Date:         Fri, 26 Jul 96 19:30:09 +0200
Sender:       Vanagon Mailing List <vanagon@vanagon.com>
From:         verbeek@the-hague.stbv.slb.com (brian verbeek)
Subject:      Re: vanagon headers

And Jim said:

> While this is good reccommended practice, VW didn't follow it on the 2.1L
> exhaust.  Each of the right side exhausts travel over to the left side of the
> engine before mating with the left side exhausts and are probably about 14"
> longer than the lefts.  It doesn't seem that VW attempted any correction of
> this by altering tube diameters, they appear to be the same diameters.

True. We can do a better job though, we have more time and we have less
interest in saving cents worth of steel, also, VW, and many other car
manufacturers, often choose reliabillity above performance, they are not
aiming as high as we, HP wise, they are dealing with the average car buyer.

> If I were building one from scratch, I'd consider combining both exhausts
> from one side and routing them through a small cat & muffler for each side.
>  You might be able to find some tiny cat & muffler intended for a little 1.1L
> or 1.3L  3-cylinder car to fit in-line along each side of the engine.  I
> don't know what resonance (or other) effect this would have by collecting
> both cylinders from one side together

# 2 and 1 follow eachother in the firing order as are # 4 and 3,
combining 1 and 3 & 2 and 4 is better because the pulses are better distributed
over the total VW flat four cylinder cycle, farther apart, i hope i'm using the
right words here btw.,

> but dual exhausts would seem the way
> to go to reduce backpressure.  Just a thought.

Not necessarily so, the other cylinders help creating the desirable gas velocity
in the system, it helps pulling the burnt gasses out of the cylinders, back
pressure can be too little as well, pulling/blowing UN-burnt gasses into the
exhaust system, loss of volumetric efficiency here, not to speak of economic
efficiency, it does help cool the exhaust valve though, and maybe the head,
reducing the back pressure can be done easily by using a larger dia tube.

Again, i'm not an expert on this, but, as well as Jim, just a thought,

Brian.