4.08 Gears @ VIR and CMP?

AntiVenom

I am building my car with the purpose of being a weekend/track/autoX car. Nothing serious in terms of competition, just like getting out there and having some legal fun.

Eventually the car will have all the bolt on mods, including ported intakes/TBs. Before those go on I am going to put a Wavetrac in the rear and figured it would be the opportune time to throw some shorter gears in at the same time. My motive is a little more pep around town, not drag strip (although I won't say 100% it will never make a 1/4 mile run)

With that, I started to do some research around gears. In a couple of threads the concern of whether or not 4.08 gears would be favorable for track use was brought up. With the general idea being that it might be favorable for some and not others.

Long story short, I would primarily be going to VIR and some CMP since I live in Raleigh, NC. Anyone have specific experience with 4.08 gears on either of these tracks and whether or not they are agreeable with the track layouts, or do you wind up out of gear or shifting too often?

Input on 3.9s would be welcome as well.

Thanks!

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jchammond

4.08:1 with stock diameter tires (26.7") would put you right near 115mph @ redline in 4th,,,,pretty good selection for a non-forced induction car...

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jchammond

That's if you have a 6speed manual.

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AntiVenom

Thx for the response. It is indeed a 6MT

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GSS138

3.9 I think is more for the auto trans than manual. I am completely happy with the 4.08 setup on all the tracks I have done on the west coast. IMO it should be part of a "track package" option or something on our car. The row more argument seems to be null and void, if anything I row less because I don't use second on the few spots that I used to. The car though is all around quicker and more fun to drive.

Just be aware that syncro rev will shut off if you redline, it can be dangerous, you need to disable it before your session if you are currently using it. Syncro will work fine though on DD. ECUTEK has a fix for it.

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jchammond

The 3.90:1 diff would be good for about 120@redline,,,+5mph over the 4.08 in 4th gear.

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jchammond

LoL,,,i got an open diff w/3.36:1 gears & look @ my qtr. time & speed.
my 4th is good for about 125.

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AntiVenom

Driving the @#$% out of that open diff.

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AntiVenom

Yea the ECUTEK Phase 2 ROM is what got me excited about changing gears. I would like the option to track with and without SRM as the car gods intended.

There is a part of me that thinks 3.9s is the wise compromise choice, but the 4.08s sound like more fun.

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jchammond

Just go with 4.36:1,,,,i think that's the lowest?

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jchammond

107mph in 4th, 136/5th(1:1)@ redline

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Mike

CMP it would be great with. VIR has 140+ mph straights though. The time to make the extra shift up a gear might negate any gains. I know at Daytona on the banking watching my harrys lap videos, I was losing 3-4 mph on the 5-6 shift.

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AntiVenom

Yea this was my concern about VIR. I've only ever tracked it in my LS1 FD RX7. Which while it had 4.10s as the FD, the trans gear ratios are much longer on the t56. So winding 4th out on the straights is all you needed to do. I digress...

Let me throw the following at you and get your input: Like you said VIR has a couple of long 140+ straights. The theoretical shift point at redline for the stock gears, running a 305/30r19|26.2" diam. tire in the back, is 125mph. Whereas with the 4.08s it's 113mph. Either way you are going to see a upshift somewhere in there. That earlier shift to 5ths 1:1 ratio would cost me some mphs by the end of the straight, correct? Which obviously is unfavorable. However, would there be any gains in the rest of the course? Also, would the loss in speed at the end of the straight, in theory, allow me to brake a little later. offsetting some of the loss in time on the straight. I only have a few track days under my belt so I am still green overall and 100% newb in the 370z. So forgive me if that last question is completely absurd.

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Read T

Agreed - CMP it would be good but VIR you might not want to go to 4.08.

For what it's worth I felt the stock gearing is pretty good at both tracks.

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AntiVenom

That's two votes against 4.08s at VIR. Since that would be my favored track I will prob stick with the stock gears and use the money towards something else (like a SC, hahah, jk, mostly...)

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