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From digest.v7.n363 Wed Oct 1 19:28:02 1997
From: "Carl Buckland" <>
Date: Wed, 1 Oct 1997 15:44:46 +0000
Subject: Dr. Gas Syncronizing Crossover Pipes

DISCLOSURE: ( This is for you anal types who think that even mentioning a supplier by name is spam. I will always mention products by name and supplier, as I think that to do otherwise is banal banter. If you are among those who thing that brand-naming is a problem, set your filters to exclude anything from me in the future.)

            I do not work for BMP, nor am I given any direct 
            compensation by them.  I do, however, buy most of my
            accessories from them, and consider them (AL and Anthony)
            real friends of BMW tuning. I would and have said the same
            thing about a number of other suppliers. I also sport BMP
            stickers on my car,  just as I carry stickers from H&R, TC
            Kline, BBS, Supersprint, Lubromolly, BF Goodrich, 
            Schrothe, and others who have supplied (at retail or
            otherwise) products for my M3 projects.(Will Turner, I
            need some stickers!)  I have been given some      
            very good pricing on some items from BMP, as well as 
            other suppliers,  usually when the item needed to be 
            tested or even prototyped.


This question from Skip:

> While we're on the subject of xxx(deleted)xxxxxx, just how much
> improved scavenging can be expected from a Dr. Gas crossover? Has
> anybody serious calculated exactly how far away to put it from the
> manifold based on wave propagation theory? If this is super-secret
> stuff, would anyone be willing to share some dyno #'s as to the
> costs vs. benefit?
> - Skip

"Dr. Gas," aka Boyd Butler, has his shop at the foot of Little Cottonwood Canyon (Alta/Snowbird). A couple of years ago, I stopped by to talk about exhaust systems, and ended up missing a big powder day to get started on a prototype Dr. Gas for the M3. I guess I could say that Dr. Gas was the start of my putting cars before skiing, something that even sex hadn't been able to do!

The prototype is still on my car, but a few dozen were made for BMP, and a few are still available. It is made from over 30 mandrels, and is incredibly labor intensive. I think that BMP sells them for around $400, but you'll have to check. Also, I believe that the Dr. Gas will ONLY fit in conjunction with the Supersprint Headers .

The crossover needs to be as close to the header collectors as possible. the headers need to be very close to equal length, so that the exhaust flow is the same out of each bank of three cyl's. The firing order goes from one collector to the other. When a cylinder fires into the front collector, there is a very strong vacuum formed in the other, as the two boxes are brought together by the Dr. Gas, and joined siamese thru a small hole in the side of each pipe. A demonstration with an air hose on a Dr. Gas is startling.

It appears that the scavenging created by the Dr. Gas forces the exhaust gases to flow much better, and hence more power. Now *where* that power is made in the power band is not known to me, but I believe that there is "some" loss at the very low end (under 2500), but there appears to be a big boost in the mid to upper range. I have been very happy with the whole exhaust system, and would reccomend it to anyone who wants more high end horsepower, and a really aggressive (but not "loud") engine voice.

I have not answered your question directly, Skip, as I don't have any dyno figures to refer to, so neither I nor Boyd nor BMP make any specific claims. It just "seems" to work. Almost all of the NASCAR teams use a Dr. Gas, as well as other exhaust parts from Boyd, which tells me that it must help (certainly *they* did dyno testing!).

Moreover, my car, which has the Supersprint headers, Dr. Gas, and a Supersprint muffler, sounds fantastic, by anyone's account. It is unique in it throaty howl, which turns into a deep waaaaaaaaaa at higher rpms. I have not heard ANY other BMW, including full race versions, that sound any better (although they are sometimes much *louder*).

There won't be anymore Dr. Gas's available when those held by BMP are sold, so don't pause too long if you want one.

Carl Buckland

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