are on there.

Looking at the parts book it seems the original arrangements was a downpipe that extended straight to the muffler/silencer then a second pipe out to the back of the car.

Was that second pipe straight? The parts book makes it look like it may have bends in it to move the tailpipe position towards the outer edges of the car.

Where were the factory hangers fitted? It looks like one behind the rear axle and one at the tailpipe.

Were the factory hangers rigid?

Thanks for any help.

David

Take a look at the resources on this same site and you will see that the 408, 409 and 410 shared the same system with three mounting points each side, the front being suspended from the chassis cross member at the rear of the engine bay, a second behind the silencer and the third under the boot floor close to the rear of the car. The trouble with this arrangement is that engine deflection under toque gets applied to the down pipes via the manifolds and can result in fractured exhaust manifolds. I believe that the arrangement was improved on the 411s with the front mountings being carried on a fairly simple A frame mounted on the gearbox which allowed the front of the exhaust run to move with the engine. I believe this might be preferable to having no front mounting and asking the manifolds to take the load, which from what you say sounds to be the current arrangement on your car.

You are right the tailpipes behind the silencers are not straight, they splay outwards and upwards, you can probably get the outward splay right by reference to the rearmost mounting point. You’ll need to get the exhaust exit point as close to the boot floor as you can, even then it’s all to easy to hit obstacles when reversing and to scrape them on the ground on car park exit ramps etc. Neither of which are likely to improve the manifolds or the exhaust system as a whole.

As you probably already know the final touch was a short stainless steel deflector

The original hangers were not rigid, but neither were they particularly sophisticated.

Roger

Thanks, Roger. I did look at the resources but only found this pic which seems to show only 2 hangers per pipe.Resources - Bristol Cars - Owners and Enthusiasts Forum

Having a non-standard engine, I haven't got the exhaust manifolds shown in the parts books. Mine are standard Dodge items for the 360 and have very little clearance to the engine bay sides.

David

David, Sorry, you're quite right, I started from the viewpoint of a 410, the 408s didn't have the front mounting, which were added, one presumes for good reason, on the 409s and then carried across to the 410s, and then, I understand, changed to a mounting via a frame on the gearbox on the 411s. Also, from my experience, for good reason.

For what it's worth I attach a not very good photo of the "A" frame mounting off the gearbox that has now been adopted on my 410.

My car also now has swept tubular exhaust manifolds courtesy of Spencer Lane-Jones. They are fantastic pieces of knitting which have considerably improved the cars breathing and appear to have reduced the under bonnet temperature, not, I imagine, that the latter is too much of a problem in Novia Scotia. They leave no space at all at the sides of the engine bay!

Roger

Nice looking headers there, Roger. Maybe one day on mine.

I am interested in the addition of a 3rd mount at the front on cars later than mine. My two exhaust hangers are rigid and I thought that odd. I'd expect rubber in there somewhere. So I am intrigued by the mount you picture because it looks as though it holds the exhaust pipe rigidly in relation to the chassis. Am I seeing that correctly? or is the upper end of the frame on the transmission? Where is there any flex in your setup?

David

David

No, you’re not seeing that correctly, the “A” frame, not that the A is closed at the top, is mounted on the rear of the gearbox, not the chassis, so the exhaust system up to that point is still insulated from the chassis by the engine and gearbox mounts

The two rearmost mountings each side should certainly be mounted on rubber.

Tony Crook claimed that the use of mild steel exhaust pipes alongside stainless silencers made for a quieter exhaust system, but it perhaps as well to remember that he was extremely good at writing up his product

Good luck

Roger