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Rpm Dropping After A Launch = Bad Launch Or Vacuum Leak ?

cobrAA

By cobrAA,
in Engines & Forced Induction

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cobrAA Mentor

cobrAA

Posted
Posted

Just trying to figured out if my RPM dropping problem is ''normal'' due to having a modded skyline gtr or this could be due to a vacuum leak somewhere.

Basicly what happens is when i lift off the clutch on a stop, the rpm usually wants to drop by about 500 rpms. So I usually end up ''sliding'' the clutch to minimise the rpm drop or else the car might just stall.

The problem is even worst when i try launching at 4-5k. as soon as i lift the clutch, the rpm goes down to like 1.5k. Is this normal or I'm having a problem ?

For reference, I'm running on map with one atmo blitz bov ( i guess this could be my problem ?).

r32-25t Grand Master

r32-25t

Posted
Posted

Yes it's normal

Hold it at 7 and side step the clutch the revs will drop but the car accelerate and the revs will begin to climb again as full traction is retained when it get back to 7 grab 2nd

Unless it really dies away in which case you've bogged it down and need more revs but 7 seems to be the number in most cases

GTRPSI Mentor

GTRPSI

Posted
Posted

So your talking about bogging down on launch?

Yep more RPM.

And a little tip, dont run a lightened flywheel, it makes life worse, heavy flywheels add momentum and push to the driveline to get you out of the hole.

cobrAA Mentor

cobrAA

Posted
  • Author
Posted

So your talking about bogging down on launch?

Yep more RPM.

And a little tip, dont run a lightened flywheel, it makes life worse, heavy flywheels add momentum and push to the driveline to get you out of the hole.

well.. this is already done im afraid.. os giken TS clutch with the flywheel.

And thanks for confirming what I thought lol.. I'm not reving enough. will try next time I go to the dragstrip, I must say tho that I didn't had my 4wd working last time so i wanted to minimise the wheelspin, actually. Maybe I was doing it wrong.

r32-25t Grand Master

r32-25t

Posted
Posted

Exactly throw mechanical sympathy out the window

dial in 7,000rpm,

pull your foot off the clutch as fast as possible and mash the accelerator into the floor and hold on,

when the revs swing back to 7 grab 2nd

MJTru Mentor

MJTru

Posted
Posted (edited)

Kml. This happened to me the first time I launched a gtr. I just got pissed off and tried to kill the thing after a 5k launch didnt work. Thats when I learned that all they like is revs. For me keep it 100rpms under redline or fuel cut. Then pop the clutch and let the bitch rip. For years I tried to beat a gtr with a gtst and never could, but the day I got a good launch in a gtr, I said right away to myself. I need an official drag strip with track bite to beat a grt off the line, and to the 1320 feet mark. Gtrs are truly street kings mate, at least for me.

Edited by MJTru
ido09s Mentor

ido09s

Posted
Posted

Piss the atmo BOV off and it should stop the stalling when coming to a stop. The problem is the AFM is registering a certan ammount of air passing through it and then your dumping it out of the system and screwing up the tune

As for launching, its trial and error

MJTru Mentor

MJTru

Posted
Posted

Piss the atmo BOV off and it should stop the stalling when coming to a stop. The problem is the AFM is registering a certan ammount of air passing through it and then your dumping it out of the system and screwing up the tune

As for launching, its trial and error

I agree. This is a big topic and if ya want the atmo bov the get a ecu that support that type of bov. Like a djetro power fc etc. Otherwise thats whats happening. There are just to much people that dont understand the system. Dont change the system that nissan designed just upgrade it. Vent it back in properly and it will stop dieing.

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