WizardBlack

I have an R33 RB25 on the engine stand right now. It's almost ready to go into my 280Z. To answer your question, I have a 7-blade HX35 and it does not clear as a direct bolt-on. For the oil feed, the factory line fits, but the stock RB oil feed banjo bolt on the stock turbo is 12mm x 1.25 while the Holset requires a 12mm x 1.50. The oil drain line fits up as per factory. For the eliminated coolant lines, a 14mm x 1.50 oil drain bolt will plug the banjo hole off on the block. I have seen people find an appropriate banjo bolt from another application and made it work. I have also heard people take a standard bolt and drill it to banjo specifications. Note that the stock banjo bolt acts as a restrictor. I don't think the Holset really needs a restrictor to avoid issues, however. The only issue is that the turbo fouls the exhaust manifold at the compressor cover. If you clock the compressor output straight towards the block (in other words, a useless clock position) it will clear since the radial diameter changes, etc. With the compressor outlet pointed down, it will not clear. I suspect you merely need another T3 flange to be used as a spacer when you mount the turbo to get it to clear, but I have not tried this yet. Note that, as others stated, the turbo and the stock exhaust manifold are both twin scroll. I have not found a twin scroll "u-weld" flange to space it out. Likewise, you will need longer studs for the exhaust manifold. Note that the exhaust manifold studs are dual thread. They are 10mm x 1.25 on the turbo side and 10mm x ??? on the manifold side. It's a coarser thread spec, but I have not measured it yet. The holes in the exhaust manifold for the studs are obviously blind, so you could just get some high grade threaded rod and cut them to length, etc. Please note that I have NOT tested fitment with the factory engine mounts, as I am doing a swap into another chassis and did not use the original mounts. I have them however, so I can test it out if anyone is interested. As a side note, another nice thing about Holsets is that the compressor wheel is balanced individually (on the '35' sizes, and some others) and the turbine wheel and shaft assembly is balanced individually. This means you can rebuild it without indexing or having it rebalanced. Just pull it apart, stick the new bearings in, and slap it back together.

Pay a visit to him and see if this jogs the memory from his melon. EDIT: Oops, forgot to put the smiley at the end. Heh heh. I've had to travel as much as 10 hours driving each way to go after deadbeats. They usually change their tune when you are face-to-face with them.

USDM STi injectors are multi-oriface and 550 cc./min. Likewise, it's very easy to max them out on the original car and they put up with 100% IDC without fluttering, so they're pretty darn tough. Many injectors won't deal with much past ~85%. I used to tune Scoobies and I pegged them on plenty of cars with no det.

Those are indeed chinese junkers. You won't find a brand new Holset for less than about $1,500 USD. The rest are copies. Just buy a used one (goes for ~$250 from a place in Washington Court House in Ohio, USA; close to me). This ebay seller has a regular supply of them and lists their specs, etc. Then buy a rebuild kit for very little money (~$50 USD) and rebuild it yourself. It's easy to do.

I am after as much as I can get; just like anyone else. :-) In all seriousness, I am just tearing the entire engine apart (after importing) to clean it all up and rebuild. My car was at 2500 pounds (with a full tank) before switching from an L28Et to the RB25DET, so I'd imagine 400 whp sounds good. At the moment, this is just the basic stuff to get it into the car. I don't plan on taking the head back off when I upgrade the turbo, etc., so I wanted to get it fixed up now. When I have all the supporting stuff done, I was considering swapping to an RB26DETT. Getting a 26 head by itself is not cheap in my neck of the woods, unless I can coax an SAU member to export to me. :-) I could always export some Summit stuff in return (since I am in the same state with them). :-) I suspect no one has a back to back comparison since you usually do much more than just that for a dyno check.

Thank you for responding. I didn't even think of the factory exhaust manifold. Might I ask a few more questions? In admiring the RB26 valvetrain, might you be able to install this into a 25 head? Are the cam journal, height, etc. dimensions different? How would the Tomei solid lifter setup in a 25 compare to a factory 26 valvetrain? Does the Tomei lifter kit allow you to utilize 26 cams if you somehow deleted NVCS oil journals on the head? The bottom line is I really want the solid lifter setup (like my previous engine; L28Et) of the 26; presuming that is most of the flow/rev difference between the Series 2 R33 RB25DET head and RB26DETT head.

Actually, some parts of the USA only get 91 octane or less (particularly People's Republic of Kalifornia). Likewise, during winter months, the additives can get a bit heavy; further reducing the octane of the fuel.

Hello, I have my S2 RB25DET that I am tearing apart (after being imported) to bring everything up to new condition (or maybe a bit better ). During the disassembly of the head, I noticed bumps in the exhaust ports right at the flange surface that go into the runners 3/4" or so. They seem like they might merely be a reinforcement of the exhaust stud holes, but it seems a bit overkill for such large bumps. Is it possible to port these all the way out? Is there perhaps a coolant jacket waiting to pounce on me if I try to remove them? TIA, Mark

I found the manual. Thank you. I think I see how they are different. I've never seen a hydro lifter of such design. I guess you get the benefit of hydro lash adjustment without the possibility of spitting a rocker or adding undue weight to the valvetrain.

Oh, so the 25 does not have a bucket, but rather a lifter that is axially inline with the valve. I take it there's no way to change to the bucket design short of buying a 26 head?

OK, now I am well and truly confused. Aren't the cam lobes riding right on top of the bucket/retainer/valve? Kinda like Subaru STi's? Where are the lifters at?

Hello, I am looking at dropping a S2 RB25DET into my Datsun 280Z. I am wondering about the entire buildup process and have been collecting a lot of information. One thing I cannot seem to find is the actual, physical design difference between RB25 valvetrain and RB26 valvetrain. I understand if they have different springs and whatnot, but from everything I have seen, they are both shim over bucket and therefore equal in design? I know RB26 cams do not cross with 20/25. What am I missing? Are the dimensions merely different? Anyone have a photo of the valvetrain of 25 vs. 26? I like the idea of the RB's rev-ability and want to know how the 25 is rated compared to the 26. Thanks, Mark from Ohio

Are any of these engines with failed pumps using bypass filtration? I understand the design spec issue and tolerance theories, but the comment about gerotor sensitivity to junk makes me wonder if it might be partially mitigated by better filtration?