Well Jack, I guess everyone else is like me and don't know enough about the
subject to comment. Without
a flow bench it is hard to know what you are doing. I was hoping others
would chime in and I could learn
a little something or get even more confused on the subject.
The thing I have noticed in looking at manifolds and heads, is that the late
TR3 and early TR4 heads are too big to begin
with. To get a small decrease in the area from the carb to valve it would
require making the head port smaller where the
intake attaches. This is what they did with the late TR4 and 4A head, thus
making it the head of choice. I guess when
we run out of 4A type heads we can start milling the early one's and putting
in a sleeve to decrease the size.
I would guess that the biggest improvement could be made in the shape of
the port closest to the valve. Smooth out the
long and short side of the turn. I have mixed feeling about shorting the
valve guide where it enters the port. Something needs
to be done but if the guide is shortened, flush with the top, will the
valve run hotter because it can't transfer the heat to the head as well?
OK Jack, how about some of your findings while playing with the flow bench.
Just waiting to build another motor.....
Dean T.
----- Original Message -----
From: "Jack W. Drews" <vinttr4@geneseo.net>
To: <fot@autox.team.net>
Sent: Sunday, November 30, 2003 2:07 PM
Subject: HS6 on GT6+
> Is it too early to start the winter technical olympics? No? Well, then,
> here goes:
>
> The six cylinder manifolds, as Bill points out, are akin to household
> plumbing, and although I've done a lot of work with TR6 ports, I haven't
> touched a TR6 intake manifold. Maybe some of the things I've learned about
> the four cylinder stuff will be of interest, though.
>
> I've had fun putting combinations of manifolds and carburetors on TR4
heads
> and running them on the flowbench. I've used TR3 manifolds both stock and
> modified, I've tried the TR4 manifolds both stock and modified, and I've
> run the Webers with the appropriate manifold. I've also made flow bench
> runs with just the manifolds and no carburetors. In addition, I've seen
> some gosh-awful attempts to modify these manifolds on engines I've taken
> apart to prep for racing.
>
> Keeping in mind that this is flow bench stuff, and not dyno data, here's
> how various manifolds and carbs rank at .500 lift, best to worst, all on
> the same competition-prepared head, same flowbench, same day:
>
> #1 - Weber carbs and manifold =100% (assume this to be the standard)
> #2 - long manifold, my mods, HS6 SU's = 95%
> #3 - short manifold, my mods, SU's =85%
> #4 - long manifold, stock, SU's = 85%
> #5 - short manifold, stock, SU's =75%
>
> This all leads to some rather fun observations:
>
> #1 - Webers: Besides being much better at mixing the fuel and air, the
> Weber setup provides the best overall flow, due in good part to superior
> manifold design. I think, but I cannot prove, that the additional venturi
> area of the Webers doesn't provide that much of an advantage, because the
> bottleneck in the whole system is the valve and seat.
>
> #2 - modified long manifold: I can get pretty close to Weber manifold flow
> with my mods, but boy, does it take a lot of work! The problem is that any
> port/manifold passage must constantly decrease in cross section from the
> beginning of the runner down to the valve pocket (or, at best, be constant
> diameter). We can do that in the head, but in the long TR4 runners, we run
> out of metal so it takes a bit of skulduggery to do it.
>
> #3 - short manifold: can be modified to match the flow of the stock long
> manifold. That doesn't necessarily mean that driveability will be the same
> because of velocity vs. torque considerations, but I haven't had a chance
> to check that out on a dyno. Nevertheless, TR3 owners, there is hope for
you.
>
> The most amusing head / manifold combination I've taken apart was one
where
> the head had been prepared by a drag race mechanic. Boy, were those ports
> BIG! And flow was very high, too. Then I put his manifold and carbs on the
> head and the whole combination flowed LESS than a stock setup!! Inquiring
> minds ask "Why?" Well, to match the manifold to the head, he had just cut
a
> big chamfer in the manifold ports to match the size of the head ports.
This
> violated the "constantly decreasing area" dictum and destroyed the effect
> he had achieved in the head. Of course, those monstrous ports also didn't
> have much velocity, so I don't know how the engine would do with Webers.
>
>
>
> uncle jack
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