Thread:

olds guys

I have a stock 455 with a 650 holley carb, and was wondering what some basic mods would be that I can do myself to gain some extra HP. The engine currently has 180 hrs from 1974, and has never been rebuilt. The boat is a 21' day cruiser with a Berkley pump, not sure of the impeller cut. Im currently spinning 4300 RPM's, and only seeing a speed of about 40-43mph. Eventually I would like to put a BBC in, but for now I'm gonna wait until this one explodes!

DONT dump any money into that Olds motor. If you want to build a big HP motor do it with a BBC. Olds arent really made to turn more than 5k rpm's unless you spend a lot of money. Just enjoy it until you blow it up. Not trying to be a dick but you have a bigger boat with an olds and its a jet. If you want power you need to go CHEVY or some may say Ford but not Olds.

Originally Posted by EVILFORCE;1221691[B

]Slap a bigger carb on it. At least a 750 maybe a 800.[/B] Take you timing as high as possible. Anything else is going to be a major expense. Manifolds, cams, exhaust. At least you can use the carb on the Chevy. JMO. But I get no respect.

Why not just bolt a toilet on top of the engine? A bigger carb is the worst possible thing he could do. 4300 RPM will NOT flow enough air through the engine to use anywhere near that much carburetor... The 650 is very close to maxing out what 455 Cu in will flow. (@ RPM)... Do the math. An engine is nothing more than an air pump, and as such, is limited to an EXACT number for CFM of AIR, at a given RPM. Throwing an excessively large carb on it will only waste fuel and pollute the oil with unburned gas..... Bigger is not always better, and in this case, it is worse....... Is the 650 a spread bore (4165/4175)? Or is there an adapter to mount a 4160/4150?? I do agree, an aluminum intake would be an improvement over the cast iron one, but 650 CFM is plenty for his application, or a mild 454 BBC for that matter............... I would look into a little distributor work, curving the timing to the boat/use, may help the motor find it's "happy spot" for a little better economy and performance.....

Ray

Originally Posted by Sanger Pete

Hmm--years ago I had a 21' cruiser 455 olds/holly 780/berkeleyJC and I was seeing 4500 rpms and approximately low 50s top speed--even on the delta. Makes me wonder about your tach accuracy, or maybe mine? At what rpm do your secondaries (vacuum?) come in?

I dont know what RPM's my secondaries are currently opening at because they dont open. With out them opening at full throtle I'm at 4000 Rpm's. I had my buddy physically open them up and the motor spun to about 4300 RPM's. I have an edelbrock 750 with mechanical secondaries that I need to rebuild and slap on. I'm not trying to make a hotrod out of this turd, but would at least like to be in the low 50's at WOT. So putting on the 750, aluminum intake, and a cam, should get me there hopefully? What cam should I try and put in????

Originally Posted by brgrcru

I'm bad, I thought it said Old Guys. Had to look twice. Damn.

Don't feel bad, I thought the same thing. I had to go look too after you mentioned this.

You can do the carb and manifold swap, (maybe even an ignition system) but there's no point in re-camming an old engine. You will just start the downward spiral of having to replace one thing after another. This will lead to a total rebuild before you know it.

There's a lot to be said for tuning as some others have hinted at. Make sure you're getting around 36* of total timing (hopefully around 3k rpm). You can get a 750 mainbody upgrade for that 650 if it the standard double pumper. I did that to mine and it runs hard.

Originally Posted by slim pickens

If you dont want to re-cam you can get a little bit more cam by going to 1.7 ratio roller rockers. might be help a small cam act bigger and pick up some HP. You can use SB Ford pedestal mount rockers that are much more common and cheap in 1.7 ratio, maybe get them used and save.
I also went to a HEI distributor and got much healthier spark over points and weak old coil.

cool. I have HEI already. Thanks.

I gained 500 rpms on my olds by adding MSD which is a good idea for the rev limiter. I do recomend a 10 qt pan and oil mods if going for any prolonged high RPM use as in mine I broke a valve off in the motor and later broke off a piston at the wrist pin. Olds motors can be very reliable unless you are pushing them too hard. Big impellers are good for them as they can pull out a stump with all their torque. I know a guy who was running in the 90s with an olds on NOS and was pretty reliable. I miss my tahiti with the olds as it was very reliable until I started trying to be the fastest on the river (18 year old logic). You can upgrade Olds motors but most will say to sell it and install a chevy because after everything is said and done you will have less into a chevy swap vs. the olds upgrades.