Other Engine Conversions - non V-8 Discussion of non-rotary engines, exc V-8's, in a car originally powered by a Rotary Engine.

SR20DET powered FB

Old 06-06-13, 02:39 PM
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SR20DET powered FB

After my 12A was found to no longer be usable, I decided to shop around for a new powerplant for my FB. After quite a bit of searching I found the S13 SR20DET black top to be the engine that would give me the most bang for the buck. This build is ongoing, but as a first engine swap attempt ever, I'd say it's going well. Pics will follow shortly. I know this swap is kind of rare, so if anyone has any questions on what I did, please let me know.
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Old 06-06-13, 06:59 PM
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Best Bang for the Buck

Where you are located you may be right, but here in Seattle, the SR20s sell for at least $1,000 more than the RB20s. I bought a complete Skyline R32 front clip for $1600 from Foreign Engines Inc,and we used everything we could in the FB including the clutch fan, radiator and hoses, intercooler, stock oil pan and numerous small pieces. I made no effort to increase the power, as this is a daily driver and I am getting more than 200 hp to the wheels. Just made my first road trip, used the boost quite a bit going over some mountain passes, and got 29 mpg round trip. My friend has an S13 with the SR20DET, has about the same performance and gets similar fuel mileage. I think you will be very happy with that motor.

I increased the weight by about 100 pounds, assume your SR20 swap will weigh about the same as the rotary. Post some photos when you can.
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Old 06-06-13, 07:05 PM
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Very not bad! It was only after I bought the engine/trans/etc. from JDM source that I found the full front clips for sale. If I had to do it over I'd probably still stick with the SR for the fact that there is a lot of cross-compatibility with US 240SX. I'd ****** up a Silvia clip and hi-ho silver!
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Old 06-06-13, 07:08 PM
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Here's the ugly duckling...
Attached Thumbnails SR20DET powered FB-image.jpg  
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Old 06-06-13, 07:13 PM
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Hood's off, engine's ready to pull.
Attached Thumbnails SR20DET powered FB-image.jpg  
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Old 06-06-13, 07:14 PM
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And here is its beastly replacement!
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Old 06-06-13, 07:16 PM
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Slight snafu pulling the old engine... Someone put a plastic garbage can and oil change pan in front of a kerosene heater in January... Fire dept thought it was funny
Attached Thumbnails SR20DET powered FB-image.jpg  

Last edited by 1981GSL; 06-06-13 at 07:19 PM. Reason: Pic was upside down!
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Old 06-06-13, 07:23 PM
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Back to business, then. Pulled the 12A, disconnected the control arms from the crossmember and removed the crossmember. Raided the local pick and pull and found an '91 240SX to donate the crossmember and steering rack. Had to widen the holes a bit, but otherwise the crossmember bolts right in.
Attached Thumbnails SR20DET powered FB-image.jpg  
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Old 06-06-13, 07:26 PM
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Engine is in! Had to carve up the interior to clear the shifter, but my interior was junk anyway, so no big loss. Widened the holes on the FB transmission crossmember and the SR's transmission bolted right up.
Attached Thumbnails SR20DET powered FB-image.jpg  

Last edited by 1981GSL; 06-06-13 at 07:35 PM. Reason: Forgot attachment
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Old 06-06-13, 07:28 PM
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Fits almost too well. Slight clearance issue with the steering box, but it's getting out of the way in favor of a rack and pinion setup, so no big deal.
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Old 06-06-13, 07:33 PM
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Built my own motor mounts from Flexane 94. Saves a considerable amount of cash compared to buying polyurethane 240SX motor mounts. Here's the writeup

How to make your own motor mounts
Attached Thumbnails SR20DET powered FB-image.jpg  
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Old 06-06-13, 08:39 PM
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Paint removal

Glad you didn't burn down your house. I have an even better way than burning it off - take the removable parts and give them to someone who does plastic media blasting. Assuming this is available where you are, it saves a lot of time for a reasonable price. We did an FB hood, fenders, header panel and doors a while back, made an old junker look pretty good, again just painting it with whatever I found in my paint cabinet. Hope you like this funky paint scheme - hey, it wasn't my idea.
Attached Thumbnails SR20DET powered FB-img_1989.jpg  
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Old 06-06-13, 09:05 PM
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Motor mounts

The SR20 is a smooth running motor, but it won't be as smooth with solid mounts as it would with shock mounting, as you get with most OEM motor mounts. I assume you realize this, but in case you or any of your readers have not analyzed this, the scheme illustrated for making your own mounts is in fact a rigid mount. You have a steel rod, bolted to the motor on one end and to the chassis on the other end. The rubber or flexible plastic is not doing much for you - it is a rigid mount. If you look at the photo above of the failed motor mount, you can see that the upper and lower parts were connected only by the rubber, which failed. Some motor mounts, particularly on big Detroit iron, have interlocking steel pieces imbedded in the rubber, so that even if the rubber fails, the two halves cannot separate.

I just used the stock Skyline mounts as shown here.
Attached Thumbnails SR20DET powered FB-final-install-modified-crosssmember.jpg  
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Old 06-07-13, 07:37 AM
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That's a good point. If the mounts are too harsh, I can always swap out to OE mounts. Did you have any trouble fitting the RB20 in the engine bay?
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Old 06-07-13, 11:16 AM
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Making it Fit

The RB motor is a lot longer than the rotary, and everyone said we would have to dishpan the firewall, but this was not necessary. We cut the entire center out of the crossmember, lowered it into place and put the shifter in exactly the same location as the original. This gave about 3/4 inch from the cylinder head to the firewall. To make the Skyline radiator work with the Skyline clutch fan, we had to trim about one inch off the core support. I had to make a small divot in the hood inner structure right at the front to clear the radiator cap, everything else had room. The only tight spot was the turbo/steering box. The engine normally is tilted to the left (driver side), and we reduced the tilt by a very small amount, and moved the crankshaft centerline to the right about 3/4 inch. This is not noticeable, and gives us enough clearance from the turbo. The SR20 might require something similar. Most of this is described here:

http://www.cardomain.com/ride/3936025/1984-mazda-rx-7/

We made some engine mods, mostly to get rid of all the clutter on top of the engine. But we still had the PVC fittings and equalizer tube on top of the cam covers. Also, one of the blogs for the RB motors said the trapped heat under the center cover was reducing the life of the coil packs and wiring. So I recently made a vented cover and relocated the PVC plumbing. Photos attached.
Attached Thumbnails SR20DET powered FB-cam-covers-stock.jpg   SR20DET powered FB-cam-covers-vented-center-cover.jpg   SR20DET powered FB-vented-cover-placard.jpg  
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Old 07-10-13, 11:11 PM
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Dude I've been thinking about doing this swap to my fb ( my fb is the same color as yours) so you used the cross member from the s13? What about the drive shaft? Custom? I'm not looking for ton of power 200-300 whp. How much have you spent on this swap? My only issue you be the wiring part. Sry lots of questions
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Old 07-10-13, 11:20 PM
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the Sr20 is a great motor for this car! all aluminum block and what not!
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Old 07-11-13, 05:02 PM
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Originally Posted by Rubbish View Post
Dude I've been thinking about doing this swap to my fb ( my fb is the same color as yours) so you used the cross member from the s13? What about the drive shaft? Custom? I'm not looking for ton of power 200-300 whp. How much have you spent on this swap? My only issue you be the wiring part. Sry lots of questions
A local pick and pull yard had a 240sx that I could yank parts from, so I snagged the crossmember, steering rack, front section of the driveshaft (240s use a 2 piece setup), steering column, and the throttle cable. Those parts ran about $200 total. I had to bore the crossmember holes out to get it to line up, but it wasn't too far off.

The engine I got shipped from JDM Source to the nearest freight depot to me for $2100. That came with the full engine, trans, ecu, and wiring harness.

Aside from that, I've replaced a lot of parts that were worn, since my FB has 144k on it. I put on Racing Beat springs with some fresh struts, and swapped out the rubber bushings for polyurethane ones since the front end was already apart. Those parts ran about $400 or so.

So in the end I've spent about 2700-3000 on the swap, but there are loads of places you can save a few bucks if you need to.

The driveshaft has to be custom made, and I'm still hunting for a place to do it that is reputable. So is the life of a man in middle of effin nowhere Indiana...
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Old 07-12-13, 03:07 PM
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Custom Driveshaft

I had my driveshaft fabricated by the guys at Shaftmasters. They do JDM stuff like this every day, and are very familiar with what you need. I spent 380 dollars for an aluminum driveshaft, including shipping, and I am happy with it. This was cheaper than any of the local shops in the Seattle area. Highly recommended.

Driveshafts - Custom Made Driveshafts- Aluminum Driveshafts and Steel Driveshafts by Shaftmasters Inc

Call or email David - he is very knowledgeable

[email protected]
Attached Thumbnails SR20DET powered FB-custom-aluminum-driveshaft.jpg  
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Old 07-29-13, 10:05 AM
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This is definitely one of the best non-rotary swaps for a first gen. Great power plant with minimal custom fabrication. Even contemplated it myself for a while, and it still isn't out of the question.

The main thing I don't like about it, is that the exhaust is on the drivers side, thus it has to be routed under the engine/trans. This just lowers ground clearance.

Will definitely be watching this thread.
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Old 07-29-13, 11:23 AM
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if you tuck it run by the shifter you can get pretty close on everything.
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Old 07-29-13, 02:35 PM
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Could you modify the rear bumper and have it come out the other side? A little fiberglass work is pretty simple for something like that.
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Old 07-29-13, 03:02 PM
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The rear is steel, the issue is the gask tank is offet to the left.
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Old 07-29-13, 03:50 PM
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Ahh gotcha. I could totally see that being a problem. Haha
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Old 08-07-13, 07:15 PM
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I was actually planning to have the exhaust dump just forward of the drivers side rear tire. Haven't decided yet.
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