411 (Series 3-5) Exhaust Tailpipes

[John Keighley]

Could somebody please let me know how far the exhaust tailpipes extend past the rear bumper on the Series 3-5 411s? I have changes the outlets to my 410 to tidy up the overall appearance of the rear of the car and while the result is far better than it originally looked, I am getting two problems:

1. When the windows are opened on the move at any speed, fumes make their way into the cabin.
2. The rear bumper has exhaust stains after the car has been run.

Obviously there is a degree of some low pressure areas around the rear of the car which is causing fumes to be sucked forwards. I suspect that because the outlets terminate directly under the bumper, the disturbance to the air around the bumper is directing exhaust in other directions instead of straight behind. Extending the tailpipes is obviously the solution but I'm not sure how far this should be. As can be seen, the exhaust stains on the bumper are quite evident.
John Keighley.

[Bellerophon]

Bristol did tests along the runway at Filton on the aero dynes exhausts and
found that if the exit was at the back of the car the fumes became
ingested, hence the cars had an exit on the RHS and thus prevented the problem.
One would need to know how the air flows over the rear of the later cars to
see where to place the pipes, wether Bristol did any aerodynamic work on the
later cars I do not know.
My regards,
Bellerophon

[Rubbond]

Amazing that you should know this!
But how could exhaust fumes get back into the car from the rear of the
vehicle?
Surely there would have to be a leak somewhere in the engine compartment??

[Kevin H]

Originally Posted by John Keighley

Could somebody please let me know how far the exhaust tailpipes extend past the rear bumper on the Series 3-5 411s?

John,
The answer to your question is they don't, extend past the rear bumper that is. BUT, there is something else you should know - on the Series 3-5 411s the exhaust pipes exit downwards. The tailpipes are blanked off a couple of inches inside the pipe. See attached photos

According to legend, Bristol did this because under certain conditions (50mph with window down 1 inch) exhaust fumes were sucked back into the car. Air flow around cars doesn't always do what one expects it to do!

[Andy Bernard]

Don't know about the 410, and I may be stating the obvious, but the 411's
exhaust pipes are blanked off a few inches in and the gas exits via holes in
the bottom of the pipes, I believe to get round the problem of exhaust gases
entering the car.

I don't have any problems with fumes, only 4 round black marks on the garage
floor from starting from cold.....

Andy Bernard

[Kevin H]

John,
I meant to say that I have seen numerous earlier V8 Bristols with exhaust tail pipes that angle downwards at the end, often with what I suspect is an aftermarket chrome tailpipe extension.

I should also mention that the Series 3-5 411s have a vent in the rear wings through to the cabin (beneath the rear parcel shelf) which could also have a bearing on why they had an exhaust ingestion problem in certain conditions.

A dodgy boot seal can be the culprit if there is any airway, regardless of how small, between the boot and the cabin.

And as rubbond said, exhaust smells can also be down to a leak into the cabin from the engine bay. Check the rubber belows on the accelerator pedal rod that runs through the firewall (it's basically a flexible seal).

Kevin

[Richard]

Originally Posted by Kevin Howard

I should also mention that the Series 3-5 411s have a vent in the rear wings through to the cabin (beneath the rear parcel shelf) which could also have a bearing on why they had an exhaust ingestion problem in certain conditions.
A dodgy boot seal can be the culprit if there is any airway, regardless of how small, between the boot and the cabin.
Kevin

The explanation is that all cars have a smaller or larger region of separated or stagnant air at their rear-end depending on the design. If the exhaust exits into this area the fumes will be dragged along with the car and enter any cavity where there is a region of lower pressure ie. leaky boot seals or open rear windows etc.
If the exhaust gases are vented downwards they will enter a region of turbulent air and thus be dissipated.
Richard

[Rubbond]

I think it more likely that (if the tail pipes dip down and then back up),
the holes and blanked off pipes are to prevent condensed water remaining
in the exhaust.

[Nick Challacombe]

I only have two black marks having a 407 and on this the exhaust exit via
a curved stainless steel pointing
downwards at about 60 degrees for the same reason. To stop the gases bing
sucked inside the car by
the vacuum created by forward movment of the car.

Nick.

[exgasman]

Just a point of interest I've recently spoken to the guy who had my 412 S1 before me and he was the person who removed the blanking discs in order to create a “venturi” effect through the bottom slots to improve the exhaust flow.
All I can say is that I very often ran with the back section of the soft top down but with the middle section of the roof in and never had the hint of fumes in the cabin.

[John Keighley]

Kevin,
That's bad luck. Hopefully, you can get the leaks sorted out and hopefully its not the main seal at the rear of the crank - it's a rope seal and if that's leaking, I am told that the crank has to come out.
All exhaust fumes in the cabin seem to be now eliminated. I've had a good opportunity to test is and there's nothing noticeable.
I do however, have to upgrade the seal along the back of the boot lid as the one that is there isn't providing an adequate seal. It is where the lid joins the lower part of the body- where the locking mechanism is located.
There is a story (a brief history thereof and a brief description of the refurbishment on this 410 published in the current BOCA Club Express magazine.
John K.

[John Keighley]

Finally,
I have been able to take some photos of the completed work to the exhaust tailpipes. Pictures 005 & 006 show the finished work. I have also added a picture to show the arrangement when the car first came back. Why I chose a 411 quadruple tailpipe arrangement is that it looks far less ungainly than the original system and significantly neatens up the appearance of the back end of the car. Although not frequent, I've been in it enough to confirm that there are no exhaust odours in the cabin now. The one thing I do need to attend to is the rear boot lid seal which isn't sealing the boot all that effectively and that will settle any other exhaust seepage issues.
John Keighley.

[armandjones82]

Try to really research if you could have the best Tail Pipe for your 411. Try also other forums and websites to really see what you can have in your Bristol Car. I, myself don't own one, but you can find one in order to really see what your car can have.

[bristolboy]

i know its not the full real deal but we fitted a rolled tail pipe to our car and it did the jobs in terms of looks. we got it from a company called aftermarketsounds heres the link anyone else just wanted a simple tail pipe Rolled Tail Pipes - Car Accessories - AfterMarket Sounds really did tidy the car up