Factory Cast Iron Exhaust Manifold

[DaveB]

Hi all,

I am just considering options for my stagea, and it occurs to me that at my 100,000 K service (which will be very soon) it would be a good idea to replace my exhaust gasket & studs/nuts, when I fix my leaking rocker cover gasket on the exhaust side.

Are stainless manifolds worth the 'upgrade' (if that is what they are) for a stock configuration (ie. low-mount turbo & heat shields) if all I want is ~200awkw?

This is a series 2/NEO setup if that makes any difference.

Thanks for your thoughts

[Tangles]

stock is good for 400hp easy

if you replace it, you'd want a GOOD brand name Jap item, not a no-name ebay/chinese special as it'll split within weeks, undoubtedly.

[Lil_Bobby_260]

the most expensive part of anexhaust manifold, so if you are going to have it off the car changing gaskets etc id change to a stainless one too. Seems a waste putting the stock one back on... you'll get ur turbo spooling up sooner and more power with a stainless. plus, they look shit hot.

[AlexCim]

Stock is fine. Just check it for cracks (Mine was cracked between 3 and 4)

Aftermarket stainless ones are shit unless you spend big money. They WILL crack if cheap.

[DaveB]

Thanks guys, 400hp beats 200kw by a fair margin, so that sounds good enough

Looks like I'll go for the stock one unless it has cracked. If it has though how much for a decent stainless manifold approx. should I be paying? I'd seen some on Jap auctions for ~$200-300 Aus (plus postage) but sounds like they might not be the go

[wolverine]

dave you can do a few things each with it's own for and against's.

1. cheapest re-use factory manifold.

2. find a 2nd hand factory manifold and get it extrude honed and it will flow much more than standard which should lower the boost threshold and lower exhaust manifold pressure = more hp earlier. cost of honing $600 ish. bolts straight back up.

3. HKS cast manifold which flows much better than factory (prob equivalent to extrude honed factory unit) but you will need to modify the dump. you also have a port for an ext gate if you wish to go that way. extrusion of this manifold also has gains. unlikely to warp or crack since it is a cast unit. manifold cost maybe $600-$700 probably with old HKS gate attached. some would say the capacity to absorb/retain heat makes these one of the best options. check legend01 effort with an RB2.1 HKS mani extrude honed + GT3040 with both turbine and comp cover extrude honed....amazing stuff. 306rwkw with around 250rwkw from 4500rpm (or thereabouts out of an RB20 engine with small valves etc). plus the HKS unit is divided should you want to look at twin scroll turbos for earlier spool.

4. aftermarket manifold like 6Boost etc probably $1000-1200 nicest design, possibly greatest hp potential but again exhaust modifications to fit.

5. cheap chinese copy = possibly some risk of cracking later.

Edited May 14, 2008 by wolverine

[Al]

Thanks guys, 400hp beats 200kw by a fair margin, so that sounds good enough

Looks like I'll go for the stock one unless it has cracked. If it has though how much for a decent stainless manifold approx. should I be paying? I'd seen some on Jap auctions for ~$200-300 Aus (plus postage) but sounds like they might not be the go

I would stay away from stainless manifolds all together, 99% of them crack, no matter how good they are, even the manifold manufacturer's will not give a guarantee that the stainless wont crack, no matter how good the material.

The std manifold is good for at least 300rwkw. If you intend to remove the manifold, clean up the ports (on the manifold only, do not touch the head) and size match them to gasket size, including the turbo flange.

If you do consider an aftermarket manifold make sure it's made from stem pipe, as these are not as brittle as stainless and will never crack. No need to go with Jap made brands either, use 6Boost or Extreme Turbo Manifolds, both are a proven Australian product. I myself use a ETM manifold, couldn't be happier. For a good quality manifold expect to pay $1000-$1300; anything cheaper and you'll be compromising power/quality/response/etc.

DON'T EVEN CONSIDER THESE $300 CHINA MADE SHIT! Total waste of money and time.

[wolverine]

i left off port matching (thanks al).

[DaveB]

Thanks Wolverine/Al. Seems like rather different thinking to N/A where it's pretty much just tuned-length extractors and that's manifold done... but obviously much greater temps/pressures to deal with here.

Couple of thoughts; would extrude honing of the factory (cast?) manifold make it more prone to cracking? I'm a little worried about cracking as it is; I've read about a few stock RB25 manifolds on here that have cracked, or in 1 case (SK's) completely broken, between 3 and 4. Plus I have a pretty noisy spool and I want to be sure the culprit is not a manifold leak.

Thanks for your advice; looks like much e-bay searching is in order (the Australian-made stuff, not no-name Chinese stuff of course)

Edit: How do you shield the heat from a tube manifold like the ETM and 6boost designs? I've come to the realisation that nothing factory is gonna fit with a custom manifold, which means no heat shield, and I've heard that exhaust-wrap shortens the life of your manifold (they overheat and corrode/crystallize or something). So how to heat shield them? This being a low-mount manifold on an RB25DET

Edited May 14, 2008 by DaveB

[wolverine]

done well extrude honing doesn't necessarily take much metal so it shouldn't be more prone to cracking. although i would ask the people doing it what you can expect.

it is the most straight forward upgrade and it will all bolt back up.

since you intend removing the manifold for another $600ish it's worth considering.

[AlexCim]

Good manifolds are around 1200.

Steam pipe is the way to go, not stainless.

6boost gets my vote.

[Al]

Well my manifold is HPC coated, which acts like thermal wrapping, but looks like chrome paint (which then dulls once heated), refer to pics above. You can also get the HPC coating in black, which wasn't available through ETM.

You are right about the thermal wrapping crystallizing the metal and causing it to crack (over a extended period of time), that is why i only thermal wrapped the dump/front pipe. To reduce the effects; paint the pipe first with heat resistant exhaust paint, let to dry, then wrap the pipe, let to dry, then paint the thermal wrap with the same exhaust paint, till fully coated.

A custom heat shield was made for the turbo (to prevent burning the paint on the bonnet) and also along the chassis rail to protect the loom, hoses, etc.

[DaveB]

Well my manifold is HPC coated, which acts like thermal wrapping, but looks like chrome paint (which then dulls once heated), refer to pics above. You can also get the HPC coating in black, which wasn't available through ETM.

You are right about the thermal wrapping crystallizing the metal and causing it to crack (over a extended period of time), that is why i only thermal wrapped the dump/front pipe. To reduce the effects; paint the pipe first with heat resistant exhaust paint, let to dry, then wrap the pipe, let to dry, then paint the thermal wrap with the same exhaust paint, till fully coated.

A custom heat shield was made for the turbo (to prevent burning the paint on the bonnet) and also along the chassis rail to protect the loom, hoses, etc.

Niiice, that's a well-prepared engine bay Are those Tein adjustable dampers?

Is you turbo heatshield aluminium? I always thought that a lesser heat-conducting metal was best? Looks like it works well enough anyway, very substantial (like, 1/4 inch thick?!)