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Listen and Learn
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Discussion Starter · #1 ·
Okay I always see people on here asking how to setup their ignition timing curve and the answer always seems to be make sure its all in by 3k rpm. So my question is why? Wouldn't tire size, rear gear, auto/manual, converter stall, vehicle weight, and power band rpm range all have an influence on when the final timing figure should be all in by? Where does this 3k come from? Is it only for carb'd v8s or does it apply to newer cars also? 4cyls?

So basically I am asking if someone could go in depth more on why it is this way and what factors determine it.

Thanks!
 

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WFO
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3000 rpm is a rough rule of thumb. Like you guessed, there are many factors that can affect the amount of advance and the rpm that it's all in by.

Generally speaking you want as much timing as early as the engine and conditions will allow. Most vehicles w/a SBC engine will tolerate full advance by 3000 rpm, unless there are extenuating circumstances like you mentioned- tire size, weight, fuel, gear ratio, etc.

That said, each vehicle should be evaluated on an individual basis; I know of no hard and fast rule that says "X timing for X vehicle/engine", other than as much as can be tolerated w/o detonation or a loss of performance.
 

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Basically, you want peak pressure from the fuel air being burnt about 15 to 20 degrees ATDC. The mixture burns slow at idle speeds. So you need around 10 degrees BTDC to give the moisture time to burn at idle.
The piston moves faster at higher RPM, so you need more advance to have peak pressure at about 15 to 20 ATDC at speed.
Above about 3,000 RPM, the gas mixture is swirling around inside so much that additional advance is not needed.
That is a very simple explanation. There is a lot of theory that has been written and studied about ignition timing. Way more than I know.
 

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Listen and Learn
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Discussion Starter · #4 ·
So would you guys agree that With a lower gear (Numerically high), high stall converter, high compression, big cam engine(like bracket car/pro street/ drag/etc...)You would get the timing in before 3k because there is less load on the engine and it will allow you to do so without detonating. Where as if you had a big heavy truck with numerically low gears and a stock converter stall speed then you would tend to bring the advance in later because of the increased load on the engine would start pinging?
 

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WFO
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So would you guys agree that With a lower gear (Numerically high), high stall converter, high compression, big cam engine(like bracket car/pro street/ drag/etc...)You would get the timing in before 3k because there is less load on the engine and it will allow you to do so without detonating. Where as if you had a big heavy truck with numerically low gears and a stock converter stall speed then you would tend to bring the advance in later because of the increased load on the engine would start pinging?
In a word, yes.

In extreme cases where the cam timing has a lot of overlap, the 'all in by' rpm is at idle- the timing is locked in at the best power total and left there, sometimes w/a vacuum advance can hooked to ported vacuum as a crutch for driving on the street.

Then there are some GM crate engines like the 502/502 HP BBC that say to use 30 degrees total timing, and the supplied distributor has heavy mechanical advance springs that keeps the total timing from coming in much before redline! Now, that's not to say the 502 will make the best power like that, but due to GM having no control over things, they recommend 30 degrees brought in slowly to be safe.
 

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Listen and Learn
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Discussion Starter · #6 ·
In a word, yes.

In extreme cases where the cam timing has a lot of overlap, the 'all in by' rpm is at idle- the timing is locked in at the best power total and left there, sometimes w/a vacuum advance can hooked to ported vacuum as a crutch for driving on the street.

Then there are some GM crate engines like the 502/502 HP BBC that say to use 30 degrees total timing, and the supplied distributor has heavy mechanical advance springs that keeps the total timing from coming in much before redline! Now, that's not to say the 502 will make the best power like that, but due to GM having no control over things, they recommend 30 degrees brought in slowly to be safe.
ah okay. Is there any reading material you would suggest that gets more in depth on ignition timing and proper tuning of engines. I just got this in the mail.. http://www.amazon.com/FBO-Systems-TTW20-Tuning-Win/dp/B00684P6OM/ref=sr_1_1?ie=UTF8&qid=1341854061&sr=8-1&keywords=tuning+to+win
can't wait to start reading through it but I wanna learn as much as I can about really understanding the correct way to tune an engine and to get it to run top notch.
 

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WFO
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That's a good question- I don't really have a good "go-to" book on ignition/timing/et cetera. Maybe someone will read this and have a suggestion. And I'm sure the book you just got will cover it but how deeply I don't know, prolly enough to help some, anyway.
 
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