Author Topic: 429 Performance  (Read 2728 times)


  • Guest
429 Performance
« on: August 19, 2006, 04:34:12 PM »
Now I know this might sound like complete madness but,... Im just about to tear down the motor in my 1966 Eldorado, during its body-off restoration I am undertaking.  While I appreciate there is a serious amount of grunt in these old motors, most if not all benefit from  tweeks and improvements, which is what I want to do whilst its in bits.

Im not talking about seriously wild cams, big valve heads multi carb jobs.  I do nt want the old girl to perform like a full on NASCAR, not with petrol here in the UK at around $8 a gallon!

I suppose what Im looking for is somewhere I can contact and get good honest sound advice on what can be done whilst the motor is completely torn down.
Maybe there is a mild cam out there, which when combined with a good blue print job gives just a bit more sparkle to the performance?

Are there any Improvements/Mods that can be made in the name of reliability and maintainability? Oil system? Carb? Heads...? anything really.
I have access to good machine shops, that when told what to do can carry out excellent work and I do know how to turn a spanner, (wrench?) myself

I dont want to fall into the trap of having it said, once Ive got it all back togethor, Ah well,.. what you should have done when it was in bits was to fit a Wang Dang Doodle to the Wiffle Valve, then you would have improved the reliablity or performance by 20percent.

Any help or guidance much appreciated.

(Member in waiting)



Michael Stamps 19507

  • Guest
Re: 429 Performance
« Reply #1 on: August 19, 2006, 04:46:16 PM »
Theres not a lot of stuff out there for the 429s unlike the 390s before and the 472/500s after it.  You should be able to get a mild custom cam ground without much more cost over a stock grind.  Other than that you just have to follow the basic rule of get air and fuel in and out of the engine as fast as possible.  Also with your switch pitch trans you have an advantage.


Chris McBride

  • Guest
Re: 429 Performance
« Reply #2 on: August 19, 2006, 08:38:01 PM »

just a couple of quick thoughts:

1.  re: Oil system?

pay particular attention during your rebuild to the oil housing/pump since it is one areaa in the 429 that has proven problematic for others; the aluminum housing is unique and sometimes difficult to find.  check for scoring, clearance, et cet - this is one area you probably REALLY want your machinist mates to flyspeck

youll find numerous posts here and elsewhere discussing that particular issue in greater detail - go to the search function, punch in 429 . . .

2.  choke tube - part of the intake manifold - prone to rusting, breaking and may lead to problematic idling

see the message string at

for pictures and an overview

3.  exhaust manifold - some report difficulty, particularly with passenger side manifold cracking; your rebuild is probably a good time for a close inspection

mr. stamps is correct - the limited production run of the 429 did not lend itself to a great number of after-market performance goodies.

you may wish to check at the forums for the 63-63 and 65-66 cadillac communities since those members would all be 429 owners

i know that the 63-64 forum has a search function for its messages; it is a handy way to hunt for further information

many have extolled the pertronix electronic ignition as an upgrade to the ignition system; an electric choke is also a big help - check the posts at the 63-64 cadillac community for further details

hope this helps; good luck

Chris McBride

Bruce Reynolds # 18992

  • Guest
Re: 429 Performance
« Reply #3 on: August 19, 2006, 09:00:14 PM »
Gday Pete,

As has been said by Stampie and Chris, there are a number of things you can do, and I would also include having the reciprocating mass balanced.  

Balancing will improve the ability to rev, and combine that with a good RV type Camshaft, plus a bit of port matching of the intake and exhaust manifolds, plus a bit of polishing of the intake and exhaust ports will do wonders.

Plus, finally, a good free-flowing dual exhaust system will get those gasses away.

An RV cam will give you heaps of low down torque, where you want it, plus reasonable fuel economy, and surprisingly, good performance up to 4000 rpm.

The Tassie Devil(le),
60 CDV


  • Guest
Re: 429 Performance
« Reply #4 on: August 20, 2006, 03:50:53 PM »
Hi Folks,

Thanks for the responses and pointers to the communities sites.

Ive already found the crumbled choke tube.  Not surprising this happens when you look at the design of it.

The Dual exhaust was the first thing to be done, 2 stainless steel job with two straight through mufflers on each side.  Should sound fruity enough without drowning out the radio or giving me a head ache.  :-)
Now thats finished the motor should be coming out in the next few weeks.

The oil pump was a good pointer.  Thanks for that, Ill get my magnifiying glass out for that one.

Re the Cam, I thought that was the case re the short production run.  Ill probably get in touch with Comp Cams and see what those guys can do for me.
From past experience I know they make super cams for Harleys, Ive got one in my 93ci Evo Softail, not a tyre shredder but it does nt half give the rice burners a fright away from the lights!



Ralph Messina CLC 4937

  • Guest
429 Rebuild
« Reply #5 on: August 21, 2006, 08:22:57 AM »

In addition to the suggestions above, I’d like to share my experience rebuilding my 429. Mine is completely factory stock, rebuilt with the best possible components and I still had my share of problems.
1.   Oil pump: Before taking the engine down check the oil pressure with a gage at the sending switch. It should be 35 psi. at about 2000 rpm. The system has a spring loaded relief valve that opens at 35 psi. (verify the speed in the shop manual)  The pressure should rise from idle almost as fast as the rpm. If the pressure is good, be very cautious about reworking anything in the pump. I cleaned any scoring on the walls and knife edges with 800 grit paper and sanded the wear marks off the bottom cover on a flat glass plate. The radial clearance between the walls and pump gears is something like .003” so tread lightly.
2.   I’m embarrassed to admit this, but if it helps someone else it’s worth it. I always try to reuse original fasteners. The new timing gear for the cam had a thinner web than the original. As a result, the ends of the bolts protruded just a hair out the back of the cam flange hitting the ribs on the block. It sounded like bad bearings and took a great deal of effort to find the cause. The bolts have rounded ends and left  only a hard to see, thin scratch on the block’s ribs. Test fit the gear to the cam flange before installing the cam in the block and grid the bolt length if necessary.
3.   Choke tube and carburetor: The rotted choke tube is difficult to find as a Cadillac part but it was used on all GM big blocks in the mid 60’s. The Cadillac part number is  518256. You may have more luck searching among suppliers for other GM brands like Chevy or Pontiac. These cars came through with either Carter or Rochester carbs. As near as I can tell it was a random process. Both carbs perform equal well, but I find the Carter is simpler, more robust and less prone to accelerator pump malfunctions. Electric chokes are available if you want to eliminate the original choke heater.
4.   Engine block machining and cleaning. The environmental regulations in the US have made rigorous chemical cleaning almost impossible. The days of boiling with caustic soda are gone and most shops have gone to detergent and water. Don’t trust a detergent based cleaning system. Get a ¼” and ½” diameter rifle brush and clean the oil galleys and valve train feeds by hand. You’ll be surprised what comes out after the block has been “cleaned”.
5.   Rocker arm shafts. Change them. My car had 80M miles and the shaft under the rockers had worn down by as much as .010” beyond the allowable spec. While there was no obvious problem, I don’t know what mischief it could have caused down the line.
6.   Exhaust manifold: the right and left manifolds are interchangeable for all ’65, ’66 and ’67 429’s except ’65 series 75 and ’67 Eldorado. It shouldn’t be too difficult to find one if needed.
The 429 is considered by some to be the 472/500’s weaker sister because of the latters size. By comparison, the big block muscle cars of the era were in the range of After market suppliers have focused on the biggest making them the baddest.  A well tuned 429 may not lay down long strips of black rubber but they will make a set of tires cry.



  • Guest
429 v 425
« Reply #6 on: August 21, 2006, 09:15:01 AM »
What are the basic differences between 429 and 425?

Ralph Messina CLC 4937

  • Guest
Re: 429 v 425
« Reply #7 on: August 21, 2006, 12:17:01 PM »

The 425 was a new engine with new architecture unrelated to the 429. I’m not certain of this, but I believe it was derived from the GM corporate 350 engine family and built by Oldsmobile. Maybe someone more familiar with later engines will comment.


Steve McCarthy

  • Guest
Re: 429 v 425
« Reply #8 on: August 21, 2006, 01:51:56 PM »
The 425 was a direct descendent of the 472/500.  It was introduced in 1977 as a lighter and smaller bored version of the 472/500s, designed to get better fuel economy, it was debored again in 1980 to 368 cu/in, again in the pursuit of better milage. The 425, and to a lesser extent the 368, have some parts exchangeability with the 472 & 500s.


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