Gtr Factory Exhaust Manifold, Turbo Side Porting

[JimX]

So I finally decided to put my HKS 2530 turbos in last week. Or rather, start the lengthy process and steep learning curve of a budget home upgrade. Once I am done, I will do a write-up of everything as best I remember for the DIY section. The factory turbos are out, but now the project is on hold while I wait for new dump pipes to arrive. So for now, this post is about the factory GTR low mount manifolds and the potential to have them ported to match the bigger turbo inlets. Or maybe an opportunity to flame an idiot for ruining his manifolds. I did some searches on here but couldn't find any information on porting them, so I did it only with some advice from wrxhoon who said to make sure I don't leave the manifold walls too thin.

A bit more background about this project, after I had removed the turbos and manifolds etc:

I noticed that the HKS 2530 inlet flange is bigger than the factory turbo flange, and hence the factory manifold turbo flange. The previous owner had used a bigger gasket that was the same size as the 2530's (and probably most other bigger GT turbos). This resulted in a nice exhaust soot template on the factory manifold, covering the section that the 2530's inlet port should also cover and showing my how much surface area is lost in the size difference (ie, heaps).

Upon closer inspection I noticed that the manifold seems to curve out underneath to a larger space, but it has been cast to form a narrower lip to match up to the factory turbos with the smaller port. I'm not sure if this is done to help with exhaust velocity, but it seems to me that the extra volume of exhaust gas underneath is just going to create turbulence while it all tries to escape the narrower turbo flange outlet. It makes sense to me that after the collectors, the exhaust continues out as streamlined as possible and into larger spaces without bottlenecks to create turbulence and unpredictable back pressure.

The size difference between the factory turbo and the GT flange sizes is very noticable (see pic, the red line is where the dividing line is between factory turbo flange and GT larger gasket size is), so I decided to get the dremel out and spend several hours over a few days making the space bigger and giving it a straight line down to where the 3 exhaust outlets meet up. I have no idea if this will help or hurt performance but I'm hoping that it will. I slipped up and scraped along the flat flange part several times accidentally, but the damage looks a lot worse than it is, I can barely feel any of the grooves I've carved and so I will either give it a quick polish to even it up, or just fill it with putty and level with a trowel before fitting, or even just leave it that way. Photos of the damage to follow later.

I'm not game enough to touch the engine side ports. I will leave that one for the experts (ie, I'll never be able to afford it). But since I already had a template drawn onto the manifold by the gasket with exhaust soot, I figured it would be the simplest, easiest mod I could do to my car at this point, even though it took a long time with my little dremel.

Anyone got any ideas or opinions of what I've done? Have I ruined my manifolds by reaming them out like this? If so can someone sell me a cheap pair before I re-assemble everything again?

[heller44]

I've finished refitting all my parts along with a pair of 2860-5's, mines dumps and stock manifolds. Did exactly what you said you did to yours, only the turbo flange as well, not the head flange as I will do that if I ever have to pull the head (match both sides).

A dremel? I went nuts with a die grinder and tungsten-carbide burrs, quicker and nastier but I suppose just like the operator .

[tommis85]

Well technically all ports should match up exactly to what they're attached to and vice versa because otherwise turbulence is created in whatever space is not matched up properly. The worse the match up, the worse the turbulence.

I'm not sure how good you are with the dremel, but I think I would have taken mine to a workshop and they can match it perfectly.

I'll be upgrading my R33 GTR turbos soon too...so I'm interested with what this thread evolves to

I've been posting my questions on here incase anyone wants to have a look...need as much advice as I can get. Sorry, don't mean to hijack this thread lol

http://www.skylinesaustralia.com/forums/R3...im-t228630.html

JimX...I might sound a bit cynical about taking a die grinder / dremel to the manifolds/ports....but sh[t dude if that works out for ya perfectly congrats! Am keen on seeing how you go - so far I've only done single turbo swaps on Cordias....never touched skylines before (only done intercooler install on my old 33 gtst)

Edited July 21, 2008 by tommis85

[tommis85]

Heller44...when you have time could you have a quick squiz at my thread? I need advice exactly on your 2860's....I'm getting conflicting advice. People on here say 2860r's (both in -7 and -5) while my mechanic insists on the smaller T2560's

[JimX]

A dremel? I went nuts with a die grinder and tungsten-carbide burrs, quicker and nastier but I suppose just like the operator .

Well, the first thing I did was use what seemed to be a die grinder in this cheapass drill bit set I have because I thought it'd be way out of the dremel's league. However, I managed to blunten it in fairly short order without taking much metal out, so rather than waste time looking for a proper die grinder from a professional tool shop I thought I'd give the dremel a shot since I had a few grinding stones in the kit. I'm surprised at the tenacity of these little stones, I went through only 2 little stones and it's virtually finished. Just not sure if I want to take a bit more metal out or not yet or if I want to neaten it up any more.

I would advise anyone wanting to try this to buy a proper die grinder rather than waste so much time with a dremel, however if I had been as clumsy with the die grinder as I was with the dremel then I would have bigger missing chunks of flange to deal with. Also if nothing else, anyone that was curious to know if a dremel can do it (as I was), the answer is yes

[GeeTR]

Good work man! M.fold > turbo fit is shocking, makes me wonder if it was done to limit power from factory?

[tommis85]

GeeTR....are they that bad are they? Personally I've never bothered to check - you think they would have done a good job with the GTR's and Skylines in general. Are stock setups like that?

[Adriano]

Its exactly what i would have done, although i would have used a die grinder. As long as the manifold is in a vice, it would be easy to avoid damaging the gasket mating surface

[Swiper the Fox]

port em...i did

[rb26s13]

port them.. or get stainless mani's

Heller44...when you have time could you have a quick squiz at my thread? I need advice exactly on your 2860's....I'm getting conflicting advice. People on here say 2860r's (both in -7 and -5) while my mechanic insists on the smaller T2560's

the -5's and -7's are sold as 2860's however they are actually GT2560R on there tags.

[tommis85]

RB26S13......I sent you a PM regarding my turbos, see what you make of it if you have time

Cheers,

Tom

[JimX]

Well technically all ports should match up exactly to what they're attached to and vice versa because otherwise turbulence is created in whatever space is not matched up properly. The worse the match up, the worse the turbulence.

I'm not sure how good you are with the dremel, but I think I would have taken mine to a workshop and they can match it perfectly.

I'll be upgrading my R33 GTR turbos soon too...so I'm interested with what this thread evolves to

I've been posting my questions on here incase anyone wants to have a look...need as much advice as I can get. Sorry, don't mean to hijack this thread lol

http://www.skylinesaustralia.com/forums/R3...im-t228630.html

JimX...I might sound a bit cynical about taking a die grinder / dremel to the manifolds/ports....but sh[t dude if that works out for ya perfectly congrats! Am keen on seeing how you go - so far I've only done single turbo swaps on Cordias....never touched skylines before (only done intercooler install on my old 33 gtst)

You have inspired me to get a closer port match with my last remaining dremel stone It's not that hard to match up fairly well, and it is also very easy to knock off the occasional rough spot of the factory cast as long as you're not aiming for perfectly smooth surfaces and matched ports. That's why I'm holding back on getting it perfect, because I cannot add metal back on if I take too much off. But since the consensus is that the closer the port match the better the flow, then the closer I get to matching the port should be some improvement. Even if I am 1 or 2 mm off, it's still better than the 5mm that the original size mismatch was (39mm across for factory, 44mm across for the 2530's)

Also, I think the thread will evolve into either "Installed the 2530's and the turbos aren't as laggy as I thought they'd be", or "Installed the 2530's and the turbos are hella laggy! Let me go back to stock..." as I won't be able to tell if this mod has improved or worsened lag at all, because I'm doing all this at once. I am hoping the former, of course. Oh, I just thought of a third option - "My modified manifolds exploded under boost"

(oh, and I don't mind the thread highjack. Everyone needs answers!)

[heller44]

Tom, what rb26s13 said.. mine were sold as 2860-5's came tagged as 2560, doesn't matter as long as the cartridge is labbelled 707160-5.. or if you get the 2860-7's 707160-7's..

Stock manifold mates up fairly well to the inlet flange on the stockers. There is a little bit in it, but nowhere near the extent that it needs to be hogged out to match up with aftermarket replacements. Bugger paying someone to do it though, throw it in a bench vise, use the gasket to scribe a mark and have at it, neaten up once done.

James.

[JimX]

Good work man! M.fold > turbo fit is shocking, makes me wonder if it was done to limit power from factory?

I was thinking the same thing! Or to make people buy an upgraded Nismo/N1 manifold, if they were ever made. Which would probably just be the same casting, but with the same bit machined out

Oh, and I tried to get a good photo of both flanges lined up next to each other, or even a before and after shot at the same angle/distance but it wasn't happening. So I have cropped one of my photos with the gasket lined up on top. It originally had the other manifold lined up but on a different angle which made comparing them impossible. You can see the shiny scrapes along the edge I machined. I think I can take some more off the lower left hand corner (the inner bit, not the lip/edge) to give it a bit more volume and symmetry.

Edit: The copper coloured thing is the gasket, obviously. I used it every now and then to make sure I wasn't going out of bounds.

[paulr33]

sorry to ask by why re-invent the wheel? whats wrong with off the shelf hks / apexi / trust items

takes out of the guess work / fitting issues etc

[tommis85]

Haha yeh, and it's hard to get hold of other people with GTR's and who are in the same boat as you! Yes, that's quite true...you don't want to have to shave parts of the block and then off the manifold again trying to even them out lol...that would be a nightmare! I'm sure that if you left 0.5 to 1.0mm remaining you should be pretty much right (I'm guessing that stock setups are worse than 1mm out too).

Offcourse, when you're trying to jam the last couple of horses out of the turbos then well, you'd match them perfectly till you cant feel the line where manifold joins turbo / block etc. But that's risky business. You'd have to shave off a fraction and then re-fit....then shave another fraction off lol.

I'm predicting that you may have 300-500rpm more lag...maybe. Dunno. But that may all be cancelled out with good flowing exhaust to help spin those turbos up quicker. So yeh, I vote for "Installed the 2530's and the turbos aren't as laggy as I thought they'd be" ...

I shall check every day and see if you have updated the post. I'm yet to decide on twins or single...

[tommis85]

Heller44.....I wonder why they would do this for but?? Confusing (for me, first time buying new turbos for any car)

Tom, what rb26s13 said.. mine were sold as 2860-5's came tagged as 2560, doesn't matter as long as the cartridge is labbelled 707160-5.. or if you get the 2860-7's 707160-7's..

I wonder what my mechanic will make of that this lol.

EDIT: it may explain why GT2560's and GT2860's cost the same

Edited July 21, 2008 by tommis85

[heller44]

sorry to ask by why re-invent the wheel? whats wrong with off the shelf hks / apexi / trust items

takes out of the guess work / fitting issues etc

What guess work? What fitting issues? Stock parts will obviously fit.. cast manifolds less likely to crack, gtr manifolds are reckoned to flow more than enough for any street oriented use, cost is free compared to megabuck jap manifolds (other than a few cutting bits).. Win / win I think. Even better the stock heat shields bolt on so it is as if it was never done. Although that is a downside, it looks as if nothing was ever done even after all the hard work fitting those buggers.

[GeeTR]

GeeTR....are they that bad are they? Personally I've never bothered to check - you think they would have done a good job with the GTR's and Skylines in general. Are stock setups like that?

Id heard over 10yrs ago how bad they are stock. 3yrs ago I saw mine and my brain exploded. "Not the Godzilla" i said. But these days i realize a restriction at that point is more of a top end restriction, then a response killer (think WRC restrictors). I still believe Nissan furiousally developed the GTR with Group A solely in mind; sketchy manifolds would limit power for the Gentleman's agreement, but allow race teams to port match IMO, any whoo...

I'd truly thought mine were a dud batch. Researching found it was v.old news to the japs. Mine looked like Jimx's. Manifolds went to Smokey; I went single.

I was thinking the same thing! Or to make people buy an upgraded Nismo/N1 manifold, if they were ever made. Which would probably just be the same casting, but with the same bit machined out

Hrrrm, the whole "stock vs aftermarket stainless"... Iv seen too much info from Japland, US and here that says when the stockers are abrasive ported (extrude hone, power port woteva) they ~match aftermarket ones for power & response. Being cast i would think they are more durable / retain heat. If i was doing twins, it'd be a no brainer in my head, but meh, im not getting into that one.

Edited July 21, 2008 by GeeTR

[JimX]

sorry to ask by why re-invent the wheel? whats wrong with off the shelf hks / apexi / trust items

takes out of the guess work / fitting issues etc

What's wrong with them is the price Even though the GTR is an expensive hobby I don't feel I have to spend money for the sake of getting it perfect. I have put off installing these turbos mostly for that reason and in the end I decided that I'd rather have a budget install than none at all. I'm not going to skimp on the tuning at all which will be the important place to spend the $$$. I don't think I'm going to get $1000 worth of value from a pair of HKS manifolds. I'm pretty sure I'll get the whole install and tune done for around $1000 including parts and labour, and I can't justify doubling that budget just for the sake of new aftermarket manifolds. (+$2000 for turbos, but I spent that 2 years ago so that doesn't count )