The reason for heating the manifold is not for emissions, it is for part
throttle low speed driving.. the as the gas evaporates into the air it
cools the intake off .At part throttle low speed the cool manifold causes
the gas to condensate and stick to the walls, this leans out the mixture and
causes missing, and then once tha amount of gas sticking to the manifold
wall gets large enough it is sucked into the cylinder cause a over rich
mixture that can foul out the plugs. There is very little HP gained by
blocking off the water thought the manifold..Because at open throttle the
air is moving so fast there is little heat picked up off the manifold.....
so better to leave it functioning...on a street car ..
Mike Kerr
Restoration Products
3730 todrob Ln.
Placerville, CA 95667
Ph# 530-644-6777
Fax# 530-644-6777
E-mail mikekerr@innercite.com
Web; innercite.com/~wolfgang
-----Original Message-----
From: Brian St. Jacques <brian@varatouch.com>
To: datsun-roadsters@autox.team.net <datsun-roadsters@autox.team.net>
Date: Friday, May 26, 2000 1:35 PM
Subject: Intake Manifold Heater
>Hi
>
>The water passage through the intake manifold is there to heat up the
>manifold, not cool it down. This was done as an emissions reducer. The
>hotter the air going through the manifold, the less dense it is and the
>less fuel you have to provide to get the correct air to fuel ratio. This
>basically allowed car manufacturers to lean out the carbs a little and get
>cleaner readings.
>
>Cold air makes horse power- ask any hot rodder. The colder the air, the
>denser it is so you add more fuel to it to get the right air to fuel ratio.
>This dense little package of explosives results in more bang in the
>cylinder when the mixture is fired.
>
>Now I have no experience tuning SU carbs, so I don't know if it is possible
>to fatten them up and move a little more fuel through them. I do agree that
>the car will run rougher in cold weather, but only until the manifold warms
>up a little. I have run dual carbs on VWs that eliminate the hot air riser
>from the exhaust to the manifold, but if they were tuned right, they ran
>really well. On the cold mornings you had to pump the accelerator a little
>to get it going, but they also had no chokes.
>
>It doesn't sound to me like anybody has had any luck bypassing the water
>line from the roadster manifold, but from my rather limited experience and
>what I have learned from others, manifold preheaters are not a good thing
>if you want to maximize power output.
>
>Is there anyone out there that can shed some more light on the subject or
>straighten me out if I am off?
>
>
>Best regards,
>
>Brian St.Jacques
>Project Manager
>Varatouch Technology
>Phone: (916) 331-6300 Ext. 321
>Fax: (916) 338-8255
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