Olds 425

[Mantra_Man]

Does anyone here have a 425 in their jet boat? I was going to have my 455 rebuilt, but the machining shop already has a 425 ready to build. So, I now I'm thinking that a 425 might actually be a good way to go. I have a 1977 18' Mantra. Any opinions??:idea:
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[OKIE-JET]

I'd stay 455 until I could afford the change to 454 chevy...Olds motors are gettin scarce enough that its harder to find parts in the future..especialy cranks. 454's are cheaper to play with, and easier to build HP without so much specialty work being done to keep 'em healthy. Just my .02

[malcolm]

As far as Olds go, the 425 is probably the better choice for an endurance engine. It's just that cubic inches always wins out. The 425's steel crank and shorter stroke make it a better revver than it's big brother. The only problem would be the different flywheel patten on the crank. Maybe a little harder to get the cam you want because of the different cam/lifter bank angle, but probably not too tough.

[mach1alaska]

Dont forget that the 425 has a slightly different flywheel bolt pattern so your drive coupler may not fit , other than that the 425 is a great engine and I wouldnt be afraid of it.

[jetboatperformance]

Second that 425s are great,a real find Knew a guy that campaigned one in a Willis Pro gasser Tom
BTW still needs a "BIG" oil pan!

[OKIE-JET]

O.K. a $5000 chevy runs like a $10,000 Olds:D

[sanger455]

I would rebuild the 455 I have 10yrs on mine and still going

[blown428fe]

My friend had a 425 in his 70 Cutlass that cam out of a 67 Starfire and that motor screamed. He beat the hell out of it and it never quit. I would go with the 425.

[Mantra_Man]

I think I'm going to go with the 425, the bottom end is all forged and I should be able to get 6000 rpm's which means a little more speed, I'll just have to find a way around the different bolt pattern on the flywheel.
I do agree a Chevy would be better, but the boat is set up for an olds with a real nice bell housing and some other components.
Next time I'll put in a 502 with a ram jet intake.:D

[mach1alaska]

most PTO flanges only use three of the bolts and only one bolt is in a slightly different position so it may not cause a problem at all, I just wanted you to be aware of it.
That 425 is plenty strong enough to hold 6,000 RPM but you will still need to put oiling restrictors and a large pan to keep from pumping all your oil into the heads( I learned that the hard way)

[oldselmn8tr]

I run one in my Eliminator bubble deck. Cam is not aproblem, Lifter angle is same as 455 in mine. Parts are not a prob. the fly wheel bolt pattern is different. One or two holes don't line up correctly on coupler,I just welded them up, redrilled and retempered. Works great. Forged pistons are hard to find, but are available and of course can have a set made up. Aftermarket rods are not readily availible. I am sure you could adapt something to work. I have surprised quite a few people with my little 425! I spin a berk A impeller 5100rpm with a stage one blueprint from Walts hot boat. Pump is a JC with a place diverter and Walts loader. I know its not a chev. or ford but it is different and I like that. My boat is a 74 so as much as I would like to be the fastest guy on the block I'll settle for different but still very respectible.

[Oldsquirt]

Glenwood Marine (http://www.glenwoodmarine.net/Catalog/FLYWHEEL%20POWER%20TAKE-OFF.pdf) still lists the PTO for the 425.

[oldselmn8tr]

Oldsquirt did they ever run a 425 in a boat or was it for the old style 455?

[Mantra_Man]

A little more about my boat...
Its a 77 Mantra Bubbledeck with a Berkeley 12JG Jet with oversized after market bowl (after rebuild)
Okay, here's what we're going with:
455
Steel Crank
Forged Connecting Rods
Alloy Pistons 9:1 comp. ratio
Grooved Cam and Crank Bearings
Edelbrock Heads:D
Oversized Pushrods & Roller Rockers:D
Edelbrock Torker Manifold
750 (or smaller) Holley Carb
Accel HEI Distributor (may change)
Electric Fuel Pump
High Velocity Oil Pump
And here are some things I could use your opinions on:
A Crane or ProComp Cam
(undecided... from what I understand the ProComp has sharp lobes that kind of scares me I'm thinking the Crane may last longer..any suggestions?)
I'd like to put a Water Pump on the motor with a Heat Exchanger & a Sand Filter...Any ideas???
I want to keep the Berkeley Exhaust Logs (thru-hull) vs Headers, but we'll have to see if Dyno says the Logs will be good enough, if not I may have to come up with a homemade thru-hull header:rolleyes: