yeah you can get it done by a machine shop. i would have no qualms about using a 26 head with 25 bolts/studs if i was building a street engine of any description. as luke said, the bolts don't locate the head and are there merely for clamping pressure. it would only be an issue for an extremely high HP engine where you were worried about the head lifting off the gasket, in which case it would be wise to run the larger bolts regardless of which head you were using.

First thing RB25 head and RB26 head have identical ports, valve sizes, combustion chamber shape and volume. There is no extra airflow or power in the basic cylinder head design. The extra airflow and power comes from the external manifolding and the twin turbos. And the RB26 manifolds do not fit the RB25 head. So if you want the good manifolds to get the power, you need the RB26 head to go with them. RB26 head is built for really heavy duty factory racing applications. It uses 12mm head bolts instead of 10mm head bolts (used on the RB25). It has solid lifters. It has sodium cooled exhaust valves. It has different valve springs because the exhaust valve stems are fatter. It also does not have the variable inlet valve timing. Although the RB26 makes no more power, it is more suitable for sustained high Hp output for homologated factory racing because it uses quite a few heavy duty parts. The Head and head gasket are located by hollow dowels so bolt sizes do not locate the head or gasket on the block. You can either drill and tap the block for 12mm, or just use a set of original 10mm RB25DE head bolts with the standard RB30 block. Guys make fantastic power with the RB25DET and the pissy little 10mm bolts. Nobody blows head gaskets. If you want to drill and tap your block, go right ahead. But if you do not do it right, those 12mm holes may end up weaker than the factory 10mm holes. It is very easy to drill a wobbly hole, and then tap it slightly oversize so the bolts are a loose fit. Personally, I would just leave the block alone and use the RB25DE bolts.

well i tell you what ill be a ginny pig and bolt it down with the 25 head bolts and post the results in a couple of months. cheers for the help

just ask Brad - spoolin imports - about rods, i have a set on the way and from what he tells me that are helping support some serious combo's. warpspeed is right. i have both a rb25 (vct) head and rb26 head and the valve sizes both inlet and exhaust are exactly the same. hence also the reason why the valves are interchangable, the valves i mean. there is not a difference between a rb25 and rb26 valves inlet or exhaust apart from the material they are made by from the factory. ps butch is just stirring up sh!t because he knows nothing about them and he is quite happy to tell you that.

So why are there so many more cam choices for the RB26 head? Is there still a decent amount of cams available for the RB25 head?

its is by far the best and most commonly used head in japan especially and the most sort after, market demand driven really.

Quote: Originally Posted by Warpspeed First thing RB25 head and RB26 head have identical ports, valve sizes, combustion chamber shape and volume. There is no extra airflow or power in the basic cylinder head design. The extra airflow and power comes from the external manifolding and the twin turbos. And the RB26 manifolds do not fit the RB25 head. So if you want the good manifolds to get the power, you need the RB26 head to go with them. RB26 head is built for really heavy duty factory racing applications. It uses 12mm head bolts instead of 10mm head bolts (used on the RB25). It has solid lifters. It has sodium cooled exhaust valves. It has different valve springs because the exhaust valve stems are fatter. It also does not have the variable inlet valve timing. Although the RB26 makes no more power, it is more suitable for sustained high Hp output for homologated factory racing because it uses quite a few heavy duty parts. The Head and head gasket are located by hollow dowels so bolt sizes do not locate the head or gasket on the block. You can either drill and tap the block for 12mm, or just use a set of original 10mm RB25DE head bolts with the standard RB30 block. Guys make fantastic power with the RB25DET and the pissy little 10mm bolts. Nobody blows head gaskets. If you want to drill and tap your block, go right ahead. But if you do not do it right, those 12mm holes may end up weaker than the factory 10mm holes. It is very easy to drill a wobbly hole, and then tap it slightly oversize so the bolts are a loose fit. Personally, I would just leave the block alone and use the RB25DE bolts. I'm sorry but you're wrong. Ask someone who has flowed the heads. You need to do short turn work and better flowing valve seat cuts to make the 25 head flow as good as a std Rb26. The ports LOOK the same but they are not. They flow better than the 25. I got told the valves are 1mm larger on one side but I haven't verified it myself. I can tell you that the valves are different in length aswell to the rb25. Also the head bolts are 11mm in the other RBs and 12mm in the RB26s

what about rod choices? Obviously the inclusion of a twin cam head on an rb30 is going to make it rev higher... are standard shot peened rod's up to the task of 8000rpm? Also, when building a 26/30, what pistons should be used in order to keep decent compression as iv heard standard vlt size/shape pistons give you really really low compression, making the engine a dog? Some original photos have not been recovered yet.

Quote: Originally Posted by RB30-POWER Sorry you lost me, To clarify what i said, i would prefer the standard RB25 bolts used with the RB26 head and standard RB30 block threads, then some dodgy guy drilling and tapping the larger hole in the RB30 block by hand and it not being perfectly vertical with the deck. You don't want head bolts pulling down on an angle at all. To bring another question to the table, can you get some jig or machine shop to tap the threads perfectly, because i wouldn't want to do it by hand? My apologies I read it wrong. And I agree with you. And as a disclaimer- I am currently doing this procedure to two RB30 bottom ends and the only thing you really need to do is make sure the block sits flat on the machine bed. It can be done in a drill press thats big enough without being bolted down so long as it sits flat. I will be using a mill but. Quote: Originally Posted by ATMO_BT1 what about rod choices? Obviously the inclusion of a twin cam head on an rb30 is going to make it rev higher... are standard shot peened rod's up to the task of 8000rpm? Also, when building a 26/30, what pistons should be used in order to keep decent compression as iv heard standard vlt size/shape pistons give you really really low compression, making the engine a dog? Std rods are great. You don't hear of people breaking them all that often but some lunatics spin their 3 litres past 8500rpm so rods are a good idea. I have had the Spool rods tested for material and they seem great. The design of them is good too. I am using these rods in my motor build now. And you don't have to rev it harder either. If you put the cams in the right spot (or keep the std ones) it won't want to rev much over 7500 anyway. Rb26 has a larger head cc than the 25 (different head that flows differently) so use a dedicated 26/30 piston from Cp or wiseco etc. using NA pistons in a 25/30 gives a reasonable CR but would most likely be too low for a 26/30 Quote: Originally Posted by ISL33P there is not a difference between a rb25 and rb26 valves inlet or exhaust apart from the material they are made by from the factory. . You should try and sit the valves next to each other before you post to prevent polluting the forum with crap. The Rb26 valves are longer because they are mechanically cammed. So they are totally different and you interchange them so you can make your Rb25 solid. You also need to change the retainers, buckets and cams to do this. Some original photos have not been recovered yet.

so standard rods are fine in a 26/30, but with the right pistons to suit? Do these pistons cost a premium when compared to say a regular rb30et forged piston?

Ok, while we are on the topic of rb26/25 heads. What limits a rb25 head as far as the hydraulic lifers are concerned? Do they limit the rev limit to say 7500rpm. The reason i ask is i already have a 25 head and want big power but dont mind limiting it to 7500rpm as reving it over that gets into big $ territory.

Mine struggle a little bit but I have VERY aggressive cams. 256 on the seat and 9.9mm lift. You can't fit more lift than that on the VVt head without major mods and I wouldn't want go much higher than that with the hydraulics anyway. If you use some 268 seat duration cams or thereabouts with 9.5mm of lift with good springs it will be fine. It will still make great power its not much of a restriction. I can do new cams for the Rb twin cams now- same sort of price to the jap cams but mine are better . Seriously but if you use that sort of profile and degree them in on the dyno you will be fine. I managed to make mine limit at 6500rpm- before we moved the cams it wanted to keep going up! And be warned the hydraulics will be noisy a bit. I hate it personally thats why i am going to solid cams to run 11mm lift and make nice noises. Some original photos have not been recovered yet.

mate take it easy no need to get your back which appears to be something common with your posts. Quote: Originally Posted by LukeVL you interchange them so you can make your Rb25 solid. You also need to change the retainers, buckets and cams to do this. so its not entirely wrong since it is possible according to you. not so much crap now is it since they were your own words.

You need to learn how to read. You said they were identical- they are not. That doesn't mean you can't put them in the 25 head- they are still different. And I'm not sure what you meant about 'getting back' ?? But I don't like people filling forums with bullsh1t lies to make themselves feel like they have big co(ks and are engine super-heroes when they have no idea what they are writing. It makes for false knowledge and deteriorates the appeal of internet forums

whats the go with the vl strut towers... im assuming the turbos/manifold and plenum all clear sweet as? What about if a high mount kit (say a 6BOOST) was fitted, would it have to be custom made to clear the passanger side strut tower?

Kyle makes the manfifolds to suit 30/26 so no dramas there. And as for the GTR plenum with a 30 block- I don't know but I am 99% sure it will fit. It fits with a full 26 and it looks as though there is enough room for it with the taller block.

sorry for the worng impressions, i suppose you have never been wrong in the past and shared that wrong knowledge ??? ............ i thought so. this is a discussion forum not an encyclopedia so sit back and enjoy. i have never claimed to have a big co(k (although the females may disagree rofl) or to be an engine super-hero (although i have done and will again do my own) but that wont stop me. its not all that hard like workshops may claim. see you on the dyno/track Some original photos have not been recovered yet.

Quote: Originally Posted by ISL33P i have never claimed to have a big co(k (although the females may disagree rofl) Haha Quote: Originally Posted by ISL33P see you on the dyno/track I don't dag... er I mean Drag race. And I don't care about dyno figures. Have fun but. Some original photos have not been recovered yet.

how about the street ? if you say no to that i think you may be lying because we have all done that.

No offence But im starting not to like this LukeVL guy... Hes taking on everybodies experiences and advice/opinions...