Saturn S-Series 5th Gear Swap

[klrv6]

Does anybody know of 5th gear changes or parts that would be availalbe for a 2002 nissan sentra XE, 5spd 1.8 base model. Yes, I just picked it up to allow the semi-retirement of the suburban

I asked in some other forums and nobody had a clue.

[lovemysan]

Cfg83, looking at the BFSC map it appears to me that the sweet spot is around 70 mph/2500 rpm. Which is nearly identical to a sohc, peak torque for me is 2400rpms, 114lb ft. I've read in the past that that the dohc makes within 3lb of the sohc until after 3500 rpm.

[cfg83]

lovemysan -

Originally Posted by lovemysan

Cfg83, looking at the BFSC map it appears to me that the sweet spot is around 70 mph/2500 rpm. Which is nearly identical to a sohc, peak torque for me is 2400rpms, 114lb ft. I've read in the past that that the dohc makes within 3lb of the sohc until after 3500 rpm.

Ok. Traffic willing, I'll give that a try on the to/from leg to work today and see what happens. Considering that I never touch 3000 RPMs on my commute, it's nice to think I might have a "stealth-SOHC" in my SW2.

CarloSW2

[lovemysan]

CFG I was merely stating that from a BSFC eff standpoint 70mph is best. However I find that 38mph is best for maximum eff. LOL. You should be able to hit 43-44mpg at 70 though. Of course there are a lot of different variables here that I don't understand how to compute.

[cfg83]

Dust -

Originally Posted by Dust

Did the Cruise control ever get sorted out?

No, I stopped working on it. I will post a separate thread on this so you can see where I left off. I may never fix it because I have a vague plan to reuse the cruise control buttons for something else. For instance, I think it would be neat to turn it a control for a fuel injector cutoff.

CarloSW2

[cfg83]

lovemysan -

Originally Posted by lovemysan

CFG I was merely stating that from a BSFC eff standpoint 70mph is best. However I find that 38mph is best for maximum eff. LOL. You should be able to hit 43-44mpg at 70 though. Of course there are a lot of different variables here that I don't understand how to compute.

Ok. I did it for fun anyway. I couldn't get up to 70 MPH average because of traffic. Instead, it's just a +12 MPH Average comparison. Here are the results :

ROUTE : 10 West -> 710 South -> 105 West -> 405 South -> Exit Freeway => Roughly 27+ miles

SCANGUAGE "CURRENT" Readings :

                   SLOW     FAST 
MPG            :   61.2     45.8 
Gallons        :    0.4      0.6 
Water Temp Max :  200.0    204.0
Miles          :   27.5     27.7
RPM Max        : 2135.0   2572.0
Hours          :    0.6      0.4
MPH Max        :   58.0     74.0
MPH AVG        :   45.0     57.0

WEATHER(.com) :

Degrees F      : 77.00      76.00
Humidity (%)   : 27.00      59.00
Dew Point (F)  : 36.50      60.00
in. Pressure   : 30.09      30.01

The problem (in my mind) is the difference in the humidity. Otherwise, these two express a decent comparison.

CarloSW2

[cookie96civic]

I'm not dead sure, but i think my civic dx is around 3000 @ 60-65, with only 100hp. My question is my new Nissan Quest runs 2200 @ 80mph and around 1600 @ 60. Is this lugging the engine? Or will it downshift before enough lugging occurs. (5spd auto). I guess it has a little more torque (255) than the civic too, maybe that helps.

[whokilledthejams]

Originally Posted by cookie96civic

I'm not dead sure, but i think my civic dx is around 3000 @ 60-65, with only 100hp. My question is my new Nissan Quest runs 2200 @ 80mph and around 1600 @ 60. Is this lugging the engine? Or will it downshift before enough lugging occurs. (5spd auto). I guess it has a little more torque (255) than the civic too, maybe that helps.

You're not lugging. Generally, engines that make a lot of their torque at low rpms can be geared to run like that at highway speeds, because they remain driveable to the average person. Essentially, the gearing is chosen so that passing in-gear isn't a trial of patience.

Admittedly, while everyone here would like a top gear tall enough to run a flying mile on the salt flats, most people want to be able to accelerate at a pace quicker than 'glacial.' Hence, at 80mph, my xB is running at something like 4200rpm. Bigger engines tend to make a lot more torque at lower rpms, so they can be geared much taller without impacting performance. The upside is better fuel economy than if shorter gears were chosen.

[MetroMPG]

Originally Posted by whokilledthejams

Admittedly, while everyone here would like a top gear tall enough to run a flying mile on the salt flats, most people want to be able to accelerate at a pace quicker than 'glacial.'

And apparently the manufacturers assume people are clueless about the concept of downshifting for acceleration or climbing! Thus we are stuck with excessive RPM at highway speeds. Let's start a petition.

PS - nice salt flats reference.

[OfficeLinebacker]

Awesome thread. Been toying with the idea of oversize tires...does this gear change have a similar effect on the speedo readings?