Rb20det To Rb25det

[DVSTRK]

hey guys just a little confussed with my situation at the moment, i have a 89 model r32 gts-t with a rb20det engine and has about 189k on the clock.....obviously pretty normal for a 20 year old car.

the mods i have so far consist of a free breathing pod filter and a turbo back 3' exhaust system, on standard boost (never been boosted before).

i was thinking on a rebuild but the price on rebuild start at 3-4gz and thats alot of money to be throwing around to recondition a 20 year old motor. so i thought id do a rb25det engine swap with lower ks, something along the lines of 100k to 120k. but id like to find out if the rb20det ecu and wiring harness will support that, and/or will the rb20det manifold and turbo bolt straight on the the rb25det due to alreadyy having a trubo back exhaust and will save abit of money on the engine buying it less turbo, less manifold etc.

i would like to know what i can keep to use on the rb25det form my rb20det and what i may need ontop to complete this project....

will appreciate all ideas!

[chrissso]

AFAIK,

The ECU will be OK, after a dynotune/remap. Some RB25s don't use igniters, some do, so check with an engineer/mechanic if this makes a difference.

The turbo is different in the RB25, it's bigger. This means you'll get less performance out of the RB20 turbo on the 25 which negates the purpose of getting an RB25 in the first place. The response may be quicker, the low down torque may be better, but overall power will probably be down. I've not heard of anyone putting a 20 turbo on a 25. People with RB20's upgrade to 25 turbos all the time.. Otherwise you might as well get another RB20.

Your exhaust can prolly be modified by an exhaust shop to fit the new turbo, if it even needs it. Pretty sure bolt patterns are the same. Shouldn't cost that much.

The gearbox from the RB25 is much stronger. I would get it, as the 25 enigine may break a RB20 gearbox.

That's all I can think of right now.

[TheProDaniel]

The ECU will work but wont have the VCT and you'll need a remap. The wiring will be different so you will need to modify to suit the 25. The manifold and turbo will both bolt on but the 20 turbo would be too small so may as well get one with a 25 turbo. Wouldn't cost much more and the power would be worth it. Other parts you can use would be alternator, starter, coilpacks (if 25 is series 1) off the top of my head

Just did the conversion myself and recommend it to anyway! Cost me a shade over 3 grand doing everything myself except wiring.

Edited February 5, 2009 by TheProDaniel

[Roy]

If you are chasing more power then great. But if the RB20 is stilol running then dont think its on its last legs because it has a 190,000kms on it. My original engine had 150,000okms on it with 70,000kms of that being me of which about 3,500kms of strictly track work. LOL yes lots of days at Wakefield and EC. A wayward spanner then cost me that motor, not the engines fault though when pulling it down the bottom end looked fine.

The motor i replaced it with was a wrecker motor so who knows how many kms were on it. I have now put 45,000kms on this engine, with power being never under 215rwkws, mostly between 235-260rwkws with plenty of track work again....engine is still healthy.

So if you were thinking a bit of preventative maintenance on the RB20 because you thought it has high kms then i suspect you have nothing to worry about. If it is still healthy then stick with it and do a few basic mods. If you have big plans for more power or need a real grunty car for the street then it is best to shop for more displacement

[TheProDaniel]

If you are chasing more power then great. But if the RB20 is stilol running then dont think its on its last legs because it has a 190,000kms on it. My original engine had 150,000okms on it with 70,000kms of that being me of which about 3,500kms of strictly track work. LOL yes lots of days at Wakefield and EC. A wayward spanner then cost me that motor, not the engines fault though when pulling it down the bottom end looked fine.

The motor i replaced it with was a wrecker motor so who knows how many kms were on it. I have now put 45,000kms on this engine, with power being never under 215rwkws, mostly between 235-260rwkws with plenty of track work again....engine is still healthy.

So if you were thinking a bit of preventative maintenance on the RB20 because you thought it has high kms then i suspect you have nothing to worry about. If it is still healthy then stick with it and do a few basic mods. If you have big plans for more power or need a real grunty car for the street then it is best to shop for more displacement

I'm very glad I did the swap but my 20 was rooted so I do agree with Roy, good advice.

[DVSTRK]

i did want to do some further mods such as, FMIC, r33 turbo, aftermarket manifold, and boost upto 15psi....but i thought that the amount of pressure on the high k'd engine would not support it and would soon after breakdown, as i cannot afford for something like that to happen...

so you guys suggest that if i do buy the rb25det, i get it complete with turbo, ecu and wiring harness?

[TheProDaniel]

i did want to do some further mods such as, FMIC, r33 turbo, aftermarket manifold, and boost upto 15psi....but i thought that the amount of pressure on the high k'd engine would not support it and would soon after breakdown, as i cannot afford for something like that to happen...

so you guys suggest that if i do buy the rb25det, i get it complete with turbo, ecu and wiring harness?

Is there any reason you expect the 20 to die? Has it been compression / leak down tested? I'd suggest doing that before you worry about a new motor. Those 20's are tough buggers (just look at Roy's).

If you do decide to go 25 I'd suggest def with turbo and it's probably easier to go with the wiring and ecu (as I did) but people have had good results with remapped 20 (Simon I think?). Here's some good info on the conversion should you wish to go down that path.

Predators Guide

[DVSTRK]

Is there any reason you expect the 20 to die? Has it been compression / leak down tested? I'd suggest doing that before you worry about a new motor. Those 20's are tough buggers (just look at Roy's).

If you do decide to go 25 I'd suggest def with turbo and it's probably easier to go with the wiring and ecu (as I did) but people have had good results with remapped 20 (Simon I think?). Here's some good info on the conversion should you wish to go down that path.

Predators Guide

no it hasnt. i think i may stick with the rb20det motor and, boost it upto 15psi after the FMIC goes in....thats probably what i would end up doing, since you guys say the 20s are "tough buggers"

would 15psi be a safe level to boost a standard rb20 turbo, considering that its got steel turbines.....from what iv heard the r33 turboes are ceramic and cannot handle high levels of boost.

thanks guys

[TheProDaniel]

no it hasnt. i think i may stick with the rb20det motor and, boost it upto 15psi after the FMIC goes in....thats probably what i would end up doing, since you guys say the 20s are "tough buggers"

would 15psi be a safe level to boost a standard rb20 turbo, considering that its got steel turbines.....from what iv heard the r33 turboes are ceramic and cannot handle high levels of boost.

thanks guys

15 will be too much for the standard, each turbo is different so when it goes can't really be guessed. People have had them go at stock boost and you wont benefit too much with the stock ecu. Best to look at getting something to suit your application, plenty of good info around here. Bolting on the 25's turbo is a good cheap upgrade.

[sly32]

yeah man i wouldnt put alot of rb20 stuff on,

so what i did is bought a front cut pretty much (no gearbox) as i already had a rb25 gearbox, it cost me $2100, for a rb25det from a 97 stagea with 70,000kms on it, comp was about 150 in all cylinders, then with the wiring loom i have a guy who does the conversion so i can run air con and wipers work, that cost me $350 for a over night job,

everything on the car will line up with exhaust and stuff like that, strut brace wont fit if u have one (might if you have a manual tps) (auto has 2 plugs so it sticks up more),

depending on if you want to keep hicas or not you will have to change your harmonic balancer if you want to keep it, (why would u),

every1 says u have to use a rb25 accel cable by my rb20 one fitted fine,

RB20 turbos are ceramic so dont even bother with putting them onto the 25,

depending on series 1 or 2 engine, series 1 can use rb20 coilpacks (so if you have split fires),

all your alternator and ps and aircon will fit the 25 engine, just make sure you put on the rb20 engine mounts onto the engine,

Hope this helps