High Speed Issues

[gunner93]

Hi All,

Had a go on her last night above 200km/h with my S15 buddies. Some issues came up :

1) Brakes felt like its clamping force is only about 30%-ish. Is it a common Nissan brake servo weakness? It was normal again when the speed dipped below 200km/h.

2) Power Commander injector duty-cycle read 100%. Is there something I should be worried about? I have Walbro 255 & stock injectors. Peak knock reading 16.

3) Car needed refuel after 48 ltrs were used up (Fuel meter needle points a tad below the quarter level). If I dont refuel, car started coughing like theres not sufficient fuel feed.

Anyone has any advise will be much appreciated.

 

[Auss15]

Hi All,

Had a go on her last night above 200km/h with my S15 buddies. Some issues came up :

1) Brakes felt like its clamping force is only about 30%-ish. Is it a common Nissan brake servo weakness? It was normal again when the speed dipped below 200km/h.

2) Power Commander injector duty-cycle read 100%. Is there something I should be worried about? I have Walbro 255 & stock injectors. Peak knock reading 16.

3) Car needed refuel after 48 ltrs were used up (Fuel meter needle points a tad below the quarter level). If I dont refuel, car started coughing like theres not sufficient fuel feed.

Anyone has any advise will be much appreciated.

1) Had you done a fair bit of braking in the spirited drive, fluid might have boiled,stock rubber lines expanding due to heat would give soft peddle
2) If you are doing regular spirited/track work than it would be a good idea to upgrade the injectors/fuel regulator, at 100% the stock injectors are maxing out
3) This is a common problem when doing track work its called fuel surge and a surge tank will stop that. When your fuel gets low it swishes around in your tank with high speed driving and it sucks air instead of fuel.

 

[slammedmind]

generally as a rule of thumb your injectors should be around the 85% mark for saftey, currently i have the same issue but ive lowered my rev limit slightly so that now i run 92% at full tilt. Im still using stock injectors but will be upgrading to 740cc soon for safety.

as for the servo issue im using enless sixpots and have done over 200kmh and had no issues with the servo? Whats the fluid like? When was it last changed and what fluid are you using?

 

[Matt_S]

Id recheck the fitment of the fuel pump. Im hoping that you put the standard 'sock and hose' back on when you fitted the walbro? Otherwise youre gonna miss the lower portin of the tank for fuel :wack:

 

[Kango]

I think you were doing 200leptons not 200km/h.

 

[gunner93]

Here's what I have :

1) Steel braided brake hoses all round with Bosch Dot 4 changed about three months back. I had new 550deg C pads, 0.5 mu coefficient friction spec with skimmed rotors. However my servo master pump remained stock. Could that be the weak link?

2) If I upgrade to 740cc injectors, do I need to retune again? I'm on Power FC btw.

3) When the Walbro was installed, the stock filter element was reused. The Walbro comes with the filter sachet too but its much smaller. How does a fuel surge tank set up in a stock S15? May have to recheck fitment like Matt suggested.

A couple of my friends during wangan got up to 230km/h so I guess mine is not from them. My speedo meter pointed almost 6 o'clock which is why I'm hunting for a ADM meter cluster with 260km/h limit.

 

[ichi-go]

1) If you are using stock brakes, then stock bmc will be sufficient. If you have upgraded, then it's best to upgrade the bmc as well. Z33 bmc will be fine if you are using upgrade 4pot and 2pot rear.

2) Yes you will need a tune again.

3) Your issues seemed to be the walbro. Is it genuine? Couple of friends had problem with their bosch pump as well, which you would need to modify the cradle for the lower portion of the fuel pickup, i would swap gtr fuel pump in and see if the problem goes away.

 

[Nicely]

The Walbro looks virtually identical to the original in shape and size, so its positioning shouldn't be an issue (check my fitting guide and you'll see what I mean).

 

[kazama]

Ichi-go, I don't think it'll be a good idea to swap a gtr fuel pump.
First, it would mean downgrading less than 200lp/h thus a retune (touch up) is required.
second, its older and mean that it might have more chances of failure.
Third, his Walbro is genuine.


P/s. Colin, you should never whack your car kau kau if the needle is below half tank.
I'll never do it in my car, not sure about the other guys here.

 

[gunner93]

Well, I actually had my fuel a tad lower than half level that night. Believe or not the fuel gauge needle than dropped rapidly after some spirited sprints.

On way back at WOT with Sentil, my warning lights started blinking and the car felt like it cant cope. Senthil pulled away from me. :furious:

All your points noted with thanks.

1) Consider upgrade BMP to Z33/R33.

2) According to the injector calculator, I need min 600cc injectors.

3) Walbro pump re-check position/fitment.

 

[silviatub]

Well, I actually had my fuel a tad lower than half level that night. Believe or not the fuel gauge needle than dropped rapidly after some spirited sprints.

On way back at WOT with Sentil, my warning lights started blinking and the car felt like it cant cope. Senthil pulled away from me. :furious:

All your points noted with thanks.

1) Consider upgrade BMP to Z33/R33.

2) According to the injector calculator, I need min 600cc injectors.

3) Walbro pump re-check position/fitment.

Hey Bro,

Once you get the car sorted out, i wont be able to smell your exhaust fumes la...you would have pulled away from me by then...

:thumbs:

 

[gunner93]

Literally thats what I smelt behind you fellas with my window was down. Rich petrol fumes with off throttle popping sound and flashes of flame out of the zorst

 

[kazama]

and not forgetting you guys bullied me by going so far in front till I can't see your lights and we had to call you guys
to ask which exit you guys turned off while I trying my best to keep up in an underpowered bimmer. *cries*