Total timing with 10.5:1 Compression

I have a 70 429ci with original iron heads and original compression which I believe is 10.5:1. It also has a slightly larger cam, 750cfm carb, Edelbrock intake, and a programmable MSD. I run fresh 92 octane unleaded but can't keep the engine from pinging when accelerating. I can easily customize the timing curve but can't seem to find one that works well. I've tried as low as 32deg all in at 4000rpm and the engine still noticeably pings. I will probably try 28deg next but that is awfully low for any real power. The engine runs well until I get hard into the throttle then ping ping ping.

I'm guessing 10.5:1 compression with iron heads is the issue. Any suggestions?

Thank you!

What's the cam specs?

dfree383 wrote:What's the cam specs?

Unfortunately I have no way to know.  The engine was in the car when I bought it. The cam has a slight slope and idles fine around 750rpm.  Idle has about 14 inches of vacuum.

How do the sparkplugs look? Carb may be lean. Also if the engine is high mileage it may have carbon buildup on the top of the pistons causing hot spots and preignition. I assume no vacuum advance on the distributor? That should not effect timing at full throttle, but just want to rule it out as a cause. Have you done a cranking compression test? This would give you more to go on, as for as what the cam is doing to cylinder pressure, and where it's at.

supervel45 wrote:How do the sparkplugs look? Carb may be lean. Also if the engine is high mileage it may have carbon buildup on the top of the pistons causing hot spots and preignition. I assume no vacuum advance on the distributor? That should not effect timing at full throttle, but just want to rule it out as a cause. Have you done a cranking compression test? This would give you more to go on, as for as what the cam is doing to cylinder pressure, and where it's at.

The engine might have 10,000 miles so not that old. Plugs are chocolate brown but I should verify the heat range. Good idea about the compression test.  I'll try to get that done this week.  I won't rule it out, but I can't imagine the engine would be lean. That 750 seems to provide plenty of fuel and works well.  I suppose I could put an Innovate wide band O2 on it to be sure.  The distributor is locked and is completely controlled by the MSD. Vacuum advance is accomplished with a 1-bar map sensor but it's disabled for now. I am just trying to get the engine to work well at WOT before I enable vacuum advance.

sounds to me like valve float JMO

gmsmkr wrote:sounds to me like valve float JMO

Pinging starts around 4500rpm and only when I'm hard into the throttle. Wouldn't that that RPM be too low for valve float?

jgkurz wrote:

gmsmkr wrote:sounds to me like valve float JMO

Pinging starts around 4500rpm and only when I'm hard into the throttle. Wouldn't that that RPM be too low for valve float?

Not if the valve springs are bad or old

gmsmkr wrote:

jgkurz wrote:

gmsmkr wrote:sounds to me like valve float JMO

Pinging starts around 4500rpm and only when I'm hard into the throttle. Wouldn't that that RPM be too low for valve float?

Not if the valve springs are bad or old

Interesting. I have no way to know the age of the valve springs. I guess I need to start saving up for new aluminum cylinder heads. Seems a shame I can't make this combo work. I'm sure the engine compression on pump gas isn't helping my cause either.

again JMO if you are 100% sure it has 10.5 comp then I would change the cam and spring with a new set of lifters..... I find it odd that you know the comp and not the cam specs as its all key parts in working together.

Edit: this is all part of buying a car already running and going of someones word for what it is

gmsmkr wrote:again JMO if you are 100% sure it has 10.5 comp then I would change the cam and spring with a new set of lifters..... I find it odd that you know the comp and not the cam specs as its all key parts in working together.

It's all an assumption. The engine internals are completely stock according to the receipt from the previous owner. The cam just says "performance grind". The stock compression was 10.5 so that's what I'm going with.

Compression ratio has very, VERY little effect upon total timing requirements unless the piston has a big lump on it hindering flame propagation.

If this engine is totally new to you then how can you assume that the timing mark is even in the correct location...?

rmcomprandy wrote:Compression ratio has very, VERY little effect upon total timing requirements unless the piston has a big lump on it hindering flame propagation.

If this engine is totally new to you then how can you assume that the timing mark is even in the correct location...?

^^^^^ Timing, marks are often off a few degrees, distributor phasing, is the distributor installed at TDC or is it off a tooth or too, and was the cam installed straight up, or advanced or retarded. Break out the dial indicator and pull a valve cover and find out what the timing events are in relation to what you are basing your numbers off of.

[quote="jgkurz"]

supervel45 wrote:How do the sparkplugs look? Carb may be lean. Also if the engine is high mileage it may have carbon buildup on the top of the pistons causing hot spots and preignition. I assume no vacuum advance on the distributor? That should not effect timing at full throttle, but just want to rule it out as a cause. Have you done a cranking compression test? This would give you more to go on, as for as what the cam is doing to cylinder pressure, and where it's at.

The engine might have 10,000 miles so not that old. Plugs are chocolate brown but I should verify the heat range. Good idea about the compression test.  I'll try to get that done this week.  I won't rule it out, but I can't imagine the engine would be lean. That 750 seems to provide plenty of fuel and works well.  I suppose I could put an Innovate wide band O2 on it to be sure.  The distributor is locked and is completely controlled by the MSD. Vacuum advance is accomplished with a 1-bar map sensor but  it's disabled for now.  I am just trying to get the engine to work well at WOT before I enable vacuum advance.[/quot  I would still do the compression test to see where it's at. What kind of 750 carb are you running? It could be running lean on the secondary side, as they open? The point about the timing marks on  the balancer being off are also spot on, and you may not really be at 32*. You could back it off to 28* and see if the pinging goes away, and how it runs there. The heat range and type spark plug is also to something look into. You also did not mention what the temperature the engine is running at?

Thanks for the guidance everyone. I'll try to get the compression and spark plugs checked today. As for the timing mark, that's going to be tough with engine assembled. The most precise way I know is with a dial indicator with the heads off. I'm not sure how accurate I can get through a spark plug hole.

The carb is a 750cfm Edelbrock. It looks like a Carter AFB. The engine runs between 185-195 depending on if I'm in traffic or on the freeway.

What temp. thermostat? I would try a 160* stat if you are running a hotter one.

supervel45 wrote:What temp. thermostat? I would try a 160* stat if you are running a hotter one.

The current thermostat is a Stant 180deg. I'll pick up a 160 and give it a try.

Compression test showed 165psi across the cylinders I sampled. I can't get to all cylinders without lifting the engine up.

The current spark plugs put in by the previous owner are Autolite 46's. The correct plug looks to be 45's, so one step colder. I'm guessing this may be part of my problem?

jgkurz wrote:Thanks for the guidance everyone. I'll try to get the compression and spark plugs checked today. As for the timing mark, that's going to be tough with engine assembled. The most precise way I know is with a dial indicator with the heads off. I'm not sure how accurate I can get through a spark plug hole.

A piston stop through the spark plug hole and a degree wheel always works at locating true TDC for me ... with the engine already assembled.

http://www.edelbrock.com/automotive/misc/tech-center/dl/carb-owners-manual.pdf Not saying this the cause of your problem, but something to keep in mind on the Edelbrock 750's. There are two of them, model #1407 and #1411. The #1411 with electric choke is set up leaner on the primaries. With 165lbs cranking compression I think you can get the preignition under control with a few minor changes.

jgkurz wrote:I have a 70 429ci with original iron heads and original compression which I believe is 10.5:1. It also has a slightly larger cam, 750cfm carb, Edelbrock intake, and a programmable MSD. I run fresh 92 octane unleaded but can't keep the engine from pinging when accelerating. I can easily customize the timing curve but can't seem to find one that works well. I've tried as low as 32deg all in at 4000rpm and the engine still noticeably pings. I will probably try 28deg next but that is awfully low for any real power. The engine runs well until I get hard into the throttle then ping ping ping.

I'm guessing 10.5:1 compression with iron heads is the issue. Any suggestions?  

Thank you!

compression is over 11 to one on all 70 429s, I bet  WRONG FUEL is your problem, it takes a lot of work to get these to run good on 92 oct.and the larger cam may be making a little more comp also

My particular engine came out of a 70 Galaxie which was rated at 360hp. Every book I have says it is 10.5:1 with the 429CJ's being 11.3:1. Maybe the books are wrong but that's where I got the 10.5:1. If the engine has been bored, which is likely, then compression is even higher.

I was able to get the plugs changed from 46's to the colder 45's. It made a noticeable difference but I still can't go WOT without pinging. I kept the total timing at 32 for the time being. Next up is to verify my timing mark, change to a 160 thermostat, and add fuel to the secondaries. I agree that I need higher octane fuel but maybe I can reduce the pinging enough to make the engine usable until I replace it in a year or two.

http://www.mustangsunlimited.com/itemdy00.asp?T1=DL284+01 Some of the early 429 4V's called for 4* BTDC intial timing, and assuming 22* mechanical advance, this would only be 26* total. From 1968 and into 1969 the intial timing on the factory most decals was 10*BTDC. A few sources list 105/1 compression for 429 2V's and 11/1 for 4V's, but most show 10.5 compression for both. In mid 1970 Ford did raise the deck height of the block, and may have used head gaskets from .022" to .050" at different times, so maybe this has to do with the differences? You said when you checked compression that you could not get to all of the cylinders. Did you pull all of the sparkplugs out and was the engine hot? If not you may have gotten a low reading. If the 165 psi is accurate I think you maybe lower than 10.5/1, the larger cam is bleeding off compression, or a combination of both. Some rebuilder pistons have a lower compression height, and may have been used. AutoLite 124 plugs maybe another option, for a colder plug to try also. It sounds like you are making progress, so keep after it and keep us posted.

supervel45 wrote:http://www.edelbrock.com/automotive/misc/tech-center/dl/carb-owners-manual.pdf    Not saying this the cause of your problem, but something to keep in mind on the Edelbrock 750's. There are two of them, model #1407 and #1411. The #1411 with electric choke is set up leaner on the primaries. With 165lbs cranking compression I think you can get the preignition under control with a few minor changes.

I have p/n 1411. I am confident it has the original calibrations. I'm a Holley guy so I'll need to research how to adjust fuel for WOT. The car runs quite well with good off idle response and power. Pinging is the only issue so I thought I'd do the Edelbrock equivalent of putting in larger main jets on the secondaries whatever that might be. Regarding the compression test, the 165psi reading was just after the car was at operating temp, 180deg or so. The spark plugs were certainly hot....    Regarding timing, 26deg total seems awfully low. Today, with the larger cam, I'm at 15deg initial and 32 total. In the end I may have to drop total to 28 but I don't want to go lower unless absolutely necessary. I appreciate the encouraging words. I will keep the group updated on my progress.

Just spoke to Edelbrock regarding my 750cfm pn 1411 carb. The guy in tech support was very helpful and suggested I first change the metering rods from .075 x .047 to a small diameter .070 x .042. I thought we should change secondary jets given the car runs so well other than WOT but he was confident this was the first step. This was because the factory calibration was for economy not performance. Stay tuned... HA!