Engine powerband and HP idea

[Shin Ryu]

I have been researching to build a 818 Coupe down the road. One of the reasons I am choosing the 818 is because it's light weight and is great for autoX track on the weekends with amazing balance for the turns. Something that I have repeatedly seen from other post is that the power output max should usually be about 400 rwhp because the power is too hard to control the car after 400. I'm sure this is plenty of power going through turns but i think the higher power cars would be faster on the straights.

I'm new with smaller engine/turbo combos, but I would think there would be a way to tune and modify the powerband to the high end RPMs where the car is capable of 500+ rwhp on the straights, but on the turns you keep the engine at the lower RPM, less powerful part of a powerband and it would be easier to maintain control. I have heard turbos are fairly adjustable. What do you guys think about this? Also this I would like the car to be fairly streetable as well. TIA

[Mitch Wright]

I chose the keep my power target on the conservative side for my EJ205, 285hp 276Ft lb Torque. My reason are:
1) Durability of the drive train, I wanted a higher drive to work on ratio.
2) Use of pump fuel
3) My budget
4) My first experience with a Subaru so I kept it simple. And I figured the car would be fun to drive with my current set up, it is.

[Hindsight]

You keep the car in upper RPM power bands at all times on the track. You modulate the power with your right foot. When you go around corners on the track, you aren't just flooring it (unless you are driving a Miata) so it isn't like there is 500WHP being put down in the turns. Just spec the build to make as much power as you want. More power will always be faster on the track assuming the driver is skilled enough to handle it. I'm running about the same amount of power as Mitch, but with more torque (320). For tight courses and courses that are mostly all curves, the power is plenty. For tracks like Road Atlanta with a lot of straights, I find myself wanting another couple hundred HP. And better brakes.

[Shin Ryu]

Thanks guys I appreciate it. You have definitely given me something to think about. I doubt I will ever realistically want 400 hp much less 500, I was just if that was a possible tactic of having a lot of power to keep up with the big dogs and maintain some level of drivablitly.

[RetroRacing]

We built our car with a target power to weight ratio in mind. For example, we compete with Cup cars and Audi R8 LMS cars at the 25h, or at least will be soon, so we looked at their power to weight ratio's and tried to either match or do better. We then looked at our target weight, calculated the required HP at the wheels, then looked at the corresponding torque numbers to see if our drive train could handle it. Go to heavy, more power required, more torque is present, more drive train thingy's break, harder on brakes. Go lighter, less power required, less things break, easier on brakes, but can be expensive...
So, we took a hybrid approach. We had a target weight of 2000lbs with driver, and 300hp at the wheels. That would give us a ptwr of .15, while a new Porsche/audi has a ptwr of .14 (at the wheels). What we ended up with was 2200 with fuel and driver, so we have .13 power to weight. Now, we carry 3 more gallons of fuel, and we are almost 1000lbs lighter, so we can go further between stops for fuel, tires and we can go deeper on the brakes all without turning up the power. Now, we could get dead even with another 10-15 hp at the wheels, but the less power you run, the less strain on everything.

In a nutshell, it's a balance between stupid speed and breaking stuff. Then there is aero.....not going there yet.

[SixStar]

Another consideration is what tuning solution you will be using. Boost by gear is an amazing advancement in power delivery for any turbocharged vehicle. It allows you to apply power in stages based on the gear position.

When we tuned the 818R on COBB we did several pulls at different boost levels to get the data needed for boost by gear. In 1st I'm barely making 280whp, 300-320 in 2nd, 350-370 in 3rd and 400whp+ in 4th and 5th.

[RetroRacing]

That is a great option! I wonder if our Haltec will do that...

[turbomacncheese]

Another consideration is what tuning solution you will be using. Boost by gear is an amazing advancement in power delivery for any turbocharged vehicle. It allows you to apply power in stages based on the gear position.

When we tuned the 818R on COBB we did several pulls at different boost levels to get the data needed for boost by gear. In 1st I'm barely making 280whp, 300-320 in 2nd, 350-370 in 3rd and 400whp+ in 4th and 5th.

Man, on my old dodge I used a springloaded valve rigged to a switch on the throttle body so I wouldn't get full boost until I mashed the pedal all the way down and thought I was slick.

[DanielsDM]

Another consideration is what tuning solution you will be using. Boost by gear is an amazing advancement in power delivery for any turbocharged vehicle. It allows you to apply power in stages based on the gear position.

When we tuned the 818R on COBB we did several pulls at different boost levels to get the data needed for boost by gear. In 1st I'm barely making 280whp, 300-320 in 2nd, 350-370 in 3rd and 400whp+ in 4th and 5th.

That's interesting. How does the ECU determine what gear it is in?

[SixStar]

That's interesting. How does the ECU determine what gear it is in?

It's actually quite simple.

Gear ratios are linear (constant), so at X RPM and Y speed you must be in Z gear.

[twgab]

If your ECU doesn't have the capability to do boost by gear you can also use an aftermarket boost controller. I used an Apexi-AVCR, You wire it to the speedo, tach, and throttle position sensor. From there you just have to set things up by letting it know witch gear you are in while driving, and subtract, or add a percentage for each gear.
It works great for higher HP cars, as I was burning the tires off in 1st & 2nd at any more than 10 lbs. of boost.