Still thinking about the Sprint-T

Thinking about the possibilities with the turbochargers linked in the last post has kept me awake at night (maybe a little more than if I hadn’t been thinking about it). OK, seriously, this has been the kind of conundrum my mind refuses to let go of.

Let’s start with the knowns and unknowns in this scenario:
1. The turbos are too small for the engine at max RPM and are flow limited so theoretically the boost curve will peak at some point before redline and decline from there.
2. The wastegates are probably too small to prevent overboost at speeds below torque peak because there is likely more exhaust flow than they can dump (the turbo is designed for a 1.8l engine and each bank is 2.65l). The corollary of this is at some point boost creep will become a problem if the engine can’t handle all the boost the turbos make and has to use the waste gate to dump some of the boost.
3. At this point how much boost the turbos will make is unknown, the only thing I do know is it won’t be as high at power peak as it will at a lower engine speed. Also unknown is how drastic the dropoff in boost will be from peak to redline. The listing claims each turbo will flow 250+ HP so I’m going to get pessimistic and say maybe 400-450HP flywheel HP which would be about 7 or 8 pounds of boost on a 5.3l engine at peak.
4. There is a possibility the engine/turbo combination can be run without connecting the wastegates to manifold pressure and without excessive boost in the low RPM range. This is the Best Case Scenario, that literally the only other thing needed is charge coolers, or running a fuel or water or water/methanol spray into the turbo inlet to cool the charge under boost, or some magics that otherwise don’t require adding more hardware to the engine. And also with this combination the possibility that the engine hits peak power at peak turbo airflow and just sustains almost 450 HP all the way to redline. That would be Seriously Best Case Scenario, peak power in a usable RPM range and no dropoff until time to shift to a higher gear because the engine safely won’t go any faster. I will still need to have some method of bypassing the turbos for running 87 octane between races unless somehow the engine will not self-destruct under boost with unleaded regular, but the probability of that is less than my surviving getting hit with a truck doing 60 MPH. It might happen once, it might even happen twice, but to bet it will happen on a regular basis is playing Russian Roulette with only one empty chamber instead of only one bullet.

Now some of this can be seen in this Engine Masters episode as their single turbo has more airflow than the two turbos I’m contemplating but still it’s a stock 5.3l LS architecture engine identical to what I’m trying to find with boost, just more airflow above torque peak than the two tiny turbos I’m thinking about, but notice how much they get out of the boost they get. Also notice they have an intercooler that will cool far more airflow than what the two tiny turbos will generate and get charge temperature down to a safe level for 93 octane and moderate boost. Also their single turbo probably doesn’t make near the boost the small twin turbos make at lower than NA peak torque RPM, so the Tiny Twins will probably make more torque below peak.

Anyway there are many things I could do, and what I really want to do is leave as much junk off as I can and not put the engine survival in jeopardy.

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