1980 Datsun 4 x 4 Pickup Truck

[Datsman]

I am told by mklotz70 that a person named Datsunaholic is the master about the 720 series pickup trucks.

 

This is the problem I have a completely restored motor with a kinda wild cam in it. The exhaust is a 2-1/4" with cat and flowmaster. The suspension is all stock but has 31" tires on it. Well I do not have the power that I was looking for I am told that it is because of the tires by one person and then by another it is the exhaust so not have enough back pressure. I tried to buy a new set of gears to no avail. then I tried to buy a rear end out of a older truck with a lower gear set which I did but found out during the swap that the splines are wrong. If any one out there especially the Datsunholic please send some advise on the project.

 

I also have a 500 CFM carb, MSD 6al box and new MSD distruibutor. I am at a total loss for which way to jump.:confused::confused:

[makya]

is it an automatic or stick shift?

 

also do you know what the gear ratio is in the axles?

[Datsman]

Yes it has a stock Brog-Warner 5 speed transmision and I believe the gears are around the 4:30 Range.

[Bleach]

I believe that 1980 4x4 has 4.375 gears.

Finding lower gears to replace your stock front diff would be difficult. The 1981 longbed 4x4 has 4.625 gears but those are non-existant now. Finding the rear axel to match would be equally difficult.

 

L20b engine has a decent amount of torque. Wild cams (longer duration) give you power at high rpms but less torque. Larger exhaust pipes do the same. You should have good power above 5,000 rpm as it is set up now. That is probably not what you want for a 4x4

 

If you switch the rear axel to an older Datsun axel with 4.88 gears the you could swap in a Toyota solid front axel with those gear ratios as well. That may be all you need. The front axel swap will require welding.

[Datsman]

OK, do you think that changing the exhaust system to say 1-3/4" with a restrictive muffler would make the difference? Or so I need to get a smaller tire set? Seems like I have to do a major toyota front and rear end swap to get what I am looking for.... can this be true or false?

[datsunaholic]

I'm not really a 720 expert... I happen to HAVE a 720, it's not a 4X4. My 4X4 is a conversion '78.

 

Anyhow, Bleach is on the money as far as gear sets go. The 720 used IFS which limits the gearing to what the R180 had- 4.375, 4.111, and even lower, which isn't what you want. Now, I have 4.375 in my '78, with the L20B. and it's fine- STOCK cam, stock exhaust. Only real mod is total removal of the emissions system (smog pump, EGR, and all associated plumbing), a Weber 32/36 carb, and of course the addition of Jeep components to make it a 4WD truck. But- it ran OK even with the stock Hitachi, until the Hitachi fell apart.

 

One thing I heard was the Borg Warner T-5 transmission. First, I don't know how the heck someone got that in there to interface it to the transfer case- the length would have presented a problem due to the small gap between he tranny/T-case, but the big thing is that 1st gear is so tall (since it's geared for a 2.8L turbo engine, since that's all the T-5 ever came in a Datsun) that the low-end, 1st gear off the line performance would absolutely suck.

 

The front gears, you pretty much nailed it- Toyota axles (both ends). Or, Jeep front, like the 70s conversions used, though matching the rear means finding a 4.88 nissan rear, since that's the ONLY matching gear range with the Jeep Dana 30. I don't know what you have now- a 1980 should have had 4.375. but you said the splines didn't match an older truck. A 1980 should have matched splines up to the late 60s. Car ones don't, but they're all in the high 3.xx range.

 

 

The "500CFM Carb" doesn't mean anything to me... what is it? Might be too big. That's the same answer as the wild cam and big exhaust- the power is there, just in the wrong place. You want the power down at the bottom, which means stock-sized breathing to get the intake velocity up at low RPMs. Stock intake/exhaust valves, stock cam (or RV type cam, not a tuner cam), etc. You can probably get the exhaust velocity up with a single change- run a stock pipe from the manifold to the cat, keep it big from the cat back.

[datzenmike]

What are you wanting this truck to do? If off-roading, you will want low and mid range power.

 

Going to larger tires is unavoidable for this, but it will cut into what low speed torque you do have. To preserve off road, and especially on road performance, a lower gear set (higher numerically) is in order. As Doug said the rear axles are pulled outward, the gear set pulled as a unit and another installed, the axles put back in. There should be no spline problem as far as the axles go. The front diff. is more problematic.

 

Never, never , never over cam a motor. It moves the power and torque sometimes thousands of RPMs higher in the rev range and leaves the idle and low speed, (where you do most of your driving) severely lacking.

 

Never, never over carburate a motor. A motor's needs should me matched to carb size. An L20 B at full throttle and 8,000 RPMs requires 282 CFM. To use a 500 CFM carb would require the poor L20B to turn in excess of 13,000 RPMs to use all of it. If bigger carbs made more power we would all be running 1050 double pumper Holleys, right? There are some slight gains to using a slightly larger carb, but it is mostly from a lowering of restriction. The engine doesn't have to suck as hard to get air and fuel. A 32/36 Weber is more than enough for a 2 liter motor.

 

The right hand side is the T-5 B/W Zcar tranny beside a FS5W71B that would have come in your '80 truck. The T-5 is very much wider.

http://i138.photobucket.com/albums/q251/datzenmike/BorgWarner4-2.jpg[/img]"]

 

Get a much milder cam and a Weber 32/36. This will immediately give you back your drivability. Forget performance, it's a 4X4, it weighs too much for an L20B to pull. Even Nissan quickly switched to the Z22 the next year. This motor was designed for bottom end power and torque. Over 15% increase in torque and at half the RPMs of the L20B! That's stump pulling power at low speed to pull that heavy truck up hills.

[banzai510(hainz)]

ask RascnJasn

He has a 620 4X4 with a L20b

I think he said the power was OK and its a stock cam with a weber DGV

 

 

yes the spline #s change if I remeber correctly

My nismo book had this info but its at work

 

 

look under Power Brute or Precision Gear to find a website for the R180 and maybe the rear diffs gear ratio lisings

http://www.precisiongear.com/powerbrute.htm

This doesnt help for gear ratio changes but Maybe the later Pathfinder rear axles are somewhat the same

[Mark_Z28]

You dont want a restrictive(backpressure) exhaust, just the right sized pipe, a good flowing muffler will be better. Its the flow velocity of the exhaust gas that makes the torque, either at upper rpms or low rpms, depends on size and type of pipe used. The smaller diameter pipe will have more velocity down low which gives you the low end grunt(if the cam and carb are set right) you need. Actually, if you want power and torque a 4.3 V6 or a V8 is the way to go for off roading. No four banger will do well off road unless its geared so dang low its worthless on the highway, unless you use an S2K engine with the 9 grand redline, lol. Stick a Weber on the truck with headers and 2 inch piping for exhaust with a free flowing muffler, maybe even a 1 3/4 exhaust would be good. Stock cam would do better also.

.

OK, do you think that changing the exhaust system to say 1-3/4" with a restrictive muffler would make the difference? Or so I need to get a smaller tire set? Seems like I have to do a major toyota front and rear end swap to get what I am looking for.... can this be true or false?

[Datsman]

Ok, I was told that the 500 CFM with the cam that I have was a match made in heaven. Well it appears that it is not true so does the weber DGV 32/36 fit on the stock manifold? If so where is the best place for me to purchase one weber carb.(EBAY)?

 

I will change out the tire size and see if that make a big difference. I didn't think that going from a 27" to a 31" would make such a big diffrence. We had this tire size on my sons 1981 and it ran just fine.

 

I was wondering if it is all because of the carb is to big.

 

Note: that I will change the exhaust after I have tried a few of the other suggestions.

 

I have had this truck for many years and want to restore it to its glory, not many of them 1980's left anymore. This one was fully loaded power steering, Air Conditioning, Etc. the works.

 

Any help that I can get will be much appreicated.

[fisch]

I just saw a used manifold on ebay that should do the trick. It already had the adapter plate. It is at 15 bucks right now. I ebayed my 32/36.

 

 

http://cgi.ebay.com/ebaymotors/Datsun-510-L-series-intake-manifold-32-36-Weber-adaptor_W0QQcmdZViewItemQQcategoryZ10076QQihZ001QQitemZ110208674738QQrdZ1QQsspagenameZWDVW

[datzenmike]

I will change out the tire size and see if that make a big difference. I didn't think that going from a 27" to a 31" would make such a big diffrence. We had this tire size on my sons 1981 and it ran just fine.

 

Your son's '81 will have the higher torque at lower RPM Z22 motor in it. It will easily out pull the L20B at lower speeds. Larger tires aren't such a problem for it.

[Datsman]

OK I bought new Stock 27-1/2" tires and put them on the old rim's. It did make a difference but still not what I was looking for. I am considering puting a toyota front and rear in it has anyone done this swap? If you have what year did you put in and was there much difficulty in the swap.

[]2eDeYe]

Yota's have 4:10 gears stock...

 

I really think you have problems elsewhere considering I have personally driven 2 yota pickup's on 33's with stock 4:10 gears and excelleration isn't a problem...with a 20R even.

 

Have you done a compression test?

[Datsman]

OK, I did change out the tire sizes, I now have 26-1/2", 29" and 31" tires and tested them all. Found that it does make a big difference between the 26-1/2" and the 31" tires for low end torque. I have settled I think for now on 29" tires. I have changed an 18" section of my exhaust and made a 1-7/8" insert in the 2-1/4" which also made more low end torque. But it still does not have the lower end power that I thought I would get. The top end is great, High rev's and RPM are not a problem. Once underway it has good power but still from zero up not what I was thinking. After discussing the problem with a few people I am told that I should swap to a L16 head for smaller ports which would give me more low end torque. Has anyone doen this swap on a L20b block and is it possible to create more low end power with this combination?

[datsunfish]

Strangely enough I swapped a 210 head onto my L18 in my 620 and the low end power compared to large port/valve head and ported mani is very noticeable.It doesnt have the same overall power range but with a motor in the back it climbs the highway hills without having to lay into the pedal.

From the way it sounds you will never get what you are looking for out of a l20b.I think they are awesome for street use but I dunno about 4xing.Your best bet would be to get a naps z 22 or 24.The 24 should give you all the torque you could ever want.Essentially the same block as the L series but the 24 is taller and would require mods to do a LZ hybrid.

[banzai510(hainz)]

How about trying a weber 32/36 DGV?

 

Private meassage RasnJasn on here

He has a L20b 620 4x4.

ask him about his power output.

 

personally anytime bigger tires are added you loose power.

 

Try stock wheels and a weber DGV. I think that 500 cfm carb is a litlle big for Low end. Dont worry about putting a different head on.

put on a more restrictive air cleaner.

 

 

MY buddys 4 runner with 22R carbed(2000cc motor) barely would do 60 across Snoqualmie Pass. But he had BIG tires and Lowered the gear ratio.