Street timing recommendations

I'm looking for advice on ignition timing of my pump-gas 451 with big cam (272@.050), currently iron headed 10.3:1 but soon to be aluminum 10.6:1.
Currently I have 22 initial (starts to fight the starter hot at 24-25). Total is 36, trying to remember the curve but think it's all in by 3000. FBO adjustable limiter plate on a stock Mopar distributor.

Also running ported vacuum advance. FBO likes manifold vacuum, but it only idles around 7-8" at 1100-1200 which won't pull the can in much if at all.
FBO can sell me a can that is all in at 8".

Since it's mostly street driven (3.91 gears), locked-out timing will not only be too advanced at low speed part-throttle cruise, but also create a hot-start problem.
Cam definitely wants more than 22 to idle the best.

What I'm thinking of is one light spring and one heavy spring with a loop. So I can crank it at about 12 degrees, and have it immediately advance once running to the start of the heavy spring, 26 or 28 degrees maybe? And re-position or remove the limiter plate so total is still 36, of course.

Or, leave the distributor where it is, but get the light-spring vacuum advance canister and hook it up to full vacuum, which will raise the idle timing into the 30's but drop when I start off.

Thoughts?

On my 10.75:1 451 with 262/266 @ .050 camshaft, I have a regular mopar perf/OE style distributor
and all I did was use one spring from the Mr Gasket 925B kit. No tricks are done with the advance plate, etc.
I run 34 to 38 total all in at idle which is typically 1100+ for valvetrain oiling purposes, and there is about 20 or 21 degrees in the plate so the advance mechanism
which only acts as a start retard.

I've been doing this since the '80s on most with big cam combinations and it seems to work fine for me for street/strip purposes.

There is probably additional driveability improvement to be found in working with the vacuum advance, but I never took the time to experiment with it.

Pretty much identical to what I have done on mine. 38 is the limit with good 91 no ethanol I'm at 10.6:1 CR. I now have an add-on timing adjustment knob from MSD that allows me to take timing out from the drivers seat for varying levels of nitrous.

Any consideration on using a programmable controller box (e.g. MSD 6-AL2 or one with timing retard) to dial-in the changes you are want?

I do actually have a Jacobs "Turbo-Timer" retard unit with two retard settings, each 0-15 degrees (the second dial is selected by a switched line, in this case the microswitch on the nitrous system), and a knob to set the rev limiter too. So I can change the overall timing from the driver's seat, and add extra retard for the nitrous, but it does not affect the curve.

Before I went to EFI I had the heavy spring with the loop totally removed and took one coil off the light spring. This made all the timing come in by approximately 2200. I have done this to several cars and it's worked very well.

What was the idle speed on those engines? If the weights are starting to move (advance) at idle, it'll never be stable.
Best idle for my cam is around 1100, although I may be able to lower it to 1000 once I get done tuning.

Is there actually any pump gas without ethanol today? Here in Sweden you cant get any pump gas without it, we have 5% in all gas, 95 and 98 octan, i belive its same your 91 and 93 octan and the rest of Europe have 10% Ethanol, maybe you are lucky in the states. I have a 493 cui stroker, 10,04:1, xe275hl camshaft 231/237@050, dynamic comp 8,03:1 with Edelbrock e-street 84cc heads, i drive it on 98 octan( same your 93) without pinging with a Fbo distributor 18 initial and vacuum takes it to almost 30 at idle on 900 rpm( manifold vacuum) and 34 full advance at 3200 rpm. The engine running great with a huge low end, really nice on the street and without any pinging what so ever.

There is some ethanol-free gas, but not many stations carry it and it's more expensive than the E10.
I've only seen premium (91..93) advertised as alcohol-free, too.

The 3 spring Crane kit included in the chart is no longer available but the rest of it might be useful

If you can limit the mechanical advance so you have between 34 and 38 degrees total timing I would set the distributor up so it has between 14 to 18 degrees at idle and all in by 1500 RPM
My old pump gas Duster stroker six pack motor would idle at 800 RPM in gear with 14 degrees timing and it would be all in(34 degrees) by 1500 RPM, that work great

Thanks Cab, but my cam will not idle that slow. After tuning I may be able to get it down to 1000, but it's happier at 1100 or 1200.
Notice in my original post I have 22 deg timing initial already, and it definitely wants more than that for a better idle, and an FBO limiter plate which is how I end up with 34-36 max starting at 22...


The other problem with your suggestion is that the advance MUST start above idle speed or it won't be stable.
It might be difficult to start advancing at 1200 and be all in by 1500
Probably simplest (if not absolutely best) to just have it all in at my idle...

I learned a lot pump gas tuning on my Duster, once I installed the Mr. Gasket 925B advance springs and shorten up the mechanical advance could make it idle at 850 in gear, 1000 RPM in neutral I think those spring let all the advance come in by 1200 RPM, maybe a little slower or faster
I was running a Comp Cams custom ground solid roller cam in that motor that was 260@.050 on the intake lobes and 266@.050 on the exhaust lobes ground on a 108 LSA installed with 2 degrees advance on the intake lobes, 106-107 intake lobe center.
My message is you can get the performance you want but you will have to try, test, different combinations until to find the one combination you like

If interested, maybe temporarily give it a try and see what you think, first set up a vacuum gauge, warm it up and
just crank the distributor to 30+ at idle, then close the throttle blades and adjust the idle mixture to keep the rpm
in the same ballpark.

You might find improved vacuum at the same idle rpm as previously, and better overall idle quality.
It might even be possible to lower the idle rpm, I can idle mine down to 850 if I want to but I keep it higher
to oil the valvetrain.

Don't rev it or drive it this way as the total timing will be way too much + it will probably not crank when hot.
It will just give you an indication of how the idle may or may not be improved.
(I'm pretty confident it will help but have an open mind/would like folks to find this on their own).

If you hate it, you can always retard the timing back to where it was.

Once you switch over to a Holley Sniper you'll have complete control of the timing curve. Then you can run any idle timing you want without having to compromise on the total advance or vacuum advance. The Sniper also has built in start retard as well as timing adjustments for temperature and a rev limiter.

I use a factory distributor with 9 degree plates in both my street driven 440's. I use a factory light spring ( I've juggled around some different ones) and the factory heavy (large loop) springs; with vacuum advance distributors. there are different heavy springs like there are different light springs. the only heavy springs that will work with high initial timing are the short ones and they don't seem to be as common (this is specific to using the vacuum advance). there were some factory solid plates that eliminate the vacuum advance which would give a nice full centrifugal distributor. this works well in low vacuum engines and can actually be set up to idle at 30+ degrees at 1000rpm. I have a couple of the FBO limiter plates and the ones I have are not accurate and I don't use them; even though I have figured them out.

On the stock car I pinned the top/bottom plates together with a small bolt/spacer to elim the vac adv & this let me get the rotor phasing dead on

some factory parts i use to convert to a full centrifugal distributor. don't know if they're still available.

Why not just disconnect and cap off the vacuum advance and leave the original hardware in place?

My fuel mileage is non-existent anyway, but I still would like to run vacuum advance while cruising, if possible.
May make it easier on the cooling system in summer.

Also wondering if there's anyone out there who can set up my distributor to provided specifications... probably another dying art.

it would be very simple to just put the light race springs in and disconnect the vacuum advance. there aren't any rubbing parts so the plate is stable. setting up a vacuum advance/aggressive centrifugal isn't difficult, I do it, but it's finding the parts. tuning is a dying art, and that's why people spend thousands of dollars on the latest gadget that they still have issues with.

Yes that will work to disable the vac adv but in my case one of my dists, the phasing was way off so I pumped up the can with a vac pumpto rotate the top plate till the phasing was dead on then drilled straight down thru the 2 plates & pinned em solid in that location

I ended up using one superlight (Mr. Gasket 925B) spring, and the OEM heavy spring with loop.

So it cranks at (estimated) 14 degrees for easy starting where the dist is currently set, idle is stable at 27 deg @ 1200 rpm, gradual advance to 35@4000, didn't want to rev the engine higher while leaning over it with a timing light. Still have the "13" (26 crank deg) slots which may be a bit too much advance at high rpm, although the inherent ignition box retard should keep it below 38. If not I can just back it off a degree or two until I replace it with an "11" (22 deg) piece.

The vacuum advance adjustment I still need to tweak, but it pulls in up to 16 deg at cruise (15" vac) which is also about right.

Now to start tuning the carb until I pitch it and buy a good one from Thumper

I run a Mallory race dist that I got real cheap. No vacuum advance on it and I run about 22 at idle and 36 total all in by 1800 rpm. I usually run 92 pump on the street and racing and have never had any detonation at all. Ron

Have you ever considered vacuum advance? Definitely a good idea for the street

I don't remember your setup - how big a cam, rear gears, etc.?