Twin Cam Distributors

Tech chat w/ Marc Matzer
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allenlofland
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Post by allenlofland » Tue Aug 28, 2007 5:44 pm

I some times wonder why I get involved with this stuff but here goese anyway, Now dont get mad, but your totally of the wall with this.
You say you have used vacuum advance with all those different engines,
WHICH ENGINES WITH WHICH DIZZIES and just where did you attach the cavuum hose from the dizzie that needs a metered vacuum.
I am afraid what you did was just left the vacuum advance unhooked and ran with it. THAT IS NOT WIZE. That poor litle vacuum cannister is a vacuum motor and it has a diaphram working inside and when that diaphram finaly gives way because you mistreated it, you are looking at some possible desasters. Secondly you are not getting any vacuum acvance operation from it unless you have a metered attachment point.
I woud suggest this. in all honesty and in the attempt not to sound over the top with this thing, BEFORE you hook up a vacuum advanced featured distributor to your car that does not already have one, read up on how they work. its not rocket science but it is a little techical for some obviuosly because to many of you all are driving around with an unhooked one on your cars right now and just waiting to a very unhappy event take place.

On another point about this. If you want to see what your dizzie with the vacuum advance on the wrong aplication is really doing, insert a t fitting with a vacuum gauge inline with your vacuum advance cannister and watch the gauge as you rev and idle the motor, NOW think to your self, is that what my distributr is doing ouch...you will see that not unlike the wings of a hummingbird, the fluttering of the vacuum cannister will not last long, and that untill it doese your timeing is erratic and fluctualting wildly NOT doing good things to your engine.
Guy Croft said in his book something to the effect that most distributors where neglected pigs .
I would suggest that running around with a 2liter engine with dual idf's 40s from an original fiat with the vacuum advance hooked up to a polution port as I have seen several times is not unlike trying to make that pig fly.
It wont do it.
AND to go one step further, Dont even MENTION what will happen to you if the advance arm that operated the diaphram in some of the fiats like the Zagato should brake. OCH now you have a complete failure of the timing.
But go ahead, hook that little hose up to the exhaust, intake or where ever it will fit, I like the brake booster, thats a real great place for it,
and dont let common sence prevail. Just as they say DO IT.
But lts not go around advocating stupidity please.
Rant over for tonight 8)
Allen & Lynette Lofland
Wichita Kansas
Back on Land with Our Fiat :)

vandor
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Post by vandor » Wed Aug 29, 2007 9:42 am

Allen,

>You say you have used vacuum advance with all those different engines,
>WHICH ENGINES WITH WHICH DIZZIES

1608, 1756, 1995cc single (32/36) carbed engines with a stock 2 liter distributor with vacuum advance.

>and just where did you attach the cavuum hose from the dizzie that needs >a metered vacuum.

To the intake manifold.

>I am afraid what you did was just left the vacuum advance unhooked and >ran with it.

Nope, connected it to the manifold, to get more advance at higher vacuum conditions.

>THAT IS NOT WIZE. That poor litle vacuum cannister is a vacuum motor >and it has a diaphram working inside and when that diaphram finaly gives >way because you mistreated it, you are looking at some possible >desasters.

If the diaphram fails the spring inside the module will simply push it to the fully retarded, or 'rest', position. There are a bunch of stock Spiders running with failed vacuum modules, and the only thing that hurts is fuel economy, as the ignition is not advanced in high vacuum conditions.

> Secondly you are not getting any vacuum acvance operation from it >unless you have a metered attachment point.

Not really sure what you mean by metered vacuum, but I do get operation of the vac advance when I connect it to the intake manifold.
The stock cars had a 'ported' vaccum source to the advance, which meant that the advance did not operate at idle, but came in as soon as the throttle pedal was pressed. Connecting it directly to the manifold gives it advance at idle aswell, but I have not experienced any ill effects from this.

>On another point about this. If you want to see what your dizzie with the >vacuum advance on the wrong aplication is really doing, insert a t fitting >with a vacuum gauge inline with your vacuum advance cannister and watch >the gauge as you rev and idle the motor, NOW think to your self, is that >what my distributr is doing ouch...you will see that not unlike the wings of >a hummingbird, the fluttering of the vacuum cannister will not last long,

THAT ONLY HAPPENS WITH DUAL CARBS! (IDFs, etc.). On a single carbed engine (like most of us have) manifiold vacuum is very steady and changes with throttle opening.

FWIW, I never had an advance module fail on me in 15 years of Fiating. I bought a lot of cars with failed ones, but none of the replacements ever failed.

Csaba

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allenlofland
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Post by allenlofland » Wed Aug 29, 2007 9:56 am

Csaba: I will not argue with you about this but i will challenge you to hook up that vacuum gauge and see what you are really getting from the intake .
Metered-Ported same thing. I got the term ,metered from Book on Webers.
As for only being a problem with dual carbs, NO its the intake that causes this, how many runners are in the single carb intake ??? two right.
Now how do you balance them.
Allen & Lynette Lofland
Wichita Kansas
Back on Land with Our Fiat :)

vandor
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Post by vandor » Thu Aug 30, 2007 12:34 am

Allen,

>challenge you to hook up that vacuum gauge and see what you are really >getting from the intake .

I did that tonight. The gauge showed 15 inHg of vacuum at idle. It does not fluctuate, only changes with the throttle being operated. The needle vibrates, I'd say ~0.2 inHg. That's too little to move the vac advance.

>As for only being a problem with dual carbs, NO its the intake that causes this, >how many runners are in the single carb intake ??? two right.

There are 4 runners that go to the 4 cylinders, and one plenum, or open area, under the carb. This open area is what balances the individual intake pulses into a steady vacuum signal.

Csaba

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allenlofland
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Post by allenlofland » Thu Aug 30, 2007 8:21 am

Csaba: I give up, if you want to have your diziie controlled by the intake rather than the throttle plate then go for it. But I dont see the advantage nor do I aggree with the priciple invlved :) To each his own.
Hows the wife doing in New orleans.
Allen & Lynette Lofland
Wichita Kansas
Back on Land with Our Fiat :)

vandor
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Post by vandor » Thu Aug 30, 2007 9:24 am

Allen,

She's doing great, should be able to graduate in December.
bye,

Csaba

Marc
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6 to 7 digit part numbers

Post by Marc » Sat Nov 10, 2007 9:42 am

Csaba, they did change from 6 to 7 digits,look at some old parts books,or call Bayless and confirm it if you dont believe me...Marc

so cal mark
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Post by so cal mark » Sat May 08, 2010 1:57 am

I have a new distributorless ignition system for the Spider avaialble at about half the price on full crank-fired system. Details are on my site at www.allisonsautomotive.com
Allison's Automotive-home of the ultimate Spider header and exhaust system
www.allisonsautomotive.com

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KevinB
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Post by KevinB » Sat May 08, 2010 5:58 am

so cal mark wrote:I have a new distributorless ignition system for the Spider avaialble at about half the price on full crank-fired system. Details are on my site at www.allisonsautomotive.com
Mark:

As this is a different product, does it deserve its own thread with and introduction and description?

Best regards,
Kevin
85 Bertone (24k orig miles)

Peperone
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Re: Twin Cam Distributors

Post by Peperone » Fri Oct 11, 2013 4:55 pm

I have one of the "distributorless" ignition systems from Allison's Automotive (listed above) in my '82 Fiat Spider. It was the best update I did to the engine. It runs like a top and I no longer have to mess around with vacuum advances, magnetic pick-up, leaky oil seals, or any of the old technology that helped perpetuate the Fix-It-Again-Tony name-calling that plagued these great little cars. Another advantage of Allison's system is that the distributor doesn't get "cooked" sitting above the exhaust manifold.

In my next Fiat Allison's distributorless ignition will be one of the first things I add unless it already has it. I don't work for Mark Allison. I have not met him in person. His system speaks for itself. I'd rather be driving my Fiat than under the hood tinkering with an antiquated ignition system.

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