defiant1

Okay. Finally decided to build the 425 I have had for years. The main deciding factor was I found a engine builder who actually has a clue about Olds engines and raced with them as well.


So, I am looking for engine build combinations you all have used or recommend for the 425.


Here is what I plan on doing so far:


- Bore it out .060.
- Use roller tip rockers (I have a set of 1.6 SBF on hand)
- Use A heads (already rebuilt with bigger intake and exhaust valves, 3 angle valve job)
- Use original connecting rods
- Use original forged crankshaft


I am open to suggestions on oil pump, intake manifolds and camshafts (45 degree lifter bank angle) and torque converters.


I also am looking for feedback on oil restrictors, main bearing girdles, and the like that are on engines that make big power and whether or not they are necessary for a street motor.


I am not building a race engine, just a suitable street motor (to go in the '70 Cutlass in the pic below). I would like to see 385HP if possible and still run a decent compression ratio (10:1).


It will be attached to Speed Demon 750 carb, dual exhaust, TH350, and 3.23 LSD.


d1

cutlassefi

Jmo. Hope this helps.

defiant1

Thank you for the feedback.


I will definite get your opinion on camshafts when the time comes as I have used one of your custom grinds on my current SBO.


As far as the overbore question you had: Should I go conservative (.030) or go bigger than .060? Am I incorrectly assuming that a bigger bore will lend itself to more HP with this engine?


d1

oldsmobiledave

7 cubic inches more displacement from 0.060" overbore vs the 0.030" overbore. This won't make any appreciable power increase in this application. Leave the meat on the block for a future rebuild.

defiant1

Based on what I read I believe there is enough material that I could go up one more time from the .060 overbore should I need to. But, I still need to have the block cleaned up and cylinders checked for damage/out of round. I may have no choice but to go .060 as the pistons were not cooperative when trying to remove, so it really depends on how bad the cylinder walls are.

I already removed a lot of the casting flash and smoothed out the oil passages in the valley of the block. I probably will use the die grinder and massage it a little more before sending it off to the machine shop.

cutlassefi

What are your plans for pistons? There are no readily available aftermarket pistons for a 425 except the crappy out of date ones from Mondello or Egge.
I offer custom pistons at a reasonable price, or let us know what you had in mind.

defiant1

So, Mark indicated I won't need oil restrictors. So what do I need to have drilled out and clearanced on the main bearings/crankshaft? Do any camshaft oil passages need to be drilled out? I am not independently wealthy so I rather do this right the first time and not risk any low oil pressure problems after the rebuild.

d1

defiant1

Yeah, that is another frustrating part of the build. I want light/strong pistons, but don't want to pay $800 for pistons either. I am open to suggestions for sure.

cutlassefi

Unless you go for the heavy antiquated forged pistons from Mondello or cast from Egge, you'll have the better part of $700 in pistons, pins and rings. But they'll be worth it, light, strong and with a much better ring pack. Or you can just fill the block with 455 parts and maybe save a few bucks.
Just clean up the drain backs and use a restricted pushrod for a little insurance, you'll be fine.

defiant1

Ok, thanks for the info. I will be in touch later on down the road with what I am looking for in a camshaft and piston/ring pack.


I was hoping for some more 425 engine build combos from the members on the site. Maybe they are just being shy...

Oldsmaniac

Years ago (1976) I built a 425 for my 67 442 vert that I bracket raced. At that time Joe Mondello was the only game in town. He had a performance guide, with engine specs, suggestions etc. Of course he had all the stuff you would need to purchase. So I used 030 TRW forged pistons at 10 to 1 CR (no longer made), a Torker intake and 780 Holley, headers. Engle 590 lift cam and kit, restrictors, his HP oil pump. I installed a Jackson Gear drive, recurved points dist, stock valve train, G heads lightly ported. I had the rods shot peaned and seams ground smooth and the side oil reliefs cut into the rod big ends. I believe the crank was cross drilled and everything balanced. The engine was very stong and would easily rev to 6500 RPM but I shifted at around 6000. This was my build. The 425 is not anything special compared to a 455, just do general good building procedures with Olds specific needs in mind. This info is dated however the engine still sits in my 67 vert and is still alive but sleeping!

pogo69

Joe that sounds like a mean engine unfortunatly not many built like that now...old school just how I like it

Oldsmaniac

67442nut

You might want to try this book.
Lots of good basic info as well as performance.
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defiant1

Good to know. Thanks for the info.