Timing help needed

Hoping the brain trust can give me some insight on a problem I have been trying to solve for 20+ years. I have a 440 I in my truck that I put together quit awhile ago. It doesn't get driven a lot but its my time and money pit since the mid 1980 when I bought it. The specs: early 1970's 440, 906 heads, comp cam 270H grind. performer intake, Holley 770 street avenger. Heavy 4WD truck. 37" tires, 4.10 gears. 4spd. Runs great at WOT or any high rpm's for that matter. Its the low rpm that I get detonation knock. I slow to turn a corner and get off the gas, then back on it it will ping. Once I up the rpm's its fine. From a slow cruise to on it, it pings if I don't immediately down shift. On the highway at 60mph and I get on it's fine. I have always figured to much compression, not enough cam. I wanted 9.5 to 1. Not sure where it ended up.
Now that I am old and just want to cruise around when I drive it, and its more of an issue now. Working on its tune recently I took a look at its distributor curve. I took some readings at idle though 2800rpm and something doesn't seem right. All the mech advance timing is "in" at 1800 rpm. So I purchased a set of Mr Gasket advance springs. I was going to just start swapping them in and see what happens but I thought there may be a know good working spring set that I could start with? Thanks in advance for any info or insight.

What is the total timing when its "all in"?

Make sure the intake manifold is sealing to the heads. Not unusual for these to leak and suck oil into the cylinders. It will ping like crazy.

Right now total is 29 degrees measured with a dial back light. In the past few weeks I have been working under the assumption there was to much mech advance. So I installed a mech advance timing limiter plate. Which does what its intended to do, but did not help my problem. So at this point I have it in the 16 degree slot. My initial is set at 12 degrees add the the 16 mech and you get 29 degrees so its right on I guess. My intention is to move the plate to the 18 degrees slot or remove all together when I replace the springs. I recently set the initial using the vacuum gauge method and the motor likes 14 degrees but trying to limit the overall timing has me setting it at 12 initial.





Ill take a look, but I don't think I have a leak. Runs to good and idles steady and smooth on the vacuum gauge. No ping at high rpms. What do use to check for vacuum leaks ? Carb cleaner?

This is a plot of my curve against some factory curves I found while researching. Mine is the green line in middle.

Are you sure your harmonic balancer hasn’t slipped giving you an incorrect timing mark? Most big blocks like a total timing of 34 to 36 degrees. Are you using the vacuum advance? If so your curve may be advancing too fast.
Ron

1) Down shift a gear or two
2) Two or three steps cooler on the plugs
3) 160 T-Stat
4) Buy better gas
5) Retard the cam a few degrees
6) Slow the timing curve
7) Is your heat cross-over blocked
8) Richen the idle and transition circuits

I've heard the Street Avengers are really lean OOTB.

its coming in too fast, need stiffer springs. what springs are in there now? EDIT chart added & all them are likely too fast for your app & the crane springs are no longer available new. if you have the mr gasket 925B springs they are too light

I have had only limited experiance with one Street Avenger carb, an 870. It was lean at idle/transition. The only fix was enlarging the IFR.

That said, I don't know if what I experienced in that application would apply to the OP's situation.

I don't think it slipped. How could I tell for sure? I did have a total of 38 degrees before I installed the limiter plate. That's why I think Ill try the 18 degree slot next, to try and get total to 36 degrees. Yes, I am using vacuum advance, but have it disconnected and plugged until I get this distributor curve straightened out. Pun intended. "If so your curve may be advancing too fast." This is what I am thinking is going on.

1) This is what I have been doing for the 20+ years of driving the truck.
2) I have been looking into this, I have not found exactly what plug is a step cooler than the one I am running yet.
3) I ran a 160 for years, same issue, I now run a 180, never have any problems with overheating, even idling in a scorching hot desert.
4) I usually get 91 Octane at 76, best around here.
5) I hope it wont come to that.
6) Working on that now. We'll see how that goes.
7) No, I've heard of that and not sure how it would be done, but always figured its a bad idea.
8) I richened the idle, that didn't help.
Thanks for the reply

Remove the #1 spark plug. Place a rolled up plug made from paper tower in the plug hole. Remove wire from the ignition coil to the distributor so the engine does not start. Bump the starter to bring the #1 cylinder up on the compression stroke. On the compression stroke the paper plug will blow out. Now feel in the plug hole using a screw driver or other tool to feel the piston top. Rotate the engine manually and feel when the piston is at the upper point of the stroke. Then see where the timing mark on the harmonic balancer is pointing. It should be real close to Zero.

Some additional info can be found online. Here’s a youtube explanation: https://youtu.be/8Fj4lgt_WyQ

Ron

Out of all the carbs I have had on the engine, Edelbrock, Q-jet, Holley thermoquad. This street avenger has been the best out of the box. I haven't touched it since I put it on. Makes a lot of power.

Yes, I think so too. I picked up Mr Gasket set of springs 928G. I did a quick comparison and all the springs in the kit are stiffer than the one in my distributor now. Well, theres a real heavy one in there and I figure Ill leave that and change just the one light one for now.

If you down shift in these conditions, you'll be at the higher rpm that you state it does not ping. I have a 4 speed car with a bunch of compression and I can almost eliminate the ping by driving technique and gear selection.

What is your cranking cylinder pressure?

Try a NGK R5670-7

Those carbs are a bit lean OOTB, 72/75s, 75/78 worked well for me.