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Discussion Starter #1
I recently supercharged my car making 352whp/290wtq @ 11psi. I know the transmission is a weak point, so I'm looking in getting it rebuilt. I do plan on rebuilding the bottom end in the future to eventually attempt to push close to 500whp. I don't mind going all out and rebuilding the whole transmission, but didn't want to buy and install parts that aren't needed.

Here are a few questions I had:

Are stronger 1 and 2 gear necessary and just rebuild 3 and 4 or should I go ahead and install stronger and longer 1-4 gears?

Which LSD should I go with: OEM or MFactory or Wavetrac? Can the OEM unit handle increase in power? Should I stick with OEM?

Stick with OEM 4.7 FD or should I change it to either 4.38 or 4.058?
 

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Man I was just thinking I need to do the math on what gears/final drive I want! I'm around 380 WHP, keeping boost at 10PSI until I get gears and radiator upgrade.

4th gear is the only gear I've heard of going out around the power numbers you mentioned. I'm sure you've noticed that longer 1-4th gears would benefit massively on street tires. 1st and 2nd gears are very difficult to modulate power, by 3rd gear I can be full throttle on a warm dry day with good tires, but my all seasons turn to smoke in 3rd. At 500 HP I suspect this would be much worse.

I'm curious about the final drive, I've not done the math yet, but I think I would not be happy with just gears.

I've not heard of any stock LSD failures, if it was a weak point I believe I would have read someone breaking one (I've read alot of 4th gear failures). I'm happy with the stock LSD, I believe the aftermarket ones are done by alot of people who track their car, as the stock limited slip can cause understeer when on power in mid corner.

Off topic, do you have any plans for heat management? After ripping on my car in 90F weather, it gets incredibly hot under the hood. I've got a couple ideas on how to help it, but looking at all options.
 

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Doing the math, Gear X gears, assuming rev limit at 7200rpm. My tires are slightly TALLER, which is factored in.



Stock. Aftermarket. +4.38 FD

1st 34mph. 49mph. 53mph

2nd 56mph. 69mph. 75mph

3rd. 78mph. 87mph. 95mph

4th. 106mph. 105mph. 114mph

5th. 137mph. 118mph. 129mph

6th 176mph. 133mph. 145mph

Stock 6th with 4.38F.D. is 191mph



In the 1/4 I ran 108mph with pretty bad 60fts, so if I do 1-4 gears and 4.38 final drive, I'd get a better launch I believe, and keep from shifting to 5th right before the finish line. These I think would get me into the 12s on street tires. I don't know anything about drag racing, but my best run was 12.4. Either way, I'm not going to change the final drive now.



One thing for sure, getting a 1-6th set for a boosted car is pointless. Would kill MPG.
 

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Discussion Starter #4
As for heat management, I do plan on getting an upgraded radiator and a carbon fiber hood with vents. My engine bay doesn't get hot really. The supercharger is cool to touch even after spirited driving (granted I haven't had this car on a hot summer day or even at the track).

I was looking at the taller 1-4 GearX gears and I believe the k20z3 5th and 6th (GearDriven website). They give numerous options. I'm trying to price out the best combo. Really looking in purchasing the transmission here soon.
 

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I've not seen the ratios for the 8th gen, why change the 5th and 6th to a 8th gen? I'll have to look at gear driven, hadn't seen what's out there last gearx gears.
 

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Discussion Starter #6
I've not seen the ratios for the 8th gen, why change the 5th and 6th to a 8th gen? I'll have to look at gear driven, hadn't seen what's out there last gearx gears.
I'm not sure..... but that's what was on their site. I calculated the MPH for each gear with their setup with a 4.7 FD and a redline set at 7500:

1st - 49mph
2nd - 69mph
3rd - 88mph
4th - 106mph
5th - 125mph
6th - 156mph
 

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Discussion Starter #8
I'm still contemplating if I need to go with a lower FD if I'm going to eventually push in the upper 400whp to lower 500whp range.
 
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