[Fot] Race headers.

[Enquiries Road & Track]

over the decades, Ive used a few different 6:3:1 designs and experimented
with all the published formula for length and pipe diameter,
 and found little (if any) measurable differences on my race cars

each one has its own unique sound but i cant say any one of them was "jsut
right"

maybe ive never managed to find the exact right combo of engine internal
design and exhaust design

i have noticed that pipes that turn sharply down where the exit from the
head sure dont work. the "best' result seems to be when the flow is more
towards the floor of the exhaust pipe and continues straight out from the
head a few inches before falling downwards

primary pipe lengths more like 22" seem to be better on race engines, but
as others have said, slightly shorter on road cars. some designs with
really short primarlies like those sold by Moss years ago, were no better
than factory cast-iron manifolds

terry
Australia


On Thu, Oct 8, 2020 at 6:58 PM John Davies via Fot <fot at autox.team.net>
wrote:

> Because the six has three pairs of pistons, moving in synch, but 360
> degrees
> out for ignition timing (EG No.1 on firing stroke, when No.6 is drawing
> charge into the cylinder) a 6-2-1 design receives impulses into the
> secondaries at irregular intervals.    A 6-3-1 gets an impulse regularly.
> This impulse will be reflected back to the other of the pair, and if the
> primary is the correct length, that impulse will be in its negative phase
> when the exhaust valve opens.      This will improve flow out of the
> cylinder, so that this design is called a "scavenger" or "extractor".
>
> The length of primary is critical.    The enclosed diagram refers to inlet
> tuning but the same applies to exhaust manifolds.    As can be seen, the
> usual length of 17-19" will boost extraction and power in the mid range,
> where it will be most useful for a road car.    An out and out race engine
> builder might consider longer, to gain at the top end.
>
> For such pure race engines, 6-1 manifolds may be considered.     Look at
> any
> F1 engine, or at the extraordinary manifold built by Gareth Thomas - see
> enclosed.
>
> John
>
>
>
>
>
> -----Original Message-----
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> Subject: Fot Digest, Vol 103, Issue 299
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