Rb26 Shuffling Turbos, Overfuelling And Map Sensor Imbalance.... Related?

[STAGTR]

G'day all,

Tried ripping off the pods and hard pipes and went the open compressor intake for a quick trip around the block. Paul, mate, you were onto somehing... I honestly thought that it would only affect AFM driven rb26's.

I couldn't believe it, but it actually made a huge difference! Still shuffles at idle and a little when backing off the throttle when cruising, but otherwise spooled nicely with no audible shuffle at pretty much all throttle openings other than ~closed. Throttle response and low/mid range torque is dramatically improved. I put the pipes and filters back on and it was there again as bad as before.

Now that's all good, but I can't drive around without filters on it... wouldn't like to guess how long the donk would last. I measured the hard pipe lengths and they ended up being pretty balanced.

Does anyone know how to sort out the intake piping issue? Should I go for the concertina style plastic piping to introduce turbulence and avoid reflected reversion pulses from the hard pipes?

Do I need to invest in a freer flowing pod apart from these "DRIFT" pods?

Should I try and put a "balance pipe" between the two intake hard pipes?

The lengths are already balanced so that can't be the only variable.

I have discovered an/the underlying problem of the shuffle. The issue with the shuffle is that the turbo's are simply trying to flow too much air for the engine to swallow at idle/light throttle at cruise and it is banking up behind the throttle plates and when the pressure becomes too great (doesn't take much at the idle condition with the low exhaust velocity) it escapes back through the compressor wheels and inlets. I stuck my hands in front of each inlet and as it shuffled you could feel the flow reversion back out the inlet... in fact, even when it wasn't shuffling at idle, both turbo's still had long periods of air flow back out the inlets.

It's clear that I need to either try fitting the stock recirc valves (and get that leakback effect) or find some other way to bleed air at vacuum and into boost transition.

Does anyone know if I could change the compressor housings to reduce this flow reversion problem? I have heard of anti surge housings which pretty much have slotted bypass holes at the compressor housing inlet. Will that help at all?

[femno]

Wow wat a read!

The rear housings must be quite small, and the front wheels quite large to be 'breathing' on idle.

I had a similar issue on a mates SR20 where it was chuffing on idle and was screwing around with the afm. Was running a very small rear housing and being coupled with a large front comp housing it caused this problem.

Just some intell on a similar situation, but obviously only single turbo.

If you fit standard GTR BOVs in the system, it should help, they actually open on idle, so you would think it would give the air thats bouncing around in there somewhere else to go..

Im really surprised CRD couldnt find a solution to your problem!

[R31Nismoid]

GTR BOV's and the leak @ idle helps alleviate this further as stated, along with the stock flex/rubber piping and seems you should never have any surge.

Good to hear the theory about surge & hard pipe kits proven in the real world once again

Gotta hand it to factory Nissan in that respect. Whilst it doesnt look nice, it works.

Its hard to say, a balance pipe between the hard pipes might well work... Trial and error continues?

Anti surge comp housings work similar to the BOV's i believe letting some air bypass/take a different path into the turbo.

I think Disco posted a pic very recently about how the flow goes actually. It could work... however its a lot of effort when GTR BOV's could be a faster/easier option.

If you need a set of GTR BOV's i have some

[jeffworld2]

just my experience:

with twin gt-ss on a 25, i was shuffling ridiculously everywhere like a train while these turbos would be pretty much fine in a gtr.

I however had custom cooler piping at around 2- 2 1/2" diameter and snakey inlets to a single pod filter (1 AFM) and Trust BOV wound up tight.

so.. It seems this is the worst case scenario and what you would do to promote shuffling

Currently have 3 inch or larger cooler piping everywhere, 3" turbo intakes to a huge pod each, NO BOV at all and thing runs like a dream. Still "blows off" the pressure in two stages when i let off the throttle, but does not chuff in vacum or anything like before.

To me this means that larger piping everywhere has an effect. Either it is because of the restriction or simply because you have a larger damping area for what is probably still occuring. My original plan was based on the two turbos having different inlet path lengths etc. especially as they were both through the 1 filter

worked for me anyhoo

[Chris Wilson]

If you had agood mappable ecu with spare outputs could you not add a re circulatory solenoid controlled BOV valve that leaked plenum air at the offending load / boost / throttle sites? I know it's a crutch, but haven't heard of this being done on the RB engine before.

[daxter]

Wow wat a read!

The rear housings must be quite small, and the front wheels quite large to be 'breathing' on idle.

I had a similar issue on a mates SR20 where it was chuffing on idle and was screwing around with the afm. Was running a very small rear housing and being coupled with a large front comp housing it caused this problem.

Just some intell on a similar situation, but obviously only single turbo.

If you fit standard GTR BOVs in the system, it should help, they actually open on idle, so you would think it would give the air thats bouncing around in there somewhere else to go..

Im really surprised CRD couldnt find a solution to your problem!

I had a similar problem on my RB25DET, front compressor wheel is too big for the exhaust, why'll my turbo does spool up fast and give strong boost through the rev range, it did surge. (making 220rwkw on automatic, 13psi)

The problem was fixed by taking off the GFB bov and fitting the stock RB25DET by pass valve. – Letting air bleed out rather than bounce back off the throttle body.

I've read the stock valves are meant to open on idle and plum back-in in front of the compressor wheel, the circulating air actually helps the turbo spool up faster.

Edited February 25, 2009 by daxter