HEI distributors and timing (first time tuner)

[Mrturner1]

So I'm trying to tune and time the 350 I just did a top end on, and I have a few questions for you distributor and timing masters. I bought an advanced timing light and have a tach hooked up, and a new balancer with a timing tab set up. Help me get this puppy timed so I can feel all the benefits of the parts I went with.

First, it's a 1970 c10, 355cid with Pro-Topline heads. Heads have 180cc runners, 67cc chambers, and 2.02 1.60's. Cam is a Comp 280H Magnum. Billet HEI distributor (unknown brand but it's got a black cap and really nice billet stem that goes down to cam) long tubes, flowmasters, and an Edelbrock 650 AVS carb.

Is there an easy way to tell how much mechanical advance that distributor has in it? And more importantly, can I just say ta heck with what is got, and buy my own weights and springs for it?

I'm definitely a beginner, so keep it simple please lol I read for hours about the 350 and timing curves and what all the parts do, so I'll understand if you get into that kind of detail. From what I'm reading, you want as much initial timing as you can get, and then make up the rest of the timing (to equal 34-36 degrees total) with the mechanical. This makes for much more low end torque, better throttle response and you don't get that rich smell at idle.

One more thing, which port on the carb do you guys like to plug the vacuum advance into? Drivers side or passenger? One is different from the other correct?

Thanks guys
Matt

[Mrturner1]

I guess I should also mention it's got a th400 with 2600rpm stall

[dazza]

I'n no expert but have been doing some reading recently and will be firing mine up within the next few weeks. Per Edelbrock, vacuum advance should go on the ported side (passenger) connection of carb.

[Wrenchbender Ret]

You can check the mech. advance by checking the amount at idle & running up to about 3000 RPM. Then turn your dial on the timing light till it gets back to the idle setting. Then you can read the amount of advance on the dial. You want about 34 degrees total & 10-14 at idle. With that much cam its best to hook the vacuum advance in the full manifold vacuum outlet. This one will have vacuum at idle. The ported vacuum will only have vacuum at part throttle.

[dazza]

Wrenchbender, would the full vacuum outlet be used also for just a mild cam?
(sorry Matt, not trying to bogart your thread)

[Mrturner1]

Originally Posted by dazza

Wrenchbender, would the full vacuum outlet be used also for just a mild cam?
(sorry Matt, not trying to bogart your thread)

No problem at all lol

[Wrenchbender Ret]

Originally Posted by dazza

Wrenchbender, would the full vacuum outlet be used also for just a mild cam?
(sorry Matt, not trying to bogart your thread)

Most of the time, yes. You kind of have to experiment. Sometimes if you get too much timing it will run rough at part throttle. An adjustable vacuum chamber is good. You can tailor the amount of advance & the amount of vacuum it takes to advance the timing. Full vacuum at idle does not always work good with an automatic trans. The idle speed will drop way down when you put it in drive or reverse.

[57larry]

or you could time it by "ear"

[Mrturner1]

Originally Posted by Wrenchbender Ret

You can check the mech. advance by checking the amount at idle & running up to about 3000 RPM. Then turn your dial on the timing light till it gets back to the idle setting. Then you can read the amount of advance on the dial. You want about 34 degrees total & 10-14 at idle. With that much cam its best to hook the vacuum advance in the full manifold vacuum outlet. This one will have vacuum at idle. The ported vacuum will only have vacuum at part throttle.

So I'm curious about the read-up I did saying more initial and less mechanical is better all around.

[Chknlyps2]

Originally Posted by Mrturner1

Is there an easy way to tell how much mechanical advance that distributor has in it? And more importantly, can I just say ta heck with what is got, and buy my own weights and springs for it?



Thanks guys
Matt

$4.97 spring & weight kit at Summit.

http://www.summitracing.com/parts/sum-g5212

[Gromit]

I recommend Bruce's writeup about your topic from his excellent build thread - I think his distributor and timing instruction starts with post #712 on this thread:

http://67-72chevytrucks.com/vboard/s...318544&page=29

[Mrturner1]

Originally Posted by Chknlyps2

$4.97 spring & weight kit at Summit.

http://www.summitracing.com/parts/sum-g5212

So there is only one kind of weight and three different spring tensions? How do you know how much mechanical advance those weights will create?

[Chknlyps2]

Originally Posted by Mrturner1

So there is only one kind of weight and three different spring tensions? How do you know how much mechanical advance those weights will create?

You would have the same amount of mechanical advance but the different combos of your weights/their weights/springs would make it happen sooner or later in the rpm range.

Use Wrenchbender Ret's explanation using a timing dial advance light at different rpm's (using a tach) to see how your changes are working.

This is a pretty good read also
http://www.73-87.com/7387garage/drivetrain/hei.htm

[57larry]

try it at 36 degrees and take it from there

[stomper]

With the new balancer and timing tab did you confirm the timing marks line up at TDC? If you are adjusting to where it runs best it doesn't matter much but if you get into studying the numbers to diagnose runability issues misaligned timing marks could be confusing.

[Mrturner1]

If you could get weights that only make 16-18 degrees advance, and get the rest with initial, wouldn't that make for much more low end torque and throttle response? And the carb wouldn't be open so much at idle because with that much initial you could turn the idle screw way down. Am I getting that right?

[67 chevelle]

Originally Posted by Mrturner1

If you could get weights that only make 16-18 degrees advance, and get the rest with initial, wouldn't that make for much more low end torque and throttle response? And the carb wouldn't be open so much at idle because with that much initial you could turn the idle screw way down. Am I getting that right?

First let me say "thats alot of cam "
Second your question above , no wrong , too much advance down low will hurt low end torque , timing is a mystical thing , if you are running vortec styled heads , heart shaped combustion chambers , they like less advance , 32 degrees total

without a load the engine will rev faster with alot of advance down low , an engine with a load on it , especial a pushing a heavy truck , in other words you truck in drive will run like poop

[Mrturner1]

Originally Posted by 67 chevelle

First let me say "thats alot of cam "
Second your question above , no wrong , too much advance down low will hurt low end torque , timing is a mystical thing , if you are running vortec styled heads , heart shaped combustion chambers , they like less advance , 32 degrees total

without a load the engine will rev faster with alot of advance down low , an engine with a load on it , especial a pushing a heavy truck , in other words you truck in drive will run like poop

lol I've been wanting a big cam since I was about 12 years old, I couldnt resist no vortex heads, I picked up a set of Pro Toplines but I don't remember a heart shaped chamber. I'm gonna toy with it today as soon as I figure out a dang lower radiator hose that will fit. Tranny cooler hard lines are in the way and the hose it had was bending over the frame...

[68 P.O.S.]

http://67-72chevytrucks.com/vboard/s...d.php?t=274806

A lot of good info in this thread, including how your vac advance should be properly hooked up.