L4N71B SWAP INTO A 620

[ghammer]

Here's one exterior shot of the finished ride. Damn photobucket is screwing up and having difficulty uploading.....I could only do one, kept logging out trying again. So for now this is it.

 

I drove it for a week, runs and drives great........gas mileage is not anywhere what I had dreams that it would be. I rough estimated it about 20 mpg. Since I broke my speedo cable the first day. New one will get picked up later today. I was hoping for mid to high 20's with the overdrive in it. I just swapped out the 4.37's and put in 3.70's. I'll try driving it again for a week and see if it will get any better? If not......might be selling it, since this was to be my commuter and 20 mpg isn't going to cut it. :(

[darrel]

You must have limo tint. Looks good with that color.

 

My 280zx turbo got 19 mpg consistently with the stock 3.54 highway and 3 spd auto. That was verified on a 4200 mile trip.

 

When I put the 4 spd auto in I also put in a 3.9 rearend. Same trip 4200 miles 2 years later it got 24 mpg. Before i sold it I put the 3.54 back in, but I didn't go on any long trips with the 3.54 in. I am sure you will get better gas mileage depending on your driving habit. I will have to get in touch with the kid i sold it to to see what he is getting. I know he has taken it on a couple of long trips, I just hope he is concerned about mileage figures as i was.

 

My '79 620 kc with what I imagine is a 3.9, could be 4.38 with a 4 spd manual is getting 23-24 in a combination of city and hiway. My 620 also has all the smog and stock carb in it.

[heretic]

Is that a fully tinted windshield? its been a long time since I've seen that done on a mini. Looks great.

[ghammer]

I love computers.....I just typed out a great reply and it just went into terminal saving post......

 

I put a weber carb on this thing. It's just on the lean side. So I know i'm not just flushing gas away. My commute is almost all freeway, about 42 miles one way and all flat. I'm cruising around 70-75 mph(guessing since I broke my speedo cable the first day), taching around 2900 rpms. I had to stop on my way home the second day and put 8.9 gallons in it. I picked up my new speedo cable today, i'll get it installed later today. Then I can try out the 3.70's I swapped in. No smog stuff on mine. I've been driving it mellow since I wanted to see what I could get out of it for mpg.

 

The back 3 windows are double layered. One layer of 5%, one layer of 20%. The doors are 35%. Only factory tinted windshield.

 

Thanks to everyone for the kind words about the truck!

[q-tip]

See hours done gets me excited about doing mine, I think I might ditch the torsion bars and mounts and just make a cross me member for the trans. Too many ideas with too little time and money....

[Xnke]

If you had retained the EGR setup, you could easily get much better mileage...assuming that it was in good working order and you have the factory carb that's setup for it. I am not sure if the Weber can do EGR or not.

 

EGR wasn't "smog" stuff, as much as it was an economy feature. The premise is that if you are adding already-burned exhaust gases into the combustion chamber, you're actually adding an inert gas...which doesn't contain much, if any oxygen, and so you can run even leaner for the same size engine...it's artificially reducing the displacement of the engine. The EGR valve is supposed to open at high engine vacuums, but there is usually a valve or something to prevent it being open at idle. At a 70MPH cruising speed on flat ground, my Z only requires 19HP to maintain that speed. Once up to speed...a beefy lawnmower engine could keep you going! You just don't need the full 2.0L displacement, so the EGR valve opens up and bleeds inert gas in. The stock carb has a method of leaning the mixture out when the egr valve opens, to maintain the lean-burn mixtures you can get away with in this mode of operation. The vacuum trigger to open the valve, though, needs to shut closed on acceleration, and the carb needs to richen up when the valve is closed...

 

Just some rambling about a good way to pick up 3-8 MPG highway, that gets universally discarded as "power/milage robbing smog equipment"!

[ghammer]

I do not believe Weber has that ability........very simple basic carb.

[darrel]

update on mileage for my stock 2.0 with 5 spd. Almost all hiway, rural hiway spd limit in colorado is 75. I did that plus 5 most of the way. 302 miles 11.9 gal. 25.3 mpg.

 

Your trans should have the correct blue spdo cog for 3.7 already. Was that taken into consideration with the 4.38 or 3.9 original rearend?

[ghammer]

Actually, I broke my speedo cable the first day of driving. I just know the mileage from home to work is 42 miles one way. At the end of second day I put 8.9 gallons in it....ugh. But yeah the trans has the right gear in it for the 3.70 gears. Now the speedo is correct and my rpms dropped all the way down to around 2400 rpms at 70 mph....better than the 2900 rpms I was doing at that speed. It's nice now at least driving around town it doesn't want to shift into overdrive at 40 mph anymore. No more having to shut off overdrive! I'm going to check mileage again this week. I'm already looking for a replacement vehicle just in case. I hate when I do this to myself....... :hmm:

[darrel]

40 is about when the lock up tc kicks in. Some think it's the od.

[ghammer]

It would shift into 4th gear with the old 4.37's in it around 40 mph just cruising around town. I would have to turn off od switch to drop it back down to 3rd. Now it's not an issue anymore. I drove it to work today and I can already tell i'm not going to get the mileage i'm looking for....sigh. I'll post it up for sale later this week. Dammit. 

[datzenmike]

It takes a finite amount of power to pull a vehicle along a highway and push the air out of the way. Up to a point you can gear it to make use of the engine power at lower RPMs but it does not go on forever and at some point you can't get any better. You aren't going to get 38 MPG. 70 is too high. Try going the speed limit. It takes 4 times as much power to go twice as fast so every bit counts.

 

The EGR can support slightly better mileage but I would say was introduced more for reducing emissions by lowering peak cylinder temperatures where oxides of nitrogen are formed. Because it 'dilutes' power, the carb has to be open further for the same power without EGR and the engine doesn't need to work as hard pulling air in past the throttle plate. Reducing peak cylinder temperatures means less heat is absorbed by the cooling system and is available for doing work. The EGR is activated by a ported vacuum source like the vacuum advance for the distributor and is not on at idle. At full throttle the vacuum is so low it is not on either.

[ghammer]

Well after double checking mileage, after swapping gears to 3.70's, I gained only a drop in rpm's at speed. My mpg actually stayed the same...lol. Having to use a bit more throttle to maintain speed at the lower rpm, since these engines have sooooo much torque...he-he!

 

For the record, I am going the speed limit. It ranges from 65 mph to 70 mph on the stretches of freeway I drive to work.

 

I wasn't hoping for 38 mpg either. If I wanted that I would've bought a 1200 and drove it downhill both ways from work...ha-ha! I thought 25-28 may have been obtainable if I was lucky. Like I said, 20 mpg is not going to cut it for me. Again, dammit.......I'll take some pics and it'll go up for sale.

[datzenmike]

I got high 20s and maybe dip into the 30s (if no wind and up hills) on long trips and anywhere below that when adding in local driving. This would have been at 50MPH.

[ghammer]

Sigh......that's like a kick in the nuts! :sick:

[datzenmike]

Is the speedometer accurate? Maybe you're going further with diff and trans change?

[q-tip]

^^^i was just going to suggest that

[ghammer]

Had speedometer calibration checked last week after changing rear gears. Dead nuts on now. Maybe it's the loose nut behind the wheel? Oh wait, that's me! Also, knew exactly how far my commute is from checking gas mileage over the years.

[q-tip]

It too bad you didn't get your desired results, the good news is you're not turning 5k on the highway anymore

[darrel]

I still think you're overlooking something. With power to the trans the OD is off. Without power the OD is on.

 

When I first got the OD, I confused the OD with the lock up TC.

[ghammer]

Transmission works flawlessly. Push the od swith to the off position, it sends a ground signal to a bosch relay, which in turn sends power to the overdrive solenoid disengaging the overdrive.

[mklotz70]

What happened to the pics?? :(

[datzenmike]

Moving them or closing PB will do that.

[darrel]

he got butt hurt because he was selling it as a pre '76 instead of the '79 it actually is. Most called him on it. but of course he had all the paperwork to make it a '79. Usually when people get hurt, they will delete what they posted, especially when it is helpful to the forum.

[mklotz70]

Moving them or closing PB will do that.

 

Yep....I could change one letter on my PB account and kill over 8000 pics on this forum and hundreds of threads.  Came close once. 

 

Holy crap Mike!  I just noticed you have 35K posts!!!  I think have of them are in the TnA threads :)

 

 

he got butt hurt because he was selling it as a pre '76 instead of the '79 it actually is. Most called him on it. but of course he had all the paperwork to make it a '79. Usually when people get hurt, they will delete what they posted, especially when it is helpful to the forum.

 

I did actually see some of that thread.  He got bashed pretty hard even though he wasn't trying to hide anything.  It hasn't happened yet, mainly because I look at very little of ratsun these days, but I can see pissed off or hurt enough to wipe everything.  I'm mainly here for the guys in the background that use this site for reference and then go "do" something.  I'm not here for those that simply use it as their social outlet and don't actually contribute.  These days....I tend to use ratsun as an archive so I can refer back to it later. :)  If I had more time, I'd put more of it on my site.  Just like PB has annoyed me with their changes......so I don't do many pics anymore....mostly vid on youtube.  Anyway......too bad he pulled the pics.  I prefer autos to manuals and would have liked to have seen them.  :)