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Thread: H.P. rating for a 455?

  1. #1
    Hi... I have a 1973 "Hardin Marine" Olds 455 motor in my boat. It's basically stock, except for the "Torker" intake manifold. But I wanted to know if anyone could give me a "ballpark" figure on the H.P. rating for this motor. Thanks...

  2. #2
    460 WJ
    I will take a guess at low 300's

  3. #3
    I have a '72 Olds 455 Rocket marine engine owners manual, it specs a few different 455s, rated at either
    365HP @ 4600RPM, 510ft-lbs @ 3000
    390HP @ 5000RPM, 500ft-lbs @ 3200RPM.
    Torque monster!
    Mine is running, soon it will be in the water..soon...

  4. #4
    Red Horse
    Bone stock dependant on heads and year. 300-390. 69-72 being highest. This is from memory. I have Mondello books but they are in storage. Try his website.
    Good luck with your OLds. THey will last a long time used as a ski motor, you can go fast with them, just for short bursts. They have an inherent oil return problem. You need a 7-10 quart pan at least.

  5. #5
    doesn't somebody have a program to tell you how many horsepower it takes to turn a certain impeller at a certain rpm?

  6. #6
    FILUCKY and if that dont have all the info you need just type in "impeller hp chart" in you search, good luck. (remember that the number it shows on the chart is the most possible HP you can have the only exception would be is you have a impeller that is way to much cut and not letting your engine get into its power band) after looking at the chart you will laugh at (on the inside) alot of guys when they tell you how much HP they think they have and what RPM their runnig. But don't try to correct them as this will only make you unpopular. Good luck

  7. #7
    Valve covers on my stock Hardin 455 says "325 HP" (and we all know that valve covers increase HP a bunch. )
    I'd guess the Torker would add a few to that.

  8. #8
    300 to 325 sounds about right to my memory of what was available stock in my Taylor when dad bought her new. Thankfully, he went for the 454 instead. All 3 big blocks rated prety close in my memory, 454@330, 455@320 or so, 460@320. They even offered a 350SB. HAHAHAAHAHAHAHAHA All were Indhomar Jet-pac packages.

  9. #9
    I've seen a number of stock hardin setups from the early 70's and they all had the hardin valve covers. The valve covers proudly proclaimed 325 HP. Not sure what they really were but I reckon that looked pretty good in 72.
    If you have different valve covers just tell everybody it's 400 ponies and they'll be happy.
    I rebuilt mine with 9.5 to 1 compression .040 over, midrange cam, roller rockers, heavy springs, eidelbrock intake, 750 holly, 8 qt. pan, hvhp oil pump, oil return lines and who knows what else. With all that it'll never see 400 HP. Maybe you can get a baseline from that.
    Peace Man!

  10. #10
    Thanks for all the replys. Now I have a pretty good idea of the h.p my motor is making. Thanks again...

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