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.

 

This gets handled with good boost control. Everybody is running tight wastegate springs and with those the boost always comes on too hard at part throttle. In practical terms this means that a 600 ft/lb engine makes 550 ft/lbs at 50% throttle. This does indeed feel unsafe.

Chris

 

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 this hits the nail on the head Chris. When racing my car I feel like I wanna shift as late as possible because there is a quantifiable benefit of increasing hp the further up you go in the rpm band. As we discussed yesterday when looking at the Motec data, I'm seeing that I'm winding the engine out to or near the rev limiter set at 7800 in certain sections on track although the target shift point is 7500. I think you said you are seeing about 1.5 sec per lap spent above 7500. Pretty much every lap I looked at I'm seeing a top rpm of 78xx. With the increasing HP, there is a quantifiable performance benefit to shifting as late as possible. In a street car, this is probably not very practical however and having a slightly falling torque curve might "feel" more appropriate to most.

 

In this thread, I am trying to get a better handle on what makes the best street engine. Street engines have to do more things well than the racing engine. It also does not have to have such rigid durability constraints.

Chris

 

The opposite of a race engine. It's useful to have the two end points in mind so you can then imagine where you want to be in between.

Chris

 

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.

 

Funny you say that, I really wanted to build a 4l motor, but when you started looking at the real world costs, I had a hard time justifying it - too many toys I don't want to give up.

Thus, the idea of beefing up the rods and valve train was born, because I really want to use those 980s.

 

I think a good street build is reliable, makes good power and gets reasonable mileage when just tooling around.

The balance between something that has good bottom end for the city, and really good power on the highway is the best all arounder.

As mentioned earlier in this thread, and in others, I find a tuned k16 car, such as Matt's a much better city car than mine, but when you put them head to head in the highway, I have a distinct advantage.

I don't think this is as much tuning as it is turbo sizing.

This is why I am very interested to see if the 980s bridge the gap between the k16s and k24s.