Don Terrill’s Speed-Talk

There’s on 1 camshaft in a 455 Pontiac, but several experts suggesting different cams

I'm not a Pontiac guy, but sounds like something's out of whack. 9.4:1 CR & 180 psi cranking shouldn't be pinging on anything better than kerosene.
Does it ping at very low RPM, or only when the revs get up to xxxx?
If you lug the engine down at WOT via a hill or the brakes, at what RPM does the ping begin?
Is that 30° total mechanical, static included? (I believe a lot of Pontiac V8s run 34-36°.)
What's the piston/head squish clearance?
Has the timing pointer been verified?
Are you using 91 octane or??
What's the coolant temp?
Any chance the carb is way lean?
Can't compare exactly with the data at hand, but the Jones cam would probably have had ~ 5° later IVL and 10-15 psi less cranking compression.

You could try a slower spark curve and/or retard the cam a couple of degrees. If all else fails, https://boostane.com/ reviews put it several cuts above most octane improvers.

Quench is .045
Comp ratio is actually 9.5
Engine pings whether total timing, mechanical + initial, is 30-36 degrees all in by 3000rpm.
Made it ping yesterday at 2500rpm by driving in 3rd gear, loading the engine by using the brake, throttle open but not WOT.
Fuel is 98 is Australia. Same as US 93

pmd400 wrote: ↑Fri Apr 06, 2018 8:04 pm Quench is .045
Comp ratio is actually 9.5
Engine pings whether total timing, mechanical + initial, is 30-36 degrees all in by 3000rpm.
Made it ping yesterday at 2500rpm by driving in 3rd gear, loading the engine by using the brake, throttle open but not WOT.
Fuel is 98 is Australia. Same as US 93

Do you have a heavier spring for dizzy to slow down the curve?

Iv put heavier springs in. Probably didn't get full advance until 3500. Afr gauge installed. Not running lean

pmd400 wrote: ↑Fri Apr 06, 2018 8:24 pm Iv put heavier springs in. Probably didn't get full advance until 3500. Afr gauge installed. Not running lean

If that stopped then it just advancing to fast, not every engine wants the same advance curve.

MadBill wrote: ↑Fri Apr 06, 2018 6:43 pm Has the timing pointer been verified?

If you didn't build the engine, I'd definitely check that. Back when i used to tune cars all the time, a number of folks brought me their cars with "timing issues" only for me to find they had not set the pointer to zero during the build, put on an aftermarket pointer without "zeroing" it, replaced the balancer, etc.

Well 1st off, you do not need a duel pattern Cam with a Intake to Exh ratio like that especially with the fast piston speed of that stroke being bigger then the Bore.
2nd, with that compression ( cylinder pressure ) and the high load of the 2.73 gears you want a minimum of 225 duration @ .050" .
Stock 6X heads without the Intake valve seal average a clearance between the top of the guide and the bottom of a stock retainer of .480" , so cutting down the tops of the guides will be needed , as will cutting the Exh guides for seals, Viton type seals by the way, NO Telfon!
With most any aftermarket spring do not attempt to use the stock oil shields.

That combo should be pretty tolerant on fuel.

Assuming the compression ratio is accurate, and the cam was degreed and in the right place

- Check TDC and make sure the balancer is correct
- Check initial afterward and total and report back.
- Make sure it's not running real hot
- Try a different fuel
- If it's still pinging bad, maybe the compression isn't what you think it is, you are lugging it too much, or the cam isn't what you ordered. Your cranking compression numbers seem to make sense, so I am banking on the ignition

BTW, I also like closing up the centers on a Poncho. We went with a 279/224 280/230 109 LSA and put it on 107 ICL for a 67 400 GTO. It runs REAL well for 4 barrel 400 HO in a 67 GTO 4 speed 3.55s. Car is a mild hot rod and blew the owner away from any cam he had in it before

As far as gear ratio for the crowd, remember, he has a Richmond 5 speed, so that 2.73 ratio acts like a OD, but the car should run like it has some gear out back in every other gear

SLR = 8.954, that'd be the same as a TKO-600 with a 3.25 gear in 1st or a Muncie with a 3.85 gear

OD = 2.73, same as a TKO-600 with a .64 and a 4.26 gear.

That car is set up pretty well, something must be not as expected. Cam is shorter, compression is higher, timing is wrong or quicker.

Some extra info:
OP says with 30 degrees of ignition timing the car will backfire out the exhaust when letting off the gas.
With 36 degrees timing the backfire goes away.
Odd.

pastry_chef wrote: ↑Sun Apr 08, 2018 2:28 pm Some extra info:
OP says with 30 degrees of ignition timing the car will backfire out the exhaust when letting off the gas.
With 36 degrees timing the backfire goes away.
Odd.

That did happen. I had vac advance disconnected. I also had initial set to 6* before tdc to get the total down to 30*. I think it was just a sudden close of the throttle combined with slowing engine speed so it was not getting a lot of advance. If vac advance was connected it wouldn't have happened. Iv had some advice to remove the dual quads and put the iron intake/qjet back on. I'll give that a go this week.

FYI,The E dual quad is not the best for your pontiac,the Offy is way better.Also your carbs are too small.I do agree that the 30 degree timing is a issue.Tom

You may be backfiring at 30 because your not burning all the fuel and that unburned fuel is then lighting off in the Exh system.

Consider oil in the combustion as a possible source of detonation.