Poor Turbo Selection - Need Help Brainstorming

[GTScotT]

Hey guys,

NB This is not for my S14, this is for a side project Sigma Turbo that my brother and I built about 5 years ago.

The setup:

Sigma Astron 2, 2.6L

Fresh head, HD valve springs, stock bottom end

Two different cams (more info after)

Magna EFI manifold, 550cc injectors, MAP based ecu, single coil + dizzy setup

Steampipe T3 manifold, 38mm gate plumbed in, full 3" TBE

3076R (3037 spec) w/ .63 AR turbine housing

The problem:

With the smaller of the two cams, 18psi nets us a tidy 150rwkw. With the larger cam the power is boosted to 170rwkw. Small cam is aimed at power from 2500 to 6000, larger from 4000 to 8000.

Regardless of which cam is in the car the car will have nearly instantaneous boost response and fall off power long before 6000rpm. The smaller cam will come off the stall fully loaded and will probably fall off at 5. The bigger (overkill) cam will still come off stall almost fully loaded (no lag) and will run out of puff possibly 700rpm later than the small one. On gate pressure (10psi) it will easily hit 7psi free revving.. It also has no boost control issues, easily controls boost through the 38mm gate without spike or drop.

We have a pyrometer in the car which tells us very basic cruising is still above 500 degrees C and a few short burst instantly shoots over 600 degrees. A few extended pulls through first and second will see the turbine housing glow white hot. Almost translucent.

AFR's are safely around the 11:1 mark and timing isnt rock bottom or crazy high either, seems to be tuned OK. The tune was done 5 years ago though and the car wasnt really worried about since then. Therefore the tuner really has nothing to say for feedback and were just wanting to progress further with it now.

Logic tells me the turbine side is a major restriction but for gods sake its a GT30.... Im worried that investing in a .82 or 1.06ar will only be a bandaid fix and will shift its powerband higher, but still be capping the power similarly where its at now. I feel like the turbine itself is just too small for the motor, and that the motor cant be compared to a more modern motor of similar size.

Please share your opinions and help me brainstorm how to get the thing going properly. I have 1000cc injectors ready to go once I work out this turbo issue (if it even is the turbo).

Cheers,

[AngryRB]

Hey guys,

NB This is not for my S14, this is for a side project Sigma Turbo that my brother and I built about 5 years ago.

The setup:

Sigma Astron 2, 2.6L

Fresh head, HD valve springs, stock bottom end

Two different cams (more info after)

Magna EFI manifold, 550cc injectors, MAP based ecu, single coil + dizzy setup

Steampipe T3 manifold, 38mm gate plumbed in, full 3" TBE

3076R (3037 spec) w/ .63 AR turbine housing

The problem:

With the smaller of the two cams, 18psi nets us a tidy 150rwkw. With the larger cam the power is boosted to 170rwkw. Small cam is aimed at power from 2500 to 6000, larger from 4000 to 8000.

Regardless of which cam is in the car the car will have nearly instantaneous boost response and fall off power long before 6000rpm. The smaller cam will come off the stall fully loaded and will probably fall off at 5. The bigger (overkill) cam will still come off stall almost fully loaded (no lag) and will run out of puff possibly 700rpm later than the small one. On gate pressure (10psi) it will easily hit 7psi free revving.. It also has no boost control issues, easily controls boost through the 38mm gate without spike or drop.

We have a pyrometer in the car which tells us very basic cruising is still above 500 degrees C and a few short burst instantly shoots over 600 degrees. A few extended pulls through first and second will see the turbine housing glow white hot. Almost translucent.

AFR's are safely around the 11:1 mark and timing isnt rock bottom or crazy high either, seems to be tuned OK. The tune was done 5 years ago though and the car wasnt really worried about since then. Therefore the tuner really has nothing to say for feedback and were just wanting to progress further with it now.

Logic tells me the turbine side is a major restriction but for gods sake its a GT30.... Im worried that investing in a .82 or 1.06ar will only be a bandaid fix and will shift its powerband higher, but still be capping the power similarly where its at now. I feel like the turbine itself is just too small for the motor, and that the motor cant be compared to a more modern motor of similar size.

Please share your opinions and help me brainstorm how to get the thing going properly. I have 1000cc injectors ready to go once I work out this turbo issue (if it even is the turbo).

Cheers,

my old man used to own one of them, they are a very lazy motor that dont like reving high, must be quite a long stroke and the stock gearing was massively long gears.. I think it would need a gt35, in a way its similar to my old Mitsubishi cordia turbo, with a small turbo it would hit a wall very early and not want to rev out, but with the bigger turbo in the ab model, it was half as big as the motor, the thing was an on/off motor but had terrific pull from 4000rpm onwards and would keep going to 7000rpm, i think the astron could be the same, it needs a big turbo.

they also have 2 balance shafts in them that would hinder the performance, when i was doing my old cordia up i was told i could remove them and balance the motor to help it wake up a bit, what about the length of the intake manifold runners? would that be a factor in the powerband?

Edited December 26, 2012 by SliverS2

[R31Nismoid]

.63 housings on RB25s have never been a great idea, it would depend on how the motor you have is flowing. Sounds like it's basically coming onto boost as soon as you've left the clutch out, 7psi free-revving... Certainly housing is too small or the cam timing is really out of whack as another idea.

150rwkw @ 18psi from a GT30 isn't tidy, it's terrible IMO. Should be 250rwkw give/take.

Side point, given its 5 years old, you sure it's a 3076 and not a 3040? They were a bit of a mismatch and with a .63 rear would be REALLY strangled given they had an even larger comp wheel than a 3076

[jet_r31]

what the duration difference between cams? [email protected] versus 240/250 ish @.50. If cam timing or anything like that is not

wrong, then it does indeed sound like the turbo is maybe to small.

generally what happens is turbine flow kills top end even with more cam duration and you just end up effictively

making a shorter power band and not increasing top end to much at all, sound like what is happening if you

are running that much more duration and only picking up 700rpm top end

My brother bought some GCG spec (3037)3076 .63 on his gemini

i don't remember the specs but it only did 190rwkw flat out on 98 octane,the T28 flange hks 2540 he had before that made 10rwkw more power. the GCG, spec thing also spooled quicker . He upgraded to a 3082 .82 and picked up a lot more power and it makes more power the more boost we shove in, should go 300rwkw+ on 30psi

ATM yours sound like what his did with dodgy GCG spec 3037(3076)

Also had problems with high egt's with both those smaller setups, if he tracked the car it would blow headgaskets after

lapping for a while on high boost

E85 or WMI would have fixed/bandaided that problem whichever way you want to look at it, but he wanted more'

power anyway

theres a few guys round here with sigmas with 3540 .82's, i think they made 250ish rwkw(manual) on 18-20psi on stock

cams, changing cams netted them 300rwkw on 98 octane

If you where in S.A id lend you a 3450 .82..lol

cheers

darren

Edited December 26, 2012 by jet_r31

[Frosty]

are you getting anymore top end power if you add boost?

[discopotato03]

Back to basics . A big capacity long stroke four shouldn't need boost from nowhere revs because in theory the big cylinders should make good low rev part throttle torque .

A 2.6L Astron is larger than an RB25 even though its head is pre historic by comparison and its more truck like bore stroke and rod wise .

To my way of thinking if this engine comes on boost instantly and its using the smallest of the three optional sized turbine housings the answer is a larger housing . It seems to be tailing off before the engines out of revs which points the same way .

Now to GT 30 UHP turbines . These are not small and actually flow quite well in appropriate sized turbine housings . Plenty of people make real good power out of GT30 turbines on RB25s but not so sure about with 0.63 AR turbine housings . Its probably a good idea to have a look at Garretts GT30 turbine maps to see how the gas flow increases using the larger 0.82 and 1.06 AR GT30 turbine housings .

You can go to a larger GT35 turbine which with T3 flanges means a bored out GT30 turbine housing anyway but its pointless IMO unless you need the larger compressor wheel GT3582R turbos generally use . I think GT35 turbos are a waste on anything struggling to make less than 260 Kw and it builds in lag for no advantage .

A .

[GTSBoy]

I think you could do well to look at a bigger wastegate too. You have quite a large turbo (with a reasonably small hot side) for a not very large amount of power. I'm wondering how much better it could be if you gave the exhaust gas somewhere else to go. Have you contemplated measuring the ex manifold pressure? Might be instructive.

[GTScotT]

Thanks for the responses guys, I appreciate the time.

I'll try to address everyones questions etc. help with the thought process. I think Darren might be onto something though.. I really don't know much about single cam motors, but ill give the cam specs here. They are both camtech cams, so the specs are on their site. Ones a stage 2 turbo cam (brother refuses to go back to it) and the other is a stage 5.

The duration @ .50 is 257*, the smaller cam was still 230*. both pretty heavy cams from what I can see. I personally liked the smaller cam but it would be on full boost when it came off the stall at 2600. at the moment its basically spooling at that point which isnt really laggy anyway. Its a C4 auto, with the 2600 stall like i said. Also it is a GCG bought turbo but definitely has the proper 3076R tags on it etc. Proper surge port 3037 spec 3076R. The tag has the correct part number and even says 3037S.

Ash when I say a tidy 150kw I really mean that it goes well for how pegged back the power is. Like it has a 150kw turbo on it and its happily doing its thing (aside from the fact it will melt down if you hang off it long enough). But I do appreciate 150kw is pathetic for what it is.

Frosty as for adding boost as stated weve tried, it just starts to get white hot. Wouldnt wanna push any further.

Disco the OE housings for these things cost a packet and a half.. So im really tentative to whack on a .82 and see what happens. You would understand the dynamics of these things better than me, do you think a larger housing could change it that much? I see it shifting the powerband upward but not freeing up 100kw TBH. Im twice as scared to try a 1.06 too.

GTSBoy I am fairly confident the WG is working fine as it holds boost really well. No spike, no drop, etc. Turn it up and down with a simple bleed valve. If you think thats not a good indicator of size capacity im ready and willing to listen. It does seem to be spooling way too early though.

[GTSBoy]

My thoughts are more that a turbo + wastegate is a complete unit, and more than that, turbo + wastegate + engine is the complete system. So whilst I understand the common wisdom that if a wastegate is observed to be controlling boost, then it must be sized correctly because otherwise the turbine will overspeed, etc etc, I still suspect that with a small housing, which will choke the flow a lot on its own, you may well end up with excessively high ex manifold pressures without actually overspeeding the turbine (and hence without losing control of boost). Big back pressure = high temperatures + low power for a given boost level. Sounds like your situation.

[black bnr32]

agreed that it sounds like excessive back pressure

check your exhaust system

check for a rag in your intercooler piping

[scotty nm35]

The 0.82 rear should be about perfect for your engine, I ran the 1.06 without too much lag in my daily 2.5L for a year. If you are worried about price you could look at the aftermarket stainless housings on ebay, I have one of the Tial copy vband .82's, running 350wkw on a GTX3076.

[jet_r31]

lol, [email protected] "should" have peak power up around 8500+ rpm with no other things limiting it...

thats a HUGE cam , would be on the largeish side for a 3540 let alone what you run..id leave that for 66mm + territory

Even the [email protected] is a decent cam, i thought it would make peak power a lot higher

, whats the serial tag on turbo? i swear it sounds just like my brothers problem..f**king did our heads in..

and it was just the shit turbo gcg made..3076/3037 my asshole...makes less power than hks2530 or 2540..lol

I really doubt changing exhaust housings will do f**k all..id be highly suprised if it did!

cheers

darren

Edited December 27, 2012 by jet_r31

[GTScotT]

LOL thanks again Darren, your experience with this sort of thing is invaluable.

I keep telling my bro to go back to the original cam but he thinks this cam is the way to go. Even camtech seem to have told him putting an adjustable wheel on it will pull the powerband down 2000 RPM and make it usable, ive been arguing that they know 'fak nating' ever since I heard that. I'll get you the tag no tonight.

Cheers for the suggestion also Scotty, but that would just screw us again with needing to change the manifold flange. This is the 3rd manifold this car has had from the start..

At the moment its looking like well either be changing housing size or might swap out to a larger precision item, maybe a 6262.. Unsure at this stage and trying to work with my brother makes things extremely difficult. I lose interest very quickly with the amount of arguments involved, and then it sits for 5 years lol. He's only interested if its being done his way, by someone else, and he gets to drive it in the end. Lol FUN.

[scotty nm35]

http://www.ebay.com.au/itm/exhaust-turbine-GT35-GT30-rear-82-a-r-Turbo-Turbocharger-housing-brand-new-/150944625345?pt=Motors_Car_Truck_Parts_Accessories&hash=item23250032c1&_uhb=1#ht_2197wt_1159

Not sure on the quality of these but they look good for the price. You would have to ditch the GCG hack housing and go external gate though.

The stainless housings like mine also came in T3 flange but they don't seem to be selling them anymore. The other option is the Kinugawa 10cm... http://www.ebay.com.au/itm/Turbocharger-Turbine-Housing-Garrett-GT30R-GT3076R-GT3037-AR73-10cm-T3-V-Band-/120916434694?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item1c272e5f06&_uhb=1#ht_1166wt_1159

[GTScotT]

http://www.ebay.com....#ht_2197wt_1159

Not sure on the quality of these but they look good for the price. You would have to ditch the GCG hack housing and go external gate though.

The stainless housings like mine also came in T3 flange but they don't seem to be selling them anymore. The other option is the Kinugawa 10cm... http://www.ebay.com....#ht_1166wt_1159

That china 4 bolt housing looks OK, if only it came in v band out.

I dont actually have a GCG hack housing on it, its all genuine garret. Got a genuine garret GT 3" Vband .63 external gate rear on it.

Some pics:

[wolverine]

There is something wrong with the setup. If the car is topping out at 150rwkw with that turbo then I would be looking elsewhere. Exhaust back pressure, cam timing etc are a better place to look IMO.

(edit: should read 170rwkw)

Edited December 27, 2012 by wolverine

[GTScotT]

There is something wrong with the setup. If the car is topping out at 150rwkw with that turbo then I would be looking elsewhere. Exhaust back pressure, cam timing etc are a better place to look IMO.

You dont think the turbo is flat out too small? The fact it does come on mega early and does a 'good job' of its 170kw (larger cam) indicates to me its running OK (aside from obvious power problem). In all other cases I've seen with whacked cam timing the car is generally laggier and down on power, plus not driving well. This DOES drive well, just has nowhere near the power it should have and gets super hot super fast. If I took someone in it and said it had a T28 they would think it was farking awesome lol.

I will redo cam timing to be sure, it was last done by my dad (highly mech skilled) but I've never done that one myself TBH. From memory the head comes off these motor with the cam gear still in place and its a double chain, so I am doubtful of faux pas on his behalf. But I will check myself to be sure.

Exhaust is 3" straight through, mufflers are straight through types without chambers or bends. Thus ruling out the exhaust, unless a sigma needs > 3" to hit 200kw which would be lol'worthy but unlikely.

[wolverine]

The Mafia had one running over 300rwkw with WMI so the 0.63 housing isn't the restriction at that power level IMO.

[GTScotT]

I know there have been numerous high power .63 results with and without the use of WMI and E85. There are plenty of RB25s on pootrol making 100KW more than I am on the same turbo...

However, this isn't an RB(of any kind) by any measure.

I have been of the strong belief that simple flow capacity is only one element of a much larger dynamic equation. Where the same CFM of flow, for the same CFM of power, will need two different turbos across two different motors.

Got to remember the Astron is an old 8v clunker with its spark plugs sharing space with its exhaust ports. A lot has changed, so we cant really compare it to results from modern motors.

Thus leading me to this brainstorm thread.

[Lithium]

Different engine dynamics from the long stroke 4 banger, I don't think the turbine side is the problem. At the end of the day the exhaust gas to supply 170kw is not going to tax that combination of turbine housing and wheel if everything else is doing it's job right.

I am curious to know if you are getting the hot turbine temp even off boost? Who tuned it? I know folks making more power than that with that kind of boost on SOHC 4G63s on a much smaller TD05 turbo.... So ythis should have no issue with making more than that turbo with everything working right