Rear window down = asphyxiation

[apache]

The 350 in my 84 K5 isnt exactly new but it did pass Ca smog check no problem a few weeks ago. I have this problem ya see. Its running a single in Magnaflow,dual 2" out either side behind the rear wheels system which I was under the impression would prevent exhaust from comming back in the rear window when open....whew fumes are so bad within a few minutes my eyes water,then a headache sets in and soon to follow Id probably pass out and be on my way to the promise land.
I havent had the top off this one yet and wondered if it typically gets worst yet fume wise? In either case any cures come to mind besides a new engine that dosent burn a quart of oil every 500 miles,LOL.

 

[dremu]

The aerodynamics of flow right around the truck are crazy complicated. Depending on wind and speed the exhaust on my sixpack can sneak in the back window, and the cab and exhaust are in different counties on that truck!

I gather the rear window deflector, dorky looking though it is, can help by creating airflow DOWN over the back window area.

Pressurizing the cabin, i.e. by running the fan full blow, also helps. Opening the vent windows might assist in this regard. Positive cab pressure means the air goes OUT the back window instead of in. 'Course, I drive with the windows down unless it's pouring rain, and then only roll them up when I'm driving slow enough that the rain gets in. (One of the few advantages to driving a truck with the aerodynamic coefficient of a brick is that rain tends to be blown AWAY from you, so you can drive with the windows down and not get wet. Heck, the full-convertible stays dry inside at 30+ in most rain conditions )

Anyway, with the top off, you should be fine at speed, as the air will flow down into the bed first. At stoplights, however, all bets are off.

You might have better luck -- at least with the top on -- with the exhaust ahead of the rear wheels.

Take a look at the CO numbers on your smog ticket; while you're allowed however many hundred PPM's (whatever the numbers/units are), a well-tuned vehicle will often only emit five or ten when the limit is 500, so just 'cuz you passed doesn't mean it's running right. Could be running rich (makes too much CO then, IIRC) ... so a tune-up and/or a visit to your local carb shop could also be in order.

-- A

 

[dyeager535]

Agree on tune. Shouldn't be THAT bad, although it is noticeable on mine, especially when you take off from a light. I notice that rolling down the drivers window helps, if not to prevent it from entering from airflow taking the fumes out once you get moving.

At decent vehicle speeds I don't notice exhaust at all, unless I'm going somewhat slow and really get on it, like up a steep hill.

 

[bp71k5]

I think it really depends on where it dumps and at what angle. I was able to notice a big difference between a right angle exit behind the rear tire and a 45 degree angle exit in the same spot. The 45 is much better especially if you can get a turn down on it so it aims towards the ground.

 

[dyeager535]

I think that's why GM had the factory tip cut at a 45* angle. Hard to describe I suppose, but even the cars the same era were cut that way, and in all cases it effectively dumped the exhaust towards the road surface. Straight cut pipe is not helping, unless you do angle it towards the ground.

Most aftermarket exhaust I see for these trucks simply points it straight out the back or the side.

 

[bp71k5]

I had it out the back and was pretty high by the time I got to work the one time I drove it that far. It was pretty bad.

 

[syclonekid43]

mine is the same way. i have no cat with a 3" flowmaster and 3" pipe. its coming out in the factory location. and wiht the back window down mit kills me. if i have the top off the truck im good to go. i hate not being able to put the rear glass down with out getting a headache

 

[buefchris]

A Tired Oil Burning Engine ,carbed And No Cat,all Ad Up To A Stinky Problem. F.i. And A Cat Will Help.

 

[syclonekid43]

mines a T.B.I motor. i figure the cat would help a little, bunoget rid of i all. i just did a fresh tune up on i with good parts.

 

[original balzer]

How far it sticks past your body pannels is also a consiteration. I tried to keep mine in close and th fumes came inside even when the window was up. Later I put on longer chrome tips and angled them oout at a 45* with the slash cut being even with the side of the truck. I also had them sticking out far enough to be in the air flow while driving.
I didnt exactly like the way it looked but the combo of that and adding the rear wing fixed the problem. The dorky wing thing will fix the problem while your moving but not when your sitting at a light. So extending the tip past the body is about the only fix at a light or stop sign ect.