620 Efficiency

[copacetickid]

I'm new to datsuns, and just beginning to learn more than the basics about cars, so please forgive my naivety. Also, think of this as a way to show off your limitless knowledge ;)

 

I bought my 620 1) cause it's effing beautiful, and 2) because I wanted a small truck to put a canopy on and a bed in the back for road trips. Being that it is for distance driving, I'm aiming for the best gas mileage possible.

 

I know this boils down to greater efficiency, but what are the best ways to get there? I'm pretty poor, but should I break down and get a weber carb and a new header? Big or small, engine or other, what should I do to my truck?

 

(stock everything L20b, 170-170-160-170 compression)

[phatdave]

Part it out here and buy a Chevy Corsica.

 

HAH! Just tune it up, adjust the valves, replace filters,oil and drive like you have an egg on the gas pedal. Make sure air pressure is correct in your tires.

 

A Weber will work better than the Hitachi thats probably on it.

 

:D

[datzenmike]

You don't say what year so I'll assume a post '74 with an L20B, not that there's anything wrong with the two smaller motors, the L20B just has a size advantage.

 

First have the motor in tune and running at it's best. In other words a tune up. Now there's no sense spending lots of money replacing stuff that doesn't need replacing if it runs good. So this is up to you. But definitely replace the fuel and air filters and the oil and filter. Always change the oil filter with every oil change. You might look at an oil that is made for lowering friction to give better mileage. Synthetic oils help a bit but are expensive and on an older motor that's worn and wasn't built to the tighter specs of to-day's cars, it can leak past gaskets and seals. Have the timing set for the grade of gas you plan to run. The timing should be as advanced as possible without pinging. Some grades with the same octane rating are better or worse for this.

 

Have the valve lash checked and/or adjusted. You want to get the most out of your engine.

 

Be sure the anti pollution equipment is properly hooked up with the right hoses and parts OR ( if you must) at least properly disconnected. There are no MPG gains to removing the smog controls, usually the engine is set up for them and runs poorly or the same, with out. With the exception of maybe the air pump, which can have the belt removed.

 

Be sure that the thermostat is the proper temp range and that it it working. In fact buy a new one and just put it in, they're cheap. Your L engine was designed to run at around 180 degrees for best efficiency. Having said that, try to keep the fuel and air a cool as possible buy installing a cool air inlet hose from the air snorkel to a place in front of the rad. Cool air will work with the octane rating to reduce pre-ignition. Try for warm engine, cool air.

 

Have a proper muffler installed. Too low a restriction can affect low speed driveability. Forget header$, a waste of money for MPG goals.

 

Use synthetic gear oil in the standard transmission and differential for reduced friction and better mileage.

 

If possible run stock size radial tires PROPERLY inflated and balanced. VERY IMPORTANT!! The wrong inflation is one of the biggest wasters of gas on a car. A front end that is out of alignment will waste gas grinding the rubber off the tires. Chec suspension parts for wear and replace, specially shock absorbers.

 

Keep your truck as light as you can, don't carry junk around in it or you will be wasting gas accelerating it up to speed and down again at every stop light for nothing.

 

Check that the breaks are not dragging (specially the E brake)

 

If you don't have one, look at a 5spd. It has an over drive gear to reduce high speed RPMs. You might also swap in a higher rear end gear (lower numerically) like a 4.11 to replace the stock 3.375

[copacetickid]

Mike, you are awesome! Sorry about the lack of info; it's a '79 non-california model and I swapped a '80 280zx 5-speed out for the 4-speed :( Didn't know how short the 5th gear was when I bought it. According to Datsunaholic the '79s came stock with a 4.11 diff, but it sure doesn't feel like it.

 

What resource should I consult on how to adjust the timing for octane level? And what grade would you recommend? Engine life is far more important to me than 4 cents more per gallon.

 

You say "have the valve lash checked", does that mean that's something I can't reasonably do myself on a weekend? I've never even cracked a valve cover off before :rolleyes:. But I learn quick. And is aligning something I can do myself too? I don't have any lasers :).

[]2eDeYe]

The valves are easy. Best thing to do is grab a Haynes manual and read the section on valve adjustment (heck reading the whole book is prolly a good idea) then take off your valve cover and read the section again.

 

You need a good set of feeler guages an a few hand tools.

 

After you feel comfortable with what your looking at and have an idea of what to do jump in there and adjust them up.

 

I think a good rule of thumb is to check them every other oil change and adjust as needed.

[datzenmike]

Mike, you are awesome! Sorry about the lack of info; it's a '79 non-california model and I swapped a '80 280zx 5-speed out for the 4-speed :( Didn't know how short the 5th gear was when I bought it. According to Datsunaholic the '79s came stock with a 4.11 diff, but it sure doesn't feel like it.

 

What resource should I consult on how to adjust the timing for octane level? And what grade would you recommend? Engine life is far more important to me than 4 cents more per gallon.

 

You say "have the valve lash checked", does that mean that's something I can't reasonably do myself on a weekend? I've never even cracked a valve cover off before :rolleyes:. But I learn quick. And is aligning something I can do myself too? I don't have any lasers :).

 

I recommend you get a Haynes, or equivalent, service manual about $20 at Wall Mart. It has pictures and instructions for minor to major repairs, adjustments and settings. There's a how to for valve adjustment, diagrams for smog hoses, carb rebuilding, brake adjusting... you get the picture.

 

To check your rear end ratio: place tranny in neutral raise one rear tire off the ground (use safety stands and block the wheels). Put a chalk mark on the tire where someone turning it can easily see it. Put another mark on the drive shaft where you can see it. Now have someone slowly and carefully turn the raised tire 10 times while you count the number of turns of the drive shaft. For example you count a little over 41 turns for 10 tire turns. Divide the 41 by 10 and you get 4.1 which is very close to the Nissan 4.11 differential. Easy.

 

For gas: run what the owner's manual in the glove box recomends, probably 87 octane, don't quote me on this. Octane rating is a measure of a gasolines ability to resist ignition before the spark plug has a chance to do so. Obviously the spark timing is essential for getting the most energy out of the exploding gas and air. Sometimes the gas ignites by itself before it should due to high temperatures, high temperatures caused by high compression or glowing carbon deposits. This is called pre-ignition or pinging and it actually tries to force the piston back against crankshaft rotation which wastes energy and more importantly, will cause severe damage to the engine. Not to worry, the proper octane level and ignition advance will protect you from this. It should be noted here that there is sometimes a difference between two fuels with the same rating. One may run better than another. Also, going to a higher octane level than you need has no effect on your mileage.

 

I would get a log and keep a record of fill ups, amounts and mileages and work out your MPG. Try different brands and record results.

 

Allignment: Camber, the amount the tire tilts out or in as viewed from the front, can be adjusted by adding or subtracting shims in the upper control arm and using a level. Not for beginners, although I did this once on my '78 frame. The tire was tilted out and I removed all the shims but could not bring in to the vertical. I found out later it had been in an accident so maybe the frame was bent.

Toe In: is the amount the tires are turned toward or away from each other as viewed from the front. Here's how I have done mine in the past with good results:

 

Truck on level surface, tires facing ahead and at least two helpers. Duct tape a 50 foot length (or longer) piece of string to rear outside edge of the front tire half way up so that when it is stretched out in front it passes across the center of the rim. Do the same with the other side.

Have a helper stretch out the string tightly in front and slightly to the side so that it is parallel to the ground and have them move slowly toward the truck and stop them when the string just touches the front edge of the tire. Do this a couple of times to be sure it's the same place. Now do the other side with another helper. When done you have two strings stretched out in the path the tries would follow if they were free to roll forwards. While your helpers patiently hold the strings, measure the distance between the two strings just in front of the truck and again out at the fifty foot mark. For toe in, the fifty foot mark distance should be slightly smaller than the closer measurement. Most car run with a very slight toe in. If yours is toed out then it needs adjusting. You can take to a shop where they will inspect all steering and suspension parts for wear. An alignment on worn out parts is a wast of time. You can adjust yourself by loosening the nuts on the cross rod and turning it to move the tires apart or together. For example: 50' radius X 2 = diameter(100) X pi = 314 (circle) divide by 360 = 1 degree or .87foot. I used 1/2 degree of toe in so .435 foot or about 5 1/4 inches.

 

The distance between the strings at the fifty foot mark should be 5 1/4 inches shorter than the distance closer to the truck for a 1/2 degree toe in. These are rough measurements and should be repeated several times to be more accurate. So it can be done at home in a hour or so by a do-it-your-self or at a shop.