# how exactly do you create the ultimate RB26 head?



## kismetcapitan (Nov 25, 2005)

it just occurs to me that I need to straighten out what it takes to build the ultimate head.

ok, starting with a raw head:
- port and polish the exhaust ports
- intake ports, port, but no polish? Knife-edge the wall between the pair of each intake ports? Not polishing would make the air tumble in rougher? Knife-edging, why or why not?

valves:
- polish the valves
- what about seating the valves? grinding out new valve seats? A. Bell details this procedure in his books, is this a critical step?
- how about widening the diameter of the valve openings? Aftermarket valves? (since stock valves seem pretty high-spec, with the exhaust valves sodium-filled, does anyone ever buy aftermarket valves?)
- phosphor-bronze valve guides. When I last rebuilt my engine, I think I had conflicting information on this - on the one hand, bronze guides would be smoother, but are softer and would wear faster than stock? Yet stock guides are brittle and can crack? There was something said about aftermarket valve guides that stopped me from buying a set, but can't remember what.

bowlwork:
- polish it out, maybe measure and equalize volume between all six?
- squish pads. This has been debated plenty. Nismo removes the intake side on the Z-tune. Some heads have had both removed. It's not a lot of material to take off really. How about not fully removing, but rounding off the edges (bowl volume check would still be required after rounding off some edge material).

valvetrain:
- hot cams, of course. For high lift cams, material has to be cut out for clearance, correct?
- valve buckets and shims: any mods other than ensuring proper clearance?
- valve springs: upgrade? do they wear out? if stock springs are good for 8250rpms, what do you get from uprated springs? Is this the key part of a valvetrain, where if it's not uprated, then spinning the engine too fast could bend a valve or otherwise create valve float?

other bits:
- skim the head if needed
- rear head oil drain, if desired
- ARP head bolts
- anything else I'm missing?


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## Simonh (May 24, 2002)

I think the first thing you have to do before you even touch the head is decide ultimate what...

power?
economy?
mid range?
torque?
boost handling?

etc


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## Chris Wilson (Aug 20, 2001)

Be aware removing both squish lands from a chamber adds a LOT of chamber volume, and it'll be very hard to run a sensible CR without custom pistons. Whether removal of the squish land is good or bad has been debated before. I asked 2 really good engine designers this question and got two totally opposing answers.....


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## [email protected] M/S (Feb 16, 2002)

> I asked 2 really good engine designers this question and got two totally opposing answers.....


depends what you want to use the head for! road,track or drag


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## r33-sky (Sep 27, 2009)

I removed the inlet squish-pad on my 25 head.
I have to pull a few dgrees of timing at 5.5k rpm I think because of this...however...
It makes a LOT of power 500bhp+ is tame on the street, and has good economy driven off boost but spirtited.
I did a club day about 40 miles from my home last saturday (at Kemble airfield) filled with fuel as I left home, the car ran all day with 2 drivers, got home with 1/8-1/4 tank of petrol still....
I'm happy with my squish-pad removal. Std. valves, exhaust 'lumps' removed and polised, inlet std but matched to runners, Tomei cams.


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## blue32 (Jan 3, 2007)

[email protected] has done a hell of alot of development work on the skyline heads over the years, give him a pm.
had some very good results on pump fuel.


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## kismetcapitan (Nov 25, 2005)

ok, getting away from the squish pad debate, I think that any head would benefit from RPM-proofing, and is that in the valvetrain? Springs and guides? More to that, or has anyone taken a stock head and spun it to 10,000rpm without throwing a valve?

On top of that, by application-specific, are you saying that big ports might be good for drag but turn the car into some kind of lumpy-idle lag monster? Then in what case would you leave the stock ports untouched?

I guess to be more specific, by "ultimate" I was thinking more along the lines of RPM than outright power, but if someone wants to enumerate what you'd do for a 600bhp street car versus a 1000bhp drag car (other than the squish pads), cause instinctually, flow is flow and isn't more better in any case? And 10,000rpm is still the same sort of strain on an engine in terms of parts moving, whether you're spinning 500bhp or a thousand?


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## Irish GTR (Apr 23, 2007)

Start of the machining of the ultimate head.


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## r33-sky (Sep 27, 2009)

kismetcapitan said:


> ok, getting away from the squish pad debate, I think that any head would benefit from RPM-proofing, and is that in the valvetrain? Springs and guides? More to that, or has anyone taken a stock head and spun it to 10,000rpm without throwing a valve?


You know Toby, that feels like a blow off to me re. the squish-pads.
I've followed your posts for years now and like your stories etc, but please do not underestimate what others have done with the mighty RB engine.
I was 2nd by .4mph over 1/3'd-ish mile to a 580bhp GTR (that was running consistent 3.7 0-60's against my 5.9's-massive wheelspin), Had the track been longer by even 50m I'd have killed everything there on top speed.
I've never dyno'd my car but it runs 1.5 kg/cm and makes big power even with it's 7.25k rpm limit.
I'm offering you proven DIY hard- earned experience, no BS.


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## Rain (Apr 8, 2006)

Irish GTR said:


> Start of the machining of the ultimate head.
> 
> 
> 
> <pic not included cause redundancy is redundant >


More pics please :clap:


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## kismetcapitan (Nov 25, 2005)

Definitely didn't mean to blow you off. I like the inlet squish pad removal mod. I'm jus fishing for more information regarding the other parts of the head that I haven't researched in depth.


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## GT-R Glenn (Nov 9, 2002)

Gary's 900hp on lowmounts engine runs the standard valves and still has the squish pads.


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## bigmikespec (Sep 5, 2008)

"dirtgarage" from Red R Racing has great experience with RB26 heads if he sees this thread I am sure his opinion would count for a lot.

And I think "utlimate" is a bit vague, is the the best flowing? Maybe but probably not, increase the flow too much and you sacrifice velocity at lower rpm... 

I think you need to match the head with the bottom end you are using and more importantly turbo selection. 

Mike


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## bigkev (Mar 2, 2008)

im very interested in this thread but what is a squish pad? am i being a complete idiot?

kev


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## r32SINGH (Jul 29, 2008)

bigkev said:


> im very interested in this thread but what is a squish pad? am i being a complete idiot?
> 
> kev


I would like to know this to


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## Corsa1 (Sep 8, 2003)

I don't think it is a good thing to remove the squish pads as they are there for a reason the proper way to do it is put a slant squish band in there but you then need to start with a blank piston crown and machine the same angle on to the piston as you have on the head this mod works best with over size valves to remove the masked area by the old squish band it all so reduces the knock limit by a faster burning velocity over the stock rb one any way that's enough typing for me I hate it.
[email protected]


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## kismetcapitan (Nov 25, 2005)

GT-R Glenn said:


> Gary's 900hp on lowmounts engine runs the standard valves and still has the squish pads.


but what about the valvetrain - springs, buckets, guides?


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## Rain (Apr 8, 2006)

bigkev said:


> im very interested in this thread but what is a squish pad? am i being a complete idiot?
> 
> kev



This is the section they are talking about


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## lightspeed (Jul 11, 2002)

Just send it to these guys......

[NAPREC-ƒiƒvƒŒƒbƒN]ƒGƒ“ƒWƒ“�Eƒp�[ƒc�Eƒ`ƒ…�[ƒjƒ“ƒO�E‹à‘®‰Á�H�E“à”R‹@‰Á�H

By the way - has anyone here drilled the head to let the air bubbles bleed out from the jacket above the combustion chamber.

Naprec have been doing it for years and I've seen the same drillings on pictures of the group A heads. They drill into the rectangular water recesses between the inlet ports.
It looks like a diagonal drilling as it eats into the edge of hole at the outside edge. Fancy doing my cylinder head but it looks kinda scary drilling into the unknown.


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## SafT (May 20, 2004)

Yeah, its not hard to do, once you have the head off you can stick a straight o ring pick up into the area you are trying to reach and get a good idea of where you should be aiming for.


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## Asim R32GTR (Sep 24, 2003)

Here is a good example of how it should be done

Nissan RB26 CNC Cylinder Head



















Asim


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## bigkev (Mar 2, 2008)

Rain said:


> This is the section they are talking about


thanks rain,

would this not result in a loss of compression?

kev


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## kismetcapitan (Nov 25, 2005)

ok, let me narrow it down a bit. 

- What do you need to do to make a head good for 10,000rpm?

- And is the effect of unshrouding simply to clean up the bowl? Or is that a part of fitting oversized valves? Oversized valves = more flow = less velocity = loss of low-end power?

speaking of flow (and drifting off-topic), I'm looking at a picture of Tomei exhaust manifolds versus stock, and the opening to the turbo is significantly bigger on the Tomei Expreme lowmount manifolds. But wouldn't this sacrifice gas velocity, and when you're shooting exhaust gas at the turbine, isn't velocity (and not overall volume) paramount? Or should I go for bigger exhaust manifolds to increase power? More power = more lag?


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## kismetcapitan (Nov 25, 2005)

bigkev said:


> thanks rain,
> 
> would this not result in a loss of compression?
> 
> kev


yep but piston crown design can make up some of it.


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## bigkev (Mar 2, 2008)

kismetcapitan said:


> yep but piston crown design can make up some of it.


so is the only point of it just to allow for bigger valves?

kev


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## tarmac terror (Jul 16, 2003)

I've looked at heads from both NAPREC and Endyn in the past and TBH I'm still stumped as to what one I'd go for.... I think either would be just as good.
As for 'rpm-proofing' the valvetrain it all depends on certain variables such as cam lift, duration as this will dictate whether or not there is a risk of valve float. Basically I would fit bronze guides and fit appropriate springs for my cam. Titanium retainers would be next and I would get the whole lot blueprinted to as tight a tolerance as possible.
As for the rest i.e porting, polishing, skimming big valves etc. that, as has been said, is really dependant on usage and I would take advice on what was appropriate for my needs.

TT


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## Stachi (Jan 26, 2008)

lightspeed said:


> Just send it to these guys......
> 
> [NAPREC-ƒiƒvƒŒƒbƒN]ƒGƒ“ƒWƒ“�Eƒp�[ƒc�Eƒ`ƒ…�[ƒjƒ“ƒO�E‹à‘®‰Á�H�E“à”R‹@‰Á�H


They're cool, they also got an "Engrish" page 

Marc


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## GT-R Glenn (Nov 9, 2002)

> but what about the valvetrain - springs, buckets, guides?


264 cams
hd springs
factory buckets
bronze guides

Just as a comparison, Gary's "DOG" of an engine that make 905hp and is considerably more torquey than it was and drives along at 50kph in 5th gear and pulls away cleanly without needing to change down, 
His son built an almost identicle engine but spent considerably more on head mods and runs bigger cams, makes less power on more boost.
*shrug*
Pity Gary's is such a dog.....


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## lightspeed (Jul 11, 2002)

Anyone here fitted beryllium copper valve seats?
What is the wear rate like on them?

I picked up a cheap set the other month (brand new Tomei) and as much as I like the heat transfer advantages the fitting cost and possible wear issues is putting me off at the moment.


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## Chris Wilson (Aug 20, 2001)

Valve Seat Technology For Stock and Performance Applications: Engine Builder


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## EndlessR (Nov 6, 2007)

A few of our head, pistons recessed, ported, cooling channel added


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## Chris Wilson (Aug 20, 2001)

How does the milled water groove help, I am not sure that I am grasping the concept of that fully.


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## HenrikE (Mar 23, 2006)

Solution to prevent hot-spots maybe?


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## Corsa1 (Sep 8, 2003)

I carn't see that will do anything but weaken the head gasket mating surace.


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## EndlessR (Nov 6, 2007)

HenrikE said:


> Solution to prevent hot-spots maybe?


in 1  

Works well and was something what was used on a few special rb26s


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## EndlessR (Nov 6, 2007)

[email protected] said:


> I carn't see that will do anything but weaken the head gasket mating surace.


doesnt cause headgasket failure or weaken the headgasket in anyway. :thumbsup:


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## Corsa1 (Sep 8, 2003)

How does it work then?


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## EndlessR (Nov 6, 2007)

[email protected] said:


> How does it work then?


It allows water to gain access to the hotspots in the head+gasket where they are most suseptable to hotspot, especially for cylinders 5 + 6.


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## kismetcapitan (Nov 25, 2005)

that head is gorgeous...


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## Corsa1 (Sep 8, 2003)

Surely the amount of water the small channels will flow will just turn to steam from the heat of the head.


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## Chris Wilson (Aug 20, 2001)

Sorry, I don't get that mod at all. Surely you want water in the cooling voids in the head, flowing from one end to the other, not bypassing the voids via the relatively cold head / block interface? Is this a mod that was used by the "works" engines in the days of Group A or something, or a new concept?


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## blue32 (Jan 3, 2007)

Just a thought, but removing material from the block near the cylinders, wont this weaken it and possibly increase the chance of cracking the block?


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## Asim R32GTR (Sep 24, 2003)

blue32 said:


> Just a thought, but removing material from the block near the cylinders, wont this weaken it and possibly increase the chance of cracking the block?


This is done to the head, not the block.


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## Asim R32GTR (Sep 24, 2003)

[email protected] said:


> Surely the amount of water the small channels will flow will just turn to steam from the heat of the head.


I have to agree with this. 

I thought the basic idea was to get water across the head, not from front to back, to get rid of hot spots. 


Asim


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## lightspeed (Jul 11, 2002)

Chris, the Group A mod is the drillings on the inlet side that I mentioned earlier.

Found numerous pictures in the japanese books.

I read the link on valve seats but it didn't say much on BeCu wear rates with steel valves. Look good for Titanium. 

Anyone here have any real world experience with BeCu seats on an RB26?


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## EndlessR (Nov 6, 2007)

Cooling chanel allows coolant to move between the noraml cooling channels on the head where normally they are not so effective at cooling. 
This is between head gasket and head, where hotspots are known to occure.
While this is not a modification that is needed on 90% or RB26 engines, for those who are looking to run lots of power, 
Water access is increased and head temp is better regulated as the Cooling channel helps water reduce the temp where the hotsports are located. 

This is what is done on some very high powered RB engines, to help with keeping head temp down. This tuning comes from Koyama san of Jun, who is adviser to RH9 group. According to Koyama san, head temp is reduced due to better cooling of the hotspots.

drawing time


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## R.I.P.S NZ (May 7, 2004)

Interesting but I'm not sure that I can see any advantage in running thin grooves like that but maybe a problem they have had has been cured by doing it, who knows.

Not knocking it at all but I've never done any similar mods and we've been fine to date at up to 1400hp.

Rob


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## EndlessR (Nov 6, 2007)

R.I.P.S NZ said:


> Interesting but I'm not sure that I can see any advantage in running thin grooves like that but maybe a problem they have had has been cured by doing it, who knows.
> 
> Not knocking it at all but I've never done any similar mods and we've been fine to date at up to 1400hp.
> 
> Rob


It also stabalizes water temp when the engine reaches it optimum temp, it doesnt go up and down (according to JUN). 

Its main use is on cars that are either high power cars performing topspeed runs, where hot spots around 5/6 cylinder are most "abunai" 
Or circuit cars that are running long duration on the track. 

Our drag cars although run alot of power, its just for a short time. 
We never blow headgaskets, just cracked blocks.


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## Sub Boy (Jan 28, 2008)

R.I.P.S NZ said:


> Not knocking it at all but I've never done any similar mods and we've been fine to date at up to 1400hp.
> 
> Rob


I guessing this would be more usefull for long distances.....I can't imagine your engines would get anywhere near as hot even with 1400hp as some circuit engines.


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## EndlessR (Nov 6, 2007)

Sub Boy said:


> I guessing this would be more usefull for long distances.....I can't imagine your engines would get anywhere near as hot even with 1400hp as some circuit engines.


Exactly, circuit engines or steet engines, not needed for drag.


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## Piggaz (Sep 5, 2002)

Rick, out of interest what would it cost to have a full blown head built with all the fruit? (PM if you like)


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## DrGtr (Jul 18, 2009)

Very very interesting thread a lot of good information on here, just my question if you know is it a lot of meat on the stock valve seats to machine them and install 1mm oversize valves or i need to change them to the tomei ones?


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## kingsley (Aug 26, 2002)

EndlessR- that head is beautiful - a work of art.

Does putting the smooth radius around the edges of the valve ports help quite a bit with flow when the valves are only part open?

Cheers,
Kingsley.


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## Chris Wilson (Aug 20, 2001)

Putting a flowed radius on the valve SEATS might. Current F1 heads radius the seats as part of the port flow.


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## Chris Wilson (Aug 20, 2001)

DrGtr said:


> Very very interesting thread a lot of good information on here, just my question if you know is it a lot of meat on the stock valve seats to machine them and install 1mm oversize valves or i need to change them to the tomei ones?



Not done this but I believe you can machine stock seats to take a + 1mm o/size valve.


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## DrGtr (Jul 18, 2009)

Chris Wilson said:


> Not done this but I believe you can machine stock seats to take a + 1mm o/size valve.


I think so too but i am just not sure. I will ask the mashinery place where they are going to machine the head so they can let me know if they can install a new ones though or if the excisting ones can be machined to 3d cut.


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## kingsley (Aug 26, 2002)

Chris Wilson said:


> Putting a flowed radius on the valve SEATS might. Current F1 heads radius the seats as part of the port flow.


Indeed so but I couldn't see the seats from the pics - I'd assume they'd have done these too. It seems logical to me that a smooth radius on the bits you can see in the pictures would also help.

Cheers,
Kingsley.


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## EndlessR (Nov 6, 2007)

kingsley said:


> EndlessR- that head is beautiful - a work of art.
> 
> Does putting the smooth radius around the edges of the valve ports help quite a bit with flow when the valves are only part open?
> 
> ...


Thank you 

Yes it helps with flow and air/fuel mixture. But we have no back to back testing of it, so its thoery none the less, which is why I am pushing Sugino san to get an Engine dyno as its much easier to test these things.

Rick


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