I've looked into the rules on CSP in the SCCA regarding rear diff gear changes. From what I can tell, I can't change the ratio. Can anyone confirm that who has more SCCA experience then I?

 

4. Transmission/Final Drive
a. Transmission
1. Transmission lubricant may be substituted. Transmission
lubricant additives are unrestricted.
2. An oil catch can is permitted.
3. Any transmission cooler(s) is permitted.
b. Final Drive1. Unless otherwise so noted on the Vehicle’s Specification
Line, the differential ratio shall be as delivered as standard
equipment by the manufacturer.2. All legitimately classified cars in Touring Class are
permitted a limited-slip differential (Quaiffe, Torsen, etc.).
Locked differentials are not allowed.
3. Final Drive lubricant may be substituted. Final Drive lubricant
additives are unrestricted.
4. An oili catch can is permitted.



Nissan
350Z Track/
Touring/
Standard/
Nismo
(03-08)
95.5 x 81.4
3498
104.3 18 x 8.5
(F)
18 x 8.5
(R)
245/40 (max)
(F&R)
3.79, 2.32,
1.62, 1.27,
1.00, 0.79
3.54 (F) 296/324
Vented Disc
(R) 292/332
Vented Disc
3325 Base model and “Rev Up” engines: 50mm flat plate restrictor
required. HR engine: two 40mm flat plate restrictors are required.
Rear differential cover, Nissan Motorsports part #99996-35TDK
is allowed. Nissan heavy duty spring kit part #99996-


all pulled from the scca rule book, you can not change final drive in the t2 class unless the manufaturer made several different types, the rule book only shows the final ratio of 3.54 is allowed to be used. hope that helps. sorry its a mess.

 

What he said^

+ the fact that most courses are kinda "designed" around 2nd gear and you may be hindered on these cars if your gearing is too short. Our second gear is not incredibly tall to begin with.

 

Are you asking about autocross or road racing? The rules scranton posted are for touring class road racing. I think you're asking about autocross, even though the Z is classed in BSP not CSP. I always thought you could change the final drive ratio in SP, but I can't find it in the rules either. Maybe someone else can clarify.

 

I am referring to autocross. In the 2011 rule book, the 350z has been dropped to the C class. The 370z is B class.

 

As per the scca national solo rules 2011 the 350z in all forms is BSP, givin that it does not state anything about differential except athorizing the LSD, if you do change the gears no one is going to go that indepth into the inspection that they would open your diff. Imho i think you would be ok with the final drive. i would call or write the scca and ask them to confirm.

 

found it, you're right... lol BSP, I was looking at street class.. seems strange why they have the the 350z in CS and then BSP. I'm slowly understanding all of this. Can be a bit overwhelming.

 

The gear ratio can only be swapped between OEM gear ratios. The general rule for the Autox ruleset is "if it doesn't say you can, you cannot."

In Street Prepared, there is the update/backdate allowance that allows you to pick and choose OEM parts (with engines, transmissions, and unibodies counted as a single part) from different years and trim levels in addition to the general allowances.

In the SP ruleset, there is no specific allowance for final drive ratios, so you have to choose between the OEM ones (3.3 for Auto and 3.5 for Manual; I don't think the Nismo has a different gear ratio.)

Note that you can change the effective gearing by changing the overall diameter of your wheel/tire combo as well. A base/enthusiast/etc. braking setup can use 17" wheels, so you could potentially reduce the overall diameter of the wheels by 2-3" from stock. However, with a non-HR manual, you likely don't want to mess with the gearing too much, because you want to be able to just hit the top of 2nd in the fastest course you'd likely see.

AFAIK, local courses to me (SE Michigan) rarely get above 60MPH, so with my HR equipped automatic, I plan on switching to the manual rear-end ratio and slightly shorter sidewalls. This should drop the top of 2nd gear from 74 to about 68, which is more appropriate for the courses I'm running.