exhaust smell in the car

[Harley818]

OK, I know a few people have had this issue, others say not.

I have an 818S, and a dual exhaust, out the back. I do not have a spoiler or rear wing.

The exhaust smell in the car is OK for short trips, or highway speeds, but at low-med speed, I get a lot of fumes in the car.
I know Hindsight modified his exhaust to exit out the side, which cured the problem. I don't want to do that.
Has anyone else come up with other solutions before I start to evaluate options?

I plan to look into the following:
1 - clear lexan to completely fill in the rollbar area.
2 - some type of under bumper splitter deflector
3 - some type of bumper extension just above the exhaust exit
4 - addition of a rear wing or spoiler
5 - any other ideas??

I don't know much about airflow around the car, so any help from those who do is appreciated.

If someone has already posted this issue and I missed it, just point me in the right direction.

[Junty]

No pictures - Im working in Korea, but I filled the roll bar area with clear lexan - making a diffuser. Fix the issue 100%

[Harley818]

No pictures - Im working in Korea, but I filled the roll bar area with clear lexan - making a diffuser. Fix the issue 100%

Thanks, that was going to be my first try. Lets hope it works the same in the northern hemisphere.....

[ben1272]

Korea (N+S) is in the northern hemisphere. :) You should be fine!

[Frank818]

Yeah #1 would be great to try.

Let us know what you do about it, VERY VERY interested to follow up on that.

[Harley818]

Following Junty's suggestion, I added a lexan barrier the size of the roll bar.

71878
71879

I cut the 1/4 in lexan to the same profile as the roller, and attached by drilling into the lower crossbar behind the seats, and two spots on the roller angle supports and tapping 10-24 button head bolts.
You don't even really notice its there.

The amount of exhaust gas is now reduced by about 90%.
Previously, I was having a lot of exhaust in the seating area at low speed.
Now, I don't notice much exhaust except when I stop at a light, and then not all the time.
At really low speed, when I come to a stop a a light, the air inertia kind of rolls into the car, but other than that, not much exhaust anymore.
I'll continue to monitor it throughout the coming week.

Thanks for the suggestion Junty.

[ben1272]

Great to hear. I'll be looking at doing this also. Keep us posted as you continue to assess the improvement.

[flynntuna]

That lexan looks really good. Have you driven a night yet? You might get some reflections from on coming headlights on your wind shield.

[Frank818]

Wow you build FAST! I thought it would take months. I don't even know where to source such a sheet of lexan.

So the bolts are tapped directly in the metal, no rivnuts not crossdrilling all the way to the other side of the bar? And it's solid enough with only 2x 10-24s?

Reflections from on-coming cars at night is something I really didn't think about, good point flynn!

[Hindsight]

Does it lessen the forward-flowing wind in the cabin? Every time I drive my 818 without a hat, I step out of it looking like that dude from A Flock of Seagulls.

[Harley818]

That lexan looks really good. Have you driven a night yet? You might get some reflections from on coming headlights on your wind shield.

Haven't driven it at night with cars behind me yet, so I'll keep that in mind and note any issues.s

[Harley818]

Wow you build FAST! I thought it would take months. I don't even know where to source such a sheet of lexan.

So the bolts are tapped directly in the metal, no rivnuts not crossdrilling all the way to the other side of the bar? And it's solid enough with only 2x 10-24s?

Reflections from on-coming cars at night is something I really didn't think about, good point flynn!

yes it tapped directly into the FFR tubing. I did that in a few places. 10-24 works fine but there is probably only 2 - 3 threads, so I only do this where there is not much load. Also over time, it might get looser due to any corrosion.
I had 3 across the bottom, and one in each roll bar brace.

[Harley818]

Does it lessen the forward-flowing wind in the cabin? Every time I drive my 818 without a hat, I step out of it looking like that dude from A Flock of Seagulls.


It does lessen the flow a bit in the cabin, and I think thats why it works.
I guess you have more hair than me Hindsight.... I'm losing mine....haha....

[bbjones121]

This is exactly what I am going to do. Glad to hear it works. Do you have the small openings sealed in the side sails? That triangular area right behind the door latches? The engine bay gets pressurized and I was having fumes come into cabin through those openings also.

[bbjones121]

The pieces that came in the kit had to be cut to fit properly.

[Harley818]

This is exactly what I am going to do. Glad to hear it works. Do you have the small openings sealed in the side sails? That triangular area right behind the door latches? The engine bay gets pressurized and I was having fumes come into cabin through those openings also.
Yes, I closed those and sealed with silicon.
Also, there are gaps at the front of the doors/windshield mounting/firewall area that need to be closed. I don't have the final wheelwell tin in yet in that area, and there is a lot of heat that comes in from the front rad etc. I closed them off temporarily till I install the tin, but I think I will do a final version that is permanent as well.

I still do get a little exhaust gas in the cockpit, but very small amounts, and usually just when slowing to a stop. Very tolerable.

[AZPete]

An easy way to find leaks in the passenger compartment is to put a light inside, then turn off the garage light. The more openings you can close, the less exhaust fumes and noise.

[autostang]

What size sheet of material did you need? I would like to order some plastic, but am out of town this week and can't measure the height and width of the roll bar.

[Harley818]

13 x 44 in is what I used.

This allows the lexan to sit on the top of my FFR firewall aluminum, and I bolted it into the front of the crossbar below the rollbar. The top reaches the middle of the rollbar.
Width is as wide as the bottom of the rollbar where it meets the crossbar. Then I profiled it to match the rollbar profile.
Hope this helps.

[autostang]

Perfect! Thanks for the info.

[alpine227]

Added to the to do list!