Thread: Estimating Horsepower

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I read that horsepower can be calculated by multiplying (MEP X Stroke Length X Surface Area of the Bore X Number of Power Strokes) and dividing by 33,000. In the real world, how do you take that power equation and estimate the power various cylinder head/valve spring/camshaft combinations produce on a given engine? How is horsepower estimated in engine mod planning?

Thanks!

ooo you need something like an engineering degree to crunch those numbers.

You would have to know the flow rates of the new heads, the various pressures involved with the springs and how that pressure translates as friction on the camshaft, and if you change the cam out then you are adding more air/fuel into the mix which changes cylinder temperatures and many many many other factors.

I am thinking of this stuff off the top of my head but, I think the way they estimate horsepower is through experience with the parts and that particular engine and engine combination. It takes eons of experience to get a really accurate power estimate.

So to answer your question that formula is WAY too basic to add in various variables to see how they change up the answer.




Blastantly pirated from wikipedia... MEP is (Mean Effective Pressure)

MEP is a useful comparison tool between different engines, and is a good indicator of the level of performance achieved by the designer and manufacturer. It measures the efficiency of the conversion from the indicated mean effective pressure in the cylinder to the output shaft and the level of pressure attained in an engine. It is important to remember that the values produced by the formula are for theoretical analysis only, and do not reflect the actual pressures inside an individual combustion chamber.

-CJP

Originally Posted by dhemi1

ooo you need something like an engineering degree to crunch those numbers.

You would have to know the flow rates of the new heads, the various pressures involved with the springs and how that pressure translates as friction on the camshaft, and if you change the cam out then you are adding more air/fuel into the mix which changes cylinder temperatures and many many many other factors.
-CJP

Are there any books on this subject though?

There is a formula that calculates horse power from torque @ 5252 RPM,,, where HP and Torque get friendly (universally accepted) HP = Torque x RPM divided by 5252. This is not debateable,,, it's the way it's done,,, period. Dyno runs measure torque and convert to HP. Follow the link for more 'light' and less 'heat.' For a great reading link, see pbh/torque-com/pbh/torque-and-hp.html I hope this helps shed some light on the subject :-) Peter

I use engine symulations that take a lot of guesswork out of planning your build. Comp Cams has a free download. If you wish, I could send you a copy of my 'Dyno' This program is great, with loads of variable parameters, including cam files, head mods, bore/stroke configurations, juice, induction boost or normally aspirated and much more to build your own model,,, tuffnuff2@yahoo.ca

Originally Posted by Maxb49

Are there any books on this subject though?

I do have a copy of "Auto Math Handbook" by John Lawlor published by HPBooks. its got alot of formulas you could use. I say go for it and use them, its not like your building a Formula one engine... or are you?

-CJP

Originally Posted by dhemi1

I do have a copy of "Auto Math Handbook" by John Lawlor published by HPBooks. its got alot of formulas you could use. I say go for it and use them, its not like your building a Formula one engine... or are you?

-CJP

Hahaha no, but I decided not to go the route of modifying my Cadillac LT1 and use money I've saved over the years to go ahead and build a hotrod from scratch. I'm just in the planning stages right now and figured I'd ask so I do the job right from the beginning (I picked up that book today). I'm thinking a car built for the street, hopefully a full size Chevrolet with 450 horsepower at the crank. I figure that should be doable with a 454 but I'm open to new ideas or input. This board is a fantastic resource and I thank everyone for their help.

Originally Posted by dhemi1

I do have a copy of "Auto Math Handbook" by John Lawlor published by HPBooks. its got alot of formulas you could use. I say go for it and use them, its not like your building a Formula one engine... or are you?

-CJP

Hahaha no Formula One engine for me but I decided not to go the route of modifying my Cadillac LT1 and use money I've saved over the years to go ahead and build a hotrod from scratch. I'm just in the planning stages right now and figured I'd ask so I do the job right from the beginning (I picked up that book today). I'm thinking a car built for the street, hopefully a full size Chevrolet with 450 horsepower at the crank. I figure that should be doable with a 454 but I'm open to new ideas or input. This board is a fantastic resource and I thank everyone for their help.

I just take the number I like the best and add 20% more to it. They don't call it "Claimed Horsepower" for nothing.