Secondary linkage on Impco 425?

[tankin]

OK, before I go and convert my vacume secondary throttle plate to mechanical, I have a question.

While disassebling my Holley to move the base plate over, I noticed 2 threaded bosses on the Impco 425 that looked to be just like those on the Holley required for mounting the secondary throttle vacume pot. I mounted it up to see how it looked and found it was a perfect fit. Even the pull rod lined up with the secondary lever. The only thing lacking is the vacume passage behind the top screw to operate the pot. Is there a port on the 425 designed for routing this source via tubing? I would be just as happy with vac. secondaries as mechanical from the driveability stand point. Thoughts?

[sleepybu]

you running bi fual

[tankin]

Nope. A Holley 4 barrel base plate is bolted to the Impco 425 to become the throttle valve and adapter to the mainfold.

[C3H8]

The two holes you used are actually cast on there for a plate that IMPCO uses on the goverened applications. A special plate and spring made by IMPCO help to open the throttle plates for those applications. IMPCO shows the manual set up for non-goverened holleys. Its interesting that the vacuum set up fits these holes. If you could find the right vac source the set up might work similar to the gasoline operation.

[tankin]

There is a port just above the power adjust screw that is at a 45* angle to the left (away from the idle adjust screw) that appears to be a candidate. The pull rod on the vacume diaphram that I have is too long to affect full opening on the secondaries, but shorter versions are available from Holley and the aftermarket.

Has anyone ever heard of this?

It's likely easier to just use mechanical secondaries, but the vacume idea is interesting.

[sleepybu]

i modded my vac sec to mach sec. It was very ez. Just one little bolt did the trick. Who can post a pic for me

[Frank]

If you have an internet account, you should be able to host your own photos. I'm in the process of setting up a web site for my car club and wrote up a procedure for publishing photos (or any other files) onto the internet:

http://www.acccc.net/forum-publishing.htm

I hope you find it useful.

[sleepybu]

thanks Frank, i should have time to go over it tomarow

[michael]

why go through the trouble?
just get a double pumper base plate.
I like the ProForm billet ones, $125usd from summit
I even took my 650dp baseplate out from under my OHG and put a Proform in

[sleepybu]

it took me less time to mod my vac sec to dp them to get a price from lordco