Why does my boost drop ?

[B-Man]

Hi Guys,

I just got the HKS 2835 tuned - Not a bad result I guess. Power comes on much sooner compared to the HKS 3040.

But you will notice that boost drops from 20 PSI to 16 PSI from 4000 RPM to 7500 RPM.

As a test, the guys jimmyd the wastegate closed via the E-Boost (somehow) so so that the gate stayed closed all the time and power kept going up to ~ 300rwkw @ ~ 28 PSI. So we know that turbo and engine is capable - Just - it seems that either the EBC or the Wastegate are not working to their best.

EBC is Turbosmart E-Boost

Wastegate is Trust Type R 45mm (SydneyKid - is this too big maybe)

Anyway here are the graphs

Cheers .

[cameron]

Have you tried a different boost controller ? I've seen some trouble's with certain EBC and wastegates. - Have you got the bigger spring in the wastegate ? (I'm sure you do)

The wastegate might be too big, and bleeding too much air out when it opens,

Airflow in lbs per minute = diameter of wastegate in mm X boost correction factor - I think thats the formula for the wastegate size.

Im sure SK can further explain.

Nice power their from the 2835, are you going to keep it or put the 3040 back on ?

Jun

[B-Man]

Hi Cameron - No just the E-boost.

But yeah - since going to the smaller turbo - and keeping the big wastegate - I'm thinking along the same lines as you - too much air going out the WG. Hence the poor old turbo is trying to pump more boost , but can't cause 4 PSI of it is going out the gate.

Bloody Wastegates - who needs then ......

[cameron]

Did it do the same with the 3040 ? The 2835 might be too small for the wastegate.

[B-Man]

I think it dropped like 1-2 PSI with the 3040 - not as significant as 4 PSI.

The Wastegat spring is an 18 PSI spring, I think - It the spring is adjustable too - I think - maybe if I make it stiffer/stonger, the WG will open slower ?? Also, might have to read up a bit more on the E-Boost, cause I recall that you can set something on them that allows for slow or fast solenoid action - or something like that .

If I can get that 4 PSI back, then I'll hit 300 for sure with the 2835. If I can get that - then I thinkI may have found the most perfect allround turbo for the RB25 :D Power and response all in one package :)

[RBVS]

not sure if the e-boost has it but with my boost control which is run buy autronic sm2. there is a section called BOOST OFFSET. what you do is log boost to rpm like you have and then add or take away psi at what revs you need to. so you have a graph with rpm values like this

2500 3000 3500 4000 4500 5000 5500 6000 6500 7000 75000

0psi 0psi opsi 0psi 0psi 1psi 1psi 2psi 3psi 4psi 4psi

autronic does it with kpa but if the e-boost has this then you should be able to tune it out.

[RS500]

RBVS,

how do u like the Autronic as a boost controller?

does it control boost well?

[RBVS]

i used to have crap boost control with it. was using a gtr solenoid then tryed the small autronic solenoid still wasnt realy happy. in the manual your ment to have a restrictor in the line then a T peace and the solenoid bleeds air out from the T.

manifold===//====T====actulator

.............restrictor l l

..........................#solenoid

i then got my hands on a apexi solenoid which sits in line

manifold=====#=====actulator

this works a treat, have great control with current set up.

having all the boost tune files and offset is good but theres a bit of messing around to get it to switch between to boost curves so you can just use a switch and not go on the laptop.

also got the option of setting boost to throttle position

its good when you can work though it all but prob over kill for your average street car.

[grepin]

I am having exactly the same problems with an Internal gated 2835 ProS. Have fitted a 22psi spring with no real help. A new theory is that the head can not flow enough air to maintain the higher boost (turbo efficiency). I am running 20psi with the same power result however drops back to 15psi at high revs. I believe Cams (more duration) which I am in the process of getting or possibly even just cam gears may give us the flow we need to hold boost. The bigger turbos like the 3040 overcomes this by providing more pressure at a lower turbine flow rate with more lag.

Have you got cams I didnt look. However this all theories so let me know if you come up with any fixes.

[B-Man]

256 / 9 Tomei poncams.....

And Exh Cam gear set at 4 ( I think)

Head has been ported slightly.

How do you test for this ?? Sounds complex and costly.

[B-Man]

When we kept the gate closed deliberately, power went to 300 @ 28 PSI then they backed off the throttle (didn't want to blow anything up - he he)

This is beyond my small brain - need the professionals helpp with this one - ha

[Sydneykid]

Hi Guys,

 

I just got the HKS 2835 tuned - Not a bad result I guess. Power comes on much sooner compared to the HKS 3040.

 

But you will notice that boost drops from 20 PSI to 16 PSI from 4000 RPM to 7500 RPM.

 

As a test, the guys jimmyd the wastegate closed via the E-Boost (somehow) so so that the gate stayed closed all the time and power kept going up to ~ 300rwkw @ ~ 28 PSI. So we know that turbo and engine is capable - Just - it seems that either the EBC or the Wastegate are not working to their best.

 

EBC is Turbosmart E-Boost

Wastegate is Trust Type R 45mm (SydneyKid - is this too big maybe)

Hi, wastegate size looks OK to me;

300+60X1.34 = 482/11=44 mm

So it must be opening too early, also I notice that the A/F ratios lean out at the same time as the boost starts to drop. I test this by plumbing the boost gauge in the line from the boost controller to the wastegate actuator. This tells you at what boost the EBC is letting boost pressure flow to the actuator. I then adjust the EBC to minimise this.

I have had no experience with E-Boost so I can't suggest what settings are required, maybe have a chat with the technical guys at Turbosmart. They should have an answer to the appropriate settings ot fix the creep.

Hope that helps

[DoughBoy]

Ok, 300rwkw @ 28psi vs 287rwkw @ 16psi. Don't you think the compressor is maxed out? The 56T 2835R flows ~44lbs/min, hack that into 440 engine hp, take out ~70hp drivetrain loss, so 370rwhp... or 275rwkw. Sound about right? The compressor is over is far right side edge of the map, so it's blowing more hot air than a cheap hooker.

Funny point that I was under the assumption that the efficiency curves on a comp map was relative efficiency of the compressor, giving some sort of heat based map. Garrett states the percentiles is actually how much turbine flow is driving the compressor at that flow/boost, hence the efficiency rating in %.

In my often wrong opinion 280rwkw is maxing out a 44lbs/min compressor, just as 330rwkw is maxing out a low/mid 50's lb/min compressor on ze humble RB25.

[DoughBoy]

Ok I am tired, checked the comp map + it's only ~41lbs/min peak flow. The shaft speed at that level for 1.4 bar is 135,510rpm. Might want to be a bit careful with overspeeding that turbo. Since teh calcs are only rough approximations (some places rate the lbs *11 for engine hp) it still seems feasable. Or is that feeble?

[DoughBoy]

Oh and idea #3, if you want a turbo combination that doesn't drop off boost, how about getting something ginormous that you'll never max out, or lowering your boost level/expectations?

[B-Man]

Jeez - I thought these HKS Turbos just started to party at 18 PSI.

I'll be careful with the Turbo. No more boost OK.

Oh and BTW, 28 PSI was just what we saw during the test with the WG closed. It don't neccessarily equate to the 300 we saw. If you get what I mean.

re Expectations: What about teh naws ? You know I want the best of both worlds don't you!

[B-Man]

I guess at the end of the day - if the spec is 41 lbs flow - that is the spec. But you know that I like to push the boundaries. Just to see if the spec is the spec or maybe just a conservative number on a bit of paper so expectations are achieved. ha ha ha ha

I'm thinking I really need a 3.0L with a RB26 head to play with now :D

[B-Man]

And if 16 PSI is max efficiency for this setup - how come when we set boost to 20 PSI it drops back to it's efficency ??

That's the bit I don't get - Should't it hold at 20 PSI ? (albeit out of efficiency range)

Or is my boost controller clever enough to know where the efficiency peak of the turbo is ?? (OK that's silly, but you get what I mean)

[B-Man]

Grepin - dude, can you post your graph ? I wouldn't mind seeing the difference between internally gated and externally gated 2835s

[Sydneykid]

Have I missed something here............

My understanding was it holds boost (doesn't drop down to 16 psi) if you lock the wastegate shut. In fact it builds boost up to 28 psi. This means it has sufficient airflow to hold the target boost of 20 psi, but the wastegate is opening. So if you get the wastegate under control it will hold 20 psi and make the 300 rwkw target.

300 rwkw +60 kw losses X 1.34 = 482 bhp

As DB said the 2835 is rated at 420 PS, it is generally accepted that HKS rate their turbos at 90% (conservative), so you can add 10% to that. This means 460 ps, so the 300 rwkw is realy stretching it. This is confirmed by the airlfow rating of 41 lbs per minute X 11 = 451 bhp.

So B-man if you do get to 300 rwkw you have done a good job and extracted the max.