A question for the drag racers

[Poppacapp]

Hey all,

I took my car to a track yesterday, and it was hooking up pretty good... they VHT'd the hell out of the track. I got a personal best but not good enough as I am having the dreaded 1-2 grind issue.

On to the question:

One of my runs, I launched the car hard, and after leaving the line, the car nose dived like it was cutting fuel or traction control kicked in etc.. then I shifted into 2nd and when the car picked up again, it nosedived and fuel cut.

I had traction control completely off(held for 6-8 seconds or however long you need to).
I am wondering if I somehow starved the fuel pump with a hard launch? My fuel level on the gauge was between 1/4 and 1/2 tank.. so I assumed it had enough fuel. But maybe the gauge is not 100% accurate?

Either way, I was curious if anyone else has run into this issue and if it was fuel level related. That is the first time the car has done that. I will try to make sure the car has full tank of fuel next time at the track also.

Thanks in advance for any info

 

[KidMoney]

Who's tune? Did it do it every time? We were having issues with this same thing but it has gotten better on its own. I've heard it is a torque management issue.

 

[_mach_]

I just installed a tri-ax with hopes it fixes my 1-2 grind. So far, on the street, I've been able to hit second hard without grind. Good luck with your problem, I'll report back as to how much the tri-ax helps.

 

[white88lx]

depending on how you were launching and shifting it may have been the rev-limiter?:shrug: Sometimes when you launch you may not know it but hit the rev limiter right before dumping the clutch will cause the drop in power and same thing while shifting

 

[VNMOUS1]

Certainly COULD be starvation if you were at 1/4 tank. I run 3/8 of a tank as my base weight config with no issues.

Banging the limiter sounds more likely.

BJ McCarty
R&D Specialist
VMP Tuning
[email protected]
(321) 206-9369 x 112

 

[GT500RedStripe]

I lose fuel full-throttle shifting if I am not over 1/4 tank. A fuel tank will just slow you down.

 

[Poppacapp]

Who's tune? Did it do it every time? We were having issues with this same thing but it has gotten better on its own. I've heard it is a torque management issue.

Dan with Pro Dyno tuned the car. That run was the one and only time it has done it. That particular run the track guy sprayed vht on my lane and i launched hard at 4000rpm. The car dead hooked with zero spin.

I just installed a tri-ax with hopes it fixes my 1-2 grind. So far, on the street, I've been able to hit second hard without grind. Good luck with your problem, I'll report back as to how much the tri-ax helps.

I have the mgw...but usually dont have a problem shifting on the street either.. but i dont do dead stop launches. Usually rolling first..car spins and hit second ok

depending on how you were launching and shifting it may have been the rev-limiter?:shrug: Sometimes when you launch you may not know it but hit the rev limiter right before dumping the clutch will cause the drop in power and same thing while shifting

Left at 4000 that run. Very hard launch on my drag radials.

Certainly COULD be starvation if you were at 1/4 tank. I run 3/8 of a tank as my base weight config with no issues.

Banging the limiter sounds more likely.

BJ McCarty
R&D Specialist
VMP Tuning
[email protected]
(321) 206-9369 x 112

Well i didnt hitbthe rev limiter when it nosedived. And when i hit 2nd gear it was nowhere near redline when it did it again. It hooked very hard in 2nd too. I guess thats why i was thinking fuel.. but like you, i was at approx 3/8 tank. Unless my gauge is off. Its wierd.. ran once after that leaving at 5000rpm because of how hard it hooked the previous run..broke traction and spun all of first bouncing off rev limiter..but it did not cut fuel. The best way to describe it is like when traction control kicks in and you lose all power at the motor..even with pedal floored.

I lose fuel full-throttle shifting if I am not over 1/4 tank. A fuel tank will just slow you down.

Yeah trying to figure out a good track fuel level. I think i will try to stay a little over half next time..and will try to have my laptop to datalog and see what happens if it does it again.

Thanks for the replies everyone.. i am hoping it was just a fluke . That particular run hooked so hard it felt like the front wheels wanted to come up. I guess them spraying vht in my tracks before the run had something to do with it.

 

[KidMoney]

It's not a fluke. I can tell you that from experience. It still happens from time to time in my car. It only happens when the car hooks as well. Never when it spins. But it has been happening less lately. It didn't happen at all this Saturday.

 

[2011 gtcs]

Do you have a wide band to make sure your not running lean.

 

[Poppacapp]

Do you have a wide band to make sure your not running lean.

Yes..my car came with a wideband from factory..although i was not monitoring it on the runs. No a/f gauge yet. Out of three runs that day the first and third were fine. Second run hard launch it did it.

 

[Poppacapp]

Here is a video of the run... you can see the car just die down and come back alive.. like fuel was cut out and came back..sort of like traction control does. Wasn't hitting rev limiter.

[youtube_browser]dl4ZAYZCAyA[/youtube_browser]

 

[heatsoaked12]

My car has done the same thing with all the nannys off as well. I believe its your clutch protection(can not be turned off) Your clutch has a switch at both ends of travel (when fully depressed and fully released). I believe if your computer detects an improper speed difference between input and output of your tranny when your clutch is fully engaged (all the way up)then power is cut . seeing as you where hooking so well there may have been some slippage detected. Is your clutch original? many miles? something for thought.

 

[Poppacapp]

My car has done the same thing with all the nannys off as well. I believe its your clutch protection(can not be turned off) Your clutch has a switch at both ends of travel (when fully depressed and fully released). I believe if your computer detects an improper speed difference between input and output of your tranny when your clutch is fully engaged (all the way up)then power is cut . seeing as you where hooking so well there may have been some slippage detected. Is your clutch original? many miles? something for thought.

Imteresting. I have not heard of that issue. Clutch is original factory unit with almost 24k miles on it. That particular launch was a good hook and harder(from inside the car) than any others I have done. But I wonder how these guys with McLeod clutches and slicks are launching harder and not having an issue? Would it just be a factory clutch issue? Thanks for the additional info.. I will google what info I can on the clutch protection.

 

[kleen93gt]

My 2010 did the same thing all last season. Would cut out really bad when it hooked, but wouldn't at all when it spun.... I took my car to Sylvain at billetproshop last October for a tvs port, fuel system upgrades, 72mm tb/127 intake, and a mcleoud rxt clutch. It was tuned by Dennis Gomes from Tasca after all the mods. When I took the car to the track after all the work was done the issue was totally gone! Not 100% sure if it was a clutch related issue, or tune issue... It launches/runs perfect now!!!

1st 2 vids is when it had the issue.

2nd 2 is after the clutch/tune..

http://youtu.be/_ixVz0lcjp0

2010 TVS GT500 11.1@129 in car - YouTube


In car of my 2010 GT500 running a [email protected] - YouTube


Pauls 10.59 Pass 4th Of July Out The Tailpipes Rd 2 - YouTube

 

[Ninjak]

Imteresting. I have not heard of that issue. Clutch is original factory unit with almost 24k miles on it. That particular launch was a good hook and harder(from inside the car) than any others I have done. But I wonder how these guys with McLeod clutches and slicks are launching harder and not having an issue? Would it just be a factory clutch issue? Thanks for the additional info.. I will google what info I can on the clutch protection.

I have not been back to the track yet with my RXT, but I to had this issue as I kept going to the track. I notice it got worst as I kept going out, and in the end, my clutch was going bad.

I have not ran officially on the RXT, but a few launches on the street, and the bog seems gone. It could be the clutch protection people talk about, so I would not rule it out. A friends 10 GT500 did the same and his clutch was gone well.

I have 9600 on my clutch when I replaced it.

 

[Stopsign32v]

I believe 150% your next mod needs to be a clutch.

Also a thing to note guys is after this run there was a very strong clutch smell back in the lanes from the GT500.

 

[kleen93gt]

Mine had a strong clutch smell too!!!

 

[BilletProShop]

clutch slip is suspected

 

[Ninjak]

ditto on clutch smell

 

[Poppacapp]

My 2010 did the same thing all last season. Would cut out really bad when it hooked, but wouldn't at all when it spun.... I took my car to Sylvain at billetproshop last October for a tvs port, fuel system upgrades, 72mm tb/127 intake, and a mcleoud rxt clutch. It was tuned by Dennis Gomes from Tasca after all the mods. When I took the car to the track after all the work was done the issue was totally gone! Not 100% sure if it was a clutch related issue, or tune issue... It launches/runs perfect now!!!

1st 2 vids is when it had the issue.

2nd 2 is after the clutch/tune..

2010 gt500 - YouTube

2010 TVS GT500 11.1@129 in car - YouTube


In car of my 2010 GT500 running a [email protected] - YouTube


Pauls 10.59 Pass 4th Of July Out The Tailpipes Rd 2 - YouTube

Your first run is exactly what mine did... So the clutch protection can be modified I assume? But the RXT wouldn't be slipping so I would think that's why the issue disappeared. Sweet running car btw. :beer: