Please explain the differences of the dyno of the RED line vs. the BLACK line in technical terms. Formulae, mathematical calculations, etc. are welcome.

 

Dunno how technical you want, but, hp is a function of rpm and tq. The black car/line makes more tq than the red car/line does at a later rpm. Because of this, the black car makes more hp on the top end. Conversely, the red car makes its tq down low, and runs out of steam up top.

If the red car makes 100 ft/lb of tq at 6,000rpm then it'd make ~114 hp.
If the black car makes 110 ft/lb at 6,000rpm then it's making ~125 hp.

Tom

 

Okay, now tell me the differences in the area under the curve as well as the outcome of 2 cars racing each other.

 

Well what you have are either two engines, or one engine under two different configurations.

Generally to get higher RPM power, you can do many things, change the cams, change advance on the cams, switch to a 4:1 header, tune the intake runners for higher rpm (make them shorter)

To get your lower RPM Power you would do the opposite. you could still change the cams, but go for cams made to make low rpm power, switch to a 4:2:1 style header, tune the intake runners for lower rpm power (longer runners)

by the looks of that graph, it looks to me like the engine with the more top end power was fitted with a racing exhaust system.

4:1 Gives better top end
Tri-Y Gives better overall gains (good street header)
4:2:1 gives better low end

what would be a better way to get some formulae out is to take two different dyno's of the same car, and make a single modification, and ask why the power shifted higher in some areas, and dipped in others, or why it gained through the entire rpm band.

To get power gains at all rpms you would need several things:

you'd want an equal length race header and stright through exhaust system, you would want a valvetrain system such equipped on the bugatti veryon, and you would want the intake manifold system off of F1 Indy cars, or the 787B Mazda Rotoary engine (Varible length inlet runner system) and tune the runners to be effective over your desired powerband. And of course ported and polished head, larger valves, higher compression pistons, lightweight flywheel, UD pulley knife edged polished lightened crank, titanium rods... all that. independant carburetors and throttle bodies. like a 4 Weber carb setup etc.. and of course aggressive ignition timing, and race fuel.

Brad


[Modified by lazerus, 1:45 PM 10/2/2002]


[Modified by lazerus, 1:47 PM 10/2/2002]

 

For a drag race the black curve would be the one you want. You would not shift until your at red line and you would keep the RPM's up high for the entire run. However, for an auto-X course your car will be slowing down, entering turns, and accelerating out at lower RPM’s so the red curve might give you better track times on a auto-X course because of it’s higher HP at lower RPM’s. It all depends on what you want to do with the car really. Peak HP is not everything!

 

Wow...these are some really good stuff here. Thanks to all for the input. Keep on coming. I want to learn more.

 

If you wanted to make this discussion really interesting, overlay a vr6 dyno plot w/ a b18c5, scale em both and we could go to town.

Tom

 

lol. =]

 

I have never paid mush attention to the HP numbers on a dyno. You feel the torque and that is also what gets you down the quater miles faster. During daily driving you would want more low end torque because that is where the engine is used most. I like to see B series engines that develope 125 ft lbs of torque at or before 3500 RPM. And I like to see flat torque curves. These 2 things would make any Honda pure joy.