Hello community, I have been having an issue with my freshly rebuilt 350 engine. Setup: - 350 engine , .020 over, comp cam 92-202-4 new lifters, springs, rods, valves, chain - stock 2jet carb with ported vacuum - stock elchin distributor with 15* vac advance When I set my initial timing w/o vacuum to 10* BTDC it idles perfectly. When I check the total timing with vac connected at 2000rpm it goes well over 40* advance and doesnt seem to stop if I keep reving it up.. The machine shop guy told me it should never go over 40* as this might hurt the engine when driving for a longer period with constant load. As I have been reading here in the forum 36-38* total advance is what I should see. Checking the distributor rotor it all looks fine to me. Springs are pretty stiff . Is this common behaviour or is there a mistake in my thinking? Thanks in advance
Alright, you may have opened a can of worms. Here's how I've read about and run my Buick big block distributors. First, if you can run manifold vacuum instead of ported vacuum, do so. Second, because of this change, you will need to set your initial timing at idle to around 14* at idle with that cam in a mild 350. Third, due to now running manifold vacuum, you will need to limit your mechanical advance with a bushing(they are readily for sale everywhere, we can send a link to you if you need it) to 20*. Fourth, it appears that your springs under the rotor are too stiff, if advance just keeps coming in. You want your mechanical advance to stop advancing at 20* at 2500 rpm, based on the 1971 Skylark you have, some heavier cars like 2750 or 3000 rpm better. (There are plenty of kits where springs and bushings come together, we will help you find one if necessary) Fifth, having 15* of vacuum advance is nice, but it's likely too much with a 2 barrel carb with high vacuum situations until the carb is past half throttle. You will need to decrease the amount of vacuum advance to around 12*, or you may experience pinging when switching quickly from light to heavy throttle. (Number 5 is the least important of your worries, but if you can, should be addressed). The result you're looking for is a car that idles on 14* of initial, plus 12* of vacuum, so 26* at idle. Cruising down the road at 2500 rpm, you'll experience full mechanical ignition timing of 34* (14* initial plus 20* mechanical, mechanical is controlled by the lighter weights and springs you have swapped in with the limit bushing) and the additional 12* of advance from vacuum advance, so 46*. And finally, foot to the floor, wide open throttle you will see 34* of mechanical advance throughout the rpm range above 2500 rpm, which will give you plenty of power and not risk damage to the engine. If you have any questions, do ask. I am not the only authority on this topic, but this is a great start. You'll be happy with the noticeable change.
Wow, what a nice and complete answer. Thank you very much! I do understand the values, their relation and the purpose of the different andvances. What gets me thinking, is why was this setup delivered like that back in the days?
Passing emissions was the goal of the day, but when looking for performance, they were a far cry shy of what could be done. I’m not sure if your car has EGR (exhaust gas recirculation) in the intake, but if so, I’d recommend you block that off. It’s just putting burnt exhaust gases back into the intake.
Ok, got it. If you could send me the link for the kit it would be great, so can start looking for the stuff I need
http://v8buick.com/index.php?threads/power-timing-your-buick-v8.63475/ I wrote the above post over 15 years ago. Ignition timing, one of the most misunderstood topics. First, there is no such thing as a stock Echlin distributor. Maybe its a points distributor, but that is likely the only thing you can consider stock. The points distributors fitted to Buick V8s over the years were VERY different in one respect. They had different amounts of mechanical advance built into them. Take a look at the various distributors and their specifications over the years. http://v8buick.com/index.php?thread...specs-1965-66-66-67-68-69-70-71-72-74.329332/ So now you go to NAPA and you buy a "stock" distributor for your Buick. The rebuilders couldn't care less about the different specs. The distributor will fit and work in your engine, but the mechanical advance may not be what you want. That is the main reason you CAN'T run whatever initial timing you may want or prefer. Some distributors had as much as 34* built into them. Do the math. You want to run 10 or 12* of initial timing? 10 +34 =44*. That's no Bueno. So, what to do? First, you need to determine how much mechanical advance is in the distributor you have. First step is to determine the part number of your distributor. It is stamped into the body on the circumference, just under the cap parting line. See if it matches with the list above. If it turns out your distributor has more mechanical advance than you want, you MAY be able to use a bushing to limit it IF there isn't one there already. If your part number is not listed, then you need to determine how much mechanical advance is in your distributor by using a timing light. The easiest way to do that is to use some very light weight springs. That way, all the timing will come in by 2000-2500 RPM and you can read it easily. The stock springs delay full advance until as much as 4600 RPM. You do not want to free rev an engine that high. Disconnect and plug the vacuum advance. You can tune that after you get the total advance where you want it. BTW, the stock distributor your 1971 350 was fitted with from the factory was 1112037.
Hello Larry, I was hoping you would pop up on this topic! When I read Your power timing topic some weeks ago it helped me a lot in understanding better this whole timing thing. Thanks for that! Checking the number was a good idea. It reads 1112110 which tells me it was made for a 1972 455 with a max advance of 14-18* at 2900 RPM. So no stock at all
That's actually a great distributor to use in stock form. Reading through your first post, I see you left the vacuum advance connected. That's a mistake. Disconnect it. See what the timing maxes out like that. Considering the specs for the 1112110, it shouldn't go past 28* with a 10* initial timing. You are looking for 30-34*. Like I said, the easiest way to check the total timing is with the lightest springs available. The ones in the Crane adjustable vacuum advance kit are my favorite, https://www.summitracing.com/parts/crn-99601-1 The yellow springs will let all the advance in very early so you can easily measure it. You'll want stiffer spring for regular driving, but for the sole purpose of checking and setting the total advance (initial + mechanical), the yellow springs are great. Once you have the total advance where you want it, then add the vacuum advance. You can limit it so that at cruise, your timing goes into the low 40's. That's fine at light load. When you go full throttle, vacuum will drop to zero, and any advance from the canister will drop out leaving you with your initial + mechanical. This kit has springs and a bushing, https://www.summitracing.com/parts/...MIuKb9kLGa6QIVXwiICR3kcQeOEAAYASAAEgKEjvD_BwE The springs aren't as good IMO, but this kit has a bushing. You shouldn't need a bushing with the 1112110, but it is possible the insides of your distributor are not stock. Rebuilders sometimes mix and match parts from different distributors. That's why you should measure the actual advance with a light to make sure.
Ok, thank you for the advice to unplug the vac and the links. Just placed the order. Will try and check again tomorrow. Are the other springs in the Crane set usable for further advance adjustment?
Yes, you can mix and match them, same as the Mr. Gasket set. Having a lot of spring choices can help you dial everything in. You can even use one stock spring and a lighter one from the kits. Mix and match until all the advance is in when you want it. 2500-3000 RPM is what you are aiming for. Leave the vacuum advance off and plugged. Just set the total advance and road test the car aggressively listening for ping. Only after you are confident that you have optimized the total advance do you add the vacuum advance in. 8-10* is all that is usually required to get you into the low 40's at your cruise RPM. You can verify all of that easily with a timing light.
Finally the answers I was looking for! A Last one: how much advance can these engines take at constant load on the highway without damaging something?
It's not really the amount of advance that you're worried about, it's the total number. As Larry said you want to be in the low, low 40's at your cruise rpm.
Cruising on the highway is light load, small throttle opening, partial cylinder fill, high vacuum. The engine can tolerate 40 -44* with no problem. Too much advance and the engine can start to surge, so it will let you know. My experience is the 40-44* is usually the sweet spot for best gas mileage. What you want is for that extra advance from the canister to go away quickly when you stab the throttle, leaving you with your initial + mechanical total for best WOT power. That is usually 30-34*, but every engine can be different. So depending on what total WOT timing you end up with, add 8-10* of vacuum advance to get you to 40-44*. After adding the vacuum advance, you can verify your cruise timing by simply leaving the VA connected. Just run your RPM up in Park to your cruise RPM, and measure the total advance (initial + mechanical + VA) using the dial back feature of your timing light, OR, if you have a plain timing light, by making a second 30* mark on your balancer and using that as a reference. To adjust your VA canister, you may need to make a limiting plate if the canister is stock, or use one of these limiters from Ken (techg8) http://v8buick.com/index.php?threads/new-product-vacuum-advance-limiter-bushings.346184/ Or, you can use the Crane adjustable VA canister. Just follow the instructions in the Power Timing thread regarding the limiter cam installation.(It is different from what Crane recommends). You can also adjust the VA spring inside the canister independent of total VA advance. The spring tension affects the rate of vacuum advance, when it starts, and how fast it goes away when you punch the throttle, all important factors in tuning the VA for your engine.
Amazing, guys! Will let you know how it went when I get all the parts and set it all up. Big thank you from Germany!
What springs you choose also enter into the calculation. Let's say you have a 3.08 rear in your car. 60 MPH is around 2400 RPM. Let's say you have your WOT timing all in a 2800 RPM. When you are at 2400, all the mechanical advance may not be in, you might be a few degrees short. You might need more VA to get you to your target of 40-44* for cruise. That's why it is important to check with a light to see exactly where you are, for your WOT timing, as well as your cruise timing.
Ok, here is what I did. I got huge spring set from the hardware store and made my own springs for the distributor. Same diameter, less stiffness. Plugged VA Then I set the initial timing to 10* BTDC and revd it up to 2500 rpm and used the dial back function of my timing light and read 36*. So that gives me 26* mecanical right? Still too much I guess, concidering 15* V/A?
I think your 1112110 distributor may not be stock. The fact that the 1112110 is a 455 distributor means that at some point, someone modified your distributor to fit the 350 engine. The only difference is the drive gear, but it may be a rebuilt distributor with different parts. Sometimes, rebuilders mix and match parts from other distributors. If your numbers are accurate, you have way more than 18* of mechanical advance. You will need to back your initial advance down to get the total advance down. 30-34* is optimal. I would not run more than 34* on pump gas.
So what would you do if it was yours? Throw it out and get something newer or try to upgrade this one with springs bushings and new VA Canister to make it work ?
@ Tripple7 would you please be so kind and measure the width of the slot for the mechanical advance? I am working on my distributor as well (see my post http://www.v8buick.com/index.php?threads/swap-mallory-with-pertronix-flamethrower-hei-iii.353936/) and would like to compare. I am a little behind, as I have not yet had time to measure advance with the light springs. THX
