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TR6 Exhaust fumes / airflows over bodywork.


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Has anyone done any work on the airflows over the TR6?

 

In my car it is very noticeable that at over 60 mph with the hood down the cockpit develops a low pressure and the exhaust fumes are drawn up over the centre of the boot lid and into the cockpit - (is that why I get "TR6 cough" after a long trip?) I have twin rear boxes so perhaps the separate exhausts are nearer to the centreline of the car than usual.

 

I was interested in the airflows over the body as perhaps moving the exhausts a couple of inches one way or the other might make all the difference. From other posts I guess that the panel behind the seats is not too successful in diverting fumes.

 

If not I will have to stick wool tell-tales over the sides / rear of the car I get someone to photograph my car from the side & rear at speed.

 

 

Alan

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I abandoned the twin exhausts in favour of a standard side exit rear box for exactly this reason. I found that using a petrol additive the problem was even worse.

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Alan,

Behind the screen and the rear bumper/rear valence there will be slow moving air. As seen in these cfd images:

http://www.esteco.com/modefrontier/automatic-shape-optimization-aerodynamic-properties-cars

http://www.worldcarfans.com/109090321478/hennessey-venom-gt-shows-its-aerodynamics/photos#3

Theres no air flow CFD simulations for airflows over a TR6 as far as I can see. Those flows are turbulent and that is presumably enough to spread exhaust fumes forwards. The fumes will linger longest with a more central tail pipe

So I would locate the tail pipe at a rear corner aimed into the fast moving air, keeping away from those central bluer regions on the cfd images.

Roughly where Triumph put it !!

I have a single pipe ending at the bottom of the valence and just inside the chassis rail on driver's side. No smells from it at all. No bumper fitted.

But blow-by coming out of the catch tank, out of the bonnet sides and around the windscreen side is smelly.

 

Test with smoke canisters, as used for flue testing ?

 

Peter

Edited by Peter Cobbold
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This document is also showing the rear air flow

post-12941-0-30249400-1432970499_thumb.jpg

 

Regards

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Gad dam it! I have this problem too!! It makes for a rather unpleasant drive out, my wife can not stand it which in turn makes my life somewhat difficult if I want to take the tr out! I too have the twin rear box set up but I was wondering about asking my custom exhaust specialist to fabricate some kind of elbow to weld on the tips to force to fumes more level and away from the air stream the gets caught and pulled in towards the cockpit...so has anyone done this?

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I've got a non standard SS exhaust based on the original dual tailpipe below the passenger tail light. The tips of the pipes sat in front of the bumper bar. I've just driven home from my mates workshop where we welded two SS exhaust tips on to the pipes to extend them about 80mm past the bumper bar. Will see how it perfoms on tomorrows drive

 

Seemed ok on the motorway coming home

 

Graze

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Gad dam it! I have this problem too!! It makes for a rather unpleasant drive out, my wife can not stand it which in turn makes my life somewhat difficult if I want to take the tr out! I too have the twin rear box set up but I was wondering about asking my custom exhaust specialist to fabricate some kind of elbow to weld on the tips to force to fumes more level and away from the air stream the gets caught and pulled in towards the cockpit...so has anyone done this?

Use flexible exhaust fittngs to test the idea?

Something like this:

http://www.motors23.co.uk/si261203180699.html

Peter

Edited by Peter Cobbold
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The images of air flow posted show saloon type cars in which there is the large low pressure area developing behind the rear of the car. With the TR hood down a major low pressure develops behind the windscreen and extends to the whole cockpit area. A secondary low pressure will develop behind the rear of the car. Even with the side windows down the relatively high pressures on either side of the car do not flow in and equalise the pressure but air /exhaust is drawn in from the rear of the car over the boot lid.

 

In my dreams I was hoping someone had developed a simple fit full width deflector panel which could attach to the top of a roll cage (and perhaps sides) presumably in high pressure air flow coming over the top of the windscreen and deflect it down over the boot lid to prevent exhaust gas pouring back to the cockpit.

 

As gases (like most things) flows from higher to lower pressures an alternative strategy I am considering is to reduce even further the pressure behind the rear of the car in order that the pressure there is lower than the cockpit by the use of underbody wind deflectors. These would be unobtrusive but might necessitate avoiding speed bumps.

 

 

Alan

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I've tried dual exhausts, and dual with extended tips, and dual redirected to one side, then with extended tips, finally a completly standard CS system (pimped with cromed tips :rolleyes:) and I've got to say that this last one is the best regarding fumes and I also like that the sound isn't deafening.

And maybe this homemade wind deflector helps, it fits tight to the cover for the top.

http://www.ijonsson.se/triumph/photo_diary.php?day=kaross&folder=kaross&id=IMG_0491

Edited by ijonsson
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I too have long suffered with the twin pipe system the car came with. The ends were originally flush with the rear edge of the bumper and the fume ingress into the cabin was dreadful. I tried slipping blingy chrome finishers over the ends to extend the pipes approx 45mm beyond the bumper line, but the improvement was only marginal. Finally, I had the pipes extended about 9cm and, together with repositioning the rear boxes higher under the boot, made the exit pipe angle less acute, to direct the exhaust at least partially away from the Kamm effect return stream. It's looks a little... phallic, but there is a noticeable reduction in fume ingress. Simon's suggestion of the downturn is my next step.

 

Paul

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Have you never wondered why Triumph painted the Kamm tail Black?

I used to run long chrome tail pipe extensions (correct style no longer available as no longer in fashion) which did reduce the fumes and headaches on long journeys

Edited by Denis
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Denis, - black hides the oil spatter from the gearbox and diff?

Peter

 

Hehehe! It might do that as well...but I doubt that was on Triumphs mind...the back draft makes the exhaust soot soil the rear end (the original test prototype vehicle was all white)

 

You'll notice the left rear light cluster over the exhaust collects soot too after a while, mainly noticeable in the clear reverse lens!

 

That's why the flat rear end of vans and trucks become so filthy after a while, so with our open cars that's why we smell it too!

Edited by Denis
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My car has a single pipe big bore system, when I bought it the back box was incorrect and the end pipe too short.

 

I experimented with a chrome trim to reduce the fumes, and it did work.

 

I eventually found a correct stainless rear box which had a longer end pipe which does not smell when driving, and has much better sound :-)

 

So I do believe that the length of the end pipe matters......

 

Steve

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Alan,

Behind the screen and the rear bumper/rear valence there will be slow moving air. As seen in these cfd images:

http://www.esteco.com/modefrontier/automatic-shape-optimization-aerodynamic-properties-cars

http://www.worldcarfans.com/109090321478/hennessey-venom-gt-shows-its-aerodynamics/photos#3

Theres no air flow CFD simulations for airflows over a TR6 as far as I can see. Those flows are turbulent and that is presumably enough to spread exhaust fumes forwards. The fumes will linger longest with a more central tail pipe

So I would locate the tail pipe at a rear corner aimed into the fast moving air, keeping away from those central bluer regions on the cfd images.

Roughly where Triumph put it !!

I have a single pipe ending at the bottom of the valence and just inside the chassis rail on driver's side. No smells from it at all. No bumper fitted.

But blow-by coming out of the catch tank, out of the bonnet sides and around the windscreen side is smelly.

 

Test with smoke canisters, as used for flue testing ?

 

Peter

Peter,

 

I have found this which equates well to a TR6

http://blog.capinc.com/2011/06/practical-flow-simulation-at-highway-speeds/

 

Which concludes with

PF-15-1024x481.jpg

I believe this expresses what we all know is happening.

I do feel there are differences as this shows the lowest pressure behind the rear bumper, but I'm sure the TR6 has the lowest pressure in the cockpit causing the exhaust fumes to flow forwards into the cockpit.

I have been trying to find any useable information on the Mercedes Aircap which fits to the windscreen. The TR6 with the roof down of course has those inviting fitting holes on the top of the screen! I think I could also appreciate a little extra sun shade up there.

 

Alan

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My car has a single pipe big bore system, when I bought it the back box was incorrect and the end pipe too short.

I experimented with a chrome trim to reduce the fumes, and it did work.

I eventually found a correct stainless rear box which had a longer end pipe which does not smell when driving, and has much better sound :-)

So I do believe that the length of the end pipe matters......

Steve

Steve

 

Did it have the bonus of stopping the exhaust build up on the rear bar, light and transom?

 

Graze

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Alan,

Neat flow simulation !

Maybe aeroscreens are the answer!

Saves the weight of the w'screen and hood.

Except for the sun tan...and except in the wet.

Peter

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Steve

Did it have the bonus of stopping the exhaust build up on the rear bar, light and transom?

Graze

That's a good question Graze.

 

I'm not sure there's much of a difference, well I can't say I have noticed one!

 

Steve

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When we went down to Cornwall last year, a 300 mile trip, everything carried in the boot reeked of exhaust fumes, vile.

All clothing had to be washed before it was wearable, didn't spoil the holiday though.

A return to a standard set up is on my mind.

 

winston

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This problem so bugs me I have now, at vast personal expense(?), bought 3 metres of 1" wide elastic and some white wool. I intend stitching a 6" tell-tale of wool every 6" and then looping the elastic around the boot lid. As the car is Damson I hope for good colour contrast. Currently I am attempting to rig a car windscreen camera on a pole in the rear of the car looking down on the boot lid. I then intend driving at speeds between 30 and 60 and filming the tell-tales. If that works I will move the elastic down to boot lid from the hinge end in 6" steps to the rear of the car.

 

If this works reasonably well I then intend to raise the elastic from the lid by 6", then 12" by the use of a foam block at either side and see what happens above the boot line. I appreciate foam will disturb the airflow but I am doing this on the very, very cheap.

 

I had wondered about the affect of an under front bumper air deflector but I see PaulAA above has the same problem with a defector. I have also just bought a behind the seats wind deflector, in the event that I get meaningful photographs without this fitted then I will photograph again with this in place.

 

Peter has suggested tail pipe extensions, I have also purchased two SS 8" extensions with a 90' bend, but before I fit these I want to check the airflow behind the car to determine the best place to direct the exhausts - yes out & down would seems a good idea but who knows.

 

I can't work out how to check the airflows behind the car - does anyone have any spare Red Arrows smoke canisters I can inject into the exhaust? More cheaply a pair of smoke canisters wired to the tail pipes might work but as I will be working on a public road I want to keep it legal and safe, I cannot see wool tell-tales and a fixed automatic camera being a danger to anyone and will require no driver input, other than perhaps shouting the speeds every 10 mph to be recorded by the camera - I wonder, can I shout louder than a TR6 exhaust?

 

This might seem excessive to some owners with a single tail pipe, but seriously I really wonder about the lung damage and coughing fits after driving for a couple of hours. The Double SS twin sport exhaust system the car came with might have to go.

 

Obsessive, who's obsessive?

 

Alan

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FWIW you might also like to try that with and without rear bumper.

Stuart.

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Have you considered getting a CO test to see if you are running a bit too rich, it may be a combination of both of your efforts.

Is the engine using a bit a oil as well?

Are you using any additives in the fuel?

John

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Stuart. Is your implication that a rear bumper "worsens" the situation ?

 

I've read this thread with interest as I experience exactly the same symptoms as mentioned by all others here. I even changed all the rear light seals (for the boot) and replaced the original factory hardtop onto the car to see if that would improve things... gave a marginal improvement, as the TR6 is "leaky" to air and fumes anyway. I also placed 60 mm exhaust pipe extenders onto the exhaust pipes..again small improvement but really not enough.

 

I suspect that an even more extreme extension would do more but look very "interesting". I have to say that the current extenders make the car look unintentionally more "butch" but extending further might be boasting :) Ah, yes, and put a much better rubber seal on the boot. Several TR6 "experts" have suggested putting weapons grade chunky rubber seals in place.

 

There are others (dare I say) who have suggested that PIs run rich anyway and CO is an occupational hazard byproduct... and thus suggest "carbs" for driveability and PI for originality. Who can tell.

 

But a forum that keeps suggesting a discussion of possible solutions going is very welcome... keep the ideas coming.

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