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Old 11-04-2007, 08:18 AM
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69 Mustang pinging after rebuild

I have a 69 mustang with a 351 windsor engine that I just finished installing after a complete rebuild. The engine was over bored .30, the cast iron heads were completely done with some mild porting and new guides, seals etc. The crank was ground slightly and of course there were new pistons installed. It has a 4 barrel cast iron Ford intake with a fresh professionally rebuilt autolite 4100 1.12 carb. I also have a pertronix ignition and coil. The new cam is a long duration higher lift cam (.5 intake, and .5 exhaust) that requires a 2200 rpm stall torque converter. Now my problem is it pings real bad upon light to medium to heavy acceleration. It quites down at cruising speed. So I have backed off the timing so far that it now hesitates and bogs down; I have even taken off the vacuum advance thinking that it was advancing too far. I suppose it could be the mechanical advance but that was all functioning correctly before the rebuild and is fairly new. Anyway backing off the timing slightly helps but does not solve the pinging issue at all. I also think that it may be running somewhat lean so I put bigger primary jets in the carb and that did not help either. I may still need bigger primary jets but I need to purchase them first. I did have some issues with adjusting the hydraulic valves, could I have them too tight and they are not closing all the way? Any suggestions? I am an experienced mechanic and I am at a loss here.

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Old 11-04-2007, 09:45 AM
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what grade gas are you using?
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Old 11-04-2007, 09:53 AM
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69 mustang grade of gas pinging problem

I have used up to 93 octane with only a slight improvement.
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Old 11-04-2007, 09:54 AM
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how much initial timing is it set to?
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Old 11-04-2007, 10:18 AM
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I'd definitely recheck valve lash, What do you say to "hotter plug"
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Old 11-04-2007, 01:59 PM
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Most people don't consider that by overboring, the compression automatically goes higher. Then if you had the heads surfaced plus decked the block, it goes higher still.

If the motor was borderline high compression when it was sold new, it would now do what you describe. Most good engine builders would have reset the compression to whatever you wanted during the build....and some don't
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Old 11-05-2007, 07:49 AM
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69 mustang pinging problem

I can use a hotter plug and I have not tried this though, so I will. Also, I have had a lot of engines rebuilt with this maching shop and we did talk about compression and keeping it in a normal range to use pump gas. I will do a compression check tonight.
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Old 11-05-2007, 04:17 PM
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What are the cam specs (advertised duration, duration at 0.050", LSA)?

Where did you install the intake centerline?

What cam manufacture?

Did you install the same piston model and head gasket?

Did you calculate the cr before putting it together?
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Old 11-05-2007, 06:10 PM
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The pinging is most likely detonation. Which, of course is bad for you new motor. You should gather your specs and start off by calculating your compression. Here's a link to a good compression calculator....
http://www.ondoperformance.com/page2.html
A good rule of thumb is if your over 11:1, you could find that 93 octain pump gas isn't good enough. You might be borderline at this point and try changing plugs, retarding your timing enriching your air/fuel mixture. Your set-up might be wanting more timing than your octane can handle.
But in any case, start out by finding out what your compression is.
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Old 11-05-2007, 06:50 PM
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Osif

Quote:
Originally Posted by oldchevy1956
I have a 69 mustang with a 351 windsor engine that I just finished installing after a complete rebuild. The engine was over bored .30, the cast iron heads were completely done with some mild porting and new guides, seals etc. The crank was ground slightly and of course there were new pistons installed. It has a 4 barrel cast iron Ford intake with a fresh professionally rebuilt autolite 4100 1.12 carb. I also have a pertronix ignition and coil. The new cam is a long duration higher lift cam (.5 intake, and .5 exhaust) that requires a 2200 rpm stall torque converter. Now my problem is it pings real bad upon light to medium to heavy acceleration. It quites down at cruising speed. So I have backed off the timing so far that it now hesitates and bogs down; I have even taken off the vacuum advance thinking that it was advancing too far. I suppose it could be the mechanical advance but that was all functioning correctly before the rebuild and is fairly new. Anyway backing off the timing slightly helps but does not solve the pinging issue at all. I also think that it may be running somewhat lean so I put bigger primary jets in the carb and that did not help either. I may still need bigger primary jets but I need to purchase them first. I did have some issues with adjusting the hydraulic valves, could I have them too tight and they are not closing all the way? Any suggestions? I am an experienced mechanic and I am at a loss here.
Thirty over will push the compression a little but a hot cam should compensate in downward direction with less dynamic compression in the low RPM range, however, in the higher RPM ranges dynamic compression will go up, regardless of the calculated static compression because of gas flow dynamics in the intake. Porting and long duration cams have cumulative effects on dynamic compression. Both reduce low speed dynamic compression and add it at higher speeds. So the net effect can be quite impressive.


The trusty old Ford 4100 might be lean in spite of jet changes, grit from the fuel system settles down on the primary jets and can obstruct them or the passages. Or the power valve can be stuck closed which will lean out high Revs or hard acceleration where the throttles are wide open or nearly so. Not to mention not enough fuel level in the bowls.

Machine operations on the head can take compression unexpectedly high, the combination of new valves that are thicker and set more into the combustion chamber will reduce chamber volume and run compression up as will contributions from head milling and decking the block. Piston's can vary by intent or by accident from those of the OEM by having a bit higher pin to crown height as well as different crown shape, say from dish to flat top. Machining can leave sharp edges behind that glow when hot. A head gasket can be mispositioned so as to hang and edge into a chamber.

Spark plug heat range could be too hot, dropping a heat range might help.

Headers and porting tend to lean out the carb. High energy ignitions can run the burn speed up increasing pressure and temperature spikes in the cylinder. One has to remember that racing engines aside, high energy ignition was developed for lean burning SMOG engines that need more energy to get the burn going. While on the subject of ignition! The timing in the distributor could be coming up too fast or it could have too much total. The engine (any and all) will only tolerate so much advance usually from 30 to 40 degrees depending upon chamber shape and size, cam timing, mixture ratio and bunch of other things. When a lot of initial advance is set high because a long duration high, overlap, late intake closing cam reduces low rev trapped cylinder pressure and this is not compensated for in total advance of either vacuum or centrifugal system, then the total timing can get into the 50-60 degree range which for sure will make the engine ping. The vacuum advance pulls the breaker plate against the direction of rotation some amount. The centrifugal moves the breaker cam or wheel into the direction of rotation a certain amount. These amounts are based upon some assumption of how much static or base timing is set by the position of the distributor. If the automatic systems have 30 degrees of movement and the manufacturer assumed that the distributor would be advanced no more than 10 degrees, then the whole thing can get to 40 degrees. If the installer finds the engine with a hot cam wants 25 degrees of initial advance, then with no other changes the total amount of available advance goes to 55 degrees, which is too much. You as the Hot Rodder have to obtain or modify the vacuum can and the centrifugal's guide slots to remove those extra 15 degrees that are put into the base setting. If you don't, chances are good there's a set of new pistons in your future.

Cleaning the old intake restores the under carb heat from the exhaust cross over. This raises intake charge temp which will make the engine more sensitive to preignition and or detonation. A cool air source from outside the underhood area can be a very big help, as can reducing operating temps. I hate to recommend a 160 thermostat, but give it a try if you haven't. 160 is a bit too cool for the oil to drive out contaminates, but if your drives are long it will be OK.

The hotter cam moved the power band up the RPM range, you can get into a spot where the original gears cause the engine to lug (high loading at low RPMs) this surely will cause pinging. Plus high stall converters reject a lot of heat which might make the return coolant, where the heat exchanger is, hotter than the engine would like.

Brands of fuel make a difference, octane number move around quite a bit with inlet charge temp. Sunoco, Chevron, Texaco, Shell do a better job of keeping their octane stable at elevated temps than say Citgo.

Of course there's aways the chance that's something inside like the cam isn't set correctly, one has to be careful when it comes to advancing the cam, as many manufacturers build in a couple/four degrees and if you add another 4, the motor is getting into trouble.

Bogie

Last edited by oldbogie; 11-06-2007 at 05:44 PM. Reason: Forgot to complete my thoughts on ignition, find after the spank symbol
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Old 11-05-2007, 07:24 PM
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Most aftermarket stock-type pistons are made to maintain the original compression with the over bore. Sometimes the dish is slightly deeper or the deck clearance is increased.
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Old 11-06-2007, 08:18 AM
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re: 69 Mustang pinging after rebuild

I definitely appreciate all of the comments. When the cam was installed it was dialed in at the machine shop. I will get the specs on the cam. No decking was done and head gaskets fit perfectly. The new pistons were designed as to not increase compression but then who knows. Also, it has been mentioned about pinging under load so I need to determine the pinging intensity under very slight acceleration, medium, heavy, and then to WOT. WOT will open the secondaries on the 4100 so I need to determine the pinging, but I have been somewhat hesitant to WOT a new engine that pings as bad as this one is doing. WOT will also lower the vacuum and cause the power valve in the carb to open and let more gas in the secondaries. I have a gut feeling that WOT won't ping but I need to test WOT at different speeds thus different loads at different rpms. I am going to try a few things and do a drive test after each to determine the improvement / solution. First I will install the old 4100 before the engine rebuild. The old 4100 is a smaller version (1.08) that is used on 289 fords so that is why I purchased a 4100 (1.12) for the rebuilt 351w. The older carb did work well as I put richer jets in the primaries and the engine did not ping. It smoked from oil consumption through the valves and pistons but it did not ping. The new 4100 could have a sticking power valve (mentioned above) which would definitely run the engine very lean. Since the power valve is vacuum driven I may look at installing an edlebrock carb and see what happens as the edlebrock does not have a power valve and I may have a low/ lower vacuum issue with all the head and cam work. If switching carbs has no effect then in this order I will, install colder plugs, install various stages of richer jets in the new 4100 focusing on the primary jets first and then to the secondary jets (depending on WOT results above), by this time I will need more gas so I will try another station of 93 octane, install a colder thermostat, and lastly readjust the hydraulic valves. The valves have no adjustment as the rocker arms are just tightened all the way down which I have wondered if that is too tight causing the valve to not close properly. If I purchase locking nuts for the rocker arm bolts then I can back them off some if needed. Doing this with the engine running is not fun but may been necessary. If all the above does little to help, I suppose that I could get a different intake but I am trying to keep this as close to original as possible. I will update after I have results. Any more things to try short of taking the engine back apart please suggest. I could try more of a racing type fuel but I will drive this car a lot in the warm months and I don't want to depend on this special type of fuel. Again thanks for all the comments. I will keep us updated.
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Old 11-06-2007, 08:33 AM
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Most pinging is caused by too high of a cmpression ratio for the fuel being burned. You need to check this first. The pistons were changed so I would be very suspicious of this. Timing is another common issue, you said you already checked this.Temperature is the third most common cause. Is it running hot. AF ratio is another possibility, not as common though.
If you are going to try a different plug, you need to go colder not hotter. I doubt it will help.
Like any other troubleshooting, dont guess, eliminate things logically one at a time untill you find the issue. Calculate the compression ratio and make sure you dont guess at anything.
If you can find a garage with a portable 5 gas, see if they will go for a ride to check the AF ratio. Timing and temperature should be easy enough to check.
If none of the above yeild any results then you can start looking at cam timing and some of the less common causes.
My bet is you got the wrong pistons by accident. Ordered one and got another.

Chet
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Old 11-07-2007, 07:41 PM
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Compression test is not too important in figuring out your problem. Most cams will have overlap and thus finding your statis compression won't help.
But you really need to gather your specs and calculate your compression ratio first, won't cost you anything to do that. I would be VERY careful about test driving it with the pinging for now. It's not a diesel and each run with pinging IS causing stress and probably shortening the life of your parts.
Very important you find out what compression ratio to the fuel your using first.
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Old 11-07-2007, 11:37 PM
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If the engine was origionally an early 4V, she most likely had 10:1 at birth. I would try an adjustable vacuum advance cannister first and if that does not fully get it, check the mechanical advance in the distributor.

If this engine has positive stop rocker studs, you would need to go to the studs for adjustable rocker arms.
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