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Discussion Starter #1
Ok folks, I finaly got the turbo swapped on my RB25, but it still smokes on the over run, no longer under power though, so some improvement,

So next job, Head off for reconning (the stem seals must be worn), and a look at the pistons.

Question is, while its apart is it worth swapping possibly good pistons and rings for uprated ones ? and if so what kind of cash would we be talking
Would the RB26 pistons fit ?

I dont plan on mega power for this car, i have to use it each day for work.

Also, would it be wise to go for a thicker head gasket ?

Any help, advise or info about your RB25 build would be very much apreciated

Cheers Mark
 

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Discussion Starter #2
Just a thought, but whats involved in putting an rb26 in ?

im thinking ecu, wiring loom, intercooler, turbos, anything else ? are the sumps the same ?
 

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Marky_GTSt said:
Question is, while its apart is it worth swapping possibly good pistons and rings for uprated ones ? and if so what kind of cash would we be talking
Would the RB26 pistons fit ?

Also, would it be wise to go for a thicker head gasket ?
If the one's in the car are OK, you don't need to swap them, there OK for 300brake+. However, if you wanted to sort this engine now, and you plan mods at a later date that will take it beyond 400-450, then you might as well do the pistons now. About £1200 for a set of forged ones. RB26 rings won't fit.

Yes, either way fit a metal gasket, minimum 1.2 but 1.6 would be better. About £300.
 

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Discussion Starter #5
Was offered an rb26 with loom ecu ect ect, for 3k, but to be honest as i stated im not going for mega power as i have to use this car each day for work and stuff, so im not going to spend a fortune.

Thanks for the help, I will check the standard bores and pistons, i know this engine has superb oil pressure so i doubt i will find too much wrong.

Gonna try and get a 1.6mm head gasket, any recomendations ?

Im going for a puter, fuel pump, press regulator ect later on, and a bit more boost, should be a nice sensible one, if there is such a thing.

Cheers Mark.
 

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Marky_GTSt said:
So next job, Head off for reconning (the stem seals must be worn), and a look at the pistons.

Would the RB26 pistons fit ?
Chances are its cracked a part of the piston on which the piston ring sits, you cant see it without removing the piston.

Why would you possibly want to put the RB26DETT pistons in, they are no different in manufactoring than the RB25DET piston.
 

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Why?

They are made of the same stuff :)

The difference is the compression ratio of the RB26 is lower than that of the RB25 so the pistons can take more boost than those in the RB25. Not a case that the pistons are stronger but that the design of the engine is taking pressure off the pistons in the RB26.

Put a thicker HG on the RB25 and drop the standard compression and they will last just as long as the RB26 ones :cool:
 

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Throttle response yes but the GTsT is still miles better in this area over a GTR due to the variable inlet cam timing.

The drop in throttle response is no worse than that of fitting a FMIC with all the extended pipework, something I dont recomend you do on a RB25DET untill you are running over a bar anyway ... till then the stock IC is fine.

Dont go for a 2mm, 1.2-1.6mm is fine depending what boost you are intending to run.
 

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you are not helping you know :mad: I'm all decided to go for an RB30 and then you drop in stuff like this :mad: :) :D
as I understood it the GTS pistons were no good much above 1.2 bar, the GTR ones were okay for about 1.5.

I wasn't planning on more than 1.4, I already have an FMIC.

Simon
 

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Hehe, thing is Si I aint keen to run a GTR at over 1.2 on stock pistons either :)

So I guess its all just about how far you are willing to push it.

I too looked into the RB30 about 5 years ago when Meggela and friends were first looking into it in OZ and NZ but decided to stick with the RB25DET due to the fact we were trying to push what a GTSt could do not what a GTSt shell could do.

It might sound odd but I dont think its really a GTSt if its a RB30, its a GTSt conversion then. Splitting hairs I know but our task was to push the GTSt as far as we could so we stuck with the RB25DET.

Actually I always expected to blow it up :D truth be told and then pop the RB30 in it but it never happened :p :D

Over 1.2bar on a GTSt and I would have to say for the sake of saftey that its time for forgies .... but we have ran them higher :D Same for the R .. 1.2bar after that there is a chance they will go so we advise them to be changed.

Its that old garage/customer question ... we cant afford to say "ach aye you will be fine m8 at 1.5bar dont you worry about it" and then boom you frag a piston and we are all the gits of the day. Fact is maybe only 1 in 5 will det a piston or crack the ring lands, problem is we cant say for sure what one will and what wont so we say .... "sorry I have seen them pop a piston over 1.2 bar"

Fact is I have seen a stock standard GTSts come in with 5 out of 6 pistons with broken ring lands ... wtf do you say then :D

Anyway, RB30s seem to be the rage all of a sudden (hehe took you all long enough ;) ) and they are a great package for the GTSt .... wouldnt catch me putting one in a R right enough :D and outstanding package price wise.

Personally I was always a fan of Mick Stanwicks stuff from SubZero :D
 

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I always liked what you did with the RB25 and for a long time I was of the same opinion that with the RB30 it wasn't a proper GTSt.

but now if I think about it I am never likely to try and prove anything on the drag strip, so all I am interested in is getting the best bang for buck performance that is reliable enough to use as a daily driver.

Simon
 

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Cant say the RB25DET we built has been anything but reliable but ... it was expensive compared to the RB30. So ... RB30 it is then :)

Ask about the engine mount issue though, I was led to believe at the time that they would have to be dropped by about and inch and a half to accomodate the taller block height of the RB30 .... not a great job if it was true.

Perhaps the reason was the cross over pipe on the RB25DET head ... this wouldnt be an issue if you were using a Greddy plenum or SubZero one. After we fitted the Greddy plenum we had bags of space under the bonnet certainly enough to accomodate a 1.5" taller block :)
 

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the plenum issue has been mentioned already so I do think it will be a problem, however I have a spare one on the way and a cunning plan :)

well actually it's not so cunning but my CF guy has been banging on for ages about making one and until very recently I couldn't figure out a workable way of doing it.

if that dosne't work then a rips or greddy one would resolve it.

I think if I decide to go the RB30 route then I might just stick a HG on there and give 1.4 a go until it arrives and see if it holds togther :D


Simon
 

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Remember that a plenum is more than just a hollow tube ... you can see on the greddy ones that it tapers towards the end to keep the pressure the same as each chamber draws of pressure on the way up to number six.

Also they are (or should be) fluted on the inside to aid airflow ..... a great example of this are the plastic flutes inside a FTO plenum ... it really is quite surprising whats in there
 

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Remember that a plenum is more than just a hollow tube ... you can see on the greddy ones that it tapers towards the end to keep the pressure the same as each chamber draws of pressure on the way up to number six.

Also they are (or should be) fluted on the inside to aid airflow ..... a great example of this are the plastic flutes inside a FTO plenum ... it really is quite surprising whats in there :)

The Greddy one relys heavly on the length of the runners leading into the head to draw in flow ... its not the best way to do it ;)

Anyway, I need to get back to work :) nice to chat if you need advise on anything dont hesitate to ask.
 
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