That "Classic Trucks" article was a step in the right direction, but failed
to explain the real importance of running heat to the intake.
The original heat riser was designed to assist cold starting, but there is
an even more important benefit of the way the original manifolds were joined
together: The heat of the (cast iron) exhaust manifold was radiated to the
(cast iron) intake, even when the heat riser is closed. When aftermarket
headers are installed on an inline, especially using an alloy intake, you
lose that source of heat and driveability suffers.
No matter what the climate, fuel vaporizes under vacuum and chills the walls
of the intake manifold, where it condenses back into liquid. Acceleration
results in a momentary lack of fuel to the engine, because the lower vacuum
can't inhale liquid fuel as well as the expected vapor. The result is a
"miss", "stumble", or "flat spot". When the liquid does enter the engine, it
is dispersed rather unevenly, flooding some cylinders but leaving the others
starving. So you have an engine that's running rich and lean at the same
time. No amount of re-jetting will overcome this, although if you install
large enough jets the problem is minimized - but fuel economy is a thing of
the past by then. A constant sooty-rich condition is the result. Whether you
are in Alaska or Death Valley,
no engine will run correctly like this.
Clifford, being a former aircraft engineer, has recognized this problem and
offers a water-heated intake manifold to minimize the condition. Heating the
intake manifold has been a long-time Inliner trick to get good driveability
and fuel mileage on engines equipped with aftermaket intake and exhaust
combinations. Running heat tubes from the headers, whether Cliffords,
Fentons or whatever, to the intake manifold heat riser flange is not as
effective as the constant heat of a water jacket, but it's a start, and does
help. Edmunds intakes were water heated but they are a rare swap-meet find
these days. Some other aftermarket intakes provided a heat riser connection,
but most just eliminated it. Fine for a race car, but bad news for a
street-driven inline.
So, cold starting is not really the reason you want heat to the intake
manifold.
Jack / Winter Park FL
----- Original Message -----
From: Antonio R. Tijerino <antonio@innercite.com>
To: Ole Trucks <oletrucks@autox.team.net>
Sent: Wednesday, October 13, 1999 12:57 AM
Subject: [oletrucks] Heat riser question
> On the current issue of Classic Trucks there is an article by Jim
> Richardson about improving the performance of the 6 Inliner. There is a
> picture of a homemade heat riser using the Fenton header and a dual
> intake. How necessary is it to have this heat riser in California, since
> it does not get very cold?. Does it help mileage and performance?
> I have a set of dual tube clifford headers and the stock manifold with a
> single Rochester carb. Can I leave the bottom of the intake open? or can
> I make a block off plate and bolt it to the bottom or I need to have the
> heat riser installed?
>
>
> Thanks,
>
> Antonio,
>
> oletrucks is devoted to Chevy and GM trucks built between 1941 and 1959
>
oletrucks is devoted to Chevy and GM trucks built between 1941 and 1959
|