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Discussion Starter · #1 ·
Hey everybody,

Just finished switching the car over to an external coil HEI set up, getting ready to hit the streets with the Bel Air. Now we are trying to get the timing as in spec as possible, but we are having trouble.

The car has around 10 Degrees of initial timing when fully warmed up with advance line plugged. The car starts fine, warmed up or not. Turns over a little slow sometimes, but not enough to the point where a non-car enthusiast would notice.
Anyhow, the motor is pinging, when it warms up, it's not as bad, but I still am worried about it. If the timing is retarded at all from the point it is at now, it starts to run like garbage. If it is advanced any more, well, it obviously runs worse...

What do I do/Check for?

Car has:
Skip white HEI Dist. W/ external MSD coil
Accel Supercoil wires
New plugs

I am buying a new Holley this afternoon- the car needs it. The Rochester that is on there now is junk. You can adjust one idle screw all of the way in, or out, and it has no effect on the car at all. Could the detonation be caused by a faulty carb?

Thanks!
 
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what grade gas you running? maybe try a higher grade. :confused0006:
 

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I don't think the carb is your detonation problem. You dont mention how much compression you are running this could be a problem if too high. Timing also is always one of the first places to look, but you need good componants to get good results. You say your "small cap" HEI is a Skip White unit, that is almost certainly suspect right from the get go. Skip White performance is selling Pro-Comp small cap HEI's and they are junk, absolute junk. Not worth your time or money even though they are not much money. Last time I saw them they were in the $35.00 to $40.00 range and you simple dont get much distributor for that kind of money.

Think about replacing that dizzy that sure could be the problem. A stock (?) small block should not detonate that is if it is stock.....

Roland
 

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What do I do/Check for?
Thanks!
First I agree - use fresh high octane fuel.

Its not just a matter of initial timing. Its the curve on centrifugal. One can't just go out and stuff in the double throw me down distributor just because its the one everyone uses on their high performance build - without customizing the curve. Even buying a high end dist - if its for a hot rod and your putting it in a stock low compression engine it ain't gonna be correct right out of the box!

The ideal ignition timing for power and fuel economy is just short of the point where detonation or pinging occurs, the correct ignition timing (the initial timing plus the advance from both mechanical and vacuum advance mechanisms) will cause the pressure created by the fuel being burned in the combustion chamber to heat the air that is pushing the piston down, to be at its peak/maximum when the piston is at about 12 and 15 degrees ATDC (after top dead center). If the peak cylinder pressure is reached before the 12 to 15 degrees ATDC you will lose power as the piston fights to compress the burning air/fuel mixture and detonation may also be experienced which can lead to engine failure. If peak cylinder pressure is reached much after the 12 to 15 degrees ATDC, the engine will just be wasting the energy the combustion process creates as wasted heat out thru the exhaust system.

The amount of ignition advance needed changes with engine speed, engine load, engine temperature, air temperature, compression ratio, the octane of fuel being used and the air/fuel mixture. A fast burning - rich air/fuel mixture (12.5 to 1 air/fuel mixture) that will produce the maximum power and will require less advance than the slower burning - leaner air/fuel mixture (14 to 1 air/fuel mixture) that is used for cruise speeds to properly burn all the fuel. A vacuum advance adds a little more ignition advance to allow the engine to fully burn this slower burning - leaner air/fuel mixture that is seen at part throttle conditions such as a 65 mph cruise. A 12.5 to 1 air/fuel mixture burns the fastest and will supply the best power, but a leaner air/fuel mixture of 14 to 1 is much better for fuel economy and also will not tend to foul spark plugs like the richer 12.5 to 1 air/fuel mixture will tend to do.

The advance curve used most on a 9.5 to 1 compression engine with a mild camshaft (duration less than 220 degrees at 0.050”) is 10-12 degrees initial timing plus 22-24 engine degrees of additional advance from the centrifugal advance mechanism. In most cases, full advance (32-36 degrees) is in by 3500 rpm. An engine with camshaft duration above 220 degrees at 0.050” will like more initial timing; however, the total timing will stay the same (32-36 degrees). In most cases when you are using a “hot rod” mechanical advance curve, the amount of additional advance from the vacuum advance should not exceed 10 degrees and not be in before 10 inches of vacuum, or performance may suffer from too much advance.

The mechanical advance should not start advancing until just above the base idle speed, too much advance with the engine speed too low may cause a ping or detonation problem, which sounds like what you are seeing. Barry Grant catalogue recommends 10 to 12 degrees of initial timing when the camshaft duration is less than 220 deg. @ .050 valve lift, 14 to 16 degrees of initial timing with less than 240 deg @ .050 and 18 to 20 degrees of initial timing with a cam with less than 260 @ .050 valve lift.

So what you should be looking for is how fast that advance is coming in! With Vacc adv plugged, Set initial to 10, run the engine up in 500 RPM increments and read where the timing is at - write it down (sometimes even graphing it can give a clearer picture). I'm not sure what comp ratio the stock 267 is - but if soter than 9:1 it should have less total adv than the above stated 32-36 (more like 30-32) - and may even like it all in by 2800-3000 RPM.
Conversly you can set the total timing at 3000 lock down the dist - then set the centrifigals to get that 10 initial that is obviously working for you (as seen by the good starts and idle qual). But best is always to bench run on a dist machine - but with the computer taking this over - it's hard to find anyone who has one now!

Once you have the centrifugal curved right you can get a vacc adv module that 10 degrees at 10"hg - run it down the highway and see how she goes - if you get a 2-4 cyl ping "burping" the throttle this would indicate needing to get the 10 degrees at a higher vacc, a stumble would indicate a lower vacc.
 

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The 267 Chevy engine was a very low performance engine. The 3.50 bore of this engine was the smallest bore ever used by Chevy in any small block. Compression in this engine had to be around 8.1 Maybe! That is taking into consideration small cc heads probably 58cc like the 305 which replaced the 267 when that little engine could not meet emissions.

Going to a higher octane gas sure "should" not be of any help and if it does help it would beg the question. Why? Why would higher octane fuel be required in a low performance engine? Factory rating which was probably very optimistic had it rated for 110 HP. The problem probably lies with the dizzy. The Pro-Comp dist is very much in suspicion as Pro-Comps failure rate is around 15 to 25%.

Any let me repeat that "ANY" qaulity distributor without doing a thing to it and I mean right out of the box should provide service that would let the engine run and function just fine, without pinging if the problem is in the Distributer. Most of these distributer like Mallory--Accell--MSD and the like actually do know how to set up a distributer so that it will run out of the box and not destroy the engine as pinging will do if left alone. It may or may not be optimal for that engine but it should perform its function with out needing to be put on a Distributer Machine to work. The manufacturer has already done that.

Roland
 

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Factory spec on the '80 4.4 Monte Carlo is 6 initial and 30 all in at 3000. 30-6 is a distributor that gains 24 degrees in 2500 RPM. The Mallory I put in my build this summer is out of the box at 20 in 2500 (gives 14 initial to get my 34 at 3000) - Roland is right, as that would be less than ideal advance not more...
But I would still check the curve before buying a bunch of new stuff - theres not much else in a dist besides the centrifiguls that would contribute to ping (except a ton of wobble and/or thrust) - and look close at the timing marks when you do - if bouncing all over the place this would be timing chain or dist wobble and thrust. If more curve is found than what is wanted I would think that if they can't get the curve right there could be other more serious issues and - the next test would be the water dissolution test - that's where you put the thing in a barrel of water to see how long it takes to fully dissolve - less than twnty five years I would seriously suspect inferior metallurgy - while waiting for the results go with a better unit as a temporary replacement.

I did notice the "Pings but not as bad when warm" - hmmm should be the other way - pings worse the warmer it gets! kinda wondering if you got any of those thermal vacc switches these smoggers are so famous for on there or some vacc leaks (could explain no response to idle mix screw as well)?

Edit: to correct above - "not much that would contribute to UNEXPECTED ping" - lol
 

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Discussion Starter · #8 ·
you guys have given me a lot to think about and consider... I am very fortunate to have people on my side who KNOW what they are talking about, instead of just guessing.

I already bought the holley this past weekend so I am going to replace that this week. I am picking up a Weiand intake manifold this weekend and I am just going to kill two birds with one stone.. I hope it's not the distributor but I guess we'll find out in the next couple of days. The skip white distributor that I got does have a lifetime warranty- so if it requires replacement then I'll give it one more shot.

I originally purchased the MSD HEI StreetFIRE distributor, but quickly learned that its coil-on-cap design doesn't work too well with my firewall... And we're not willing to alter the firewall. So I chose the SkipWhite dist. because of its HEI set up, while still retaining the small size of the original distributor. I had heard good things about skip white stuff, and their 99.9% possitive feedback rating with over 70,000 transactions reflected this... But hey, you guys know what you're talking about.

I'm going to throw the new carb/manifold on since I've already got it.. hopefully the issue will stop. IF the distributor is bad, it wasn't when we first put it in... The care has been run/driven with the distributor previously and there was no issue with pinging.. But there is no telling.

I will keep you guys posted..Thanks again
 

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Discussion Starter · #9 ·
let me ask this-

I was always under the impression that the timing tab on this 267 CI represented ONE degree per mark...Sourced a forum and that was the response I got. I realized at work that an alarming ammount of SBC's utilize a 2 degree/per mark set up... Which is correct? I feel really, really dumb for asking.

Secondly, how do you measure the advance when the mark appears wayy before the tab (as you are measuring vac/mech. advance)? I feel like it is a dumb question, just like the other one... but I gotta ask
 

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Peak to peak two degrees - peak to valley one.
 
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