RB20 Cheap turbo upgrade.. few questions

[Cool Hand Luke]

If i use a RB25 turbo, does the dump have to be changed from my 25? Im asking a heap of questions i know, but i want to make sure i go the right way, and since i have quite a good dump pipe, dont want to get another one made which i will have to with a VG30 turbo. Also is the compressor outlet on the RB25 turbo the same size as the 20?

[Cubes]

Nope... The RB25 turbo is a direct bolt on replacement, everything is the same to the RB20DET turbo.

The VG30 requires a little bit of modification to the turbo compressor outlet. As the VG30 one is larger than the RB20.

If you get a BB core VG30 which is around the $500 mark all the existing oil/water lines will bolt straight in.

[Cool Hand Luke]

hmm, think i know what im going to go towards.. as much as i would want more power.. How much more power could i squeeze from the VG over the 25 if they were both at the same level of tune?

Ultimatley i know i'll be dissapointed if it has poor throttle response, hense the VG wont keep me satisfied over the 25

[Roy]

Ive got an RB25 turbo in my garage, looking at it your RB20 dump pipe will bolt up to it as they seem to have the same flange pattern.

I guess that makes sense as they are both generic T3 housings.

An RB20DET requires less air at any given RPM compared to a RB25 or VG30 at that same RPM.

Joel is that true, or is it an assumption. (Note for the senstive, this is not a challenge, just a question resulting from a geniune interest... so Joel, schools in and im listening)

The equation to work out CFM of an engine reqiures engine size, (ok that supports what you are saying) and also engine efficiency. Whether the engines have the same efficiency i have no idea.

[Cubes]

It is true..

This is why a larger capacity engine doesn't have to rev as hard to make the same power. I.e RB26 compared to a RB30.

The RB30 is using similiar amounts of air at 7000rpm to the RB26 at 8500rpm.

As mentioned earlier, its the luck of the draw.

If you get a good turbo it will last if you don't it could die on standard boost.

Also just as a note the VG30 turbo has a smaller compressor but larger exhaust compared to the RB25 turbo.

You could get really technical about the efficiency.

The RB25 head is known to flow better than the RB20 head so... theoretically that will allow more head room for more boost as there is more of a restriction to the airflow which in turn creates boost.

But really I think both are twin cam heads unless you are running up over 400hp where the RB20DET head starts to hit a brick wall, that is were the ability for air to flow in to the pots of the RB20DET will start to require more and more boost to get the same amount of air in with comparison to a more free flowing head (RB25).

Do a search plenty has been posted on this for a while.

I think Sydneykid made a good post also.

He also stated that the force (boost) on the exhaust/compressor wheels also pose a problem.

[Roy]

Just read the Performance forum posts, it still sounds like a game of paper, scissors, rock.

The theory sounds right, but its practical application may not be as pronounced as a snapshot of the theory would have you believe.

Luke if the VG30 needs mods to fit, id strick with the R33/34 turbos.

The variability of steel wheel/ceramic wheel, ball bearing/plain bearing VG30 turbos getting around, plus the age of the turbo all go against it.

Based on the experince of others with regards to lag and power the RB25 turbos sound the way to go. When its time to upgrade to your bigger turbo again, i think you will move the RB25 turbo a litle quicker as well.

Oh yeh sorry to throw another spanner in the works, i saw your post rebuying hte VG30 turbo.

If my boy Luke says he can run 50psi, then my boy can run 50psi. Or is that eggs?

[Cool Hand Luke]

haha, i could eat 50psi, but my stock bov wont permit it .

Im going to buy the RB25 turbo, found one. Is there any way from the outside with the intake pipes on that i can tell its a 25? Or do i have to measure the compressor wheel?

[Cool Hand Luke]

hey whats you meanins with that theres signature boy?

[Cubes]

lol... I was looking at that wondering also..

Do a quick search Luke I remember some one posting info regarding what numbers the compressor cover has on it for the RB20/25 & VG 30 turbo's

[Roy]

Thats what i tell myself when i look at my engine bay:(

[R32 GTSTT]

how would a rB20 head go on a Rb30 bottom end, what type of internals could you use?

[Roy]

Be sure to check with someone that knows RBs well. I think you will find that the RB20 isnt the best option head to be uing with RB30 bottom end.

The head stud diameters are different diamters and im not sure about the effect the smaller combustion chamber has on the larger bore/compression ratio

[Bl4cK32]

Its the rb25de non turbo head that bolts straight up.

[R32-GTS]

Originally posted by Bl4cK32

Yeah mate - not all of us have the supply of parts, and spend grands on tuning to squeeze out 250kw out of an rb20. How much money do you think it would cost to get 250 kw out of it -10g?

Now compare it to say an rb30 bottom end with a 25 head. Im told this engine produces the same output as the rb20det with no turbo. 10g compared to say 2g for a rebuilt motor package. Thats what I was trying to say.

Comments like this make me think how many idiots there are.

I got around 300kw;'s at the engine using a hi flow rb20 turbo front mount and a rechip. Gee how much did i spend. not even 2k so far.

[Roy]

Me runs and hides!

[Roy]

Lets keep it civil guys

Ive seen in a dyno chart of an RB25/30 NA engine with i recall about 120rwkws. I suppose thats kinda RB20 turbo power.

My thoughts are that 250rwkws isnt all that difficult if you aleardy have say 200rwkws.

You already have ECU re-tuned, most likely a better fuelling system, full exhaust/filter, clutch blah blah blah. So other then bigger injectors it really comes down to turbo slection which is what Luke is asking.

[R32-GTS]

RB30 NA's dont put out 120kw;s at wheels. I had one with a few mods was lucky to push out 98kw;'s at wheels.

Im not knocking the RB30DET as im building one myself , but you cant take away the power a rb20 can make with reasonably small mods.

u can make 300hp at wheels outta them with stock injectors , ECU , and AFM.

[Bl4cK32]

I find it hard to believe you got 300kw with the std injectors, fuel pump etc. Don't the std inj. run out at 240-250?

Dont make F*kn stupid comments r32-gts, we're here to share info, not bag the crap outa each other.

[R32-GTS]

Well basically your a "net parrot" who has no first hand experience but comes on here thinking he knows it all with things that "you have heard" . Grow up and get some first hand experience before saying things you dont you.

[Bl4cK32]

Hey f*kwit, I did'nt say I knew it all. Second, Your the one who said youve got 300 kw only on a std rb20 high flow, retune ecu & FMIC.

Makes me understand why everyone who comes back from perth says everyone there is up themselves.