Subject: [Fot] Race headers.

From: John Davies via Fot <[email-masked]>
Date: Thu, 8 Oct 2020 09:57:24 +0100 boundary="----=_NextPart_000_01EA_01D69D59.6C6EF6F0"

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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

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From: Enquiries Road & Track via Fot <[email-masked]>
Date: Thu, 8 Oct 2020 20:54:18 +1000

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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 <[email-masked]>
wrote:

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<div dir=3D"ltr">over the decades, Ive=C2=A0used a few different 6:3:1 desi=
gns and experimented with all the published formula for length and pipe dia=
meter,<div>=C2=A0and found little (if any) measurable differences on my rac=
e cars</div><div><br></div><div>each one has its own unique sound but i can=
t say any one=C2=A0of them was &quot;jsut right&quot;</div><div><br></div><=
div>maybe ive=C2=A0never managed to find the exact right combo of engine in=
ternal design and exhaust design</div><div><br></div><div>i have noticed th=
at pipes that turn sharply down=20

where the exit from the head

sure dont work. the &quot;best&#39; result seems to be when the flow is mor=
e towards the floor of the exhaust pipe and continues straight out from the=
 head a few inches before falling downwards</div><div><br></div><div>primar=
y pipe lengths=C2=A0more like 22&quot; seem to be better on race engines, b=
ut as others have said, slightly shorter on road cars. some designs with re=
ally short primarlies like those sold by Moss years ago, were no better tha=
n factory cast-iron manifolds</div><div><br></div><div>terry</div><div>Aust=
ralia</div><div><div><div dir=3D"ltr" class=3D"gmail_signature" data-smartm=
ail=3D"gmail_signature"><div dir=3D"ltr"><div dir=3D"ltr"><div dir=3D"ltr">=
<div dir=3D"ltr"><div dir=3D"ltr"><div dir=3D"ltr"><div><br></div></div></d=
iv></div></div></div></div></div></div></div></div><br><div class=3D"gmail_=
quote"><div dir=3D"ltr" class=3D"gmail_attr">On Thu, Oct 8, 2020 at 6:58 PM=
 John Davies via Fot &lt;<a href=3D"mailto:[email-masked]">[email-masked]=
am.net</a>&gt; wrote:<br></div><blockquote class=3D"gmail_quote" style=3D"m=
argin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left=
:1ex">Because the six has three pairs of pistons, moving in synch, but 360 =
degrees<br>
out for ignition timing (EG No.1 on firing stroke, when No.6 is drawing<br>
charge into the cylinder) a 6-2-1 design receives impulses into the<br>
secondaries at irregular intervals.=C2=A0 =C2=A0 A 6-3-1 gets an impulse re=
gularly.<br>
This impulse will be reflected back to the other of the pair, and if the<br=
primary is the correct length, that impulse will be in its negative phase<b=
r>
when the exhaust valve opens.=C2=A0 =C2=A0 =C2=A0 This will improve flow ou=
t of the<br>
cylinder, so that this design is called a &quot;scavenger&quot; or &quot;ex=
tractor&quot;.=C2=A0 =C2=A0 <br>
<br>
The length of primary is critical.=C2=A0 =C2=A0 The enclosed diagram refers=
 to inlet<br>
tuning but the same applies to exhaust manifolds.=C2=A0 =C2=A0 As can be se=
en, the<br>
usual length of 17-19&quot; will boost extraction and power in the mid rang=
e,<br>
where it will be most useful for a road car.=C2=A0 =C2=A0 An out and out ra=
ce engine<br>
builder might consider longer, to gain at the top end.<br>
<br>
For such pure race engines, 6-1 manifolds may be considered.=C2=A0 =C2=A0 =
=C2=A0Look at any<br>
F1 engine, or at the extraordinary manifold built by Gareth Thomas - see<br=
enclosed.<br>
<br>
John<br>
<br>
<br>
<br>
<br>
<br>
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k">[email-masked]</a>&gt; On Behalf Of<br>
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Sent: 07 October 2020 18:16<br>
To: <a href=3D"mailto:[email-masked]" target=3D"_blank">[email-masked].=
net</a><br>
Subject: Fot Digest, Vol 103, Issue 299<br>
<br>
Send Fot mailing list submissions to<br>
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