Rb30(26)dett Head Porting

[=premo=]

Hi,

Darren, LEWIS ENGINES is fair busy at the moment so im thinking about doing a port job myself (with a lil bit of guidence from him if he has time).

Does anyone know where the RB26 head lacks in flow, what curves work best, and what section of the port needs most work?

keeping in mind its going on a RB30 block.

[R31Nismoid]

Depends on the goal, what you want out of it etc etc

[N I B]

Home port jobs should be no more than a very simple tidy up as you can go backwards so easy.Most heavy handed amature port jobs flow less than stock.

[=premo=]

not looking for shitloads of power, looking for reliability and midrange power. its for daily driver/G1 drift. i understand that i dont need to do a port job but if i have the oppertunaty to do it i may as well even if its only to put less strain on the engine.

stock or high flow GTR-32 turbos, stock cams, forged Airies pistons (fair sure there for 8.5:1 with 26 head), shot pined rods. so nothing to insane.

any ideas/tips for the port work?

(i have access to all machinery and a flow bench)

Edited December 27, 2006 by =premo=

[RB30-POWER]

I wouldn't touch it at all period, unless you know what you are doing and have had previous experience porting that type of head. Its just to easy to make it go backwards as already stated.

On the topic however, here is a good job

http://www.calaisturbo.com.au/showthread.php?t=64627

[Bl4cK32]

Cubes and myself had Chris Milton do our rb25de heads. The usual deshroud and a 3 angle valve job (ask cubes for details) as well they didnt polish the inlet to help the fuel / air mix properly (or something like that).

It is a damn good job done (ive got pics somewhere), as Cubes and myself dont have to run as much boost as some to get good numbers.

[=premo=]

yeh fair enuf. 3 angle and all that is a job ill leave to Darren (i dont want to break his seat cutting tool).

Darren knows how to port heads very well but he doesnt have time to do it, so im just trying to learn a lil to see if i can give it a go. he can give me the calculations for comparing the exhaust to inlet flow ratio's but it would take too long for him to teach me where and how to make them flow more.

[Roy]

I understand its the exhaust side that hurts the RB26 head. But i still wouldnt do anything more then match port the manifolds.

If you are serious about doing it then i would grab on old RB20 head do all the chambers etc differently and get plenty of practice. The take the RB20 head to your friend and gt him to explain the parts you have done right and the ones you have done wrong.

I still wouldnt mess with an RB26 head...get it wrong they are lots of money to replace. The money is far better spent on some decent turbos rather then stockies that are a concern or hi flows

[R31Nismoid]

If your only keeping the stocker turbos/steelies etc.

Then you really dont need to go too far at all, really just a very very basic touch-up seems to be what everyone aims for unless its going over the 350-400rwkw mark, which you wont be so you dont really need to worry about that

[=premo=]

so clean em up a lil, get rid of the lumps from the studs/match ports and get rid of the sharp edges on the vaulve guides on the exhaust side?

any other idea's or specific problem spots?

[proengines]

If you have access to a flowbench it makes it easy to see where you are going. Where you will make the biggest difference is to work mostly on the exhaust port and try to bring the exhaust up to around 75% of what the inlet flows.

What I would do if I was you is:

-Blend the bowls on both intake and exhaust, that is the area under the valve seat where it is machined. Smooth the transition from the machined bowl into the cast area.

-Smooth the short side radius so it doesn't have a sharp edge there, don't remove any more metal than is needed to get a radius there.

-Knock the bump out of the exhaust port to make the port evenly oval and blend this back up the port.

-Remove any dags in both the intake and exhaust ports.

-Sand the ports smooth. I use 80 grit porting rolls and flappers, dont go any smoother than 80 grit and leave it with the sanded finish.

-Dont knife edge the intake divider, leave it with a smooth radius. You can knife edge the exhaust divider as it wil give you a little extra port.

-I use a 3 angle intake cutter, 20/45/65, with a 1mm seat. For the exhaust I use a Serdi or Newen radius cutter, also with a 1mm seat.

-back cut the intake valves at 30 degrees, from to about .5mm from the seating area.

-Unshroud the valves in the chamber with a radius cutter (about 2mm radius) from the top of the top cut on the seat to the edge of the chamber.

-Smooth out any bumps in the chamber and radius the top edges of the chamber carefully.

That should be enough to make a noticeable difference, especially on a 3 litre. Some people say you don't need to port them because they are turbo'd etc.. but if you make the engine more efficient it will always make more power or the same power with less boost.

Most heads are designed to flow really well but the reality of making them means that by the time the initial design is cast and machined they never work as well as they were supposed to. All you need to do is get it as close to what the initial design was. If you want some photos let me know and I'll dig some up.

[=premo=]

thank you. your input is exactly what i needed. this way i dont have to ask Darren every 15min "what should i do here"

why leave the intake divider?

does it make a difference leaving a sanded finish in the chamber?

pics of seats and vaulves would be excellent just so i can make sure im following you right. also of the exhaust port to show how you blended the shape back.

thanks again

[DVS JEZ]

the reason the inlet side is left rough is to create turbulence which in turn mixes the air/fuel better.

mainly focus on the exhaust side.

cheers

Jeremy

[=premo=]

so it would be pointless leaving a sanded finish in the chamber. and the exhaust ports should be polish smooth.

[TriniGT]

Proengines, can you post some pics, that would really help.

[Sayajin]

Here is a bit of info about porting a head for an RB30:

Street car: R32 GTS4, 100% stock unmodified internals, standard g/box, 10.21@134mph. 600whp. Fastest street skyline in NZ.

R33 UK001 GTR, RB30, stock head, cams etc 646whp (4wd roller dyno) 10.77@133mph heavier than stock.

www.ripsltd.com

Per Rob over at RIPS NZ.

646WHP with COMPELTELY stock head.

-Sayajin

[dontfeelcold]

Thats max horsepower. What turbo's did they use?

I think alot of people forget that the goal of porting sometimes isn't just for outright power, but for improvements in midrange power. ie street use and circuit racing.

[NXTIME]

RIPS use a GT42R on the R33 GTR.

[Sayajin]

Thats max horsepower. What turbo's did they use?

I think alot of people forget that the goal of porting sometimes isn't just for outright power, but for improvements in midrange power. ie street use and circuit racing.

Very true....

-Sayajin

[The Dan]

so clean em up a lil, get rid of the lumps from the studs/match ports and get rid of the sharp edges on the vaulve guides on the exhaust side?

any other idea's or specific problem spots?

Don't remove the stud lumps...just improve their shape by getting rid of the sharp bump on the inner edge and lowering the height. If you remove it you will end up damaging the head.