setting timing WT 400 16x,

Where should i start with timing?  Running a 68 400 WT block  (10.75:1) with stock 16X heads, stock dual exhaust manifolds, Holley 750 vac sec on an Edelbrock performer Pontiac intake, stock HEI with vac advance working correctly.  Cam is a RAIII imitation grind.

Getting alot of light to mid throttle ping at 9deg BTC with vac hose off.  If I back down to 7 deg to decrease the initial advance, and ping I really loose performance.  

I have a recurve kit, and an adjustable vac advance kit and began to experiment, but it really is alot of work changing springs up against the firewall when the car is hot.

Any suggesstions for initial timing, spring color recurve, and total advance based on experience?  I searched the archives and could not find anyone with a similar combo.

Thanks  

Any compression ratio over 9.5:1 with iron heads is going to need race fuel.  
professional hi-performance engine builder

Horsepower sells engines and torque wins races

Here's a perfect example of too much compression ratio for the octane level of the fuel available, or not enough octane for the compression ratio. Which way you look at it determines how you fix the problem.
Let me explain, an engine with that much CR was designed to run on 100 Octane leaded fuel 40 years ago, today we have ethanol blended , unleaded pump gas with...at best, 94 Octane. I know some guys may seem to get away with it, by running less timing, richer mixtures and cams with more overlap. But the truth is, for your engine to perform at it's peak, you need to give it the right fuel or lower the compression ratio to 9:1. The easist way to lower CR is to change to larger chamber heads. You could also go with dished pistons, admittedly more costly, especially if you've just rebuilt it with new flat-tops.
Your other option is to pay at the pump, buy the best octane you can get and add a good octane booster, or find a source for racing fuel (very pricey!).
Regardless of your approach, timing can be baselined at 10-12 degrees at idle (vacuum line diconnected and plugged) and 32-36 total all in by between 2000-2500rpm. You will need either a dialback timing light or a timing tape on the balancer (or mark the balancer at 10 degree increments) so you can check total advance. Be sure to check at higher rpm to be certain you aren't getting more than 36 degrees. Curve kits are a trial and error deal, start with the lightest springs and work your way to the heaviest, it's ok to use one lighter spring with one heavier on as well. Get your mechanical advance dialed in, then adjust your vacuum advance to get clean transition from cruise to acceleration with no surge while cruising.
Also make sure you aren't running way too lean, pull the plugs, you want a nice even tan color on the porcelain, jet the carb accordingly.
Yes, it's alot to work thru but patience and persistence will get you there.
Steve  
A little help... 'cause we don't all have to learn the hard way!

Thanks Steve-

Yeah engine was rebuilt a 4K ago.  bought it that way.
Do you rec. any specific octane boost?  The guys at the local AutoZone said most of what they carry is useless.  Although it would be useless to them in today's engines , I guess.
Plugs look good, almost too clean.  Porcelin is practically white, even after a few WOT blasts.  I am looking to richen-up the mixture a bit.  Running 66 on the primaries, and 79 on the secondaries.  Maybe that would help.
Would a thicker head gasket lower the CR?  Looking for a cheaper alternative.
What number head would be a large chambered head?

Thanks again for the advice Steve,

Rich  

When jetting your carb, generally you want to go two jet sizes at a time, if you have 65's, go to 67's and so on to get in the ball park. I always startby jetting the primaries, drive it around at cruise speeds without getting into the secondaries, then check your plugs. Jet the primaries to get the tan color, then move to the secondaries. You need to make a couple of 1/4 mile, WOT passes to check the secondary jetting and change the jets as required to get the mixture to where the plugs stay tan after full throttle passes. Once you are in the ball park, you can use 1/4 mile time slips to tune your jetting on size richer or leaner from your ball park.
It sounds like you have a lean condition that is aggravating the pinging issue. Get the jetting worked out and the timing to see how it works before changing your heads. I've used 104+ Octane boost in the past and I've heard the NOS brand is good, but haven't used it. You can also try blending race gas with 94 octane pump gas as well.
Steve  
A little help... 'cause we don't all have to learn the hard way!

Thanks steve.  Once the weather breaks here in the northeast (heard 12" snow on Tues) Ill give it a try.  Found a local airstrip that will sell me 100 octane fuel in the spring.  

Yep, winter sucks! We've had about 10" of snow this week in Eastern Ontario (just across the St Lawrence river from Ogdensburg NY, but they've got more!). I couldn't resist any longer and fired up the Bird last week, backed out in the driveway and let it run for 1/2 hour. April is still a long way off!
Steve  
A little help... 'cause we don't all have to learn the hard way!

I have run mid to low 12's for years with a 73 400 block (2 barrel catalina) # 13 heads that were milled .005 ( I believe this is well over 10:1) on Sunoco 94 . No problems to date . The trick I found to this is to make sure the vacum advance isn't starting too early , there should be absolutely no vacum at idle and it shouldn't start untill the carb is actually raising rpm. To adjust this put a gage on the carb where the dist hooks up and let idle , adjust the secondary idle until vacum is present (raise idle) , then back off to find '0'. You will have to go back and fourth between the timing and idle mixture a few times to find the perfect setting . The vacum at the intake manifold will be at it's highest here , this will also help if power brakes don't have quite enough vacum to operate correctly .  

I thought that vacuum was highest at idle.  As the throttle cracks open, vac dropped, I thought.  Maybe at the distributor port, there is no vac at idle??

If so, is it possible to get 0 vac at idle?  Makes sense then to limit vac advance.

Rich  

Rich, if you check the vacuum ports on the carb, you will find that some ports have vacuum at idle (unported) and some only get vacuum when you start to open the throttle (ported). That's what he's talking about, when set up this way the vacuum advance doesn't begin until you step on the gas, at which point the amount of vacuum available to pull the can is already reduced.
All of this is fine and will help make your engine more tolerant of lower octane (also getting the cooling system right so it runs as cool as possible helps), but the safest means of avoiding detonation is the right octane.
Steve  
A little help... 'cause we don't all have to learn the hard way!

I should have specified ported vacum (thanks Steve) , it should definately be "0" vacum at idle or baseline timing wouldn't be set with the vacum line disconnected (what would be the point). My cam also has .507/.510 lift at 242/246 duration which probably helps a bit . I have also run this way with a 455 that had .476/.480 lift at 230/232 duration , it was more sensitive but it worked , that motor had over 3600 1/4 mile passes on it before it gave in (mileage unknown before I got my hands on it). You may also want to check the condition of the power valve and if the correct number is installed . Hook up a gage (with a line long enough to put it in the car) to an unported (manifold) vacum and drive , the reading at cruise should be 1 or 2 numbers higher than the number stamped on the power valve , if it is higher the intermediate fuel supply isn't enough and may be creating a lean mixture , this could cause the spark knock and increase temp . After all of this is done if jetting is right you may have a hesitation when taking off at full throtle , if this happens don't increase jet size increase the size of the squirter . Octane will make all of this easier to do but the more fine tuning you do the cheaper it will be to enjoy your pontiac (less money on fuel)...  

Jpataki, and Steve-

Thanks for the help.  The car does run hot at cruising highway speeds, too.  I cant wait for the weather to warm up to try all these tricks.

I think I had a steady 15" Hg at idle from a manifold vac source.  Never checked it at cruise, though.  
 
3600 1/4 mile passes on an unknown mileage 455??!!
Very impressive.  Man, and I was worried that some occassional romping on the throttle, and a small smokey burn-out now and then might break something.

I talked to a friend at a local small airport.  I can get 100 octane no lead (heads rebuilt) in 5 gal increments currently at $4.25/ gal.  He said he may even let me blast down the airstrip a few times!!

Thanks  

Just a word of caution. Airplane gas is not racing fuel.They put some weird additives in that fuel as it's designed to run in cold and very thin air. Try to find a automotive racing fuel in your area. I'd hate to see you hurt the motor.  

Warning, race fuel will destroy pistons. It is highly oxygenated as it is meant to burn at high altitudes. This increase exhaust temp by 500deg or more. The best Octane booster is VP110. The max compression that can be run with that cam is 9.5 or 10:1 if you live at over 3000ft alt. You can reduce compression by going to a thick Cometic Gasket by 1 full point. Other wise you will need to go to a much larger cam shaft, or a custom grind with allot of overlap to reduce cranking compression. Do a compression test. If it is over 210, then you have too much compression and airflow for the cam size.  

Thanks for the warning about racing fuel!  Well, pulled the old car.  All kinds of binding on the secondary butteerlies.  Bit the bullet, and purchased a new 770 street avenger holley with electric choke.  What a difference!!  Just adjusted the floats, and the idle mixture, put one lighter spring in the secondaries.  Car fires right, does not lean out and has plenty of power.  

base timing is at 13, with about 34 deg mech all in by 2400rpm.  Compression psi cranking is 180-190#.  I need to pull LESS vac advance though.  Seems to be coming on a bit early.  Total advance with vac connected is about 55 degs!  And thats with the vac can turned down.