hello guys,new to this, hope you can help me,tuning problem with a 403 cannot get it to completely stop pigning detonating:1978 403 block bored .030,probe pistons,cam extreme energy 268h-10:268-280,224-230 at .050,485-490,heads 350 big valves ported cfm 217-167,compression 10.2,performer rpm,quadrajet stage 2,proform HEI,compression test 150 to 160 ,running 91oct pump gas, tryed a lot of things ,timing at 25 total with slow curve

 

Did you try backing the timing off a little more and readjusting idle? you might need to run 93 oct or add a booster to get it to go away with that compression. It it a constant ping or only at high rpm? That and winter gas is crap to begin with...

 

at the moment runs ok without ping till 2500 but after that no more power produced with no ping .when i retarded the timing it ran ok but never got the idle good and was very hard to sart. tryed a few octane booster without success .

 

You might want to invest in a wideband as well. Just because the carb is a "stage 2" doesn't automatically make it correct. Could be too lean.

 

o yes ,the car is in the garage now since its winter here in quebec canada . so no winter gas problems.

 

wideband ?

 

Wideband O2 sensor. Reading plugs is not only a lost art, but modern gas makes it even more difficult. The wideband sensor will tell you exactly what the carb is doing, which makes proper tuning much easier.

 

thanks guys, i will look into wideband o2

 

Get NGK 5670-8 spark plugs, very cold. It helped my 9.5 to 1 350 with an aggressive timing curve and the small 204/214 cam

 

25 total at what rpm?

 

26 at 2500 rpm , tryed more, faster curve at first (hp curve all in by+- 2500) really didn't work , now the best running is 14 at 1000-23 at 2000-26 at 2500 no vacuum. this is a used engine that was in a street-strip car with a 292 comp cam that was gone trough and was great but the shop changed the cam because my application is more street than the last owner that only drove to and from the track and this thing made 420 hp dynoed before with other cam and carb and ran like a bat ot of hell !

 

i rode in on a drag pass once with the last owner and thats why i wanted it !!!


by the way it always used pump gas at the track !

 

Is it pinging under light throttle or WOT?

 

does not now !but not even close to what its supposed to be power and torque

 

starts well, vacuum good runs ok like a stock engine up to 2500

 

25* total is way too low. Somethings not right there IMO...Not familiar with a Proform distributor? Hopefully thats not a replacement spec unit for the 78 OEM 403 Olds? If so theres part of the problem. That distributor curve is way too lean for a performance build. Get a new unit with a custom curve or have this one recurved to your compression, fuel, rear gearing and cam card(highly recommended). Sounds like this dist may even have a weight limiter bushing thats too aggressive...not allowing full advance?? Counter intuitive to the ping I know but it sounds like theres several systems that need to be dialed in here. Mainly timing and fuel curves.

Try heavier springs on the centrifugal weights. Try one heavy and one med. Then two heavy etc.... E.G. bring the centrifugal all in at 3000 vs 2500. Whats the total timing event at 3000? 25* total??? Again way too low.

I've had the most success with 350/400/455s using Autolite plugs, tips ground back, 12-14* base timing at idle with carb adjusted for its highest vacuum reading. Then another 10-12* at idle with vac advance canister running off manifold vac not ported carb signals. Now your at 20-22ish at idle. Then bring the rest in 36-38-40* total, all in at 2700-3000(street engine). You generally will get better performance out of a street car running a vacuum advance can. As long as you have a decent vac signal with the cam. You want the vac canister you can adjust the limit/travel, not a variable vac rate can.

You also sound lean at the carb secondary circuit at the higher RPMs. This tells me the door spring is too tight or the jets are too lean or both. Does it sound like you're getting full travel on the AVS (secondary valve) at WOT? May need to tweak the secondary door spring one way or the other. The carb might need to have smaller secondary rods and larger jets? What size secondary rods, jets are in there now and what letter is stamped on the secondary hanger?
As Joe mentioned read the plugs and exhaust tips. White = lean. Brown is where you want to be even slightly black. Some like to run rich of stoich some like lean. You need to find its sweet spot. And the wide band O2 sensor will take the guess work out of the fuel system as it will show you immediately whether you're rich or lean of stoich.

Another thing to consider is heat. I run an insulator under the carb as well as riser crossover block offs(remove the stove in the drivers side manifold if your running a stock ex mani). Heat will make a car "ping". As will 91 and below octane gas. Some 104 wouldn't hurt.

Super tuning is the name of the game. Every system will need to be attended to. Small adjustments on one system at a time keeping track of each adjustment. It takes time without a dyno, so be patient. Now if you can afford some dyno time that will save you time and yield the best results.

 

There are many articles on how to tune an HEI. Your settings are not that far off other than your total sounds really low. I'm thinking you've got your vacuum advance bringing in too much and driving your total with vacuum over 50 at cruise when you advance your timing to where it should be. Try disconnecting (and leaving it disconnected)your vacuum advance and set your timing back to 34-36 all in at 2500-3000, then take it for a ride. If the pinging goes away then you need to limit your vacuum advance to 10.

 

Follow Mark's advice and get it tuned with a wide band. You need 10 degrees more advance, no wonder it is down on power.

 

I'll add run the highest octane fuel at the pump as suggested above.

 

Sounds EXACTLY like my 403

gotta run right now, but I assure you it can be done
Story lost to a crash at ROP
I might have saved some of it
Or I can go by memory or go fire it up and measure timing...

As I recall the vac adv was REQUIRED to get20+ degrees at idle, which gave vacuum high enough to start right and not stall. Then, since OEM VA can gave too much timing at higher rpm, I limited the VA action to about 11 degrees.

It took a while but the right configuration is great.

 

already did the timing mods sugested and the secondary actuation looks fine but i assumed the stage two carb had preety rich jetting and its supposed to take care of idle problems w/ perf cam ,that may be a big part of the problem there ! so i will get the specs on that and may get a wideband sensor .spring is coming soon so i have work to do and i thank every one for your help and keep you posted on my progress .

 

Have some questions about that compression number (and someone please x2 my math) .

403- Standard bore is 4.351 +.030 overbore= 4.381
Stroke- 3.385
350 heads- Which heads? I am going to assume that aren't #8s and are in the 68-72 family. I am going to use 66cc for this exercise as that is what my #6 heads CC'd at.
Pistons- I can't find probe pistons for the 403. It is my understanding that probes are a 3cc dish.
Deck- I'm using a hypothetical .020 deck clearance for this exercise.
Gasket- .040 felpro?

I'm getting a static CR of 10.98:1...? Which would explain all of this. What am I missing here?

 

you are mistaken these #8 heads started in 1973 and are79cc.but thanks.

 

Unless they are a custom piston, Probe doesn't make 403 pistons. The Arias forged are 3cc and I have found the #8 heads CC around 77-78 compared to the 79 number. Either way I calculated you are in the high 9's for compression with #8 heads. The cold NGK plugs I mentioned will make a difference.