Gearing/Tire size issue?

[TT/Ameasap]

Took the TTA to the track last Friday and logged a few runs. This was the first time the car has seen the track since its been built. My rear gearing is 3.54 and im running a 26'' tall tire. I thought I would be ok ...maybe on the the upper side of the RPM range, but I could fix it with taller tires. Well.. Im at 5500 RPM just pass the 1/8 and climbing. My first run, I ran out of RPM at 6k. and shut it down 100ft or more before the finish line. Im not totally convinced a taller (28'') tall tire will get me at 5800 through the traps. Just open for discussion.

 

[BEATAV8]

that precision converter is slipping too much. calculate your slippage using one of the performance calculators.

http://www.tciauto.com/tc/racing-calculators

I bet you are around 18 or 20%. Maybe more.....

 

[TT/Ameasap]

To add some info:
The drop in each gear from 1st to 2nd 750 RPM and 2nd to 3rd is 850 RPM drop.

 

[TT/Ameasap]

that precision converter is slipping too much. calculate your slippage using one of the performance calculators.

http://www.tciauto.com/tc/racing-calculators

I bet you are around 18 or 20%. Maybe more.....

What is the trans ratio so I can load it in on the calculator?

 

[BEATAV8]

1 in third gear

 

[TT/Ameasap]

Roughly 12% slippage

 

[BEATAV8]

that's reasonable, a lot better than I would've thought. still too much, but not devastating.

either way, bigger tire, better converter will get it under control. play with the calculator to see what will work best.

My PTC is "loose" for a PTC, it's at 8%. 5850RPM, 133mph, 3.42 gear / 28" tire.

 

[BEATAV8]

also, expect when you change tire size (larger) it will load the converter more and make it slip more, and when you turn up the boost and make more power it will also load the converter more and make it slip more.

 

[TT/Ameasap]

I think Im gonna start locking it at 95mph through the chip. That should drop the RPM a little.....Im going with a taller tire for sure. Maybe 29''. Seems like the converter is doing well at the low 11 power, but it will see a lot more here shortly. I turned the boost down for the track outing for a baseline. Its going to see 21psi with new slicks. Thats about where Im going to run on the street most of the time.

 

[BEATAV8]

multi disc or single disc?

multi disc will really grab hard, could rip apart a stock input shaft. single disc will continue to slip some, but will add some extra grab.

 

[TT/Ameasap]

Multi disc.
The tranny was built at Jimmy's.. I think stage 2 or something like that. Has billet servo.

 

[BEATAV8]

best to ask him about the input shaft

 

[TT/Ameasap]

I do know that is the best shifting tranny I have ever felt.

 

[TT/Ameasap]

Still debating taller tire or add weight to gov.?
Tranny shift hard in reg. street driving. I hate to play with the TVcable too much, but I might try a couple clicks loose. IDK it shifts at a reasonable rpm while cruising.
Would like to make a 1/4 mile pass at 5800max

 

[BEATAV8]

Vern was getting close to his RPM limit too. Around 5250 through the traps, stock heads and cam. He has a 3.25 gear and 26" tires. 6-7% slippage. We talked about leaning it out some to see if he can get a little more RPM out of it, and maybe manually shifting the 2-3 since it was only around 4900 or so by itself. I think the shift point will be more or less inconsequential to the RPM through the traps. All that will matter there is the tire dia, converter, gear, and power.

 

[TT/Ameasap]

I think 28'' tall tires and locking the converter in 3rd will get me to where I need. Its gonna be close, but I have a line on some 15" wheels with 28's.