DIY supercharger for the 97-99 A8, with used car story inside
08-22-2007, 08:00 PM
#32
AudiWorld Senior Member
ECU tuning is a bigger deal for the A8
Unlike the older RS4s and the 03 RS6, the A8 ain't turbocharged. It is child's play to dial up the boost and add more fuelling while hiding the extra boost from the ECU on a factory turbocharged car, but quite another to install and program boost on a car that never had it.
AFAIK, the only way to get a factory ECU to handle this, you would have to borrow one from a 2003 RS6 which had: a 4.2 V8; a 5HP24 Auto Tranny (sound familiar); two turbochargers and 450 HP in stock trim. It also had 9.5:1 compression (ours is 10.8:1 - way too high!) and God knows what else done to the internals...different piston material? oil sprayers on the underside of the pistons? If you are serious $$$ about turbocharging this car, you are shopping for the wrong engine.
I would love to see some detailed engine bay shots on an RS6. The only way I can see to get them in there is to "borrow" some space from the back of the wheelwell ...so you will need to fabricate those out of sheet metal..better make that aluminum with plenty of clearance/heat shielding.
Now if you could get an RS6 brain, would it actually work? How do you get it to talk to the Immobiliser system (especially if your A8 doesn't have it)? Is stability control integrated into the the RS6 ECU or is it separate.
IF and this is a GIGANTIC IF, a tuning firm has figured out a way to swap not just the MAPS, but the ENTIRE PROGRAM from an RS6 to an A8 by reflashing the stock A8 ECU, then that is a horse of a different color. If someone has done that, then have at it. Otherwise there is no way in Hell that you can achieve the two must haves: 1) a serious well executed install and 2) the likelihood of passing your emissions inspection
The easiest way to do a no holds barred install where passing inspection is not an issue is to use a stand alone aftermarket ECU in a manual tranny A8 (and there is only one of those that we know of); or use a piggy back (a half-measure and still might not pass inspection and will likely throw codes); or a rising rate fuel pressure regulator and MAYBE some way to pull timing on boost with knock control...but above a few pounds of boost, this is asking for an blown engine. And again, there is not much headroom on an engine with 10.8:1 compression that runs on premium already, so what's the point? The compression ratio has to come down out of the stratosphere for this to work.
I don't mean to **** on the parade, but this is not the car to try the casual workarounds on. It is already close to the edge and held there by a well integrated control system. There is, in my humble opinion, precious little margin for error. I doubt it will long survive the "work-around-the-existing-control-system" method you've outlined.
The workaround methods are tried and true in the import tuner 4 banger market, but this came at the cost of many blown civic motors before they got it right. All the half-assed electric intercept boxes and variable fuel pressure tricks go away if you can properly hack the factory ecu, and I don't know of anyone that has at a reasonable cost on the 4.2 A8. Solve that and the rest is comparatively easy: packaging, plumbing and reinforcing all the weak links.
There is a reason you haven't seen it done that often or for anything remotely resembling reasonable money: It is a massive undertaking to do right and to do at a level which matches the quality and workmanship of the rest of the car.
AFAIK, the only way to get a factory ECU to handle this, you would have to borrow one from a 2003 RS6 which had: a 4.2 V8; a 5HP24 Auto Tranny (sound familiar); two turbochargers and 450 HP in stock trim. It also had 9.5:1 compression (ours is 10.8:1 - way too high!) and God knows what else done to the internals...different piston material? oil sprayers on the underside of the pistons? If you are serious $$$ about turbocharging this car, you are shopping for the wrong engine.
I would love to see some detailed engine bay shots on an RS6. The only way I can see to get them in there is to "borrow" some space from the back of the wheelwell ...so you will need to fabricate those out of sheet metal..better make that aluminum with plenty of clearance/heat shielding.
Now if you could get an RS6 brain, would it actually work? How do you get it to talk to the Immobiliser system (especially if your A8 doesn't have it)? Is stability control integrated into the the RS6 ECU or is it separate.
IF and this is a GIGANTIC IF, a tuning firm has figured out a way to swap not just the MAPS, but the ENTIRE PROGRAM from an RS6 to an A8 by reflashing the stock A8 ECU, then that is a horse of a different color. If someone has done that, then have at it. Otherwise there is no way in Hell that you can achieve the two must haves: 1) a serious well executed install and 2) the likelihood of passing your emissions inspection
The easiest way to do a no holds barred install where passing inspection is not an issue is to use a stand alone aftermarket ECU in a manual tranny A8 (and there is only one of those that we know of); or use a piggy back (a half-measure and still might not pass inspection and will likely throw codes); or a rising rate fuel pressure regulator and MAYBE some way to pull timing on boost with knock control...but above a few pounds of boost, this is asking for an blown engine. And again, there is not much headroom on an engine with 10.8:1 compression that runs on premium already, so what's the point? The compression ratio has to come down out of the stratosphere for this to work.
I don't mean to **** on the parade, but this is not the car to try the casual workarounds on. It is already close to the edge and held there by a well integrated control system. There is, in my humble opinion, precious little margin for error. I doubt it will long survive the "work-around-the-existing-control-system" method you've outlined.
The workaround methods are tried and true in the import tuner 4 banger market, but this came at the cost of many blown civic motors before they got it right. All the half-assed electric intercept boxes and variable fuel pressure tricks go away if you can properly hack the factory ecu, and I don't know of anyone that has at a reasonable cost on the 4.2 A8. Solve that and the rest is comparatively easy: packaging, plumbing and reinforcing all the weak links.
There is a reason you haven't seen it done that often or for anything remotely resembling reasonable money: It is a massive undertaking to do right and to do at a level which matches the quality and workmanship of the rest of the car.
08-22-2007, 11:06 PM
#33
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Re: ECU tuning is a bigger deal for the A8, but a better deal
Brian I will Explore just about every possible part and method to make this work . I sincerely appreciate you're posts as they give me more ideas how to approach tuning, so thanks!
Base timing on any NA 4.2L Audi is not harsh. The motor given the highest grade pump gas can do 6 psi. I don't think turbochargers and supercharger should be compared when it comes to tuning. I've done a Pactel DFI system for a turbocharged car, it took near 2 months just to get proper fuel maps. And a Whipple charged Chevy took maybe 3 days
Base timing on any NA 4.2L Audi is not harsh. The motor given the highest grade pump gas can do 6 psi. I don't think turbochargers and supercharger should be compared when it comes to tuning. I've done a Pactel DFI system for a turbocharged car, it took near 2 months just to get proper fuel maps. And a Whipple charged Chevy took maybe 3 days
08-22-2007, 11:17 PM
#34
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Re: You still....ever wonder why a lysholm doesn't have a bypass valve , blow off valve or wastegate
The pressure under and over each blade is equal, I'm not talking about the cases entire volume.
this is an example: 14 psi Eaton supercharger, throttle shuts abruptly rotor stack wants to reverse like a turbocharger, hence the need for pressure release AKA blow off valve.
A whipple charger AKA Lysholm, full boost 14 psi full on to redline, throttle shuts no reverse rotation, I'll be fair and say maybe 10-15 percent difference in pressure,no reverse rotation of rotor stack
this is an example: 14 psi Eaton supercharger, throttle shuts abruptly rotor stack wants to reverse like a turbocharger, hence the need for pressure release AKA blow off valve.
A whipple charger AKA Lysholm, full boost 14 psi full on to redline, throttle shuts no reverse rotation, I'll be fair and say maybe 10-15 percent difference in pressure,no reverse rotation of rotor stack
08-23-2007, 09:33 AM
#38
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Audi tuning...
I know next to nothing about tuning an audi, but I've done a number of Fords. You don't need a "blower" ECU. Here are the parameters you need to tune:
Mass Air
Air Temp
Air Pressure in manifold
Fuel pressure
timing vs load table
Mass Air
Air Temp
Air Pressure in manifold
Fuel pressure
timing vs load table
08-23-2007, 01:03 PM
#40
AudiWorld Senior Member
Re: The fact that there actually are home-grown, 1-off bi-turbo S8s disproves all your points.
Huh, I am not saying it cannot be done. It is just dammned difficult. I recall reading about a one off bi-turbo in...Brazil???.Details???)..maybe...but the emissions control scheme there is likely different if not non-existent. So, that disproves nothing. The US is a lot stricter.
If you are going to own the car in, say, California, you need a CARB number or the car will never pass. Other States vary, but anywhere an OBDII machine is being plugged into the car, you have to have a stock ECM or an OBDII compliant aftermarket ECU assuming there is such a thing.
So that leaves you with three options: (1)reprogramming the stock ECM which was not set up for boost in the first place (no MAP sensor for one) I'm sure it can be done, but you need a near genius level programmer to do it or; (2) electronic piggybacks and maybe supplemental injector(s)?) which the stock system doesn't "See", (and hope you don't chronically throw codes which would also be an emissions test deal-breaker)or; (3) a combination of rising rate fuel pressure regulator on boost further taxing the less than stout fuel pump and a black box to pull timing on boost. Far from optimum, but sure it will work, and there is zero safety margin if any part takes a dump because the ECM has no clue what is really going on. Thankfully the stock system does have a knock sensor, so it will pull timing on detection, but will it be enough?
The fact that a system can be built with a standalone is useless in my part of the world. Its got to be able to pass the Big Brother OBD2 hook-up and the sniffer.
Oh, and Greenbird, Ford is the only Auto Mfr I know of that actually opened up its ECU code book to the aftermarket making Ford ECU tweaks comparatively easy. But again, the A8 doesn't presently have the means to measure positive pressure, so you would have to at least swap the MAF for a MAP sensor.
In short, if someone has figured out how to recode a stock normally aspirated A8 ECU for FI, then the rest is worth doing. If not then you've got serious limitations and risk not being able to get it approved for the street.
If you are going to own the car in, say, California, you need a CARB number or the car will never pass. Other States vary, but anywhere an OBDII machine is being plugged into the car, you have to have a stock ECM or an OBDII compliant aftermarket ECU assuming there is such a thing.
So that leaves you with three options: (1)reprogramming the stock ECM which was not set up for boost in the first place (no MAP sensor for one) I'm sure it can be done, but you need a near genius level programmer to do it or; (2) electronic piggybacks and maybe supplemental injector(s)?) which the stock system doesn't "See", (and hope you don't chronically throw codes which would also be an emissions test deal-breaker)or; (3) a combination of rising rate fuel pressure regulator on boost further taxing the less than stout fuel pump and a black box to pull timing on boost. Far from optimum, but sure it will work, and there is zero safety margin if any part takes a dump because the ECM has no clue what is really going on. Thankfully the stock system does have a knock sensor, so it will pull timing on detection, but will it be enough?
The fact that a system can be built with a standalone is useless in my part of the world. Its got to be able to pass the Big Brother OBD2 hook-up and the sniffer.
Oh, and Greenbird, Ford is the only Auto Mfr I know of that actually opened up its ECU code book to the aftermarket making Ford ECU tweaks comparatively easy. But again, the A8 doesn't presently have the means to measure positive pressure, so you would have to at least swap the MAF for a MAP sensor.
In short, if someone has figured out how to recode a stock normally aspirated A8 ECU for FI, then the rest is worth doing. If not then you've got serious limitations and risk not being able to get it approved for the street.