Turbine housing back pressure

[RBceffy25]

 

Hey

I recently had my 25det Neo on the dyno. Won't hold boost after about 5500. Apexi ax53b70 on 16psi with standard manifold,  3in bellmouth dump into KTS dual front pipe into 3in flex pipe into 3in stainless catback which measured 2psi of pressure at the o2 bung in the dump at full noise on a power run. Worth noting it's running type b poncams, standard cam gears. 

We checked the bov (r33 gtr item) for leak on the dyno and the intake plumbing had 25psi plumped into it before dyno to check boost leaks etc.

It seems to me the wastegate is blowing open so I'm thinking of plumbing into the turbine housing to check this as it has a bung I've got a bolt in, blocking it off. 

 

Any help or advice at this point would be greatly appreciated, will provide pics of dyno sheet upon request, if desired.

 

edit: forgot to mention it's running a new turbosmart eboost street ebc.

Edited March 14, 2017 by RBceffy25

[KiwiRS4T]

Tried dropping the exhaust? How much power was it making? Got a chart? What spring on the ebc?

[RBceffy25]

Have not dropped the exhaust as it was only making 2psi back pressure. Makes just under 320rwhp with boost dropping off. It has the Apexi/ihi actuator on it that comes with the turbo. Correct me if I'm wrong but I think they have a 14psi spring. We haven't played with the preload as we were running out of time but looking at the green curve (sp1, boost control off) i think it needs more preload than readjust the ebc to suit. However I would think that this should not cause the boost to drop off. The pink curve, he put a bit more boost into it to see what was happening but backed off early when it started losing power.

Sorry for the crappy pic

 

Edited March 14, 2017 by RBceffy25
Bad photo

[GTSBoy]

Looks like the downtime involved a database crash and restore.  Some posts lost.  The ones I made in this thread were to the effect that 2 psi of backpressure post turbo seemed like a lot for only 320 rwhp.

[R_34]

I tends to agree, I work on engine bench for a living and OEM manufacturers are designing exhaust system to have backpressure around 6 to 8 psi at peak power.

So 2 psi for an exhaust without cat and 3inch system seems on the high side. I didn't mesured backpressure on my car though.

[Dale FZ1]

Quick search on turbocharger spec found this old thread:

If that's correct, OP is probably experiencing the flow limitations of a relatively small turbocharger.

320rwhp from a unit apparently capable of supporting 380ps @ crank would be quite acceptable.

It's probably not making any more hp with more boost simply because it can't inhale/exhale more air and maintain efficiency.

2psi pressure in the exhaust at full noise is nothing to sneeze at.  More telling would be comparing that figure with the turbine inlet pressure, and boost pressure with TIP.  Pressure differential across the head, and across the turbine is where it's at.

More hp probably requires upsizing what's now old spec.

[RBceffy25]

Is is making more power with more boost. The boost is falling of causing the power to flatten out. Looking at the curve, I believe there is a little more in it if boost holds steady. Compare this old sheet I found with mine. His is a 25 s1 with same supporting mods minus cams. 

The tune needs a slight touch up for idle/cruise as we ran out of time on the day so when I put it back on the dyno I'll bung into the turbine housing for a pressure reading. I'm also going to delete the straight through resonator and put a more free flowing muffler on it before it goes back on. I have wondered wether my cams are a tad big for the turbo but I'll continue to go through a process of elimination before I consider it more seriously.

 

[RBceffy25]

On that note, can anyone recommend an unrestricted muffler? Preferably jap brand

[Dale FZ1]

The original overlays showed the tuner punching extra boost in mid range, and it made extra hp earlier.  Makes for a more lively response.  All good things.  Boost tended to fall away after 6000rpm to broadly similar levels.  So broadly similar power number - quite predictable.

No mention (that I could see) regarding cam spec being non standard.

This Apexi turbo seems broadly similar in impeller dimensions to a Garrett GT2871 - something with which I have experience on a RB25.  It fell away after 6000rpm too.  Bloody good little turbo provided you want a good street performer and don't expect big hp numbers.  This one seems the same.

Second dyno sheet really only shows boost bumping up in 1-2psi increments.  If you want to establish its limits and are happy to pay, have the tuner bump it up to 18-19psi and see what happens.  Predicting more mid range and falling away after 5500.

Earlier comment stands - if you want a bigger hp number, get onto a more modern bigger turbo.  The total effect might surprise you.  Others (pm Discopotato03) have previously thrown around lots of discussion in this area.  Bigger turbo won't necessarily mean poor response, and it will make much bigger numbers if that's what you need/want.

 

 

 

[RBceffy25]

I mentioned cams in the first post. Type b poncams.

Not sure what you mean by punching extra boost but yeah my tune is at 16psi which along with the cams would account for the fatter midrange etc. and the other guy is 15-15.5psi. My tuner tried a run at 18 psi to see if it would still fall off at the same point - which it did so he backed off. But with my engine being a cammed Neo I would expect it to make a little more midrange and top end.

My brothers motor, a 25 s1 with poncams and supporting mods etc running a hks gt-rs kit - which is verily similarly spec'd to the Apexi. I think he had similar dramas until he sorted the exhaust and may have swapped actuators then had a sweet flat boost curve. Will have to confirm that with him though.

He is losing 1 psi overall from around 5500 onwards whereas I'm dropping 4psi overall. Our boost curves are quite different in this regard and is my main point of focus. This keeps bringing me back to potential back pressure issues which I'm suspecting might be either blowing the gate open and/or restricting flow. I'm not interested in big numbers at this time as it's internally standard bar the cams and will be my daily for at least the next 12 months.  All I want to achieve is a flatter, more consistent boost curve, find out what it yields and find out if I can achieve this by making the entire system as efficient as possible. If the turbine pressure test and fully unrestricted exhaust reveal nothing I'll concede defeat haha.

[Dale FZ1]

10 hours ago, RBceffy25 said:

I mentioned cams in the first post. Type b poncams.

Not sure what you mean by punching extra boost but yeah my tune is at 16psi which along with the cams would account for the fatter midrange etc... My tuner tried a run at 18 psi to see if it would still fall off at the same point - which it did so he backed off.  my engine being a cammed Neo I would expect it to make a little more midrange and top end.

..a 25 s1 with poncams and supporting mods etc running a hks gt-rs kit .. similarly spec'd to the Apexi... had similar dramas until he sorted the exhaust and may have swapped actuators then had a sweet flat boost curve. Will have to confirm that with him though.

I'm suspecting might be ...blowing the gate open. ....  All I want to achieve is a flatter, more consistent boost curve, find out what it yields and find out if I can achieve this by making the entire system as efficient as possible.

My bad re: the cams.  Scanned the post and missed it.

Re: punching boost into it.  There's 3 runs on that first overlay. Green run shows (IMO) lazy boost control that was resolved with the red run, basically pretty consistent across 4000-6000rpm.  That looks pretty satisfactory to me, but the pink run simply added more in that same range.  That's what I meant by punching extra boost, simple turn of phrase.  End result is 240 rwkW which compares VERY well with any GT-RS equipped RB25 running pump 98 without water injection.  (Bear in mind the variability across different dynos etc.)

The grid lines on those graphs always make it hard to determine exactly what boost number it's producing, but yeah I can see the consistent trend in the top end.  Can't fault your drive for trying to improve what's there, and a muffler change (or delete altogether for testing?) plus wastegate actuator change to a big diameter canister/diaphragm are both legitimately likely to help if you're pursuing a flat boost curve.

When it's all done though, you're not likely to make much more than another 10rwkW unless you go E85.  Discopotato03 reported about 270 running a GTRS, head fitted with poncams, oversized exhaust valves, and E85 blended down to about E50.  From memory he was pretty skinny on providing dyno sheets for that setup, or the subsequent GT3076 setup, but I'll be surprised if it wasn't starting to roll off (meaning torque plummeting) at 6000rpm. That all adds up to a lot of effort and expense, which is something you'd have to weigh up for the likely outcome(s).  PM him for advice/experience, or perhaps he might chime in on this thread for all to see.

Worth noting that total system efficiency is also impacted by the inlet piping and filter, intercooler piping, and intercooler spec.  Every little bit counts when it's an efficiency hunt. Be interesting to compare what you have got vs what your brother has. There's been some decent input in a couple of threads by Stao from Hypergear.

Torque characteristics are largely impacted by mass airflow, and boost is a measure of resistance to that airflow.  If there's a future upgrades plan, I'd run what you've got until there's money to fit a different spec turbocharger with bigger mass airflow capabilities.  You'd probably find those poncams also able to make more impact in that situation.  This sort of thing has been discussed/dissected/commented on over many years in this forum, so worth looking around if that helps your understanding and decision making.

Don't know anything about the other modification path you're on, but at ~320rwhp it would be very desirable to make sure money is being/has been spent on suspension/brakes/tyres to make use of whatever it's making.

Good luck with your project, keep us updated with progress.

Edited March 17, 2017 by Dale FZ1

[RBceffy25]

Gotcha  

Yeah, I'll try to dig up my brothers dyno before he went e85 just for a comparison. I think he made around 260. When he did go e85 his GTRS put out a very impressive 300kw. At this point though he had a revised straight through exhaust, revised fmic plumbing, GTR itb's and hpi manifold. Maybe he can chime in as well and confirm or correct that info haha.

Yeah man the rest of the car i.e. Brakes, suspension, driveline, charging system, fuel system etc was done before the motor even went in. I've entirely built the car up myself with one goal in mind and that is to have a safe, reliable and somewhat comfortable street car I can daily without worry of defects while maximising response and drivability.

The rest of my setup consists of an Apexi super suction kit into the ax53b70 out through 2.5inch cooler piping through a HDi GT2 core into standard intake with a stocko r33 gtr bov. Probably the biggest let down is the shitload of intercooler plumbing required with the crossover plenum etc. and I'm not sure how the HDi cores stack up to the other brand name stuff but it was new sitting on the shelf so wasn't going to waste.

There are plenty of things I'd like to do with it but I'm at a point where I figure if I can get that 10kw more out of it cheaply I will, otherwise I'll just drive and enjoy it as I feel the chapter of this car is almost done in my life and I would rather turn my attention (and wallet ?) to another project in the future.

We said goodbye yesterday to Gary Snow of Tokage Racing Imports who sadly lost his battle with cancer earlier in the week. He imported this chassis for me when I was 20 (now 30) so it's become something of sentimental value to me and my friends and family.

Perhaps as a last throw I'll put another set of injectors in it on e85 down the track when i retire it from daily duties. 

[KiwiRS4T]

17 hours ago, RBceffy25 said:

On that note, can anyone recommend an unrestricted muffler? Preferably jap brand

I looked at a bunch of Japanese mufflers and they all had restrictions smaller than the inlet and outlet sizes so ended up with a locally made muffler.

[RBceffy25]

26 minutes ago, KiwiRS4T said:

I looked at a bunch of Japanese mufflers and they all had restrictions smaller than the inlet and outlet sizes so ended up with a locally made muffler.

Cool thanks for the info man ?

[discopotato03]

No my 271 RWKW figure was on E70 with that GTRS . I highly doubt the head work valves or Poncams did much for it because that poor little GT28NS111 turbine and 0.64AR turbine housing was a big limitation for a 2.5 liter engine . It got to 17 pounds of boost but fell off to 14 higher up . The Blitz return flow IC replaced the R34 SMIC just before that tune .

Not an ideal turbo for an RB25DET but still better than the OE ceramic Hitachi .

I maintain there is no mid sized turbo out of Garrett because the gooses still have that big gap between GT28 and GT30 turbines . The cropped GT30 or GT29 as it's now called is a total waste of time . I kid you not that GT30 UHP turbine has been around since about 1991 when it appeared in HKS spec Garrett turbos like the 3037 .

I used to argue with their production engineers that the aftermarket was screaming out for something like the larger 60mm NS111 turbine . But no the morons instead glitzed about with billet wheels on prehistoric turbines . They know the problem they refuse to fix it .

That aside E70 or 85 will allow you to push ignition timing numbers and get sort of reasonable looking power numbers from restrictive turbos . Not the best way to go but I suppose choking on exhaust is better than detonating to death .

A .