rb26 RB26 Internals with NEO Head

[Lopin18]

First off, ive read a lot.... i just need some info that noone has so far shared in old posts... everyone just changes plans or has the engine done but doesnt go into detail of what they experienced. And a lot of users seem to recommend using the Neo head on RB26s but no info on what really has to be done etc.

Right now i have a RB26 crank, forged rb26 rods and forged rb26 pistons, plenty of RB blocks and several Neo Heads. Hence why im trying this out. I got a RB26 head but its damaged extensively.

I know they fit. Some have done it but i havent had the confirmed info about this:

 

- CR seems to be around 11:1

- Some have gotten valve damage, others havent.

 

Has anyone heard for sure or has confirmed information of what the CR is on this combo? Or what work was done to lower the compression? I know if i open up the head from 51.5cc to 60cc ill go down to 9.2:1 according to calculations with Deck Piston Height to zero and a 1.2 HG.

Also what about the piston to valve clearance. Some seem to hit valves but Mr Bizzle removed the quench pads and had some work done which i dont know and ran this combo for some miles. I have zero experience dealing with Piston Valve clearance, but ill test with clay soon if i dont find info.

A friend of mine did this same combo but with an RB25 crank w/ rb26 pistons and Neo head, i think he should have been 1 or 2 mm below deck (piston/deck height) due to the stroke difference and he ran it for a couple of miles on stock ecu and had massive detonation damage, broke ringlands and melted the quench areas but no valve hit.

 

 

http://forums.hybridz.org/topic/88037-rb26-crankrodspistons-in-rb25-neo-block-crazy-compression-ratio/

 

 

Edited December 26, 2017 by Lopin18

[BakemonoRicer]

Just use a 26 head mate.....

Don't fluff around with 25 crap.

Do it once do it right.

[Ben C34]

The neo head has vct. Use that.

[KiwiRS4T]

If you have all this gear lying around then I would dummy it up instead of relying on theory and calculations. Put the crank,  rods and pistons into a block and see where the pistons go. You should be able to work out if the pistons and valves are going to collide and if not drop the head on without bolting it down and check the clearances. You should be able to take measurements and work out the CR

Once you have done that pull it apart and measure up to see if you the bores are ok (and compatible with the pistons you have).

[Dobz]

^^This

It's unlikely you'll find the exact info you want/need so the best option is to put your hands and head to work and see how you go.

[Lopin18]

Ill do it indeed, just wondered if i could get someone with first hand experience. Im pretty much a newbie when it comes to these measures, ill have to read a bit how to. 

Even if i get clearance, i still havent figured out how will i go about lowering compression, i dont want to mess with the quench pads, specially since i have dome pistons and i dont know if that combination would cause issues (detonation wise, mixture quality and burn etc.)

I cant use the RB26 head because there are none here (Dominican Republic) and whoever has one wants quite a bit of money. 

 

Ill post back soon when i test all this out.

[KiwiRS4T]

You may not have to lower the CR but if it is more than a thicker gasket you could make a spacer with a HG either side.

[GTSBoy]

You're going to need pistons.

The RB26 is olde schoole RB style combustion chamber.  The Neo is neu schule combustion chamber design.  Smaller volume, flatter valve face angle.  With both the 25Neo and the 26 using the exact same rod from the factory, despite the different stroke, it should be very clear that the piston pin heights are different between the engines.  So trying to use 26 pistons under a Neo head is likely to lead to wrongness.  But you can't use Neo pistons (to suit the head) in the 26 block because they end up at the wrong height.

Your dummy assembly and measurements should show you where stuff is finishing up and where the problems are.  Break out the burette and do your own CR measurements.  Do not molest the combustion chamber, trying to find extra volume.  It would defeat the purpose of using the Neo head in the first place (apart from the obvious VCT benefit).

You're going to need pistons.

[Lopin18]

GTSBoy That would be the correct way but i cant fork out 1000usd for forged pistons, that doesnt include all labor and work. But i have 2 plans currently. I was given forged 26 internals and a 26 crank. So i can do a full 26 but i dont have the head. Hence the neo head. Ive been speaking with local tuners and porters. All of them fall back into "How is the valve clearance" So im gonna try that, i think its a safe and productive research. If it has clearance then ill just increase the CCs on the neo head from 51.5cc to 60cc. That should give me 9.5:1 CR. I COULD use 11:1 with fuel, but i dont like it, even if im getting all this for free i dont want to blow the engine for giggles.

Btw as far as ive read all 25,26,neo blocks are the same height no? I know the 26 crank has 73.7 stroke compared to the 25's 71.7 stroke. Neo pistons have a unique design, 26 has a lower piston pin. Comparing neo vs 26 seems to have no meaning due to the different design. Rods are all the same as far as ive read.

Second plan is to rebuild a stock neo, since i have more than enough parts. That was the initial plan, until i got this donation. Hehe.

 

[Lopin18]

Ok, so i got to work on the engine.

Tested:

RB25 neo Block, RB26 Crank + Neo Rods + 26 Pistons (All OEM), Neo head (kind of confused, ill say why later), used old stock headgasket, ARP Studs on head.

 

Torqued crank with old bearings to around 50ft, then loosened to 30 ft to avoid any damage since these are old bearings on a diff crank etc... Torqued the head with 4 arp studs. 2 on the 2nd row from the front, 2 on the second row from the back. Torqued to 50 ft. 

Gave it plenty of clay all around. Engine was 100% on timming. Everything bolted down. Only Main studs and head were torqued to mild settings, but i suppose it was enough. 

 

Results:

Almost no valve to piston danger. Only one exhaust valve got into the clay and it was on its closest, almost 3mm away from the piston. Quench area pressed the clay but it was very big. I didnt pay much attention to that but from the pictures i took i think it has a 1.5mm space between the piston/head quench.

 

Im just wondering why im getting such a huge space on the quench area. Ill retry the test with the forged engine done and ill torque properly everything and ill be CCing the head i used to confirm this is the Neo head because i found it weird that i had so much clearance (pretty sure it is physically but i wanna recheck).

 

All in all, im confused, i was expecting it to be waaaaay closer and the quench area has me thinking, but im sure i gave it enough torque to squish that HG. I think its safe to say that i can use the head, ill only work out its CCs to lower compression. Also i got a RB26 head, but its being welded to repair dropped valve damage and i gotta order lots of parts to fix it. Ill try the neo head and i think ill use the RB26 head when its ready, but i will test the neo head on the running bottom block.

 

Oh yea, those pistons and rods were in another block with an RB25 crank, they sat like 1mm below deck, when i used the 26 crank, they were pretty much flush with the block. So Im wondering really hard why i had such a big quench.

Edited December 30, 2017 by Lopin18

[Lopin18]

Ok i cant edit the post.

New findings on HG and Heads.

If im to use the 26 head on the Neo block, i have to block off the VTC feed and i have to add material to a corner since you get a very thin seal (3-4mm) between the 26 head and the neo block on the coolant passage. In this combo i can use either headgasket, the holes dont match but i think coolant flow should work out (but its gonna be restricted)

RB25 Neo head with Neo Block, same, cant use the 26 headgasket, you would mix the oil and coolant and u would have to block it off and lose VTC.

[Dose Pipe Sutututu]

On 26/12/2017 at 4:45 PM, BakemonoRicer said:

Just use a 26 head mate.....

Don't fluff around with 25 crap.

Do it once do it right.

You sir sound very uneducated saying that 

I would happily take a RB25 NEO head.

[Ben C34]

4 hours ago, Lopin18 said:

Ok i cant edit the post.

New findings on HG and Heads.

If im to use the 26 head on the Neo block, i have to block off the VTC feed and i have to add material to a corner since you get a very thin seal (3-4mm) between the 26 head and the neo block on the coolant passage. In this combo i can use either headgasket, the holes dont match but i think coolant flow should work out (but its gonna be restricted)

RB25 Neo head with Neo Block, same, cant use the 26 headgasket, you would mix the oil and coolant and u would have to block it off and lose VTC.

You would then run an external feed to the vct like when doing a 25/30.

[Lopin18]

Ok, so finally got the block machined etc etc etc.

Got the bottom end done, torqued etc. Today i did a dummy assembly again. Block got decked, piston deck clearance was affected, so the piston stands right now at 0.3mm over deck. 

Repeated the same thing as before, clay on piston 1 and 6 this time. Torqued the head im gonna use (it was decked before, this time it was straight so no further decking was done). Stock used HG, ARP, all of them, to 80 ft/pounds. 

 

This time i got more valve contact on intake and exhaust, intake was just a touch logically, exhaust went down from 3mm to 2.5mm, this time i used a good caliper to measure it and i repeated it on piston 1 and 6 just to be sure. So im positive i have 2.5mm piston to valve clearance. Next up im ordering a HG, prolly going 1.4mm Tomei, work the head combustion chamber to get the compression down (im removing both quench pads for a change, ive found over 3 stock neo engines that completely melted the intake side of the piston and its always limited to where the quench area is, i dont know if theres something with temps and the quench area intake side but.... i took a look at a VERY expensive RB26 head that a friend has, this thing is revved to 11k rpms and had over 1k hp, a local record setter so im taking if from his head that removing them isnt a leap to hell, im no expert in this im just using the quenches to avoid a suspicion i have and to get those ccs i need)  ill set the engine up soon. Thanks to the people who always leave a trail of tips and info to pick up, hopefully this helps out someone someday.

Edit: Oh yea, first test was with Stock Rb26 pistons, this test was with SC7310 CP Pistons.

Edited January 29, 2018 by Lopin18