Poor Turbo Selection - Need Help Brainstorming

[wolverine]

Sure we can argue that different engines require different things but ultimately turbos are air pumps. When you are making power well under the capability of the compressor and turbine then there is something wrong with the setup.

I have been down the path of changing turbos and then cams following the best advice of some performance shops but ultimately poor tuning was the main cause of much hairpulling and significant expense on my behalf. There was also the question of cam timing which led me to getting everything pulled off and re-timed amongst the many things that were done.

If the work had been done to the car at a high standard in the first place I would have saved thousands of dollars chasing my tail. I would double check the cartridge number on the turbo since that costs nothing but I am pretty sure the issue lies elsewhere.

[KiwiRS4T]

Put an adjustable cam gear on the less aggressive cam and get a good tuner to experiment with different cam timings. Also just in case do a pull with the exhaust dropped.

[GTScotT]

Short of the cam having skipped a tooth I'm doubtful that the problem is as heavily dependent on the tune as you guys may think. I have looked at the maps in the past, and know the AFs. Theres a reasonable amount of timing about the place and its neither rich or lean, from what I can tell its tuned OK.

I wont put the tuners name to it as I dont believe hes to blame, plus I think forum rules are against it anyhow. I have had and had friends with multiple other cars tuned by the same tuner all with peachy results.

Lith what is your gut feel? Again I dont think it can be compared to a SOHC 4G63 as its a much longer stroke motor.

My gut feel says garbage head design with the long stroke below is making it overspeed the turbine an an early rev, and its willingness to hit high boosts is hand in hand with its inability to take on more flow. So while 18psi worth of 3076 should be 300kw worth, its really only 18psi with a motor as efficient as an RB.

I should note that on gate pressure it makes a relative amount lesser power, and feels more along the lines of 120kw than it does 170. Same goes for if you take it back to 16psi etc. We arent keen to push more than 18 as its already getting white hot very easily.

Lith the EGT are ALWAYS above 500*C, a squirt or two and its above 600. I dont want to thrash it to see what happens then lol. Trying to keep the block reusable so we can rebuild it once this is sorted.

[GTSBoy]

The old Astron makes 65-70% of the power the NA RB25 does. Add 18 psi of boost with the same turbo that should be good for 300 on an RB25, and you'd expect to be able to do 200 - 210. This one is faling fairly well short of that, and with a monster cam. Something is fairly well wrong.

Adjustable cam gear on this thing is only ever going to be a tweak. I wouldn't get too carried away with the idea of adjusting the timing.

One thing that springs to mind though, and this is harping back on my thought that the exhaust manifold pressure might be excessive, is that a big cam duration + high ex mani pressure = recipe for shitfullness.

[jet_r31]

It probally would make 200-210..if it was manual ...it has a auto with converter. Be interesting to see what it made

with a tighter converter..although thats not going to stop it laying over and playing dead up top...lol

But with that ridicilous cam, it should make a heap more..suprised its has a 112 lsa..thought it would be 114+

Be interested to see why they have done that with these motors, not usually the norm with a turbo grind,

or even there other grinds RB etc

I had a look at some pics of my brothers GCG 3076/3037..the exhaust wheel on his was much smaller than his 3082

should see if he still has the serial for it

cheers

darren

Edited December 27, 2012 by jet_r31

[ARTZ]

Has it had much/any head work Jas?

[GTScotT]

No head work Dave, luckily! Otherwise id be majorly pissed. At least Ive got the excuse ATM that its just a POS sigma lol.

Darren would you consider selling your spare 35R or take some ransom money so we can trial it and send it back? If its too much hassle I understand completely.

[wolverine]

Why don't you grab a can of petrol and a lighter? It would be the kindest thing to do.

[GTScotT]

LOL I hope your laughing with me and not at me.

I've not dismissed anything anyone has said, and I will be looking into mechanical timing at the earliest possible time per your comments.

Short of that I do want to 'cost effectively' trial a larger hotside.

[ARTZ]

Dunno it just sees. Like it must be restricted somewhere...just wondering if between the big cams and turbo it just can't breathe.put stock cams in what happens??.

Maybe its a blocked cat

[GTScotT]

LOL if it had a cat.

Its literally just a pipe under the car.

With the smaller of the two cams it had less power but IMHO a better powerband. Ive been trying to get the smaller cam back in it for months (along with a .82 housing) but the bro just wont have it. Wants proof this combo isnt good before he does anything.

Might just take it off him for a while and work out some things myself. I want to do a COP setup too which should help with getting the big numbers once it can actually flow them. Have LS2 coils ready to wire in.

[Dale FZ1]

...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.

...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.

Consider whether the cam spec has excessive overlap and not suitable for forced induction? Exhaust valve opening way early could cause hot gases to blow out through the turbine leading to high EGT and not hitting the potential power output. Running an adjustable cam gear won't alter the phasing between inlet and exhaust, so the overall valve timing is either advanced or retarded, but the relationship between valve events does not change. Try another cam grind altogether, but only after you spend the time/effort by checking cam timing against the card that presumably was supplied by Camtech..

If your brother won't play ball, then close the garage door and let him to it while you do your thing.

[simpletool]

You dont think the turbo is flat out too small?

Flat out...HELL NO.

If a GT30 with 0.63 doesn't make 200rwkw ++ then there is something else wrong. Period.

I'm beginning to suspect a blockage of some sort (either intake or exhaust - or cam set incorrectly) coupled with resultant ignition timing being way too low.

1. Put the mild cam back in and check it is dialed in correctly.

2. Pull back the boost pressure (I'd suggest 13psi)

3. Try and run some more ignition timing

4. Check for boost leaks, intake/exhaust blockages

P.S. The mention of virtually every crappy of mis-matched turbo available in one thread is making me nauseaous. (2540, 3082, GCG turbo, GT30 w/.63 hotside.....urrrghhhhh).

[msports180]

A good mate played with Sigma Turbo's years ago, no matter what combination we put on it the exhuast always got BS hot, take it for a thrash and be glowing like anything. That was with a stock motor to, std cams etc. From memory he used a stock sigma turbo manifold/gate combo with everything from the Std T3 they used to a huge 1.06 rear size T4 combo. Was mint to drive, punchy as, good fun just didnt like to rev.

[GTScotT]

Thanks again guys.

Thanks for mentioning the phasing too Dale (and your other great info), I hadent considered it too much. Been too consumed by my SR build. Im going to be really keen to see this cam now. Once ive double checked mechanical timing i will actually rotate the motor by hand to see the valve events take place. Being a single cam with over rockers it will be easy to see the transition from exhaust to intake stroke on the same cylinder and ill try work out if its got some crazy overlap going on.

Daniel I will definitely run though those things yeah. I still do feel the .63 will be too small though. Maybe hope is still on the cards for the GT30 though.

Neil how sure are you the factory T3 was a 1.06? If so thats good info and gives me an indication that these things do at least need a big housing.

[GTSBoy]

Neil how sure are you the factory T3 was a 1.06? If so thats good info and gives me an indication that these things do at least need a big housing.

That's not what he said. He said "from the Std T3 they used to a huge 1.06 rear size T4 combo", meaning a range with the std T3 at one end and a very large T4 at the other end.

[msports180]

That's not what he said. He said "from the Std T3 they used to a huge 1.06 rear size T4 combo", meaning a range with the std T3 at one end and a very large T4 at the other end.

Exactly.

Either way it was big for a relatively small motor, but as you mentioned large displacement type agricultural, sooooo much torque. Always got hot, burnt the paint off the motor. We had the stock SU draw through carb on it at first and just couldnt get enough fuel in it, loved it.

[jet_r31]

Consider whether the cam spec has excessive overlap and not suitable for forced induction? Exhaust valve opening way early could cause hot gases to blow out through the turbine leading to high EGT and not hitting the potential power output. Running an adjustable cam gear won't alter the phasing between inlet and exhaust, so the overall valve timing is either advanced or retarded, but the relationship between valve events does not change. Try another cam grind altogether, but only after you spend the time/effort by checking cam timing against the card that presumably was supplied by Camtech..

If your brother won't play ball, then close the garage door and let him to it while you do your thing.

I did touch on that re: the 112 LSA...which is unusual, even if the camshaft wasn't the culprit,(id be suprised if it was, only by the fact the other cam should make heaps of power aswell..) and you went bigger on the turbo

later id be getting that bigger camshaft reground on a 116LSA definitly

cheers

darren

[GTScotT]

Have the CHRA number now, sorry for the delay. Part number is 700177-5007. I hope that bestows a little more faith in some lol.

Discos part number thread:

http://www.skylinesaustralia.com/forums/topic/104500-garrett-gt30-turbine-based-bb-turbo-and-chra-numbe/

Darren do you think the LSA could be causing that much grief? Considering the super quick spool and shifted powerband I cant help but think the turbo is mostly to blame.

Its essentially getting onto power and coming back off exactly 2500 RPM in both directions. I tend to think that if something was as fundamentally wrong as has been mentioned that the outcome would be a lot worse.

Unfortunately the original cam was what became the smaller of the two cams (114 LSA) and we dont have a stockie anymore. A magna cam also doesnt fit due to the water pump extension.

Short of spending crap loads of money I dont think there is a simple solution, and I dont seem to have many people agreeing that the turbo is the issue lol.

I am fast warming to the idea of an RB in this thing

[discopotato03]

Your call , personally I thing "big cams" as in long duration ones are a bit pointless in an engine that doesn't rev and was intended to have a torquey low to mid range . Opening the valves earlier and closing them later tends to kill the cylinders trapping efficiency at low revs - robs your effective cylinder filling and creates all kinds of reversion issues .

Long cams are designed to make an engine breath better at high reves where all the gasses are moving fast enough in the right direction .

I suggest you start with a factory standard camshaft because you know it will work at normal revs and keep the valve train stable .

Generally OE turbo cams don't have much overlap and IMO what does help is more lift rather than more duration .

Heat wise you may find that Astrons are not very tolerant and for what Mitsy used them for that may not have been an issue . They did come from the carby era when power outputs were not very high for the capacity and emissions standards not so strict . ULEV engines have to be able to cope with running at higher temps and changes in design and material spec attempt to make them reliable .

You have a choice here with the Sigma and Astron , try to develop it or go to a later car or even engine like say a 4G . Neither is going to be cheap to do properly and even if you got it right how is everything that makes a Sigma what it is/was going to cope .

I've been there trying to modernise older cars and in the end its not worth it - to me anyway . I think if you want a RWD car better to buy something like a Silvia because all of its suspension and drive line systems are so far ahead of what 80s era Smegmas had . To a degree most Nissans are Mecano sets and better gear often bolts up / plugs in . Maybe better again an R32 GTST because at least you get a Skyline bolted onto your RB six

.A .