Hi All,
i've been reading this forum for a couple of weeks and I have searched and read all of the articles on the olds 455 and jets in general. I am new to boating and I recently bought a 1973 Rogers jet boat with an olds 455 and berkely pump. This boat is old it has stock everything. I don't need super performance out of it but i do want it to run like new.
This is how it behaves:
It planes out at 3800 RPM and I haven't pushed it above 4600 RPMs and at these revolutions it goes 50 miles an hour (GPS). I know these boats should do at least 60~65 MPH. I looked at the carburator at WOT and noticed that the secondary butterfly valve never opens so its starving two jets from air. The engine runs great no misfiring smooth like there is nothing wrong. But there is this lack of power! I think I want to change the carburator and intake manifold. Carburator for the reason mention above and intake manifold because it rusty since it was sitting for 5 years.
Can you guys please let me know how to get designed power from this engine and maybe carburator and manifold recommendations. Also maybe some pointers about the impeller. i don't understand what loose means (in terms of impellers anyways).
Thank You Very Much!
For a carb, I run a Holley Marine 750 w/mechanical secondaries. With a jetboat, you'll want mechanicals as opposed to vacuum. As long as your cam is stock or mild, a 750 should suffice. As for an intake, again, with a mild cam, you could getaway with an Edelbrock Performer. I think they are good from 1500-5500 rpm. If you bump up the cam at all, I would go with a Torker Manifold (single plane)
Dekmaster,
Loose pump?
Probably so with the RPm's you mention. The impeller fits into a wear rin in the body of the pump. If the wear is excessive due to misuse of the pump or just alot of use, the suction of the impeller and thrust are lost through gaps between the impeller and the wear ring.
If you look up through the intake grate of the pump you may notice the edges of the impeller are slightly rounded. These and more things to do with the bowl can cause the boat to plane out at higher rpms. It may be a good bet to have a pump shop look at your pump.
Hotdogz has good advice regarding the motor. Just make sure you pay attention to the oiling system. These motors are notorious for pumping oil into the valve covers and starving the pan.
Walter
The Q-Jet carb has a little link on one side that is tied in to the automatic choke. It won't allow the secondaries to open before the choke is full open.
Just a thought
If you can turn 4600 rpms @ 50 mph, your carb and engine are fine. Your problem is the pump. Q Jets don't have vac secondaries and will do more than fine for your needs it sounds like. The holley isn't needed. Put your money into pump work and you'll be as happy as ever. Either turn the pump over to a shop or re-do it yourself, miles ahead.
Another good place to dig up any Olds info is
www.realoldspower.com
good luck.
Don't forget that losing the stock, cast iron intake and going with aluminum will drop about 50 lbs. off of the boat! Ok maybe not quite that much but those things are heavy. I have good results with my quadrajet but when I find a decent deal on a Holley I'm going to try it.
Welcome to the boardsI had a stock 455 olds at one point in time and she was acting like that with a quadrajet carb. i bolted a holley 750cfm vac secondaries right out of the box from autozone for only $200 and she woke right up. Another good thing is to loose the stock"boat anchor" intake and add a place diverter and you will notice a difference. I am with the other guys about checking the jet. BUT, if it runs well then leave it for the summer! TRUST ME, once you start disassembling your boat sometimes it takes alot longer than you think to puit it back together
Just my lil' ole' 2 pennies though
396
seho, it'll probably cut more than 50 lbs!!!
My boat had a marine holley on it when I got it. I tossed it in the round file. I replaced it with a Q jet from a '78 Caddy 425. This is an awesome carb. The 800cfm variety with factory 74 jets and enlarged air bleeds. The non Olds part which who cares is the side entrance fuel inlet. I spliced an aeroquip fitting on to the Q-jet inlet fitting so I could run aeroquip lines from the mechanical pump to the carb. We built a spacer to be able to use an aftermarket tall style flame arrestor and incorporated a tube through the side to be able to pipe in the vent from the fuel pump housing. Keepin' it legal I guess...:wink:
And to agree with what old guy said, make sure the lock out from the choke isn't your problem which it probably is. You can test it by backing off the choke all of the way which should keep the lock out from occurring. Very easy to do. The lock out linkage or arm is obvious and very visible. Take a look. and get a pic if you can.
I actually had the boat checked out before i put ti in the water and the mechanic said the impeller had a couple of nicks and scratches, but that's from normal wear. How can I adjust the choke to open up the secondaries and if this indeed is the problem how would it affect the engine if the secondaries don't open up?
Thanks Again!
Dennis
What is the stock horsepower of the olds 455. What kind of impeller should i use. Also what should I be looking for in a jet pump tuneup.
Thanks
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