mikeb75's build thread

As driveslikejehu said, the only real benefit of A2A is simplicity, if you can make it work. Less weight and if you can make 100 % "passive" cooling work no need for fans- but the aerodynamics over the back of the car are... challenging. I thought the coupe would be a bit cleaner, but think I need to add some deflectors to the A pillar to clean up the airflow. I looked for a CAD model, but being cheap didn't want to pay for the one that I had found, which in the long run would be cheaper than buying a scanner or the number of hours required to model it myself... but nose, face and all that.

I was pleased that an off the shelf 3" Lexan NACA duct would fit in the quarter window space:
Attachment 214875
But, as Hobby Racer and J R Jones noted, the airflow in that area is poor - especially running open windows as the track day organizations I run with require. I did some early string testing and a track day with the solution but didn't see great results. After much searching I found outer scoops for the NACA ducts from a custom vendor in England... and paid almost as much in shipping and duty fees as I did for the parts last year.
Attachment 214876
Attachment 214877
Attachment 214878

These are the "large" NACA scoops (I guess things run small in England). They're OK, but given the poor location and dirty airstream that's got to be going on there, I think there's room for improvement... if needed. I figure with a roll of clear PETG and a little bit of time I could print up a much more aggressive scoop inlet (maybe not old 911 whaletail size...) that gathers more air.

Went to Summit Point (Main) on 1 August.
Attachment 217117
Attachment 217118

Day started wet and rainy, which is daunting in a car with no ABS or TC. Went out, did some recon laps, car felt pretty good actually (new tires helped). Eventually, as I was getting up confidence and speed found the limit at 9 and had a quick half spin. Kept the car (mostly) on the track, took it to the pit & got checked over. Was OK, went back out, did more laps, locked the brakes into 1 and had a slow speed gravel excursion. I was releasing pressure, but I didn't know you need to come fully off the brakes when they're sliding on wet asphalt. Backed out, took it to pit and discussed with my instructor.

Sessions 2, 3 and 4 through the rest of the day were mostly to fully dry. I worked on threshold breaking into 1 and 5 and sweeping through 6 without any brakes at all. Overall a fun and successful day!

The A2A intercooler worked as well as I could expect - the ambient air temps were around 70/80*. I was driving on the boost gauge a little bit, I think the engine is overboosting in 4th and 5th (21+ psi on a 20 psi map), which causes immediate fuel cut. Need to get the engine retuned. But the intercooler hot side was showing up to 200* (as expected). The cold side did get up to 140* after several hard laps, after which I took a lap to cool it down, but it would stay at 120-130* pretty consistently. Given how much latent heat is trapped in the coupe with the flat bottom I run, I'm happy with those results. I'll look into adding some NACAs to the underside to get additional cooling into the engine bay, but the IC body was rather hot to the touch after session, so I think it's a function of turbo & engine heat at this point.

In summary, if you want to run A2A in a coupe, you need the largest intercooler core you can fit and at least 4x3" hoses worth of airflow over it. Ducting from the roof scoop is not enough, nor the quarter windows, but all those combined seem to flow enough CFM at speed. The IC needs a good plenum feeding it, I strongly recommend separating each air source into it's own separate channel so there are no cross or back flow issues - less complicated then an A2W solution and lighter weight at the expense of the performance/very steady IC temps of A2W.

I disabled the water/meth injection this session, that's an additional factor I'll add in when the engine is retuned. That does add back some weight/complexity in the long run.

The car needs a re-alignment, it was a bit darty/tramlining down the main straight, so the rear is probably out of spec.

I'll post vids (if the GoPro behaved) when I can.

Sounds like you had a good day!
Summit is a fast track. Did car and motorcycle track days there a long time ago. Haven't been there with the 818 but did it a couple years ago in the Cayman. End of that long straight really tests your brake setup. We used to say, 6-7-8- you can always go faster.

Session 1: Wet. Spin. Off at turn 1.
https://rumble.com/v6x3436-friday-at...session-1.html

Session 3: Dry. Hitting overboost on front straight and between T9 and T10
https://rumble.com/v6x3890-friday-at...session-3.html

Session 4: Dry. Exploring taking T6 without braking after T5.
https://rumble.com/v6x38wk-friday-at...session-4.html

Hi: I wasn't able to access the videos....I'd love to see them.

Great setup! Thanks for posting

Car is at the shop getting a retune. They discovered that the stock boost controller wasn't managing the turbo wastegate properly, so new EBC installed. Tuning with meth/water (for additional cooling), but the engine threw a coolant hose during the session today, so not done yet.

While the car is at the shop I had them throw it on the scales. The wet weight is 2215. Cross weights are funky, but once I get the engine tuned I'll turn attention to the suspension, so no need to corner balance at this time:
Attachment 217592

As a reminder this is a Coupe:

• Front and Rear glass
• 40 Lbs of steel plate under the driver and passenger seats
• EJ207
• 5 spd
• Water/meth pump
• Caged interior
• Over built wing mount/rear crash structure
• Light battery
• Kirkey Aluminum seats (2x)
• Boyds fuel tank
• iWire harness

I'm OK with the weight as it stands, but know there's room to cut some (a little) additional weight out. Guess I need to go on a diet again.

A little bit of don't ask questions if you don't want to know the answers... but, realistically, my goals are drivability and being able to complete a 20 minute track session without overboosting or overheating. So, I need to remind myself I'm not chasing a number on the dyno sheet, I'm chasing lap time!

The tuner map notes:

Code:

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Redline 7300 rpm
Boost cut 19.5 psi
Boost target 18.5 psi peak
Target AFR 11.0:1
Water/Meth system active

---

Attachment 217647
265 HP @ 6375 RPM
nearly 250 TQ from 3K to 5K.

The turbo is on the smaller side and twin-scroll which I think explains the torque curve; it should definitely be more drivable now. I only took it up and down the road to put it on the trailer last night when I picked it up, but it felt better at low speed in the parking lot - for whatever that's worth.

The old map definitely had a higher boost target set, but the tuner noted at above 7500 it's just pushing hot air (he confirmed the 200* outlet temp). One of the issues the shop found was the OEM boost solenoid was not up to the job, noted boost creep at 0 duty cycle. So that was replaced by a COBB 3 port boost solenoid, now the boost control is solid.

The only other issues during the tuning session were popping off the upper coolant hose at the elbow to corrugated tube joint - which I think we're all quite familiar with, and concerns about the meth consumption. I initially had a 375 mL/min nozzle installed and the tuner was concerned the tank wouldn't last a session. We downsized to a 225 mL/min nozzle - 3.5 gal/hr at 100% duty, which the controller is not set up for. It's progressive - maxing flow at max boost... but track :). Looking forward to scheduling the next track session as soon as I can.

Love the torque curve... As I'm learning to track faster with my R, I'm using the torque more. Staying in a higher gear, letting the boost get me off the corner seems to be yielding better lap times than wringing out a lower gear.

Yea, when I tracked the STI I used to plow it into a corner and then let the AWD pull the front to the apex and then rode the turbo ramp curve to track out, since it was a single scroll there was a delay between WOT and having all the torques. The 818 with the dual scroll is a decidedly different beast with a lot of different technique needed. The car definitely likes trailbraking on the big "whoa-up" events (T1 and T5 on Summit Main).

During a typical lap I only shift a very few times: 4 to 5 on the front straight, 5 to 4 to 3 into T1, 3 .to 4 on short straight into T3, 4 to 3 at T5 and then 3 to 4 between T9 and T10.

Torques are fun.