SOHC-DOHC swap

[Florida240sx]

89 240sx I did the swap and the car started and rna for about 5 seconds before stalling(2year old gas mixed with new) Went to start again and battery didn't have enough juice.Got new battery and my friend dropped a wrench and crossed connections and sparks flew.

Replaced all the fuses with known working ones. Fuel pump wasn't turning on so I hot wired it. There was a mouse in the car an ate one or 2 lines lol. Fixed them all but couldn't trace the fuel line problem...As it is now Car cranks over but no Ecu power so no spark injector firing etc.What power sources is there for the ECU? Only guess left is that the harness is fried...

[BMAR240SX]

Wow you have been to hell and back

[rogoman]

There are several fusable links to check. I assume when you did the conversion, you used the DOHC ECU and it's wiring harness. If so, here's an ECU wiring diagram:

[Florida240sx]

What is sources are needed to make the ECU turn on?

[180fan]

the power comes from the grey or brown plug up at the front of the engine bay

[carcrazyguy]

Maybe I am not understanding the thread properly but did he swap a DOHC into an SOHC car, as in the NA 2.4 for the NA 2.4?If so, what would be the purpose? The hp gain is quite small, and in reality, the SOHC has much better response right off idle, slightly better fuel economy, and is, well, already in there for "free".Once again, I am relatively new to the forum, and maybe I am not following this one correctly...maybe this swap has something to do with a turbo or a different DOHC?

[Florida240sx]

DOHC has more power. Also between me and my friends we have 6 240's all have dohc. Whenever one of us upgrade to better parts the other car gets the old/new part. Also I know the DOHC engine very well, compared to nothing about the sohc.

Getting a new wiring harness and starting over again.

[carcrazyguy]

DOHC has more power. Also between me and my friends we have 6 240's all have dohc. Whenever one of us upgrade to better parts the other car gets the old/new part. Also I know the DOHC engine very well, compared to nothing about the sohc.

I still don't understand why anyone would go to that trouble for 15 hp (on paper). In reality, the difference is much less than that would seem. I have owned both, and in reality, the SOHC feels stronger because of the immediate response. In other words, except when you are above 4000 rpms, the SOHC pulls stronger - and this is pretty much a factor of the single intake valve per cylinder, plus the DOHC doesn't have a "butterfly" like Toyota uses with their older DOHC engines. Yes, I realize that the DOHC pulls consistently up to near redline, but I if you don't flog your 240 you would rarely use the upper powerband increase.

BTW, Road and Track got the exact same 0-60 for both models, with a slight advantage to the SOHC in 0-50, 70, 80, 90 (and tied to 30, 40). The SOHC was even slightly quicker in the quarter mile. They said, "the change is not for increased power, yet for flexibility". In my opinion, I also think Nissan was simply trying to milk a little more life out of an old (truck) design, and make the engine a little more like all of the competition at the time - everything else was DOHC by 91. Otherwise why would they bother?

So maybe now you can see why I cannot see going to all of that trouble for a little more hp (on paper). I am new to the forum and notice everyone is going swap crazy with 240's, but this is the first time I have seen such a swap as you are attempting, and still don't see the logic.

BTW, even if the DOHC is slightly faster, the SOHC engine bay is easier to work on due to more clearance in places, it gets better fuel economy, and is much easier to drive in normal situations thanks to the low end launch. Heck, I am torn every time I buy another 240 - I like the SOHC better, as well as the older SE fabric and seats, but the 91-93 cars have the newer front end and better looking wheels. Nissan was messing with us, as usual.

[Florida240sx]

There is countless people that have done this swap.... I did it because I know the dohc engine. Also easy to find dohc replacements while most SOHC need to be rebuilt.(all that I could find)

[carcrazyguy]

There is countless people that have done this swap.... I did it because I know the dohc engine. Also easy to find dohc replacements while most SOHC need to be rebuilt.(all that I could find)

Actually what is to know? The head and intake are the only substancial physical difference other than minor stuff - slightly different harness, ECU programming, etc. Unless you dog your car, you should never have to tear into those things anyway, and they are actually simplier on the SOHC if you did.

I have yet to see a single SOHC engine needing rebuilt, however I am sure there are some out there. But in reality, there is no overriding reason one version would be measurably less reliable than the other, and neither ever seem to need a rebuild unless a previous owner overheated one or similar. 200K is nothing on either version.I can find easily 20 engines of either version right now at my local junkyards here (in east TN) and all of the cars were running when wrecked, of course, so there is no shortage of the engines. For that matter, I could probably get plenty of flawless SOHC 2.4 Stanza engines from cars driven by little old ladies for $400, assuming they will go in 240's without too much hassle.

But if you are telling me that you had a bad SOHC, and only could find a DOHC to replace it, then now I finally understand. I was just assuming you initiated the swap of a perfectly good SOHC thinking it would make for faster car somehow or for some other benefit.

Anyway, I was intially assuming your SOHC engine was good. If so, then you can surely see why I was puzzled as to why you would make the swap.For a real performance boost, a turbo would do wonders for an SOHC for likely less money and hassle than a DOHC 2.4 swap that doesn't actually increase aceleration at all. But in reality, if someones engine is good, and they are not lookng for turbo performance, just leaving the SOHC alone would have saved them enough money to take a serious summer vacation, and would save a whole lot of labor, not to mention trial and error (aka frustration).

[Florida240sx]

First SOHC in it was a blown headgasket, I got a replacement that had 110k on it. Timing chain is slapping real bad. Intentions with the car was always to engine swap it(RB/VG) but my friend wanted a 240 and could only afford stock replacement.