Help - have cam card, need timing advice (beating a dead horse, I know)

1559 Views 5 Replies 2 Participants Last post by Ocean-Angler, May 19, 2012

Ocean-Angler

Discussion Starter · May 18, 2012

Sorry to bring up another timing uestion as its been hammered out soo many times.

But I have my Cam card, and wanted to get an idea of what my timing should be. And Ive also heard the, advance till max vacuum, then back off... but with a "bigger cam" this might note ven happen..

Heres my dilema -
I have a non vacuum advance dizzy. MSD 8551. So whatever my base timing is, theres no vacuum advance to add.

My cam is 230/236 duration @ .050 on a 350 with a 108LSA

If I go for the recommended.. 22-26 degrees advance at idle from what Ive seen, dont I need a timing retard box, since im gonna eat my flex plate??

Right now its about 18 degrees, not to mention IT BOUNCES! wtf.. it bounces about 4-6 degrees at idle.. ignition Box, new dizzy, ne plugs, new wires...

Cam Specs -
@ 50 TDC 17* overlap 7* intake opens 10* exhaust opens
BDC 43* intake closes 46* exhaust

And I read this, seems sorta close to mine, but IM running about.. 9.5:1 CR

glen242 said:
I agree with that, BUT, a lot of people don't really know their CR.

That being said, I am running 10.3 CR with a XE274 cam on 89 octane. Timing is 37* all in by 2600 rpm + 14* vacuum advance @ 12". I set the timing with the vacuum advance plugged, and shoot for all in by 2500 -2800 rpm. Do this by adjusting the springs. I don't care where the initial timing falls. The springs I use pull in some advance at idle, but this is not a problem. Hook the vacuum can up to the manifold vacuum port, not ported. At idle you will get, in my case, 14* vacuum + what ever your initial + centrifugal (if it is kicking in at idle). If I remember correctly, at 950 rpm idle, the timing light shows about 30*. This is ok. Don't worry about initial timing, no one drives at idle, and once you get into it, vacuum advance goes away.

BTW, running a 383 with aluminum TF heads on 89 octane with no problem.

So what should my base timing really be...? And if its over 20, Im guessing I should have a timing retard box/control for my start ups right?

total timing about.. 34-40? right ( remember I have NO vacuum advance)
ALl in by 2500?
I have a 3000 stall, 3.55 gears, and 26" tall tires...

thanks again for the help tech gurus

Oh, I was thinking I need a vacuum pump/canister, because RIGHT NOW, at 18* timing my vacuum is only 10ish

See less See more

Save

1 - 6 of 6 Posts

Greg T

· #2 · May 18, 2012

My 10.6:1 388 is running 21* initial with a 15* mechanical advance without issues. Total falls right in at 36* right at 3k rpm. With a tight 108* LSA I would think you'd want about 22* or more. Try it. If you have starting issues you can put a kill switch on the dash. Kill the ignition, get the starter going then engage the ignition. A montary push button works great.

Save

Ocean-Angler

Discussion Starter · #3 · May 18, 2012

F-BIRD'88 said:
The timing at idle is fluctuating because it is idling part way up on the centrifugal advance curve, instead of on the true base timing.
Slow down the engine idle speed and you will see.
The cause is the advance springs are too light tension.
Install one of the next stiffer advance springs to stablize the
timing at idle so the curve does not start until the motor is off idle. (1100rpm)

If you want more true base timing you need to limit the mechanical advance travel
stop. You do not want more than 36deg max advance at rpm.
The advance stop bushing sets the length of the advance curve.

The advance springs set the rate of advance and when it starts to advance.

Slow the engine idle speed and read the true base timing and go from there.

You want the power valve to stary closed at idle. read the manifold vacuum when idling in gear and select a power valve accordingly.

Get the GM starter motor rear mounting bracket for your starter motor.
If its hard to restart hot with agressive base timing install a ignition power interupt switch . It goes on the small red switching wire on your MSD box.

thanks guys
So your saying, install the stiffer springs, which are going to give me a slower advance, even though I want a faster advance because of the stall and the gearing: to solve the issue of timing bounce right?

F-BIRD'88 said:
You want the power valve to stary closed at idle. read the manifold vacuum when idling in gear and select a power valve accordingly.

Youre talking about the power valve in the carb right?
How do I know its closed or open or..?

As for the starter, I have a high torque mini starter. It doesnt have difficulty turning the flexplate even at 20* advance, BUT it wants to grind teh starter when its that high.. wouldnt it be better to go with a timing retard... this way I could set my timing at about 23* base, and retard it to 13* just for cranking?

And for the total of 36*, isnt that before a vacuum advance.. so on my SBCs with a vacuum advance, it ends up being about 46* total... so since I have no vacuum advance, wouldnt I want about 46* total ??
thanks for the help so far

Save

Ocean-Angler

Discussion Starter · #4 · May 18, 2012

I also noticed -
when the cars hot, it doesnt want to start so quickly. it just keeps turning over and over, and I have to dump tons of gas in the carb.. any ideas there? This isnt what youre referring to when you say its hard to start when its hot? I assumed you meant the starter doesnt want to crank..
the strater cranks fine, but the engine doesnt want to fire up so quick when its hot, needs lots of gas..

Save

Ocean-Angler

Discussion Starter · #5 · May 18, 2012

F-BIRD'88 said:
Find someone who knows what they are doing to fix your car.

Everything you said is wrong. DO it exactly the way I said.

The eninge has a long cranking time until it fires up, when it hot becasue it has too mcuh over vapourized fuel in the intake manifold that will not burn.

It does not need lots of gas . it needs lots of air and cranking time to purge out the too hot too rich air fuel mix and draw in a fresh mix that will burn.

If the starter motor is grinding it is not shimmed right or is wiggling on its mounting bolts. These should have a rear brace as well. 2 bolts is not enough to support the starter.

just hold the throttle open and crank it and purge out the rich mix.
Do not pump it. when hot.

The simple interupt switch works better. takes all the strain off the starter motor when hot cranking. Nothing is going to happen until that too hot air fuel mix is purged out of the hot intake. hold the throttle open a bit and crank it, 1-2-3 count, then throw the switch. DO not pump it. It will start instantly as soon as the cylinders see a combustible mix.

If you want vacuum advance get a vacuum advance distributor.

you want around 24 initial and 36 total. 10-12deg advance curve.
that begins just off idle.

Alright, im trying to follow you here on everything.

Starter -
its a high torque mini starter, and Im looking for a rear brace, but currently cant find any for a high torque mini starter.

Timing -
If I use the heaviest, least advance bushing, its the black one, and it gives me 18*. So if Im at 24 initial, + 18* Ill be at 42*
Before reading this, I ordered a timing retard module, which allows me to retard the timing at high RPM. I can set that to retard the timing 4-6* @ 4,000 RPM..
As for the springs, the stiff springs, would give me total timing in by 5500RPM instead of 3,000 like the light ones. So this is your recomendation correct?

Im just trying to clarify here, not second guess you.

Considering my setup
195CC comp ported AFR heads 2.08 valves, 350 CI, 9.4:1 or so C.R., Crane ignition box, MSD 85551, RPM air gap intake 230/236 @ .050 duration 108 LSA cam , 3000 Stall, 3.55 gears, short tires, 700R4 trans , 3600lb car- using the stiff springs is recommended - to eliminate timing bounce. Will they also be good for my setup, or should i go slightly lighter and still see if timing bounces?

Id like to do the interrupt switch you recommended. what exactly does that do?

See less See more

Save

Ocean-Angler

Discussion Starter · #6 · May 19, 2012 (Edited)

Since Im learning here, I still have a few questions.
Saw the link, Ill order that bushing. Thanks.

So I followed your initial advice of using heavier springs to eliminate the timing bounce at idle.
I went with the heavy spring, and the medium spring, and it slowed the bounce down just a little, but its still bouncing a fair amount.

Are you saying now, to use lighter springs then the ones I already put in, but by switching to the custom 10* bushing, that bushing is also going to aid, and will cause the bounce to be gone?

Or is the new recommendation for 1 light and 1 medium spring to give me the better advance (which makes sense) , but doesnt help with the timing bounce?

thanks
oh yea, any recommendation on where Id get the rear bracket for a mini starter..?

Save

1 - 6 of 6 Posts

This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.

Top Contributors this Month