Curious what you all think of this dyno read out? Options

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Several twists and turns I’m getting close to getting that XN turbo big bore engine back to me. This is the one that had a very elaborate homebrew turbo set up turns out was only running on three out of four cylinders when I did the initial teardown. I ended up having to swap the case out for another one because when it was rebuilt for the first time it was developing crazy high will pressure hand given all the unknowns and some funkiness with it that we discovered we decided it would be better to just use another case

Shop let me know going in the carbs I gave them would be snappy and responsive but probably leave horsepower on the table. The shop also noted that this was not run using optimized headers and exhaust is probably a bit restrictive for this sort of build.

Thing that really jumps out to me here is that the engine is making lotta torch, or at least seems to be a lot of work, down low and had a very usable or p.m. That, to my son white uneducated eyes, suggest that should be fun for regular street use. What do you all think?

[Rufus]

Curious what you all think of this dyno read out?

Shift at 4500 rpm for max acceleration ...
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Shift at 4500 rpm for maximum acceleration?

Nope. Shifting near peak torque engine speed will leave a lot of acceleration “on the table”. (Remember you want maximum torque to the rear wheels; not "upstream" of the tranny … each gear multiplies input torque differently based on ratio.) For maximum acceleration you always at least want to rev to peak power (unless for some bizarre reason that’s above redline or there’s a concern about mechanical weakness). Optimum shift points can’t be accurately determined without first knowing gear spacing. For optimum acceleration, the power and torque to the final drive (any point “downstream” of the transmission) at the shift rpm equal the power and torque available to the final drive at that vehicle speed in the next higher gear (@ WOT of course). Optimum shift points are determined from the available power / torque at the final drive as a function of vehicle speed for each gear. The points where available power & torque in one gear fall below that available in the next gear is the optimum shift point. Often optimum shift points are over the peak power rpm (assuming redline permits). Because gear spacing is not necessarily the same from shift to shift in a given gear set, optimum shift points can vary from one shift to another.

Maybe not the best example, but a random chart from an old college textbook will show the idea. Note that “propeller shaft rpm” is final drive rpm not erpm, and is proportional to vehicle speed. The peak power and torque values differ from gear to gear due to slightly different throughput efficiencies based on gear ratio. The differences in peak torque are additionally related to the different torque multiplications of gears.

So what about the curves not crossing in the chart? One must assume the curves end at engine redline. Therefore torque and power available for acceleration will immediately drop after each shift. This could be avoided with narrower spacing / more gears. The goal being to maximize “area under the curve(s)”.

If vehicle aerodynamic drag (in hp) is plotted on the same chart as final drive power, top speed is predicted by the point where drag crosses available power.