Another Long, Drawn Out 620 Build

[partytron69000]

Greetings Ratsun!  I'm in the early stages of my 1978 620 KC build and wanted to start documenting now rather than later.

 

For a full backstory on the truck, check out my intro thread.

 

Truck details as it sits:

1978 Datsun 620, King Cab, L20b w/ 5 speed transmission.  Odometer reads 73,000.  I used to think it hadn't rolled over yet, but now after spending so much time with the truck, I think it's at least 173,000, but probably not 273,000.  The L20b is still running great, but I'm just not a fanboy of numbers matching original cars, so I feel no remorse in liberating it from the truck and passing it on to another Datsun enthusiast. 

 

 

Inspiration:

 

While I'm not planning to completely copy this 620, it's certainly an inspiration from a styling perspective.  Ace Rakes/@datsmo_racer has been super helpful in passing along details about their truck to help me in my planning.

 

 

Aesthetically, I'm a big fan of ratty hot rods, so I have no plans of doing any paint/bodywork.  But underneath the patina and grime, everything else will be mostly restomod'd.

 

The Game Plan:

 

My game plan for the truck has shifted slightly over the years, but for the most part stays the same:  Look Cool (to me) - Go Fast.

 

I've done engine swaps in the past with bolt on mounts/adapters/off the shelf swap components in other chassis's, had machine shops build KA's for boost before, and am just generally a handy person.  One of the main goals of this project is to challenge myself and build on skills I haven't had a chance to work on before.  I have a very spacious workshop that should be completed in about a month or so and was specifically designed to be my project car workshop, so I have no reservations about tearing into the truck myself and learning new skills along the way.

 

So here's my high-level plan.  Would absolutely love to hear feedback or suggestions from the community on other cool techy things to add in.  My only request for feedback is, if the extent of your comment is "you shouldn't do that/keep it stock/that's a lot of work", my blanket response is thanks for your concern :).  The list is kind of in order, but I'm aware things will have to shift around to be efficient in the build process.

 

Suspension:

   - Bag kit, universal 3 link kit, and shock relocation tabs from BC Fab w/ BC Fab proprietary remote controller (wireless, uses radio frequency and not Bluetooth)

      - I may need to rethink the specific model of bags I use, because I want something with a fairly rigid sidewall in order to accommodate spirited driving.

   - Tank and compressors mounted on bed frame rails under bed (hidden)

   - Cut/raise bed level to accommodate notched frame

   - standard performance/slight upgrade KYB shocks front/rear

 

Brakes:

   - D21 hub/spindle/rotor conversion in front

   - Slap as big of calipers in the front as I can that will fit behind 15" wheels

   - Figure out some rear axle swap that gives me LSD, a decent gear ratio, disk brakes, and isn't made of glass.

 

Exterior Styling:

   - Dapper Lighting 575's (clear glass, black housings, HDR RGB halos)

   - BRE style chin spoiler (definitely want urethane and not aluminum)

   - Fender flares

   - Wheels and Tires

      - US Wheel Rat Rod (Series 68) (15x10 -44; 205/50r15)

      OR if I decide to buy once, cry once

      - Watanabe R Types (Aluminum) (15x9.5 -19; 205/50r15; 1.25" spacers)

   - Fender mirrors

   - Hidden hitch receiver (hide behind license plate; fabricate flip up license plate mount)

   - Hand Painted shop truck lettering for the fake speed shop name I come up with

   - Rust encapsulation/conversion treatment

      - I don't have any ankle vents yet, but I don't plan on doing any real body work to the truck.  I like the ratty exterior and a restomod'd interior/drivetrain.

   - MAYBE a tailgate spoiler, still unsure

   - LED tail lights, hopefully built by Jamie Gardner/@evilsil80

 

Interior Styling:

   - Reclining bucket seats retrofitted with heat elements

      - I'm a big fan of Corbeau seats from past experience.  I'm really not caught up in the big brand game of bucket seats.

   - 4 point harnesses

   - Harness bar (interior mounted)

   - Custom sheet metal center console

      - either flocked black or upholstered (my next door neighbor does custom auto upholstery, how convenient lol)

   - Sheet metal door cards and kick panels

      - again, either flocked or upholstered

   - Dash cap

   - Custom LCD 3 3/8"s gauges ran off raspberry pi and Shadow Dash MS (see below about MegaSquirt)

   - Period correct aftermarket steering wheel/hub

   - GPS speedo sending unit

   - Apple CarPlay head unit (mounted in custom center console)

   - new upgraded kick panel speakers and slim powered subwoofers under both seats (must have symmetrical butt rattling)

   - Seam seal entire interior

   - Insulation (haven't decided on type yet)

   - Black carpet/headliner

   - Keyed switch panel

 

Engine/Powertrain:

   - KA24E, full rebuild for boost

      - Short block:  decked/honed, stock crank, forged rods, 8.5:1 forged pistons, ARP hardware everywhere

      - Head:  Decked/valve job, solid lifters (maybe? thoughts?), valve springs/retainers, maybe a cam, DIY P&P, ARP head studs, MLS head gasket

      - Intake:  S13 intake manifold converted to MAP sensor OR custom intake plenum converted to MAP sensor on factory D21 manifold runners

      - Throttle body:  dependent on intake; will stay drive-by-cable

      - Top mount fuel rail/injectors (will spec injector sizes when I cross that bridge)

      - Coil on plug/near plug conversion

      - Electronic wastegate (you'll see why)

      - Ball Bearing turbo, somewhere around 60-68mm.  I don't have a target HP goal for the engine, but I've daily driven high horsepower cars, and it's not convenient 75% of the time.  So if I had to guess, I'd like a turbo capable of 500hp, but still fun to drive when backed off to 250-300hp.

   - Boost actuated exhaust cutout (either electronic boost reference sent to motorized cutout, or find a mechanical cutout that operates similar to a wastegate, or even just use an actual wastegate as a cutout)

   - MegaSquirt 2 ECU

   - Quick switchable fuel/ignition tunes (valet/teenage son tune, daily tune, send a rod to the moon tune)

   - Figure out some rear axle swap that gives me LSD, a decent gear ratio, disk brakes, and isn't made of glass.

   - Retrofit cruise control (still need to research how to accomplish this with a drive-by-cable TB and it be true cruise control and not just a locked throttle position)

 

Other:

   - Retrofit D21 AC system OR use as much of the 620 and D21 AC systems I can and then add on a Vintage Air kit to it to finish it out.

   - Master battery disconnect

 

Here's my donor truck.  1994 D21 with a KA and 5 speed trans.  $600 bucks, not too shabby.

 

 

I'm also brainstorming for names for my project/truck and I'll take your suggestions.  My ideas so far are:

Couples Therapy

Doghouse

But Why?

 

Special thanks to @]2eDeYe, @Stoffregen Motorsports, @datzenmike, and @thisismatt and the rest of you on this board for always being so helpful and informative. 

Time to party! 🥳

 

[Stoffregen Motorsports]

First off, great shop. Fill it up with tools and a pile of cash quick. You'll need it for this project!

 

Second, for a go-fast ride, I might consider coilovers instead of air bags. The ride won't change, but the tuning of the suspension will be much easier with coils/shocks. And it will be more compact in the suspension areas giving you more room to make adjustments if needed. Or to make things adjustable, like control arms, etc.

 

Rear axle - Toyota, all day long. Parts availability, slightly added width and basic swap. No brainer. For slightly wider, try a 86-95 rear axle from an IFS equipped 4x4. They measure out to 58.5" wide, which is slightly wider than what you have now. You can build a limited slip diff with new gears and bearings for about $1000. You can't even find a LSD unit for a Datsun diff, and if you could, it would cost you $1000.

 

Last thing - and this is more of a philosophy than anything. Make the truck sound, with zero squeaks or rattles. Install new window rubber and felts as well as door seals too. This makes the truck nice and quiet, and you'll want to drive something quiet. Rattle traps are destined for the side yard within five years because nobody can stand the noisy ride. I'm going through the same thing with my rescued-from-the-scrapper full size Jeep Cherokee. Rattle trap when I first got it running, and many hours later, it only needs window channel felt to be quiet inside.

 

Good luck and I look forward to your progress reports.

[partytron69000]

@Stoffregen Motorsports thanks for the props on the shop. I am very blessed to be able to build the shop of my dreams a good 10+ years earlier in life than I planned, and I don’t take it for granted. 
 

I’ve thought about coils or even the air cup coils from Fortune Auto. But when I say spirited driving, I don’t mean track days or drift events. Really just hooning around from one stoplight to the next. So if there’s a more compelling argument to go with coils over bags for this project, I’ll for sure hear it out, but I’ll never check a lap time in this truck so I find it hard to justify a highly tuneable suspension. I’ve also loosely accepted the fact that if I don’t like the performance of the bags, I can just reuse my mounting brackets for coils from QA1, and uninstall all the air system components. Thoughts?

 

I have lots of hands on experience with the R200 rear end, and I’ve kept them together even with hard nitrous launches. Is a H190 that much weaker than something like a R200? I know the weak point on those is the CV axles, not the center section. Just trying to think if I really NEED to beef up the rear end or if I can live with single leggers and drum brakes. Has anyone ever found the limits of the H190 before?

 

Ditto on the rattles and squeaks. Already got started with new door and window rubbers this summer, but there’s still little details that will need to be addressed. 
 

Edit: the hardbody and roadster forums all claim ~285ft/lbs is the max for a H190 before it shears axle splines or some other shock event explodes the 3rd member. So I guess I’ll forget about saving money with the D21 axle and just shop for a Toyota axle or Ford 9”. Oh, and I did confirm I didn’t fall ass backwards into the rare H190 LSD that some KA 2wd D21’s came with. Bummer. 
 

@Stoffregen Motorsports any chance you want to spoon feed me Toyota models to look for axles from? I hear you’re the expert 👀

Edited September 28, 2022 by partytron69000

[thisismatt]

What'd the shop set you back? Putting in a mini split or two?

[partytron69000]

10 minutes ago, thisismatt said:

What'd the shop set you back? Putting in a mini split or two?

The cost of a second house 😅. It’s designed to be much more than just a workshop. I work 100% from home, so moving my home office out there in the lofted space, man cave area, full bathroom, 16ft ceilings. The project name for the workshop is Buy Once, Cry Once. 
 

Here’s the AC unit. 5 ton York

 

Here’s what the shop looks like today. AC crew is almost done with the rough in. Then it’s on to drywall, trim, paint, and button up finish work on AC/electrical/plumbing. 

[]2eDeYe]

Someday I will have a shop like that. Nice space. 🙂

[Stoffregen Motorsports]

I don't know what you have planned for walls, but in a shop space, I always use 3/4" plywood to skin the walls. This gives you plenty of space to screw things anywhere you want on the walls. In my current shop, the downstairs shop space, I left the plywood bare, but upstairs, I went over it with beadboard for a finished look.

 

To clarify, you're not thinking of doing an IRS swap are you? The R200 is strong, but it's not a solid axle.

 

The H190is a strong diff, but with the plentiful supply of old Toyota axles, I might consider one anyway, even if you're not thinking of throwing performance parts at it right now. It will leave the door open for future mods without having to recreate all your suspension brackets.

Edited September 29, 2022 by Stoffregen Motorsports

[partytron69000]

1 minute ago, Stoffregen Motorsports said:

I don't know what you have planned for walls, but in a shop space, I always use 3/4" plywood to skin the walls. This gives you plenty of space to screw things anywhere you want on the walls. In the downstairs shop space, I left the plywood bare, but upstairs, I went over it with beadboard for a finished look.

 

To clarify, you're not thinking of doing an IRS swap are you? The R200 is strong, but it's not a solid axle.

 

The H190is a strong diff, but with the plentiful supply of old Toyota axles, I might consider one anyway, even if you're not thinking of throwing performance parts at it right now. It will leave the door open for future mods without having to recreate all your suspension brackets.

Going full drywall throughout for a finished look. Going for that ultra modern look where everything’s black!

 

100% not doing an IRS swap. Way too overkill for what I’m trying to accomplish.

 

Yeah, I updated my response to you with what I learned about the H190 and it exploding around 285ft/lbs. I like the Toyota axle idea, and I started researching last night. One of the 58.5” axles from a early 90’s 4wd T100/4Runner seems like a good fit. The hard part seems like finding them at junkyard prices with the 3.07/3.15 ratios I’m looking for. I think a reasonable progression would be to get the Toyota axle with an open diff and low gears so I can do the airbag swap and get running with the L20B right away and still have highway gears. And then once the KA-T goes in, change the ratio to exactly what I want and get a LSD in it. 
 

Another option I’m considering is a Ford 8.8”. Seems similarly priced to Toyota axles, seems easier to find (I may just not know where to look for Toyota axles) and is equally strong. Only downside is factory 4 and 5 lug axles whereas I get matching 6 lug with Toyota. 

[Farmer]

You can also look into using the rear end out of a 94-97 rodeo, passport or simular 4x4. Rear disc, 6 lug and dana44. Has to be shortened 2inch each side

 

Heres a build thread that talks about it and other stuff that may help you

https://ratsun.net/topic/52633-620-with-sr20det-with-ac/

[Farmer]

I ask him about it before he disappeared from ratsun

All responses

 

It was from a Rodeo.  I forget the year, but I can look it up later.  The later years were an Isuzu corporate rear end and not a Dana.  I had my rear end narrowed here in town ( Mesa, AZ).  The only reason I went with the Isuzu is because it has the same bolt pattern as the Datsun so the rear discs are also a 6 bolt pattern.  The axles had to be ordered from another shop.  It's an expensive mod.  I thinks it's almost a thousand bucks with narrowing, new custom axles and new bearings.  Parts for the Dana are also easy to get. 

 

Also, when the guy narrowed the rear end, I had him relocate the spring perches and because I have a different engine/trans I had to measure the pinion angle and match it with the spring perches. 

 

I've seen guys do their own axle housing narrowing.  It's not rocket science, but it takes a good welder and it is very critical the ends are straight.  I read an article where a guy found a tube he placed inside the housing to line it up and then welded them up. 

___________________________________________

 

Here's the approximate breakdown off the top of my head:

 

$200  narrowing housing and moving perches inward

$400 custom axles

$200 new bearings

$ 50 Dana 44 to Nissan adapter flange.

 

so I guess more like $850.

 

I think my diff is a 94 or 95.

_____________________________________________________________________________

 

I got the axles from Mitchell Differetial.  I wasn't sure how accurate the measurement needed to be so I just sent them my old axles.  Some axles are possible to respline depending on how they are built.  I can't remember if it was possible or not with the Dana 44 axles.

 

http://mitchelldifferential.com/custom-axles/

 

________________________________________________________________________________________________

 

 

[partytron69000]

1 minute ago, Farmer said:

I ask him about it before he disappeared from ratsun

All responses

 

It was from a Rodeo.  I forget the year, but I can look it up later.  The later years were an Isuzu corporate rear end and not a Dana.  I had my rear end narrowed here in town ( Mesa, AZ).  The only reason I went with the Isuzu is because it has the same bolt pattern as the Datsun so the rear discs are also a 6 bolt pattern.  The axles had to be ordered from another shop.  It's an expensive mod.  I thinks it's almost a thousand bucks with narrowing, new custom axles and new bearings.  Parts for the Dana are also easy to get. 

 

Also, when the guy narrowed the rear end, I had him relocate the spring perches and because I have a different engine/trans I had to measure the pinion angle and match it with the spring perches. 

 

I've seen guys do their own axle housing narrowing.  It's not rocket science, but it takes a good welder and it is very critical the ends are straight.  I read an article where a guy found a tube he placed inside the housing to line it up and then welded them up. 

___________________________________________

 

Here's the approximate breakdown off the top of my head:

 

$200  narrowing housing and moving perches inward

$400 custom axles

$200 new bearings

$ 50 Dana 44 to Nissan adapter flange.

 

so I guess more like $850.

 

I think my diff is a 94 or 95.

_____________________________________________________________________________

 

I got the axles from Mitchell Differetial.  I wasn't sure how accurate the measurement needed to be so I just sent them my old axles.  Some axles are possible to respline depending on how they are built.  I can't remember if it was possible or not with the Dana 44 axles.

 

http://mitchelldifferential.com/custom-axles/

 

________________________________________________________________________________________________

 

 

This is awesome, thank you!  The more I keep digging into it, the Ranger 8.8 may be the one. Wouldn’t need to cut down the housing, can find one with good highway gears easy, and there’s about 10x as many for sale on eBay/Facebook than early 90’s T100/4Runner axles.  I can live with 5 lugs in the rear since I’m buying new wheels anyways. My only concern is running 1-2” of lateral pinion offset since the Ranger 8.8 is passenger side offset, but apparently hot rod guys have no problems with it.

[partytron69000]

Damn, this is down the street for $500. Might have to go get it just for the convenience factor. 
 

https://imgur.com/a/XpHJt1x

[Stoffregen Motorsports]

4 hours ago, partytron69000 said:

Going full drywall throughout for a finished look. Going for that ultra modern look where everything’s black!

 

100% not doing an IRS swap. Way too overkill for what I’m trying to accomplish.

 

Yeah, I updated my response to you with what I learned about the H190 and it exploding around 285ft/lbs. I like the Toyota axle idea, and I started researching last night. One of the 58.5” axles from a early 90’s 4wd T100/4Runner seems like a good fit. The hard part seems like finding them at junkyard prices with the 3.07/3.15 ratios I’m looking for. I think a reasonable progression would be to get the Toyota axle with an open diff and low gears so I can do the airbag swap and get running with the L20B right away and still have highway gears. And then once the KA-T goes in, change the ratio to exactly what I want and get a LSD in it. 
 

Another option I’m considering is a Ford 8.8”. Seems similarly priced to Toyota axles, seems easier to find (I may just not know where to look for Toyota axles) and is equally strong. Only downside is factory 4 and 5 lug axles whereas I get matching 6 lug with Toyota. 

Ok, be careful there. A T100 axle is not the same as a pickup or 4Runner axle. The T100 axle use an 8.4" diff (vs the mini truck 8" diff) which is harder and more expensive to get parts for. It also has shims for the side bearings vs the threaded adjusters of the 8" diff, which makes them harder to build.

 

As far as I know, a 3.70 R&P is the highest ratio available, but I may be wrong. It is the highest ratio I have personally set up. Stock was 4.10 in most Toyota 4x4 mini trucks.

 

[EDM620]

Damn I have garage envy, that's a nice size for a shop. Some guys don't like lots of sunlight but you can run those solar tubes to bring daylight into the inner area of your shop.

 

You've planned lots of interesting things into your build, I'll be watching your progress.

[partytron69000]

I really do think automobiles are sentient creatures. She must have heard me talking about replacing her 🫠. Just a heater hose leak. 

Edited October 5, 2022 by partytron69000

[Stoffregen Motorsports]

I agree. There is a soul in there somewhere.

[datzenmike]

 

200mm is 10mm larger diameter than an H-190. Larger diameter allows thicker stronger gears with the same ratio.

 

LSD differentials place more load on them with two tires providing traction. One tire spinning acts like a fuse and limits the torque felt by the differential.

 

From Club 1200....

 

diff	inches	max. torque capacity
H145	5.71	~100 lb. ft.
H150	5.91	~125 lb. ft.
H165	6.50	~225 lb. ft.
H190	7.49	~285 lb. ft.
R200	7.88	~300 lb. ft.
Ford 8	8.00	~325 lb. ft.
Ford 8.8	8.80	~500 lb. ft.
Ford 9	9.00	~600 lb. ft.

 

285 vs. 300?  

[partytron69000]

2 hours ago, datzenmike said:

 

200mm is 10mm larger diameter than an H-190. Larger diameter allows thicker stronger gears with the same ratio.

 

LSD differentials place more load on them with two tires providing traction. One tire spinning acts like a fuse and limits the torque felt by the differential.

 

From Club 1200....

 

diff	inches	max. torque capacity
H145	5.71	~100 lb. ft.
H150	5.91	~125 lb. ft.
H165	6.50	~225 lb. ft.
H190	7.49	~285 lb. ft.
R200	7.88	~300 lb. ft.
Ford 8	8.00	~325 lb. ft.
Ford 8.8	8.80	~500 lb. ft.
Ford 9	9.00	~600 lb. ft.

 

285 vs. 300?  

Just to clear up any confusion, I’m not suggesting I do a R200 IRS swap. Was just providing anecdotes.

 

The 8.8 or a Toyota 8” are the way I’m going. Searching online for the next 5-6 weeks until my workshop is done for a Toyota one since it’ll give me the correct pinion angle without shortening axle tubes. The Toyota ones seem real tough to find though. If I get into the shop and still can’t find one, I’ll have to go with the 8.8 out of the Ranger and decide if I want to run a little bit of lateral pinion angle or cut down axle tubes and get custom axles. Don’t really want to pay for custom axles but if it’s my only viable option, I will.

[Stoffregen Motorsports]

Just found three, but they're in NY and PA.

[Stoffregen Motorsports]

Changed the search area to Southeast and found too many to show here.

[partytron69000]

 

21 minutes ago, Stoffregen Motorsports said:

Changed the search area to Southeast and found too many to show here.

Thanks. I’ll dig into that junkyard parts finder search engine more. 

[partytron69000]

Made a promise to myself this wasn’t going to be a dead thread and I’m seeing this one through. So here’s a shop build update. Waiting on the garage door to show up, black turf carpet in the loft, and little punch out work here and there and we’re done. The 5ton HVAC unit was a clutch decision. It’s 20-45 degrees in middle Tennessee right now and shop can hold temp comfortably with the thermostat just set to 55 (and that’s with just a tarp over the garage door opening). Definitely fucked up my budget though and can’t afford a professional epoxy floor right now, so looks like it’s time to roll up the sleeves and get to work myself 🫣. 
 

Shop pic

[thisismatt]

Looks great. Nice to see one with the inside finished out

[Duncan]

I recently got a Ford 8.8 from a junkyard and it has limited slip.  90's Ranger trucks (mostly) all had them, and the Explorers had a disc brake option. 

 

A quick online search, and you can easily find the legend to decipher the tags they place on them.  I'm not saying it's better than any other axle, but they are plentiful and cheap in the junk yards. I was able to find a brand new Ford (Made in USA) ring and pinion for $200 shipped to my door. 

 

 

 

 

[partytron69000]

NOT DEAD YET.

 

Figured I owed a periodic update. Shop’s 99% complete and finally looking like somewhere I can actually work efficiently. Super happy with how it’s all turned out. Tools finally properly sorted and finally in a big boy box and roll cart. Picked up my 2 post lift last night from the freight yard. One of the casters on my Amazon special shop hoist decided to ejecto seato while holding 1,300lbs offloading the lift off the trailer, so that was….fun 😅. 
 

First on the to-do list after the lift gets installed is helping my buddy with his SW30 Turbo project that needs a trans swap and a new turbo. Then next up is bags, wheels/tires, and flares on the 620. 
 

I love this truck so much, it doesn’t bother me at all to keep it stock for now. Such a great truck, I’m never selling it, so this thread will never end, just may become longer than expected 🤣. 
 

Be good Ratsun! 🥳

 

https://imgur.com/a/NRPfy3c
video of shop layout, lift, and the flimsiest caster wheel China has ever made.