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Discussion Starter #1
I have a big tire 4 link nitrous car. 2950 lbs, 16x32-15s MT tires. 4 link 52.5" X 5.75" conventional head 588 BBC plus 2 foggers. 300TB and 300 at .4 seconds. gears 4.56 with a 1.80 PG. The car has been [email protected] I have been fighting tire shake all year. It shakes at the gear change. Do you have any suggestion on how to stop the shake? Here is a racepak graph from last night. I had to pedal it. Thanks
 

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^^^THIS^^^ Most guys will tickle a degree or two of gear retard at the shift, then put it back in.

Also, how much rpm drop is there at the gear change?
 

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Discussion Starter #4
^^^THIS^^^ Most guys will tickle a degree or two of gear retard at the shift, then put it back in.

Also, how much rpm drop is there at the gear change?
Just under 1100
 

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Discussion Starter #5
I have the MSD 7531 box. How do I pull timing at the shift and ramp it back in?
 

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I have the MSD 7531 box. How do I pull timing at the shift and ramp it back in?
Gear retard. You can make a dot map dropping it out and putting it back in.

And IMO, especially if this is an 1/8 mile car, that 1100 rpm drop may be a tiny bit aggressive for it. Maybe bump up the nitrous, and/or have the converter altered a little. Just make sure you send them some good data to read.

Like I said, just my opinion.
 

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Can't see a graph...is the drive shaft rpm spiking at the 1-2 or does it flatten out/drop....sound like it's falling off the tire either from lack of power ( shouldn't be an issue) or slippage in the trans/converter....
 

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Discussion Starter #8
Can't see a graph...is the drive shaft rpm spiking at the 1-2 or does it flatten out/drop....sound like it's falling off the tire either from lack of power ( shouldn't be an issue) or slippage in the trans/converter....
The drive shaft graph in the picture I posted was arching up to the shift point. It went into shake exactly at the shift. The previous run it spiked or spun the tire at the shift and then quivered the tire. The engine/drive shaft ratio right before the shift was 1.84 it was 1.07 at the 1/8th. This is an 1/8th heads up car.
 

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loosen that converter up to drop about 800 rpm at the shift. 1100 is lugging it a little too much. this may not solve all of your problem tho. go with pulling out some time then.
 

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Also, I would think that if you knock some timing out on the shift, your converter will have a larger rpm drop on the shift because it will be making less power. Might have to address both at the same time.
 

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Mark, graph came up for me finally...If that was my car I would short shift it at 7400-7600 rpm. The first portion of the rpm graph looks good until it lays over at 7600 ish rpm. I would guess the g meter lays down as well in that area. My opinion is that the tire is flattening out in first before the gear change, shifts, then knocks the tire off.......Easy to check, short shift it and see if it picks up.....
 

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Discussion Starter #12
Thank you I will try short shifting to see what happens. I will also contact my converter guy with the information that has been gathered so far.
 

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Discussion Starter #14
On the dyno naturally aspirated it made peak HP at 7800. 7800 is where I have programmed the shift. The racepak shows 7860 to 7890 before rpm changes direction.
 

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Shift lower with the nitrous it will run faster, the valves open longer with the lower shift, plus nitrous is all torque lower it 400 then -200 then -200 and so on see where it runs the fastest
 

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Discussion Starter #16
Does anyone think I have too much drive shaft speed at the hit?
 
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