Hello All, First time long time. I'm having pinging in 4th gear. I just came back from the carb guy so all is good there. I'm in CA so the best gas is 91 and I added a can of 104 Octane boost. The motor is a 1970 SF with a stock cam and pistons. How much will be gained by trying to move to initial 8*BTDC from 10*? My lightest spring don't seem strong enough to return the distributor weights. What should my plan be for my 1969 GS 4 speed? Cheers, Mike
Mike, have you checked total advance? Good chance the distributor advance stop is pounded out and your advance is over 32 deg, If it is get a brass one and put it in.Then check total advance and adjust initial advance accordingly. gary
As I'm sure Larry the Wizard will be along shortly to school you on timing and that initial timing doesn't matter nearly as much. You need to know what your total advance is and set that to 32°-34° when it is all in. The initial will be what it will be until you dig inside and adjust the advance, springs and advance stop. I like my advance all in by 2500RPM and set at 34° with good gas and 32° with cheap gas. My initial runs about 18° but as long as it will crank, I don't car nearly as much what initial is set to.
As stated, first thing to do is measure the total advance and see what it is, and when it is all in. The engine only runs at the initial advance while sitting at a stop light at idle. As soon as you accelerate away from the stop, the mechanical and vacuum advance add timing. Engines will ping when subjected to high loads with too much timing. Initial advance matters not when trying to diagnose a pinging engine. Guys get hung up on initial timing specs thinking that's all there is to adjust, so much so that they think a particular engine gets adjusted to the specs in the book regardless of what else has been done to the engine in the car. Book specs only apply to an all stock engine with the original distributor that it left the factory with. A 40+ year old engine is unlikely to have the original distributor, probably been replaced at some point. Notice above the stock distributor for the 70 SF engine is the 1111984. It has 30-34* of mechanical advance. With 8* of initial advance, that means the total at WOT can be 38*- 42*. That doesn't even take into account the vacuum advance at part throttle. An unmodified vacuum advance canister has 14-18* at 16" of vacuum. With light springs that bring in mechanical advance sooner, it is easy to over advance the ignition timing with vacuum advance at light load. That would produce ping at part throttle when you went to accelerate. Get a timing light on the engine and see what is going on. Check the distributor part number as well.
Check for that bushing in the distributer. But what you want with a stick car and "higher" compression is a slower advance curve. A stick car does not act like an automatic car with a nice stall converter. More like an automatic car with the tightest converter ever except worse. Start with a bit less initial advance but add more mechanical to get the usual total. You don't need as much initial as a typical automatic because you are always in neutral when idling and the engine gets really lugged down pulling out. The curve has to be slow and steady to stay away from ping down low or if you are trying to accelerate hard in 4th gear from cruise rpm. I'd say shoot for maximum mechanical advance around 3500 rpm or a few hundred rpm above cruise rpm. Use vacuum advance to add advance when cruising easy. That will drop out if you acelerate hard in 4th gear.
Besides the potential Rod bearing damage from pinging, the power loss is more then if you ran 2 degrees less timing.
Ok. I had to go to work. It is a 4 speed with the original distributor. I have been reading Larry's post for a while now. Its set at 10* BTDC now and the vacuum advance is disconnected for now. The carb guy seemed to not recommend it as he threw away the vacuum hose. I'm not sure about the brass stop on the mechanical advance and where it is. The centrifugal advance is likely a few degrees more than 10* plus 34* but likely close. The springs are relatively light but not the lightest. My basic question is "Is the pinging caused by not enough advance or too much advance?" I should note the engine only has a couple of tanks of gas since the rebuild and only has an issue in 4th at WFO on my test hill. The rear end is the performance ratio 3.68 or something. Thanks for all your help. Cheers, Mike
Too much advance. The question is what is the ignition timing maxing out at. That is easily measured with a timing light. Do you have one?
I got one. Likely 44* 46* would be what I remember. What color advance springs should I try? For my car...all in by 2800 rpm's?
Anytime you disable the vacuum advance on the oem distributor the rotor will be out of phase with the cap terminals. You should never just disconnect the the vacuum advance and leave it that way without correcting and locking in the rotor phase. I perform that modification on every oem distributor we set up. (Some folks won't agree with this mod) 44-46* is too much timing for your stock engine. Limit it to 32. Larry
I don't like where this is going. Forget trying to do this yourself. Take your distributer or whole car to somebody who does recurves and get it done right. Maybe the carb guy knows somebody. Maybe the engine builder. Pinging going up hill for a test is going to damage something and then the blame the engine builder will rear up. You know how Buick kept your car from pinging? They put big stupid springs in to slow the advance rate down. Even the heaviest springs that come in a recurve kit are way faster than the factory springs. There is no way you need "all-in" by 2800 rpm. For now, to save yourself some heartache, retard your initial advance to 2-4* so you only have a total of 32-34* and then get it done right.
WOW, WAAAAAY to much total timing, about 12 degrees too much total You say 4th gear, up a hill, wide open throttle? No wonder its detonating! Your really lugging the engine in fourth up a hill WOT, and your also beating the crap outta your bearings
X2 with Larry, I forgot about this small but very import fact when you disable the vucuum advance! Another over looked fact is that cylinders 5 and 7 fire consecutively and as such run hotter at part throttle Carb openings , and at times over 100 degrees at full throttle ! If your tune is good and all of your plugs are looking light tan ( coloring will take some 200 miles) ,but 5 and 7 a shade or two lighter, then going one step colder on those two plugs may just be the ticket to getting more advance into the motor and having it be Ping free, or atleast having the ping gone! In fact trying colder plugs in those two cylinders is cheaper then cutting half of your 20 gallon fuel tank with premium!
OK. Thanks for all the input. I returned the springs to the originals. They are heavier than what I had in. I plan I driving it both with and without the vacuum hose to the can (I hope you all mean the vac. advance module and not the reservoir can I see on Ebay! ). I see where the brass bushings goes now. Where do you get one? I should have said it earlier...I'm an original guy. That why I bought the stock cam this time. I really don't what to re-curve the original distributer. I want it just like GM supplied it. Mostly... Thanks again for all the comments, Mike
Mike, all your questions get answered on the first page of my timing thread. http://www.v8buick.com/index.php?threads/power-timing-your-buick-v8.63475/
OK> Testing with higher gage springs still disconnected vacuum advance hose from carb. Worse but different. Best NAPA in town. Knows all about the brass limit, but doesn't know how to get one. I think I'm going back to the last spring set and the bushing. One of my spare distributors has a bushing made of rubber but I'll likely destroy it while removing. Larry I reread your link. Can it ping both on too much and too little advance?
No, it pings from too much advance. The Mr. Gasket kit has a brass bushing. https://www.summitracing.com/parts/mrg-928g Putting in heavier springs does not reduce the amount of advance, it just changes the RPM where all the mechanical advance is in. Is there something stopping you from simply putting a timing light on the engine and determining EXACTLY how much advance you are getting?
I'm with Larry, put a timing light on it and rev it until the mark quits advancing. If you don't have a dial back timing light, you can make marks on the balancer every 10 degrees with some white out.
