1986 2.8L V-6 Pontiac Fiero - convert from speed-density to mass flow

I'm toying with the idea of an electric supercharger for an 1986 Fiero 2.8L V-6. It would provide 7 psi of boost to 3750 rpm and then tail off to about 4.5 psi of boost at 5500 rpm. I have looked at the PROM for an 1989 turbo 3.1L (RPO LG5). This uses speed density with a boost fuel multiplier for MAPs greater than 100 kPa. I can't see how this would work with the operating curve of the electric turbo so am thinking I need to convert engine to mass flow fuel control. I'd like to stay with something GM. I know the 94-95 3800 supercharged V-6 (RPO L67) uses mass flow. However that engine also has cam and crankshaft positioner sensors that the Fiero 2.8L V-6 does not have.

Anybody got any recommendations?

Have you looked at Dynamic EFI EBL_Flash which supports 1, 2, or 3 bar MAP? https://www.dynamicefi.com/EBL_Flash.php

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This uses speed density with a boost fuel multiplier for MAPs greater than 100 kPa. I can't see how this would work with the operating curve of the electric turbo so am thinking I need to convert engine to mass flow fuel control

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it might. do you know how it works exactly?

you don't exactly need fine control over your boost fueling with that engine and that fairly small amount of boost especially considering it will only be run occasionally so economy and emissions are of no concern.

as long as your multiplier can land it anywhere between 10.5:1 and 12.5:1 or so in boost it probably wont explode and will make close to its peak power. spark would be way more critical.

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Anybody got any recommendations?

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bigger engine?

sorry had to say it

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I can't see how this would work with the operating curve of the electric turbo

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The turbo code should be fine with the curve of the electric turbo. Roughly speaking, the code will use the F77 table and the MAP value as a multiplier to the main VE 100kPa cells that match the rpm of the engine. I actually used a similar boost curve on a 2.2 turbo project once due to small injectors.

so it uses the rpm axis but then goes linear with the map ? that'll work fine

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Originally Posted by steveo

it might. do you know how it works exactly?

bigger engine?

sorry had to say it

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I have a fleet of 4 Fieros:
1984 with 2.3L HO Quad 4
1986 with stock 2.8L
1988 with 4.9L Cadillac
1988 with 3800 supercharged

So I already some higher horse power engine. The electric supercharger is more of a learning project. The electric motor technology is already there. A 10 HP brushless DC motor is small and light. Bigger motors are available. What limits the motor size is energy storage. Lithium titanate batteries are available. These can discharge/charge fast and stand lots of cycles. Super capacitor technology is on the way

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Originally Posted by 1project2many

The turbo code should be fine with the curve of the electric turbo. Roughly speaking, the code will use the F77 table and the MAP value as a multiplier to the main VE 100kPa cells that match the rpm of the engine. I actually used a similar boost curve on a 2.2 turbo project once due to small injectors.

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I'm new to tuning but that explanation seems like the 3.1 turbo application could be made to work. So I started to dig into the details. The 3.1L turbo was rated for 205 HP @ 5200 rpm. The 3.1L N/A was rated for 135 HP @ 4800 rpm. The ratio of the HP's is 1.52 so one would expect that the 3.1L turbo needs at least that much more fuel. The boost multiplier table for the 3.1L turbo is as follows:

kPa multiplier
90 1.000
100 1.031
110 1.063
120 1.094
130 1.125
140 1.188
150 1.188
160 1.188
170 1.992
180 1.992
190 1.992

I doubt that turbo had more 160 kPa of boost. The multiplier at 160 kPa is 1.188 but the engine needs 1.52? So I take a look at the volumetric efficiency table and here is a comparison at 100 kPa:

RPM 3.1L T 3.1L N/A
800 74.8 65.7
1200 84.4 71.5
1600 86.7 72.7
2000 90.6 78.9
2400 91.8 80.5
2800 94.9 81.2
3200 100.4 84.4
3600 104.3 86.7
4000 109.8 87.1
4400 104.4 80.5
4800 99.2 75.5
5200 94.1 69.5
5600 85.9 61.7

So if we ratio the VE's at 5200 rpm and multiply by 1.188 we get 94.1 / 69.5 * 1.18 = 1.61 or about the right amount of fuel.

My understanding of volumetric efficiency is that it is a measure of how well the cylinder fills. At 100% VE the pressure in the cylinder during the intake stroke is the same as the intake manifold pressure. Values higher than 100% are possible on highly tuned N/A engines where some of the velocity of the intake charge is recovered as pressure and the cylinder pressure can exceed the intake manifold pressure. I doubt that the 3.1L is such an engine. At 100 kPa there is essentially no boost. How can the mere presence of a turbo charger effect the VE that much. It seems like GM is fudging the VE's and then doing less correction with the boost multiplier table. Very Strange.

I also compared the VE's for the 3.1L N/A to the Fiero 2.8L N/A. My understanding is that the 3.1L is just a stroked 2.8L. The Fiero 2.8L made 140 HP versus 135 HP for the 3.1L. So it is very strange that the VE's for the 3.1L are substantially higher than the 2.8L. For example at 4800 rpm and 100 kPa the 3.1L VE is 75.0% and the 2.8L VE is 64.9%. That says that the 2.8L is flowing less air but it's making 5 more HP??? The power enrichment AFR for the 3.1L at 4800 rpm is 11.9 vs 12.0 for the 2.8L. So I am beginning to think that the VE numbers are more relative than absolute and GM just makes up for it elsewhere like in the base pulse constant. The 2.8 has a base pulse constant of 224. The 3.1 calibration constant table does not have a base pulse constant but it has a "number of cylinders" value of 192 which is probably the same thing. So 224 / 192 * 64.9 = 75.7. That about matches the VE for the 3.1L.

At the end of the day I can change all this data to make it work for my build. It's just confusing the way GM has gone about this.

in the end they have these tables but it's up to the calibrator to achieve the desired output.

if the engine needs a bit more fuel somewhere during development of the tune, and whoever wrote the ECM's software doesn't have a special table to handle it, they'll just jack it up wherever they feel like it like, VE or whatever. even the injector constants usually get fudged at the factory. you will end up doing the same for sure. don't overdo it when it comes to precision with these things, your engine cares less than you do.

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My understanding of volumetric efficiency is that it is a measure of how well the cylinder fills. At 100% VE the pressure in the cylinder during the intake stroke is the same as the intake manifold pressure.

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yeah pretty much. with 7psi i might start at like 40% airflow than normal 100kpa ve and go from there, although you'll just have to trial and error.

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So I already some higher horse power engine. The electric supercharger is more of a learning project. The electric motor technology is already there. A 10 HP brushless DC motor is small and light. Bigger motors are available. What limits the motor size is energy storage. Lithium titanate batteries are available. These can discharge/charge fast and stand lots of cycles. Super capacitor technology is on the way

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hey i get the idea. that stuff used to be a total joke and now it's possible to make some power with it.

this dork i met spent like half his life putting a turbo he inhereted from somewhere in his 2.8 camaro for a 'learning project'.

he had a friend weld some exhaust for the up and down pipes and it actually didn't look bad. no intercooler, no blowoff valve, it made 7 psi at first, but on free boost with the wastegate hose hanging so the gate stayed shut, it made 9psi flat out, so we just said screw it and left the hose hanging. the lag wasn't too bad either.

i assisted in tuning it to near the limit with him with 91 octane. it's a maf car. bigger injectors, bigger fuel pump, cooler thermostat, oil cooler, the usual budget turbo stuff.

it still runs great, but he still gets his ass handed to him by rednecks with a cam swap in their junkyard trucks and toyota prius taxis that aren't even trying to race him

i bet if the waste gate on my 2 litre subaru was stuck open and i had a 500lb load of sandbags in the trunk i'd still kick his ass from a dig

if it were me i would just make the whole car electric before i put one of those things in there

but this is just for conversation and if you want to do an electric supercharger rig i'm all about supporting your tune

the fiero is especially challenging to add this stuff to, i know that. not much room there.

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Originally Posted by steveo

in the end they have these tables but it's up to the calibrator to achieve the desired output.

the fiero is especially challenging to add this stuff to, i know that. not much room there.

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Actually I have plenty of room to put an Eaton M62 with a 10 HP motor in the trunk (which I rarely use). Then poke a hole in the trunk wall and run a 3" intake into the engine compartment through an in-line liquid-air intercooler then to the throttle body. The nice thing about the electric supercharger is unlike a turbo you get max boost as soon as you go WOT and there is no parasitic load on the engine. Biggers motor are available to take the engine to it's ultimate boost limit. The real limit is battery storage capacity but that's changing as we speak.

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The nice thing about the electric supercharger is unlike a turbo you get max boost as soon as you go WOT and there is no parasitic load on the engine. Biggers motor are available to take the engine to it's ultimate boost limit. The real limit is battery storage capacity but that's changing as we speak.

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do you leave the batteries isolated and charge them when you get home? otherwise having zero parasitic loss is physically impossible. the energy to turn that thing has to come from somewhere, and the losses from a motor driving a generator driving a motor will always be greater than driving it directly because physics. you're just moving or spreading out the loss with energy storage

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Originally Posted by steveo

do you leave the batteries isolated and charge them when you get home? otherwise having zero parasitic loss is physically impossible.
the energy to turn that thing has to come from somewhere, and the losses from a motor driving a generator driving a motor will always be greater than driving it directly because physics.
you're just moving or spreading out the loss with energy storage

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While this is absolutely true, IF one had enough battery to store enough energy prior to (say) a 1/4 mile run, the parasitic load could be minimized during that following 1/4 mile run.

Makes me think of precompressed air 'supercharging' ...

of course, in fact if you got wise with a bigass solenoid, you could easily disconnect the charging load while the supercharger was active and recharge your supercharger with your superchargercharger (alternator) during normal driving conditions, so you could at least have zero parasitic load while on boost. but you can't call that zero parasitic load like it's free energy, you still have to make up for it later.

a supercharger that is active all the time gives you an effectively larger engine throughout throughout the operating range, this is kind of more like electric nitrous isn't it

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How can the mere presence of a turbo charger effect the VE that much. It seems like GM is fudging the VE's and then doing less correction with the boost multiplier table. Very Strange.

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Older calibrations were developed manually, through trial and error and repeated drive cycles. There are (were?) numerous combinations of calibration values that can produce the desired end result. Over the years a number of GM "fudges" have been discovered and in some cases folks who want to see honest values in their calibration have invested painstaking effort into making sure tables such as VE reflect accurate information.

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the losses from a motor driving a generator driving a motor will always be greater than driving it directly

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I have not seen anyone try to produce a forced induction system using an exhaust driven turbine to generate electric power to operate an electric compressor. With a storage device in between this could be a reliable way to divorce the compressor and turbine. I would expect inefficiency with this system to be lower than the supercharger powered by the vehicle's primary charging system.

there have been lots of experiments with generating electric energy from exhaust. you can get power both directly with a turbine and also with direct thermoelectric generators. there's probably a reason you don't see them around much - if the tech was that good they would probably throw it in hybrids, but i would love to be proven wrong.

actually in the case of a turbo, when your egts and flow are high enough to make a turbine generate usable power, is exactly when your engine needs boost to make more power. there is zero reason to decouple a turbo except maybe for some lag reduction, which isn't really a problem with modern turbos anyway