Boost drop

[jaboc03]

I have a s13 redtop sr with a t28 turbo. When I have the boost set at 14psi it holds it till about 5500 rpms, then it starts to drop off to about 10psi. What could be the problem?

My Mods:T28 TurboGreddy bov type-sGreddy 3in. downpipeGreddy fmicGreddy Pro-fec B boost controllerApexi N1 cat-back exhaustApexi S-AFCIIWalbro fuel pump

[MadSideways]

It has to do with volumetric efficiency. You're having airflow problems and back-spooling the turbo, not good.

There are a few things that can be done. Run full 3" intake and exhaust, from the turbo all the way back, and then a test-pipe and intake plenum.

That will solve 99% of your airflow problems.

After that, you'll need to look into a high quality waste-gate, because the stock one is not really that great and prone to boost-creep.

[jaboc03]

I have 3in. piping from the turbo all the way back to the exhaust. I have thought it might also be the MAFS.

[goldollar]

Does it only do it at 5500 rpms. Have u checked for any leaks it sounds like u might have a slight vacum leak, problly from a semi-loose intercoller pipe coupling.

[180crafter]

I agree...

Most likely you are building boost, and then when you hit a certain point, something is leaking. Also check BOV and Brake Booster.

[DriftBandit]

Most likely wastegate, I have the t28 turbo and I loose boost after 10psi, I am going to try the HKS adjustable actuator.

[dj_lennon_franz]

small turbos cannot hold high amounts of boost at top end...simple as that...go with a T3T4 and see what happens at top end =)

[jaboc03]

Well I tightened all of my intercooler piping and my bov and it seems to hold it a bit better. It still drops off a bit though. So I guess it might be the wastegate. What can I do to fix it?

[swappedcrx]

im goin thriugh the same thing with a similar set up pulsar turbo hks wastegate and a avc-r i made this boost leak checker thing and chased most of my leaks away. i will post a pic today. im still having a leak somewhere though. you can tell if its your wategate if the car doesnt miss. my car doesnt like to rev past 4.5k without missing like a SOB(leak). if its the wastegate you car simply will meter the correct amount of air and will run fine albeit slower than it should thanks to the earier opening oth the wastegate.make sense?

[180crafter]

Not really....

[jaboc03]

Mine runs fine, there are no problems at all. The only thing is that boost problem.