# GT Head Cooling Modification



## doyle4281 (Dec 10, 2008)

Hello, I am in the process of building an RB26 for a Z32, being used primarily at the drag strip. I have ditched the factory ITB setup for a RIPS plenum, and 90mm throttle body, which eliminates the factory idle control functions. This now opens up the possibility to modify the plenum base with the "GT head cooling mod", which is said to increase cooling effiecency for the cylinder head. I have searched and seen some very breif writes ups on the process, but nothing to very specific. I have seen the JUN diagram, but it is a little to general to for me to base the setup off of. If anyone has any detailed information concerning the arrangement, I would appreciate the help. I will be documenting the process to help those who would like to do this in the future. Thank you

Tap sizes used? 
Fitting sizes used?
Hose sizes used?
Hose routing?
Location of remote reservoir?
Plumbing?


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## doyle4281 (Dec 10, 2008)

Any help would be appreciated....


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## lightspeed (Jul 11, 2002)

Jun looks to be dash 6 hoses tapped into the inlet manifold. 

I assume that Jun drill the head the same as Reinik did back on the Group A cars to let the water jacket above the combustion chambers breathe. Naprec offer these drillings as part of their head modification program.
Will be drilling mine soon. I am using an ARC header tank with dash 4 lines and the stock bleed screw plus a fitting in the firewall end of the water/air manifold. Seems to be a decent solution without going the full drag style of the Jun method.


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## DrGtr (Jul 18, 2009)

it will be good to make a HOW TO thread with this when you do it.


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## mambastu (Feb 13, 2002)

lightspeed said:


> Jun looks to be dash 6 hoses tapped into the inlet manifold.
> 
> I assume that Jun drill the head the same as Reinik did back on the Group A cars to let the water jacket above the combustion chambers breathe. Naprec offer these drillings as part of their head modification program.
> Will be drilling mine soon. I am using an ARC header tank with dash 4 lines and the stock bleed screw plus a fitting in the firewall end of the water/air manifold. Seems to be a decent solution without going the full drag style of the Jun method.


Theres an interesting build thread on SAU which shows a head modified by HKS which had holes drilled in interesting places:


















Are these the holes that you're taking about ?


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## lightspeed (Jul 11, 2002)

Absolutely- have lots of pics in japanese books of this mod. Allows any steam or air to escape the cooling pocket above the combustion chamber. The drilling cuts into the manifold face to get the angle to miss the head stud holes.


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## doyle4281 (Dec 10, 2008)

lightspeed said:


> Jun looks to be dash 6 hoses tapped into the inlet manifold.
> 
> I assume that Jun drill the head the same as Reinik did back on the Group A cars to let the water jacket above the combustion chambers breathe. Naprec offer these drillings as part of their head modification program.
> Will be drilling mine soon. I am using an ARC header tank with dash 4 lines and the stock bleed screw plus a fitting in the firewall end of the water/air manifold. Seems to be a decent solution without going the full drag style of the Jun method.


Thank you for the response. I was curious if smaller diameter hose could be used, as the JUN setup uses rather large hose. Do you think the -4, like you are using, will be be effective in a high power street/drag setup? Also, after the three lines from the plenum go to the small tank, where specifically to the others go? The JUN diagram has some inconclusive hoses. It looks like one goes to an overflow tank, and a large one goes to the radiator? Thanks for the help


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## lightspeed (Jul 11, 2002)

Return hose from bottom of header tank to rad lower hose. Bleed from top of radiator to header tank. Either blank off radiator cap or make a dummy one. Header tank has new rad cap. Overflow past rad cap goes to stock overflow bottle.


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## doyle4281 (Dec 10, 2008)

lightspeed said:


> Return hose from bottom of header tank to rad lower hose. Bleed from top of radiator to header tank. Either blank off radiator cap or make a dummy one. Header tank has new rad cap. Overflow past rad cap goes to stock overflow bottle.



Does the hose coming from the header tank get spliced into the existing lower hose? If so, would it be okay to weld an extra inlet to the lower radiator tank for this hose? Aside from that, could you elaborate the routing the bleed hose? This information is very helpful. Being in the US, gtr's are not easy come across.


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## lightspeed (Jul 11, 2002)

Yes, T into lower rad hose. Weld in would be fine at bottom of rad.
My bleeds are top of rad, bleeder screw hole in inlet manifold, fitting in end of waterway on balance tube above inlet manifold. All bleeds back to header tank. Dummy rad cap on rad. Head drilled 6 locations as pics above. Balance tube holes to manifold enlarged 1mm.
Also have ARC top rad hose swirl pot with air bleed back to header tank.


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## mambastu (Feb 13, 2002)

lightspeed said:


> Absolutely- have lots of pics in japanese books of this mod. Allows any steam or air to escape the cooling pocket above the combustion chamber. The drilling cuts into the manifold face to get the angle to miss the head stud holes.


Any chance of a scan of the pictures showing exactly where to drill in the head...would feel a bit nervous about having a go at that without clearer pictures ! 

The ARC kit seems to throw in an extra swirl pot on the top hose too, wonder how necessary that really is ?


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## lightspeed (Jul 11, 2002)

I'll put some pics up when I've drilled it. Those pics above are pretty good. It's kind of obvious when you look at the head on the bench where you are need to to be aiming for.


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## DrGtr (Jul 18, 2009)

i have almost got the picture but is someone willing to scan these papers and do a quide with pictures or schematic drawings of this setup?
And if you be so kind explain the benefits from doing this, do we know how much difference are these mods doing into temp wise?


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

ZZZZZZzzzzzzzzzz

From 2 years ago

http://www.gtr.co.uk/forum/100080-seeking-better-cooling-distribution-block.html


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## DrGtr (Jul 18, 2009)

Glenn can you post once more the pictures on here please?


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## DrGtr (Jul 18, 2009)

mambastu said:


> Theres an interesting build thread on SAU which shows a head modified by HKS which had holes drilled in interesting places:
> 
> 
> 
> ...


can you post the link please?


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

5 sec search on google images, RB26 collant mods


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

Maybe a "search consultancy" business might be a good sideline for you Glen?

Troll threads, give your paypal account to the asker, get $5, google search and send them the info.....


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

I still find it amusing that some people can't think outsdie the square.


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## doyle4281 (Dec 10, 2008)

This thread went downhill fast. Thanks for for being so helpful Glenn:GrowUp:


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## freakazoid3 (Jan 19, 2008)

Yea Glenn no point in sending us back in time for pics that aren't there anymore 
Repost them please


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## freakazoid3 (Jan 19, 2008)

And when I was in Uni they told us never to get info of Google as the source wouldn't always be reliable...


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

Doyle 4281 seriously go **** yourself...
Ive actually attempted to help you, although its beyond me why you cant help yourself, Ive posted a link to a really good thread on exactly what to do and how to do it...
Which still has btw a really good photo of what to do
Ive also looked on google for pictures and taken the time to put them on photobucket then post them here...
Its not my fault you need someone to hold your hand and wipe your ass for you ...
**** you


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## bigmikespec (Sep 5, 2008)

I will add to the thread but won't complain like an old man with hemorrhiods that it took 5secs of my life: JUN RB26 Cooling System Modifications


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## Glen (Jan 21, 2011)

Oooh thats a cool mod. Learn something every day.


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## doyle4281 (Dec 10, 2008)

Does anyone have any recomemdations as to what diameter the hoses should be off of the plenum base. -6 or -8?


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## Bolle (Feb 8, 2005)

I saw that COCKPIT WAKO R33 SKYLINE GT-R also has some kind of mod:
CAR FEATURE>> COCKPIT WAKO R33 SKYLINE GT-R - Speedhunters

Wonder how this setup works?
It looks like this mod is easier for us that run standars throttels.


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## doyle4281 (Dec 10, 2008)

Bolle said:


> I saw that COCKPIT WAKO R33 SKYLINE GT-R also has some kind of mod:
> CAR FEATURE>> COCKPIT WAKO R33 SKYLINE GT-R - Speedhunters
> 
> Wonder how this setup works?
> It looks like this mod is easier for us that run standars throttels.


That looks to be more along the lines of a swirl pot with an extra line to the coolant chamber. Here is a link to some general information on that, if you are interested. The purpose appears to be constantly removing air from the cooling system, helping prevent pump cavitation and hot spots.

Sumo Power: Engine Tuning, Modified & Performance Japanese Car Parts


Does anyone know if it will be okay to use -6 hose instead of -8 hose for the GT head cooling mod. Also, does anyone have pictures of the fitting welded to the plenum rather than threaded in? Thank you


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

Yep, I know pretty much everything there is to know about this mod ..
Thanks


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## doyle4281 (Dec 10, 2008)

GT-R Glenn said:


> Yep, I know pretty much everything there is to know about this mod ..
> Thanks


Thank you Glenn. Do you feel that -6 will be just as effective? Also, is it possible to return the coolant coming from the bottom of the header tank to the hole in the block behind the thermostat. Some say that the header tank gets returned to the bottom of the radiator, others say the top. My plans were to eliminate the heater hose fittings, which would leave the hole behind the thermostat. What do you think?


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## doyle4281 (Dec 10, 2008)

After putting this on the back burner for a while, I am revisiting it, and trying sort out the different plumbing options. After working with a few LS engines, I found that the factory cooling system offers a similar setup to what some call the "gt head cooling mod", and could offer some information for those that are considering it. Great article below cooling systems....

Pirate4x4.Com - The largest off roading and 4x4 website in the world.


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