Twin Turbo 928 fixed and back out there terrorizing the streets!
07-04-2014, 02:18 PM
#841
Nordschleife Master
Thread Starter
The slow mapping from cell to cell with new rpm and load breakpoints is yielding some results. The car is now making about 492 axle hp at 8.5 psi boost. The 8.5 psi boost level, the knock constrained optimal fueling is about 11.3:1 across to board after the turbo has spooled. Rich or retarded, that is the question, in each sell.
07-04-2014, 02:26 PM
#842
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I'd rather be rich.
07-06-2014, 12:37 PM
#843
Nordschleife Master
Thread Starter
Both seems to work ok for some people:
On a more serious note, the stock '87 S4 engine does not want to go over 700 rear axle hp on 93 octane pump gas. We're hitting a wall there, no matter which direction we approach it. With higher octane gas, we could make more at lower rpms. With bigger cams, we could could make a bit more at higher rpms. But with stock S4 cams, trying to compensate the cams falling on their faces with boost at 6000-7000 rpm produces a very non-linear map that is a nightmare to tune.
We must be up to 125 dyno runs over the last two months alone, some longer some shorter, with this particular combination. [Edit: more than 300 overall by rough estimates.]
On a more serious note, the stock '87 S4 engine does not want to go over 700 rear axle hp on 93 octane pump gas. We're hitting a wall there, no matter which direction we approach it. With higher octane gas, we could make more at lower rpms. With bigger cams, we could could make a bit more at higher rpms. But with stock S4 cams, trying to compensate the cams falling on their faces with boost at 6000-7000 rpm produces a very non-linear map that is a nightmare to tune.
We must be up to 125 dyno runs over the last two months alone, some longer some shorter, with this particular combination. [Edit: more than 300 overall by rough estimates.]
Last edited by ptuomov; 07-16-2014 at 07:20 AM.
07-06-2014, 12:46 PM
#844
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Both seems to work ok for some people:
On a more serious note, the stock '87 S4 engine does not want to go over 700 rear axle hp on 93 octane pump gas. We're hitting a wall there, no matter which direction we approach it. With higher octane gas, we could make more at lower rpms. With bigger cams, we could could make a bit more at higher rpms. But with stock S4 cams, trying to compensate the cams falling on their faces with boost at 6000-7000 rpm produces a very non-linear map that is a nightmare to tune.
We must be up to 125 dyno runs over the last two months alone, some longer some shorter, with this particular combination.
On a more serious note, the stock '87 S4 engine does not want to go over 700 rear axle hp on 93 octane pump gas. We're hitting a wall there, no matter which direction we approach it. With higher octane gas, we could make more at lower rpms. With bigger cams, we could could make a bit more at higher rpms. But with stock S4 cams, trying to compensate the cams falling on their faces with boost at 6000-7000 rpm produces a very non-linear map that is a nightmare to tune.
We must be up to 125 dyno runs over the last two months alone, some longer some shorter, with this particular combination.
Åke
07-06-2014, 09:45 PM
#846
Both seems to work ok for some people:
On a more serious note, the stock '87 S4 engine does not want to go over 700 rear axle hp on 93 octane pump gas. We're hitting a wall there, no matter which direction we approach it. With higher octane gas, we could make more at lower rpms. With bigger cams, we could could make a bit more at higher rpms. But with stock S4 cams, trying to compensate the cams falling on their faces with boost at 6000-7000 rpm produces a very non-linear map that is a nightmare to tune.
We must be up to 125 dyno runs over the last two months alone, some longer some shorter, with this particular combination.
On a more serious note, the stock '87 S4 engine does not want to go over 700 rear axle hp on 93 octane pump gas. We're hitting a wall there, no matter which direction we approach it. With higher octane gas, we could make more at lower rpms. With bigger cams, we could could make a bit more at higher rpms. But with stock S4 cams, trying to compensate the cams falling on their faces with boost at 6000-7000 rpm produces a very non-linear map that is a nightmare to tune.
We must be up to 125 dyno runs over the last two months alone, some longer some shorter, with this particular combination.
Could you JUST please try to use some e85? All you would have to do is increase the injector size and fuel pressure and maybe the fuel pumps (but I thought you said you were 044x2) Then tell us what you find when you start adding fuel and timing and the increased mass in the exhaust pushing on the turbine.
Just TRY it. What do you have to lose? You hit a wall with 93 (and probably pretty safely).
Keep it to about 11:1 AFR on the petrol scale. You can go fatter, but you would need different spark plugs and I am trying to not make you work too hard.
07-06-2014, 09:59 PM
#847
Nordschleife Master
Thread Starter
Could you JUST please try to use some e85? All you would have to do is increase the injector size and fuel pressure and maybe the fuel pumps (but I thought you said you were 044x2) Then tell us what you find when you start adding fuel and timing and the increased mass in the exhaust pushing on the turbine. Just TRY it. What do you have to lose? You hit a wall with 93 (and probably pretty safely). Keep it to about 11:1 AFR on the petrol scale. You can go fatter, but you would need different spark plugs and I am trying to not make you work too hard.
If you can't drive it from one side of the country to the other and fill it up at any gas station along the way, then it isn't what I am looking for to accomplish with this car.
Last edited by ptuomov; 07-14-2014 at 10:24 PM.
07-14-2014, 07:57 PM
#849
Nordschleife Master
Thread Starter
A short video clip:
250 dyno pulls and up to 20 psi boost (currently at 17 psi), and the stock engine isn't having any problems.
One note on rpm-specific boost control. Right now, we're running a very simple linear boost ramp up that starts kicking up boost from 4500 rpm. That's not squeezing everything we can from the car. The way we've got the absolute most out of the car in terms of right tune is to set the boost set point to a different value for each 500 rpm segment. This allows us to, among other things, very closely to trace the LH load row right smack in the middle. I've said this before, but I say it again: rpm-specific boost control is the cheapest horsepowers you can ever buy in a turbo car.
250 dyno pulls and up to 20 psi boost (currently at 17 psi), and the stock engine isn't having any problems.
One note on rpm-specific boost control. Right now, we're running a very simple linear boost ramp up that starts kicking up boost from 4500 rpm. That's not squeezing everything we can from the car. The way we've got the absolute most out of the car in terms of right tune is to set the boost set point to a different value for each 500 rpm segment. This allows us to, among other things, very closely to trace the LH load row right smack in the middle. I've said this before, but I say it again: rpm-specific boost control is the cheapest horsepowers you can ever buy in a turbo car.
Last edited by ptuomov; 07-16-2014 at 07:24 AM.
07-14-2014, 10:29 PM
#851
Nordschleife Master
Thread Starter
A couple of still shots of the hot-rodded engine
Here are a couple of photos of the hot-rodded engine with the hot-side components on.
The turbos will be a bit bigger than these that are attached to the engine on the stand.
The compressor covers are unmodified pieces, so that's another thing that is different with the turbos that actually fit the car.
The turbos will be a bit bigger than these that are attached to the engine on the stand.
The compressor covers are unmodified pieces, so that's another thing that is different with the turbos that actually fit the car.
07-15-2014, 10:46 PM
#854
Nordschleife Master
Thread Starter
07-17-2014, 02:08 PM
#855
Nordschleife Master
Thread Starter
The final dyno graph with the stock engine
Here's presumably the final dyno graph with the stock engine. Let's call it about 650hp at the rear axle, that's close enough for government work.
This is not the highest dyno graph we've produced. These settings leave enough of a margin of safety relative to the knock threshold on 93 octane pump gas, however. There are no surprises in the torque curve either, so the traction is going to be relatively predictable. The car is also not terribly sensitive to the gear which you're on, given that the flat part of the torque curve extends for a pretty wide range (3600-6700 rpm are over 500 lbft).
If I were to end the project now and just the drive the car, I'd leave it with these settings and I probably wouldn't have to think about tuning or settings again. I wouldn't be surprised if this calibration would be the starting point for some future twin turbo 928's with a stock engine.
This is not the highest dyno graph we've produced. These settings leave enough of a margin of safety relative to the knock threshold on 93 octane pump gas, however. There are no surprises in the torque curve either, so the traction is going to be relatively predictable. The car is also not terribly sensitive to the gear which you're on, given that the flat part of the torque curve extends for a pretty wide range (3600-6700 rpm are over 500 lbft).
If I were to end the project now and just the drive the car, I'd leave it with these settings and I probably wouldn't have to think about tuning or settings again. I wouldn't be surprised if this calibration would be the starting point for some future twin turbo 928's with a stock engine.