Naprec 1.5 Os Big Valves

[James_03]

Hey guys,

Thinking of running these shortly:

http://www.rhdjapan.com/naprec-forged-big-valves-set-rb26dett.html

Trying to get info on what I will need to order parts wise to run them.

I know they are 6mm exhaust guides instead of the 7mm, was just going to pick these up with the valves:

http://www.ebay.com/itm/Supertech-6mm-Exhaust-Valve-Guide-24-pcs-Nissan-GT-R-RB26-RB26DETT-/301266390742

Anything else I am missing?

[bigmikespec]

Supertech or if you can Ferrea, forget Naprec. Supertech make parts for Tomei.

I think Nitto do valves too?

[James_03]

Yeh I did read about supertech doing parts for Tomei. I read a post by fitzpatrick speedworks about the trumpet angle on the Ferrea valves being a lot better then standard 16 degrees vs 20 on Ferrea.

I'm just trying to justify if it's even worth doing the valves when I have the head off. It made 620hp @ all 4 on 25psi on e85 last time it was tuned (26/30). This time going back I am chasing 30-35. The head currently has grex 272 cams (10 lift intake, 10.5 exhaust) and HKS step 2 springs I believe, and some unknown porting from Japan on both in and ex.

I was going to change over to supertech dual valve springs, as I am unsure if the single HKS step 2 springs are up to the task of that much boost, and I thought I would look at valves while I am at it. I have searched up and down the forums to try and see what standard valves are good for in terms of HP. From what I head read on other forums, the port job has a lot to do with the end result also, according to a post on Peformance Forums. What's your opinion bigmikespec?

I was quoted roughly 2k in labour and parts to fit the larger valves, which is quite an outlay given I don't really know if it's justified.

Should I look at doing valves, or just springs, or neither? I was also considering running a larger duration/lift cam on the ex side too.

What's everyone's thoughts?

Cheers.

[Piggaz]

Yeh I did read about supertech doing parts for Tomei. I read a post by fitzpatrick speedworks about the trumpet angle on the Ferrea valves being a lot better then standard 16 degrees vs 20 on Ferrea.

I'm just trying to justify if it's even worth doing the valves when I have the head off. It made 620hp @ all 4 on 25psi on e85 last time it was tuned (26/30). This time going back I am chasing 30-35. The head currently has grex 272 cams (10 lift intake, 10.5 exhaust) and HKS step 2 springs I believe, and some unknown porting from Japan on both in and ex.

I was going to change over to supertech dual valve springs, as I am unsure if the single HKS step 2 springs are up to the task of that much boost, and I thought I would look at valves while I am at it. I have searched up and down the forums to try and see what standard valves are good for in terms of HP. From what I head read on other forums, the port job has a lot to do with the end result also, according to a post on Peformance Forums. What's your opinion bigmikespec?

I was quoted roughly 2k in labour and parts to fit the larger valves, which is quite an outlay given I don't really know if it's justified.

Should I look at doing valves, or just springs, or neither? I was also considering running a larger duration/lift cam on the ex side too.

What's everyone's thoughts?

Cheers.

Rightio,

I have had the full effort NAPREC "RB26 drag kit" + the "RB26 drag combustion chamber kit" done to my head which was ported by HKS Japan. I chose to only take out the intake squish pad.

Whats in the head is listed below;

- NAPREC Big valve

- combination valve guide https://translate.googleusercontent.com/translate_c?depth=1&hl=en&prev=search&rurl=translate.google.com.au&sl=ja&u=http://www.naprec.co.jp/product/p004&usg=ALkJrhhLdKu4fyLlk8pZTewN2weuv0jj9A

- heat-resistant sintered sheet ring

- the cam cap stud bolt ,

- valve guide replacement

- sheet ring replacement

- the race for the seat cut (protruding alignment)

- water jacket air vent hole processing

- oversize jacket plug-in processing

- 1.0 surface Labs until mm

A custom set of cams were made using an Alfa Romeo Naturally Aspirated lobe of all things that measured 260 @ 10.85 mm with a very agro ramp rate. The HKS step 2 springs valve floated with anything more than 19 psi/5500 RPM from memory. They got ripped out and replaced with supertech single springs. Not an issue so far.

Below is the final result using a 2.8L/-5/E85/9.0:1 comp combo.

Turbo's are well and truly finished. What is interesting was at 19 psi (where the gates were set) it went 441 KW.

How much of that was down to the valve size itself, who knows.

The -5's are coming off and a single 8374/1.05 is taking its place.

I hope this helps.

[bigmikespec]

If the ports are not being opened up a lot I am not sure that bigger valves will do much for you. Does the head have any porting?

[James_03]

Some good info there Piggaz appreciate it, especially about the valve springs. Not too sure how I didn't see float before 25psi if that's the case.

I bought the head from Japan already ported, so yeh it has in and ex already ported. I had a guy look over it at a cylinder head place, and he seemed to believe that whoever did it, did a pretty good job of it.

Had bronze guides in it when I got it, all the guides on ex side where flogged out. I put this down to the standard exhaust valves absorbing more heat through the valve stem itself over other aftermarket valves. This was another reasons I was thinking of going valves/new bronze guides. The replacement guides that they fitted where non bronze type, just some they had made up to fit.

[bigmikespec]

Go for it then, replace the guides with bronze ones (I got Nitto ones) and replace the valves with +1.0mm oversize, at least they can recut the seats so it is all perfect again. Maybe try the Nitto valves.

[Piggaz]

Talking to RAMS cylinder heads last year, anything over 1.0 mm OS, you need to replace the seats for larger ones. 1.0 mm you can recur the factory ones.

[James_03]

Talking to RAMS cylinder heads last year, anything over 1.0 mm OS, you need to replace the seats for larger ones. 1.0 mm you can recur the factory ones.

That's interesting, as the majority of the cost to go the Naprec valves was due to having to replace the seats when I spoke to my cylinder head guys. Where did you source the Nitto valves from Bigmikespec? I can't seem to find them for sale anywhere online.

Definitely going to go 1mm OS now, just tossing up between Nitto or Supertech. Can't really afford the Ferrea kit, it's nice, but it's a little too much of a stretch once I factor in labour costs as well.

Thanks to Piggaz and Bigmikespec for the input, appreciate it.

Edited February 10, 2016 by James_03