Jump to content
SAU Community

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

cobrAA

By cobrAA,
in Engines & Forced Induction

 Share

Recommended Posts

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.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share
Go to topic listing


  • Similar Content

  • Latest Posts

    • joshuaho96
      Troubleshooting - motor wont turn over

      By joshuaho96 · Posted

      I have seen a case where the starter motor shorting against the casing caused a massive voltage drop + so much EMI that it caused all the sensors to spew garbage data at the ECU. Test the battery to make sure it has acceptable CCA/capacity first, I have gotten "brand new" batteries before that couldn't even power a 10W light bulb without dying probably because it sat in a warehouse too long without being charged. Only easy way to diagnose this 100% is put an oscilloscope on the battery and also look at key sensors to see if there's any clues.
    • joshuaho96
      Baron's R34 GT-R build thread - car in Japan for 5 years -_-

      By joshuaho96 · Posted

      There's a bunch of smaller shops that don't quite attract Singer money but are still hiring from that same pool of labor. Those are the body shops that you go to when you can't afford a Singer, but your old Porsche needs some serious bodywork. You can't exactly take those cars to the usual insurance body shops. When I say restomod, I mean they'll do something other than 100% OEM/OEM-equivalent aftermarket parts R&R. In the Porsche world this would be stuff like taking a 50k 964, doing a bunch of deferred maintenance/unwinding the nightmares the previous owners did to the car because a lot of people that own these cars tended to be penny wise, pound foolish types, then maybe some relatively simple off the shelf modifications to things like suspension, transmission, engine, headlights, etc. and you've spent 130k USD. When even the worst houses in the poor neighborhoods are worth 1M USD and the nice houses in wealthy neighborhoods are worth 3-10M USD suddenly 130k spent on a 50k car seems cheap.
    • Murray_Calavera
      Troubleshooting - motor wont turn over

      By Murray_Calavera · Posted

      Hoping to get a few ideas to help troubleshoot this issue, I'll try to keep it short.  A mate popped the motor in his 2018 LDV T60 with the 2.8 turbo diesel motor. He swapped it and I was his phone a friend when he got stuck.  The new motor is in, however it won't fire. The battery is literally brand new, when you crank it the volts very quickly (say 2 seconds of cranking) drop to 8 volts and the engine stops turning over. Watching the belts, I'd say they move about 5cm before coming to a stop. We put a booster pack on, no change.  The only potential issue I'm aware of is, when we pulled the motor the grounding strap was still attached. The strap copped a thrashing before we realised what was going on. It looks okay-ish but it's going to be replaced to rule it out.  The main challenge is, I wasn't there for 90% of the work. This is his first time doing any major work on a car and he was learning as he was going. He thinks everything has been put back together properly, however I'm not entirely confident that this is the case.  It would be good to get some ideas about what else to check. The car isn't spitting any codes so that doesn't help.  I've attached a photo, because why not lol.   
    • funkymonkey
      Did anyone here buy the crashed N1 R32 GTR at auction?

      By funkymonkey · Posted

      I mean an N1 came with a minimal paint thickness compared to dealer models. It’s probably had a ton of vinyls and stuff possible a race paintjob or two over the years. you don’t buy an N1 for its stunning good looks or comfort 🤣 you buy it to send it and measure how much air you can get on the hill at Bathurst
    • GTSBoy
      Baron's R34 GT-R build thread - car in Japan for 5 years -_-

      By GTSBoy · Posted

      Yeah, but "restomod" implies Singer and things like it, which implies drug money / trust fund maturity.
×
×
  • Create New...