rayaapp2 Posted October 23, 2013 Share Posted October 23, 2013 Ive dug around and now have a head ache from reading all the kids with their stupid responses and misnomers regarding this subject. A bunch of myths and legends out there. Ive seen engines set up this way so I know it can be done, but no one has elected to post the secret sauce, or at least that I can find. I have an RB26 cylinder head and many rb25 bottom ends. The head was for an RB30 build that I opted out of. Im basically building an RB26 engine but Id like to use my rb25 block for ease of installation into the S30. I can use my already custom oil pan and pickup. I have everything but a set of new pistons as far as OE parts go. Is this as simple as bolting the head on? Im concerned about oil passages and coolant passages. I would think that the VCT would have an extra feed port the 26 wouldnt have. I suppose if it does I just need to block it off. If the passages are incompatible that would be a road block. Ive also read tid bits regarding the head bolts being different sizes, but Im running ARP rb25det studs that claim they fit the rb26, so either my ARP box is wrong or more than a few kids are posting information regarding the RB30 blocks. Anyone here played with this combo. Anyone have a solid link they want to toss my way? Quote Link to comment Share on other sites More sharing options...
rayaapp2 Posted October 23, 2013 Author Share Posted October 23, 2013 Ok well there is one answer... I will have to address the feed to the VCT and hopefully make it work with the cometic head gasket. Quote Link to comment Share on other sites More sharing options...
winstonusmc Posted October 24, 2013 Share Posted October 24, 2013 Dont worry about the head bolt size as the alignment dowels are the same size. The front coolant passage is a different shape due to the VCT oil feed being in it on the RB25. I put an RB26 head on an older RB25 from the R32 and it bolted on. The 10mm head bolts will be strong enough to handle any power that the block and pistons can put out. Dont worry about the 1mm gap in the hole as the dowels will locate the head for install and the clamping force will hold it in place. Many people put the 25 head on the 30 block which is the same in reverse as to what you are doing. Some I have talked to have said you can simply have a plug machined for the oil passage and drive it into the hole to block the oil feed for the VCT. The coolant passage is close enough to not cause any leaks. Quote Link to comment Share on other sites More sharing options...
rayaapp2 Posted October 24, 2013 Author Share Posted October 24, 2013 Which head gasket do you go with? Im using the cometic gasket for the rb25.. which one will seal better? Or does it matter once the oil passage is plugged? Quote Link to comment Share on other sites More sharing options...
winstonusmc Posted October 24, 2013 Share Posted October 24, 2013 Not really sure which one would be any better considering that either one would match up to the head or the block. You might have to fudge the coolant passage seal with some RTV. One of the mechanics I knew in Okinawa said that if you use the 26 head gasket, all you had to do is put some RTV over the oil supply and the gasket would be over the hole and be enough to seal it. Quote Link to comment Share on other sites More sharing options...
rayaapp2 Posted October 28, 2013 Author Share Posted October 28, 2013 (edited) I have come up with a plan.ill get some pictures. Im gonna use the rb25det gasket. Im going to weld up the cylinder head to match the coolant passage and plug the galley for the vct. ray Edited October 28, 2013 by rayaapp2 Quote Link to comment Share on other sites More sharing options...
flatrate Posted October 30, 2013 Share Posted October 30, 2013 (edited) I currently have an endyn prepped rb26 head on my rb25.. it was easy.. I had the front coolant passage welded and reshaped..I tapped the vct hole and grub screwed it shut.. I used 11mm (stock diameter) rb25 arp head studs.. dowels are the same size.. I haven't had any issues... been together a little over a year like this Your on the right track.. I've seen other guys mod the blocks coolant port.. I found that to be retarded.. Edited October 30, 2013 by flatrate Quote Link to comment Share on other sites More sharing options...
rzamvilla Posted October 30, 2013 Share Posted October 30, 2013 Guys in Australia do this... I wonder why. Can you guys point out as to why you are going with the 26 head. As far as pros of going with it. I've heard it has better flow characteristics, and well it is "safer to rev higher" due to solid lifters. Now, if you have the 25 block, are you going to go with the 26 crank as well? Quote Link to comment Share on other sites More sharing options...
rayaapp2 Posted October 30, 2013 Author Share Posted October 30, 2013 custom pistons later and I will be using the RB26 crank for the displacement. Im going with the 26 head because of the CAM options, and the exhaust manifold I want to run fits better on the 26 even though its was designed for both. Im only giving up the RB25 Greddy intake... which is the only downside for me. I like the longer runners and large plenum that will be lost. The 26 has slightly bigger valves as well. If I didnt have the 26 stuff around already I would have stuck with the 25 head(smaller cams unless I spend gobs to convert to solid lifters) and installed reducer studs on the exhaust. As I understand it I will still be limited by the 25 block. But its not much weaker than a std RB26 block. Its the N1 block I would need to go for more power, but I have my power goals set and they should fall within a reasonable range that the block can support. My biggest issue right now is the oil pump. I have collars, and stock RB26 as well as an N1 oil pump. Its so much fun trying to figure out what to run there. Im tempted to spend the money on the Tomei or something else, but Im not convinced they are all that much better... perhaps a dry sump is in my future. I also have to change the RB25 oil filter adapter to the rb26 one to clear the IAC and lines under the rb26 manifold it seems. I have the parts, I just need to assemble and check. Another thing Im considering is having all the valves replaced in this head, but there are a lot of choices there. Ferrea and Brian Crower seem reasonably priced, but I have no idea if they are any good. Its too bad I cannot source reasonably priced OE Nissan replacements. Then Im going to have to re-shim the whole thing Im sure and source shims, which I havent even looked into yet. This is a long project, can you tell? Quote Link to comment Share on other sites More sharing options...
flatrate Posted October 31, 2013 Share Posted October 31, 2013 (edited) Just get a decent oil pump i run a Tomei, Dry sump's are expensive... is this a street car? The IACV and that little box will fit under the intake manifold... i still use the OEM 25 oil cooler as well..it doesnt bolt on correctly anymore however it can work with a bit of trickery I's using Ferrea 1mm OS valves.. I have a full set of OEM RB26 valves springs buckets etc Edited March 3, 2014 by flatrate Quote Link to comment Share on other sites More sharing options...
rzamvilla Posted October 31, 2013 Share Posted October 31, 2013 Well on top of that you will at least have the individual throttles, which seem to be a thing to have. So ditching the greddy plenum is no big deal, you can get a sale on it to continue funding your project IMO.. Quote Link to comment Share on other sites More sharing options...
rayaapp2 Posted October 31, 2013 Author Share Posted October 31, 2013 I have all the rb26 stuff like the IAC and oil adapter. I just have to install them. If you want to part with those valves I might be interested. I might not need them, but as I found with the RB heads in general, people store the in bad places and valves get bent so its good to have spares and if I can use OE valves to replace a few rather than a whole set Id rather do that and save a few pennys. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.