I have been working with my timing and pinging during WOT acceleration. I had a distributor in that allowed 32 degrees advance based on my initial and mechanical advance. I would retard the initial to 6 btc but was still experiencing the pinging with 93 octane gas.
I replaced the distributor with a correct 1111449 and I added a bushing to the cent adv stop, because it had a slight wear, and to get it to about 10 distributor degrees using a protractor. I my have missed the mark a little. With the initial timing set at 9 degrees dtc at idle I am getting about 16 degrees mechanical for a total of about 24-25 BTC.
I am going to re verify those numbers tonight. But it was was all in by 2500 rpms. I still had some very slight pinging but not near as bad with the other distributor. So I was wondering if 25 degrees BTC was to low and I the manual specs for the 1111449 distributor states the max dist degree is 9-11 at 2300. Which seems real close to my numbers. 9-11 dis degrees is 18-22 at the crank. 18 + 9 initial is 27 degrees BTC.
I am going to lower the initial a couple more degrees to see if I can get a little more of the pinging out on straight 93 octane.
Does any one have any knowledge if what I am doing is correct?
I like Dan Jensen and follow him on tips and tricks when it comes to tuning Pontiacs. I've had pretty good luck doing this: Total mechanical advance from 36 to 42 degrees, and I try to get it in by 2,500 rpm. That’s a lot quicker than the factory setup that brings in all the advance by 4,000-4,500 rpm. With that said, every engine is different and some experimentation is required to find the sweet spot.
“For a high-compression engine with a mild cam, I’d probably want a little more mechanical advance because they can’t tolerate as much initial timing as a low-compression engine can. Most 400s [except Ram Air IVs] have 10 degrees of initial timing, but I like around 12 degrees initial timing as a rule of thumb. Pontiac engines seem to like that.â€
With initial timing set to 12 degrees, and mechanical advance bringing the total to between 36 to 42 degrees by 2,500 rpm, some additional tweaking will get you to your engine’s optimum setting.
I like Dan Jensen and follow him on tips and tricks when it comes to tuning Pontiacs. I've had pretty good luck doing this: Total mechanical advance from 36 to 42 degrees, and I try to get it in by 2,500 rpm. That’s a lot quicker than the factory setup that brings in all the advance by 4,000-4,500 rpm. With that said, every engine is different and some experimentation is required to find the sweet spot.
“For a high-compression engine with a mild cam, I’d probably want a little more mechanical advance because they can’t tolerate as much initial timing as a low-compression engine can. Most 400s [except Ram Air IVs] have 10 degrees of initial timing, but I like around 12 degrees initial timing as a rule of thumb. Pontiac engines seem to like that.â€
With initial timing set to 12 degrees, and mechanical advance bringing the total to between 36 to 42 degrees by 2,500 rpm, some additional tweaking will get you to your engine’s optimum setting.
Ya that does not work at all for this build. 9 degree initial and 32 total and it is pinging like crazy on 93 octane gas. 95-96 Octane and it is nice and quite. I was hoping to get it running better on 93 octane. Seems 25 degrees, 9 initial and 16 mechanical quieten it down a lot. a couple more degrees may do it. Why is it requiring so much retard?
Good questions. A couple things come to mind. 1. Make sure your timing marks are accurate and TDC matches your mark on the harmonic balancer. 2. Sometimes pinging can be caused by overheating. Is your car running at around 190F, verify, don't trust the gage. Does it get louder (pinging) as it warms up? 3. Does your timing repeat and not adjust itself/wander when rechecking after a few days? I know your engine is newly rebuilt so the timing chain should still be tight. 4. Check the up/down play on your distributor. Should be no more than 1/32". 5. Don't lean out your carb too much, a lean condition will cause pinging. Try 1/2 turn more out and drive it. 6. Don't get too hung up on the actual timing degree numbers. Many racers time their cars by feel and what your particular engine likes. Called "power timing". Start at 9 degrees and move ahead a notch at a time and drive it. When pinging stops and you get the best throttle response back off a notch and you're done. No Timing light needed. Hope this helps.
Ok, let's step back. What is your current compression ratio? If you have 68 heads and are running 10+ to 1 on an iron head stop now. Buy aluminum heads.
Why are you looking at timing specs from 1968? You cant buy 1968 gasoline anywhere, and it didn't have the alcohol we have in ours today. Those numbers are potentially way off today.
Step 1: Disconnect the vacuum advance. Step 2: Verify your timing mark is STILL at TDC. Yes, in 50 years many of the harmonic balancers rubber rings between the hub and weight dry up, allowing the timing mark to move where it shouldn't be. I recommend buying a new balancer with etched timing marks for about $60, or you can try to determine top dead center with an indicator placed thru the spark plug hole and hand rotation the engine. Once you are SURE you know where TDC is, go to step 3. Step 3: Set the initial timing at 10-12 degrees and then read the total timing off the etched balancer you added or a $6 timing tape from Jegs.
Retard the ignition until it doesn't ping under load, then a degree or two more. Check your total timing. I can only run about 32 degrees on premium gas with my 9.5 to 1 455.
Ok, let's step back. What is your current compression ratio? If you have 68 heads and are running 10+ to 1 on an iron head stop now. Buy aluminum heads.
Why are you looking at timing specs from 1968? You cant buy 1968 gasoline anywhere, and it didn't have the alcohol we have in ours today. Those numbers are potentially way off today.
Step 1: Disconnect the vacuum advance. Step 2: Verify your timing mark is STILL at TDC. Yes, in 50 years many of the harmonic balancers rubber rings between the hub and weight dry up, allowing the timing mark to move where it shouldn't be. I recommend buying a new balancer with etched timing marks for about $60, or you can try to determine top dead center with an indicator placed thru the spark plug hole and hand rotation the engine. Once you are SURE you know where TDC is, go to step 3. Step 3: Set the initial timing at 10-12 degrees and then read the total timing off the etched balancer you added or a $6 timing tape from Jegs.
Retard the ignition until it doesn't ping under load, then a degree or two more. Check your total timing. I can only run about 32 degrees on premium gas with my 9.5 to 1 455.
Motor has 4000 miles on rebuild from experienced engine builder. It is suppose to be 9.2 compression with dished pistontons. 0 deck 16 iron heads .30 over. The cam is XE262H some people are saying the cam is the issue. It make too much cylinder pressure they say.
As far as looking at original specs, I just want to see what they was at originally on 100 octane gas to see if 25 degrees was bad.
It seems like the balancer is still correct I just pulled the distributor and set it at tdc before removing it and it was at number one.
Initial at 10-12 is to much. Already done that. I will get some more number this evening.
I set it at 6 degree initial and 22 total with vacuum advance disconnected. Seems to have good power very little pinging on initial wot. It is a little bit worse at 9 degree initial and quite a bit worse at 12 degrees inital. My distributor is giving me 16 degrees mechanical advance.
Don't know what else I can do with out adding 110 octane. Right now it is very drivable on 93 octane just not sure how the 22 degree timing will effect it.
Besides the extra cyl pressure, many say that they produce a ticking of pinging sound because they slap the valves shut so hard.
The Voodoo cams are said to have a similar steep opening ramp, but close the valves more gently, thus not making the ticking sound. Pontiac engine builder Paul Carter also says that, in his experience, the Voodoo cams do not promote detonation like the XE cams do.
Most say that cams with more adv duration will "bleed off" some of the cyl pressure, reducing the chance of detonation.
So, something like an 068, might solve your pinging problem. For a little more performance, the Summit 2801 is sort of a high lift version of the 068. So, it should make more power. I like the looks of it for a mild street 400.
And, the 262 Voodoo should reduce pinging, and increase performance, since you should be able to increase your total timing. The low timing is said to promote overheating.
Thanks OldSkool, Maybe one day I will get the nerve to disassemble the motor and replace it. I hear a lot of people using the summit 2801 and I hear about the voodoo. Maybe something I should check into doing. I do not understand the the technical details of the cam and how it effects everything. Would be nice to learn.
I have a WQ short block in the basement. Gives me something to practice with.
I have been working on the and the consensus is the xe262 is just building to much pressure. Also some one took the piston cut .100 and the diameter of the piston to roughly calculate the cc depth and came up with a possible compression of 9.7. Also someone calculated the dynamic CR at 7.71 roughly.
I checked the compression in each cylinder on cold motor. Came up with 1 180 2 180 3 170 4 175 5 175 6 172 7 175 8 176
So it looks like there may be no way to get the timing right on 93 octane. Either I keep mixing or plan to swap the cam for something bigger. Lots of people like the summit 2801-2802. Seems to be a go to cam.
My current timing is set at 6 degree initial with 16 mechanical and still hearing slight ping on 93.
"Motor has 4000 miles on rebuild from experienced engine builder..."
What does the builder have to say about this problem? He should be able to resolve this pretty quickly if he knows what he's doing.
16 heads are gonna be at least 75CC's...dished pistons will add another 25 CC's...??? That's quite a bit of volume in there. Right?
It's been 5 years since the build. So not sure what he would do. I don't understand why it did not show up on the dyno. I know he had a lot of trouble that he kept planing on the carb. I can only assume he was running race fuel on the dyno.
As far as the cc the dish was cut .100. Someone calulated it as (24cc / .180") x 0.100" = ~13.3cc. This was based on his piston. His was 24cc with a .same valve relief. This would put the CR 9.6.1
Couple of points I thought of while reading the posts above. Setting the distributor advance 9 degrees and getting 16 mechanical. You were pretty darn close, remember the distributor shaft turns at 1/2 the crank shaft. 9 degrees of the distributor is 18 degrees crank.
A camshaft can affect the dynamic compression ratio and thus cylinder pressure, by when it causes the intake valve to close. Compression of the fuel/air charge in the cylinders will not start until the intake valve closes. An engine with a 10:1 static compression ratio.can have a high dynamic C/R with one camshaft and a low dynamic C/R with another camshaft.
Maybe your camshaft was put in advanced, that would cause the intake valve to close earlier which in turn will raise the cylinder pressure. It's cylinder pressure that causes detonation, if one fires the plugs too soon or has a camshaft that closes the intake valve too soon, or has too high a compression ratio, the pressure will build higher than the octane rating of the gasoline can handle and PING.
16 degrees mechanical advance isn't that much, I think 20 degrees is about normal. I would want the advance all in at about 3,000 to 3,200 rpm. Set the initial to get a smooth idle and easy start, don't worry what the numbers are. Then check what your mechanical is with a dial back timing light or use the aforementioned timing tape. Try driving your car in second gear and give it a WOT run, if you have no detonation advance the timing two degrees, keep going until you get pinging then back it off two degrees. That is the total timing you want. If that results in an initial timing that is two low or too high to idle or hard starting adjust your timing curve to keep the total at the required number but increase or decrease the initial to something that works. If you are getting the detonation to stop at say 26 degrees total but your initial is then down at say 5, plug your vacuum advance to manifold vacuum, that will give you more advance at idle and keep the 26 that works for total.
I'n not an expert but that worked for me while trying to solve my detonation problem.
Couple of points I thought of while reading the posts above. Setting the distributor advance 9 degrees and getting 16 mechanical. You were pretty darn close, remember the distributor shaft turns at 1/2 the crank shaft. 9 degrees of the distributor is 18 degrees crank.
A camshaft can affect the dynamic compression ratio and thus cylinder pressure, by when it causes the intake valve to close. Compression of the fuel/air charge in the cylinders will not start until the intake valve closes. An engine with a 10:1 static compression ratio.can have a high dynamic C/R with one camshaft and a low dynamic C/R with another camshaft.
Maybe your camshaft was put in advanced, that would cause the intake valve to close earlier which in turn will raise the cylinder pressure. It's cylinder pressure that causes detonation, if one fires the plugs too soon or has a camshaft that closes the intake valve too soon, or has too high a compression ratio, the pressure will build higher than the octane rating of the gasoline can handle and PING.
16 degrees mechanical advance isn't that much, I think 20 degrees is about normal. I would want the advance all in at about 3,000 to 3,200 rpm. Set the initial to get a smooth idle and easy start, don't worry what the numbers are. Then check what your mechanical is with a dial back timing light or use the aforementioned timing tape. Try driving your car in second gear and give it a WOT run, if you have no detonation advance the timing two degrees, keep going until you get pinging then back it off two degrees. That is the total timing you want. If that results in an initial timing that is two low or too high to idle or hard starting adjust your timing curve to keep the total at the required number but increase or decrease the initial to something that works. If you are getting the detonation to stop at say 26 degrees total but your initial is then down at say 5, plug your vacuum advance to manifold vacuum, that will give you more advance at idle and keep the 26 that works for total.
I'n not an expert but that worked for me while trying to solve my detonation problem.
Thanks for all the detail. That is sort of what I have been doing. I keep retarding the timing to were I am currently at, total is 22 Initial 6 and mechanical 16 from here it still pings slightly. If I do hook up the vacuum advance on manifold, would the vacuum advance be active with part throttle? It should drop under wot which would pull the timing back down. Sounds like it would work. I'll give that a shot. I will try lowering a couple more degrees and see what happens.
Harold what is the Lobe Separation Angle of the XE262 cam? I was looking at the XE268 some time ago and thought the LSA for these cams was 106 degrees?
I ended up going with the Summit #2802, but what is interesting about the 2801 or 2802 is that the LSA is 114 degrees. When I ran my dynamic CR with the 2802 the cam allowed me to bleed off enough compression that the cylinder pressures peak at around 170-175psi, which from what I understand is optimal and at the top end.
With a tighter LSA you will have higher compression and more likening to detonate - more time to build pressure. I would look into this further - not taking anything away from all the great feedback so far.
Thanks for the info. I was looking at the 2801-2802. The 2801 has 112 LSA and the 2802 has 114 LSA. The 2801 is close to the 068 but it had a 116 LSA. The 2802 is closer to the 044. If I make a change it may be to the 2801. I had my XE nitrated to harden it so it would not wear as easy.
I'd keep adjusting the timing until the ping is gone, or nearly so. A little bit of slight ping once in a while you could most likely live with. After you have the timing set where it works check the numbers. 22 is fairly low, but with the cam change you are not dealing with a stock engine.
It is, as mentioned above, imperative that you confirm your timing mark on the damper is at top dead center. Use a piston stop to aid in making sure it is where it's supposed to be. If not all those numbers don't mean a thing.
Also, as mentioned above, a lean mixture and high heat will increase the chance of detonation. Do you have a stock jetted carburetor, do you have a good fuel pump, is the float bowl emptying when you mat the gas pedal?
You have a pretty stock build except for the camshaft. If you get the timing set to a point where the detonation stops and the engine idles and runs normal, who cares what the numbers are? Just drive it. If you get the timing set to a point where the detonation stops but will not idle or cruise with that timing you most likely have a component problem. All things point to the camshaft if the rest is stock.
Your camshaft should have came with a cam card showing all the specs. One of the specs will be the point at which the intake and exhaust valves open and close. Check that with the specs of the stock Pontiac camshafts. The Pontiac engineers where smart guys and they designed camshafts that worked well in the Pontiac engines. Of course as mentioned earlier they also had the advantage of good leaded gasoline, the kind I used to buy for $0.25 a gallon. Pontiac engineers designed camshafts for Pontiac engines and did a better job of it than Comp Cams could ever hope to. If your cylinder pressure and dynamic compression ratio is too high with the Comp camshaft, maybe look into getting one closer to stock. If your engine was made with a 68 camshaft maybe a 67 or 66 will work well with the crappy gasoline you're forced to buy. I'm sure Melling still makes stock spec camshafts, they made the one that your engine came with from factory.
Pontiac engineers generally .designed camshafts with a fairly wide lobe separation angle and intake centerlline of around 112-113 with a few exceptions. Aftermarket grinders such as Comp Cams stray from that. Seems like Comp likes to suggest camshafts that make horsepower at high rpm range and don't worry much about torque. What works for a small block cheby isn't going to work in a Pontiac engine. Pontiac engines are made with more low end torque and usually make their power at a lower rpm.
I have two different carburetors. Both build for my specs by Cliff ruggle and Quadrajet Power. Both run great, no hesitation and with 96 octane, can run great. So don't think it is a lean condition. If I bump the octane up by using 110 racing fuel, if I get it around 96 I'm fine. I can not use some of the octane booster like Klotz Octane Booster. It does not seem to help. But 2.5 - 3 gal of 110 to a tank does.
The carburetors should be good, Cliff seems to know what he's doing. If not heat or lean condition then it's timing or high cylinder pressure. I know it's been five years but why not call or drop in to see the engine builder? Just ask him what he thinks about the detonation, can't hurt and he may be able to give you the answers you need. He knows the engine better than anyone, he built it.
Remember every engine is different, especially when something as critical to engine running characteristics as the camshaft is changed, factory and accepted modified specs for timing wont work the same with yours as it does with one like mine. Factory specs go out the window. Mine runs best at 28 degrees total and 16 initial. My distributor with 20 degrees mechanical got some modifying to get it to work in my non-stock 428.
I know it's been mentioned before, I forgot if you answered, did you check the timing mark is actually at TDC?
The ex262h builds a lot of torque. My numbers are 445 ft-lbs @ 3200 and pulls to 5100 rpm 361.5 hp. So the cam does a good job on a stock motor. The dyno numbers are good.
The LBS is 110° duration 262/272 compared to 116° duration 288/302 on a 068 quite a bit difference.
Took me a while but I found the cam card, your intake valve, if you installed the camshaft straight up, closes at 57 degrees after BDC. I couldn't find a cam card for an 068 but it has an intake centerline of 113 degrees, and a duration of 288 degrees. Making a big assumption that the lobe is symmetrical, I calculated the 068 intake closes at 77 degrees after BDC. Even if your camshaft and the 068 camshaft were identical, the 262 intake centerline of 106 compared to the 068 intake centerline of 113 would make about half a point difference in dynamic compression ratio, the 262 being higher than the 068. With the added duration of the 068, 288 degrees, compared to the 262 degrees of the 262, the difference in dynamic compression between the two camshafts is even greater.
I don't know what camshaft you had in your engine before you had it rebuilt, but if the available fuel was marginal before, and the swap increased the dynamic compression ratio, it will be worse now. That's making another big assumption, that you had a camshaft with a later intake valve closing point than you do now.
You did say at 6 degrees spark advance initial and 22 total you eliminated most of the ping and the car ran well, why not leave it there, or a little less, and not worry what the numbers are? As long as it runs OK who cares what the timing light says?
Thanks Al. I think I have it working pretty good now. I have my initial at 9 at 800 rpm with 13 additional in the mechanical weights in distributor for a total of 22, less vacuum advance. I was able to WOT all though gears with no ping, I have the vacuum advance set on ported vacuum and 44-48 cruising rpms. I am seeing 16 psi of idle vacuum.
Well temperature change and the pinging returned. Well nothing else to do but mix fuel and prepare to change the cam out.
Before you go yanking the camshaft out, you might want to call Cliff, since he built the carbs you are working with, give him your symptoms and motor specs and see what he thinks. He is also an engine builder and may have some additional insight.
Well temperature change and the pinging returned. Well nothing else to do but mix fuel and prepare to change the cam out.
Before you go yanking the camshaft out, you might want to call Cliff, since he built the carbs you are working with, give him your symptoms and motor specs and see what he thinks. He is also an engine builder and may have some additional insight.
Ya I have been communicating with him. He along with several others believe the cam is to small. The tight LSA 110 builds to much pressure in the cylinders. They also believe my CR is more around 9.6-9.7 which is much more then the 9.2 the builder stated. Cliff and others seem the XE comp cams are better for low compression motors. They think the only fix is to switch it.
Well since I'm not going to stop the pinging with what I have, I added 2 1/2 gal of 112 octane 14 gal 93 octane. Octane should now be 95-96. Set the timing back to 13 initial with total 32 and it runs great. No pinging, runs really great! WOT though all gears breaking traction in all 4 gears.
Only time I heard a ping was in 4th at a lite throttle around 2000 and went WOT and I heard a slight ping but with rpms up in 4th gear and rpm around 3000 WOT no ping.
Like I say with this setup I could not ask for better power just wish I did not have to run on 96 octane.Hard to believe just adding 2.5 gal a fill up take care of it.
That’s good news Harold. I’ve always had to use octane to get to maximum advance without the ping. Each time I fuel up I measure the gas to octane ratio exactly the same so I can leave the advance at its maximum, just short of the ping. Though many won’t agree, I also keep my temp under 180. Any hotter I can get a ping under WOT unless I retard the timing a bit. It just runs stronger with the extra advance. It’s not a daily driver, so for me the mixing is well worth it.
Yes that is about what I have been doing for 4 years. I would like to be able to just run 93 octane so I will be researching to install a slightly larger duration cam and wider LSA. May just go with the Summit 2801. The XE262 lift is .462/.47 and the 2801 is .44/.46 so I would think my valve springs would be good and not have to change them.
Before you pull the engine apart and spend a bunch of $$$, why not try lowering the total timing some more? You said it ran good with 6 initial and what was it 26 total? Try dropping the total down another couple points, if it runs good you wont have to change out the cam. If a lower total makes the initial too low to idle properly, you can always modify the distributor to give you more initial with less total, or leave the distributor un-modified and use manifold vacuum for the vacuum advance to get the idle advance higher with the total lower. Doesn't cost anything to do that and if it works that could save you some cash. If it doesn't work your only out some time.
Ya I've taken down to 22 total, It helped in cooler weather but after the weather got warmer, it did not. I'll either keep mixing fuel or decide to swap it. I have a WQ short block that I want to build for it. I wanted to wait a while on it though. This motor only has 4000 miles. Hate to take it out so soon. It would not cost too much if I swapped it. I probably spend 120 or so extra in 110 -112 octane a year.
I'll start researching what I need to focus on to swap. I think I just do the summit 2801 cam. People that use it seem to like it. It would be nice if I did not have to mess with the valve springs but I'll see.
