Cloud7659

Hello everyone.

Im extremely new in the world of 240s. Infact, not even a day has past since I got mine. Its a 1992 rolling shell. I bought it off of a friend for $200 .

Ive been looking into replacement engines and stumbled upon this forum. I found a number of interesting offers on RB20DET engines. My question is, how difficult is the rb20 swap. I have rebuilt and installed 13b rotary engine sin rx7s before but have never worked with a 240. I have an engine lift and the right tools available, but difficulty wise, how would you all rate it. It seems like a spacious car to work on and Im interested in the power output of the rb20.

Does then engine bolt right into place or do I need custom mounts? Do the stock driveshaft and differentials work or do I need different ones? Any input would be useful. Thanks in advance

Yellow4g63

You can buy a mount kit or use the Stock R32GTST Xmember. That will bolt up to the 240. Mckinney and tophat have mount kits. I have both, started with the tophats and then switched to the Mckinney. You can use the Stock driveshaft from a 5speed 240 and it will fit up. The swap isn't very hard it sounds like your not new to pulling and installing motors so it shouldn't be to hard for you at all. If you do the Factory Xmember way you can put the motor in up from the bottom. I did mine down through the top with the tranny attached. It was a pain in the *** because all I had was a chain . The Rb20 isn't anything to write home about in stock form. Some peoples RB20 have put out 200+ with stock intercooler and 3" exhaust. I wasn't so lucky mine only put down 183hp on 91 pump gas at stock boost. When I turned the boost up to 12psi it jumped to 218hp. The RB20 is cheaper to start but it might cost more in the long run to fix up. PFC for RB20 isn't as cheap as the Rb25. No big companys make a Intake manfiold for the RB20 so thats going to cost big buck. I got one from a Company in NZ that makes them. It was $1300 after shipping+paypal fee's and some dutys that had to be paid. Hope that helps

Cloud7659

Thanks for the reply. If you could go back, would you have done the RB25 swap instead?

jonpowell

Of course he would! MWA HA HA!!!

Cloud7659

LOL, yeah I bet, but how much harder is it to drop in an RB25DET inside a 92, are the benefits of the 20 vs. the 25 really worth the extra $$/work?

jonpowell

Benefits include:
A)Higher compression for more off boost power
B)Newer engine meaning apossibility of lower milage and newer technology
C)Higher displacement meaning more potential
D)Better turbo pushing more air at the same CFM
E)Stronger transmission meaning it can handle more juice before popping

Deficits include:
A)Higher price tag
B)Need a custom driveshaft
C)Lower redline

Cloud7659

What driveshaft is needed? and also, is the stock differential compatible/recommended?

Cloud7659

maybe a 300zx driveshaft?

jonpowell

First post yes
Second, no...a complete new custom or modification to the stock driveshaft. The 300 ZX will fit in the RB25 transmission, but is not the correct length for the 240SX body

Cloud7659

So Im set with the differential. for the rb25 I would need a xmember, maybe custom mounts (which I have no idea where to get), and for the rb20 I need the same excedpt no driveshaft. I actually don't know where to get these parts, can you guys point me in the direction of a list of places or maybe a writeup. Thanks for all the help so far.

jonpowell

No crossmember needed, use the 240SX one....mounts from www.mckinneymotorsports.com MAY want to get a limited slip differential if yours isnt...

Waynehead05

i've been wanting to do the rb20 swap for a while now but everyone keeps telling me... no man it's not worth it. it's not a very good motor blah blah blah


what's the lowdown? what are common problems for it?

driftjunke

I love my Rb20's putting down 300 plus with bolt-on's. They bolt right in with our mounts, are cheaper than SR20's, sound better, have more torque and out rev the RB25, yes the 25 has more power stock because of displacement, but hey the 20 is cheaper, more money for mods.

Eric

jonpowell

Out rev....that is such a TIRED arguement. Stock redline on an RB20 is 7400...stock on an RB25 is 7200. Doesn't make up for the fact that most RB20DET's dyno at around 180 at the wheels in stock trim in a 240SX and the RB25DET's dyno for around 240 at the wheels. 200RPM still don't make up for about 60HP less!

RB20DET WAS a good motor in its time, but it was replaced by the RB25DET for a reason! The Rb20 just didn't cut the cake anymore so they replaced it with more displacement, higher CR, better turbo, Variable Valve Timing, stronger transmission, etc...

The RB20 is a viable choice for its pricemark, however if you can afford the extra, hold out for an RB25.

Thank and good night.

Cloud7659

hmm....now Im really confused. The RB20 drops right in, no mounts and no xmember necessary, also its compatible with the driveshaft of the 240. Basically, its a drop in and go engine (except for the basic water pump, timing belt, hoses, etc.) But, ofcourse, its weaker than the 25. I knew this but 60rwhp difference? Thats alot!

Now, the RB25 starts out costing more + the $ for the kit from mckinney. It comes out to about 1700 more than the RB20. Not to mention that most engines don't come with intercoolers so theres another pretty penny right there.

Its a really tough decision. Could I increase the rb20's performance to 240rwhp with less than 1700. Probably yes, but Im guessing it would be less reliable. Confusion.