04 AT G35 sedan... is there any negative to running 3.7 FD gearing with an open differential?... I realize that as long as I'm there I should have LSD installed (and if I do I have decided on Quaife)... I am on the fence about the LSD but am very much interested in 3.7 FD

Is there any reason not to run 3.7 with open differential?

 

Same reasons not to run an open differential with the stock FD. I would suggest looking into doing LSD at the same time just for good measure. Hell, I would opt for a LSD long before the FD, but that's just me.

 

running open Diff is the worst thing you could do.........

 

Hmmm, that's odd... I've read boatloads of threads on a half dozen websites and have seen countless posts about the 3.5, 3.9 and now recently 3.7 FD Wow factor... I haven't seen nearly the amount "bang for the buck" responses from LSD.

Don’t get me wrong, please... I'm not asking which one I should do or which one is better... I'm simply asking is there a drawback of any kind by running 3.7 with an open differential.

I realize getting an LSD is a good idea - and maybe I will... but again, the question: Is there any reason not to run 3.7 with open differential. If there is, please explain.

Thanks in advance.

 

Why would you go with the 3.7 and not the 3.9?
I would go with both LSD and FD at the same time.


You don't see many of the 'wow' factor threads with the LSD's because most people installing the FD already have lsd.

Also, think about it. If you are putting your power down faster with the new FD gearing, why wouldn't you want to put that to the ground, instead of losing it to spin at the path of least resistance?

You could get a turbo and up your power to 500whp, but if you can't put that power to the ground, it's useless.

 

Wouldn't the 3.7 be a better choice for AT coming from 3.3? Just curious.


To the OP, get the LSD, no question.

 

yes, coming from AT 3.3... 3.7 is the choice I've made... (not interested in 3.9) - would have gone 3.5 but only recently did I even find that 3.7 is an option...

I understand the point of putting the power to ground... and that's precisely why I started this thread... I am concerned about the open differently not allowing full use of TQ from the 3.7 gears... Fluid1 can you elaborate on the negative effect – this is almost exclusively a street driven vehicle with only occasional track use… do you feel primarily in cornering I might have a problem?…

In response the fact that I don’t see a lot of” wow” factor from LSD compared to gears – Many of the threads I’ve read people are doing LSD without FD and the “wow” isn’t as dramatic as I’ve seen the FD reports… All that do LSD are not doing FD. However what I think you are saying is that most that do FD have LSD – which is why I bring this topic… to see if it’s a huge negative to do FD without LSD… so far I’ve heard what I already know… It’s a good idea and it should be done… but haven’t heard why I simply should not do 3.7 w/o it - other than Fluid1 indicating it’s not going to get the power to the ground, which I would like a more specific understanding – please.

 

one of the drawbacks to using a 3.7 or 3.9 is the rpm,s you will be seeing on the highway.i am seeing 3000 rpm,s with the 3.5 at 70 mph,i would figure about 3300 for the 3.7 and maybe 3500 for the 3.9 and that will kill your gas mileage.but the shot out of the hole would be very nice.

 

Yes, this is precisely why I don’t want to go 3.9 - Lately I have been doing exclusively city (street) driving so it would be no big deal... but for much of the year it is not uncommon to do 50 miles or more (daily) fwy driving... with 3.3 I'm at 3Krmp doing 80... I have heard some say 3.5 brings them to 3150 or so and others say higher... I think it was Andy from Performance Nissan who did 3.7 and says it's closer to 3500 @ 80... I guess it depends on the car. But yes, that's why I'm going 3.7, an equal balance I guess you could say...

 

Meh, I never think that an AT would mod.....my bad. 3.7 should be great with the AT.

To the OP: I should not have to elaborate at all. If you are spending the $ to make your car faster, then spend the $ to put the power to the ground. Otherwise you are paying to have your tires spin more than they do now. Ask anyone who knows WTF they are talking about.
Once you get that power down, I would think about an ECU reflash or a UTEC so you can 'gain back' some rpm's by upping the limiter a little.....if you are a frequent redline visitor.

 

I have TS ECU - redline is 7200, I'm not concerned about that... and I'm not exactly sure the theoretical 5% or so TQ to the ground is going to cause any more traction issues than I have now (which isn't really much to be concerned about as it is)... I just had a similar post on driver...

When you say “ask anyone who knows WTF they are talking about”, are you suggesting I’m in the wrong place?… I posted here so I could ask people that know WTF they are talking about.

Thanks for your response.

 

Oh, I was in no way meaning that the way you read it/took it. I meant that if you were to hear from other people who know what they are talking about and have had experience would say the same thing I did.

Going from a 3.3 to a 3.7 is a theoritical gain of more like 10% than 5%. Going from a 3.5 to a 3.7 would be more like 5%.

Feel free to hit me up on PM's if you'd like more detailed explanations, or if you have any other questions you'd like answered without any BS.