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Discussion Starter #1
I've searched this and came up empty so I'll ask.

At what rpm do I want to see max advance with timing?

How much should I try to get as well?
 

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You want it all in by 3,000 rpm...but sooner can be better. Basically, get as much timing in, as soon as possible, but without detonation (pinging).

The amount of total advance will depend a lot on the motor/vehicle, and what it can handle with the gas you're using...somewhere around 32-36* depending....maybe a touch more.

This, of course, is assuming you have the vacuum advance unhooked. At a steady cruise, the engine can handle more advance....as much as ~50* depending again on engine/vehicle/fuel, etc.
 

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Discussion Starter #3
I've just turn it up to 34* from 30*@ 3000 RPM and and it really brought this thing to life!In 2nd gear it will break loose just by standing on the throttle.It's a mild 396,so I'm unsure of how much timimng it needs.

Thanks for the quick response,Paul
 

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Discussion Starter #5
How do I know when it too much?
 

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All my small inch BBC liked timing. I use to run them at 40 or more. You should be able to hear it rattle when you go too far. I never had any problems but I ran a high number gear and a loose converter so the motor wasn't under some hugh load at low RPMs. Your total package will influence what you can get away with in my experiences. RM
 

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How do I know when it too much?
If you're getting detonation/pinging under a load, you need to back it off a degree or two.
Bear in mind, however, that you can be on the verge of detonation and not hear the pinging...so be careful, and err to the side of caution ;)
 

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There are a few threads on the subject but unfortunately people use
vague, search engine worthless titles for their questions like "need help!"
or (here's the one you want): Learned a New trick today

The reason for ignition advance is the speed of combustion takes longer than you might think. In the early days of internal combustion engines, the cylinder was lit at TDC because this made sense. The engine's weren't very efficient until it was discovered the air/fuel mixture must be lit before TDC while the piston is still rising for peak cylinder pressure to occur after TDC. This means that pressure is building and opposing the piston's upward travel. This pressure can be considered "negative torque" as it's resisting the crankshaft's natural rotation. The losses are acceptable because we get more torque on the downward stroke. At some point however the negative torque on the upstroke is higher than the positive torque gains on the downside resulting in a net loss of power.

The test for optimum total advance to to test the engine underload on a dyno or dragstrip. Advance the timing in increments until the power begins to flatten out. See my sample chart in link.

It usually best to err on the side of caution because an engine may favor more timing on some days due to weather/temp conditions and want less on others.

A sign of an efficient engine is one that makes best power with the least amount of advance. Vortec's often make best power at 32-34 degrees while Camel humps might require 38-40 degrees.
 

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There are a few threads on the subject but unfortunately people use
vague, search engine worthless titles for their questions like "need help!"
or (here's the one you want): Learned a New trick today

The reason for ignition advance is the speed of combustion takes longer than you might think. In the early days of internal combustion engines, the cylinder was lit at TDC because this made sense. The engine's weren't very efficient until it was discovered the air/fuel mixture must be lit before TDC while the piston is still rising for peak cylinder pressure to occur after TDC. This means that pressure is building and opposing the piston's upward travel. This pressure can be considered "negative torque" as it's resisting the crankshaft's natural rotation. The losses are acceptable because we get more torque on the downward stroke. At some point however the negative torque on the upstroke is higher than the positive torque gains on the downside resulting in a net loss of power.

The test for optimum total advance to to test the engine underload on a dyno or dragstrip. Advance the timing in increments until the power begins to flatten out. See my sample chart in link.

It usually best to err on the side of caution because an engine may favor more timing on some days due to weather/temp conditions and want less on others.

A sign of an efficient engine is one that makes best power with the least amount of advance. Vortec's often make best power at 32-34 degrees while Camel humps might require 38-40 degrees.


Right on the money and great advice here. I have ours set at 36 for right now till we can drive the car and start fine tuning it. We have fully worked over double humps on our 355.
 

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I've got the camel humps, with a street/strip cam, and that thing loves timing. It's 40 degrees @ 3000 r's, wondering if it'll take more. 91 gas, Magnum Comp cam 292. Not to steal thunder on this thread, but since it's the same issue, want to save thread space here. It idles around 1100-1200 out of gear, 500-600 in gear, but then wants to stall once the electric fan comes on with the lights on. Might I need a new alternator to go with maybe more timing?
 

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Discussion Starter #11
Thanks for the link Paul that's what I wanted to read.I've had a couple other small tuning issues that I've been sorting out as I go.This motor is tired and I can afford to loose it,if anything is done wrong it won't be a big deal.I really enjoy learning and practicing with it,this should help me to be more comfortable with my other engine when I put it in.

Thanks for all the input,guys.I appreciate it!:)

Paul
 

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You won't hurt the engine even if you do advance it too far unless you leave it there for a long time and put a lot of miles on it or race the heck out of it. In other words, you aren't going to hurt anything experimenting around with your timing.

In addition to "Camel Hump" heads, most other other non-Vortec aftermarket performance heads like more timing than 36 degrees. I run Sportsman IIs with a fairly radical solid roller cam and have 38 degrees total. It has a slight heistation if I set the total to 36 degrees. Zero hesitation at 38. Radical cams also like more timing - especially initial timing. I know a lot of guys that run 40 degrees total with no problems.
 

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Here's a chart from an engineering text book:
Note that it's doesn't show detonation point but it does show how deviating too far from optimum timing loses efficiency. I agree that 38 is best for most SBC's with Gen 1 head but slightly less than optimum is better than slightly more. I'd rather run 36 than 40
 

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I've got the camel humps, with a street/strip cam, and that thing loves timing. It's 40 degrees @ 3000 r's, wondering if it'll take more. 91 gas, Magnum Comp cam 292. Not to steal thunder on this thread, but since it's the same issue, want to save thread space here. It idles around 1100-1200 out of gear, 500-600 in gear, but then wants to stall once the electric fan comes on with the lights on. Might I need a new alternator to go with maybe more timing?
The alternator is probably not the problem. My guess is you have the classic low torque condition that comes from your combination.
Increase the base advance but you'll have to restrict the total to 40. That means getting into the distributor and closing up the advance slot.
 

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I am with Paul on the idea of setting the base timing , it may be too low , also what kind of converter is in the car ? if its a tight converter it will pull the motor down alot in gear. I belive that the base timing is low because you say you have to idle @ 1100 out of gear
 

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The alternator is probably not the problem. My guess is you have the classic low torque condition that comes from your combination.
Increase the base advance but you'll have to restrict the total to 40. That means getting into the distributor and closing up the advance slot.
Pardon my ignorance, but I'm not sure what the advance slot is. Since the new dizzy is out of the car right now, I would be more than able to fudge with it this weekend. What I have done to it is replaced the springs to med/light combo, turned the vacuum advance one turn from fully in, but I seemed to have lost the vac advance limiting tang that bolts inside the dizzy.
 

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I am with Paul on the idea of setting the base timing , it may be too low , also what kind of converter is in the car ? if its a tight converter it will pull the motor down alot in gear. I belive that the base timing is low because you say you have to idle @ 1100 out of gear

I got what I think is a TCI saturday Night Special converter, advertized as "2,000 rpm's above stock", in a powerglide. Just to reinterate, I didnt mean to hijack the thread, just had a few related questions. :beer: :beer: :beer:
 

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The alternator is probably not the problem. My guess is you have the classic low torque condition that comes from your combination.
Increase the base advance but you'll have to restrict the total to 40. That means getting into the distributor and closing up the advance slot.
Disregard. I did some research and "learned" what the advance slot is. :beer:
 

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Discussion Starter #19 (Edited)
OK played with the timming after fine tuning the carb first.The initial timing is 15* and @ 3000rpm it 34* and it is running really well.I still need to get to a track to dial it in perfect,but it's much more responsive now.

Thanks for the help and explanations as to how and why timing is important to be set correctly.
 

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I disconnected my vac advace, plugged the line, ran her up to 3000-3500 RPM had set my light to 36 degrees, and turned the dist till the timing mark was at zero and set it. Then rehookup the vac advance. now its running 20 degrees cooler, seems to pull a lot harder Still has a few drivability issues, but now I need to play with jetting and squirter issues to dial it in.

The point of the telling, is is this the logical way to have went about this?


Steve

Thanx in Advace

Steve
You shouldn't get hung-up on any pre-conceived advance "number" like 36 degrees or any other for that matter. 36 will usually put you in the ballpark but is by no means the "magic" number for every engine. You need to fully experiment with the timing and get it optimized before fooling with the carb (as far as changing components) too much.

My engine likes 38 degrees total advance. 36 doesn't quite cut it but is pretty-close. At 38 it runs absolutely fantastic. You need to play around some more before automatically assuming you have to change something in your carb. Find your upper limit as far as advance goes. After that, you may want to play with the curve some. If you go right to 36 degrees and don't experiment any further, there's a chance you're not going to get the most out of your engine and could make things worse by jumping to the carb and changing out jets and squirters and power valves prematurely.
 
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