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Lightweight engine for a 620


makya

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Hey guys. Long time, no see. 

 

   I sort of stopped coming around after I sold my custom cab dually to ^#&#,$*?? 

And parked the 4x4. 

 

Anyway, I'm looking to see what you guys can suggest for a lighter weight engine than the stock l20b.  I've thought about retrofitting an sr20de from a g20 and using older components, but I know you guys know swaps better than I do.  What I'm looking for:

 

~140hp, more or less

Reliable

Light

Preferably hook up to a 4sp auto or 5sp manual.

Relatively simple engine management (or can be retrofitted to obd-Ii or earlier controls) 

 

Basically, I'm re-doing the '75 std. Cab 4x to do some light offroad/camping/overland trips, and I want to do something light and reliable.

 

Any ideas are appreciated, thanks in advance 

Pics included of the old build for attention

0021b6.jpg

35acscd.jpg

Edited by makya
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4x4? it sure is NEVER going to be light so take that out of the equation and Get a KA24E or KA24DE. They are around 145 hp. ]2eDeYe owns a 4x4 KC and sells custom engine and transmission mounts. Been done a hundred times so well documented, no surprises, dependable

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I'm at 3500 lbs right now with an l20b. For a 4x thats light. I'm just looking to shave a 100 lbs or so on the motor, and then I'll be cutting weight elsewhere as well. (Aluminum diffcover and hubs on the 30,  aluminum covers on the transfer case, etc...

Ultimately,  saving a few pounds here and there, makes up for adding weight later (gear, water, tent, lights, etc...)

And a newer engine makes it easier to source parts on a trip when necessary 

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Wow, good to see you still around and still have the 620 😄

L series is pretty light to begin with, then so is a 620 haha.

 

The SR is a powerful motor and turbo might be nice. 

 

All that said, I love my KA and would choose the power over the L any day. 

I also like the parts availability over the L & SR motors

 

B0D0AB4B-8021-4146-A70D-6F77C8A8B42E.jpeg

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2 hours ago, ]2eDeYe said:

Wow, good to see you still around and still have the 620 😄

L series is pretty light to begin with, then so is a 620 haha.

 

The SR is a powerful motor and turbo might be nice. 

 

All that said, I love my KA and would choose the power over the L any day. 

I also like the parts availability over the L & SR motors

 

B0D0AB4B-8021-4146-A70D-6F77C8A8B42E.jpeg

 

2 hours ago, ]2eDeYe said:

Wow, good to see you still around and still have the 620 😄

L series is pretty light to begin with, then so is a 620 haha.

 

The SR is a powerful motor and turbo might be nice. 

 

All that said, I love my KA and would choose the power over the L any day. 

I also like the parts availability over the L & SR motors

 

B0D0AB4B-8021-4146-A70D-6F77C8A8B42E.jpeg

Hey! Good to see you again! I'm really wanting to do something different for a datsun. I'm not worried about the cost of it this time, which is why i thought of the sr. 

I also thought about going totally out of the box and using a boxer motor. Ea82s are super light, and would make it easy to keep the truck lower with 35's on it. They used a variant of the 3n71, so I might be able to swap input shafts and make it work, the engine might be too wide though. 

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1 hour ago, Icehouse said:

I'm with Steve, get the KA, super cheap and make good power.  Also super easy to hook up to your existing L series transmission.  

I may just go that route, I'd like to do something  a little different this time.

 

I still have the hybrid motor in it, but it needs a refresh.

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I vote KA! 

I am really happy with the KA in my 620 - and its not even running at tip top shape (super rich, I think its in loop mode as I figure out an O2 sensor issue) 

SR would be great and slightly lighter, but remember on of the big benefits of the KA is its displacement and low end torque. Especially on a wheeling rig where you dont want to have to ring the engine out all the time.

KA is a super easy swap too, about as drop/bolt in as you can get if you use RedEyes mounts. Just need some exhaust work and a driveshaft.  The Megan Racing/Knock off header clears the steering box and linkage. With a angled flange coming off it you can clear it inside of the torsion bar too with a 2.5" pipe. 

You'll notice wheel and tire weight savings far sooner then 100lbs of engine weight... hell by the time you load up the cooler with beer and ice you probably adding that 100lbs back in 🍻

Edited by demo243
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O2 is open loop while engine warms up. One of the inputs to the ECU is a temperature sensor. When warmed up the system goes into closed loop mode and the mixture is regulated with input from the O2 sensor. It also goes into open loop at full throttle when the mixture is run richer for better power output and the O2 sensor output is ignored.

 

So look at the temperature sensor and the throttle position switch. It may think the engine is cold or at full throttle all the time

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2 hours ago, datzenmike said:

O2 is open loop while engine warms up. One of the inputs to the ECU is a temperature sensor. When warmed up the system goes into closed loop mode and the mixture is regulated with input from the O2 sensor. It also goes into open loop at full throttle when the mixture is run richer for better power output and the O2 sensor output is ignored.

 

So look at the temperature sensor and the throttle position switch. It may think the engine is cold or at full throttle all the time

I’ll check those out.

 

Don’t want to jack this guys thread... but... Doesn’t idle cold, so the idle is set mechanically and require hold it open a little bit on start up. Once warm it’s ok- makes me think that’s IACV related. Then once it’s running with the O2 plugged in it will drive fine and then suddenly fall flat on it’s face, then run fine again. Always stumbles right at the least opportune moment, like pulling out into traffic... with the O2 unplugged it’s runs fine, but very rich (stinks), and isn’t quite as peppy. I’ve got the engine stripped down as much as possible so that all probably doesn’t help either... might try and carb it like my 510 is this summer, potentially with bike carbs, kinda interested in a Mikuni HSR conversion.
 

The only major complaint I have with the KA is how tight everything is in and around this intake... makes it a pain working on it...


Anyway, sorry to thread jack OPs post...

 

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If you have the throttle adjusted to keep for cold idle you IACV will not work correctly.

Have you pulled codes? Do you have a thread?

 

-end hijack. 

 

How wide is the boxer engine? 

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29 minutes ago, ]2eDeYe said:

If you have the throttle adjusted to keep for cold idle you IACV will not work correctly.

Have you pulled codes? Do you have a thread?

 

-end hijack. 

 

How wide is the boxer engine? 

I do in my sig.

 

always wanted to throw a turbo boxer Subaru engine in one of these... although I’m a big fan of keeping it in the family... I bet changing spark plugs would be a bitch!!! Gotta pull the engine 

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28 minutes ago, 5t341tH said:

rotary engine

No low end torque in a rotary. Guys were trying to put them in samurais, but they were having to use 8:1 transfer case gears to get them to work off road. 

The ea82 motor is about the same weight.

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7 hours ago, ]2eDeYe said:

If you have the throttle adjusted to keep for cold idle you IACV will not work correctly.

Have you pulled codes? Do you have a thread?

 

-end hijack. 

 

How wide is the boxer engine? 

Its about 28 inches wide, 24 inches tall and about 18 inches long, with the intake and exhaust mounted

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Rotary, boxer.... why make things more difficult??? complex and expensive??? Those tires are way to large for 4.375 gears.... get some 4.875s. You have an engine and it's already in and running and it weighs about 280 pounds. The KA is100 pounds more! You are not going to find another that weighs 100 pounds less. Weight doesn't matter on a 4x4.

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8 hours ago, makya said:

Its about 28 inches wide, 24 inches tall and about 18 inches long, with the intake and exhaust mounted

 

 

22" between the frame rails. Would likely require major surgery.

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4 hours ago, datzenmike said:

Rotary, boxer.... why make things more difficult??? complex and expensive??? Those tires are way to large for 4.375 gears.... get some 4.875s. You have an engine and it's already in and running and it weighs about 280 pounds. The KA is100 pounds more! You are not going to find another that weighs 100 pounds less. Weight doesn't matter on a 4x4.

I get it Mike,  you don't want me to do it.

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3 hours ago, ]2eDeYe said:

 

 

22" between the frame rails. Would likely require major surgery.

Thats what I'm thinking. But I've built plenty of rockbuggies over the years, so I know I can do it, im just trying to figure out which way to go. I'm trying to go with roughly a 35" tire on as little lift as possible. I've bobbed the bed, pulled the motor and front axle mounts, and I'm going to look at input shaft height and what I would need to do to the front and rear frame rails to make something new work. I may Notch the rear rails and do hoops to allow for some articulation at lower height.

I'll probably message you or ask for input later, are you still on the other forum at all?

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21 minutes ago, makya said:

I get it Mike,  you don't want me to do it.

 

No! it's just the limitations you set. Is there a 280 pound 140 hp engine? I just say forget the weight and the world is your oyster. For crawling something with low speed torque.

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1 hour ago, datzenmike said:

 

No! it's just the limitations you set. Is there a 280 pound 140 hp engine? I just say forget the weight and the world is your oyster. For crawling something with low speed torque.

Thanks, 

The boxer would fit those parameters,  but it wouldn't be my first choice. 

A lot of what I've built over the years are challenges, and I've built a hybrid motor, put a 350 in a 70's Celica, a 460 in a 73 f100 ranger, worked on competition rock crawlers, drag cars, etc..

 

Really I want to do some thing different. 

 

I know I'm going to try some hydroforming on this project somewhere also (maybe as paneled gussets in some tubing? ), fenders will be cut to keep it low, probably use some lowrider tricks to raise the fender wells, etc...

 

Like I was kind of saying above, im just bored and trying to think of something that interests me. I might fall back to a normal swap, but I'd like to exhaust my options first. 

Edited by makya
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20 hours ago, makya said:

Thats what I'm thinking. But I've built plenty of rockbuggies over the years, so I know I can do it, im just trying to figure out which way to go. I'm trying to go with roughly a 35" tire on as little lift as possible. I've bobbed the bed, pulled the motor and front axle mounts, and I'm going to look at input shaft height and what I would need to do to the front and rear frame rails to make something new work. I may Notch the rear rails and do hoops to allow for some articulation at lower height.

I'll probably message you or ask for input later, are you still on the other forum at all?

 

Once you remove the frame from the equation anything is possible. 🙂

I have an account over there still and at the weird new place, but mostly for tech/reading purposes.

Hang out here mostly, have more than a couple Datsuns in the fleet, lol. 

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On 12/15/2020 at 11:49 AM, makya said:

Thats what I'm thinking. But I've built plenty of rockbuggies over the years, so I know I can do it, im just trying to figure out which way to go. I'm trying to go with roughly a 35" tire on as little lift as possible. I've bobbed the bed, pulled the motor and front axle mounts, and I'm going to look at input shaft height and what I would need to do to the front and rear frame rails to make something new work. I may Notch the rear rails and do hoops to allow for some articulation at lower height.

I'll probably message you or ask for input later, are you still on the other forum at all?

Why only 35's? Cut the fenders and lower the shit out of it and still run 37's or even 40's. Lots of trail rigs are running 40's with 2-3 inches of up-travel these days.

 

I don't remember what the frame profile looks like on a 620, but you could always cut the frame off around the VIN and raise it. Move the motor back and push the axle forward so the crank pulley is behind the axle centerline. For gearing, use a 280ZX turbo T5 bellhousing, a Jeep T5 trans and a Dana 300 with 4:1 gears. I've never built this combo, but I have done the research and it seems like it should work. 

 

This guy sells adapter plates for KA24 to GM "manual/auto trans" - https://www.bobsautomotivemachine.com/products/

 

I don't think I have ever seen a 620 built into a serious trail rig, but I can picture it in my head.

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Really it sounds like you are looking for entertainment as the primary goal, with the weight/power of the engine as secondary.  In that case, I ask what do you want to put in it?  What seems like a lot of fun to mess with?

 

TDI w/ Toyota Trans is small with good power that can be made.

Cummins makes 4 cylinder diesel crate motors just for powering small offroaders.

VQ35w/ obd1 vq30 engine controls

VH45 to D21 transmission

4 cylinder turbo Sky/Soltice motor w/ Colorado trans/tcase

 

Or really go down the rabbit hole.  "Home Built by Jeff" on youtube is building a 60s alfa romeo with  ferrari Modena V8 connected to a BRZ 6 Speed for front engine/ rear wheel drive fun.

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