WEmery7451@aol.com wrote:
>In a message dated 12/10/01 9:28:28 PM Pacific Standard Time,
>kaskas@earthlink.net writes:
>
><< In my long dyno testing of this engine I found that a single pipe was
>better
> than a dual combination. >>
>
>Kas's little black book says to use 2 1/2" OD tubing. I have known of people
>who used larger than 2 1/2" diameter tubing. Is it to be assumed that the
>larger OD tubing hurts rather than helps?
>
>I might be using 2" tubing. If so, another attempted upgrade. This is the
>four cylinder engine.
>
>
Two anecdotal experiences, from which you can draw your own conclusions:
1. I ran my engine on an engine dyno for a day. We did several runs
with different length pipes but all with 2-1/2" diameter. Kas's results
were that best hp was with a 45" pipe and he exited it just ahead of the
right rear tire.On my engine we got the following results, ranked lowest
to highest hp (yours may be different):
112" of 2-1/2" pipe (to back of car) -- baseline -- lowest
57" -- 3 hp more than base
42" - 4 hp more than no pipe
57" , same carb settings, -- 5 hp more than no pipe
57", carbs leaned by 4 flats -- 6 hp more than no pipe
Why these lengths? Well, first of all I wanted to see what the 42"
results would be. However, I didn't want to route it out the side and
put up with tearing off my exhaust pipe because it was the lowest part
of the chassis. This might not be as big a problem as I envisioned.
I then determined that if I made it 57" long, it would end behind the X
member but in front of the fuel cell. I tried this at the track, putting
a downturn on the end to deflect the hot gasses downward. The first time
I drove through the paddock on a dirt road, I was totally engulfed in a
cloud of dust and dirt.
Then I reasoned that since I didn't want my pretty car getting all
dirtied up all the time, I'd sacrifice hp by running it out the back,
but hopefully minimize the loss by increasing to a 3" pipe from the 57"
point to the rear of the car. It works fine, probably giving up a few
hp. Handicapping myself since I'm asuch a good driver. Ahem. However --
2. A couple of months ago a chassis dyno became available to me. I put
my car on it and did several runs. On one of the runs, all the settings
were identical to the previous run, but suddenly we had 3 more hp at the
rear wheels. Why? After puzzling over this for awhile, we discovered
that the flex pipe connecting the collector to the exhaust pipe had
split and was leaking badly -- giving us 3 more hp.I guess I would
conclude that running the pipe all the way to the rear of the car does
indeed rob a few hp, even though the diameter is larger, but I must
admit that with my sorry driving ability I'd be hard pressed to tell the
difference of three hp, but at least my car stays clean..
Now if I could get significantly more flow through the head, I might
make an exhaust change so I can beat a Porsche somewhere.
As they say, "Go figure".
--
uncle jack - red, white, and New Blue
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