Shifting the powerband in a boosted LS1

[pancake]

The LS1 C5 Corvettes have a supercharger kit available by ECS that uses a restrictor plate in the air inlet while running a smaller pulley so that it creates boost earlier and quicker, while restricting the top end.

The theory behind is according to ECS is that the power on the low and mid range is greatly increased versus running a bigger pulley without a restrictor as the bigger pulley will just spool lower and create power up top.


The LS1 already is a very top end happy car so adding a centri really emphasizes that powerband. It doesn't feel like much until after 4k and then feels like a rocket between 4500-6000rpm.


Instead of a restrictor plate, is it possible to use a smaller pulley and have my tuner pull timing and artificially reduce power on the top end somehow? Are they theoretically the same in terms of the end result?


I'm not a tuner but I'm trying to learn. I feel like this is an advanced topic I don't understand yet.

How much leeway does tuning give you if you want to "shift" the powerband a little bit so that rather than having ALL the power at the top end between 4000-6000rpm, you make it start lower around 2500+. Like stated using either a mechanically restrictor plate (and small pulley) ... or is it possible entirely electronically with a tune?

[kingtal0n]

I think you are a bit mislead.

If you put a restriction on the intake of something (engine or supercharger) it will reduce the amount of airflow in terms of volume/time overall.

There is absolutely nothing to gain by doing that. There is no additional boost or power being made through the use of a restriction-anything on the intake side.
The caveat being that we correctly use the word restriction to imply a reduction. Whereas a "slightly small diameter tube" may experience lower pressure and increased velocity, which is not a restriction under all circumstances (e.g. below turbulent flow reynolds numbers and situations where momentum of fluid flow isn't negatively impacted by the small diameter tube).

[mecanicman]

The short version, you bought the wrong supercharger kit. Centrifugal superchargers are entirely rpm dependent for boost. The smaller kits like you have dont really start to make a lot of air until the higher rpms. If you want boost from off idle up you should look at a positive displacement blower. Typically full boost or close to it off of idle.

[pancake]

The short version, you bought the wrong supercharger kit. Centrifugal superchargers are entirely rpm dependent for boost. The smaller kits like you have dont really start to make a lot of air until the higher rpms. If you want boost from off idle up you should look at a positive displacement blower. Typically full boost or close to it off of idle.

Makes sense. I haven't bought the kit yet but I was doing some research if it's possible to tune it with a smaller pulley than normal so that boost builds up faster/lower in the RPM range while reducing power up top.

I think you are a bit mislead.

If you put a restriction on the intake of something (engine or supercharger) it will reduce the amount of airflow in terms of volume/time overall.

There is absolutely nothing to gain by doing that. There is no additional boost or power being made through the use of a restriction-anything on the intake side.
The caveat being that we correctly use the word restriction to imply a reduction. Whereas a "slightly small diameter tube" may experience lower pressure and increased velocity, which is not a restriction under all circumstances (e.g. below turbulent flow reynolds numbers and situations where momentum of fluid flow isn't negatively impacted by the small diameter tube).

The idea is that rather than using say a 3.8 pulley that is the best fit for the engine needs with the power up top... you pulley down to say 3.4 which will cause the supercharger to spin up quicker and earlier. It creates more power. But using a restrictor plate in the intake (basically reduces the diameter of the tubing) it reduces the flow of air up top (according to this theory) so you aren't pushing your engine to harmful limits.

It's quite a popular idea for c5 corvette ECS supercharger kits. Logically it makes sense to have the blower spin earlier and faster using a smaller pulley, therefore more power in the mid RPM range. But I don't know if it's true, I haven't really seen any dynos that compare back-to-back that an actual restrictor plate/restricting the intake tube WITH a smaller pulley, will create more low and mid RPM power.





Theoretically, if I purchased a pulley that's 1 size smaller than my engine normally requires, would a tuner be able to accommodate and adjust to it by pulling timing to make less power or is that not how it works?

[kingtal0n]

nope can't really use timing like that, not reliably or efficiently enough to be considered.

power comes from being able to react fuel in a productive manner during appropriate connecting rod/crankshaft angles
power is the portion of energy extracted to do useful work over time, meaning as efficiency of power transfer increases, heat lost to the environment decreases
for example if you upgrade steel driveshaft to aluminum, now you put more power to the rear wheels and less energy is lost as heat

the same thing happens in the combustion chamber when an ideal amount of fuel and air combine during the correct rod angles (timed properly) power can be transmitted through the drivetrain over a pressure integral (the integral of pressure over piston area in the combustion chamber as time increments and rod x stroke angle is favorable)

however if we have the same exact amount of ideal fuel and air in the same exact chamber but timed it incorrectly (lets say timing was far too late) the evolving reaction has nowhere to 'put' the energy (no useful work can be done, its too late) so the entire contents of energy winds up in the chamber as heat and little to none work. This will raise the temperature of combustion chamber, piston, rings, valves, exhaust tubes, turbines, everything will get very hot, very fast, if power stroke is mis-timed, and the engine will have a meltdown quickly if the power output was high (e.g. 500hp worth of airflow will melt things pretty fast in most engines with retarded timing or lean air fuel ratio)

Superchargers are antique technology and should not be considered for majority of applications since 2016. The control of airflow as you have noticed is just one of many flaws.
Turbocharging can increase spool and control top end power using the wastegate as it was intended, no need to use any kind of restrictor. Size the turbo properly for the application and it won't be any slower to go than a centrifugal unit.

[Ben C]

if you upgrade steel driveshaft to aluminum, now you put more power to the rear wheels and less energy is lost as heat

What?

[kingtal0n]

if something drops on the ground the energy is lost as heat, gravity accelerated the object and it gained kinetic energy but when it hits the ground the energy must go somewhere for the object to return to rest.

don't we lose energy to heat due to inertial moment of driveshaft being turned (rate of change over time)
some energy lost dissipates as heat
some less energy is required by the engine to turn the driveshaft, by conservation if less total energy is being used then less is being wasted as heat. Since some is always lost as heat.

once the shafts are both spinning we would say the lighter shaft contains less kinetic energy (mv^2) thus less energy was required to get it to that speed. But I was trying to think of an example where rotational speed was increasing (acceleration) not just steady state total energy thus considered the ends (joints) of mechanical energy transfer for such a driveshaft as getting lighter, there being less friction, less energy dissipated as heat. A more efficient gear train.

adding info related to torque, timing:
above where I said "the engine will have a meltdown quickly" I never really discussed how fast, and what an engine would tolerate under typical conditions.
As a real world example first, torque management in the ECU is used to pull timing between shifts. The brief reduction of timing removes torque (any amount you want for as long as you want) by sending timing to the -10 to -30*~ ranges.

Torque mgmnt will help prevent tire spin between shifts, which preserves the transmission's internals and remove shock from the drivetrain components in general, also the vehicle is safer with inadequate tire at wot with high power output (less likely to die because of a shift) so I highly recommend using it and all my tunes utilize it to some effect, its worthy of discussion and my time to add.

The brief episode surely 'puts fire into the exhaust tube' as we have been discussing the EGT and temperature is going to rise dramatically in the brief instant of -30* of timing with 70lb/min airflow and fuel to match, it's heating up.

Which, for turbocharged applications, is not a bad thing from the start. If the turbine is anywhere under max temp it will appreciate any burst of heat and during a shift, and boost seems to rise over a baseline because of it. As long as EGT is being monitored there is no issue, and we can use things such as 2-steps, or gentle-cut revlimiter, torque management, IAT sensor switching, 9th injector in the exhaust, nitrous, many ways to put heat and raise volume of exhaust gas per unit time going into the turbine and get it moving faster. These are each small improvements that overall, if racing to really win, you need every trick. Assume nitrous, methanol, ice, water, toluene, leaded aviation fuels, and of course ethanol is available in any quantity and that creative use of each is possible with OEM internals in a variety of applications (nissan toyota chevrolet for sure) well in the 400-1000rwhp ranges for 2L to 6L respectively (about 200bhp/liter when turbocharging is generally possible as a rough minimum for daily drivable specimens using OEM internals, some will do a bit more than that) these stats set the bar for built engines: it must be producing over 201hp/liter to even be considered, and I don't think just 1 extra hp was worth the effort. So to use a random quantity lets say 300hp/liter is our new target. 2L engines need 600hp and 5L engines need 1500bhp in order to be worth the effort to 'build'. Or at 250hp/liter minimum (5L = 1250bhp built)
Honestly even for 250extra HP at five liters to me, it isn't worth the 10 times cost and time potentially wasted. Not saying all builds go bad but if you are new to them... they tend to go expensive waste of time direction. some know how to get away with it and understand there is a way. But you aren't going to like it unless you live next door to the people who build that exact engine all day long, kind of thing, as a novice.

Back to the torque management. So you are logging egt and using TQMGMNT to pull timing and barely see anything because it is very brief. However if we remove that much timing and try to redline the engine it won't happen. So we can't even test an engine acceleration with -20* of timing in the first place. We are looking at the same combustion reaction from a different perspective. If we remove all the timing but leave just enough of timing to get the acceleration term. And then the engine ran from say 3k to 6k, that reduced state of timing would show up on the EGT plot (in rpm or time) as increased rate of temp rise, even a stock engine will climb rapidly in EGT with reduced constant timing.

Is that a bad thing? What I am trying to show is that, it's not always a problem, and it doesn't become a problem unless the temperature is going TOO HIGH. Say you ran the engine from 3k to 6k not just once, but twice or thrice. Now you've taken the first run's heat, and added some of that to the next run, and NOW something could melt down. Drag cars have a cool-down period between races which can be maximally effective (or not). The same can be said for pre-warming such items as turbines. Temperature control is an underlying element of the racing sport, and it is often best done automatically i.e. arduino controls the water injection based on egt, or at the very least some kind of water pump to move liquid into the regions where heat capacity is welcome or fast heat removal (scary term, heat).
I say heat removal because we can imagine the water molecules flowing in towards the hot object, getting close an evaporating before they reach the surface of the hot object, turn to gas and carry away heat. The phase change (liquid->gas) carries the heat away as long as the hot gas state water molecules can leave the region (open surface, area element).

The same thing happens if the engine runs leans, say a WOT run at 15:1. EGT will rise rapidly and at first- there is no issue... for a moment or how long? It depends how big the engine is (displacement and physical geometrical/volume right?) and more importantly: how much power is being produced. Alot of power means alot of airflow and alot of heat will be generated by the lack of fuel. Power will suffer because even though heat is energy and all the extra heat makes the engine more efficient (which should mean more power) the overall lack of sufficient quantity of fuel molecules during critical connecting rod/crankshaft angles means that less fuel molecules were able to release their energy at opportune moments and overall the total energy extraction quantity is less because energy comes from the fuel being opened up and turned into CO2 and H2O at the exact moments of correct angles inside the engine. Some have tried injecting water H2O along with using lean air fuel ratios to help combustion intermediates complex and form during the reaction reported success is good, but I've never tried it yet for cruising so I can't comment yet on whether the net energy seems to be positive. and I would never risk a 15:1 wot run with a brittle cast piston on the hopes of injected water making up for insufficient fuel. Just spend the fuel.

Which brings us to the true nature and use of water and the reason I bothered typing all this. Besides all those other potentially toxic and corrosive fuels I listed, water is harmless in our context, biocompatible, and extremely useful for carrying heat away from parts. EGT can be controlled, generally, through the use of water injection. The max inlet temp for turbine of borg warner's most affordable series is around 1380*F to give an idea of what our target should be based on.
In a brittle cast piston application the temp should be kept low to protect the pistons. Factory turbo engine's using cast pistons typically utilize piston oil squirters for cooling. So if you take an engine without those extra little helpers, and add a bunch of boost, you need to find a way to also cool the pistons down. E85 seems to do a pretty good job but water can always be used with anything.

[kingtal0n]

https://www.w8ji.com/rotating_mass_acceleration.htm

What does a rotating mass actually do?

A rotating mass does not really consume or dissipate energy. A rotating mass stores energy. The rotating mass eventually either returns energy to the system in a useful way, or something converts the stored energy to some other form of unwanted energy. The conversion might be with a friction, converting to heat. The energy stored might be helpful, like the smoothing of cylinder pulses in an engine flywheel. The energy stored also might not do anything at all, or the stored energy can even be harmful, reducing acceleration or braking.

Accelerating an unnecessary rotating mass requires energy, and the acceleration process saps some of the horsepower we have available to accelerate our vehicles. Reducing available horsepower affects acceleration in a very predictable manner, and the horsepower amount needed to spin something up gives us some feel for how important a part change might be.

[Ben C]

Thanks for the theoretical crap that doesn't matter.

[kingtal0n]

Thanks for the theoretical crap that doesn't matter.

I guess I didn't explain it properly?

The only thing that matters is friction. It's the opposite of what you are probably thinking if you are an engineer.

Engineers might look at this problem and see the kinetic energy as a problem. Is that what you are doing?

Because kinetic energy in the shaft can be useful, and re-used, such as during a shift or engine braking.
In other words, it isn't usually a good idea to 'upgrade' a steel driveshaft to aluminum simple for the sake of reduction to kinetic energy investment.

This is why I neglected kinetic energy and focus on the friction, which we truly lose, mostly as heat.

The true parasite of driving the shaft is the friction event where heat is created and energy is lost at mechanical transfer interface, such as between gear teeth.
From this I infer that the true benefit of lightening the shaft is improved efficiency at the working ends of such a shaft, reduced heat energy loss,
it is on the way to the vehicle will achieve a higher economy, more power makes it to the wheels, less needs to be created by the engine to maintain a cruise.

[Jay@HAP]

Classic kingtalon.