Im not well schooled on this and advantages of different weights and springs in a distributor. I am changing over from CC dist to vacuum advance and I work at autozone. We had 3 different part numbers. The only difference was how stiff the weights felt. I got the middle of the road in them because I wasnt sure what all that means in terms of performance or anything else.

So Im asking you fellow thirdgenners to take me to school and "learn me some distributors". If what I have isnt the best I can just change them out with kits... thats about all I know about them so take me to school boys (or girls).

WesDog

 

First off..get a timing light off the shelve at work and make sure its adjustable..meaning it will go up to at least 40 degrees.Or get one of those harmonic balancers that have the marking up that high,and a regular timing light will do.Your looking for somewhere between 32-35 degrees total advance at 2500-3000 rpms.Again... correct me if I am wrong..its been awhile since I did this.It all depends on the gas you use,compression ratio,camshaft..etc.But you want full advance in around that rpm..Heavier springs wont let the advance come in till a higher rpms..lighter ones will come in quick...maybe too quick..I had to use a heavy and light spring together on my Chevelle days to get 32 total.Total timing is base timing/centrifical/and vacuum advance added together..

 

total timing usually doesn't include vacuum advance.
So base timing, what you can change by rotating the distributor, might end up around 14*. Mechanical advance, on a stock style distributor, will be around 20*. 34* total. This is the advance you have at WOT.

Add in vacuum advance, and you should want around 52*, this is cruise timing.

Read the article Damon put on the main page of TGO. "HEI timing" or something. I think i'm using a light spring, and a medium spring or something like that.

 

Disconnect the vacuum advance while setting up the distributor. Vacuum advance is used for part throttle operation only and is controlled by a vacuum signal. Vacuum advance can also be adjustable with an aftermarket vacuum pot.

The springs control how fast the advance comes on. The weights and center cam determine how much advance.

Use an advance timing light or a balancer with timing tape or a balancer with degree marks. Set your base timing to where ever it idles best. Using the timing light and tach, increase the rpm until the timing stops advancing. You should be at total advance before 3000 rpm. You can mix and match the springs until you get the advance rpm set. One heavy and one light spring isn't a problem.

Now you have the advance rpm set, it's time to set the total. You need to know what base timing you're going to want to use because if you decide to change it later, you'll also change the total. Lets say you're going with 10* base timing and you're going to want to set total timing to 34*. That's 24* of mechanical advance. Again, you can mix and match the weights and center cam to get the desired advance. Bring the rpm up until you are at full advance and record the total advance. If not at 34*, change the weights or center cam until you get it to where you want it.

This is a lot of trial and error adjusting. Later on if you want to change the timing to see if the engine runs differently, You can bump up the base timing from 10* to 12* but you will also be changing the total timing from 34* to 36*. If the engine makes more power at 36* but you want the base timing back to 10*, you need to change the weights again to get 26* of mechanical advance instead of the 24*. Now when you set the base timing back to 10*, you're total timing will be 36*

What base and total timing is best? Each engine is different. Unless you have time for a dyno tune, it's a guess as to what to use.

Now on a race car it's a lot easier. My distributor is locked out to full advance. No vacuum or mechanical advance. I set my timing to 37* and it's there all the time. My ignition has an adjustable timing retard for starting. Below 500 rpm, the timing can be retarded up to 20* to help start the engine without it kicking back. Once the engine is started, the timing goes to full advance. This isn't recommended for a street car. My race car also has the advantage of being able to crank the engine over before turing on the ignition which also helps in starting.

 

Total timing = base + mechanical (centrifugal) + vacuum. How could it not be TOTAL without vacuum.

 

when setting timing the vacuum is disconnected, because at WOT there is no vacuum therefore you don't take that into account when setting up 32-38 max at 3k RPM.

 

During part throttle operation when a vacuum signal is created, the vacuum advance will change the timing based on the engine demand. It's a variable signal that will change with engine load. It's not something that can be set however an aftermarket vacuum pot can be installed that's adjustable to control how much vacuum advance the distributor will get. That's why race cars don't have a vacuum advance. It's a variable that can't be controlled going down the track. Under high load during launch, there is no vacuum signal however at high rpm when engine load decreases, the vacuum signal will increase and the vacuum advance will start to work. At WOT and high rpm, you normally want to retard timing, not increase it for more high end power.

When setting up a distributor you only need to set the rpm at which the distributor is at full advance with the springs and set the weights so that your base and mechanical advance equal the best total advance that the engine likes.

When you read about setting total timing, you'll see references for anything from 32 to 40 degrees. If you included vacuum advance, it could be as high as 50 degrees. Since vacuum advance is limited to what the vacuum pot is capable of giving, it's not really adjustable and the total vacuum advance can be on at just about any rpm because it's controlled by a vacuum signal depending on the engine load.

 

Are the ACCEL distributors like the MSD in that they have the advance stop bushing in them? With an MSD you use different size bushings to adjust the total advance and use the springs to control when the advance comes in. So if you wanted 36* total you could use the bushing that gives you 25* of advance and install the distributor at 11* initial. Then you find out which springs will give you fill advance at your desired RPM. For example my particular setup is the 25* bushing with 1 light blue and one heavy blue spring (so all timing is in at 2800 RPM) and the distributor is installed at 12*.

Just a quick side note, you may have problems with starting if you set the distributor up with a lot of base timing and light springs. You can end up with too much timing during cranking which will cause the motor to kick back. If this comes up, you'll need to either use a stiffer spring to slow down the advance or you'll need to use a different bushing with more advance in it that lets you use less base timing.

 

From what I read on most posts, most cars are their daily drivers that they want to play "Ricky" on the weekend. So If you have a vacuum advance, and you set up your intial and mechanical advance for racing trim, while driving down the road the engine is most likely going to ping from the excessive advance added by the vacuum system. Like stated, if the vehicle is for racing only, there is no need for a vacuum advance, but I see very few people who "only" race their cars.

 

36* at WOT provides most power for most SBC motors.

Add in vacuum advance, and you're at around 52*, at low load cruise. This doesn't ping, and runs totally fine.

 

52 degrees with todays gas..I don't think so. I bumped my timing on my L98 to 12 degrees and it pinged all the time. Dropped back to 6 and it's fine. Just 6 degrees made a big difference.

 

Your car is computer controlled. That 12* is base, then once you plug back in your EST, what's timing at at idle? Ask on the PROM boards, what cruise timing generally is, with old style SBC heads (ie, not fast burn style ones).

I'm not old enough to know what old gas would be like using, but I do know I run 52* timing at cruise, no pinging. Read that tech article, I don't think Damon is wrong on that one.

 

With light loads it's fine. It wont ping until you get into close to wot in which case the vacuum advance goes away anyhow. 6* is a big jump. Timing adjustments are usually made a degree or two at a time. A single degree can make a huge difference in HP

 

I have the MSD PN8361 and timed it with heavy springs. 12base and 32 total.
I'm running vortec heads.

My question is this 32 degrees is all in at 4k. Can this be bumped into a closer RPM range? Like have total time in by 3k?

 

yes, and it's a good idea. Toss one heavy spring, and use a light spring in it's place. Or dual medium springs.
You should have a chart that came with it, telling you roughly what RPM the timing will come in at, with which springs.

 

I have a timing light that is adjustable it has a **** on it from 0-65. I got the distributor with the light springs which means that it will advance the timing faster as the rpms go up than a heavier spring correct? I can change these out with a kit that has different springs/weights. I guess what I was wondering is if there is really that big of a difference in the weights in terms of everyday use. I can see where it would come into play in racing or high performance use but what about just day to day stuff. This car definately isnt a hot rod... yet

I wont be setting the timing anytime soon I dont think. My #4 doesnt fire and Im taking the top end apart to look at the cylinder and see if I lost a ring or if there is a hole in the piston. I pulled the valve cover with it running and everything was working like it should. I had plenty of spark so Im just gonna pull it apart and take a look and see whats going on. The engine is .040 over so Im afraid if its a ring its bye bye block.

Im not running anything extreme its just a stock 350 engine with the crap smogger heads. I was just wondering if there was really a big difference with the springs/weights as far as just a daily driver type car.

Im about to go out and pull the head off. I got the intake off yesterday and found a nice big wasp nest with about 50 red wasps in it under the parking lamp... I counted 13 stings on my left leg.. when I looked down I couldnt see skin only wasps from my knee to my foot.. ouch. I taught them a lesson in life with some wasp/hornet killer poor little suckers were twitching around like crazy just stinging the air and each other.

I have a new performer intake and a 600 edelbrock carb to put back on there and I might put one of those cheap rv type cams that come in a kit with the lifters for like 50 bucks in it if the engine is ok.

I can get the hooker 2055 headers ceramic coated with the y pipe at work for 500 bucks... is that a good deal or not? I havent priced headers in a while but the stock 305 exhaust is really crap.

Well enough off topic stuff thanks for the answers guys.

 

Answer: It just is. When hot rodders talk about "total" advance it's just initial + max centrifugal. No vacuum advance. This is one of those phrases that's been around since forever so lots of people use it, but it doesn't really describe what you might think it's describing.

52* advance at light throttle with a SBC is certainly possible, especially with an EGR valve. Even a non-EGR motor with some compression can easily take 45, sometimes as high as 50, assuming you're not running high compression and/or using cheap gas (Vortec and other "fastburn" heads may not want or need this much timing). Usually when you get up in the 50-55* range you're talking about a low compression motor and/or with a functional EGR system.

Heck, I run as much as 46* advance in my supercharged 383. At WOT when the vacuum advance goes to zero it never sees the high side of 28*, but at part throttle and no boost a ton more advance is possible.

Also- I forgot I wrote that HEI article. I just went back and re-read it. It's still pretty good. I might change a few minor points, but basically I wouldn't change anything major.

 

Crazynights- a lighter set of spring in that MSD will help your low/midrange torque considerably. 4000 RPMs is way too high. There isn't a small block made that needs any more advance over 3000-3200 RPMs. And in a short-spurt type situation where you're revving quickly through the low RPMs (dragstrip use only) it can be almost a 1000 RPMs lower than that in some cases. Since you have to drive on the street I don't recommend bringing it in any quicker than 2800-3000 RPMs, especially in a manual transmission car where the engine can get "lugged" at too low an RPM sometimes. In short, around 3000 would be just peachy.

Put in the 2 blue springs in place of the heavy silver ones that are installed in the distributor from the factory and you'll be set up a lot better for a performance application. The difference should be noticable in the seat of your pants, not just a few ponies on the dyno.

Most guys who run Vortecs report that they get their best performance around 32* total advance (see post above for explanation of that term if you haven't read it yet).