I have a 340 of unknown origin with stockish heads 525 solid cam 248@ .050.I am currently using a 3310 vacume secondary 750 holley and I can't seem to get the timing right.I have to retard the timing to stop detonation but that leaves me with not enough initial.......thoughts?BTW using a msd dizzy

Pro billet ? Mech advance only ? If so, you can use a combination of the springs and bushes included to get the most suitable advance curve.

Edit: Link to instructions: https://documents.holley.com/frm29056_8534_85345_8543_8544_0817.pdf

They make bushings to limit total curve get one of those kits. I think the smallest sweep is 8-9 degrees. Or better fuel.

I used the msd lite blue/silver spring combo in my small block and set total at 36* with a flat top and 38* with a dome. All in by 2000rpm. Better fuel as suggested.

I am using the 21 deg swing bushing.......I am going to change it for less swing ,I am using the stiff advance springs,

What distributor are you using? Factory, aftermarket, etc???

I ask b/c the aftermarket MP ones did eventually adapt the Mallory mech. advance mechanism, which then meant you could use their Advance Curve Change Kit (part# 29014) to tailor accordingly.

I've had this in my setup for a number of years now, using 2 PINK springs which gives me 21 advance @ idle (800 RPM) and a full 35 at 2000 RPM.

Mallory of course makes their own line of Mopar SB distributors, but if I was to buy one now I would probably caugh up the $$$ for one of the programamble curve ones!

Take a look at the attached Curve Change Kit insturctions.

Just for info, I have it written down that we used the Blue bush and the lightest (sliver) springs. This was on a mild 318, KB flat tops, 302 heads with a XE 268 H cam and 3.23 rear gears. Pinking has never been a problem.
HTH's

I am using a msd pro distributor with the 18 deg bushing.....I have been turning it clockwise to try to grt rid of the ping......the further I go the more it doesn't want to idle in gear with a reasonable idle speed.....starting to think maybe a dp carb with 4 corner idle would help

You should look into a 10 or 14 degree bushing so you can up your initial timing and not get total timing out of bounds.

Someone is still making those bushings.

You want to reduce the mechanical advance so you can have between 14 BTDC and 20 BTDC at idle and 30 to 34 BTDC revved up with all the mechanical advance in all the way
Try that and let us know your results and how that works on your car please
Have you or did you verify TDC on the balancer and with the #1 spark plug out? If not, you might want to

Try locking it out and set the timing around 34 or 35. Maybe more with decent gas.

I know, it won't work. But try it.

You are going to need 24-26 degrees of initial timing and probably no more than 34 total. That makes getting the curve correct a beeotch. And it NEEDS a curve. Don’t lock it out or get it “all in” by 2500 because that’s not what the engine wants.

So get your initial correct and then work on the curve. My best guess is the engine will want 29-30 degrees at peak torque and then after that you have to bring in the rest of the timing it about about 2 degrees per 1000 RPM or close to that.

If you have a Chrysler distributor it’s going to be damned near impossible to get that type of curve without making the advance weights a bunch lighter. And then you will still be using the stiffest springs you can find. Where you remove the weight is critical. Get it off the big end as much as you can without compromising the pin where the spring hooks up.

I will say trying to do this in the car with a timing light is also near impossible. You need to find someone close to you with a distributor machine and who knows how to use it. That will make it much easier.

FWIW, I had an engine on the dyno that lost 40 foot pounds and 30 HP below peak torque because the curve wasn’t correct. Locking it out made it worse. Locked out timing or super quick curves do not make power.

EDIT: you are using an MSD distributor. That makes it a SKOSH easier because it’s easier to trim the advance weights and if you wonk a set of weights they are easily replaced.

Baldwin performance has a distributor machine and offers this service. Contact William Baldwin@Baldwin Performance, He can get you what your looking for.

A 340 w/ that much cam is gonna need a loose converter and want some rpm. If you don't lock it out, at least run somewhere around 25 degrees initial and the light springs.

^^^^^^^^^^^^THIS^^^^^^^^^

Baldwin is why I bought my distributor machine. Plus, he’s a top notch world class guy.

I am using 91 octane pump gas.....I'm starting to think this is a high compression motor....I didn't build it,the truck came with it in the doghouse.....a 10-12 deg distributor bushing for my msd pro would be great if I could find one BTW I am using rn9yc plugs,hoping a cold plug would help?

Every small block I have built likes 36° total timing, no vacuum advance and 16-18° initial with full advance in by 2000-2500 RPM. Didn't matter what heads, compression ratio or camshaft.