"Quicker" advance curve; any benefit?

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MopaR&D

MopaR&D

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I'm running a Summit billet distributor in my 360 (hooked up to a 2007-vintage Mallory HyFire-6A box) and I'm wondering if I might get a little more bottom-end grunt if I have the mechanical advance come in faster. It's a 5.9L Magnum short block with ported Edelbrocks and a custom-grind cam 222/226* at .050" on a 110 LSA. It's only 9:1 compression with the stock Magnum pistons and while the low-end torque is ample, I've found this engine is also very detonation-resistant; it runs on regular gas and I've found max power total ignition advance to be around 44 degrees BTDC (yes I know that seems very high but I have the "open chamber" Edelbrocks and I'm at 5000' elevation). Any more advance and it starts to ping slightly, any less and it doesn't pull as hard in the higher revs.

Anyway my current driveline setup is a 904 with a cheap 2600-stall converter and 2.94 gears in the 8 3/4" rear; I have a 3.55 ring and pinion and will be changing to those gears in the near future but it would be nice to get a little extra grunt with the tall gears for now, if possible. Currently there's 20 degrees of mechanical advance (so 24 initial, 44 total) that is all in by 2200 RPM. Could there be any gains by having it come in earlier or does that seem about as good as it'll get?
 
What's the part number on the ignition box and what is the advance curve like now?
 
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yellow rose said:
What's the part number on the ignition bad and what is the advance curve like now?
Click to expand...

Part number for the ignition box is 6852M

Advance curve was kind of buried towards the end; 24 initial, 44 total all in at 2200 RPM
 
MopaR&D said:
Part number for the ignition box is 6852M

Advance curve was kind of buried towards the end; 24 initial, 44 total all in at 2200 RPM
Click to expand...


I gotta read better.

I like that box.

Even at your altitude, 24 initial and 44 total would seem to me to be the limit.

Are you sure the damper hasn't slipped? Is the timing light accurate (seen many that weren't)?
What do the plugs look like. That's the definitive answer as to what the total and initial are.

If the plugs say it's slow and late on timing, I'd lock that mother out.

Something sounds hinky to me.
 
@yellow rose Here's a pic of a plug I just pulled now...

20190921_210457.jpg
 
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MopaR&D said:
@yellow rose Here's a pic of a plug I just pulled now...

View attachment 1715397448
Click to expand...


Wow. That plug is actually pretty close. That's damn fine tune up.

If you look at the ground strap, the kinda wide line or mark you see in the middle of the curve is what your initial timing is. Not in degrees, but where it's at on the strap.

If you were down here, where I'm at (pretty close to sea level...I think maybe 800 feet or so...where I grew up I raced at 120 feet or something and the corrected altitude would go less than sea level) Id say you have a bit too much initial. Where I'm at, I'd like to see the mark just up from the curve (towards the center wire) but where you are at, you've nailed it.

The mark you see that's closer to the shell is also pretty close for where you are. At sea level, I'd rather see it up from the shell a bit. But where you live, where the ducks on the pond wear oxygen masks, you've about nailed it.

It looks like you might (maybe...possibly...but I doubt it) be a skosh (and it would be a blonde skosh) hot on heat range. Again, up there where the bird walk rather than fly from lack of air, it looks like you've nailed it.

I can't see WOT but it even looks like you've nailed your idle and cruise tuning.

I must say, I'm impressed. You've pretty much knocked it out of the park and blew the threads out of it on the way out.

BTW, I don't care what the timing light says. You've nailed it. The numbers don't matter to me. Just use those numbers with that timing light.

You should be happy. Most guys don't get their tune up anywhere near that.
 
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Pretty much what has been said.
Maybe take a couple out of the total..but the plug says it's right where it wants to be.
Looks like my own plugs, brown ring down inside near electrode base...make sure you have that, if not, up the secondary jet
 
Heck yeah thanks! Glad to see I'm finally getting the hang of it after a decade or so lol... I have a wideband O2 sensor and AFR gauge which helped with tuning but I made sure I didn't get caught up in absolute numbers, I just went 'back and forth' until I found what the engine liked fueling wise. I was running it for a while on 20 initial, 40 total which even then seemed like a lot but I figured screw it, I haven't got it to ping yet let's see how far it can go... turned out it liked even more!

My timing light is a parts store one about 6-8 years old, I'm looking at vintage ones for sale online, mine seems to work fine but it feels like a cheap piece of plastic.

Looks like I need to get going putting in those 3.55 gears
 
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All in by 2200 and TC stall at 2600? Timing all in any earlier does not make sense to me....???

Your altitude is lowering your effective DCR by a full point; no wonder it is detonation resistant! So there is the torque issue; it's cylinder pressures are lower than a stock 225 /6 at sea level. (And combustion temps are low too.) One you get to that high elevation, the sea level build thinking goes out the window.
 
nm9stheham said:
All in by 2200 and TC stall at 2600? Timing all in any earlier does not make sense to me....???
Click to expand...
That's what I thought too.

At part throttle I think it's impossible to make that combo detonate.
I ran a very similar combo at 11/1 Scr at 930ft, on 87E10. Cruise timing sometimes was over 60 degrees. Sometimes I would forget to dial it back when I got into town. So she mightabin running an extra 10 to 15* at part to moderate throttle. That combo was a manual trans so it only took a short time to feel my mistake. Thing is it never made a peep under the hood. At 930 ft.

yeah get them 3.55s in there,pronto, then snug up your seatbelt.
 
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mopowers said:
What plug is that?
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NGK V-powers, they're basically stock replacement Magnum plugs.

nm9stheham said:
All in by 2200 and TC stall at 2600? Timing all in any earlier does not make sense to me....???

Your altitude is lowering your effective DCR by a full point; no wonder it is detonation resistant! So there is the torque issue; it's cylinder pressures are lower than a stock 225 /6 at sea level. (And combustion temps are low too.) One you get to that high elevation, the sea level build thinking goes out the window.
Click to expand...

That's what I thought but just figured I'd make sure and ask. I've been expecting this engine to behave like my old 360 but that had 10.5:1 compression, unported stock Magnum iron heads and a small (too small!) cam. All things considered the bottom end torque on this engine isn't as soggy as I expected it's just these 2.94 gears are giving it a hard time, I can tell it wants to rev up much quicker than it's able to due to the tall gears. I can currently hit almost 70 mph in first gear and third gear is useless for accelerating unless I'm on the freeway going 80 mph.

Also my cam was custom ground by Racer Brown specifically for 3.55 gears anyway.
 
MopaR&D said:
NGK V-powers, they're basically stock replacement Magnum plugs.



That's what I thought but just figured I'd make sure and ask. I've been expecting this engine to behave like my old 360 but that had 10.5:1 compression, unported stock Magnum iron heads and a small (too small!) cam. All things considered the bottom end torque on this engine isn't as soggy as I expected it's just these 2.94 gears are giving it a hard time, I can tell it wants to rev up much quicker than it's able to due to the tall gears. I can currently hit almost 70 mph in first gear and third gear is useless for accelerating unless I'm on the freeway going 80 mph.

Also my cam was custom ground by Racer Brown specifically for 3.55 gears anyway.
Click to expand...



Racer Brown IS Jim Dowell. He is an awesome guy and I can't say enough good about him. He is my go to guy with Cam Motion second.

What did he grind you if you don't mind my asking?
 
MopaR&D said:
2.94 gears are giving it a hard time, I can tell it wants to rev up much quicker than it's able to due to the tall gears. I can currently hit almost 70 mph in first gear and third gear is useless for accelerating unless I'm on the freeway going 80 mph.
Click to expand...
LOL. Yes I had a 3.08 rear geared car with 14" tires where the 1-2 shift was at 55 and 2-3 at 85. But with an 8.3 DCR at sea level, that made up for the lower gear fairly well. You're getting a double-whammy there...
 
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