I have a nicely built slant, bored 60 over, cammed, 9:1 compression. However, it has been pinging under load, when hot, over 3K rpms. I use 91 octane premium.

It only does it when it is good and warmed up. I've tried different timing settings, recurved the dist so it doesn't advance so much at high rpms, octane booster.

I took it on its first real road trip last weekend. I drove about 150 miles to the some local mountians. It was pinging gooing up the mountains, and I was regretting taking it, but once it was up to about 4,000 feet elevation, it stopped pinging and ran great.

Where I live, it has been over 100 degrees everyday this summer. So I am wondering, did the cooler air, or the thinner air reduce the ping? Another question, This engine when built, had a 4bbl, is my 2 bbl starving the engine? Will it ping when not enough gas is getting to it?

It can cruise just fine at 3000 rpm, but one I need more power and step on the gas, the pinging starts. Any ideas?

couple suggestions:

carb... what kinda 2 barrels do you have? carter small 2 bbl or holley big 2bl?

how radical is your cam?

do you have heat riser on your exhaust manifold? sounds to me like you're driving in hot weather condition... I'd cut off the heat riser. I used to have ping under heavy load above 3k rpm and when I removed the heat riser it improved considerably. Other thing that caused ping under heavy load when revving high was the vacuum advance pod kickng in (with some good cams, the engine is producing more vacuum in the 3.5-3 k rpm band than idling or under mild acceleration) stiffen the spring and you're good.

how good is the atomization on that carb? if the atomization is bad, it might be "artifically" lean....

did you degree your cam? you know for sure it's properly centerlined and not retard? a retard cam might cause pinging....

How much total advance do you have dialed in? I have 28º BTDC... with a 7 governor (that's 14º BTDC initial 14ºBTDC mech advance) and a 6.5 vac can.

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Juan Ignacio Caino

Please use e-mail button istead of PM'ing. I do log in sometimes but I'll be answering quicker thru e-mail.

the cam is a 256 duration, 470 lift. Carter BBD, with about 290? cfm. The engine was built by Doug Dutra, so I'm sure the cam is fine.

I don't know about the atomization, but the person who rebuilt the carb took into consideration my cam and had the cam specs before he rebuilt it (didn't want to do a "stock" rebuild with the cam I had).

The dist was recurved to have about 30 total at 10 initial (recurved a 15R govenor to approximately 10R), but I found that it was faster at about 8 initial and losing some top end with the recurve, but still had pinging regardless, so I don't really want to go less with the govenor.

I am curious, how did you "remove" the heat riser?

What kind of spark plugs are you using (brand and type)? Have you "read" the spark plugs (examined the tips to see if they're running too hot)?

I respectfully disagree with Argentina-Slantsixer; I do not think altering your heat riser in any way will materially affect this problem unless it is presently stuck in the "heat on" position.

The thinner air up in the mountains not only reduced cylinder pressure but also made the mixture richer. Note that an overlean mixture will tend to cause pinging! The 100° air down where you normally live also reduces cylinder pressure, which means less tendency to ping than if the intake air were cooler.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Does it ping when you floor it at 3000rpm or just when you ease on to the throttle? If it only pings under partial throttle you just need to tighten the vacuum advance cannister.

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heat riser is good for stock engines, as you "climb up the hill" (talking about engine hop up) I respectfully disagree with you Dan, unless you live in an extremely cold climate area as you do... But we're talking about a hot climate area, so the heat riser plus the BBD are a bad combination IMHO. That motor was set up with a holley 4bbl from Dough? if so, and knowing that he really goes the extra mile about everything he does, that particular engine must be put together thinking on that kind of carburetion, at least one big holley 2 barrels (500 cfm or so...)

In my personal experience, I always had my slants with stock exhaust systems till one happy day back in the late 80's when I decided to give "Cañossilen" (great custom exhaust shop from Argentina that has been on the business since 1959 at the very same place, and managed by the original owners, one of them is the exhaust master and he did my car back then and I always have turned my cars to his hands ever since then) a shot. Performance went up drastically as well as mileage, believe it or not, I picked up some mpg on cruise condition. Since then I've learned 2 things: against his advice I had my last slant's ex system set up with no heat rising (he manages to provide heat riser "trick" device from his headers). He told me that I wouldn't be able to drive the car in the winter and this not only hasn't turned out to be true but I really loved the way she behaves during both winter or summer, and I kissed goodbye all the pinging when driving in hot weather issues that I had. The other thing I learned is that balancing true duals will give me back some (if not all) the low end torque and solve some annoying resonances. I learned this from you and others at some post here.

Going back on topic, while I mostly agree with you about the ex heat riser probably not being the first culprit on RDJ's car, I don't think that a good strong slant with nice cam and added flow as his cam permits, will take any advantage of heating the intake using the exhaust gas (oem heat riser). What's the point of using high octane premium if he heats the intake? intake charge will be less dense but in fuel... so when hot there's a chance of going apparently lean! and he has increased CR... Also I'd blame it on that BBD... and the vac can sure needs to be checked.

RDJ, I'd check first if unplugging the vac line to the vac pod on the distributor cures the problem... Then I'd go after the carb, suspecting it of being too lean (or probably the needles aren't woring fine).

You haven't mentioned nothing about overheating so I'll asume that your cooling system is doing fine at any engine operation range of RPM...

_________________
Juan Ignacio Caino

Please use e-mail button istead of PM'ing. I do log in sometimes but I'll be answering quicker thru e-mail.

heat riser is good for stock engines, as you "climb up the hill" (talking about engine hop up) I respectfully disagree with you Dan, unless you live in an extremely cold climate area as you do... But we're talking about a hot climate area, so the heat riser plus the BBD are a bad combination IMHO. That motor was set up with a holley 4bbl from Dough? if so, and knowing that he really goes the extra mile about everything he does, that particular engine must be put together thinking on that kind of carburetion, at least one big holley 2 barrels (500 cfm or so...)

In my personal experience, I always had my slants with stock exhaust systems till one happy day back in the late 80's when I decided to give "Cañossilen" (great custom exhaust shop from Argentina that has been on the business since 1959 at the very same place, and managed by the original owners, one of them is the exhaust master and he did my car back then and I always have turned my cars to his hands ever since then) a shot. Performance went up drastically as well as mileage, believe it or not, I picked up some mpg on cruise condition. Since then I've learned 2 things: against his advice I had my last slant's ex system set up with no heat rising (he manages to provide heat riser "trick" device from his headers). He told me that I wouldn't be able to drive the car in the winter and this not only hasn't turned out to be true but I really loved the way she behaves during both winter or summer, and I kissed goodbye all the pinging when driving in hot weather issues that I had. The other thing I learned is that balancing true duals will give me back some (if not all) the low end torque and solve some annoying resonances. I learned this from you and others at some post here.

Going back on topic, while I mostly agree with you about the ex heat riser probably not being the first culprit on RDJ's car, I don't think that a good strong slant with nice cam and added flow as his cam permits, will take any advantage of heating the intake using the exhaust gas (oem heat riser). What's the point of using high octane premium if he heats the intake? intake charge will be less dense but in fuel... so when hot there's a chance of going apparently lean! and he has increased CR... Also I'd blame it on that BBD... and the vac can sure needs to be checked.

RDJ, I'd check first if unplugging the vac line to the vac pod on the distributor cures the problem... Then I'd go after the carb, suspecting it of being too lean (or probably the needles aren't woring fine).

You haven't mentioned nothing about overheating so I'll asume that your cooling system is doing fine at any engine operation range of RPM...

_________________
Juan Ignacio Caino

Please use e-mail button istead of PM'ing. I do log in sometimes but I'll be answering quicker thru e-mail.

I'd suggest reading the plugs, and a couple of things with the "recurve"...

What vaccuum can are you running? (when does it kick in), and what did you use for springs and what tranny are you running?

At this point I think you have too much vacc. adv. going on at the wrong time, and possibly the springs might be a little light, among other things...

-D.Idiot

When I first got the engine, it had Champion RN12YC. I then changed them to NGK NGK ZFR5N gapped at 0.40. I also did the HEI conversion. After talking with DD, he thought the NGKs might be a tad hot for this engine, so I am going to install the Champion RN12YC again, gapped at ???.

The counterweight on the exhaust manifold heat riser had a really tight spring, so I reduced the spring tension on it. Has anybody installed a cold air induction on a slant six, or is this overkill? Would a bigger carb or bigger jets on the BBD help?
A little more than ease, but not floored will cause the pinging. How do you tighten the vacuum advance?

why did you use the BBD instead of the 4 barrel? economy or tuning bogs?

also, as DI says, maybe the springs are too light (or one just broke, happened to me! )

_________________
Juan Ignacio Caino

Please use e-mail button istead of PM'ing. I do log in sometimes but I'll be answering quicker thru e-mail.

You insert a 3/32" allen wrench thru the vac port (where the hose attaches) and turn the screw counterclockwise (stiffens the spring) or clockwise (lightens the spring) you want it to be stiffer (so it kicks in and out at higher vac readings) Try 2 turns at a time and test drive it...

_________________
Juan Ignacio Caino

Please use e-mail button istead of PM'ing. I do log in sometimes but I'll be answering quicker thru e-mail.

I am running a 2 1/4 single exhaust. Dual exhaust are in the plans, but maybe I should go sooner than later. As far as engine overheating, it has been running about 190 around town, but on the trip last week, it got up to 210 going uphill and pinging. but when I got to flat area and cooler temps, it cooled back down.

Then today, I cruised about 20 miles to the junk yard, it is about 103 degrees outside, no real hills, the car was running at about 200 degrees, which kind of surprised me, it hasn't been running that hot before.

BTW, at the junk yard, I got a gauge cluster limiter from a 72 Dart, if my factory temp and gas gauge don't work better with this limiter, I am going to try the technique you described in an earlier post (after I changed out the fuel tank sender plus and didn't fix the fuel gauge) upgrading the limter.

I did it after I went up the mts, before I drove down. Maybe made a slight difference, but it is hard to tel, but still pings

I will try to tighten the vacuum today.

By the way, the Offy 4 bbl intake doesn't have a connection to the exhaust manifold, correct? IF it doesn't, how does it bolt to the exhaust manifold?

RN12YC is the same heat range as ZFR5N, so no change there. If you want to try a cooler plug, try an Autolite 63 (or if you are masochistic enough to keep pushing your luck with Chumpions, an RN9YC).

The counterweight on the exhaust manifold heat riser had a really tight spring, so I reduced the spring tension on it.[/quote]

OK, so that's really probably not your problem.
The factory installed cold-air induction on most all slant-6s starting in '76 (thermostatic air cleaner with cold air duct running to front of engine bay). This is not where your problem is coming from.
You don't need a bigger carburetor. We won't know what your jetting situation is like 'til you read the plugs. Take the car for a run, get it to ping, then pull off and yank a spark plug or two and see what the tips look like.

BTW, if you are running the metal ring washers on your plugs, it will cause them to run hot...remove them!
With an allen (hex) key inserted into the vacuum can's hose nipple. Turn clockwise to tighten. But I agree with the diagnostic technique advised above: Disconnect the vacuum advance, plug the hose, and see if it still pings.

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.