Starting Build and doing research

[GSDKinked]

While I am tinkering with my Rb25DET and getting it to run 100%. I am close but it has me questioning the reliability of the engine so I want to build a replacement. I want to spool my 35R like a 30R. The .70 A/R compressor housing, and .82 Exhaust or better. And have it be reliable. Any ideas comments or suggestions?

Debating between a Rb25 or and RB30/26.

I have been snooping around the aussie forums and zilvia.. But i trust the aussie forums more. lol

Modified by GSDKinked at 9:46 PM 2/2/2010
Modified by GSDKinked at 9:53 PM 2/2/2010

[GSDKinked]

Also is it really worth it to use RB26 internals on an RB25DET? If I did and used solid lifters and etc in the head would i have the same rev range as an Rb26?

[boosted98gst]

Also is it really worth it to use RB26 internals on an RB25DET? If I did and used solid lifters and etc in the head would i have the same rev range as an Rb26?

On a well tuned rb25 the gt35r is fine for stock engine, even on stock valvetrain its all going to depend on the tune. if you're worried about spooling a turbo faster, displacement is whats going to help you. If you're wanting to go solid lifter and run a big 10+mm solid lifter cam your going to sac low end. All your torque in the lower rmp will be gone and will be evened out back in the higher rpm's past the stock redline. If this is going to be more of a drag/race car then anything this would be what you would want to do. To be honest that tiny 35r would not need that much of valve train mods, a good tune will help. My liter 2 liter has no issue spinning a 37r so your inline 6 should have no problem., what you really need to do is fix all the issues with the car and get to know it better before making a big decision, it seems like you should be reading some more stuff about similar set ups ect.

[GSDKinked]

Thank you for your response. And the current issue right now is that the motor at around 2000-3000 rpm. It feels almost unbalanced but once it's above that it's fine.

And the reason I am so eager to build is because I will know the exact history of the engine. Not to mention there are a lot of killer deals on Rb25DETs, RB26 blocks and even RB30s. I plan to finish this build by the middle or end of summer.

[Coolwhip]

You'll want to take a good look at your goals and budget.

If you have a large budget and goals of 600hp...- you mentioned you wanted to go solid lifters, quicker spool, etc. Well the best route to take is with a greater displacement and a head already equipped with solid lifters. A RB26 is the best solution for out the door performance in that case. To increase torque and power delivery by increase displacement then of course the next step is to look into a RB30 bottom end.

If you have a smaller budget and goals of 600hp... (I'm quoting 600hp as it's the 35R range you mentioned using)- you would be fine going the RB25 route. Solid lifter, stoker kits, etc. get pretty expensive afterwords, if still toying with the idea. But a mild RB25 setup with supporting mods can render the power needed with a fraction of the above budget. Yet both setups will not render the same power delivery.

Either way, not a difficult to make power in either of the platforms.

Email me if I can help with anything

[GSDKinked]

Hmmmm I would love to go with an RB30/26 but being a college student and all it is probably out of my fiscal reach. So the built RB25DET is my best option......right now I have a choice to pick up a block and crank that's ready for assembly. Or pick up a blank canvas (Block, and crank) close by me for cheap. I'm tempted to go with the already finished (machine wise) block and crank.

[eh?]

Sounds like you really want a VQ35.BTW when you build a motor, you machine your block to accept your pistons. So unless you are getting pistons with that block don't bother, you will have to machine it again to have the right piston to wall clearance.

[Coolwhip]

BTW when you build a motor, you machine your block to accept your pistons. So unless you are getting pistons with that block don't bother, you will have to machine it again to have the right piston to wall clearance.

+1

[GSDKinked]

Sounds like you really want a VQ35.BTW when you build a motor, you machine your block to accept your pistons. So unless you are getting pistons with that block don't bother, you will have to machine it again to have the right piston to wall clearance.

Well then I might as well start from scratch and just get an entire bottom end. And go from there. I guess I will have to check the forums again for bottom ends or cheap motors. I know Raw has a bottom end for sale....I'll have to shoot them a message.

[GSDKinked]

Well Rawbrokerage came through with an exception bottom end for me to start my build. Next on the list is crank collar and 86.5mm pistons.

[240z4u]

I know someone with a bottom end that is newly rebuilt, never ran forged pistons etc.... email me if your intersted.

[eh?]

I have a new crank collar for $70 shipped if you want..

[GSDKinked]

I know someone with a bottom end that is newly rebuilt, never ran forged pistons etc.... email me if your intersted.

Sorry guys, I bought this bottom end because I want to build my first motor. I already have an RB in the car but I am iffy about it because I don't know it's past plus I love learning new things. And "built not bought" is something I strive for. Thanks for the offer though. And eh? I will probably be ordering all my stuff from Rawbrokerage. They are awesome and extremely helpful.

[johnny butt]

how much was that bottom end?

I am getting the urge to build me a new block / head.

[GSDKinked]

$470 to my door.

[robbie2883]

just fyi, i would mic those cylinder walls and check for any defects in the walls before ordering pistons. if for some reason they are not straight or need to be bored they might end up larger then your target piston size.

[GSDKinked]

just fyi, i would mic those cylinder walls and check for any defects in the walls before ordering pistons. if for some reason they are not straight or need to be bored they might end up larger then your target piston size.

It's going to the machine shop before i order anything period.

[Sil240]

Good luck, keep us posted. Read before you order. Read before your cut,bore,machine etc...

[GSDKinked]

Alright, so it's been a while since I updated this. School and work and bills got in the way, but I have stock OEM pistons that just came in. And i am curious as to what to do next. My goal for this block has changed alot, and I just want to build as close to an OEM block as possible with a couple upgrades here and there. I plan on using ARP hardware, and dismantling the pistons in order to take them through a parts cleaner, inspect them and etc. If all is good with them and the cylinders, I will be sending out the pistons/rods/bearings out to be coated by swain tech.

Any suggestions and etc?

just fyi, i would mic those cylinder walls and check for any defects in the walls before ordering pistons. if for some reason they are not straight or need to be bored they might end up larger then your target piston size.

It's going to the machine shop before i order anything period.

[l0nestar]

You did not state which turbo you are going to run, I am assuming the 35r for this. More or less a blueprint with a few upgrades?

If you are positive the pistons are clean / free from defect, having them Swain coated is a good idea. I would use 26 rods if they are available. With the head disassembled, have a basic valve-job done, possibly clean up any of casting flash on the ports. Consider replacing the valvesprings with OE or OE upgrade (Tomei). OE timing belt. Get the cams and rotating assembly micro-polished. Also have the rotating assembly balanced. ARP head studs and rod bolts. Keep the hydraulic lifters.

Honestly, I would also consider having the shop who is doing the balancing assemble the head and block.
I don't have a moisture / humidity / temperature controlled assembly room at my shop, do you?

[Darius]

I'm in exact agreement with l0nestar except I'd still assemble the block myself to save a lot of labor costs. Most machine shops don't have humidity or temp controls anyways. It is usually hotter than hell in all the ones I've been in LOL! I would have also recommended putting in forged pistons, but you said you were on a budget and had new OEM pistons on the way.

With respect to the turbo, I'd go smaller if you're putting stock pistons back into it (3076R with 0.82 exhaust housing). It will spool faster than a 3582R and will still support as much HP as the stock pistons can handle.

[GSDKinked]

You did not state which turbo you are going to run, I am assuming the 35r for this. More or less a blueprint with a few upgrades?

If you are positive the pistons are clean / free from defect, having them Swain coated is a good idea. I would use 26 rods if they are available. With the head disassembled, have a basic valve-job done, possibly clean up any of casting flash on the ports. Consider replacing the valvesprings with OE or OE upgrade (Tomei). OE timing belt. Get the cams and rotating assembly micro-polished. Also have the rotating assembly balanced. ARP head studs and rod bolts. Keep the hydraulic lifters.

Honestly, I would also consider having the shop who is doing the balancing assemble the head and block.
I don't have a moisture / humidity / temperature controlled assembly room at my shop, do you?

Ummm no, 35R is too laggy for my tastes. I will be running a turbo equivalent to a 30R but with a divided .75 exhaust housing. And isn't there a difference between the 25 rods and 26s? (in terms of length and etc)

I'm in exact agreement with l0nestar except I'd still assemble the block myself to save a lot of labor costs. Most machine shops don't have humidity or temp controls anyways. It is usually hotter than hell in all the ones I've been in LOL! I would have also recommended putting in forged pistons, but you said you were on a budget and had new OEM pistons on the way.

With respect to the turbo, I'd go smaller if you're putting stock pistons back into it (3076R with 0.82 exhaust housing). It will spool faster than a 3582R and will still support as much HP as the stock pistons can handle.

I'm saving forged pistons for the block that is in the car right now. This other one I just OEM to OEM+. I am only shooting for 450whp which is more than possible on a healthy and fresh RB25 with some upgrades.

[eh?]

No way should you stick oem pistons in a new build, it's a time bomb ready to go off if your >400whp. When RB pistons break they break clean with no signs off heat stress and I don't think swain coatings will help at all. I wouldn't coat internals unless I was chasing massive power (ie 800+whp). Spend that money on ceramic coating the turbo and exhaust manifold.
Rb25 forged supertech pistons + rings can be found for less than $500 if you look around. They just need to be modified a bit if they haven't been already.
Why don't you build this motor? Unless there's something seriously wrong with the current motor it makes sense to build this motor and sell the other motor when you pull it out. Just take your time to acquire all the parts if you don't have the cash right now.

[GSDKinked]

No way should you stick oem pistons in a new build, it's a time bomb ready to go off if your >400whp. When RB pistons break they break clean with no signs off heat stress and I don't think swain coatings will help at all. I wouldn't coat internals unless I was chasing massive power (ie 800+whp). Spend that money on ceramic coating the turbo and exhaust manifold.
Rb25 forged supertech pistons + rings can be found for less than $500 if you look around. They just need to be modified a bit if they haven't been already.
Why don't you build this motor? Unless there's something seriously wrong with the current motor it makes sense to build this motor and sell the other motor when you pull it out. Just take your time to acquire all the parts if you don't have the cash right now.

Reasons I want to use OEM pistons is that I am reading ALOT over in SAU and GTRcanada. These guys are pulling down amazing and RELIABLE numbers 300 RWKW (400+) hp using nistune and etc. Alot are doing it on stock internals, and only when they chase larger numbers like 500+RWKW are they upgrading internals and etc. Also, I would like to have a mildly built RB25DET in my S14. I have no reason to go crazy with this block simply because it doesn't require much to make it stronger, reliable and powerful. Plus my S14 chassis is going to damn near stripped so speed is not an issue. From my understanding RB25DET pistons can't take detonation and heat very well at all. People who grenade stock motors are doing so with poor tunes, and engines with poor heat management and etc.

I believe that with ARP hardware, RB26 Pistons (coated top and skirts), coated Rb25 rods, coated bearings, and balanced crank, I should be able to hit my numbers reliably and control my heat issue. Controlling heat is a major deal when it comes down it. The less heat transfer that occurs the less stress that part is under. This also keeps my exhaust temps up and flow high.

As for the manifold, exhaust housing and etc. Those will all be coated as well. I'm taking my time with this and learning from what i read in the forums/shops. I am not going for crazy numbers

[eh?]

It's not just poor tunes and heat. It's just plain stress from increased cylinder pressures from more boost/air. The piston rings lands are just weak and can not handle the increased cylinder pressures over time.Coating will not help strengthen the pistons . You're better off cyro treating them (if that even works)
Yes it may be able to handle it for a couple years but why not spend the few hundred extra dollars on forged pistons if your spending money on a rebuild now? Mine lasted 4 years @ >450whp 100% stock, when I pulled it there was no sign of heat or detonation Just cleanly cracked ring lands.

I'm speaking out of experience here, all you need is forged pistons. forget the coatings. If you're not going to put forged pistons in it you might as well leave it 100% stock.

[Darius]

Yes, there is a difference between RB25 and RB26 rods; the RB26's are a heck of a lot stronger. They are a direct drop-in since they have the same big end, small end, and center-to-center dimensions. Just add new bearings.

You can use RB26 pistons in an RB25 head, but they will lower the compression to around 8.0:1, if I remember correctly. That would suck, I wouldn't do it.

I'm confused because you keep saying this is only a mild build on this RB25 block, but you are going through the effort and money to coat all the bearings, pistons, turbo, etc. If you are only shooting for 400hp, leave it 100% stock like eh? recommended or throw some forged pistons in there and it will be ready for bigger power or better longevity however you want to look at it.

[Zacho2]

Yes, there is a difference between RB25 and RB26 rods; the RB26's are a heck of a lot stronger. They are a direct drop-in since they have the same big end, small end, and center-to-center dimensions. Just add new bearings.

You can use RB26 pistons in an RB25 head, but they will lower the compression to around 8.0:1, if I remember correctly.

I was under the assumption RB26 rods+pistons had to go in as a combo. At least that is what I did.

OP: If I had to do it again, I would by far use 26 rods with some aftermarket pistons. The stock cast pistons don't tolerate too much. Also, I'm using a 30R on my 25 and I have a feeling 450whp may be a bit of a stretch on pump gas (91) at a reasonable boost level.

[Darius]

Like I stated in my previous post, you can use RB26 pistons but I wouldn't recommend it unless you're building a drag car or something and you want super low compression. It woudl be a total dog off of boost. You don't need to use RB26 pistons with the RB26 rods. I used RB25 forged pistons on RB26 rods to maintain CP's measured compression ratio of 8.5:1.

[GSDKinked]

And this is the type of information i love and seek. Hmmmm, well I guess I should really truly build this motor to OEM stock and go balls out with the engine currently in the car (once removed). I guess my next move would be to clean up the block and etc. Any recommendations or anything?

[Darius]

That is a sound plan. You'll be surprised how fast the car will be with "only" 400hp. You might even be satisfied with that level of power and decide not to build a second motor on the side. Who knows?