Race car and exhaust fumes

[M_Motorsports]

Reconditioning a '72 240 race car and have had it out for a few HPDE events to work out issues.  One is the exhaust fumes that enter the car while on track.  Symptoms are watery/burning eyes and taste of exhaust.  I know of all the problems 240's have with negative cabin air pressure and exhaust kicking back thru the exterior of the car.  Being a race car it tends to have a lot of gaps and missing gaskets/seals/trim.  My exhaust end under the car and not carried all the way back to the rear bumper.  I have noticed a few other race 240's with Lexon rear windows that several 2-3 inch round holes are cut across the top or bottom of the windows.  I assume they were having the same problem and added the holes so exhaust could exit the interior while the side windows are down.  Have any racers found this to solve the problem or are they only adding more spots for the fumes to enter?  Should the holes be across the top or bottom of the window?  If you have done the cuts were they done by a glass company or a diy?  Any other way to exit this exhaust?   Would extending the exhaust pipe farther back be of much help?       Thanks. 

[Chickenman]

Used to race 240Z's back in the late 70's. Fully gutted but never really had any exhaust fume issues.

 

I think your number one problem is your exhaust exiting under the car. Extend it all the way to the rear. That helps a lot. Make sure you extend it a good distance past the rear of the car . About 6" to 8" past the rear valance is good. There is a low pressure area right under the rear Valance that will suck in fumes if you cut the T/Pipe off too short. 

 

Never had to cut any holes in rear T'gate glass or any where else. No one else did either.  Not saying that cutting holes in the rear Lexan won't work. Just that we never had to do it. What we did do however is run a drivers air duct blowing air from the A pillar onto the driver. Drivers window was open ( removed )  and so was passenger side. 

 

Install the W/Strip that seals the Hatch if you've removed it. That is one W/strip that you must keep in place. On the inside of the Hatch is a large rectangular hole that is covered by a trim panel. 90% of cabin fumes are sucked up from the T/Gate latch opening, then circulates through the T'gate and get sucked into the Cabin of the car. Seal this rectangular section off with a thin sheet of plastic or aluminium. Glue it in place with Silicone RTV and a few well placed Pop Rivets or screws. Even 3 mil plastic Drop sheet will work. 

 

If you are not using the factory latching mechanism ( Hatch pins ), close off the latch hole with a small patch panel. Seal it with RTV. This is in a very low pressure area and will suck fumes in. Hatch pins create their own problems, so think about sealing those as well if you use them and have drilled thru holes in the hatch. 

 

Couple of other things. Use gaskets or RTV to seal the T/Lights. Although this is not as big a deal as the Hatch latch hole. On the inside of the left quarter panel you will find a hole ( or two ) for the Antenna grommet. Stick a rubber plug in it. 

 

The 1/4 panels to wheel house seams are sealed with Black Mastic. It often dries up and falls out. Break out the RTV or Mastic sealer again and re-goop. 

 

Other than extending the exhaust ( which has to be done ), these steps add next to nothing to the weight of the car. And really eliminate fumes.

 

Sealing the large rectangular hole section of the T' Gate helps immensely on a Race Car or a street car. 

 

I've employed most of the above sealing tricks on my street car, and it's now a pleasure to drive. No more fumes!!!

Edited August 4, 2017 by Chickenman

[northwoodz]

I've also read that if you kick the exhaust out to the side of the car it helps because it keeps fumes away from the low pressure area behind it. 

[Chickenman]

I did that on my race Datsun 1200. I'm now partially deaf in left ear... 

[M_Motorsports]

Thanks for the suggestions Chickenman and Northwoodsz.  In further research I may be causing more exhaust to enter the cabin by having the 2-3 inch holes placed in the rear window due to the neg. pressure.  Upon checking, there is so many openings under the rear (fuel cell) and back of the car I don't know how I would seal everything.  I will have my exhaust person try and maneuver the exhaust farther back and/or out the right side.  

[clarkspeed]

A common problem.  A good seal around the hatch is usually enough to correct if exhaust exits at bumper.  I know some racers that have an exit under the car just past driver, but don't know their struggles.  On my last car I ran oval exhaust tubing to cross over and exit on passenger side in front of rear wheel.  Never smelled exhaust when driving, ever..  But did wear an ear plug in right ear.

[seattlejester]

Aluminum tape is pretty good at holding a seal. If you really want it to last sticking it top and bottom on clean surfaces will work pretty well for patching up even fairly large holes without breaking out the welder. 

[Tony D]

I did that on my race Datsun 1200. I'm now partially deaf in left ear... 

This is the wonderful advantage of an RHD Car, just keep that window closed and kick it out the left side!

[Chickenman]

I could have put it out the right side I guess. But somehow I think that would have only made me deaf in the right ear.

 

Mid 70's. No Earplugs ( Cotton Wool ) and no DB limits. We finally got some DB limits around 1978. 110 DB at 100 feet... LOL.

 

I was blowing 112 DB at 9,200 RPM with the side exit. Went to rear exit and got it down to 108 DB with a spiral core muffler.  Sex, Rock and Roll and Loud race cars... Yeah Baby!!! 

Edited August 22, 2017 by Chickenman

[gira]

Here is the real answer. I've been racing Z's for 20 years, all different build types. Get a helmet with a fresh air vent. It's a foolproof method. I always have used the fuel rail cooler fan from the fuel injected ZX because it blows just right and doesn't use gobs of power. There are many brands of this. I prefer the helmet with the top air inlet as it doesn't bind and distract you when you turn your head back and forth.

You can chase fume leaks until you're red faced, literally. This is the only thing I have depended on. We run 110 octane leaded fuel. Believe me, you know for a day or two that you were on the fumes.

 

Greg Ira