I'd be grateful for some opinions on what may be happening with my FRPP 392 stroked 351W.
This motor has an Edelbrock performer carb, a Lunati Voodoo roller cam, ally GT40 heads and an MSD billet replacement distributor, no spark box.
It's done 20,000 miles since I built the car, but has always had a tendency to ping under load, some times but not always. It's starting to bug me, and I'm worried about potential damage to the motor.
I always run super-unleaded, which over here is billed as 97 octane and is the best available. I was running the ignition timing at 12° at idle (around 800), with an all-in figure of 28° at 2,500. I've backed this down to 10° at idle, which will give 26° all-in at 2,500, but it's still pinging on pick up, from 1000 rpm upwards if the foot's hard down. The weird thing is it doesn't always. And it can vary with the same tank of gas. The distributor has vac advance, which is connected, but on the MSD billets this is non-adjustable. Can't be down to this anyway, I'd have thought, as it only pings under load (no vac).
Is there any history of distributors like these sticking in an advanced position? Could it be a distributor fault? I've had it apart and can't find anything wrong.
Not sure what to do next - I've had Unilites before with no trouble, so maybe a new distributor is next?
try to lock out the vacuum advance function first by either getting the kit mentioned in the MSD PDF below or removing, as noted, the advance dashpot entirely, either essentially killing the vacuum effect. Can't say that I've heard of MSD ditzys having sticky mechanisms but it's not unheard of with old, dirty and high mileage GM and Ford OEM ditzy's.
How do the plugs look? Oil fouling can and will cause pre-ignition/knocking but this is typically a progressive thing that keeps getting worse.
give that a go Bob. Not sure how much farther I can go with this distributor. I've ascertained that it doesn't ping at 28° all-in, so have tried to adjust the lower rev curve to suit that. I have the stiffest springs, both of them, and the biggest bushing to delay advance as much as possible. Yet still it will ping sometimes when I pull against load (medium throttle-pedal pressure, not flat out). Odd!
Just to be clear, I'm still a big fan of using a vacuum advance on all but race engines but here the goal is to eliminate a possible variable. If it still pings post the advance removal, then it really becomes a mystery. Don't know if you have another used ditzy to swap in for a test of whether it's the ditzy or something else.
Have you tried a different gas supplier (gas station)? Is the engine running at the same vacuum levels when new/broken-in? Same engine temp ranges? Fuel pressure still good (5+ psi for a Holley)?
This message has been edited by machoneman from IP address 220.127.116.11 on May 6, 2013 5:10 PM This message has been edited by machoneman from IP address 18.104.22.168 on May 6, 2013 5:05 PM
I've never been entirely convinced by this MSD distributor. It has a vacuum advance can, but unlike other dizzys I've had this is not adjustable. There is no facility to use an Allen key in the pipe connection hole to limit the vacuum advance.
If I find I need, or want, to change the distributor, would a Duraspark be a good idea? Performance Distributor advertise a Ford Duraspark which is matched to the engine. I don't know if they would be able to match to this motor easily. I would guess that a stroker 392 with several modifications is not going to be straightforward, but it might be worth trying them.
If I were to switch to a Duraspark, would I need an ignition box, fancy coil etc. or would I be able to just change the distributor, make the connections and away we go? I have no box, ballast resistor etc. at present.
Just seems to me a Ford part may be better than aftermarket, but...
If the engine though still pings after the vacuum advance is disabled, something else must be in effect here. Still not convinced that it's solely a faulty distributor. As the other Albert (Roger of Canada!) noted, I'm a fan of one step at a time to isolate. Still have thoughts of a weak coil losing spark energy (easy to check at night by yanking them off one at a time), maybe heat/age weakened spark plug wires (squirt them with a mist of water from a pump spray bottle), fuel pressure, maybe a remote chance it's a timing chain issue (pull the fuel pump, use a stiff wire with a hook end to pull in/push out the chain through the timing cover hole) or leaky intake manifold gaskets (believe IIRC you are NOT using the blue Fel-Pro Printo-O-Leaks (Seals). Doubtful on the last two but again it's nailing down the more obvious before buying a pricey new distributor!
in the middle of removing the vac advance can - but I'm not entirely sure I understand this.
I guess I'm removing the vac can to ensure that it can't be advancing the ignition at an unwanted time, under load.
Why not remove the vac pipe, and plug both ends instead?
Now I'm in the distributor, I can't see anything obviously wrong with it. The weights are moving freely and the springs are tight (I'm using the heaviest two in the kit, with the thickest bushing in the kit - in other words, having set the max advance at 28 I have worked backwards to give the latest start to advance possible, and the least amount of advance possible using the MSD kit. All that's left to me now is to reduce initial advance by rotating the entire distributor. Seems odd as although this is a bigger stroker it's no drag racer.
I'll get on and test with no vac can.
As I understand it, other possible causes of pinging under medium-hard acceleration are:
plug leads (although I've had three sets on while it's been pinging)
low fuel pressure
If the distributor doesn't do it, I'll have to make a rolling road booking and hope the car misbehaves whilst it's on there.
Oh, and my ign leads have no water to dangle in, unlike Albert no.1's.
I mean Albert....hah. Yes, do just that: plug the manifold port, leave the vacuum can's port open (makes no difference) and run it.
The MSD PDF though mentions the spare plate if one wants to permanently remove the vacuum advance can. Hey, if it's easier, I'd go for it.
If it still pings, can you get a hold of even a gallon or two of race gas? Run it low, add the good stuff, give it a spin. I'm just wondering of the true octane of the gas you're buying is lower than posted.....it's not impossible someone messed up.
I'll give it a go. I was wondering a bit about gas, but as drag racing doesn't happen anywhere near me, and most UK track racing requires pump gas, finding anything better is unlikely. The gas I've been using with the pinging has been from all over, not just one outlet.
I think I need to go through this setup a little - check the hydraulic roller lifter adjustment, check the fuel pump pressure and fuel lines and see if there's anything going on inside the Edelbrock. I wonder if it's intermittently going lean on me, causing the pinging.
Do you set hydraulic roller lifters the same way as flat hydraulics? Just touching, then 3/4 turn more?
ordered an adjustable vac can.
Thanks for the advice Duke. Not sure manifold vac will work with this, I've tried it before and couldn't get the idle low enough. Having said that the adjustable can might well help this. I'll report back when I've tried.
I never use the manifold vac. for vac advance on a other than stock motor, (unless there is a definite off idle problem, then I will try it.) It can solve some idle problems sometimes by opening the throttle plate more at idle not using manifold vac. KB
Oh dear ... pinging ... premature detonation brought on by crap timing or low octane fuel!
That would be pinging 101 and, I thought, a good place to start.
But after a winter of discontent, mine turned out to be a vaccum leak (a combination of a torn gasket under the Edelbrock carb and, the main culprit, a distorted cork gasket (which should never have been placed under the intake manifold. With poorly organised spark plug wires as a new (and very recent) suspect.
Your description of your distributor interior sounds familiar. Except, isn't one spring supposed to be stronger than the other?
That is enough from me. Because when they administer the pinging exam I would be lucky to get away with a C-minus! ("could do better". I am sure Bob and others will soon get this sorted.