Destroke a '67 429?...

[John Bryan #21196]

I'm getting ready to rebuild my '67 429 and am thinking about taking some compression out so I can run today's fuel without pinging. Does anyone have experience with de-stroking one of these engines? I imagine it involves a cam design change in addition to shorter rods. Any advice on this or other life topics is appreciated.

John Bryan #21196
1967 Cadillac DeVille Convertible

["Cadillac Kid" Greg Surfas 15364]

How about just using 93 octane and driving the car.  I've been doing that on my '66 (same compression ratio) fror over 20 years.
Greg Surfas

[76eldo]

You don't have to do anything that drastic to run the car on today's fuel.

But, if you want to get in touch with guys that really know modified Cadillacs, go here:

http://www.modifiedcadillac.org/forum/index.php

Brian

[Dave Shepherd]

Due respect but you need to look into what destroking an engine entails, crank, rods and pistons are different, also the cam has no bearing on changing stroke, double or thicker head gaskets are one option to lower compression, or finding low compression " export" pistons or running it the way it was designed as mentioned.

[cadillactim]

If you're having a problem with pinging, retard the timing just a little. That' what I do on my 67, and I use 93 octane.

Tim

[62droptop]

i run mostly 87 in my 62 390 and hat had 10.5 : 1 compression
just did a close to 4700 mile trip in 15 days
no issue running mostly regular
even running the daylights out of it
 

it runs very happy with the cheap stuff except when i play real hard or tow with it
then i give it the good stuff

a lot of work to destroke ,and it will not necessarily lower compression ratio,only give you less cubic inches

you need a low compression piston if that is what you want , but why would you want to make your car have less power and efficiency that it could  have
the higher the compression(within reason) the more power  the engine can make, and most of the time more efficient as with the extra power the engine doesnt have to work as hard
if you are worried about compression ratio, you could always open up the heads a bit to give more volume,therefore less compression

[Glen]

Also check your vacuum advance.  I had light pinging on my 68 ELDO for years.  Then I found the replacement vacuum advance was going to 22 degrees of advance and max advance on my car was supposed to be 12 degrees. 

[Gene Beaird]

As the others have said, that engine should run okay on today's fuel.  You may have to run premium, but it's better than beating the ring lands down over the rings with too much pinging.  If the engine is already burning a fair amount of oil, that will lower the effective octane of the fuel, and make the car more prone to ping.  A rebuild should help there, too. 

If you're going to rebuild the engine anyway, you may want to look at having the shop clean and polish the combustion chamber.  I don't know what the combustion chamber of a 429 looks like, but if there are any sharp edges in there, that can cause hotspots that can cause pre-ignition.  That can help lower the compression ratio a bit, but mostly eliminate the hotspots. 

You can also have some valve reliefs cut into the pistons, or perhaps even have the piston crowns cut a few thousandths, but you're starting to run into more money for custom machine work.  Rebuild the engine all stock, and tune the engine to get rid of the ping should be all you need. 

[bcroe]

I made a big reduction in pinging by changing the timing chain.  93
octane helps, and/or retard timing as needed.  There are knock sensors
to do this for you.  Or some water injection can cure ping (till you run
out of water). 

It would be a whole lot simpler, to just transplant a used 425 or 500
engine (with transmission), designed for unleaded. 

good luck, Bruce Roe