Help I Have Axle hop! - Pontiac GTO Forum
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post #1 of 13 (permalink) Old 03-11-2006, 12:28 PM Thread Starter
 
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Help I Have Axle hop!

Well guys Her is the skinny, I took my 04 got for the first time since getting the car to the track. You all have been here I am sure. I will admit this is my first time with an IRS rear end in a car and I probably need some driving classes with it. but the axle hop was terrible! my 60 ft was bad 2.48 with the rear end jumping around like it was going out of style(street tires) Like I said i kow I am not the only person that has this problem but I am the only one whom hasn't fixed it yet! I need to know if anyone has found some remedy's to eliminate this problem?HELP!!!! So I don't dissapoint GTO lovers everywere! And yes i will be excepting all wise cracks about my driving. Help Please? btw car is bone stock.
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post #2 of 13 (permalink) Old 03-11-2006, 12:36 PM
 
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You're launching with too much RPM. 1700 to 2000 RPM tops. 26 psi in the rear tires, too.

Hope fergyflyer sees this -- as he has the most experience here on the quarter mile in a GTO.
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post #3 of 13 (permalink) Old 03-11-2006, 06:46 PM
 
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We need to know what you're doing to launch the car currently.

I drive an '05 A4 bone stock and have gotten 60' times of 2.0 at a track with very good prep. At a track with crappy prep I get 2.1 60s every time. I am currently launching between 1500 and 2000 RPM with the T/C off.
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post #4 of 13 (permalink) Old 03-11-2006, 08:20 PM Thread Starter
 
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ok when staging I launch about 1700rpm. I really don't warm the tires up in water cause I am running street tires, and we all know heating the tires up isn't a really good idea on street tires it just make them hard but I do spin them enough to clean the junk off of them from the pits. My reaction time are great but 60's suck and the axle hop is terrible too. what exactly you want to know about the start? my trap speed isn't bad even with axle hop and poor 60' my trap speed was 103mph. but my quarter was 14.02. traction control off

Last edited by alptbird; 03-12-2006 at 02:37 PM.
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post #5 of 13 (permalink) Old 03-11-2006, 09:58 PM
 
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I don't know what you're doing wrong then. When I launch at 1700 RPM I get a 60' of 2.1 and a 1/4 mile of 13.4 seconds. If you're getting so much wheel hop that you're getting 14+ second 1/4 mile times then you're doing something very wrong.
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post #6 of 13 (permalink) Old 03-11-2006, 11:30 PM
 
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I saw this and had to save it. I'll be heading to the track soon and I've been trying different techniques. Saw this and gave it a shot. Seems to work fairly well for me. Wheelhop was minimal. I'll find out more when I get to the track.

2005 0-60 times
________________________________________
There seems to be some concern about the 0-60 times on the 2005 GTOs. GM quotes one set of times and the magazines report another, slower result.
From the engineer who runs the test at Milford, here is what he does to produce the 4.6/4.7 second times:

Vehicle prep
Full tank of fuel
Tire pressure checked
Vehicle weighed to ensure baseline

LS2 Manual
Launch at 2200-2500 RPM
Quickly release clutch as accelerator is depressed to WOT
Modulate as necessary (only in first gear)
Power shift to second gear

More Explanation
Launch RPM is higher for the LS2 than the LS1. Launch at 2200-2500, depending on road surface. Once a stable launch RPM is reached, clutch is quickly released and at the same time the accelerator is applied to WOT. This is where the skill comes in. Depending on the road surface grip, it may be feasible to leave the accelerator on the floor and continue with the run, as long as there is is not a great deal of tire slip. Tire slip is a good thing, the tire's coefficient of friction increases with some slip, but too much wheelspin and the coefficient of friction drops off rapidly. If too much slip develops, the vehicle must be "pedaled", this is, the accelerator must be modulated to reduce the engine output but still keep the tires at peak friction. This is the part that takes practice. Depending on surface, it may be necessary to quickly go WOT at the initial launch, then roll off the throttle to 75% pedal and slowly increase pedal, monitoring tire slip. Listening to the engine and tires is key.
When it comes time to shift, continue to hold the accelerator at WOT, apply the clutch, change gear and release the clutch. A powershift is worth about 0.2 seconds over a normal "lift throttle" shift for a 0-60 run.

Wheel Hop
Controlling wheel hop can be difficult. Different tires can cause hop more than others. One way to reduce the chances of getting into hop is to perform the launch as stated above. This quick lauch shocks the tires and produces wheel slip which usually does not go into wheel hop. If the vehicle goes into hop, there are two ways around it. One is to modulate the throttle, reducing engine torque and setting the tire. The other is to apply more throttle, and try to power through the hop.

LS2 Auto Launch
Lightly apply throttle to take out drivetrain lash, but do not exceed 1000 RPMs and do not stall the converter. Release brake as the accelerator is depressed to WOT (depending on surface, it may be necessary to not apply WOT initially, but go quickly to about 75% and roll into the throttle depending on the sound of the engine and tires. Modulate accelerator as necessary (careful not to roll off the throttle too much to cause a 2nd gear upshift).
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post #7 of 13 (permalink) Old 03-12-2006, 02:45 PM Thread Starter
 
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2nd night at the track.

Thanks for the input everyone. if there is more out there i could use it.I track tested some more last night and and made alot of passes. my 60' by the end of the was 2.11 trap at 108mph at 13.89 Is this normal for this car? Friday night I used the same lane over and over again I switched lanes saturday and had more hop on one than the other. so bad track prep? but the axle hop is still there and I just know I am gonna break the half shafts if I keep it up too much. are there any suspention upgrades to help out? what is the most effective?

Last edited by alptbird; 03-12-2006 at 02:47 PM.
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post #8 of 13 (permalink) Old 03-12-2006, 09:05 PM
 
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108 at 13.89? Strange things are afoot at the Circle K.

I've NEVER had a trap speed of over 105 and I've gotten as low as 13.4 seconds. I understand that you're running an '04 and it should be a bit slower, but I never realized that the speed would be that much higher.
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post #9 of 13 (permalink) Old 03-12-2006, 09:28 PM
 
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You'll have to take a look around. From what I've read here and the LS1 site. Drag bags help quite a bit.
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post #10 of 13 (permalink) Old 03-12-2006, 09:55 PM
 
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Wow, I don't know what you guys are talking about. I don't think I've ever experienced wheel hop in my 05. I never take my car to a drag strip. Is the surface that different from plain old asphalt?

If I'm being really aggressive I launch way above 1700 RPM. More like 4000 - 5000.

Lot's of smooth wheelspin in first for an instant and then the tires hook up as you modulate the throttle. Run right up to 6000 and shift to second letting the clutch out very fast while pouring on the throttle. Gets a nice maybe 10 ft chirp out of the tires.

Then run it up to 6000 RPM again and shift to third. Again let the clutch out fast and pour on the power. Get another short chirp out of the tires and well, I usually run out of road at this point.

The only imperfection in the GTO launch is maybe a little wandering of the rear end when the spinning starts in 1st. But, that's easily controlled with steering.

The spinning may not be the ultimate "hook up" but at least I don't beat my car to death with wheel hop and I never have to back out of the throttle to stop the dancing rear end.

Last edited by Wing_Nut; 03-12-2006 at 10:08 PM.
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