Engine cutting power after hard cornering...

[CSG Mike]

I didn't get much of a response in the "engine" subforum, so I figured I'd repost this here where it's probably a much more relevant topic.

We experienced a power cut after "Lost Hill" at Buttonwillow last weekend.

Here are the circumstances:
- As always, all electronic aids are off.
- Power cut only happens when we are going for a fast lap, and "jumping" the berm at the top of the turn; the car is momentarily catching air here.
- Fuel was at 75% full
- Does not happen ANYWHERE else on track, even on other turns where catching air is requisite for a fast lap.
- Power cut occurs a few moments AFTER the turn.

You can clearly hear in the video that it sounds different from the power cut you hit when you hit the rev limiter. That cut is a complete shutdown on power, while this one is more of a machine gun sound like hitting a fuel cut.

Video:

[ame="http://www.youtube.com/watch?v=NYHG_nArnGo"]BRZ cutting power after a corner... - YouTube[/ame]

[LSV8]

need dry sump

[7thgear]

maybe the sudden vertical transition (airborne) is messing with the fuel sensors, i'd send Toyota an email.

[celica73]

Well, I get nothing out of the video, but it would seem that in your case, the fully defeatable traction/stability control isn't fully defeated.

I was just reading about someone in a Mini Cooper that is having similar power loss issues when a back tire gets picked up under braking. If he doesn't get all the way off the throttle and back on it, power stays down (ice mode?)

Are you a left foot braker? If so, how close to the brake is that left foot when you crest the hill?

[dsgerbc]

Originally Posted by 7thgear

maybe the sudden vertical transition (airborne) is messing with the fuel sensors, i'd send Toyota an email.

Over-reactive rollover valve/sensor maybe?

[CSG Mike]

Originally Posted by celica73

Well, I get nothing out of the video, but it would seem that in your case, the fully defeatable traction/stability control isn't fully defeated.

I was just reading about someone in a Mini Cooper that is having similar power loss issues when a back tire gets picked up under braking. If he doesn't get all the way off the throttle and back on it, power stays down (ice mode?)

Are you a left foot braker? If so, how close to the brake is that left foot when you crest the hill?

I don't left foot brake for this turn... :p

The strange part is that this doesn't happen for any other turns where I get a decent amount of time on two wheels...

Originally Posted by 7thgear

maybe the sudden vertical transition (airborne) is messing with the fuel sensors, i'd send Toyota an email.

There are two other turns at this track where you get a "significant" amount of air (enough for for photographers to get pictures of cars on two wheels), and I don't get the power cut on either of those, even with fuel as low as 1/8 of a tank.

Originally Posted by LSV8

need dry sump

We've speculated that perhaps there's a large dip in oil pressure, but unfortunately we don't have any data acquisition in the car... yet.

[Element Tuning]

It's fuel starvation and I've been experiencing it when there is a long left to right transition. To the people that haven't experienced it, I say you're not going fast enough It's a problem with the saddle tank setup and siphon system. I only get it at one track with high gas levels so it's not a problem everywhere.

[philstar]

Originally Posted by Element Tuning

It's fuel starvation and I've been experiencing it when there is a long left to right transition. To the people that haven't experienced it, I say you're not going fast enough It's a problem with the saddle tank setup and siphon system. I only get it at one track with high gas levels so it's not a problem everywhere.

I swear I had the same problem but I wasn't sure while at a local drift event. Did you mean with high gas levels? or do you mean low gas levels?

[gmookher]

yeah how much fuel was in the tank?

[Element Tuning]

High gas level means even if I have a 1/2 tank at session end I can experience the fuel starvation. At lower levels fuel starvation can occur in more places. It just depends on the track really with what gas level you can get away with.

Button Willow has two places that can cause fuel starvation. It's been awhile since I raced there but on 13 cw the left/right drop at 4-5 cotton corner low on gas and with high gas levels the long left sweeper 8 and then the sharp right drop at 9 lost hill.

It has nothing to do with the elevation drop its the siphon on the driver's side sucking air and not filling the surge tank on the passenger side which houses the fuel pump.

[cobrabyte]

I used to get fuel starvation on my Elise in long, sweeping curves. Fuel pump was on one side of the tank and the tank wasn't baffled. Sounds like the same symptoms you're having.

[CSG Mike]

Just to clarify, in the video posted in the OP, the car had over 75% full in the tank.

[CSG Mike]

Originally Posted by Element Tuning

It's fuel starvation and I've been experiencing it when there is a long left to right transition. To the people that haven't experienced it, I say you're not going fast enough It's a problem with the saddle tank setup and siphon system. I only get it at one track with high gas levels so it's not a problem everywhere.

I'm experiencing it at Turn #13 on this diagram. The BRZ is WOT through 9, 10, slight lift on entry for 11 (to accommodate understeer), and WOT through 12 to the braking zone for 13. The fuel cut ONLY happens if we take #13 very aggressively and get a good amount of air from jumping the berm at the apex of #13.

Speeds are ~78 at apex of 9, ~97 on exit of 11, and on the limiter of 4th entering 13 (~107).

Thoughts? Your input is greatly appreciated! I'm glad someone finally thinks I'm not on crack :p

[Element Tuning]

Originally Posted by CSG Mike

I'm experiencing it at Turn #13 on this diagram. The BRZ is WOT through 9, 10, slight lift on entry for 11 (to accommodate understeer), and WOT through 12 to the braking zone for 13. The fuel cut ONLY happens if we take #13 very aggressively and get a good amount of air from jumping the berm at the apex of #13.

Speeds are ~78 at apex of 9, ~97 on exit of 11, and on the limiter of 4th entering 13 (~107).

Thoughts? Your input is greatly appreciated! I'm glad someone finally thinks I'm not on crack :p

Yeah your problem is really 12 as that long hard left starves the siphon so your surge tank isn't being filled. The reason you feel it is because it takes time for the surge tank to empty....you're running what's left in there. The siphon just can't fill the surge back up fast enough by the time you hit 12.

The fix we do on the Subaru Impreza is to replace the siphon side of the tank with a fuel pump. This way you will keep the surge tank full much more aggressively.

The popping sound is the engine running lean and misfiring. You may need to be full at Button Willow. Next time start full and follow uo with us.