Detonation at WOT

[Rich Herr]

I'm having a issue with my car detonation at WOT.  If you ease into the second carb it fine, it's only when you stomp on it.  I have a 428pi with bk/bj carbs and the cam below.  Dual point mechanical advance only dist. 35* total dwell.  6* intial timing/32* all in timing.  C7AE factory ford cast iron heads.  Less than 5% leak down, 230-240- psi compression numbers.  Idels currently at 17" of vacuum at 850 rpms.  3.50 rear gear if important. Currently running 92 octane pump gas.  Didn't know if the fuel is the issue and should be running 106 or a carb issue or something else.  Any suggestion would be appreciated.  Compression is about 10:5.

Thanks
Rich Herr
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[TA Coupe]

You forgot the important part. How much compression are you running?

     Roy

[Bob Gaines]

I would like to know what octane fuel you are currently using besides the compression ratio previously asked for.

[Rich Herr]

The compression is about 10:5 and running 92 octane from the pump.

[pbf777]

    Although I have stated previously that compression testing numbers really are not a good determinant of the actual "measured" or "mechanical" compression ratios, for a number of reasons, but if your instrumentation and testing process was at least somewhat of the norm, those values of "230-240 psi" seem somewhat high for what one might think is a "10.5" example, at least "dynamic" wise, or being compatible with "pump gas". 

    Scott.

[TA Coupe]

Although I have stated previously that compression testing numbers really are not a good determinant of the actual "measured" or "mechanical" compression ratios, for a number of reasons, but if your instrumentation and testing process was at least somewhat of the norm, those values of "230-240 psi" seem somewhat high for what one might think is a "10.5" example, at least "dynamic" wise, or being compatible with "pump gas". 

    Scott.

I was thinking the same thing Scott. I was thinking he had more like 12 to 1 compression ratio.

     Roy

[Bob Gaines]

You can doctor your gas with some race fuel to see if it makes a difference. If it makes a difference you can either keep race fuel on hand or use what I do and instead use a octane booster to doctor my gas on the cars that need it.
  http://www.wildbillscorvette.com/OctaneSupreme01.htm

[68blk500c]

Thanks for that link, Bob!  I used REAL LEAD product years ago with great results.  Lost track of it, but now found.
Use caution when handling this leaded product.

[Road Reptile]

Rich,
One important thing to do is read the sparkplugs. Might also suggest a Dyno run to watch it under load to monitor air fuel and timing. Hope this helps.
R.R.

[TA Coupe]

This is the octane booster that I use:

https://www.summitracing.com/parts/MEF-100132

Unless your head has hardened seats, then get some lead substitute to put in also.

      Roy

[Kent]

I raced a lot of FE´s and also I have driven them on normal roads and in my opinion all FE´s need 95 Octane due to the head design + piston clearance between the heads at top dead center. Thats also the reason why spark plug reading is not really effective as they usually should be grey when the engines ran perfect. I measured a lot of FE´s on the Road and adjusted them and when I even went to safe rich settings the spark plugs were white-grey which has to do with the combustion chamber setup from the factory.

For your problem it would be good to know if the popping comes when you are at normal throttle and then hit the pedal hard to the floor which would tell me your second carb is reacting to fast. Maybe it's also just fuel as I said I never would go under 95 with these engines. Also please take a close look to your ignition is there enough voltage at the Coil+Distributor and at the end check your spark plug wires and more important the spark plugs and gaps. Sometimes just spark plugs can cause this problem. I only use NGK since 25 years.

[TA Coupe]

Kent, do you know how ninety five octane in Germany compares to ninety two octane, here in the united states?

      Roy

[Rich Herr]

Thank you to all.  I will test it out and see if it solves the issue. 
Rich

[FL SAAC]

The compression is about 10:5 and running 92 octane from the pump.

We usually get our fuel at two sites bear our home

Noticed similar issues at one if the sites that we get what we thought was 93 octane 100% of the time

On a late Friday night coming back from an event a tanker was dropping a fuel delivery.

I noticed he had two hoses leading from the truck to the ground

Got friendly with the driver how you doing tonight,  how long in the job, you like it, what dont you like.

As he was dropping 9,000 gallons off

Asked him what was he dropping,  he pulls out the invoice and says looks like all regular 87 octane

problem was that one the tanks was the 93 super unleaded I was getting

Called the state and reported them, find out they have had many incidents of misfueling at this site.

Lower octane that posted on the pump

Guess were I don't purchase fuel anymore

The new cars with the computer controlling  everything are more forgiving our older cars are not , they ping or diesel on with low octane fuels.

So when you think your getting 93 octane sometimes you are not

Best of luck

[camp upshur]

Certainly it could be one of many reasons as mentioned.
It might help if you could determine when you are detonating.
Many engines detonate at peak tq rpm because they are advanced curved for total advance at peak horsepower rpm. Maximum cylinder pressure is at max tq rpm. Max HP is later and it requires more spark advance.
For example, using generic numbers, a stepped curve, set to say 35 degrees at peak tq rpm and then advancing at a rate similar to 1 degree/1000 rpm to peak hp rpm, to say 38 degrees, is how some tailor around peak tq rpm detonation.
This used to be considered exotic/expensive tuning, but advances in things such as a programmable MSD (cleverly hidden) have brought this into the realm of the 'small guy'.