Any Way to Estimate Horsepower?

Is there any way to estimate horsepower once you've bolted on a bunch of performance mods? I have a 79 CJ-5 with a freshly-rebuilt AMC 304 V8. It's been slightly over-bored and has all new components. In 1979, I believe this motor with the stock 2 barrel was rated around 150 horsepower. I have added an Edelbrock Performer 650cfm 4 barrel matched up to an Edelbrock Performer intake manifold. I have a K&N air filter, Dyno-Max long-tube headers flowing through cats and turbo mufflers to dual exhaust out the rear. I have an MSD ignition, brand new distibutor, wires, plugs, etc. I've also removed most of the original smog canisters and other choking equipment. With all of this, can I assume I've added at least 100 horsepower? Or is that too hopeful? Any ideas?

 

Judging from real dyno tests I've seen after adding components I'd say 100hp might be a bit optimistic. Maybe 50 or 75 but it's honestly anybody's guess unless you dyno test it. Unless you want to do like most Ebay sellers do and just say "this engine is putting out at least 400hp."

 

100hp is way optimistic, especially if you are running the stock cam. I'd say less than 50, but we might as well get a dart board close our eyes, and pick whatever number we hit.

There is also the issue of how hp was tested, i know in the 60's and early 70's they used gross hp, not counting all your accessories. they have since transitioned to net rating, which should include all that stuff. and even recently the SAE changed they way HP is measures, and some cars took a hit on ther rating.

FYI from jeeptech.com, here are the ratings for the 304...

anyway, you've definitely increased your power. If you are happy with the performance, then the number dosent really matter. I find the stock 304 in my 72 makes more than enough for any situation, so i dont care if its "only" 150.

 

I'm not a big fan of max HP numbers for trucks anyhow. Chasing big HP numbers leads a truck guy to do the wrong things. For example, some people are tempted to put on heads with big valves, RPM or Torquer intake manifolds, long duration cams with a badass sounding idle, and high CFM carb. Great engine...for a Gremlin or AMX. Or maybe a mud drag Jeep. But all of those things detract from what most 4-wheelers really want: low end grunt. It's probably better to gage Jeep engines by area under the torque curve between 1500 and 3500 RPM to get a realistic sense of how it will FEEL when driving it on the trails. Lots of big cams create a huge hole in torque curve right where a truck driver wants it most.

I think you built a good engine for a Jeep. There is probably a fair amount of torque left on the table by adding an aftermarket TORQUEY camshaft and a bump in compression though. The camshaft is the heart of a build. The camshaft dictates where the builder wants to make power. The ideal compression ratio is determined only AFTER a camshaft has been selected. The best manifold choice should complement the RPM range where the cam wants to live. Same with valve size. But stock camshafts aren't too bad for a truck intended to have low end grunt so I'm not necessarily recommeding that you change anything.

Another big improvement would be a valve job with blending of bowl area right before the intake valve seat. If you have installed hardened seats they can sometimes form a step where they meet the cast iron. For low RPMs the valve and valve seat contours are most important. For mid-range the critical area is the intake port bowl. For high RPM the porter will pay more attention to the intake port runner area.

Chilly

 

And because I answered every question you DIDN'T ask, here's how you can do better than estimate HP. There is a device called a G-tech or G-tek or whatever that mounts to a windshield or dashboard. It has accellerometers in it so it'll extrapolate HP and torque estimates when you do some roll-on tests. I suspect you enter some paramters such as vehicle weight and probably other things like gear ratio? It poops out the figures after the run. Pretty cool little gizmo and a neat way to evaluate piecewise upgrades to an engine.

 

There's also Desktop Dyno, but it's not free: http://www.proracingsim.com/desktopdyno.htm

 

It's been awhile and I probably have the equations wrong, but here goes. Figure acceleration in a straight line over a measured distance w/ a=1/2 mv2(squared, don't know how to superscript here) where a is acceleration, m is mass, v is velocity(actually the change in v start to finish). Then using f=ma where f is force, m is mass, and a is acceleration, find f and convert to HP (power is a force applied over a distance). Just remember to convert everything to matching units and you'll get real world HP.:v6: