VSS has no bearing on engine RPM, completely independent. Not sure how the Z ECU computes the RPM, it's generally tied into the ignition/crank position sensor. Maybe a bumped harness somewhere?

 

Did i read somewhere about Cruise control being messed up with the gear install? I have the base model, so no cruise control. Just thought i read something about it.

Not sure man, but something is reading different. And all the conections are tight.

Todd

 

Could be a fluke with the utec maybe? The cruise control being messed up is just for the autos, and only seemed to happen on some autos. My cruise is working perfect, no different than stock. I guess I can see it not working on an auto, but the MTX's cruise is based purely off the VSS reading. Maybe latent current on a signal wire somewhere? I know I had that happen on my wideband (constant amount, had to pull .3v out of the formula or so for the voltage to lambda/af translation) on my turbo ZX2.

 

My 3.5 --> 3.3 FD eliminated my CC in 6th gear. After a few seconds it shuts off. Works fine in 5th though. Seems every car is slightly different in how it reacts to the change.

 

Odd I haven't heard of anyone losing CC going from the 3.5 to a 3.7 or 3.9 (or 4.08) with the 6MT. You'd be the first... but you went the other way. I wonder what the difference was?

Still doesn't explain aceman's rpm deviation, given it's completely separate from the tranny/diff. I wish I knew more about the Z ecu lol

 

It is odd

But i was able to compensate for it

So, all is good now.

Since you have the gears, do you notice any difference in your redline? I know its tough to see with out logs. I thought there was a difference, but i needed the logs to verify it.

Next time you out driving around see if you notice it hitting the rev at say 7300rpm or not.

let me know
Todd

 

The redline actually hitting slightly earlier than set on the UTEC is a known thing. Todd-any way you could have possibly set it at 7200rpm's but never truly taken it there-maybe shifted at 7000rpm's? I need to buy another serial-usb adapter, I lost mine and cant get into my UTEC at the moment. Im setting my real rev limit at 7500rpm's so I can stay in 4th through the traps in high boost. 7200rpm limiter FTFL

 

Yeah I've watched it. Still smacks the rev limit where it used to. I have no problem getting to 113mph in 4th by the digital speedo and still haven't smacked the rev limit. 5th gets to 145mph, no problem. And based on my gearing calc for my 275/40/18 tires 4th gets to 114 and 5th gets to 145.

 

7500rpm HR redline with my tires let me get to 132 in 4th on the stock 3.5 fd

 

Well guess what... Your correct

I just went back through maybe 15 logs, and in everyone it hit around 7000rpm... Well hmmmp... I did not know that this was a known thing.

So, the gears did not change anything. its a issue with the UTEC

Well, its set correctly now.

Your going to rev to 7500rpm Bert? I did not think the stock springs and valves could handle that? I know you have a built bottom end, so you dont have to worrie about the rod bolts.

Interesting

Todd

 

I do 134mph with 3.3FD and 7200 rpm's! Imagine what 7500 rpm's will do I need a plenum that works (maybe Cosworth?) so I can make power past 7000rpm's and shift at 8000...

Todd-sorry I shoulda mentioned that earlier lol. BTW-stock valve springs/retainers on that blue Z at our track day, 600whp revving to 7500rpm's with no issues. Id set yours off at 7300rpm's (actual) for "safety", a shift from 1-2 @ 7300rpm's NA is AWESOME and helps times a lot since you can shift fast.

I run JWT valvetrain/retainers so Im good to zing it up there...

 

7500 rpm is about 141 based on my tire size

 

lol, glad you sorted it aceman. That was why I asked if you had logged rev-limit hits in the past. It wasn't a known issue by me either, but one I just ran into and resolved earlier this week. At least now it is confirmed for me that this is a common utec issue and not some wierdness with my unit.

 

I have read about people with exactly that problem.

Apparently the CC determines whether to activate by comparing the speed calculated from the wheels with the speed calculated from the transmission. If there is too big a delta, the CC aborts and quits. Changing the final drive changes the relationship of the transmission and FD speeds... thus messing up the CC sometimes. I also believe the CC stops functioning above 90 miles per hour. That's why it stops working in some gears... it thinks it's going too fast. I don't know if the UpRev guys could fix this in a flash or not, but you can monitor all the CC events with Cipher. I did that to help test a brake boost module for a friend.

I have links to some of this information by a Nissan Tech. If you are really interested, I can look i up and post a link.

I'm also planning to go the 4.08 route. I've been trying to decide between a 3.91 and a 4.08 and finally decided on the 4.08 because of all the reasons you stated and also because my G35 Coupe is even heavier than your Z's.

 

Does the Z have speed sensors on the wheels (yeah, there are the ABS sensors..) ? I could be wrong, but generally the vehicle speed is calculated primarily from the VSS in the trans. I don't think I've ever turned on cruise over 90, but I guess I could try it to satisfy our curiosity. I've cruised at speeds of 80+ without any problem and used my cruise to pass people on the highway instead of using my foot heh.

I would be curious to see it...

Good choice.