Thread: 70 429CJ Buildup Questions

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Paul,

Thanks for your thoughts on piston selection. The engine came with 2366 flat tops so I'm not sure how the prior owner ran it on pump gas all these years.
The valve train does have the stamped rockers, poly lock adjusters and guide plates and I was hoping to use the stock components with the new cam. Thanks again for your time Paul.

Dwayne

Originally Posted by DwayneD

Paul,

Thanks for your thoughts on piston selection. The engine came with 2366 flat tops so I'm not sure how the prior owner ran it on pump gas all these years.
The valve train does have the stamped rockers, poly lock adjusters and guide plates and I was hoping to use the stock components with the new cam. Thanks again for your time Paul.

Dwayne

Dwayne,

When the 429 CJ came out in 1970, pump gas premium was 98 octane and pump gas regular had an octane rating greater than most of the premium fuels available today at the local filling sations. Further, the OEM 385 Series distributors have next to no mechanical advance whasoever. Install an aftermarket distributor and that bone stock engine might detonate like crazy on today's pump gas, depending on the fuel's octane rating and overall quality.

Within your own observation you already noted the primary reason for ther engine's ability to run on pump gas all these years: it had 2366 flat top pistons. With the little ol' 3.59" stroke, the uncut heads, the undecked block, the flat top pistons (maintaining maximum quench pad effectiveness), the real-world compression ratio was actually around 10.3:1 with those mixture-motion-inducing flat top pistons. Add the lack of advance curve from the OEM distributor and suddenly that engine will have an easier time resisting detonation than any round dish-topped piston with an aftermarket distributor of any kind.

You will be increasing the stroke from 3.59 to 3.85, presumably milling the heads during their reconditioning, decking the block, etc, which will increase compression ratio to a level that is far greater than the 429 engine (assuming the same flat top pistons), and the method with which you want to bring compression back to a reasonable level is by using dished pistons....and there-in lies the issue with detonation. This is why I suggested the "D"-shaped dished pistons. If you are unfamiliar with the differences between the two dish designs and what I mean by "quench," then please let me know. And again, at this point I would recommend the P2404's as they are a piston that is superior in design to the L2404s and will offer a better match to the engine block's OEM deck height, which will allow you to go down to absolute zero-deck and not risk running into cylinder head/intake manifold fitment issues as a result. Detonation will be reasonably under control.

Paul

Paul,

The P2404s are ordered. You are correct, the machine work has been done on the heads and they did need to be shaved slightly and hardened seats installed. I have no idea what effect different shaped pistons have regarding the combustion process so any info you could provide would be greatly appreciated. I'm also not adverse to picking up a book and learning about it that way either if you could recommend one.
Golan's Racing has the block and will be machining it this upcoming week so the pistons should be here in time for them to finish hone it to spec. They're not going to deck it yet per your suggestion to mock build the short block first. Thanks again for the info.

Dwayne