So I'm neck deep into my first jet boat project and can't find any recent threads on stuff, and I have a fair amount of Olds experience (built several big blocks over a 10 year period, flowed lots of heads on a flow bench, daily drove a Streep/strip 455 engine swapped car for several years, am a full time mechanic and own a shop, etc.) so I thought I'd share:

Not sure where to start.  Bought the boat a year ago from a non mevhanicalguy wjod pumped the engine full of 15 qts of water.  Local Hot Boat guy checked out the boat/pump half and gave it the thumbs up.  Always wanted one and the deal was right so I took it.  Emptied things out and a few days, a coil, some wiring, and a carb rebuild later I had it dryed out and running in my shop.

Leaking freeze plugs replaced, replumbed EVERYTHING (the reason it was full of water - no pressure relief and headers plumbed ahead of engine with no pressure relief).  New control cables (not tryna die or run aground).  Rewired everything (sketchy wiring is a pet peave), put it in the lake.

Ran pretty decent 4200 rpm, sounded ok, wouldn't idle, 45+ year old gauges... 

New gauges, new switches, new vac sec carb it didn't seem to run any better, but at least I can see some info on the gauges.  Now we're getting somewhere. 

Runs good for about 2 minutes and dies.  Let sit for a minute, repeat.

15 fuel filters later (hey it's old - who knows what was in the tanks right?) And I realize it's the tanks coming part on the inside (or at least the liner) and plugging things up.  Let it sit a minute or two, sediment falls to the bottom of the filter, yay, 2 more minutes of run time!  New aluminum fuel tanks to the rescue.

Now it occasionally gets hot... Hmmm. Runs for a few minutes at normal temp - then gets over 220 as it shuts down...  (Am I sure it's a fuel problem?  Maybe it's a hot ignition module?). I'm getting steam out the headers the whole time...

Double pumper carb with fuel pressure gauge, new recurved distributor, new (good) coil, new ignition module, ignition timing set to 12* initial, 34* @2800.  Starts and runs great,. REALLY responsive, kind of excited.  Still can't get it to idle quite right and it's missing worse.

Let's see what the vacuum gauge says about idle mixture...  Uh-oh.  Needle bounces.  That's bad...  Valve covers off - 3 stuck exhaust valves and corresponding bent push rods.  Dammit.  Not sure if it was me or the previous owners, but here we are.

How does a gear-head shop owner living his childhood jet boat dream fix bent valves?  Aluminum cylinder heads.  Modern airflow technology is great stuff... 

That's where I am now.  Lots of pictures along the way.  Feel free to ask questions. 

Side note - I know this thing won't ever be fast because Olds, but I'm trying to get it together to be the lake hero for a few weeks, while my buddy with a 548 v-drive fixes his broken rocker arm and guide plate.  Rocket power ftw.

Still having some issues with the place diverter, have a new cam but not for now, then I have a loader to try and see where I can get...

Plumbing is currently pump - pressure bypass - tee - ?water pump? - thermostat housing - out.  Headers are cooled from the water crossover in the front of the manifold then runs to a Hardin/cp tee valve with new spring and ball in it, but I?m going to move it to the back of the manifold and add a pressure gauge to the front so I can see what?s going on.

***when I pulled the heads I found 3 of the ?steam holes? (upper coolant passages from deck to head) partially plugged, and a 4th one (rear most passenger side) completely plugged and I had to ?rod it out? with a small rat tail file to open it back up.  Hopefully that?s my cooling problem solved. ***

Haven?t run it long enough to have a feel for ?normal? operating temp.  Had no thermostat in it before, put a marine 140 in it to try and get some consistent #s from it but haven?t run it in the lake with it yet.

Vac sec carb had 72 primary, 4.5 power valve, and the lightest spring I could get in it.  Double pumper still feels snappier but that could be ignition timing?  For now I?m retiring the 4160.

Vacuum adv is disconnected.  Bought a block-off for it, but it was for clockwise normal HEI.  Olds is CCW, so I await my ups man again?

New push rods are oil restricted.  That?s the best I have for now - and running 5w-30 so more oil runs back to the pan.  If I was pulling the short block I?d put the restrictors in above the mains, and rering and possibly re-piston it, and put on a 10qt pan.  I don?t really want to get into that this summer, hence the delay on doing the cam.  Plus when I do, I want to plate the stringers with aluminum and just clean up the mounting situation.

On the impeller - is there a way to tell?  Without pulling apart the jet drive?  I was told most Olds boats came with "A" impellers?  My plan is to run/tune it until it wants to go above 5000 rpm (msd 6al chipped at 5200) and then add the loader, and if that won't pull it down enough look at a different (AA?) impeller.  Good plan or no?

I have a thing for olds engines (obviously), but as far as building a short block goes I?m mixed.  I know the limitations,  and if I ever want to go fast it?s BBC or turbo LS realistically, so why spend on the olds?  On the other hand, it's a heavy boat, and probably never going to be incredibly lake-beatingly fast vs a Hondo or Daytona or Rogers or similar...  But I have a soft spot for rocket motors, so that makes it cool.

Still cool and fun though.  Haha

Thanks man.  I'll revisit the gate valve and thermostat.  It?s got the double stack housing (bypass to the top after the water pump inlets, braided (see pic) goes to the back discharge does that make a difference?  As I understand it, it discharges cold water all the time, until it discharges (some?)  hot water once the thermostat opens?

So - maybe everyone has seen this, and knows what the weight difference is between stock cast, and aluminum heads on an Oldsmobile 455.  After searching I couldn?t find an answer, so I did it myself.  The aluminum heads save about 25 lbs each.  The aluminum heads were weighed with 7/16 studs and guide plates, the cast iron ones without. 

These were ?G? castings but it doesn?t really matter.  I?ve spent more than a little time with ?stock? olds stuff, and despite the internet lore about C castings being good, and other related fairy tales, they are all basically the same - at least as far as the flow bench and scale are concerned.  I will say the J heads flow the worst, but only by a little.  They all suck.  For comparison?s sake, I was doing a lot of playing around on the flow bench at the time.  A 4.8L LS head flowed quite a bit more, and the turbulence in the Olds head was so bad it sounded like the air was being dismembered as it went through the port, as opposed to nice smooth flow.

Progress...  Time for a trip to the sand bar. 

Ran it this weekend finally.  4700 rpm is about all it's got, but it's reasonably fast.  Haven't gpsed it yet, but my buddy has a 50ish mph outboard boat and we just walked away from it.

For those following or with something similar, it's a .030 over 455 with aluminum heads, torker, and a 750 double pumper.  Roughly 12* initial timing, 36-38 overall, 76 primary jets, 86 secondary, 4.5 power valve.  Big cam of unknown specs, idles about 1200-1300 rpm in the water.  I think an A impeller but don't really know for sure.

Good work! looks like your making good progress.  With an alum head, header and cammed 455 if your still only turning 4700 RPM you might already have an AA impeller in there.  Keep digging and let us know your updates.