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My RB25 build up and questions?

DETurbine

By DETurbine,
in Engines & Forced Induction

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DETurbine Enthusiast

DETurbine

Posted
Posted

Ok my rings or ring lands just went out on my RB25DET and am going to be taking it to the machine shop once the season ends. As of right now I plan on putting Wiseco pistons in (8.4:1), ARP head studs, shot peen the stock rods, and 1.5mm metal head gasket. How much power do you think this setup is capable of? There is a guy here in the USA that made 586rwhp on the stock RB25DET motor (not even an aftermarket headgasket or studs). I am thinking I should be good to about 700hp.

After all the machine work is done I am going to be making an adapter stud plate for the exhuast manifold and intake manifold and will be putting on the RB26 twin manifolds with Z31 turbos on (capable of around 600hp) and also the RB26 surge tank with the indavidual throttle bodies off and a RB25 throttle body welded on the end. I also just purchased HKS cam gears and am wondering if I can run both of them or if I can just run the intake cam with the VVT? or is it better to cancel out the VVT and run both HKS cam gears?

This is in my USDM 240sx if wanted to know. I am shooting for a low 11's on this setup if not lower. Traction is going to be the problem. Going to be a cheap setup, but to me that's the way to go ($2000 into all the parts and machine work for the internals and $2000 into all the bolt-ons (turbos, manifolds, injectors, etc...)

Any suggestions would be great.

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GTRgeoff Grand Master

GTRgeoff

Posted
Posted

Sounds like it will be an absolute pig to drive on the road with that low compression and a metal head gasket which would lower the CR even more, but only a little. Otherwise, I would expect a good quarter mile machine.

I've used the standard gasket and GTR conrods with Arias forged pistons and have O ringed the block. The GTR rods are much sturdier and a cheap insurance and are usually a straight fit. There are a few sets for sale on the forum and you may just need a resize on the big ends to ensure perfect fit and is my only suggested change to your plan.

Don't try to tap the head to locate the exhaust manifold studs but cut and weld the manifold instead. Also if you could get an Australian Falcon 80mm (I seem to recall) throttle body that would help from my understanding of such things.

Clint32 Mentor

Clint32

Posted
Posted

deffinately change the rods if you have a early rb25 and if chasing more than 600hp i would go new rods anyway, cheap for you in the states.

I have seen the rb26 manifols used with a plate bolted to the head with countersuck bolts to the head and then studs to the manifols, a lot easier than cutting welding the manofolds but does crate more places for things to go wrong

Sydneykid Grand Master

Sydneykid

Posted
Posted

My 20 cents worth..........

By the time you do the work to the RB25 cylinder head, it would be chepaer to buy an RB26 top end and sell the RB25. RB26's have a lot of other advantages, solid followers, valve springs, valves, collets, valve seats, combustion chambers, water jackets etc etc. Plus you have a much greater choice of cams at half the cost. Std RB26 cams are much better than std RB25's, if you want to save some money.

Until you get over 750 bhp there is no reason to change the throttle bodies, waste of time and money for no good reason. Unless you have a crappy ECU that can't handle multiple throttle bodies and the complex MAP sensor signals they produce.

No VVT on the RB26 cylinder head.

Low 11's, with decent tyres and propper suspension setting I would be looking at a low 10. There area few R33 Skylines here running 9's with ~650 bhp, and you have a weight advantage on them.

RB25 conrods are nitrided, shot peen just bounces off, doesn't do much. Waste of time, Geoff;'s suggestion of RB26 rods is much better. For the price of forged rods in the US, personally I'd be using them, build it once build it right.

Hope that helps :)

Sydneykid Grand Master

Sydneykid

Posted
Posted
What about 9:1 CR instead of 8.4? Add alcohol injection..

We have 2 stock RB25's in the US that have pushed near 600rwhp with 9:1 CR and stock HG's.  Why not try 700hp with  9:1 with a metal HG and forged pistons?

Standard rod bolts?

Dizzo Apprentice

Dizzo

Posted
Posted
Low 11's, with decent tyres and propper suspension setting I would be looking at a low 10.  There area few R33 Skylines here running 9's with ~650 bhp, and you have a weight advantage on them.

Hi, just wondering are those skylines GTR's or GTST's and are they very streetable? Also I'm guessing you buy a Gtst 33 for say 16K but to get it into 9's would cost another 16K?

Sydneykid Grand Master

Sydneykid

Posted
Posted
Hi, just wondering are those skylines GTR's or GTST's and are they very streetable? Also I'm guessing you buy a Gtst 33 for say 16K but to get it into 9's would cost another 16K?

GTST's and they are quite streetable, not everyday and unless engineered, not legal either. As for budget, you won't get much change out of $30K for the necessary upgrades.

DETurbine Enthusiast

DETurbine

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Thanks for all the information. I think I will be sticking to the RB25 head. I would love to get a hold of an RB26 head, but would be looking more then I want to spend or would spend on the RB25 head. I will not be drilling and tapping the head or block in order to have the RB26 intake and exhuast manifolds to work, it is simply an adapter plate with two extra studs. Going to make them with my friend and will be made for under $100. As I said, wish I could do the RB26 head, but don;t have the money for that. Anyone have a set of GTR stock rods?

Also would you guys recommend getting rid of the VVT and equiped my HKS came gears on there or would I be better off just putting the HKS intake gear on and leaving the VVT?

maximajim- how much are the CR 9.1 pistons?, if I can get them with the rings under $700 then I will go with those.

Possibly might go with those mattering on pricing.

Sydneykid Grand Master

Sydneykid

Posted
Posted
They were 850 with wrist pins from Ross. I'm sure you can get a cheaper set from Wiseco.

That's US dollars. So $A1,250 plus freight $150 plus 10% import duty plus 10% GST = $A1,700

Yep, that's about right. :)

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