Boost Dropping Off

[da spike]

Guys,

What is happening in my car is that the boost is dropping off. The car is a R33 S2 with a std turbo and a Apexi AVC-R boost controller and I have the boost set to 13psi and what happens is that it hits 12.5psi and then 13psi at about 3500-4000rpm but then after that the boost starts to slowly come down and before redline it goes all the way down to 11psi.

Now I had the car on the dyno and the difference between standard boost (9psi) which was 176rwkw and 13psi which was 186.7kw. I think the problem is that the boost is dropping off because at the top of the power curve I'm only running 11psi...hence the poor rwkw result at high boost.

Any ideas what could be causing this? My guess is that it could be the avc-r... but any other suggestions?

Thanks

[Krishy]

does your boost controller have a boost limiter setting....similar to the greddy profec b spec II's????

also i am assuming that your running stock turbo.....if so then your stock turbo might not be able to handle 13psi throughout the rev range.....as in efficiency of the turbo is going out the window....also the dyno figures dont tell much as it could be a number of things as to why your making 186 rwkw on 13psi sounds a bit low.....about 10kw low....try it with a manual boost controller and see if the boost is still dropping......and see if it makes a difference

I have got a S1 R33 and it made some good power on decent boost with stock turbo ...... loook at the sig

[da spike]

I dont think that the avcr has a boost limiter setting... these damn avc-r's are so hard to setup properly...

And I know that 186kw is too low thats why I posted this topic

By the way my exhaust is a 3" from turbo and 3.5" catback. Could it be that I dont have a high flow cat? I bought the exhaust 2nd hand and not sure what cat it has...

[Krishy]

  da spike said:

I dont think that the avcr has a boost limiter setting... these damn avc-r's are so hard to setup properly...

And I know that 186kw is too low thats why I posted this topic

By the way my exhaust is a 3" from turbo and 3.5" catback. Could it be that I dont have a high flow cat? I bought the exhaust 2nd hand and not sure what cat it has...

mmmm i would say that power being a bit low could be due to stock cat still in the system....get a xforce high flow cat and get it redynoed see if it makes a difference

[R31Nismoid]

details of exhaust?

If the exhaust is 3", decent flowing etc, then it'll be either the fitment or setting on the AVC-R.

[da spike]

The exhaust is a 3" stainless steel dump x-force I believe and the catback is 3.5" mild steel also x-force as well. Also all gaskets were changed when the exhaust was put in (about a year ago), there are no leaks.

Is there somehow I can check if the cat is a hi-flow cat?

[mad082]

well as long as the cat is 3" then it shouldn't really be an issue. i was running 14psi on a cheap nasty 3" cat and it only dropped about 1psi at high rpm (like about 6000rpm and above). however when i had a different boost controller on it was dropping about 3psi. the controller i was using that held was one of the cheap turbotech $30 ones. the one that dropped boost was a turbosmart dual stage.

also what sort of intercooler do you have? and what sort of air filter setup?

and as someone said above, 186kw for 13psi seems rather low. so there could be a fuel or timing issue as well

[zoom]

It is normal for a r33 gtst stock turbo boost to drop off at high rpm as it reaches its limit.

I've got 185rkw with the usual modes and was running 14psi but was dropping to about 11psi.

Than I added exhaust cam gear and went back to the dyno and i've got close 198rkw and the boost still dropping like before ie. 14 to 11psi.

So it seems like it's nothing wrong with your setup (ie boost controller) if you haven't got any cam gear fitted.

[R31Nismoid]

to check if the exhaust is OK

drop it from the dump, on the dyno.

If its still dropping boost - as i said, AVC-R settings/install

[da spike]

The intercooler is one of the cheapies from Just Jap and the airfilter is a Apexi Power Intake, also got a walbro in-tank fuel pump.

Really it is not running 13psi when it makes 186rwkw... its really running 11psi.

Also I got the car tuned by Toshi on the forum.

AFRs are in the 11's and sometimes dropping to 10.5.

Edited August 12, 2009 by da spike

[da spike]

Here is the dyno sheet...

[Krishy]

where are you getting your boost reading from??? as in where is it hooked up to

[da spike]

  Krishy said:

where are you getting your boost reading from??? as in where is it hooked up to

Have a look in the pics, the clear tube is the boost gauge, its hooked up to the same place where the avc-r is getting its reading from.

[Krishy]

ahh ok i am running mine from the plennum......maybe give that a go and you might see a difference....use the nipple that the stock line uses....sorry i dont have a pic as i am away on a business trip mate