weird smell problem with different wheels

[zeteclotus]

Been playing with tyre sizes as my alloys need new tyres I had a set of 185/60 13 on steel wheels which fit very well, nice handling and fit with standard springs but the steel wheels do not look that nice.

Faster 0-30 time as well I will worry about the speedo later:)

So i put the Alloys back on with 165 /80 /13 these are quite a bit bigger about 1 inch all around.


The 1 inch in height difference causes the exhaust to come inside the car!!!

I really did not belive this, so I swaped the wheels back, sure enough no exhaust smell !!! ( The tyres are not rubbing anywhere)

Has any one else noticed this?

I am going try moving the exhaust pipe but I think its more to do with the wake behind the car, so I might have to lengthen the pipe?

[1964 S1]

Some people have noticed this before on +2's. Lengthening the exhaust tip is an easy way to find out if that's the problem. It does seem to be caused by the wake, as you say, behind the car.
[ ...... reflective update....... the +2 has wind tunnel technology incorporated in it's design. Maybe they found a Kamm effect design beyond "normal" ranges, pushing and sucking air, including muffled exhaust gases (through loose fitting boot/trunk seals?)... ]
Does having the windows up or down make a difference? Maybe it's being sucked in through the fresh air outlets on the roof pillar....

[ppnelan]

It's a 'special feature' that allows you to remotely detect whether the boot lid is open when you set off. If it is, you will soon begin to feel queasy as exhaust fumes are sucked into the interior...

This is why a lot of +2s have long tailpipes that protrude well beyond the bumper. I think they (including mine) look a bit naff though... Perhaps it is possible to seal up the boot & any boot floor holes to stop this effect?

Matthew

[1964 S1]

.... as Pee Wee Herman said.... everyone has a big,
BUT did they come from the factory with exhaust fumes in the cabin? A stock exhaust didn't stick out too far... maybe it is that rubber seal on the rear deck lid....
Mine has a dual chrome tip sticking well out from the back bumper, no boot latch at all, and no fumes,,,(well, maybe some oil smell from the engine bay....)

[zeteclotus]

What suprises me is the ride height effecting the length the tail pipe needs to be.

I am going to when I get a chance. lowering the output pipe from the exhaust. I suspect this might work and would also explain why some people have a problem and others need 8 inch exhaust pipes.




My boot seal is air tight I have even tried putting masking tape over the join.

Taped up the boot side vents holes shut the windows -no smell turn the heater on an it sucks exhaust in! And the exhaust is not leaking near the front.

Extending the exhaust pipe solves the problem but I know I am going to hit my shin on it when in the garage.



Does any one have a airtunnel pictures of a +2?

To stop the fumes with the high tyres I seem to need about an 8 inch tail pipe!!

Currently made from a piece of 2 inch blue band water pipe bit heavy but was just the right size for the test.

Apparently the tail pipes on an XJS are shaped to stop just this effect. I don't belive it as I have driven xjs's with missing tail pipes and still not had the exhaust in the cabin problems I seem to have with the +2

I am thinking of of running the exhaust straight up through the bonnet and over the roof ! solve the fume problem and the ground clearance problem in one go!

[handi_andi]

What about trying a pointy down adapter piece on the end? that way in theory at least ensuring a good venturi effect sucking the exhaust out.
Andy