<div dir="ltr">over the decades, Ive used a few different 6:3:1 designs and experimented with all the published formula for length and pipe diameter,<div> and found little (if any) measurable differences on my race cars</div><div><br></div><div>each one has its own unique sound but i cant say any one of them was "jsut right"</div><div><br></div><div>maybe ive never managed to find the exact right combo of engine internal design and exhaust design</div><div><br></div><div>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</div><div><br></div><div>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</div><div><br></div><div>terry</div><div>Australia</div><div><div><div dir="ltr" class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div><br></div></div></div></div></div></div></div></div></div></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Thu, Oct 8, 2020 at 6:58 PM John Davies via Fot <<a href="mailto:fot@autox.team.net">fot@autox.team.net</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin: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. A 6-3-1 gets an impulse regularly.<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<br>
when the exhaust valve opens. This will improve flow out of the<br>
cylinder, so that this design is called a "scavenger" or "extractor". <br>
<br>
The length of primary is critical. The enclosed diagram refers to inlet<br>
tuning but the same applies to exhaust manifolds. As can be seen, the<br>
usual length of 17-19" will boost extraction and power in the mid range,<br>
where it will be most useful for a road car. An out and out race 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. Look 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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