rb25 head modification questions (porting)

[RBVS]

hi, i hope someone can shed some light for me.

1. if i took my 25 head to be ported what would be done?

2.if i were to die grind the inlet bigger to the valves would i be increasing flow for better or worse. (like using to big intercooler pipes)

3.for each cyclinder there are two valves (as you know), the inlet splits into two, if if I were to grind the split down so it was one would that increase flow or would it create turbulance?

Cheers Tim

[rev210]

Depending on what sort of power you decide upon leave most of that 'porting' alone.

If the head requires a reco' then just get the combustion chamber bowl area cleaned up a little. The radius on the stock head aren't too bad. The intake and exhaust ports might like a bit of smoothing to remove cast imperfections although the ports themselves even with 'the bumps' will still flow a large amount of power.

With power of the order of 450hp or less the rule 'ain't broke don't fix it applies' and you even save time and money yay!. With the die grinder you can smooth things off but, without experience in matching the ports evenly don't try to increase the size of anything.

[Sydneykid]

Hi guys, I keep hearing the "RB ports aren't too bad standard" line. Well I reckon they are pretty average really, lots of dags, casting marks, misaligned manifolds, thick and protrusive valve guides etc etc.

The turbo engine story goes "don't worry about the porting, just turn the boost up some more". Well I don't subscribe to that, I'd much rather make my power target at the lowest boost possible. So by porting, polishing and matching I might be only able to save say 0.1 bar, but even that is worth it. I can run higher static compression, more ignition advance and the engine will build boost faster because it flows better.

I have a rule, if I take a head of one of our engines, I ALWAYS get it ported, the manifolds matched and internally polished and equalised combustion chambers .

As the Rev said RBVS, if you are doing it yourself, remember less is better. It is so easy to take too much out, and remember you can't ever put it back.

Hope that helps.

[Steve]

Dont the heads flow around 95% efficiency?

Isnt it a big risk to start messing with 95%, for so little gain, there is huge chance of error?

Match porting manifolds on the other hand....

[Busky2k]

I totally agree with Sydneykid. The SR/RB heads still have alot of potential with them. After all, they were designed with stock power levels in mind.

Even just a quick polish/degag/match port, there is definitely some gains to be had with a small amount of effort!

[RBVS]

ok cool , i was thinking just a clean up and a polish. i can see were the gasket sits and there are marks (black) , ring around the the openings which i was thinking of cuting back as in let air and exhast gasses must be hitting.

mite be important to match inlet but exhast and turbo manifold bigger you can get em the beter or what?

i will be doing my self, but will take great care, not going to go nuts

[RBVS]

any coments on, when a port is done do they cut back the split to the valves?

or just make all holes bigger and do it even.

[mambastu]

I ported mine a few months ago and posted some before and after pictures which might help you on this thread http://www.skylinesaustralia.com/forums/sh...ghlight=porting

[Bl4cK32]

what was the result with the head mambastu? (power wise?)

[RBVS]

I ported mine a few months ago and posted some before and after pictures which might help you on this thread http://www.skylinesaustralia.com/forums/sh...ghlight=porting

THANKS!! that was a big help. I did a search but gave up to soon

[mambastu]

what was the result with the head mambastu? (power wise?)

I haven't actually fitted the engine to my RS13 yet. Should be going in the car in a couple of weeks time with various other goodies on it so I'm not going to be able to give a 'before and after' result I'm afraid.

When I've run it in I'll post up the dyno results and we can speculate how much power I've gained (or lost ) from it