outward differences of rb20-rb25

[the_momo]

i am looking at getting an s14 with a rb25det. the question is that it has been raised that the motor in the car might be an rb20 and not an rb25det. i can see that it has the 2500 plug cover, but it also has a knock sensor, which i have been told the rb25 doesnt have. also, it has top feed injectors, which i know the rb20 has and the 25 ahs side feed. it may have been swapped for ease of injector swapping. i am lost. just wondering what i should look for. either way, i am still gonna get it, as its a fantastic deal and i well i want it either way. just wondering. thanks.

[Joe]

dead on easiest way to tell is the VTC hump on the timing belt cover

RB20

RB25

see the hump on the left side of the RB25 timing belt cover? thats ONLY on the RB25 engines

there are tons of other differences, but thats a dead giveaway

[Carl H]

skinny intake manifold plenum vs the rb20's donkey one, rb20 also has the 'eccs' badge on it.

[themadscientist]

How about the obvious? The casting mark is down by where the front pipe hooks up to the turbo exhuast outlet. The square machined pad by the bellhousing. The RB25DE in the R32 used topfeeds so it may be a converted early NA motor if it looks like an RB20 but is stamped "RB25"

[gbaz77]

if they have that intake arm that goes over the valve covers, the rb25s BOV is horizontal. the BOV on the rb20 is vertical. in other words, the top of the BOV for the RB25 is pointing toward your firewall, the top of the BOV on the rb20 is pointing toward the sky/hood.

[the_momo]

thanks for the replies guys. the stamping says rb25, but it very well could be forged on there (grinded off and restamped), i think the only difference that is still there would be the cam gear. the intake is aftermarket, as is the bov. so ill check. thanks again. also, i havent been able to find a metal headgesket (not necessary but it is in pieces so why not) for the rb 20, plenty for the 25 but none for the 20 yet. thanks again! as soon as i get it, ill post up pics of the car and the rebuild (what there is of one, basically just a put it back together thing) and numbers, etc. oh and also, any where i can find some general info type stuff on the motor (20 and 25) for things like timing, torque specs, etc? any help is greatly appreciated...oh and i know about that oh what do they call it again...oh search!!! but i would just like to put it out there as so many have already responded, maybe i can pic all of your collective brains just a little more.... thanks again!

[the_momo]

also, what is the plausability of switching the head form the 25 to a 20? that is the question that has been raised to make me wonder what is actually in there. thanks again.

[themadscientist]

If the motor is apart then just measure the bore. The 25 is 86mm, the 20 is 78mm if memory serves.

[the_momo]

ok thanks, the na converted motor seems most likely. i know the person who originally owned it has been known to do that sort of thing to other motors and or cars. i e sr20de silvia with a turbo on it....sr20det!. thanks for the info. ill measure it tonite.

[the_momo]

i am going to assume that it is an na motor as it has raised pistons (not dished) and it has the hump on the intake cam gear cover. thanks for the input! oh and i measures the bore, its 86mm (or someting within that area, my calipers arent the greatest, but they work.)

[Darius]

The RB25DET and RB26DETT both have domed pistons 86mm in diameter. The RB25 has a hump on the intake side of the timing cover as well as a hump on the valve covers towards the firewall. I would guess that if the guy says it's an RB25DET and from what you describe, it sounds like it truly is an RB25DET.

[gbaz77]

here is a link where you can download the FSM (factory service manual), all the torque specs and whatnot are in here. 580 pages of holiness. http://www.speeddreamz.net/fsm/r32all.pdf

[the_momo]

i owe you a beer my friend. thanks for that, itll be used frequently, believe me! an i do think it is an rb 25. thanks for all the help guys, i really apreciate it. and like i said, ill be posting up pics as soon as i get it( when i can get my other 240 out of the garage. anyone want it??? its in the classifieds. thanks!)

[the_momo]

that pdf link doesnt work anymore. i tried to open it and it goes to an odd site, please help i forgot to save the file and i reallllllly need it!!! rebuilding the motor in a few days and i need the specs, timing setup etc. thanks!