Surfer69

Before my engine rebuild had Qjet curved perfect per Lars' instructions at total of 36 with no pinging at WOT and initial at 12 deg. Now with new cam and intake but same carb I'm down to 8 and 30 total and still getting some pinging at WOT.

Maybe answer is obvious that jetting is now too lean, it was on rich side compared to stock but I'm not sure, need some opinions. :confused:

Chuck Harmon

Your new cam and intake manifold may be creating much higher cylinder pressure than before. In other words, you are cramming more air/fuel into each of the cylinders now than you did before with the old setup. It is this higher cylinder pressure that is causing pinging. If you left the old cam and intake but upped the compression ratio with a piston change you would also have increased the pressure. Most people understand higher compression causes pinging or knocking, but don't understand the same thing can happen when you drastically improve the breathing ability of the engine.

Try adding higher octane gas (100 r+m/2) if you can find it and see if that takees care of the problem. If it does and you can bump the timing back up to 36-39 degrees, you are in for a real treat!!

Chuck

p.s. I should also add that if you changed plugs with the wrong ones, i.e. longer reach plugs for aluminum heads vs. shorter plugs for iron heads. The exposed threads from either the plug or the head willget very hot and start to glow causing preignition. A mixture that is too lean will increase the liklihood of preignition, but I would give Lars the benefit of the doubt in setting your QJet up correctly.


[Modified by Chuck Harmon, 3:31 PM 10/9/2003]

The Money Pit

Your cam has fairly short duration which when coupled with iron heads and decent compression could easily cause the pinging. I'm not sure what the compression is you're running,but in addition to the compression a fresh engine typically will run hotter than after the rings seat.Let it break in for a bit before you start worrying too much about slight pinging that only happens when you're on it hard.This problem may fix itself in time.

Surfer69

Good comments, thanks. I did get a runon for the first time ever the other day which now you guys might have just explained.

Also I should have said distributor curved per Lars not Qjet.


[Modified by Surfer69, 8:26 PM 10/9/2003]

blunsford

You could also try a colder heat range of spark plug, a cooler thermostat, richer jets in the carb

Smokehouse69

Check your balancer, last year JB was having a nagging problem with pinging on his 69 BB. Lars took a look at his car on a visit to Texas and found that the balancer had slipped and his timing was much more advanced than it originally seemed.

Surfer69

Balancer is brand new. I checked again and noticed I was passing my 36 mark by a hair even when initial was set to 8. A while back I had opened my slot in distributor slightly because even with no springs and advance at 12 I was not reaching 36 total. Then I noticed slot was too long allowing to much past 36 and I needed a sleeve on the tiny stop post to control max total.

Well now I notice this sleeve is gone which explains everything. I had bubba'd the sleeve using red rtv which didnt hold. Only choice is a little JB to hold new sleeve on. Cant find old sleeve either. :eek:

Well we'll start over and pinging should go away now. THX