what to time my engine at. - Team Camaro Tech
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post #1 of 6 (permalink) Old Jul 3rd, 03, 09:32 AM Thread Starter
 
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Location: Thunder Bay,Ontario,CANADA
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I have a 1967 camaro with a 454 engine with open chamber heads, 11.0-1 compression, dart intake, 850 holley, with a billet distributor. i'm having a heck of a time with the timing i have heard that 32 degrees advanced is what it should be at. i'm pretty confused since tuning is not anything i'm good at can anyone help.... let me know if you need anymore info. p.s. its built up to LS6 spec and i can find them anywhere on the net.
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post #2 of 6 (permalink) Old Jul 3rd, 03, 10:23 AM
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Sean
 
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you say 32 deg. advanced, do you mean that its 32 degrees total? if so, i'd actually try more total, around 36. and if you mean initial, i'll bet its real hard to turn over . the only info i would be curious about is are you familiar with timing, enough to know how to achieve, and what is your total timing. if so, get your total at 36, all in by 3000 rpm, or so. if you aren't clear, just ask questions and somebody here can surely help. good luck [img]graemlins/thumbsup.gif[/img]

Sean

1968 rs with an old school 354" SB2.2 pump gas motor.

Repetition does not transform a lie into a truth.

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post #3 of 6 (permalink) Old Jul 3rd, 03, 01:20 PM
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Total advance depends on fuel also. If you're octane limited you might not be able to hit 36 without pinging. Stock engines like as much as 42 degrees or so.

A distributor machine is a cool tool to dial in the timing and really helps understand what all is going on. But you can do it the old fashioned way.

Typically you have two types of advance. Mechanical and Vacuum. The Mechanical advance consists of two weights attached by springs inside the distributor. As RPM increases from about 1200RPM or so, the mechanical advance starts bringing up the timing. Often the mechanical advance will be "all in" by 2000-2500 RPM depending on the application.

Vacuum advance raises the timing at idle. This gives you better off-idle response, raises idle speed and smoothnes, and helps with hard starting. Vacuum advance gets it's vacuum source from the intake manifold where vacuum is high near idle and falls off as the throttle is opened. Emissions controlled cars will use ported vacuum to reduce nitrous oxides at idle, but manifold vacuum will perform better. Vacuum advance quickly drops off as load is applied to the motor and RPMs increase. Vacuum advance has no effect at Wide Open Throttle.

Ball park timing figures are 8-12deg base and 36 total. This means you start with the idle timing mark at 10-12deg. The mechanical advance will add about 16deg of advance at the crank (or 8deg at the distributor shaft) at high RPM (2500). Vacuum advance should bring idle advance up to about 20deg. This is about 10 crank degrees above base timing (or 5 cam degrees). Also, since the vacuum advance is active at idle, you must disconnect vacuum advance to set the base timing.

Base timing should be measured with the vacuum advance disconnected and the port plugged. Fine tuning of the advance will be a cut-and-try process. You'll want to give the motor all the timing it can handle without pinging or detonation. The "knobs" to turn are...

1) Change the one or both of the mechanical advance springs to a heavier srpings (slower advance rate) or lighter springs( quicker advance rate). You can also get different weights, but usually one set of weights and three different sets of springs will allow you to tune the advance how you want it.

2) An 'adjustable' vacuum advance will have a spring weight adjustment inside the diaphram housing to control the vacuum level required for full vac. advance. (Stock units often aren't adjustable) Vacuum advances can also be had which limit the amount of vacuum advance. Check out Crane's adjustable advance and advance limiters.

-dnult

Dave
========================
68 Coupe, 350 w/ Edelbrock Performer RPM heads, cam, intake, 700R4, Dave's small body HEI
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post #4 of 6 (permalink) Old Jul 4th, 03, 05:22 AM Thread Starter
 
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Angry

You guys are a big help but let me get this straight..... I have a mechanical advance so does this mean i set the timing at 10-12 dgrees and then rev the engine up to 2500 rpm and check if the timing is a total of 36 dgrees at the crank which is where i'm measuring it at with a timing gun? Does this sound about right. BTW i'm running gas with a Octane of 92 and an octane boost.Thanks for your replys. [img]graemlins/beers.gif[/img]
Happy Fourth Of July My Friends South Of The Border!!!
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post #5 of 6 (permalink) Old Jul 4th, 03, 06:20 AM
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Your explaination is correct. It's nice to have one of those timing lights with the offset knob on the back. That way when you rev it up, you can crank the knob until the timing marks line up on 0deg and read the timing off the back of the timing light. Only thing is, some of those timing lights are a bit inacurate. But that's usually Ok since you aren't shooting for precice numbers, but rather getting all the timing you can get without causing detonation.

As for 92 octane at 11:1 compression, you'll have to be ever aware of pinging and detonation. As a result, you'll want to sneak up on the timing values for your car. For example, start with the heaviest advance weight springs. Take it for a drive. If you don't hear any pining, replace one of the springs with the next lighter spring. Drive it again, and if you still have no pining, replace the other heavy spring with a lighter one and so on. When you encounter pining, back up one setting on the springs.

Vacuum advance adjustment is similar, but must be done while driving the car with a load on it.

Also, If you find that your destributor advances too much, look for ways to limit the advance. Some weight kits will limit the total advance. I knew a guy who drilled the advance plate installed stops to limit the advance.

Crane sells a little star wheel that mounts on the vacuum advance canistor mounting screw. It's purpose is to limit the amount of vacuum advance. But what it really does is set the baseline position for advance. This makes it necessary to reset base timing and ultimately ends up knocking off a few degrees on your overall timing. That's the method I am using.

-dnult

Dave
========================
68 Coupe, 350 w/ Edelbrock Performer RPM heads, cam, intake, 700R4, Dave's small body HEI
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post #6 of 6 (permalink) Old Jul 4th, 03, 06:41 AM Thread Starter
 
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Angry

Thanks For your Help Dnult its much appreciated. [img]graemlins/thumbsup.gif[/img]
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