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Steves_TR6

Exhaust Fumes, is my pipe too short !?

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Hi Guys

 

My TR6 continues to run brilliantly following the PI service earlier in the summer :-)

 

However I have noticed I am getting a bit of a headache and slight sick feeling after driving it sometimes.

 

I wonder if this might be caused by exhaust fumes getting sucked back into the car?

 

i have a single big bore exhaust, sounds great!, which ends below the rear bumper.

 

I recall reading that the pipe needs to extend beyond the bumper to avoid fumes being drawn into the car, as you can see on the attached photo my pipe isnt long enough to extend past the bumper....

 

I shall check under the car for leaks too, but i think the pipe is sound.

 

any thoughts ??

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Hi Steve

 

I have also read that it should be at least level with the bumper but better past it. Do you use lead replacement as i have just stopped using it and the fumes i sometimes get are no where near as bad now, just a thought.

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Hi Kevo

 

No lead replacement used, am on Shell V Power Nitro and unleaded head.

 

I suspect it's the pipe, will check out the cost of a new SS back box, and the length of the pipe!

 

Steve

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Clamp a beer/bean can around the tailpipe with a jubilee to extend it, as a test.

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Great suggestion, before spending your hard earned ;)

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I like the beer can suggestion, also has added benefit of needing to empty a can first!

 

Boot seal is ok I think, will check.

The problem is with the roof down, so not thinking fumes coming in thought the boot? ( and car has aluminium bulkhead and new rubber hoses)

 

Thanks for the input :-)

Edited by SDerbyshire

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I've always considered this was due to the Kamm Tail aero effect! Hence the dirty back after a long run...and why they painted the tailend Black!

Edited by Denis

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Chaps

 

Despite best endeavours, I am still blighted by a continuous smell of exhaust fumes in the cabin.

 

I am largely convinced that the source of the fumes is the exhaust pipe outlet. With the roof up, there is practically no evidence of fumes in the cabin (evidenced by the fact that at end of a run, my clothes don’t smell, my head doesn’t throb and my lungs don’t burn) and I am therefore certain that there is little or no leakage though firewall or boot seals.

 

In addition, the wife’s (unused) emergency scarf smells vaguely of the cat repellent it shares the boot with, rather than exhaust fumes. The boot seals must therefore be reasonably patent.

 

Armed with this certainty, I fitted boy-racer chromium pipe finishers to the (unbranded) stainless steel twin exhaust pipes, which had previously ended slightly short of the outer line of the rear bumper.

 

IMG_9457.JPG

Thus extended, the pipe outlet sits 45mm beyond the bumper (as in the image below). The net effect was no improvement whatsoever.

 

IMG_9453.JPG

 

The engine is not particularly smoky, but it does use a little oil and the currently rich mixture adds to the soot content of the exhaust. Indeed, the pipe finishers are already heavily blackened inside. Peculiarly, however, there is very little build-up of sooty deposit anywhere else on the tail of the car.

 

I am at a loss to know where to look next. Do any of you wise ones have a suggestion for the next step? The astonishingly mild autumn is forecast to give way to heavy snowfall this week, so I have tomorrow or next spring to find a remedy.

 

Paul

Edited by PaulAA

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Under bonnet fumes can come out the bonnet sides and swirl around the screen pillar into driver's face. Hood down or up - but the window glass has to be down to get the full flavour of burned oil and petrol. It might be a leaky exhaust manifold/head join or manifold/downpipes or somewhere around there.

 

Peter

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Sorry to hear that the 'extensions' didn't work for you.

 

I bought a cheap stainless trim that extended the single pipe on my '6 about 2 inches beyond the bumper, and it did make a significant difference.

 

I shall now try to identify my exhaust and find a suitable replacement back box.

 

Not sure what to suggest, have you checked for exhaust leaks further forward?

 

Steve

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Hi Paul,

how about strapping a large holdall type bag on the boot to give a spoiler effect (only as an experiment)

This may disrupt the airflow curling back from the pipes.

 

Roger

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Thanks, chaps.

 

Peter, I omitted to mention that I languish in fumes with the hood down and the windows up. However, it is also true that I get a lungful when standing at lights, which would negate the vortex theory. I will investigate the manifold further...

 

Steve, proof, as ever, that prosthetic enhancement is more about vanity than sanity. But you're right and I'll be looking for leaks.

 

Roger, would that be a tugging at my right leg I detect..? However, after a cheerless meeting this week, you've prompted me to daydream about strapping a certain large holdall-shaped client a short distance from the back of the car. It may not solve the source of the fumes, but I would have fun trying.

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I agree w/Peter. You may have a leak somewhere up front of the exhaust exit. Especially in light of your update about getting them when you're stopped. Make sure all your firewall grommets are in good condition as even small gaps can suck into the passenger compartment those wonderful underbonnet smells. They can be small (so not noisy), but enough to stink things up. Stuff coming out the back rarely comes into the compartment at a stop.

 

You're problem, by the way, is a real drawback to classic car ownership - the one of fumes. It really drives me crazy to come out of a drive smelling like exhaust....

 

Best of luck tracking down your fix.

Dan

Edited by YankeeTR5

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Thanks, Dan. I'm pretty sure the tub is reasonably well sealed - there is practically no smell when the roof and windows are all up. I also sense that the fumes come in wafts when the top is down - there isn't a continuous pong in the cabin...

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Hi Paul,

as with most convertible sports cars the airflow in the front seats tend to go in a forward direction - that's why your back gets wet in the rain.

As mentioned previously the airflow also curls around the windscreen to come in the sides dragging with it anything produced up front.

 

With the door wondows in the up position is the smell there - it should be if it is coming from the back.

With the windows up the airflow at the driver position should still be going forward.

As it pops up above the front screen it will produce a large vortex that curls over the top of you dragging more air in from behind.

Somehow you need to smooth this flow out (hence my comment about the holdall shaped banker strapped to the boot)

 

How big is the lip on the front screen capping. If too big it could disturb the airflow and affect the vortex above you - have you tried tapping over it to smooth it.

 

Are there screen demist vents on a TR6 (like those on a 4/4A) if so direct the airflow to these and turn the fan on.

Or open the side vents

This may help to reduce the forward airflow bringing the smell.

 

Roger

 

PS - aeroscreens

Edited by RogerH

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My car suffered from fume ingress and did all the usual suspects, lamp seals, sealed up the panel between the fuel tank and cabin, but I found the boot lid seal was the major culprit which fixed 95% of the problem. At time I had standard twin pipe then a falcon twin silencer exhaust system.

 

Since the car was rebuilt, fumes in the cabin have not been an issue – all seals replaced again plus a had a new body shell. Now I’m not suggesting that as a solution as it works out rather expensive…J

 

I’d suggest the lid isn’t sealing so well, you could try a smear of Vaseline on the boot seal and check for witness marks on the lids.

 

 

However, in order to rid my bumper of the exhaust haze I too have added a chrome tail pipe extension. Similar to the one mentioned earlier, it curves downward and extends about 4 inches at the moment as its not actually permanently fixed. Works a treat, not sure if its “legal” but has passed a few MoTs.

 

Having looked at the various single exhaust pipe systems on Tr6s I have noticed that many follow the rear valance up a steep angle to exit just below the bumper. The exhaust I use dis not like that, it has a more flat attitude which maybe throws the exhaust fumes rearwards and less up into the kamm tail vortex?

 

One problem having the flatter tail pipe is it is more prone to damage on high kerbs when reversing (as I discovered once!) which could be why the majority of tail pipes do rake upwards.

 

Good luck, the fumes problem is a real pain and very frustrating.

 

Mark.

 

 

 

https://www.dropbox.com/sc/aowsz0tyigtxjou/w_qyczKHEH

https://www.dropbox.com/sc/ymzfkd7otrd6shh/grYutlKlJF

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I suffered this with my 6 too and it was exacerbated by using a fuel additive. In the end I fitted a standard exhaust, the side exit variety, which eased things no end. I think maybe Triumph got that right.

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Where can one obtain exhaust muffler extenders for the TR6 ? It feels like something that extends at least 6 inches and ideally turns downwards rather than push fumes straight towards the boot would be a better design that an upturned one.

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No one believes my Kamm Tail aero effect then (Post #9) :rolleyes:

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Although the Kamm Tail effect is validated, the aerodynamics of exhaust emission are complex and relate to multiple variable factors including velocity and air movements. Old professor Kamm probably could have solved the TR6 exhaust-aerosol-in-boot effect if it'd been put in front of him.

 

I believe it's due to the fact that the exhaust pipe is just far too close to the boot and with the engine emission (chemical) compositional content of a 1969-1974 TR6 to contend with, ingress is an ever present hazard. TR6s appear to mainly run rich, and that is always going to be unhelpful for emission quality and attendant smells of exhaust particulate/vapour.

 

Creating distance between the exhaust gas emission point and the critical area close to the boot "may" just help ameliorate the problem.

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The tailpipes might be better directed downwards into the fast moving air that has come from under the car.

The standard upkick to the pipes puts the plume into slow moving air.

See Fig 10 here:

http://www.helsinki.fi/~hvehkama/publica/uhrner2007.pdf

So might be worth angling them down instead, into the 'yellow' air stream in that figure.

Or shooting it out to the side.

Edited by Peter Cobbold

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