SBC Timing/total timing NEED HELP

Don't be tricked by the vac adv.

Initial is always measured with vac adv disconnected. After you are done measuring, reconnect adv, remember Ported has no vac at idle, manifold does at idle. I perfer manifold, but you need to test each to your preference. You can see the curve start/stop by connecting a tach and raising / lowering the RPMs and watching the cent adv. if you want, Plot the curve without vac adv connected. You really don't need a SUN machine but it helps.

 

Looking to buy # 375 GM centerplate and #41 GM Weights

From any GM HEI distributor.

Going to try something..if anyone knows where i can get this stuff, leme know

 

OK

What should my timing be 'all in' by? Right now its at 2400rpm

Im thinking about putting in 2 medium springs VS 1 medium and 1 light

 

bump for the morning crowd

 

You want it all in as soon as you can get it there without detonation. I would go with the light springs and work my way back up if it pings. If you have no detonation leave it. With a low compression engine, this will really wake it up by getting cylinder pressures up at low RPM.

 

I thought I want it 'all in' @ 3000rpm?

 

Its about 9-1 I run 93 gas in it

 

Usually in a performance sbc you will want the timing in at or before 3000rpm, how much sooner depends on other factors...springs are easy to change so you can play with that to see what your car likes.

My motor is similar to yours, and I have it at 36 all in by 2600, without vac, the vac can I have adds another 10 degrees of advance, and is hooked to manifold.

Total timing is easy to set with the dial back light, I usually set my timing at 36 and then go back to see what the initial is and that tells me what is in the dizzy. At 36 total I then check initial and have 14 which leaves 22 in the dizzy. Most gm dist have 20-24.

 

3k is a safe point, and as pointed out every engine is different. The faster it comes in the more responsive your engine will be typically. That is why I say start with the light springs and see what happens. Chances are it will be responsive, but it might also detonate. Even if it does not detonate, you can try going one spring size up and see if it helps, but usually more timing early is better for "seat of pants" performance

 

This is a heavy truck with a manual transmission too btw

(if that makes a difference)

At 60mph Im running 3000rpm 3.73:1 rear gear and 3spd on the column tran

 

checked for vacumn leaks with starter fluid. No increase in idle when I let the ether at it

 

bump to the top for morning crowd

I reset my float level/drop too just cause. My total timing is at 36* vacumn advance is plugged to manifold vacumn. I havent checked my total timing yet either.

My vacumn can could be adding too much vacumn also btw?..

 

WHAT TIMING IS SET AT CURRENTLY

Idle with vac advance hooked up 33*

Idle with vac advance disconnected/plugged 19*

Total (3k) with vac adv plugged 28-29*

Total with vac adv hooked up 47-48*



This is with Mr gasket weights and medium springs on 93 octane gas.

It seems to run/start best at these settings. Sometimes takes a little time for it to 'spin' over before it starts fires up.

Idle is about 750-800 (I re set it), vacumn advance is hooked to port behind the carb pulling full manifold vacumn.

Thanks guys

 

Bump for opinons from the eve crowd

 

Ok guys, Why am I only getting about 10* centrigul/mechanical timing?!?!?! Seems sorta low?... Shouldnt I be getting around 20* mechanical?

Anyway, Sometimes it starts up great/sometimes it turns over a few times before it starts. Is this timing or carb problems?

Thanks

 

anyone

 

19 degrees initial and 29 total isn't where the motor wants to be. With the vacuum advance unhooked a good starting point for a SBC in a heavy vehicle is 6-8 degrees initial and 34 degrees total timing....all in by 3000rpm.

Don't worry about the vacuum advance until you get the dizzy sorted out.

 

The variables checking distributors on the car are:
- Accuracy of TDC timing mark.
- Quality/accuracy of timing light, whether dial back or not.
- Accuracy of degree marks (if using timing tape)
- Accuracy of tach

If a 19 year old invests the time to realy understand the principles and confirms his measurements a few ways then I'd expect the results to be good.
If a 49 year old blindly follows a few poorly understood steps, then the results might be disappointing.
If I ever get a professionally prepped distributor I will use a timing light for initial installlation timing relative to a verified-buy-me-on-the-car TDC mark, and map out the curve and total timing as well.

Running smooth does not mean running the best it can.

 

Holy crap! Wars have been resolved faster and less complicated than this thread.........

 

I understand. I made a TDC checker tool with an old sparkplug and a bolt the balancer is new (machine shop recommended it) I checked it anyway its just about perfect) turn motor till you hit bolt mark, turn motor other way till you hit mark halfway between the marks is tdc which equaled my slot in balancer)

Anyway, Its just a 60 equus adj light

So idealy I need 26 degrees mechanical for this??! What weights should I use?