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04-13-2012, 09:25 PM | #1 |
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In defence of the sbc dist
In my nondiscript shop among a few other endeavors I convert sbc dists
for use in 8ba's, probably 80 or 90 a year. Early on I shortened the post about 5/8" so it configured closer to the Loadamatic. Very quickly I decided to leave the length alone to gain more wiggle room up on top which makes point adjustment much easier. I also added a clamping pad which duplicates the one on the Loadamatic for obvious reasons. I originally built 1/2 with the vac can and 1/2 without. I now build 100% with the can after observing its positive effect during customers dynomometer trials. All that being said the true value of these converted distributors is the ease with which they can be "recurved" without being removed from the motor. Yank the cap and rotor and everything is there looking back at you. Most that I build are simple single point units with GM or equiv heavy duty points....good to go 6 or 12 volts. I routinely twist my stroker to 5500 without a hint of point float. I certainly 'get' not liking the style because it really does scream GM but in my opinion it can't be beat for it's function. Charlie ny |
04-13-2012, 10:49 PM | #2 |
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Re: In defence of the sbc dist
Those SBC distributors are good. I have one in a blown Flathead with a boost retard vac. can. Has points and works good. I like the older cast iron type from '57 til they went to aluminum housings.
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04-14-2012, 05:04 AM | #3 |
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Re: In defence of the sbc dist
Charlie, in your opinion, would there be any performance advantages to be had, say on an early 221 ci, 21 stud, '35 engine, that would justify the work and conversion of parts necessary to convert from a front mount distributor to the top mount 8ba style, in order to use a modified sbc distributor like you mention in your post here? I do understand the advantage of having the distributor up in an area for easy access but I am wondering about all other possible advantages. Thank you.
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John "Never give up on what you really want to do. The person with big dreams is more powerful than one with all the facts". Albert Einstein Last edited by JM 35 Sedan; 04-14-2012 at 07:27 PM. |
04-14-2012, 12:25 PM | #4 |
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Re: In defence of the sbc dist
JM,
I'd stay with the front mounted dist and change the internals to the 11A, very easily done. Without a timing mark on the motor I usually move the initial timing setting up one additional graduation from where my KRW machine says it's in spec. I set the vac brake to almost eliminate detonation. An additional concern with the dist on the right front corner is interference with the RH water pump. Charlie ny |
04-14-2012, 03:39 PM | #5 |
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Re: In defence of the sbc dist
charlie what points gap do you set them to thanks
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04-14-2012, 06:42 PM | #6 |
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Re: In defence of the sbc dist
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8ba dist dwell 30 degrees Front mounted dist each set 22 1/2 degrees, total 35 degrees. At 70 years old a feeler gage is too subjective. Charlie ny |
04-14-2012, 06:43 PM | #7 |
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Re: In defence of the sbc dist
OOPS my last post was to 52.......not 54. Apology.
Charlie |
04-14-2012, 07:47 PM | #8 | |
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Re: In defence of the sbc dist
Quote:
Charlie, I've heard and read about changing the internals in a stock '35 distributor to the 11A and apparently that is a good thing for those early distriibutors on a 21 stud engines. What I have been planning to run on my Avatar 5w coupe is either a H&C dual point, dual coil distributor or a stock crab distributor. I was wondering if a modified sbc top mount distributor might have any performance improving potential over the H&C or crab? Just wondering since I probably prefer the looks of any front mount over a top mount anyway unless there are some real gains to be made by going sbc top mount, Thanks for your advice.
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John "Never give up on what you really want to do. The person with big dreams is more powerful than one with all the facts". Albert Einstein Last edited by JM 35 Sedan; 04-14-2012 at 08:02 PM. |
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04-14-2012, 08:08 PM | #9 |
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Re: In defence of the sbc dist
Charlie, another senior moment?
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04-15-2012, 02:57 PM | #10 |
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Re: In defence of the sbc dist
For the past few yeas I've tried to explain the benifets of a properly tuned engine. I some times think it falls on deaf ears. With proper tuning it can giveexelent performance and economy, but you have to work at it and understand the principales behing the systems involved. Old carburetors by design do not atomize the fuel ad well as ne ones. New carburetors have more methods for fuel delivery and atomize the fuel better.
Ignition systems have to operat in several areas, like power. In the past all we thought of was how much power we could get from one of these engines. Today we have to cinsider fuel economy and the ignition system plays a big part in that as well. Using an ignition system that does not provide for this is a wast of fuel and damaging to the engine. The question," should I use a GM distributo"? can be answered this way, only if you want the best performance and economy at a reasonable cost. And it works on 6 or 12 volts. MSD also makes a similar distributor that works on 12 volts. Once you have one of these YOU have to tune it for your application. If you don't mind wasting gas, washing your cylinder wall with excess fuel distorying the rings, then by all meand don't use it. AS for the early distributors, using the 11A advance mechisum will help in these areas, only if they are in proper working condition, but we're wotking on improving them too. |
04-15-2012, 07:51 PM | #11 |
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Re: In defence of the sbc dist
To repeat myself...getting advance right on an engine is one of the BEST hopups you can do, for performance and economy. Load adjustment...vac advance!...is important for power and economy, as you can't do much of your driving at full throttle (unless that's a pretty sad motor!)
Getting basic curve and load curve right can be felt in your driving more than most hop-ups, and you can do a lot for very little money. The Chevy is the distributor that is easier to tune and alter than any other, both because of basic design and because there are parts available to alter all aspects of mechanical and vac curves any way you want. |
04-16-2012, 08:26 AM | #12 |
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Re: In defence of the sbc dist
Charlie,
If I am running a stock engine will I be able to use the stock vacuum source on the carb? I know the loadamatic distributors have some shortcomings and was wondering if this might be a worthwhile improvement. Ron, To be fair, I think a lot of the info on tuning is newer with so many more ways to measure results and collect data. You would think everything there is to know about the simple concept of a four cycle engine has been written but they seem to be learning new things all the time. The computer controlled systems has changed it all.
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04-16-2012, 08:41 AM | #13 |
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Re: In defence of the sbc dist
Frank,
The Loadamatic will only work with the vac source ABOVE the throttle plates as is ported on the back of the 94 carb. Guaranteed less performance if you use manifold vac. However the SBC type dists require use of manifold vac...BELOW the throttle plates. Charlie ny |
04-16-2012, 08:49 AM | #14 |
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Re: In defence of the sbc dist
Ditto :
On what Ole Ron and Bruce had to say, saved me a lot of one fingered typing!!! |
04-16-2012, 11:10 AM | #15 |
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Re: In defence of the sbc dist
The beauty of the GM style vacuum system is: It works well with any carbonation system.
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04-16-2012, 11:46 AM | #16 |
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Re: In defence of the sbc dist
If you put in a GM dist how do you adjust the advance curve. Or is it adjusted when you buy it.
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04-16-2012, 12:46 PM | #17 |
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Re: In defence of the sbc dist
To fine tune the curve advance can be done with the springs as to when (rpm) the advance occurs.The amount of total mechanical advance in degrees is achieved by the length of the advance slot as well as a bushing on the advance pin inside the dist.(shorter the slot less total advance)
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04-16-2012, 01:11 PM | #18 |
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Re: In defence of the sbc dist
And more can be done with springs...typical mod kits give you 3 different weights plus your originals. These can be mixed, like one light and one medium, and with some bending on the end loop a spring can be made to have no effect until travel takes up the length of loop, giving a quick curve that slows down.
One of the Chevy's advantages is that all is up top and you can mess with it with little effort. Cans are available in various degrees, limiters can be added, and the points can be accurately set on running engine with no tools except the driver or allen key turning the adjustmen...I hope they gave whoever designed this thing a GOOD parking place at GM! |
04-16-2012, 02:36 PM | #19 |
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Re: In defence of the sbc dist
Same with the vacuum several people make adjustable ones and you can control the amount of advance in cruise. One of the best engine management systems around.
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04-16-2012, 04:33 PM | #20 | |
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Re: In defence of the sbc dist
Quote:
Dollar for dollar, I think the converted GM window distributor gives you the most for your money. If you can afford a highly sophisticated and very expensive full computer-controlled ignition system, then lucky you. However, you need to understand that the more complex the system, the greater the likelihood of failure. Another vote for the GM distributor. The best one-liner I can think of for setting any flathead ignition system is set the maximum advance first... and let the initial fall where it may. |
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