Twin Cam Distributors

Tech chat w/ Marc Matzer
Marc
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Twin Cam Distributors

Post by Marc » Tue Jul 11, 2006 6:52 pm

The 124/131 series engines have been fitted with several different distributors in various models.The 1438cc block mounted distributors,the 1608cc exhuast cam driven distributors and the 1995cc electronic distributors all have a a centrifigal advance of 14 degrees.The dual point distributors fitted to the other engines have 19 degrees initial advance at the distributor.For racing or hot street performance ,14 degrees(28 at the crank)is best.If a point type distributor is desired,the best exhuast cam driven unit is Fiat part # 4272975.It has a light weight balanced nylon rotor which works well at high rpm.A 1995 cc electronic distributor can be fitted to any year engine.Alternativley,one of the dual point distributors can be modified by replacing the inboard advance wieght stop with one of larger diameter to restrict initial advance to 14 degrees,28 at the crank.
The distributor on the 1438cc engine is mounted on the left front corner of the engine and is driven by a jackshaft.The distributor on all other sized engines used in the USA version cars is mounted on the exhuast camshaft cambank housing driven by a gear spline machined into the exhuast cam.The larger engines all have the original block mounts,also some larger European engines use the block mounted distributors.Any car mounting IDF,DCNF,DCOE series Twin carbs,must use the exhuast cam mounted distributors becuase of clearance issues on the intake side,(carb distributor interference) .

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allenlofland
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dizzie ?

Post by allenlofland » Wed Jul 12, 2006 10:33 am

you say "A 1995 cc electronic distributor can be fitted to any year engine"
What doese one do about the vacuum advance feature in this dizzie for the older cars that do not have a port for vacuum advance. ?
Allen & Lynette Lofland
Wichita Kansas
Back on Land with Our Fiat :)

Marc
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Vacuum port

Post by Marc » Wed Jul 12, 2006 6:27 pm

Mechanically it fits,you will need to find a tapping on the carb or intake on the engine you want to adapt to.There are many ways to do this.you could use a Fiat 75 to 78 master vac tee fitting on the manifold and use an inline plastic vac/reduction/check to the hose going to the distributor.

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allenlofland
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Dizzzie

Post by allenlofland » Wed Jul 12, 2006 8:25 pm

Mark : I might mention this for others, It has been tried and tested over and over and adapting the 2liter dizzie to the old carbs will not work with the Vacuum operated advance system. There is no provision for a balanced vacuum port before 1980 on the fiat carbs. this requires the removal of the advance mechanism in the dizzie, a dooable project but then you have to recalibrate the springs and weights, something that is beyond most of us. Best to just remember to at least tie of the movable advance plate in the dizzie if your going to run the 2 liter Dizzie on other than a 2 liter FI. Better yet, get the older dizzie with out the vacuum advance.
Mark: as for vacuum porting from another source, that wont work, it has to be a balanced port and there is none available on these engines. One source of good info is Terry Terasakis, sorry if I mis spelled his name but he has been working with these for some time and has converted a few for folks, He has the equipment to test dizzies and recalibrate them.
Another thing to remember, if you have a dizzie with vacuum advance and wonder if the vacuum is correctly hooked up, remove the hose to the dizzie and tie it into a vacuum gauge and watch it, If it fluuters like a humming bird you have a problem, that is what happens when you try to run one on the wrong engine, just think what that is doing to your timeing as you run down the road :( Another one of those little gotcha's from the camp fire.
\
Allen & Lynette Lofland
Wichita Kansas
Back on Land with Our Fiat :)

Marc
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vac source

Post by Marc » Thu Jul 13, 2006 8:22 am

Allen good info!your right.If you keep the engine stock,not a different carb or intake you would have a problem.The tee fitting wiyth check inline works perfect as I have converted a few for customers.I am lucky I purchased those Marelli plex units for myself years ago.They are something like the units Terry converts from one of those Electronic Dizzies.I like the term Dizzies for a distributor!You put a smile on my face.

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racydave
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Post by racydave » Mon Oct 30, 2006 6:24 pm

I modified the dizzy on my 79 2L and am not using the vac adv. Its a job for a crazy person, esp if you do not have a spare dizzy. You can not get alot of adv on orig set up. The centrifugal arms do not actually use their full travel, I modified arms from a small block kit and springs. They fit against cam and adv the whole cam, as the orig had free travel and not as much total adv given. In the end I got approx 10* static and 38 total. The curve on this was set w emissions and the old junk carb by the factory. With 1800 intake and new used carb, the dist changes really helped. It has good pull in low ranges, and accelorates very well, esp with secondaries opened. Without a better cam it does peak before red line. Im looking into cams???? :shift: Ps I would not recommend anyone tearing up their dizzys, it is best left to a pro with a dist machine.
1979 spider 2000

Marc
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Distributors

Post by Marc » Wed Nov 22, 2006 6:32 am

They are very complex and most of us dont have the equipment to work on them.There ar some modern crank angle sensor systems I am looking into; a Marelli system through Guy Croft, and Millers Mule has available parts to adapt the Ford Esis system.The way to go!
You can experiment with different size springs on the stock dizzies.There are 2 springs,one heavy ,one light.Remove the heavy spring and take another light spring from a spare dizzie and replace the heavy one with a light one.It can give you a faster advance.
You want 14 degrees total advance,28 degrees at the crank.
It was set up for the Ralph Nader equipment and what a mess!Dave you have any pics of your mods?I would like to post them for people to see...Marc

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E Prod Racer
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Post by E Prod Racer » Tue Mar 06, 2007 12:53 am

Marc,
You wrote:
"If a point type distributor is desired,the best exhuast cam driven unit is Fiat part # 4272975.It has a light weight balanced nylon rotor which works well at high rpm."

I don't know of any dizzy in my inventory that has a 7 digit part number, so what is PN#4272975? I do know that the dual point from my '74 Spider (Crane converted) is marked S-144CAY, and clearly doesn't work with the dual IDFs. The advance range is too broad, and doesn't allow enough initial advance to make the IDFs happy.

I searched my parts stocks, and found 2 single point units marked S-144. I used the S-144 unit on an old ITC 1608 Spider racer years ago, and found it to be a very good dizzy. Both these S-144s have the nylon rotor. Is this single point S-144 the one you referenced? I hope so, because I am swapping out the Crane plate from the dual point to the single. Don't know why I converted the dual point in the first place...
Bill McMahan
MAC Autosport, Ltd.
Colorado's AWD Dyno Performance Shop
EP FIAT 2L Spider
'74 Abarth Stradale project car
http://www.macautosport.com/index.php?o ... itemId=231

Marc
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S-144!

Post by Marc » Fri Mar 16, 2007 10:23 am

Yes,
the S-144 is the model to use and the one I am refering to.as far as the part no#,I will check my reference for that #,and recorrect that.The single point has 14 degrees initial advance like the 2 litre electronic,28 at the crank.The dual point has 19 degrees initial advance to aid in cold starting on the stock engines which is not good.You could try putting on a softer spring on the advance plate,two soft ones instead of the one stiffer and one softer as it comes stock.Can you use electrnic ignition in that class?Or adapt a Ford edis system with a crank angle sensor,maybe find a Marelli plex distributor with the mechanical advance type plate.
Last edited by Marc on Sun Mar 18, 2007 4:05 am, edited 1 time in total.

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racydave
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Post by racydave » Fri Mar 16, 2007 5:41 pm

Honestly, I have just started looking at Distributorless systems. I did many "things" to my Dist. Basically improving the fit between the weights and their cam will give you some added range. I also needed to "modify" the lower side of the rotor to clear the weights. Sounds scarey, but I have put 3 or 4 hundred miles on it since. Since I do want to put alot of road miles in it this year, I want a system I know I can rely on!!! So I am curious and follow all related threads. The Ford edis? sounds interesting. Would you need a TPS and MAP sensor??? There are more systems related to EFI engines. I think a coil over system would be the trick! I I know that dists in general arent the most reliable and accurate devices for controlling your spark, just look at any ign oscilloscope pattern on a dizzy system and you can see alot of curvature and timing deviations. I would be happy at this point if I could find 5 or more HP.
1979 spider 2000

Marc
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Post by Marc » Fri Mar 16, 2007 9:03 pm

http://www.millersmule.com/ Dave check out this site,Jason makes adapters to fit this system on to your short block,its the way to go...it adapts the Ford system to the car.You will need a list of parts,Jason can help you .I am lucky as I purchased the last two marrelli plex201 ignition systems Bayless had left,which was years ago.Its basically a 2000 distributor with a mechanical advance plate installed.Individual coils are the best way to go as you now see this on all newer cars.

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Fiat 7 digit part #s

Post by Marc » Sun Mar 18, 2007 4:03 am

Part # for the dizzy is correct,seems Fiat swithched from 6 digits to 7 digits sometime in the late 1960's.
Last edited by Marc on Sat Sep 15, 2007 10:17 am, edited 1 time in total.

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racydave
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Post by racydave » Sun Mar 18, 2007 2:33 pm

I am investigating Megajolt jr system, and am putting parts list together. I might do this, Will post more when I have it all figured out. Dave
1979 spider 2000

Marc
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Modern ignition

Post by Marc » Mon Mar 19, 2007 6:31 am

Dave!
Keep us posted!Somone mentioned cost to me with these systems.Alot of money for 5hp more.If we could find an easy way to modify a 2 litre distributor so it works without the vac advance,that would be most cost effective.Of course ,not as good as a modern dizzy free system.Use Magnecor wires and Iriduim spark plugs,they make a noticable difference.Also I like the dry coil system with a high performance ignition module from Vicks,works great with the marrelli Plex 201,and is something you can feel especially in the high rpm ranges.Too bad they dont sell these anymore.Bruces has a modified electronic dual point dizzy conversion I saw at his shop.It a full electronic non vac advance points free dizzy,made out of a worthless dual point dizzy.A little pricey but will work good on any TC,something to consider.

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Post by vandor » Tue Aug 28, 2007 3:19 pm

Boy, the amount of misinformation available on the internet is just amazing!!

First of all, not all cam monunted dizzys have 14 degrees of centrifugal advance!! Just the electronic ones have either 11 or 14 (?), depending if it's from a carbed or FI car. The points ones are not all the same either...

As far as vacuum advance, I don't see why one couldn't use it on an earlier engine, I've done so on 1608, 1800, 2000 engines without any problems.
The only difference is that the vac advance operates at idle aswell, but it does not seem to hurt anything. Vac advance gives 2-3 better mpg on the highway, I'd never leave home without it! I got 31 mpg with 2000 carbed engine, try that w/o the vacuum advance!
Even if one does not want to use it, why remove it? If the vacuum hose is disconnected the vac advance will not change the timing.

As far a Fiat part numbers are concerned, they did NOT change from 7 digit to 6 digit. Sigh...

Csaba

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