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.

[Rubbond]

Thanks Kevin for your mention.
I would however challenge any engineer to devize a car design that would be
able to suck exhaust fumes back into the vehicle from behind the rear
bumper!
As an anecdote I was recently in the Science Museum in London with my son
(and was actually able to park in my old spot next door when a student at
Imperial!).
In the museum were of course fantastic steam engines and aeroplanes,
including the Rover JET 1, but when I saw as an addition what they claimed
to be a capsule that had actually landed on and returned from the moon, I
thought, no, that couldn't be possible in the 1970's.
I mean, consider the faulty door seals, and leaky exhausts!
Where were Bristol then?
With best regards,
Andrew Knox.

[UK6]

Bent Exhaust Tips (Tips for the unwary!)
As an aside, you will recall that the original XJ6 tail pipes had a curious
'S' bend. As you elaborated, the airflow helped direct the fumes away from
the car. My father in the 80's didn't like the look of his old XJ6's tail
pipes, so, you guessed it, he replaced them with some straight stainless
sections. After only a few miles, it became apparent that the fumes were
being reingested into the rear of the cockpit and indeed, stained the rear
hood lining. The message - the factory knew what they were doing!

Brett

Ps Downward tips more than likely make a quieter car.

[Bellerophon]

Aero Dynes were designed for the rear window to be left open when
travelling in order that a through flow of air through the car be established, and
would allow the heating to work properly.
Tony Crook was always insistent that the rear window be left open as anyone
who rode with him would know.
One word of warning regarding the exhaust protruding beyond the rear bumper
on the V8's. It can be very costly if you reverse into anything as it is
very easy to break one of the exhaust manifolds, which are not easy to
replace.
My regards,
Bellerophon

[Kevin H]

See attached image which is an excerpt from a (Dennis) Sevier Lecture published in the Bristol Owners Club bulletin issue 41 (Summer '76)

[Rubbond]

As a child I flew regularly from Hurn airport to Cherbourg in a Bristol (3
cars and 12 passengers).
I'm sure however you couldn't open the windows!
The stories about their cars are getting weirder and weirder!
Andrew Knox.

[David Olivant]

I remember many years ago ownning a Hillman Imp with an openong rear
window. The handbook stated that under no circumstances was the car to be
driven with this window open, as exhaust fumes would be sucked into the
car.
Regards,
David

[Hydroglen]

The issue of fumes varies from car to car. It depends largely on the roof
line and design of the trunk (boot) and the angle of the exhaust pipe.
But why would Hillman go to the expense of fitting an opening window, and
then tell you not to open it? Maybe it was for necking couples, who having
parked in a secluded lay-by, wanted to avoid steaming up the windows!
Dorien

[David Olivant]

Necking couples! Have you ever been in a Hillman Imp?
David

[Hydroglen]

Seen one once....well it's the only reason I could think of, for a window
that can be used ONLY when parked!
Dorien

[Kevin H]

Here in Australia the earlier iconic Holden "panel van", loved by surfies and tradies, used to have a large window which hinged up from the roof at the back. I'm sure this was intended only for use when parked but it was common to see people driving around with it open on a hot day.

Of course being a van with only front seats it was much more practical for amorous activities as well. Surfies would often have a mattress in the back!

It looks like Holden might be planning to make them again http://www.holden.com.au/concept-cars/sandman-panel-van-

Back to John's problem. The cheapest and quickest solution to the exhaust stains has to be aftermarket exhaust tips that point downwards. But I suspect there's also a leak into the cabin from either the front or rear of the car.

[Nick Challacombe]

Kevin Howard wrote " The cheapest and quickest solution - has to be after
market
exhast tips that point downwards."

Just like the 407, the first use of a V8 in a Bristol.
Makes me think that the problem was always there and
an effective solution found. The 407 handbook advises
that the rear windows should be left open when driving
to facilitate the movement of air in the cockpit.