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RB25 Powered KC

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Does anybody have experience with this engine swap? I see it fairly often on other Datsun vehicles but the 620KC/RB combo seems to be uncommon. I am planning to start this summer and was wondering if the Datsun gurus knew of any glaring issues before I dive in. Any and all input welcome, thanks!

 

P.S. I am thinking a ‘77-‘79 KC for this project. 

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The big problem will be room in the engine bay..... isnt that a straight 6 vs the 4.. 

But I say go for it...

you'll probably have to sacrifice the firewall or do some remote radiators or something.....

Most likely will need to convert to coilovers to get the torsion bars out of the way... not to mention your adding weight to the front... at least I believe that year 620 has disk brakes and ball joints right, so that's good.... 

Do you have access to the motor or is that the next step?

I would try to get some measurements 

To see what you really have for room....

 

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I know of a guy in Washington that has begun the swap. I dont know if he ever got it done, we lost touch but he for sure cut out his firewall to clear the motor. I think he kept stock rad location though. 

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It won't fit but anything can be made to fit if you sacrifice something like the firewall and heater or put the rad in the box. Not exactly a great idea when there are lots of other insane V6 swaps that actually do fit. There is huge risk to doing this, mainly to the 620 that ends up in the wrecking yard when the builder runs out of money and/or ideas to make it work. Think about it. There's probably a good reason why there are no RB swapped 620 driving around. 

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The reality of cutting out and replacing sheetmetal is something most guys don't have the skill set to handle. You need more than a torch, a sawzall, a hammer and a welder to put it all back together in a manner that doesn't look like ass, trap water or leak water. So if you're not a sheetmetal guy, or not willing to spend to have someone do the sheetmetal work, I say don't do it.

 

But...if you are willing and able, go for it. That would be a sweet swap.

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The guy that did a 510 rb25 crashed into a tree ,too much fwd weight. There is a 521running around down here near Inland Empire ! was for sale .

 

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I forgot to say a guy wants me to do a rb25 in a Datsun 610 ,I have been putting him off for six months , I believe will be a decent swap  with bigger longer engine bay with R200 in back and roll cage .

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A 4-cyl turbo would still have some challenges but would be a much better fit. SR20DET or even set up a KA24 for forced induction and put that in there.

 

I have seen a couple 620 trucks with an L28 installed. One had the radiator and battery relocated to the bed. The other cut the firewall back so that the engine could be pushed further back to fit the radiator up front.

 

The torsion bar suspension often gets in the way of a turbo and/or exhaust of any 620 engine install.

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Thank you all for the quick and informative replies; I will start this off by saying the goal is to avoid all trees lol. Working with *approximately* rounded numbers, I will have about 150-200 lbs of added weight in the engine bay alone. Not to mention a lot of space to make up to fit an in-line 6 with a 5(6?) speed manual. I am hoping to avoid relocating the rad, that’s not something I would undertake voluntarily.  Unfortunately I do not have my hands on an engine at this time, I was hoping to get some warning/reassurance from the gurus here before putting any money into the swap. Many thanks for the advice so far. 

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My advice if wanted -buy redeyes motor mounts and put a sr20de(NON TURBO) in there and enjoy almost twice stock horsepower ,smooth and great gas mileage. Maybe later take on bigger job . I also have one here with coil overs and no torsion bars in front for exhaust clearance ,Its all work not trying to crush dreams.

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An open mind...you threw me off guard. That's not the norm around here!

 

What angle are you approaching this project from? Are you going to try to do the work yourself? Or are you willing and able to pay someone to do some of it for you? If the latter, then what are your expectations?

 

If I had this job in my shop, I would suggest two or three options.

 

Option A - Fabrication only. To fit the engine, make firewall (and/or floor) mods and build motor mounts, I would guess you'd be looking at 30-50 hours of fab.

Option B - Fab + mechanical. Add another 50-100 hours for plumbing, linkages, exhaust. More than likely I'd double that for a clean and nice looking turbo install.

Option C - Turnkey. Sky's the limit. Add time for electrical, suspension and brake upgrades, gauges/dash, pedals (if mods required to fit), HVAC fit around firewall mods, fit and finish, powder coating, etc.

 

 

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1 hour ago, Stoffregen Motorsports said:

An open mind...you threw me off guard. That's not the norm around here!

 

What angle are you approaching this project from? Are you going to try to do the work yourself? Or are you willing and able to pay someone to do some of it for you? If the latter, then what are your expectations?

 

If I had this job in my shop, I would suggest two or three options.

 

Option A - Fabrication only. To fit the engine, make firewall (and/or floor) mods and build motor mounts, I would guess you'd be looking at 30-50 hours of fab.

Option B - Fab + mechanical. Add another 50-100 hours for plumbing, linkages, exhaust. More than likely I'd double that for a clean and nice looking turbo install.

Option C - Turnkey. Sky's the limit. Add time for electrical, suspension and brake upgrades, gauges/dash, pedals (if mods required to fit), HVAC fit around firewall mods, fit and finish, powder coating, etc.

 

 

I guess I did forget to mention I am new here lol. And I would be looking at doing the work myself with the help of some experienced friends. I guess I never put the timeframe into perspective but I’m not (that) worried about spending the time to do it right. Tuning and final aesthetic application (ie paint, wrap, etc) are out of my wheelhouse and would definitely require outsourcing, but that’s a fairly small part of the process IMHO. 

 

2 hours ago, hosestop@msn.com said:

My advice if wanted -buy redeyes motor mounts and put a sr20de(NON TURBO) in there and enjoy almost twice stock horsepower ,smooth and great gas mileage. Maybe later take on bigger job . I also have one here with coil overs and no torsion bars in front for exhaust clearance ,Its all work not trying to crush dreams.

 A very valid suggestion and I must say I do love me a good old blacktop, though I will say staying NA would make the goal of a “way too fast” street truck a bit more difficult. No dreams crushed; a realistic opinion is always welcome. Decisions decisions!

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Stoffregens hour estimate is for professional mechanics in a fully outfitted shop. Adjust hours accordingly. This can actually be enjoyable if you have the space and tools. The six cylinder is ambitious and folks around here hate to see a good truck get scrapped because someone bit off more than they could chew.

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Not trying to talk anyone in, or out of anything here, just sharing some perspective on expectation vs. reality. I LOVES me some RB goodness and totally understand the draw in stuffing one up a 620 hood. Back in the 80s there was a 510 L26 that was showing up at car shows in SoCal that I studied. Like a 620 RB with front rad would have, the tranny bell, head, intake and exhaust (custom made) where pushed back 4-6" so the fire wall dash, wheel, and seats were shifted back to match. The entire pedal box had to be custom built to narrow and offset it to the left. It looked ridiculously small and cramped down there. When I finally asked the guy for advice on doing the swap on my car, his passionate response was "Don't! It looks cool, but it's a HUGE amount of work that actually destroys the car." His advice was to build a stout L20B and so I did. In hindsight, I'm still grateful. Fast forward 30 years, I built a really fast SR20DET 510, and even with tons of aftermarket support and shared first hand knowledge of the swap, it was WAY more work to do it right than I ever expected. Here in the states RB25s aren't supported much at all, and you'd be hard pressed to find anyone with first hand knowledge on swapping one into a 620. It's way too easy to make assumptions about how it's all going to work, but trust, once you start skinning that cat there'll be one unexpected issue after another. An SR20 de, or det swap is better suited to the truck, and more fun than should be allowed on the street. 

 

Either way you go, best of luck on the pursuit.

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20 hours ago, bottomwatcher said:

Stoffregens hour estimate is for professional mechanics in a fully outfitted shop. Adjust hours accordingly. This can actually be enjoyable if you have the space and tools. The six cylinder is ambitious and folks around here hate to see a good truck get scrapped because someone bit off more than they could chew.

Yes, those are estimates based on the fact that I do this for a living. Thanks for clarifying.

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14 hours ago, paradime said:

Not trying to talk anyone in, or out of anything here, just sharing some perspective on expectation vs. reality. I LOVES me some RB goodness and totally understand the draw in stuffing one up a 620 hood. Back in the 80s there was a 510 L26 that was showing up at car shows in SoCal that I studied. Like a 620 RB with front rad would have, the tranny bell, head, intake and exhaust (custom made) where pushed back 4-6" so the fire wall dash, wheel, and seats were shifted back to match. The entire pedal box had to be custom built to narrow and offset it to the left. It looked ridiculously small and cramped down there. When I finally asked the guy for advice on doing the swap on my car, his passionate response was "Don't! It looks cool, but it's a HUGE amount of work that actually destroys the car." His advice was to build a stout L20B and so I did. In hindsight, I'm still grateful. Fast forward 30 years, I built a really fast SR20DET 510, and even with tons of aftermarket support and shared first hand knowledge of the swap, it was WAY more work to do it right than I ever expected. Here in the states RB25s aren't supported much at all, and you'd be hard pressed to find anyone with first hand knowledge on swapping one into a 620. It's way too easy to make assumptions about how it's all going to work, but trust, once you start skinning that cat there'll be one unexpected issue after another. An SR20 de, or det swap is better suited to the truck, and more fun than should be allowed on the street. 

 

Either way you go, best of luck on the pursuit.

My old friend Ralph Kenyon owned that 510, though he did not build it. I remember helping him rescue it from years of blackberry growth alongside a barn in Napa. The work didn't look that great at all once you started to notice all the bondo chipping off the firewall.

 

Another friend of mine took the same approach you suggest. We built him a long rod 2300 fo his 240Z. Yes, a 4 cyl in a Z car. The pushed back motor and lighter weight made that car scream. It also had the roof chopped off to make a roadster 240Z. They did a beautiful job.

 

What's that old Colin Chapman saying? "Add lightness." Weight savings is potentially worth more than HP.

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The worst part is how are you going to do a clutch job down the road ? trans does not come out bottom , trapped in there above frame (must remove motor and trans as one split bitch job on floor ), I am doing with removable tunnel , and the dagger -really a bitch doing sr20det in a truck also , maybe check out done 521 if someone knows him on here Tanker ! Please how many turbo det 620s ever were done  finished , the Red one I did is in Texas now with Toyota  lifer.

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If you're taking the time to do all of this work, it would be easy enough to modify the crossmember to be able to remove it for maintenance.

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Again, all valid points and I hadn’t considered the issue with the clutch, though I do agree a (fairly) simple crossmember modification would allow for much easier maintenance. Again this post is just to get opinions before I start investing in the project. Many thanks for the advice thus far. 

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Xmember has torsion bars assembly  , another reason to get rid of torsion bars for coil over hotrod shocks. Just to make trans come out bottom.

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2 hours ago, hosestop@msn.com said:

Xmember has torsion bars assembly  , another reason to get rid of torsion bars for coil over hotrod shocks. Just to make trans come out bottom.

I will make a note of that, thanks for the info!

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