RB25DET rebuild ideas

[Guest KILLER-T]

well as Meggala knows from my SDU thread i have a dead piston and now i am looking for ideas to rebuild my beast should i get forgies or get some GTR pistons and were to get the best price.Any idea's are most welcome

[meggala]

glad yopu brought the topic here adam it should good the main weak ness with the rb25 for hi power applications is the high compression on our fuel thats why you need to drop it the rb26 pistons are a great one cause you get a bit of capacity you know you can even put rb26 crank and rods in as well. and remember forced ran 10 .6 from an rb25 but was running c16.

cheers

meggala

[meggala]

glad yopu brought the topic here adam it should good the main weak ness with the rb25 for hi power applications is the high compression on our fuel thats why you need to drop it the rb26 pistons are a great one cause you get a bit of capacity you know you can even put rb26 crank and rods in as well. and remember forced ran 10 .6 from an rb25 but was running c16.

cheers

meggala

[japtaxi]

I should have a set of RB26DETT factory pistons for sale soon once I paid the workshop and get the car/parts back.

[meggala]

did you do it jap taxi I want to here about the results

meggala

[Guest KILLER-T]

Thanx but i have decided to go with a set of forged pistons because i think it will be alot stronger and wont be worried as MUCH about doing another ring land or melting one.And can someone please explain the benifits of replacing the cams with GTR ones or something aas good does it mean that i will have a higher RPM range? :?

[meggala]

gtr cams aren't nessacary unless you change the profile if you change the profile the you get more power but loose a bit down low cams can make a huge difference to a car.

I had a group 3 vh commodoreit was stock I fitted cams a different exhaust and got the carbie redone and the car went from a 14.9 1.4 mile time to 13.5 . but they also increase the wear to an engine just as adding more boost will but the results are great.

talk to a pro about what to do and which profile will suit you

your stock cams are 240 the 3 main up grades are 256 264 and 272256 or 264 should be adequet.

but cams aren't cheap 500 -1200

While you have the head off I would get the ports on it cleaned up and flowed a bit and I would also invest in a japanese metal head gasket.

cheers

meggala

[Guest adam]

if youve blown a piston land, are rebuilding and have to pull head off ect you will defintely have to get a new head gasket, im surprised youve been able to pull 300hp without having any dramas with th head gasket previously.... but definately get a metal head gasket.

as for the rebuild factor depending on how much money you have theres endless things which can/need to be replaced in this situation. alot of engine rebuild centres refuse to rip apart the engine to replace 1 piston as its not worth the labour you have to pay to rip apart the engine. theres some things such as hoses/belts which you should check and possibly replace while the engines out of the car....

[Guest KILLER-T]

the things i have asked the mechanic sofar are new timing belt, water pump,metal head gasket,forged pistons,and im not sure about cams yet i didnt know they shorten the life of your motor im sure there will be other suprizes like bearings or something once the motor is in bits 8O

[Guest [ryan]]

adam what the hell is that song playing in the background of the 0-120 movie? its f**ken mad

[Gradenko]

I'm a bit concerned about the number of RB's doing in pistons. KILLER-T, was there anything wrong with the tuning of the engine which led to the blown piston ring land? Or was it a case of a slightly worn motor being pushed to its limits with high compression?

I always thought that the rb25 was strong enough to handle a new turbo with a bit of boost, as long as fueling was looked after and boost was kept sensible. But it looks like we should be using precautions to make sure engine internals don't get damaged. At the 300hp point (or killer-t's level), what should we be doing to protect the engine? Lowering compression seems bit excessive when running moderate boost with no pinging, so when does a thicker head gasket become a nessacity?

[meggala]

the three that died (mine included) mentioned here have one thing in common too much boost not enough fuel Ie they were leaning out. adam and I both didn't have up rated fuel pumps. and killer t or ADAMQ as he is know on SDU hit the abolute max of his injectors I think ?

that is why if you go for a turbo up grade you need a bigger fuel pump and injectors thats why I call it a big step up. injectors 500-1200 fuel pump $200-450 turbo 400-3k .then you need to take in to account

tunning

meggala

[Guest adam]

everyone knows that when upping the boost with new turbo which will flow better than standard you need to upgrade fuelling. my car has an upgraded fuel system with standard injectors.

i think the main concern here is the so-called 'tuning' that is taking place.

we go into dyno tuning places to increase boost and run it on the dyno to make sure that the A/F ratios are safe to not have a blown engine. im not sure on figures but both mine and adamq's engines (RB20 and RB25) should internallybe able to handle the amounts of power we put through them.

it seems certain tuning companies strive to make you happy in the short run saying look heres a dyno sheet saying you made 300rwhp arent we good, oh dont worry about that other line being over 15 that doesnt mean anything..... however in the long run the reality is the engines dont last and were stuck with a disclaimer shoved in our faces denying them any responsibility and being left with a big rebuild debt and no car.

i for one am going to a)change tuners and b)go for a more reliable A/F map as having the car off the road for a month has shown me its better to have 250rwhp for 3 years than 350rwhp for 3 weeks

[Guest KILLER-T]

I still dont know for sure what killed my motor i dont think it was fuel because the injectors were @85% on the power fc screen and the avcr screen i have a bosch fuel pump so you would think that there is enough fuel getting to the motor.The only thing that i can think of is that the dudes fixing my split cooler took it for a squirt after they fixed it .The avcr was on self learn mode it was putting in extra duty on the boost solinoid to compensate for the crack in the cooler loosing boost and once fixed it was boosting to 1.5bar.

Apart from that it has done 100000ks i was suprized it made as much power as it did before it blew :lol:

[meggala]

very true Adam the reliability is the big thing.

It has made me rethink my power goals as well I want 190 rwkw with upgrade fuel pump but no injector up grade if I cant do it the 180 will have to do.

cheers

meggala

[Gradenko]

KILLER-T, its unfortunate that the avcr didn't "learn" itself back to the preset boost pressure. I'd say running 1.5bar (for how everlong) would have had a big part to play.

adam (r32 adam), please name names. I'm sure none of us here want to be caught out by shady tuning places. But yeah, reliability is important. Even after the simplest of mods (cat back), i was off to the local dyno place, not so much for the power reading, but to check AF ratios. I knew beforehand that these cars run very, very rich but I needed to be sure the fuel pump wasn't on its way out or that the injectors weren't clogged.

So yeah, keeping an eye on AF ratios is a good start. But perhaps replacing the head gasket, early on, with something stronger would be a good precaution too. Came across Ben Ellis's starlet gt while doing a bit of light reading today (HPI no17). The car put out a fair bit of power (fmic, turbo) and ran great, until it died. Turns out the standard head gasket was getting a bit old and leaked coolant into the engine. Coolant was eventually used up and the engine over heated, lots of damage done - block was un-useable.

So on engines that take as much stress as ours do, it doesn't look like we can stand around waiting for the head gasket to go. Not saying everyone should go out and buy metal gaskets, probably only those with engines that are starting to get a fair bit different from factory trim.