Hks Low Mount Flange Change

[Šime]

Hey all, just wondering if anyone has ever changed the flange on an old HKS RB20/25 low mount manifold I've got one with a T3 divided flange but I want to run a turbo with a T4 divided inlet flange.

Does anyone know if it’s possible or advisable to weld a T4 divided flange onto these manifolds?

Or is it easier to just sell the manifold and get a whole new manifold such as a 6boost?

[Ben C34]

Ive done pretty much that to an rb30 manifold years ago. As it is cast, it needs to be welded correctly or it will crack later (preheat, controlled cooling etc)

If you take it to a reputable welder it would be no worries. And not cost much.

[wolverine]

If you are talking about a low mount cast manifold I thought they already come with the correct stud holes for a T4 and all you need to do is refit the studs.

I am sure my manifold has both.

[Šime]

Mine doesn't have the holes for the T4 studs, but the flange is large enough that they could be drilled / tapped. The ports are still the smaller T3 size though.

[scotty nm35]

Nothing a die grinder won't fix.

[Šime]

Does it matter if the flange couldn't be ported out all the way to the full T4 size? Does it need to perfectly match the turbine inlet or do I lose much if it doesn't?

Just asking cos I think the edges of the openings would come closer to overlapping the existing T3 stud holes if they're ported out to the full T4 size.

[discopotato03]

What turbine housing and turbo are you looking at using ?

A .

[Šime]

Still deciding, but leaning towards a BW EFR (probably 7670) with 1.05 housing.

[GTSBoy]

If the manifold port is smaller than the exhaust housing inlet, provided it's not massively smaller it will still be OK. It's called an anti-reversion step (when it it occurs at the head face!) What it will do is locally make the gas speed higher with a small region or turbulence downstream the step, but it shouldn't be too ugly and should cost you power unless you are trying to work the turbo all the way up to the limit of what the exhaust housing can flow.

[scotty nm35]

Agreed, 6boost actually makes this into his T3 flange design to improve the gas speed into the turbo, apparently keeps the response loss to a minimum. It's still a much larger opening than the nozzle of the turbo, so it won't be much of a restriction.

[GTSBoy]

If the manifold port is smaller than the exhaust housing inlet, provided it's not massively smaller, it will still be OK. It's called an anti-reversion step (when it it occurs at the head face!). What it will do is locally make the gas speed higher with a small region of turbulence downstream the step, but it shouldn't be too ugly and shouldn't cost you power unless you are trying to work the turbo all the way up to the limit of what the exhaust housing can flow.

Good grief. Just read my post which can't be edited now and saw all the typos that I hate from other people in it. So I fixed them here so I don't look like an illiterate moron.

[XRATED]

Most of the old HKS cast low mount mani's I've had or seen were all T4 flange, and have had the T3 bolt pattern drilled and tapped into the flange face... there is f-all difference in the actual 'hole' between T3 and T4... nothing that can't be sorted out with a die grinder anyway.

So if you have a manifold with a T3 flange (is it cracked?), I can't see why you wouldn't be able to drill and tap a T4 flange bolt hols into it.

OR... swap it for one with a T4 flange already?

... The other thing is that some turbo's just don't fitt on this manifold on and engine with the engine mounts on. I doubt the big ass comp housing on the BW turbo's will fit.

Just out of interest, is it cracked through the divider? every manifold I have seen is or has been cracked.

[discopotato03]

I don't think there's any way to hide a turbo of that size so probably not worthwhile worrying about a manifold that looks even vaguely "production" .

If you can live with a less exotic but more compact dryer Garrett do T4 TS turbine housings for the smaller and medium sized GT BB turbos .

[Šime]

The divider doesn't look like it's cracked.

Is the fitment issue because of height or width?

GTSBoy, thanks - so a lip of 2 - 3 mm would be ok?

[hypergear]

Might want to dummy it up first. I've had a HKS low mount manifold that came with a TA45 turbocharger. its a tight fit, only few mms from hitting the engine mount. If that is the case then you might want to change the turbine housing's entry flange then bolting on an adaptor in between.

[GTSBoy]

The divider doesn't look like it's cracked.

Is the fitment issue because of height or width?

GTSBoy, thanks - so a lip of 2 - 3 mm would be ok?

2-3mm is probably alright at the lower end of that range and getting a bit excessive at the upper end of the range. If you apply a little die grinder action you can improve that most of the way around.

If you're worried about the old T3 stud holes, then perhaps you could/should weld them up when getting the T4 holes put in. If you didn't want to do that, you just don't die grind too close to those and open up the majority of the rest of the ports to remove some of the lip.

[wolverine]

BW EFR will be a very tight fit since a GT30 framed turbos need a shave of the engine mount.