If the car pings under heavy acceleration, is the timing too far advanced, or retarded? Which way should you adjust the timing to fix the problem? This is assuming there is no other cause but the timing....poor fuel, etc.
Try setting timing to factory spec(9 degrees advanced at idle with vacuum advance disconnected) and see what happens. LOTS of other contributing factors...
I'm a hobbyist. Not a professional. Don't be hatin'!
Pinging is too much timing for the octane. If it is only a slight amount of pinging in a small rpm and load range you should be able to recurve the distributor to eliminate it but a wide rpm range will require retarding the timing.
Thanks, I took her our today, and I've got a bit of pinging. The main reason for the questions was a buddy of mine was telling me I needed to increase the timing if it pinged. It didn't make sense to me and I wanted to confirm my thoughts. I've got the timing at 12 adv. and it runs great, but has some pinging. I'll try and bump it down to 10 and see how she is. I'm running 92/93 octane.
92/93 doesn't work with a stock set-up. You will get pinging and eventually piston damage. You are running the same heads as I have and mine will ping with 93. Not a good thing. I add 110 racing fuel from Sunoco to solve the problem. You will also like the added performance.
Jim, just to make sure.. I've got 16 heads, but I had the pistons dished to lower the compression to 9.5:1 approx. I was told and thought I would have no problems with pump gas and this combo. I'll try and bump the timing down, but we'll see. What exact combo are you running? I'm always interested in.
I have two cars with Pontiac 400's. They both have 62's which are the same as 16's execpt they have more bolt holes for air conditioning components. My 69 is stock and the 79 has pistons to lower the compression. I'll post a link to the exact pistons at the end. Both need some octane boost over the 93. I read that you had 16's but I didn't know which pistons you have.
I'm hoping I don't need to add octane. The cost of gas is up enough, but thats the price. This is one reason I dished the pistons, to ensure pump gas. Jim Butler designed the motor with me and recommended the pistons. I'm going to do some Dyno tuning this weekend, (I'm posting a separate post about that), and hope we can tweek it to 93 Octane.
It's going to be interesting to hear the results. I've often wondered exactly what would be the best thing to do if the racing fuel dried up. I like the added octane and performance you can get from it. It's always good to have a plan B if/when things change.
Go for another test drive with the vacuum advance disconnected and plugged. If you don't have pinging, you need to get an adjustable vacuum advance canister and dial that in properly to eliminate the pinging when it is reconnected.
If it pings at mid rpm and not high, slow down the mechanical advance curve. If it pings at higher rpm but not mid, restrict the amount of mechanical advance. If it pings at low rpm, reduce the initial timing.
Your dyno guy should know how to dial in the right advance curve.
Finally put a Crane adj. advance can on. I set the limiter plate to fully limit the amount of Vac Adv. (about 12 deg vac adv btwn 10-15 in. Vac). I spoke with Crane tech 2x, and although helpful, they did not seem very knowledgeble in the installation setting for the adj. can and limiter plate. Finally figured it out after a couple of hours.
Performance is good. I may have had a bit better part throttle response with 18-20 degrees of vac adv. coming in around 5in. vac, vice the 12 degrees at 10in vac, but the response I'm getting now is strong, and I have no ping. I may play around with it some more to see what the max I can get is, but due to my location, it is difficult to tune and test on the roads.
The lower the actuation vacuum the harder the throttle has to be pressed to cause the extra advance to be taken out by the canister. It acts a bit backwards from what would sound normal because you're going from high vacuum at light throttle to low vacuum at heavy throttle. A high number for the vacuum advance to be all in at means that it will take less throttle opening to get to that point. That means that you'll have less timing at a given load and less pinging as a result. Limiting the timing means that you're starting at a lower total timing amount as well.
Adjust the vacuum canister with the small Allen wrench until you just get a small amount of pinging as you quickly press the throttle, then go back until that is gone. Then change the amount of timing that you have with the limiter, adjust the canister again and so on until you have your throttle response (and fuel mileage) back to where you think it should be. This can be done over the space of a couple of weeks and is checked in normal driving, no need for special conditions. This will be good practice for tuning your EFI system!
I think I'm getting this right. I used the limiter plate and reduced the total amount of vac. adv. allowed to approx 12 degrees, since the 18 degrees I was getting of the original can caused pinging. I also adjusted the vac can to a range of 10-15in of Vac. 15in. is the max the can would allow, and this matched the original can too. The original can ranged from 5-15in Vac. If I adjusted the new Vac range toward the 5-15in range, I'd increase the chance of pinging, but also provide for a greater range of time the vac advance would be active. Correct?
I'm pretty happy where it is at now, so I'll probably leave it there so I don't screw it up. Your description of tuning with the Vac Can is excellent. Much better than the instructions that cam with the can.
Actually you will know if you've gone too far on the limiter if the car seems to sputter at steady state speeds. So as you follow TOHCan's recommendation, just keep uping it until that happens. If the pinging during throttle tip in starts to come back before you reach this point, then adjust with the allen wrench.
You should be able to walk it in pretty quickly, so why wait? And since you already have the values don't worry about "screwing it up" you know how to get back to the original settings. Tuning is fun! (When it goes smoothly)
