Sentra Spec-V Joining the club

[Daox]

Originally Posted by SuperHatch

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.

That is likely going to give worse mileage. You don't want to use less throttle, you want to use more throttle to decrease pumping losses. This is why P&G works so well.

[SuperHatch]

Originally Posted by Daox

That is likely going to give worse mileage. You don't want to use less throttle, you want to use more throttle to decrease pumping losses. This is why P&G works so well.

I'm not trying to start an argument with you, but that is not always the case.

The point I was trying to make is that if the ultimate goal is to accelerate from 30-40MPH and at full throttle that would take 15 second in 6th gear at 2000-2300RPM, but at half throttle that would take 4 seconds in 3rd gear at 4000-4500RPM, less fuel would be used in the latter.

The above numbers are arbitrary, I didn't look up SER acceleration rates or gear ratios to determine exact figures.

[evilskillit]

Thanks for the info superhatch. Its hard to say, it could be knock, I'm not flooring it at 1800rpm or anything, I'm takling like applyin an extra 5% throttle to keep the car from losing too much speed while going up an incline at 2000rpm, or maybe when accelerating away from a stop light at moderate throttle but shifting at 2500 rpm, which drops you down to about 1900 in the first 3 or 4 gears. As long as I barely apply enough throttle to accelerate its ok but a bit more makes the clicky noise. The engine has variable timing and a knock sensor. I was wondering if it was knock but I'm not certain of that, it may just be some other noise that is less conspicuous as the exhaust note gets louder. The difference between the engine making clicks vs smooth noise is a few % throttle at engine speeds below maybe 2100 or 2200rpm.

FWIW I never really try to haul butt at or below 2000rpm, if I really need to move with some alacrity I'll drop a gear or 2. But say I'm in my neighborhood rolling at 30mph in 4th as in hit the incline towards my house if I dont drop to 3rd it'll start making clicky noises as I climb. I think once I get something, anything, scangauge, vacuum gauge, etc it'll give me a better idea of how the engine is behaving at that time.

[AeroModder]

You share bolt patterns with the Honda Accord. Going for some stock steelies with low rolling resistance tires and smooth hubcaps would help.

The "knock" could be sticky lifters. Run some Seafoam through the crankcase before your next oil change.

[Daox]

Originally Posted by SuperHatch

I'm not trying to start an argument with you, but that is not always the case.

The point I was trying to make is that if the ultimate goal is to accelerate from 30-40MPH and at full throttle that would take 15 second in 6th gear at 2000-2300RPM, but at half throttle that would take 4 seconds in 3rd gear at 4000-4500RPM, less fuel would be used in the latter.

The above numbers are arbitrary, I didn't look up SER acceleration rates or gear ratios to determine exact figures.

I'm not trying to argue either, just getting facts straight. Anyway, actually, what I said is always the case. BSFC charts show that higher loads always provide more horsepower per amount of fuel used. Therefore, running at lower loads will always be less efficient. If he used full throttle at 2000-2300 vs full throttle at 4000-4500 it is somewhat arguable which is more efficient because we don't have a specific BSFC chart for the engine. However, running an engine (near) full throttle will always be more efficient than half throttle.

[evilskillit]

Originally Posted by AeroModder

You share bolt patterns with the Honda Accord. Going for some stock steelies with low rolling resistance tires and smooth hubcaps would help.

The "knock" could be sticky lifters. Run some Seafoam through the crankcase before your next oil change.

I used to have a set of 15" steelies off of my 93 240sx. Oddly some random stranger traded me them for a set of 17" alloys so now my winter and summer wheels are both 17" alloys.

Both sets are a bit undersized because I bought sportier tires. I need to get some taller tires so I can cruise at a bit lower RPM on the highway instead of higher. Tho having your speedo say you're going faster than you are does help save gas by going slower than you mean to, and its saved me from more than a couple of tickets.

[SuperHatch]

Originally Posted by Daox

I'm not trying to argue either, just getting facts straight. Anyway, actually, what I said is always the case. BSFC charts show that higher loads always provide more horsepower per amount of fuel used. Therefore, running at lower loads will always be less efficient. If he used full throttle at 2000-2300 vs full throttle at 4000-4500 it is somewhat arguable which is more efficient because we don't have a specific BSFC chart for the engine. However, running an engine (near) full throttle will always be more efficient than half throttle.

You are correct that higher loads always generate more horsepower.

What you are not considering is the torque multiplication offered by lower gear ratios.

[Daox]

Perhaps we are trying to make different points here. I am trying to say high load is always going to be better than low load.

I think you're talking about what gear to use and what rpm range to use.

[SuperHatch]

Originally Posted by Daox

Perhaps we are trying to make different points here. I am trying to say high load is always going to be better than low load.

I think you're talking about what gear to use and what rpm range to use.

I appologize for not being clear enough in my original reply, but the is exactly what I'm talking about.

Lugging a motor at high load and low RPM is less efficient that dropping a few gears to accelerate.

Originally Posted by Me

The point I was trying to make is that if the ultimate goal is to accelerate from 30-40MPH and at full throttle that would take 15 second in 6th gear at 2000-2300RPM, but at half throttle that would take 4 seconds in 3rd gear at 4000-4500RPM, less fuel would be used in the latter.

[04NissanSpecV]

You are running 91 octane I hope otherwise its gonna knock at low rpm and be like