Posted By: GTX MATT
Detonation questions - 440 - 04/23/10 03:27 AM
Ive been playing with the distributor in my 440 for the last two days. I did get the car to pick up alot below 3500 rpm but heres my problem. The distributor is a stock 1966 440 single point unit.
The advance plate is stamped 8, so it has 16 degrees of total mechanical advance. First off this seems extremely low for a stock dizzy. I know alot of people would like this instead of having to weld up their slots, but I would have to run 22 degrees of initial to get to 38, I think the starter would kick back against that.
It doesnt matter anyway because anything more than 13 degrees of initial pings. Thats only 29 total. It is a stock 68 440 with headers and 2.94 gears and it is the 350 horse engine. Is it possible that cylinder compression could be that high with this cam that I can only run 29 degrees of total timing? This is with Sunoco 93 octane.
Also, I occasionally get a weird sound that sounds like the sound of a hot exhaust pinging after you shut the car off. Its not the marble/rattle sound of detonation, but it is a weird sound and seems to happen more on hills, but the amount of gas you gives it doesnt effect it and its not consistent, it will do it once, then maybe ten seconds later, then stop. Is this anything to worry about?
Posted By: RapidRobert
Re: Detonation questions - 440 - 04/23/10 03:51 AM
(1) Stock oe AVS? (2) is your heat riser sending heat up/across the intake? (3) how hot is the eng running? (1) convert to afb/eddy 2 step rods/jets. Check what size of rods/jets your AVs has then get an eddy strip kit w similar size rods/jets in it and epoxy the domed rod caps to make them flat then slightly richen the "cruise" step of the rods. (2) block the heat riser off at the ex manifold flapper valve and install a blocked valley pan metal gasket (3) how hot. EDIT and use 2 step jets from the kit the same or very close to your current size. MORE EDIT swap those 2.94's for some 3.55's especially if you have 15" tires
Posted By: v10
Re: Detonation questions - 440 - 04/23/10 04:47 AM
If the dizzy is old it could be wore out. The shaft sometimes walks around causing odd firing.Grab the rotor and check side play of the shaft.
I always switch to electronic anymore myself.Points are a pain.
Posted By: GTX MATT
Re: Detonation questions - 440 - 04/23/10 05:24 AM
Yes it is the heat riser is operating, it will be blocked soon as im switching to a Summit 224/234 cam (which will ease the issues for sure) and swapping the intake and blocking the heat riser. It runs at 185 on the nose and does not change.
The carb is an OOTB Holley 770, I haven't played with that yet because I figured I'd be wasting my time since that cam will be changed within a month. I've heard these run lean on the secondaries but My plugs are slightly carboned with a golden brown underneath and a little bit of oil around the outside (not on the groundstrap). It could just be that it runs on the primaries and idles so often and that those are setup a little on the rich side. It does burn some oil, about a quart in 1000 miles.
I have 225/70/15s and a 3.55 sure grip is in the waiting to swap in, but im waiting as im converting to 11 in brakes and want to do it at the same time since I have to pull the axles for both. I have to buy the drums still.
Posted By: ireland383
Re: Detonation questions - 440 - 04/23/10 10:44 AM
Could be sucking oil into the chambers. I had a ping at higher RPM and changed the secondary spring to the purple one, ping was gone.
Posted By: Dodgem
Re: Detonation questions - 440 - 04/23/10 12:49 PM
I'll bet the distributor bushing is worn right out and wobbling around like an old drunk and your point gap changing from 0 to .045??
Hope the vacuum advance is unhooked for intial tune then on ported vacuum later.
Posted By: GTX MATT
Re: Detonation questions - 440 - 04/23/10 11:13 PM
Vacuum is disconnected. I wouldnt call it a pig, but it doesn't run like a 440 should. What play should I look for in the distributor? Up and down or??
Posted By: v10
Re: Detonation questions - 440 - 04/23/10 11:41 PM
Not up and down. Side to side movement of the shaft.
Posted By: GTX MATT
Re: Detonation questions - 440 - 04/23/10 11:48 PM
Alright that makes more sense. How much play would be acceptable?
Posted By: v10
Re: Detonation questions - 440 - 04/23/10 11:51 PM
No movement to very little. It sounds like yours is very worn out and will move a lot.
Posted By: v10
Re: Detonation questions - 440 - 04/23/10 11:54 PM
Remember any movement will change your points gap.
So very little.
Posted By: 68LAR
Re: Detonation questions - 440 - 04/24/10 12:17 AM
All of the suggestions so far are good ones. I have three questions; 1. How long have you owned the car. 2. When did this start? and 3. What changed?
Posted By: can.al
Re: Detonation questions - 440 - 04/24/10 12:21 AM
..'69 shop manual shows initial timing at 5 btdc.
for a total of 35 that would mean mechanical must be 15 x 2 + 5 for 35 tot. w/0 vac advance
at 13 initial + 30, tot would be 43,add vac advance..and it should ping
your distributor must be marked wrong.
Posted By: v10
Re: Detonation questions - 440 - 04/25/10 04:53 AM
I think you will be pleasantly pleased with the difference.
Posted By: v10
Re: Detonation questions - 440 - 04/25/10 05:25 AM
As the shaft moves around it would change your points gap and your timing (causing your ping)
Let us know how things work after the change.