Jump to content
SAU Community

Recommended Posts

Hi, could anyone help with this problem please?

I've had the standard turbos reconditioned, when this was being done it was recommended to fit a slightly larger compressor wheel to each turbo & machining the housings to suit. The car is standard apart from air filters & a larger exhaust (HKS dump pipes, HKS front pipe, cat replacement pipe & 3in cat back)

Now when driving at a cruse/light acceleration (0 vac/boost) at anything below about 4,500rpm the recirculation valves are constantly cycling open close open close. When this is happening, if the throttle is opened a little more it gets worse (manifold pressure surges from 0 up to 5psi & back to 0 again & again)

if the throttle is opened almost fully, this surging stops & the engine begins to accelerate. It also seems to be running allot richer when accelerating with these turbos.

Most things have been checked & the only problem seems to be that the turbos are pumping too much air at the wrong time or something like that.

Has anyone had there standard turbos reconditioned and had bigger compressor wheel's fitted with no problems?

Does anyone know if something could be done to correct these problems without going back to original size compressor wheels?

Thanks

Sounds like you are experiencing compressor surge. Not entirely uncommon when people high flow turbos.

It is caused because the turbine wheel/housing is now miss matched to the compressor whee/housing.

Get the exhaust housing machined out.

If you do a search, this problem has come up before. Also, BOOSTD had a few problems in this area when he changed the compressor wheel on his turbo.

Originally posted by Steve

Sounds like you are experiencing compressor surge.  Not entirely uncommon when people high flow turbos.

It is caused because the turbine wheel/housing is now miss matched to the compressor whee/housing.

Get the exhaust housing machined out.

I've been told that my power dip/surge problem is also possibly due to compressor surge. I get different symptoms though, it's all fine until about 5000rpm, then the power starts to fluctuate (and even then this problem didn't happen while the car was <190rwkw or so). No weird sounds or drops in boost, just alternating loss and gains in power twice before redline. Does this sound like it could be the same thing?

When you say to get the exhaust housing machined out, do you mean the bit that bolts onto the manifold or the bit that bolts onto the dump pipe? I had a look at mine when it was off and it didn't seem like the latter would accomplish much because I'd still be stuck with the smaller wheel (it would just open out to the dump pipe a few millimetres sooner).

And to do the former I guess the manifold would also need to be machined out to be of any use.

Oh wow my specialty,

GtstGtr Your problem does sound like comp surge as Steve said. There are a stack of ways to get around it. Firstly depending on how bad it is. If it isn't to bad a small amount of efficientcy can be taken from the comp wheel buy machining a small lip into the snout down near the compressor inducer blade. This lets air escape past the blades when the turbo wants to surge. Will reduce flow but maybe only a couple of kw's worth. All standard GTs25T turbo's have this if you want to have a look at what I 'm talking about. Basically what is happening is your small turbine is spinning up the compressor faster than it was designed to which brings it on boost earlier, therefore into the surge zone of the compressor map. An adjustable cam gear can help you control how quickly the turbo comes on boost also. With my own turbo experimentation I found that my turbo needed to spool up a great deal later,1000rpm later in fact and there for the only way was to machine out the turbine snout--->increase the clearence between the wheel and the housing. Power increased by over 50rwkw.

What you want !

1. less inlet resistance, less outlet resistance and/or

2. More Lag

Fixes

1. Bigger A/R comp cover

2. Machine a grove into the comp snout

3. Control boost with adjustable cam gear or two stage boost controller ie 12psi till 4000rpm then auto switched to 15psi

4. Machine out turbine snout and leave original wheel (grealty increases flow and gives more lag, however less aggressive boost response as compared to a larger wheel)

5. Larger turbine wheel.....works the same as no4 but will give better spool up and cost alot more.

6. More restriction in the inake before the turbo would help to.

Thanks for your replies everyone.

Compared with standard turbos would there be any advantages using these mismatched turbos with either the exhaust or compressor housings machined out to compensate?

The ceramic turbines have been replaced with some sort of steel turbines, as far as I know they are the same spec. The compressors that were fitted supposedly pump 10% more air each than standard.

Guest RedLineGTR

if its a good turbo shop they should be able to tell u everything...what will work and what will not...the question u are asking they should know if they know thier stuff..if not i wouldnt of gone to them..my 2 cents might not be the case.

Originally posted by RedLineGTR

if its a good turbo shop they should be able to tell u everything...what will work and what will not...the question u are asking they should know if they know thier stuff..if not i wouldnt of gone to them..my 2 cents might not be the case.

If it was a good turbo shop, they would have got it right in the first place?

Another possibility is the turbos have been re-assembled "out of phase" (a mate had some on a 33 GTR, and they had been assembled so the wastegates weren't operating at the same pressure).

Watch the boost gauge when the problem is occurring - apparently, compressor surge causes the boost to jump all over the place.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now


  • Similar Content

  • Latest Posts

    • The average previous owner for these cars were basically S-chassis owners in the US. Teenagers or teenager-adjacent. I often tell people that neglect is easier to fix than something that was actively "repaired" by previous owners.
    • Update 3: Hi all It's been a while. Quite a lot of things happened in the meantime, among other things the car is (almost) back together and ready to be started again. Things that I fixed or changed: Full turbo removal, fitting back the OEM turbo oil hardlines. Had to do quite a bit of research and parts shopping to get every last piece that I need and make it work with the GT2860 turbos, but it does work and is not hard to do. Proves that the previous owner(s) just did not want to. While I was there I set the preload for the wastegates to 0,9bar to hopefully make it easier for the tuner to hit the 370hp I need for the legal inspections that will follow later on. Boost can always go up if necessary. Fitted a AN10 line from the catch can to the intake hose to make the catchcan and hopefully the cam covers a slight vacuum to have less restrictive oil returns from the head and not have mud build up as harshly in the lines and catch can. Removed the entire front interior just shy of the dashboard itself to clean up some of the absolutely horrendous wiring, (hopefully) fix the bumpy tacho and put in LED bulbs while I was there. Also put in bulbs where there was none before, like the airbag one. I also used that chance to remove the LED rpm gauge on the steering column, which was also wired in absolute horror show fashion. Moved the 4in1 Prosport gauge from sitting in front of the OEM oil pressure gauge to the center console vents, I used a 3D printed vent piece to hold that gauge there. The HKB steering wheel boss was likely on incorrectly as I sometimes noticed the indicator reset being uneven for left vs. right. In the meantime also installed an airbag delete resistor, as one should. Installed Cube Speed premium short shifter. Feels pretty nice, hope it'll work great too when I actually get to drive. Also put on a fancy Dragon Ball shift knob, cause why not. My buddy was kind enough to weld the rust hole in the back, it was basically rusted through in the lowermost corner of the passenger side trunk area where the wheel arch, trunk panel and rear quarter all meet. Obviously there is still a lot of crustiness in various areas but as long as it's not rusted out I'll just treat and isolate the corrosion and pretend it's not there. Also had to put down a new ground wire for the rear subframe as the original one was BARELY there. Probably a bit controversial depending on who you ask about this... but I ended up just covering the crack in the side of the engine block, the one above the oil feed, with JB Weld. I used a generous amount and roughed up the whole area with a Dremel before, so I hope this will hold the coolant where it should be for the foreseeable future. Did a cam cover gasket job as the half moons were a bit leaky, and there too one could see the people who worked on this car before me were absolute tools. The same half moons were probably used like 3 times without even cleaning the old RTV off. Dremeled out the inside of the flange where the turbine housing mates onto the exhaust manifolds so the diameter matches, as the OEM exhaust manifolds are even narrower than the turbine housings as we all know. Even if this doesn't do much, I had them out anyways, so can't harm. Ideally one would port-match both the turbo and the manifold to the gasket size but I really didn't feel up to disassembling the turbine housings. Wrapped turbo outlet dumps in heat wrap band. Will do the frontpipe again as well as now the oil leak which promted me to tear apart half the engine in the first place is hopefully fixed. Fitted an ATI super damper to get rid of the worn old harmonic balancer. Surely one of the easiest and most worth to do mods. But torquing that ARP bolt to spec was a bitch without being able to lock the flywheel. Did some minor adjustments in the ECU tables to change some things I didn't like, like the launch control that was ALWAYS active. Treated rusty spots and surface corrosion on places I could get to and on many spots under the car, not pretty or ideal but good enough for now. Removed the N1 rear spats and the carbon surrounding for the tailpipe to put them back on with new adhesive as the old one was lifting in many spots, not pretty. Took out the passenger rear lamp housing... what do you know. Amateur work screwed me again here as they were glued in hard and removing it took a lot of force, so I broke one of the housing bolts off. And when removing the adhesive from the chassis the paint came right off too. Thankfully all the damaged area won't be visible later, but whoever did the very limited bodywork on this car needs to have their limbs chopped off piece by piece.   Quite a list if I do say so myself, but a lot of time was spent just discovering new shit that is wrong with the car and finding a solution or parts to fix it. My last problem that I now have the headache of dealing with is that the exhaust studs on the turbo outlets are M10x1.25 threaded, but the previous owner already put on regular M10 nuts so the threads are... weird. I only found this out the hard way. So now I will just try if I can in any way fit the front pipe regardless, if not I'll have to redo the studs with the turbos installed. Lesson learned for the future: Redo ALL studs you put your hands on, especially if they are old and the previous owners were inept maniacs. Thanks for reading if you did, will update when the engine runs again. Hope nothing breaks or leaks and I can do a test drive.
    • No those pads are DBA too  but they have colors too. I look at the and imo the green "street" are the best.
    • I’m not sure what happened I told them about sonic tunes free OTS tune and the next the I know .. I was booted..   To funny 
×
×
  • Create New...