Preferred torque curve for 996 Turbo
#31
Turbo DI cars can get LSPI when "lugging". This is an issue with B9 S4/RS4s if you don't shift them manually. I'm sure other platforms fall in the same boat. They need a ton of load in order to downshift, the result is full boost at very low rpm. High boost/load with low rpm can cause some nastiness on DI motors. You also have lower oil pressure at lower rpm which isn't great if you're getting knock. Pretty sure they make oils now that are supposed to help combat LSPI.
#32
Chris
#33
RL Community Team
Rennlist Member
Rennlist Member
Isn't that what you guys are doing already? Limiting torque to a specific value and not exceeding it?
I think it is a really cool engineering exercise to be able to extract 900hp but limit torque to 500ft/lbs in a 'flat' manner.
I know it's comparing apples to oranges, but there was no way we could do that with a diesel; when I built the 6.4, I have enough fuel to support well over 750hp, but the torque was insanely high, almost 1700ft/lbs, and almost 1000 of this were available just off idle.
We could not tune to the level (at least with the Ford ECU) that you guys are able to do, and to be fair, the thing was pretty much useless to drive in 2wd and would most certainly eat tranny's, so that left us with pulling boost and limiting fuel.
Net result was 500whp, and a little over 1100ft/lbs, with a gearbox rated for about 25 percent more. Torque is as flat as Saskatchewan, and it can be driven in 2wd except for in the rain, but there was no way we would ever have succeeded in achieving a high power, low torque scenario.
Should also note that all of this is happening in a 4200rpm spread, with a lot of head work.
Not sure how else to preserve the gearbox in this scenario, most certainly cannot do what you guys are doing.
I think it is a really cool engineering exercise to be able to extract 900hp but limit torque to 500ft/lbs in a 'flat' manner.
I know it's comparing apples to oranges, but there was no way we could do that with a diesel; when I built the 6.4, I have enough fuel to support well over 750hp, but the torque was insanely high, almost 1700ft/lbs, and almost 1000 of this were available just off idle.
We could not tune to the level (at least with the Ford ECU) that you guys are able to do, and to be fair, the thing was pretty much useless to drive in 2wd and would most certainly eat tranny's, so that left us with pulling boost and limiting fuel.
Net result was 500whp, and a little over 1100ft/lbs, with a gearbox rated for about 25 percent more. Torque is as flat as Saskatchewan, and it can be driven in 2wd except for in the rain, but there was no way we would ever have succeeded in achieving a high power, low torque scenario.
Should also note that all of this is happening in a 4200rpm spread, with a lot of head work.
Not sure how else to preserve the gearbox in this scenario, most certainly cannot do what you guys are doing.
#34
Ok, so the flat torque curve is more desirable than a falling torque curve.
I think for a road car a slightly falling torque curve feels a little more natural. To me the flat torque curve feels like this mad rush for redline: Appropriate in a race car, but maybe less so in a road car. Probably a matter of opinion, especially if you don't have a self imposed torque limitation.
I would guess that everyone would agree that getting the flatness established sooner would be better. The Powdrhound example gets flat at 4k. What's optimal? 3k, 2k? People talk about "lugging" sometimes. That is another term without a specific meaning. Most of the modern DFI 2.0 liter 4 cylinder engines can get to peak torque at 2000rpm. Is this lugging?
Chris
I think for a road car a slightly falling torque curve feels a little more natural. To me the flat torque curve feels like this mad rush for redline: Appropriate in a race car, but maybe less so in a road car. Probably a matter of opinion, especially if you don't have a self imposed torque limitation.
I would guess that everyone would agree that getting the flatness established sooner would be better. The Powdrhound example gets flat at 4k. What's optimal? 3k, 2k? People talk about "lugging" sometimes. That is another term without a specific meaning. Most of the modern DFI 2.0 liter 4 cylinder engines can get to peak torque at 2000rpm. Is this lugging?
Chris
#35
Chris
#36
Chris
#37
RL Community Team
Rennlist Member
Rennlist Member
Not everyone has the budget or desire to build a monster engine like powderhounds but would love to better understand what are the bolt ons or tuning needed to get to that perfect street car engine. In my case I'd love to get the most low end torque possible while preserving the stock rods without running out of too much steam up top.
#38
RL Community Team
Rennlist Member
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I'm glad that this is the intent for this. It is hard to say what is the best street engine as everyone has a different use case for how they use their car. Some like fast highway driving/pulls and others like canyon carving getting out of turns quickly. As for myself I'm in the tight canyon carving category but I also have to deal with the extreme heat of living in Texas in the summer. This is why the work you and powderhound have been posting has been interesting because y'all are trying to make good power at lower boost to mitigate heat.
Not everyone has the budget or desire to build a monster engine like powderhounds but would love to better understand what are the bolt ons or tuning needed to get to that perfect street car engine. In my case I'd love to get the most low end torque possible while preserving the stock rods without running out of too much steam up top.
Not everyone has the budget or desire to build a monster engine like powderhounds but would love to better understand what are the bolt ons or tuning needed to get to that perfect street car engine. In my case I'd love to get the most low end torque possible while preserving the stock rods without running out of too much steam up top.
Thus, the idea of beefing up the rods and valve train was born, because I really want to use those 980s.