Timing

[Black Girl]

Gentleman. My 360 smog block, alum head, 204/214 cam, stock converter, 69 dart likes 20 initial and 38 total. I'm using today an fbo plate at the 18 slot and changing the heavy spring for the light one in the kit.
I have slight detonation at hard throttle. Should I switch to the 16 slot or jump up to the next spring? Thanks guys!

 

[TrailBeast]

Gentleman. My 360 smog block, alum head, 204/214 cam, stock converter, 69 dart likes 20 initial and 38 total. I'm using today an fbo plate at the 18 slot and changing the heavy spring for the light one in the kit.
I have slight detonation at hard throttle. Should I switch to the 16 slot or jump up to the next spring? Thanks guys!

In upper rpms the mechanical advance is probably maxed out, so any further spring changes will likely make zero difference.
Try the 16 position of your advance plate.
38 total seems a bit too much anyway.

Or, just pull the base timing back a couple of degrees.
That will bring your total down as well without having to mess with the limit plate.

 

[Newbomb Turk]

Why the light springs? You say 38 total but at what RPM?

 

[RustyRatRod]

Generally, the small blocks work best at 34-36 total. There are exceptions of course. I'd just pull the initial timing back 2-4 degrees.

 

[abodyjoe]

sure it isn't leaning out?

my small blocks usually like about 17 initial and 35 total..

 

[TrailBeast]

Why the light springs? You say 38 total but at what RPM?

It’s common to remove the ONE heavy spring and replace it with the light spring.
This brings in the total (without vacuum) to all in about 2,500 rpm or so.

 

[Black Girl]

Why the light springs? You say 38 total but at what RPM?

I was trying to bring it all in close to the converter stall. Is that not correct?

 

[Newbomb Turk]

I was trying to bring it all in close to the converter stall. Is that not correct?

I doubt it. In most cases you want less timing at peak torque and more timing at peak power.

If you make peak torque at say, 3500 (that’s probably a bit low but that’s a close guesstimate) and you have your timing all in by then (or if it comes in even earlier than that) you are killing power at peak torque.

With your cam I would guess (at least as a starting point) 18, maybe 20 initial and by peak torque I would be around 24-26 and once you are past peak torque you want the curve to gain 1.5-2.0 degrees per thousand RPM. So that would mean at 6000 you should be 31-33 total.

If you are using a Chrysler distributor you will need to reduce the weight of the weights to slow the curve down, otherwise you will need to use springs that will close a barn door to get the curve correct.

 

[Dan the man]

I don't mean to highjack this thread but are you saying that bringing in the advance all in around 2500 is not good? Just asking cause 2500 seems to be the norm. Also I may not be understanding exactly what you're saying.

 

[Newbomb Turk]

I don't mean to highjack this thread but are you saying that bringing in the advance all in around 2500 is not good? Just asking cause 2500 seems to be the norm. Also I may not be understanding exactly what you're saying.

Yes, that’s what I’m saying. That’s coming from a guy who used to lock everything out. Or at least bring it all in by 2500.

It’s a big power killer. I won’t do that any more.

 

[Black Girl]

I doubt it. In most cases you want less timing at peak torque and more timing at peak power.

If you make peak torque at say, 3500 (that’s probably a bit low but that’s a close guesstimate) and you have your timing all in by then (or if it comes in even earlier than that) you are killing power at peak torque.

With your cam I would guess (at least as a starting point) 18, maybe 20 initial and by peak torque I would be around 24-26 and once you are past peak torque you want the curve to gain 1.5-2.0 degrees per thousand RPM. So that would mean at 6000 you should be 31-33 total.

If you are using a Chrysler distributor you will need to reduce the weight of the weights to slow the curve down, otherwise you will need to use springs that will close a barn door to get the curve correct.

Thanks for response. This RV cam makes power off idle and it is done at 4800 w/355 gears I'm in second gear in what seems like a blink of an eye. Before the fbo plate I was at 15 initial and 38 total the total on the plugs looked good but the idle was dirty, so 20 was where the vacuum stopped rising.
I think I'll try the next stiffer spring tomorrow. Btw I loved you in the movies brother!

 

[Dan the man]

Yes, that’s what I’m saying. That’s coming from a guy who used to lock everything out. Or at least bring it all in by 2500.

It’s a big power killer. I won’t do that any more.

Is 3500 rpm's better?

 

[Newbomb Turk]

Is 3500 rpm's better?

It depends on the engine. If you are making peak torque at 4800 (like I expect my engine to do) why would you have full timing at 3500?

You wouldn’t. Peak torque is the highest volumetric efficiency you can have. A tightly packed chamber requires less timing than a lesser filled cylinder.

You have to match the timing curve to RPM, load, throttle position and even the power curve. Vehicle weight makes a difference.

Assuming an engine or any family of engines wants a specific curve is walking on thin ice.

And EFI does not fix it. It still has to be programmed and all the tuning errors of the past 50 plus years won’t die quick enough.

 

[AJ/FormS]

Alloy heads do not need big timing on the street.
I too have a 360 with alloy heads, with 3.55s, but with a 4-speed.
If your heads are closed chambers, and your pistons are at or near zero-deck, then you are pushing a chitload of cylinder pressure with that tiny cam. In which case, mine didn't seem to care about the Power-timing from 32 to 36 so most of the time she is at 34 degrees.

But if your pistons are still stock 8/1's;
well yur on your own lol. In this case, the alloy heads are sucking up an easy one point of compression, until you put some heat into the chambers, at which time, they are still sucking an easy half a point.
So, as far as the engine thinks, if it could think, most of the time, an 8/1 engine it behaving like a 7/1 engine. Therefore, it's gonna want extra advance all the time, in the "cold Chambers."

Now, when I'm talking cold or hot here, this has nothing to do with the coolant temperature. This has everything to do with the chamber temperature.
Loafing along, the chamber temperature is cool, while the coolant temp is at or near the minimum coolant temp set by the thermostat. when you hit the gas, the chamber temp scoots up in a heartbeat. Normally, cast-iron heads are not gonna change their temp much in the 3 to 5 seconds that you are gonna be at WOT, so the chamber temp is gonna rise quickly.
But alloy heads will suck that heat out, and put it into the air all around them , and into the cooling system. This reduces your chamber temperature. Heat is power so, to compensate for this, it has for years been said, that you need an extra half a point of compression.
Well, I'm pretty sure, that's not enough, cuz my engine likes up to 11.3, the highest I have tried, and have run it up to 195 psi cranking cylinder pressure, still on 87E10; and With NO DETONATION, at up to 36* advance at WOT.

So like I said, if your pistons are down in the hole, you're on yur own..
But I can tell you that, about 1 degree per 100 rpm, starting from 20* at 2000 rpm, is gonna be close. So then
25* at 2500 will be fine going to 34* at 3400 is pretty much guaranteed to be close. If you get detonation under power somewhere, between stall and "all-in", just slow the rate of advance down to say 8/10th degree per 100, and delay the all in for a couple of hundred rpm.
If this makes her sluggish with the 3.55s, I'm not surprised, just get a higher-stall convertor, like say a 2800/ problem solved.
What the timing is at idle, the engine doesn't much give a fiddlefart about, so long as;
the engine doesn't stall when you put it into gear, and
doesn't clang/bang the trans when you put it into gear, and
she drives away smoothly when you granny take-off.
If you can get your Transfer slots properly set, it will do this with any timing from 5 to 15, and I never even take the vacuum gauge out of the toolbox. That gauge is for diagnostics, and, as regards a performance street engine like yours, is not much good for anything else.
Best of luck to you.

 

[Newbomb Turk]

Alloy heads do not need big timing on the street.
I too have a 360 with alloy heads, with 3.55s, but with a 4-speed.
If your heads are closed chambers, and your pistons are at or near zero-deck, then you are pushing a chitload of cylinder pressure with that tiny cam. In which case, mine didn't seem to care about the Power-timing from 32 to 36 so most of the time she is at 34 degrees.

But if your pistons are still stock 8/1's;
well yur on your own lol. In this case, the alloy heads are sucking up an easy one point of compression, until you put some heat into the chambers, at which time, they are still sucking an easy half a point.
So, as far as the engine thinks, if it could think, most of the time, an 8/1 engine it behaving like a 7/1 engine. Therefore, it's gonna want extra advance all the time, in the "cold Chambers."

Now, when I'm talking cold or hot here, this has nothing to do with the coolant temperature. This has everything to do with the chamber temperature.
Loafing along, the chamber temperature is cool, while the coolant temp is at or near the minimum coolant temp set by the thermostat. when you hit the gas, the chamber temp scoots up in a heartbeat. Normally, cast-iron heads are not gonna change their temp much in the 3 to 5 seconds that you are gonna be at WOT, so the chamber temp is gonna rise quickly.
But alloy heads will suck that heat out, and put it into the air all around them , and into the cooling system. This reduces your chamber temperature. Heat is power so, to compensate for this, it has for years been said, that you need an extra half a point of compression.
Well, I'm pretty sure, that's not enough, cuz my engine likes up to 11.3, the highest I have tried, and have run it up to 195 psi cranking cylinder pressure, still on 87E10; and With NO DETONATION, at up to 36* advance at WOT.

So like I said, if your pistons are down in the hole, you're on yur own..
But I can tell you that, about 1 degree per 100 rpm, starting from 20* at 2000 rpm, is gonna be close. So then
25* at 2500 will be fine going to 34* at 3400 is pretty much guaranteed to be close. If you get detonation under power somewhere, between stall and "all-in", just slow the rate of advance down to say 8/10th degree per 100, and delay the all in for a couple of hundred rpm.
If this makes her sluggish with the 3.55s, I'm not surprised, just get a higher-stall convertor, like say a 2800/ problem solved.
What the timing is at idle, the engine doesn't much give a fiddlefart about, so long as;
the engine doesn't stall when you put it into gear, and
doesn't clang/bang the trans when you put it into gear, and
she drives away smoothly when you granny take-off.
If you can get your Transfer slots properly set, it will do this with any timing from 5 to 15, and I never even take the vacuum gauge out of the toolbox. That gauge is for diagnostics, and, as regards a performance street engine like yours, is not much good for anything else.
Best of luck to you.

Oh come on. Not this again. There isn’t one shred of evidence that says aluminum heads will take more compression than iron heads. In fact, engine master debunked that nonsense.

I’m betting my engine, which will be at least 12:1 on pump gas with IRON HEADS won’t be any more detonation prone than if it had aluminum heads.

And I’m betting that if the engine pulls to say…6800 that it will require close to 35 degrees of total timing.

This total nonsense that aluminum heads have superior heat conductivity THAT REDUCES detonation needs to quickly die.

There is no basis in fact that the aluminum head can transfer heat so fast it can get rid of heat in nanoseconds. That’s just straight horse crap.

 

[Dan the man]

It depends on the engine. If you are making peak torque at 4800 (like I expect my engine to do) why would you have full timing at 3500?

You wouldn’t. Peak torque is the highest volumetric efficiency you can have. A tightly packed chamber requires less timing than a lesser filled cylinder.

You have to match the timing curve to RPM, load, throttle position and even the power curve. Vehicle weight makes a difference.

Assuming an engine or any family of engines wants a specific curve is walking on thin ice.

And EFI does not fix it. It still has to be programmed and all the tuning errors of the past 50 plus years won’t die quick enough.

Thanks a lot for this information. I like to learn different things. I seen that some street cams stop pulling at 4800 rpm's, what rpm would be good for that situation?

 

[MopaR&D]

Oh come on. Not this again. There isn’t one shred of evidence that says aluminum heads will take more compression than iron heads. In fact, engine master debunked that nonsense.

I’m betting my engine, which will be at least 12:1 on pump gas with IRON HEADS won’t be any more detonation prone than if it had aluminum heads.

And I’m betting that if the engine pulls to say…6800 that it will require close to 35 degrees of total timing.

This total nonsense that aluminum heads have superior heat conductivity THAT REDUCES detonation needs to quickly die.

There is no basis in fact that the aluminum head can transfer heat so fast it can get rid of heat in nanoseconds. That’s just straight horse crap.

The myth that Engine Masters debunked is that aluminum heads need more compression to make the same power/torque as iron heads which is untrue.

Aluminum has much less tendency to have hot spots in the chamber. Heat transfer away from the chamber is too slow to matter but localized heat buildup is a lot less with aluminum.

The 8.2:1 iron-headed 360 in my D200 pings with 34 degrees total timing but the 9:1 aluminum-headed 360 in my Duster is happy with 36. MANY factors at play there and I have yet to optimize the curve in the Duster engine (getting really sick of mechanical advance control!!) but overall the aluminum-headed 360 is far less sensitive to ignition advance.

 

[Bewy]

If your engine likes 20* initial, leave it there. It is telling you something. Low comp engines need more timing, all else being equal.
You have two options: reduce the total. Taking 2-4* may cure the detonation...& not hurt the top end. Other option is slow the centri adv curve.

 

[Newbomb Turk]

The myth that Engine Masters debunked is that aluminum heads need more compression to make the same power/torque as iron heads which is untrue.

Aluminum has much less tendency to have hot spots in the chamber. Heat transfer away from the chamber is too slow to matter but localized heat buildup is a lot less with aluminum.

The 8.2:1 iron-headed 360 in my D200 pings with 34 degrees total timing but the 9:1 aluminum-headed 360 in my Duster is happy with 36. MANY factors at play there and I have yet to optimize the curve in the Duster engine (getting really sick of mechanical advance control!!) but overall the aluminum-headed 360 is far less sensitive to ignition advance.

No, the ONLY way they drove the iron headed test into detonation and run on was to load it down to death and force it to do that.

That would be the same as pulling a 6% grade that’s 4 miles long and you never down shift while pulling a trailer.

That’s exactly what they did. Until that point, the iron headed engine was no more detonation prone than aluminum heads.

Go watch it again.

If guys had EGT’s and they watched them while loading the engine like that they wouldn’t do it. You can drop the temperature just by downshifting to pull the load.

Aluminum is not any more detonation resistant than iron.

I’ve been proving that for 35 plus years.

 

[Killer6]

No, the ONLY way they drove the iron headed test into detonation and run on was to load it down to death and force it to do that.

That would be the same as pulling a 6% grade that’s 4 miles long and you never down shift while pulling a trailer.

That’s exactly what they did. Until that point, the iron headed engine was no more detonation prone than aluminum heads.

Go watch it again.

If guys had EGT’s and they watched them while loading the engine like that they wouldn’t do it. You can drop the temperature just by downshifting to pull the load.

Aluminum is not any more detonation resistant than iron.

I’ve been proving that for 35 plus years.

To that end, My '66 383 with a closed chamber head & shim gasket defied detonation, I ran as much as 52° total with no vacuum....just to see. Had no top end but never pinged once, having squish &/or swirl is more of a primary factor, given the same quality of mixture.

 

[Newbomb Turk]

To that end, My '66 383 with a closed chamber head & shim gasket defied detonation, I ran as much as 52° total with no vacuum....just to see. Had no top end but never pinged once, having squish &/or swirl is more of a primary factor, given the same quality of mixture.

Exactly. Every engine is different and they will require different timing curves.

Yours is a perfect example of getting the curve right for what the engine wants.