Why dont this work!

Petrol Head

Senior member
Mar 16, 2004
West Sussex
Cruising area
Solent + south coast
Boat name
Black Widow
Boat make
Donzi 30' sportsboat
2* 454
Why dont this work!

1 HP per hour =half a lb of fuel per hour

Take the RPM times it by the C.I. get C.I. per min.Divide that by 1,728 to get CFM, times that by 60 to get C.F.H divide by 12.4 to get lbs per hr, take one fourteenth to get fuel Lbs per hour out of a 13:1 mixture. Divide by two to get the horse power produced by the fuel going in.

Naaah cant be right!
Times by two and laugh! :drain:

I wanted to work backwards to see if the claims for what could theoretically be got out of a 750cfm on a 454 in terms of HP could be even be considered realistic.

So I thought Id take the volumetric through put split the fuel out of the mix and get the weight.

Times by two and laugh!

Thanks for the corrections.
100% efficiency =488HP?
interesting but...

Thanks for that! But thats not it.

I was looking for the HP ceiling limit based on the fuel input to a certain sized engine.

Calorifically, with 100% efficiency, you can't pull extra HP out of a hat.

So I split out the fuel and got the numbers although they are still lower than I posted.

Just been on Hot rod and I cant see their claims being realistic.
I.C.Engine Fundamentals exam... 2nd attempt.

I think this is right.:banana: ,but I thought that last time.

RPM/2 * C.I =C.I.M.
CIM/1728 =C.F.M.
get 1/14th of mixture (13:1 ratio).
convert 1/14th C.F.M. to lb per min
convert to lbs per hour
Times 2 for HP per hour

Freelance anorak... with no honour
I 'll take it off tomorow!:hugegrin:
And the reagtta stuff.

The mathypoos was not about forecasting my engines.

I didnt want to work out the real HP of a motor.

I wanted a flat reference point for what a blank motor would consume in petrol and as a result a loose idea of the HP you could expect from that fuel, in a motor that sizeat a given RPM.

No frills or gains.

Just C.I.M. of mixture into HP. not realistic at all but a yardstick to measure from.
Matt said:
Don't worry, I have a selection of scary babies.

HUH, we have the real things ere!

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