Looks Like Garrett Slipped Another Gtx30 Variant In .

[Ben C34]

Check out the exhaust and and cat before you jump in to changing the dump. I don't think it would be that bad.

[juggernaut1]

I changed to a 3.5 inch dump off my GT30 turbine together with 3.5 inch exhaust on my SR and made 40 more hp at 4000 rpm at the same time I swapped out a GT3071 to a 52T 3076. So I concur with DP's previous comments.

Your boost curve does seem lazy for that size turbo - 19psi at 4,000! Also you can see the power fall over up top and converges towards the lower boost setting even though more boost is being used. IMO there is an exhaust restriction post turbine housing.

[wolverine]

Got in touch with Hyperdrive yesterday. Turns out there was some confusion about the turbo and he thought it was a T28 based turbo (e.g. GTX2867), which was why he wasn't surprised at power level. Once we clarified that it was a GTX30 with 0.82 housing he said he feels like it should be making significantly more and that he agrees the restriction is somewhere in the exhaust.

Suggested next steps were a different dump pipe, larger open mouth as per Disco's comment above, and potentially check the cat to see if any restrictions there.

I need to take the car back to get a wheel stud replaced, so will discuss plan of attack for new dump and if anything else worth changing at the same time.

Photo and or brand of cat?

[AngryRB]

If you look at the power and boost curves, it looks like once the gate opens around 3800rpm, the power curve chokes then recovers after a 1000rpm,

I would guess this is gate return pipe merging gases at a 90degree angle causing back pressure on the turbine wheel, both flows are fighting each other

If you have a proper dump, you'll probably gain 30kw's at 4000rpm, if you wind the boost up to 20psi at that point you might see 40kw's,

both gate return and dump should flow in the same direction, probably has the effect of making it more like a 2.5inch dump.

[Ben C34]

Modify your current dump . It is a good base to start with.

Cut off the existing 3 bolt flange flange and gate pipe, extend 3 bolt inch bit down to just past underneath the car, put a flange there, that gives gives you plenty of space to extend the gate pipe longer and make the merge much nicer.

It is the way it is currently because it fits in place of the factory dump pipe.

[Ben C34]

Not necessarily like this but simmilar

http://cdn.skylinesaustralia.com/forums/uploads/post-29905-1166490974.jpg

[M@&k]

Photo and or brand of cat?

I'll see if I can find out.

For dump was thinking a 3.5" bellmouth and taper back to 3" at cat. Or maybe just get bigger cat at same time, I guess they're not that expensive in grand scheme of things.

[wolverine]

Venom cats are pretty well priced and George is pretty helpful.

[M@&k]

Have a couple of photos, one of cat (not sure if anyone can ID from pic), and one showing exhaust looking from rear muffler towards mid muffler.

Have been doing some more research. Went back and had a look at Mick-o's results with the GTX3071 on 98. Comparing dyno plots; his 33 made more boost earlier, and more power everywhere. I appreciate there are differences in setups and whatnot, but seems like there's something not quite right with mine. Have overlay plot showing both which I could put up.

Also for those interested found some interesting comments from a Garrett employee on designing exhausts to get the most from turbo engines. In summary, have as little back pressure as possible, try to have smooth expansion on outlet (as opposed to sudden increase), and properly designed split system is best, but well designed bellmouth is also good.

Link here: http://www.tercelreference.com/tercel_info/turbo_exhaust_theory/turbo_exhaust_theory.html

[Mick_o]

Mark that cat looks ALOT like a stocker to me!

Wonder if its gutted or not?

At a glance thats your 1st restriction found. I know I said this before but the cross flow cooler will be hurting you. I pulled 1 out last week and they are only 65mm thick and the tank inlet and outlet are smaller than 2.5"

If restrictions like this hurt my cars performance (evo 9) im sure as shit restrictive pipework will be hurting your power and response also

[M@&k]

Thanks Mick. I'd be surprised if it's the stock cat as system was installed only a couple of years ago, but could very well be a low performance one. Looking at Venom cats; it's only $220 for a 3.5" 450 series, so will probably upgrade for piece of mind if nothing else.

Regarding the intercooler, I remember you pointing out that was potentially an issue and the tuner agrees. Not sure what brand of cooler you pulled out but the Blitz SE one I have is 620 x 266 x 76 mm and piping seemed fairly large.

I'm thinking I'll try with exhaust mods and stronger actuator first, and if I don't see a decent improvement then will consider Plazmaman intercooler kit as next step.

[discopotato03]

From pics I've seen that looks like what some mobs put up as a compliance cat .

What I did was have the dump made up in 3.5 inch and used the XForce cat as a reducer . By this I mean bought the cat as a 3" generic (flangeless) and had the 3.5 flange fitted further up the inlet side cone .

I use a 200 CPI one because I didn't want the exhaust to stink , even then it did on 50/50 PULP/E85 but on straight 85 it's ok .

A .

[AngryRB]

Hard to tell from the pictures but id check that theres no reductions in pipe size at the flanges, and no reducer in the muffler.

[Ben C34]

As per your link seeing as a well designed split dump is prefered, do you think you will go with my suggestion of modifying your current dump?

[M@&k]

From pics I've seen that looks like what some mobs put up as a compliance cat .

What I did was have the dump made up in 3.5 inch and used the XForce cat as a reducer . By this I mean bought the cat as a 3" generic (flangeless) and had the 3.5 flange fitted further up the inlet side cone .

I use a 200 CPI one because I didn't want the exhaust to stink , even then it did on 50/50 PULP/E85 but on straight 85 it's ok .

A .

You may very well be right Disco. Exhaust was fitted when the car was pretty much stock, and before I knew much about what is needed. I imagine the current cat on there is pretty cheap.

I was thinking of getting a 3.5" cat and reducing after, either just after the cat or towards the rear muffler... If I get it changed I figure might as well be a bit conservative to remove any doubts.

What's the latest with yours anyway? Still sorting out injectors?

Hard to tell from the pictures but id check that theres no reductions in pipe size at the flanges, and no reducer in the muffler.

I've never noticed any reductions in the pipe work anywhere. Tried looking in the rear muffler yesterday and didn't notice anything suspicious, but it's hard to tell as I have twin outlets on the back so can't look straight in.

As per your link seeing as a well designed split dump is prefered, do you think you will go with my suggestion of modifying your current dump?

I'm certainly not against the idea, just that from many previous threads seems like a bellmouth dump is easier to get right. Given they'd have to patch up the hole where it currently merges, wonder if it wouldn't be easier to make from scratch anyway?

At the end of the day I'll probably go with what Hyperdrive recommends. Just waiting for this bloody replacement wheel stud to be sorted so I can book in.

[Ben C34]

You would cut the 3inch pipe off before it merges and extend it alone with wastegate pipe. Merge back together at the bend under the car. Heaps easy.

[M@&k]

Fair enough. Sounds like an option and will put that on the table for discussion too.

The other reason I've been thinking of getting the dump remade is to increase to 3.5". I realise it's probably overkill for what I have, but at least then I can rule out for sure as a possible restriction. Aaaand should be suitable if I go bigger later (e.g. GTX3071).

[lcxu105]

So what sort of power would one be likely to make with a gtx3076r on a rb25 neo and what sort of rpm would it spool up at?

[scotty nm35]

I have seen over 400wkw with the GTX3076 and I would expect it to hit hard around 4k, but it really depends on your setup. Externally gated and running ethanol will let you wind more boost in.

Personally I prefer the GTX3071 for the road, as it comes on a fair bit earlier and is capable of 350 odd on e85.

[lcxu105]

350kw or hp at rear wheels