Replacing That Tired 455

[Elimin8Jet71]

Hey guys.... I wanted to get some opinions on an engine swap for my 18' Jet boat with a Jacuzzi 12wj. I have got most of the fixins to build up a Small block 406. 10.4 compression Edelbrock RPM heads and a Comp solid roller cam... this motor makes a about 430hp and 485 ft/lbs at 5000RPM (thinking Jet Pump opperation range...) How do you guys think this will do in place of the stocker 455?? Let me know if you want more info....
Thanks

[devanwon]

why did you remove the 455, what was wrong just wear and tear??

[Elimin8Jet71]

iI have not replaced it yet... but it is tired due to some wear and tear..
The 455 has never been fresh since i got the boat... I tried to pump some life into it.....Did a leak down test on the 455 a couple seasons back, and i found a couple of cylinders with nearly 80% leak down past the rings.. I took the motor apart to re ring it...i threw some new bearings in it since i was already there. Since then... the oil has never looked really good in it.. and another leak down test is showing that the rings are letting go again...
The block is already .040 over and the crank is sitting at 20 over on both journals..... I just figure that with a small block, I don't have to worry about notorious Olds 455 oil starvation problems...

[hkunz]

I looked into doing a swap, too, when I wasted my bearings. It would cost about $1200 to buy all the stuff (logs, maybe scrolls, motor mounts, etc) to put in a different motor.
Instead, drill out the oil returns from the heads in both the block and heads, put restrictors in the mains, get restrictor pushrods, get zero-gap rings, and a big oil pan, and put her all back together. Some stuff you may already have, and much of it you'd have to replace if you put in the SBC.
I was in the same boat, literally - I've got a SBC sitting, waiting for something to run in, but a refresh of the 455, now 468, makes better sense for a family boat.

[devanwon]

yeah exactly, as long as you do the oil mods you will have a engine that should last a long time.

[Elimin8Jet71]

I do suppose that getting the necessary rigging to get the small block in there might not be very cost effective... How large does the oil return need to be punched out too and does any one know what these 455 blocks can be punched out too??? I would probably be looking around for a new crank....don't think the one in there can be re-used again.. The motor already has about a 12 quart pan on it, and where can i find some restrictor push rods??
Thanks again

[Mark Sims]

go to realoldspower.com and you will find everything you need from parts to how to do it. My olds has run for many years now with no problems. I take it to 5000, just dont go much over that.Stay away from mondello. His parts are way to high.

[Elimin8Jet71]

go to realoldspower.com and you will find everything you need from parts to how to do it. My olds has run for many years now with no problems. I take it to 5000, just dont go much over that.Stay away from mondello. His parts are way to high.
Great thanks for the info....
Not sure if the tach is 100% accurate, but i don't think it has ever spun that jet past 5000rpm... Right now i keep it under 4000rpm and it will only see over that in pretty short bursts for no more than 20-30 seconds...;)
If i can get this boat to stop porpoising....I am sure that it could see the 65mph range with the Olds in it....:D Right now it starts to porpose around 50-55mph range. I am hoping that a place diverter will fix most of this problem...if not i guess i might have the check and see how much "hook" is on the bottom of the hull...

[hkunz]

They make pistons that go to 0.060" over, I don't know what the wall thickness is at that overbore.
I'd just take it out to the gasket size, check both the heads and block.
I got the restrictor pushrods from Mondello, walked in, paid cash, saved some from list price.
I have a line on a crank, haven't even taken delivery of the engine yet that it would have to be pulled from. Mine will clean up, even though it looks bad.
Where are you located?
Depending upon the impellor and boat size, you should be getting well into the 60's with a semi-stock 455. We hit 67 with low compression pistons and an "RV" cam, and an "A" impellor. I'm thinking of replacing the impellor with an "AA", but I don't know enough about that yet to even think about it.