Jump to content
SAU Community

Recommended Posts

So yeah...I need to give my answer to my machinist tomorrow morning so I searched around and couldn't find any REAL WORLD info. only some flow bench result and such. so Have anyone seen true before and after dyno graph? to which point is porting worth it? for 1000$ what will I gain?

I only know 2 persons who did porting on their head and it's gtr-dad and mitch32. I spoke with Mitch32 he went straight to porting so he never had a before dyno graph, don't know for gtr-dad.

My machinist swear by porting but I mean.. that's his job, he won,t tell me it's worthless LOL.

I'm sure it's a nice mods but is the head of a RB26 already maxing at 500whp ? isn't more something you do when your at 650+ ?

Link to comment
https://www.sau.com.au/forums/topic/369363-porting-rb26-head-on-500whp-setup/
Share on other sites

Most heads have a minor tidy up. Seems to be all you need really.

You still going Garrett -9s? If so its a tough ask to be able to say it's worth it dropping 1k on porting.

You'd benefit more IMO from spending the money on just a solid reco on the head so that it's all in fresh order and won't give you issues later, is reliable and set for many years.

I looked at this in a fair bit of detail when I was building my rb26/30.

My findings (which were reflected in my build) were:

-It is possible that cleaning up the heads - especially the exhaust ports - may help. Some advocated removing the "humps" in the exhaust ports (look at the head, you'll see what I mean).

-However, the vast majority of people I spoke to advised against actually changing the shape of the chambers or runners, preferring velocity to outright flow capacity.

-In my view the tolerances on the head are pretty good in terms of port matching, but you can get a better match by using the gasket and light work on the head, and also the plenum connector and the exhaust manifold.

-In terms of paying money for someone to actually shape the ports, I was advised that it would be preferable to spend the dollars on oversized valves (assuming the cams and cam train is being done anyway).

In any event, I ended up finding a new head that was being sold from an abandoned build, which had 272/10.5mm cams and springs, buckets etc together with a cleaned up head and standard, re-ground valves (new ones where required).

In the end, it flowed enough for 380rwkw, which is slightly more than 500 hp. And being only "cleaned up" rather than ported as such, it doesn't induce lag or anything.

In summary, I'd say don't take the risk with porting for a 500hp setup, unless you are super confident the guy can improve over the factory head (I'd be wanting dyno graphs etc).

yeah it can be a bit hit and miss. my advise with messing with heads is less is more.... especially if you don't really know what you are doing.

on a 26 head from my experience.

no need to go overboard enlarging inlet or exhaust ports. you want velocity. but some work is good.

be careful what you do with the squish pads. altering them drastically changes engine behaviour.

there are very good gains to be had in the short turn radius, again provided you know what you are doing.

CC'ing the chambers so they are equal is also of benefit as is removing casting marks, dags etc that can cause hot spots.

exhaust hump removal is a tricky one. it's there because of the hump created in the water jacket by the exhaust studs. removing too much means a very thin wall left...

Im running -9s comfortably at 450awhp

Yeah I'm not saying you can't make more than 400hp at the wheels with that turbo but if you're going to tell me your RB26 is standard bore and stroke, runs on 98 and under 22psi of boost, then I would say you are wrong. You can, however, make 450rwhp UNCOMFORTABLY if you want to pump in 30psi of boost and water meth injection or 30% meth or E85 etc.

-9's are smaller than -7's and you can only ever expect 400rwhp out of -7's. Sure a little more can be had but usually that will be related to the fuel being used.

-9s are bigger than -7s Dan.

-7s are the same size as R34 N1.

-9s are GT-SS equiv, larger than R34 N1 :)

Incorrect

The 707160-7 has a 44.5mm inducer and 60mm exducer on the comp and the same 53.9mm turbine that all the 2860R turbo's share

The 707160-9 has a 44.5mm inducer but only a 59.4mm exducer on the comp wheel.....smaller :(

Ye i know the exd is slightly smaller... but...

-7 is a 55 trim

-9 is a 56 trim

Slight difference, higher trim = more flow.

Garrett even make note on their website that the -7 is a N1 OEM Replacement.

I've never seen -7s make more tha 300-310rwkw, where every -9/GT-SS car makes just that bit more 310-330rwkw on average.

Ye i know the exd is slightly smaller... but...

-7 is a 55 trim

-9 is a 56 trim

Slight difference, higher trim = more flow.

Garrett even make note on their website that the -7 is a N1 OEM Replacement.

I've never seen -7s make more tha 300-310rwkw, where every -9 car makes just that bit more 310-330rwkw on average.

Yeah you're right, the higher trim will have a higher flow. I just can't see 450awhp comfortably....neck ringing yes maybe......DEFINITELY NOT a 500hp setup

Either way it really is a poofteenth. The -7 is slightly more responsive too

Its funny too cause the maps garrett supplied are so different it doesnt even seen logical.

Max flow is around 22psi for both turbo's @ around 31 lh/min the difference is the -9's are slightly more efficient.

Few things can be done to the head for your power output.

- Leave the squish area as is.

- Clean up inlet ports with 80grit, and knife edge the splitter. (remeber just to clean up and not take away mass amounts of metal).

- Smooth out pockets inlets/exhaust (you will feel a sharp edge that pretty much extends around the whole valve seat)

- Remove the exhaust bumps and polish exhaust ports.

The main key here is to not take away too much material, and just clean up the ports.

I ended up doing this to my build myself as this was requested to be done by my tuner, purchased a head porting kit and went away with it with guidence from my tuner. Running -5's on a forged rb26. Tunner says it will crack the 500hp mark no problemo's but we will see.

Max flow is around 22psi for both turbo's @ around 31 lh/min the difference is the -9's are slightly more efficient.

Sorry for the hijack, but does that mean that anything over 22psi will just add heat and therefore there's never any reason to run more than 22?

Also, is there diminishing returns just before 22, so while 18->20 might give you a decent increase, 20->22 will give you much less?

Im running 17psi on -7s, and wondering how much further its worth pushing them.

Sorry for the hijack, but does that mean that anything over 22psi will just add heat and therefore there's never any reason to run more than 22?

Also, is there diminishing returns just before 22, so while 18->20 might give you a decent increase, 20->22 will give you much less?

Im running 17psi on -7s, and wondering how much further its worth pushing them.

ACtually in reading the compressor map the -7's have no more to give over 20psi of boost. But it will also depend a little on setup.

Edited by rob82

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now



  • Similar Content

  • Latest Posts

    • Well, I'm tired. I'm tired because about 4PM yesterday, before today's appointment someone immediately bought my bumper. They couldn't get it any other day as they're on the way back to NSW. So I had to do that big GTR conversion I had been planning. Unfortunately, the information on SAU about what you need and how this is done is incomplete. So what should be a simple bolt on affair, yeah, it's not. Did you know if you use all GTR items the bonnet won't close? This little manuever sent me into about 1am the night before trying to dodge a way to get it closed. I will have to revisit this in the next few days  - or maybe not, I may let a body shop figure it out. It all needs to come up and my motivation to pull the bumper off is low. It also seems to hit things in the bay where the GTT bonnet didn't. Yes I used 100% new OEM GTR items. Today, I had the joy of driving to the dyno looking like this: Given I had roughed in the fuel and given sensible but pretty conservative timing, I didn't really bet on having the car drive out any real difference than when it drove in. Sadly due to a miscommunication and laptop fun and games (and almost bricking the dongle, prayers and firmware updates indeed), I ended up using HP Tuner credits to licence the car that was already licenced. So in the end my laptop was used. It turns out my butt dyno is still well calibrated after all this time. The 325kw was on 74% Ethanol, the 313kw line was on 98. The other line is the 'before' line which was 281kw. While the numbers are pretty low, they're pretty in line with what you'd expect. Even if US dynos bump the whole result up about 50KW, gaining 10-15% is similar gains.  The curve of the cam is pretty much spot on with what was discussed as well. All this said, it still feels bad to not see the number you secretly want to see. Even if the car drove great beforehand, and I knew pretty confidently the car would drive out much the same way it drove in due to the nature of a wellish dialled in LS1 not gaining much if anything at all from being tuned from where it was. As expected, the car isn't particularly sensitive to running it at anywhere between 12.0 and 13.0 - And the initial timing at 20deg and 12.0 made 308KW. So 3 degrees of timing, and leaning it out to 12.7 for 5kw, anything above stopped giving any benefit until E85 (which has an additional 2 deg as before). Car itself behaved entirely fine. I found out that 100C = 1.15V! IAT at about 7pm was 19C. I might mess with the bonnet mounting.. but given the REO NEEDS TO BE CHOPPED TO FIT A GTR BAR this is possibly something I may leave gathering (more) dust until it returns to paint jail.
    • It sounds farrrrrrr too cold at your place Duncan... Here I was thinking our 10 degrees overnight is getting cold...
    • oh yeah, reminded this morning....bin lids frozen shut too
    • In my case not, because of total reno. But yeah.
    • Did you use an electronic speedo drive? Does you speedometer read all the way to 180km?
×
×
  • Create New...