Bob,
After hearing several favorable comments I picked up a used copy of "The
Sports Car Engine - It's Tuning and Modification" by Colin Cample (Robert
Bentley Inc, 1965). Outside of EFI (electronic fuel injection) and ECM
technology (electronic control module) I can't imagine how the internal
combustion engine has changed that much where this book would not apply.
Although back then Mr. Campbell was able to cover transistorized ignitions.
Without going into any detail there is an explanation about how a properly
tuned exhaust hastens the evacuation of gases (scavenging) and creates a
vacuum, or negative pressure, that helps to pull new air/fuel mix sooner
into the cylinder. This tends to cool the incoming charge (cooler charge =
denser charge = more power) but also will dump some of that new charge out
of the cylinder unburnt (higher fuel consumption). This effect is optimized
when the the pressure waves of each cylinder are not interfered with by
other cylinders. The lowest performing exhaust is the type where all
cylinders meet together into one common chamber right out of the head (a la
stock TR and most stock engines). The longer the tube length and lesser any
sharp angles of flow is more efficient. Also, the tube length shortens as
the desired RPM range moves higher. I guess that is why Top Fuel dragsters
have such short individual headers.
So, while I do not think any of us are going to go out and try to design and
fabricate our own header, it certainly appears that using a well designed
header will improve the flow, and thus the performance, of any engine,
Triumphs included.
NFI, but one header that I've been eyeballing is a "pulse" header. Looking
at it I realized that each pair of the three pairs of pipes is coming from
the two cylinders that are in opposite phase of one another in the firing
order (i.e. 1 and 6). Pricey but imteresting. Maybe some day... And as we
all should know, not all headers are created equally. Most usually require
some modification. But there a a few that can be a REAL pain in the tail to
install.
Also, head wise, it is recommended that any sharp edges be smoothed out in
the intake and exhaust runners (for flow efficiency) and combustion chamber
(to prevent pre-ignition). There is one particular area on the intake side
just behind the valve that is a fairly pronounced sharp step. It needs to
be smoothed out to a radius. All sharp edges in the combustion chamber need
to be smoothed out just a bit. Both Kas Kastner and David Vizard address
this and more in their respective publications.
Of course, let's not forget why much of this is done in the first place -
hotter cam profiles that allow the engine to breathe better. In my mind
that is the crux of the whole approach one needs to take when deciding what
to do with their motor. Once you decide on a cam then the rest falls into
place. Hotter the cam the more radical the modifications needed to make it
work to its fullest potential.
Greg Dito
CD6250L
----- Original Message -----
From: <RazorBobSr@aol.com>
Besides milling to get 9.5 or so,what else would u guys/gals do to a head
to make it flow air better??
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