Porting Rb26 Head On 500Whp Setup?

[MJTru]

Well I just took the humps out today. There is so much material for the stud that is basically the same as the opposite side.

But after removing it I feel as nothing was compromise. That just left me woundering why it was there in the first place.. I do think that it makes a difference in performance do to the fact that every article I read on making the rb26 a power house its always removed. Wellas for material thats felt over I feels its plenty. The same as the opposing side.

My big scare is setting the valve clearance now. Now that like a half an hour ago I finished installing the valves. It looks really good.

I cant believe what the manual is saying the gap or clearance is.

If I remember right the intake is .045 cold and the exhaust is .038 cold. This sound to big to me. Know that I im sure im wrong. Its say +- .003 is this right.

[BlindspottNZ]

My opinion (based on research in engine building books etc and doing the head on my car)

Do not touch the inlet side (port match to the gasket if you must) personally I left the inlet side alone totally - the surface roughness of the runners and the shape of the inlet devider where it splits into each valve is designed to create a small amount of turbulence to help atomise the fuel and create a more efficient burn, i.e. dont polish or knife edge here.

Clean up the combustion chamber of any nastiness; mine was rough around the spark plug threads in particular. The idea is not to reshape anything drastically as the factory design is good. Personally I gave the lips of where the valves recess into the head a very slight chamfer as it is a 90º edge here. The lip sits slightly proud of the face of the valves so has no effect on valve sealing (you can see what I mean if you slot a valve into an empty head and see where it sits when closed). A full CNC multiangle valve job would take out quite alot here and radius this 90º down to smoothly flow into the valve seat...

I removed my exhaust humps - they would cause turbulence at the port itself where the two valves' flow's merge. This would negate any benefit which may (or more likely may not) exist from the faster exhaust flow due to the venturi effect caused by the hump in that one ex port runner per cylinder. The nature of the venturi effect
itself creates turbulence at its exit hence the need for diffusers on underbodies etc... Having both ports uniform also allows the two flows to meet with equal amounts of energy flowing in unison out and into the manifold. Ideally this means that each valve will now be running at the same pressure and flowing an equal volume - this leads to more efficient use of the combustion chamber itself as it can now flow evenly... Anyone ever notice different amount of carbon build up on two ex valves in the same cylinder when you open stock RB...?

Knife edge the exhaust collectors and polish everything up. Use exhaust gasket to port match the exhaust ports, better to be safe and not go too far. Keep in mind if your ex gasket does not sit firmly on the exhaust studs and has a little bit of play (holes are larger than studs slightly) of where it will sit when its actually about to be torqued not where you are holding it for a template

Give the whole thing a bath to remove any grime and crap from it, I used hot water with lots of detergent and it came out looking new after a couple of overnight soaks (obviously totally bare head).

Don't forget to change the valve stem seals. Don't bother ordering them from Nissan Aus, I got a quote in WA for a set $345 hahahahahha ended up getting Supertech ones from the US for $45, OEM ones were $40 or so.

Don't pop out the valve springs with a socket and a hammer when you are drunk and in poorly lit thickly carpeted room, the retainers are small.

[SiR_RB]

When changing the valve springs did you reuse the original valve locks?

[Shoota_77]

I replaced mine. Obviously the lower the kms the engine has done the less likely they would need replacing but if you're chasing big power you'd be mad not to. When you see what a dropped valve does to your beautiful forgies and cylinders you do anything you can to avoid that!

[BlindspottNZ]

I reused the retainers as I kept the standard valves and springs (running poncam does not need tougher springs unless you are being abit silly with the revs heh). Due to their small size and the way they sit/are loaded I think the risk of them actually breaking is pretty non existant - the only failure I can see happening to them is if you are revving so much that you have valve float and due to the limited force of the spring pressing on the cap holding the retainers in (seat pressure), they could pop out?

This would be the same with any retainer OEM or aftermarket and would be to do with the seat pressure exerted by the spring. This doesnt mean that the outright stiffest springs are best it may have more to do, in a high rev/high temperature situation, with the material the springs are made from and how much more elasticity they have in the heat - ie how much the seat pressure they provide from cold varies when they are hot, as they get hot and soften they become more elastic.

If you have changed to significantly lighter valves than stock you actually need less seat pressure to seal them at speed than the stock ones..

[SiR_RB]

What if you run stock valves stock retainers and upgraded springs, worth upgrading locks or keep standard cos the valves are standard?

[BlindspottNZ]

In my opinion upgrading the retainers is not necessary, the extra pressure from the upgraded springs makes it even more unlikely for them to pop out as there is less chance of valve float at revs... they are held in by the spring pressure so as long as spring pressure does not slacken and let them move around/come out its all good

While it is safer to have stiffer springs, I honestly doubt they are really neccessary if the engine is not been revved over 7000RPM and your cams have a smaller lift than say 9.5

If someone has seen valve float in an RB occuring on a dyno with stock springs under this speed or with cams smaller than this then I am incorrect

Poncams (which dont require uprated springs) go up to 9.15 lift and the stock rev limit is around this, so I would imagine it would be well within the OEM springs capacity...

[SiR_RB]

My mates had valve float with 270 poncams 9.1 lift, running 23psi, was even worse when they started to adjust the cam gears !