Boost Creepin'
#21
It is what you want because you get lower boost at peak torque than you get at the top where the head is choking so you have a safer curve AND will make more power. Stop and consider it for a moment and you will understand.
You can. Definitely rework it I've done a few wastegate on turbo arrangements and wastegate on cast manifold (rb25/45mm Turbosmart hypergate are popular here) so you can make it flow awesome and it will hold perfect boost within the psi.
What annoys me is the common misconception about boost pressures. If you are trying to stay under a torque limit your boost curve should look opposite to your n.a torque curve which gives a flat torque curve.
You keep the torque below your limit and flat rather than with a big midrange spike to the limit and heaps less everywhere below (waiting to spool) and above (head is flowing less and less as revs rise and it chokes but boost pressure remains the same).
Dann
You can. Definitely rework it I've done a few wastegate on turbo arrangements and wastegate on cast manifold (rb25/45mm Turbosmart hypergate are popular here) so you can make it flow awesome and it will hold perfect boost within the psi.
What annoys me is the common misconception about boost pressures. If you are trying to stay under a torque limit your boost curve should look opposite to your n.a torque curve which gives a flat torque curve.
You keep the torque below your limit and flat rather than with a big midrange spike to the limit and heaps less everywhere below (waiting to spool) and above (head is flowing less and less as revs rise and it chokes but boost pressure remains the same).
Dann
Last edited by nitrodann; 12-07-2014 at 06:49 PM.
#22
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Thanks for explaining that, it makes more sense now. I guess I'm too hung up on boost pressure determining the limits of the motor. Once I get the wastegate source moved to pre-intercooler I'll bump up my overboost protection and see how it handles going to redline.
#24
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If I was creeping to 180kPa, I'd make my lowest boost 180kPa.
Having a torque curve like a centrifugal SCer on a turbo car is weak and lame and something only an Aussie would do purposefully.
you're leaving 3psi off the table between 3500 and Redline. That would probably bring you power up to 240hp/240tq.
Having a torque curve like a centrifugal SCer on a turbo car is weak and lame and something only an Aussie would do purposefully.
you're leaving 3psi off the table between 3500 and Redline. That would probably bring you power up to 240hp/240tq.
#26
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When I initially posted I was on rx8 yellow injectors, a couple posts up I swapped to id1000s. Megalogviewer showed 95% duty cycle and the car wanted to go lean at high rpms even when I kept adding fuel so they were definitely at their limit on stock fuel pressure.
#27
If I was creeping to 180kPa, I'd make my lowest boost 180kPa.
Having a torque curve like a centrifugal SCer on a turbo car is weak and lame and something only an Aussie would do purposefully.
you're leaving 3psi off the table between 3500 and Redline. That would probably bring you power up to 240hp/240tq.
Having a torque curve like a centrifugal SCer on a turbo car is weak and lame and something only an Aussie would do purposefully.
you're leaving 3psi off the table between 3500 and Redline. That would probably bring you power up to 240hp/240tq.
Dann
#29
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I hadn't considered that, I'll take a look at it tonight.
I dropped my intercooler pipe off the. bungs to be welded on it. I went ahead and did one before and after the intercooler so I will have 2 options to play with. I should have it back tonight.
I dropped my intercooler pipe off the. bungs to be welded on it. I went ahead and did one before and after the intercooler so I will have 2 options to play with. I should have it back tonight.
#30
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Took a small baby step in the right direction I guess. I got my intercooler piping back from the welder and hooked up the wastegate right out of the turbo.
I also checked on ScottyP's recommendation. The banjo bolt on the wastegate was exactly 90 degrees off of a direct flow. I marked the bolt so I could line up the line perfect. Not sure how much difference it made, but any little bit helps.
I datalogged a pull that was considerably better, but still disappointing. You can clearly see boost climbing slower, I'm assuming that's attributable to Brain's recommendation of running a pre-intercooler wastegate source. Having the wastegate open at 7psi, then hitting 14.5psi boost cut before redline sucks, but at least I'm getting closer.
I assume the only way to actually fix it is to correct the wastegate setup like Savington suggested.
I also checked on ScottyP's recommendation. The banjo bolt on the wastegate was exactly 90 degrees off of a direct flow. I marked the bolt so I could line up the line perfect. Not sure how much difference it made, but any little bit helps.
I datalogged a pull that was considerably better, but still disappointing. You can clearly see boost climbing slower, I'm assuming that's attributable to Brain's recommendation of running a pre-intercooler wastegate source. Having the wastegate open at 7psi, then hitting 14.5psi boost cut before redline sucks, but at least I'm getting closer.
I assume the only way to actually fix it is to correct the wastegate setup like Savington suggested.
#33
What if you run EBC and ramp up the boost to see if you can level off the boost all the way to redline. I really think all this is due to the 90 deg bend at this point it seems it may as well be internally gated. At the WG vent I think it would be ok to have bends but ideally I would think you would want that wg right on the port. (drunk thoughts)
#34
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Because all 95% of us here with this sort of torque output all have broken motors...
what I'm really suggesting is this:
if you want torque like you're suggesting why are you building turbo setups and not rotrex setups? the reason you install a turbo is torque and area-under-curve, not your pansy *** setup.
I had creep issues back on an old setup:
wanna guess which one of those configurations was better than the other?
it's also funny that my torque output, when holding boost flat, looks closer to what you drew...
having more torque at 7000RPM is much more dangerous than more at 4000RPM. I'd argue that the cylinder pressures at 4K in my examples are still less than that at redline. And that my friend is what bends rods.
what I'm really suggesting is this:
if you want torque like you're suggesting why are you building turbo setups and not rotrex setups? the reason you install a turbo is torque and area-under-curve, not your pansy *** setup.
I had creep issues back on an old setup:
wanna guess which one of those configurations was better than the other?
it's also funny that my torque output, when holding boost flat, looks closer to what you drew...
having more torque at 7000RPM is much more dangerous than more at 4000RPM. I'd argue that the cylinder pressures at 4K in my examples are still less than that at redline. And that my friend is what bends rods.
Last edited by Braineack; 12-12-2014 at 07:41 AM.
#36
Brain.
I have found that in order to hold torque dead flat from peak to redline you need boost to increase past 4500rpm. I have found this tuning stock motors with ms2 rpm vs tps boost control.
Holding flat boost will result in a drop in torque.
There for in order to hover at a specific torque (240 for example) boost needs to steadily increase past 4500rpm by a few psi, I tend to see 16 or 17psi at redline on typical 2560 setups. Some might describe this as creep. Call it what you will.
I have found that in order to hold torque dead flat from peak to redline you need boost to increase past 4500rpm. I have found this tuning stock motors with ms2 rpm vs tps boost control.
Holding flat boost will result in a drop in torque.
There for in order to hover at a specific torque (240 for example) boost needs to steadily increase past 4500rpm by a few psi, I tend to see 16 or 17psi at redline on typical 2560 setups. Some might describe this as creep. Call it what you will.