Sentra Spec-V Joining the club

[evilskillit]

Hey everybody. Just wanted to introduce myself. My name is Matt and I have a 2003 Sentra SE-R Spec-V. Its the sporty model. My first love is performance, but I also enjoy saving money and understand that good economy when commuting and performance aren't mutually exclusive.

I live in the Kansas City metro area. I commute about 40 miles a day total. 90% of that is highway. I could take a 34 mile commute on side streets instead, but there are a lot of stop lights.

EPA average for my car is apparently about 24. I reset my trip meter every time I fill up. When I divide my miles by my gallons on fill up I'm usually around 28.5, 32 being my personal best and 25 being my worst.

I would like to start working on getting even better mileage, I know its possible. I have a few caveats tho. I bought the car based on its performance and value, I'm not going to sacrifice any performance. I know there are however a lot of things you can do to improve economy and performance.

I bought the car new, am the first owner and still have a lot of respect for its looks so I won't be able to bring myself to do smooth wheel covers, rear wheel arch covers, boat tails or anything like that

Fist, along with getting some kind of nice MPG instrumentation I think I would like to start working on some sort of under tray and maybe front end opening blocking (especially if I can find a separate bumper to work on and then install.

After I get 5 posts I'll put an image up somewhere for people who don't know what the 2003 Spec-V looks like. (from what I've read on the site its slipperier than I would have thought.

[SVOboy]

Welcome to EcoModder

KCMO?

Even if you don't want to do smooth covers, there are some aero wheels that look good and can make a big difference, as far as wheels go.

[evilskillit]

KCMO? Um, Kansas City, Missouri.

As for changing wheels, doubtful unless I found some freak good deal. The B15 Sentra runs an oddball 4 lug pattern that isn't shared with a lot of other cars. Also wheels are expensive, and I'm cheap.

[SVOboy]

I was asking if it was KCMO, since you didn't specify, and everyone know the Kansas side is where no-good people live.

Gotcha on the wheels. Luckily I've gotten really good deals on all the wheels I've bought

Just out of curiosity, what's the lug pattern? 4x113.5?

[evilskillit]

Nope, 4x114.3

I think its only used by Nissan on a few models for a few years, tho the 4 lug 240sx, used it, so that may help. I think it was used on a few certain Hondas as well, but not many as most used 4x100 or 5 lug I believe.

[VegasDude]

The biggest FE gains won't be made with aero-mods unless they are pretty extreme. You can double your EPA estimate by simply driving different. A partial grille block and a front air dam won't change the look of the car but could give you a few more MPG on the freeway. You'll see a big difference sticking to 55 MPH and taking it easy on the surface streets as well. I have a similar longer distance freeway option on my commute but I can get far better mileage by sticking to the streets and timing the lights. But, my commute is only 22 miles round trip, so it doesn't take too long even when topping out at 35 MPH.

[Daox]

Welcome to the site.

VegasDude hit the nail on the head. Check out the 100+ hypermiling tips (link at the top of the page).

[evilskillit]

Yeah, I've read the tips. I do try to follow them to some extent. I'm working on my light timing and trying to resist high speeds, especially on the side streets where I can do 45 without fear of getting shot at Things that improve highway MPG are pretty ideal for me tho since my house is less than a mile from 2 on ramps and highway driving represents at least 85% of everywhere I go.

As for changing my driving style I'm working on it, getting pretty good at light timing. But I won't know what amount of throttle or what shift points net the best MPG till I can get a Scangauge or the like. Certain things I am a bit apprehensive about are things like P&G. I'll glide down hills but I'm not really willing to put that level of wear on my starter (my car doesn't start instantly, it takes a second), or possibly even on my clutch and transmission if just pulsing and gliding without killing the engine. I'm very particular about wear, I'm pretty proud of the fact that when I changed my gear oil for the first time at 80,000 miles (yeah, way too long) that there was no metal what so ever on the magnetic drain plug and gear oil was still in great shape. I know I can rev match to help ease the engagement portion of p&g, and I'm pretty good at it, but increasing my clutch usage / gear engagement by a factor of 10 is something I'm not totally comfortable with.

One fun thing about this car tho is that it has a pretty close ratio 6 speed but with a decent torque band and the 6th gear helps you get that extra bit of higher speed mileage compared to the 5 speed version. One thing I do wonder about is if you apply any amount of throttle beyond a few percent at engine speeds below about 2200rpm the car makes a noise that sounds like a playing card stuck in some bicycle spokes. I'm not sure if this is a bad thing or if its normal. I hear it in a lot of cars, but that doesn't mean its a good thing. Maybe some of you other low rpm cruisers can enlighten me as to what that noise is and what it might indicate.

[Daox]

Clutch wear really isn't bad once you get the technique down, and starter wear is next to nothing if you bump start (which is extremely smooth with a little practice). I have yet to hear of someone who had to replace their clutch early, and we have some members with tons of miles on their cars.

I dunno what you mean about weird noises at high loads and low rpms. My car and other cars I've driven gets louder (intake/exhaust) when you open the throttle, but thats it.

[SuperHatch]

Sounds like load induced knock. Load can be defined as actual cylinder fill rate versus theoretical maximum fill rate (Volumentric Efficiency/VE). If at 2200RPM the VE is 90% than the 2.5L QR25 (if memory serves me right) engine in your sentra is actually flowing 2.25L worth of air every 2 revolutions of the crank. (2.5*.9). At part throttle the fill rate is lower since you are restricting incoming air flow with the throttle plate, which is why a vacuum gauge reads vacuum. The engine is trying to flow that full 2.25L of air, but you are restricting it. High Load (in my book) would be defined as using 85-100% of the available VE.

High load at low RPM produces high cylinder fill rates, and since the burn rate of 2.25L of fuel mixed with 0.173L of fuel (assuming 13:1 AFR at WOT) is fixed, we adjust ignition timing to produce maximum torque. The piston velocity changes as RPMs increase, but the burn rate remains relatively constant. This is why ignition timing generally advances as RPMs increase. This is not always true since VE also changes as RPMs increase, so the timing does not ever ramp up at a fixed rate because the VE generally drops off as RPMs rise.

Too much load at low RPMs will require very little ignition timing advance since the piston is moving so slowly. The factory tune on your car may have a little too much timing at those RPM/Load points which is causing slight knock. Lets face it, if you want to get somewhere faster, you don't floor it at 2000RPM in sixth, you downshift a couple gears to increase your torque multiplication and put the engine in a more efficient power producing part of the rev band.

I would venture to say, that if you are putting enough load on the engine at 2000RPM to induce knock, you should downshift at least one gear. You will probably accelerate quicker with less throttle input and as a result, use less fuel. A fuel consumtion calculator like scangauge or MPGuino will help prove this point.